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OUTLINES

OF

ANATOMY AND PHYSIOLOGY,

TRANSLATED FROM THE FRENCH

OF

H. MILNE-EDWARDS,

DOCTOR OF MEDICINE, PROFESSOR OF NATURAL HISTORY AT THE ROYAL

COLLEGE OF HENRY IV., AND AT THE CENTRAL SCHOOL

OF ARTS AND MANUFACTURES, IN PARIS.

By J. F. W. LANE, M. D.

BOSTON:

CHARLES C. LITTLE AND JAMES BROWN.

MDCCCXLI.

Entered according to Act of Congress, in the year 1841,

By Charles C. Little and James Brown,

In the Clerk's office of the District Court of the District of Massachusetts.

BOSTON:
r-RlNTED UY l'Hl.KMAN AND BOLLES,

WASHINGTON STREET.

TRANSLATOR'S PREFACE.

The subject of Anatomy and Physiology, until quite recently,
was never presented to the scholar, or to the public in general.
Previous to that period its study had been limited to medical
men only, and a certain degree of opprobrium even was at-
tached to those engaged in Anatomical pursuits. But such a
change has been gradually wrought in public opinion upon
this subject, that now no system of education is considered
complete, without some acquaintance with the human form
and structure be included. The prejudice is fast passing away,
nay has already passed, which has so long kept back from the
many a knowledge of the healthy exercise of their organs and
functions ; and which no doubt in a great degree prevented
more rapid advances from being made by physicians them-
selves in the intimate structure of the organs. Upon the im-
portance of this study to the medical student it were needless
to enlarge — the information obtained from it finds daily use
with all, whether in diet, ventilation, clothing, broken bones,
running, walking : not an act of the body can be performed
without calling in question some point of physiology. But

IV TRANSLATOR'S PREFACE.

let ns bear in mind, that the present is strictly a physiological
view of man, and no where does our author so much as pre-
sent a glimmer even of his psychological state. This limited
view may however serve as a stepping stone to the other ; and
from this point how vast, how illimitable the field of Natural
History appears.

There are many excellent works upon the same subject, but
they are too minute and abound in technicalities; to supply
the deficiency arising from this cause, and at the same time
furnish the medical student with an elementary work, has
been my object in this translation. In the language of the
author, " the age and characters of some of my readers has,
perhaps, made it necessary for me to pass rapidly over certain
functions ; but I am not aware of any important omissions in
this sketch of the phenomena constituting life. My aim has
been to be clear and concise, and from the nature of my work
I have been compelled to limit myself to facts, and to pass
over in silence the opinions and hypotheses, with the discus-
sion of which our treatises on physiology are so filled." It
was my intention to have added a series of notes, but upon
a reperusal of the work they do not seem so necessary as at
first ; the few remarks which have been appended will not, I
trust, be found wholly useless.

TABLE OF CONTENTS.

Page
Preliminary Remarks, 1 — 19

General Characters of Living Beings, . . 3 — 8

Anatomical and physiological characters common to animals and
vegetables, 3— Nutrition. 3 — Proofs of the existence of the
nutritive movement, 4 — Duration and origin, 6 — Structure,
6 — Chemical composition, 7 — Review of the characters of
organized beings, 8.

General Characters of Animals, . . • . 8, 9
Chemical composition, 8 — Faculties more varied than in vegeta-
bles, 9 — Definition of the word animal, 9.

The Functions of Animals and their Organs, . 9 — 16
Organs, 9 — Apparatus, 10 — Function, 10 — Object of different
functions, 10 — Classification of the functions, 1 — Difference
between the functions of different animals, 10 — Division of the
vital labor, 11 — Consequences of this law, 12 — Effects of
mutilations, 12 — Experiments upon fresh water polypi, 13 —
Experiments upon earth-worms, 14 — Localization of the differ-
ent functions in the superior animals, 16 — Examples to be
chosen for the study of these functions, 16.

))l X^

vi contents.

Organic Tissues, . . . . . . 16 — 19

Materials forming the organs, 16 — Muscular tissue, 17 — Ner-
vous tissue, 17 — Cellular tissue, 17 — Mucous, fibrous, bony
tissues, etc., 19 — Elementary structure of the tissues, 19.

The Functions of Nutrition, . . . 20 — 151

The Nutritive Fluids, or the Blood, . . 21 — 33

Liquids contained in the body, 21 — Effects of desiccation, 21 —
Experiments upon the vibrio, 21 — Relative proportions of the
fluids and solids, 23 — Nature of the fluids, 23 — Blood, 23 —
White blood, 24 — Red blood, 24 — Globules of the blood, 24
— Form of the globules, 25 — Structure of the globules, 25 —
Coagulation of the blood, 26 — Chemical composition, 27 —
Proportions of the serum and globules, 28 — Uses of the glo-
bules, 29 — Effects of hemorrhage, 29 — Transfusion, 29 —
Influence of the form of the globules, 30 — Application, 31 —
Influence of the blood upon nutrition, 32 — Influence of the
organs upon the blood, 32 — Arterial and venous blood, 32.

Circulation of the Blood, ..... 33 — 41

Necessity of a circulatory movement, 33 — Apparatus of the cir-
culation, 34 — Heart, 34 — Vessels, 35 — Arteries and veins,
35 — Capillary vessels, 36 — Discovery of the circulation, 36 —
Proofs of the existence of the circulation, 38 — Greater and
less circulation, 39 — Direction of the blood, 39; — Crustace-
ous and mollusca, 39 — Fishes, 40 — Reptiles, 40 — Mammi-
ferac and birds, 40.

Apparatus of Circulation in Man, . . . 41 — 46

Heart, 41 — Aorta, 43 — Veins, 44 — Vena-porta, 44 — Pulmo-
nary artery, 44 — Pulmonary veins, 45 — Structure of the blood
vessels, 45.

Mechanism of the Circulation, . . . . 46 — 54

Contractions of the heart, 46 — Course of the blood in the arte-
ries, 48 — Influence of the arterial coats, 49 — Pulse, 50 —
Rapidity of the blood in the different parts of the body, 50 —

CONTENTS. Vll

Influence of the curvature of the arteries, 50 — Influence of the
division of the arteries, 50 — Communication of the arteries,
51 — Course of the blood in the veins, 51 — Passage of the
venous blood across the heart, 53 — Less circulation, 54.

Absorption, . . . . . . . . 54 — 67

Definition, 55 — Proofs of the existence of absorption, 55 —
Mechanism of absorption, 56 — Imbibition, 56 — Capillarity,
57 — Endosmosis, 57 — Transport of the absorbed liquids, 59

— Apparatus of absorption, 59 — Venous absorption, 60 —
Lymphatic absorption, 60 — Proofs of the venous absorption,
60 — Proofs of the lymphatic absorption, 62 — Lymph, 62 —
Lymphatic vessels, 63 — Circumstances influencing absorption,
63 — Permeability and vascularity of the tissues, 64 — Mass
of the humors, 65 — Nature of the absorbed substances, 66.

Exhalation, and the Secretions, .... 67, 68
Transudation, or Sanquineous Effusion, . . 68

Exhalation, . . . . . . . .68 — 72

Mechanism of the exhalation, 68 — Circumstances which influ-
ence exhalation, 69 — External and internal exhalations, 70.

Secretions, 72 — 75

Theory of the secretions, 72 — Secretory organs, 73 — Humors
secreted, 75.

Respiration, . . . . . . . . 75 — 98

The vivifying properties of the air depend upon the oxygen con-
tained in it, 77 — Production of carbonic acid, 78 — Azote,

79 — Pulmonary transpiration, 80 — Modifications of the blood,

80 — Theory of respiration, 80 — Source of the carbonic acid,

81 — Source of the vapor expelled, 83 — Recapitulation, 84 —
Activity of the respiration, 84 — Birds, 84 — Mammiferse, 84

— Inferior animals, 85 — Influence of animals and vegetables
upon the composition of the atmosphere, 85 — Relation be-
tween the activity of respiration and the vivacity of motion,

Vlll CONTENTS.

86 — Circumstances influencing the extent of the respiration,
86.

Apparatus of Respiration, . . . . . 87 — 92

Skin, 87 — Special organs, 87 — General characters of the respi-
ratory organs, 88 — Differences with regard to the mode of
respiration, 88 — Gills, 88 — Trachsea, 89 — Lungs, 89 —
Lungs of Man, 89.

Mechanism of Respiration, . . . . . 92 — 96

Structure of the thorax, 93 — Dilatation of the thorax, 93 — Con-
traction of the diaphragm, 94 — Motion of expiration, 94 — Ca-
pacity of the lungs, 95 — Frequency of the respirations, 95 —
Modifications of the respiratory motions, 95.

The Influence of Respiration upon the other Functions,

96 — 98

Upon the circulation, 96 — Upon the absorption, 97 — Upon the
pulmonary exhalations, 97.

Animal Heat, 98 — 105

Difference in the temperature of animals, 98 — Temperature of
the marnmiferae and birds, 99 — Hibernating animals, 99 — In-
fluence of age upon the production of heat, 100 — Influence of
the temperature, 101 — Influence of exercise, etc., 101 — Cause
of the production of heat, 101 — Influence of the nervous sys-
tem, 101 — Influence of the blood, 102 — Influence of the
respiration, 102 — Temperature of the different parts of the
body, 104 — Power of resisting heat, 104.

Digestion, ........ 105 — 142

Aliments, 106 — Phenomena depending upon the lack of aliments,
106 — Hunger, 106 — Death from inanition, 107, — Nature
and properties of the aliments, 107 — Modification of the ali-
ments by digestion, 109 — Scat of the digestive process, 109 —
Digestive apparatus, 110 — Prehension of the aliments, 112 —
Mouth, 113 — Stoppage of the aliments in the mouth, 113 —

CONTENTS. IX

Mastication, 113 — Teeth, 113 — Mode of formation, 114 —
Structure of the teeth, 1J5 — Chemical composition of the
teeth, 116 — Development of the teeth, 116 — Form of the
teeth, 117 — First dentition, 118 — Second dentition, 118 —
Muscles of mastication, 119 — Influence of mastication upon
digestion, 120 — Insalivation of the aliments, 120 — Saliva, 120

— Salivary glands, 121 — Deglutition of the aliments, 121 —
Mechanism of deglutition, 124 — Gastric juice, 126 — Delay
of the food in the stomach, 127 — Formation of the chyme, 128

— Peristaltic movements of the stomach, 128 — Duration of the
digestive process, 129 — Cause of the transformation of the ali-
ments into chyme, 129 — Intestines, 130 — Small intestines,
131 — Fluids contained in the small intestines, 131 — The
liver, 132 — Bile, 133 — Pancreatic juice, 133 — Pancreas,
133 — Delay of the chyme in the intestine, 133 — Chyle,
134 — Intestinal gases, 134 — Large intestine, 134 — Ccecum,
135 — Colon, 135— Progress of the remainder of digestion
in the large intestine, 135 — Theory of digestion, 136 —
Absorption of the chyle, 138 — Chyliferous vessels, 138 —
Chyle, 139 — Mechanism of the chylous absorption, 140 —
Uses of the chyle, 141.

Urinary Secretion, 142 — 148

Urinary apparatus, 142 — Urine, 143 — Source of the urine, 144

— Circumstances influencing the activity of the secretion, 145

— Gravel, and urinary calculi, 147.

Review, 148—151

Functions of Relation, ...... 151

Contractility, 151 — Volition, 152 — Sensation, 152 — Instinct,
152 — Intelligence, 153 — Expression, 153.

Nervous System, 154 — 166

Nervous tissues, 154— Encephalon, 154 — Parts protecting the
encephalon, 155 — Vertebral column, 155 — Dura mater, 155

— Arachnoid, 156 — Pia mater, 156 — Encephalon, 157 —

B

X CONTENTS.

Cerebellum, 160 — Optic lobes, 161 — Spinal marrow, 161 —
Fibres of the encephalon, 162 — Nerves, 164 — Ganglionic
system, 165.

Sensation, ........ 166 — 174

Sense of tact, 167 — Sensible and insensible parts, 167 — Influ-
ence of the nerves upon sensation, 167 — Functions of the spi-
nal marrow, 169 — Part taken by the brain in the perception
of sensation, 169 — Review, 170 — Nerves of sensation and
motion, 171 — Functions of the anterior and posterior roots of
the spinal nerves, 171 — Cephalic nerves, 172 — Anterior and
posterior columns of the spinal marrow, 172 — Great sympa-
thetic nerve, 172 — Special senses, 173.

The Sense of Touch, 174 — 179

Structure of the skin, 174 — Dermis, 175 — Rete mucosum, 175
— Epidermis, 175 — Pores, 176 — Perspiration, 176 — Hair,
176 — Nails, 176 — Seat of the sensation, 176 — Tact and
touch, 177 — Apparatus of touch, 177 — Use of this sense
ITS.

The Sense of Taste, 179— 1S1

Taste of bodies, 179 — Seat of the taste, 179 — Structure of the
tongue, 179 — Nerves of the tongue, 180.

The Sense of Smell, ..... 181 — 185

Odors, 181 — Olfactory apparatus, 182 — Mechanism of the
smell, 184 — Nerves of smell, 184 — Uses of the sinuses, 185.

The Sense of Hearing, ..... 185 — 196

Auditory apparatus, 1S5 — External ear, 185 — Pavilion of the
ear, 185 — Auditory duct, 186 — Middle ear, 187 — Cavity,
187 — Internal ear, 188 — Acoustic nerve, 189 — Mechanism
of hearing, 1^9 — Nature of sound, 1S9 — Use of the pavilion
of the ear, 190 — Use of the auditory duct, 191 — Uses of the
tympanum, 191 — Transmission of sounds through the cavity,
192 — Internal ear, 192 — Uses of the air contained in the

CONTENTS. Xi

cavity, 193 — Utility of the cavity, 193 — Eustachian tube, 194

— Uses of the bones of the ear, 194 — Modifications of the audi-
tory apparatus, 195.

Light, 196 — 224

Apparatus of vision, 196 — Globe of the eye, 196 — Iris, 197 —
Anterior chamber, 197 — Ciliary processes, 198 — Crystalline,
19S — Vitreous humor, 19S — Retina, 198 — Choroid, 198 —
Optic nerve, 199 — Ciliary nerves, 199 — Mechanism of
vision, 199 — Course of the light in the eye, 204 — Uses of the
aqueous humor, 204 — Uses of the pupil, 204 — Uses of the
crystalline, 205 — Formation of images upon the retina, 205 —
Uses of the choroid, 206 — Perfection of the eye, 206 — Ach-
romatism, 206 — Aberration of sphericity, 207 — Presbytia,
208 — Myopia, 208 — Uses of the retina, 209 — Muscles of
the eye, 211 — Uses of the nerves of the eye, 212 — Percep-
tion of images, 212 — Form of objects, 213 — Position of ob-
jects, 213 — Distance of objects, 214 — Size of objects, 216

— Motion of objects, 216 — Education of the sense of sight,
217 — Parts protecting the eye, 219 — Orbit, 219 — Eyebrows,
220 — Eyelids, 220 — Winking, 221 — Tears, 222 — Lachry-
mal apparatus, 222 — Apparatus of vision in animals, 223.

The Intellectual and Instinctive Faculties, 224 — 232

Perception, 224 — Memory, 225 — Reasoning, etc., 226 — In-
stincts, 226 — Relation between the development of the brain
and the intellectual faculties, 226 — Facial angle, 227 — Sys-
tem of Doctor Gall, 229.

Motions, . 232 — 280

Contractility, 233 — Muscles, 233 — Muscular contractions, 234

— Influence of the nerves, 235 — Galvanic experiments, 236

— Theory of muscular contraction, 237 — Nerves of voluntary
motion, 239 — Functions of the spinal marrow, 240 — Brain,

240 — The striated bodies, 240 — Cerebellum, 240— Respira-
tory movements, 241 — Functions of the medulla oblongata,

241 — Involuntary motions, 241 — Laws of muscular contrac-

Xll CONTENTS.

tion, 241 — Passive organs of motion, 243 — Skeleton, 243 —
Cartilages, 243 — Bone, 243 — Development of the bones,
244 — Structure of the bones, 244 — Form, 245 — Articula-
tion, 245 — Action of the muscles upon the bones, 247 — Force
of the muscles, 248 — Levers, 250 — Skeleton, 253 — Verte-
bral column, 253— Head, 258 — Cranium, 258 — Face, 260
— Thorax, 263 — Ribs, 263 — Superior limbs, 263 — Scapula,
2C3 — Clavicle, 264— Muscles of the shoulder, 264 — Hu-
merus, 265 — Ulna and radius, 265 — Hand, 266 — Carpus,
266 — Metacarpus, 267 — Phalanges, 267 — Inferior members,
268 — Iliac bone, 268 — Femur, 269 — Tibia, fibula, and pa-
tella, 269 — Foot, 270— Tarsus, 270 — Metatarsus, 271 —
Phalanges, 271 — Muscles of the leg, 271 — Animals with an
internal skeleton, 271 — Standing, 272 — Locomotion, 276 —
Progression, 277 — Swimming and flying, 278.

The Voice, 280 — 2S8

Mechanism of the production of sounds, 283 — Acquired voice,
287 — Singing, 287 — Articulation of sounds, 287.

Functions of Reproduction, .... 288 — 295

Creation of animals, 289 — Spontaneous generation, 291 — Nor-
mal generation, 292 — Generation by slips, 292 — Oviparous
generation, 292 — Viviparous generation, 293 — Development
of the foetus, 294.

Appendix 303

ANATOMY AND PHYSIOLOGY.

PRELIMINARY REMARKS.

The object of these lessons is to make known th ° e bj ?eLo!L
the most interesting points in the history of animals,
to signalize those which are useful or injurious to man,
and to show their respective influence upon industry and
riches in general.

To do this, the principal phenomena, which charac-
terize their mode of existence, must first be exposed,
and their form and structure described ; the means
indicated, by which naturalists distinguish between
them, and recognise with certainty all these beings, the
number of which is so great as nearly to terrify the
imagination. It must be shown, how they live, how
they are distributed upon the different parts of the sur-
face of the globe, how they contribute to the well-being
of man, or prove noxious to his industry, of what riches
they are the source, and of the means to which we have
recourse to procure them, or to draw from them and
appropriate to our own desires a portion of the products

1

2 ANATOMY AND PHYSIOLOGY.

they furnish. In other words, these lessons will be
devoted to the teaching of comparative anatomy and
physiology.

The simple announcement of the subject on which 1
propose to treat, will suffice to make its interest and
importance appreciated. In truth, where is the man,
whose curiosity has not been a thousand times excited
by the sight of the singular animals, which people all
around, and which present at every instant of their lives,
phenomena so remarkable, and, often, so incomprehen-
sible ? Who, when reflecting upon these phenomena,
and the actions we ourselves execute, does not experi-
ence the desire to scrutinize the interior of these com-
plicated machines, to know by what agents, by what
mechanism all these movements are executed ; to exam-
ine the processes, by which all organized beings assim-
ilate to their own substance the foreign substances by
which they are nourished ; and to inquire the uses of
the different organs, of which the body is composed. In
short, every enlightened man must perceive, that the his-
tory of animals producing pearls, silk, and wool, which
furnish us our daily food, or lend us their power, is of
no mean importance ; and no one can remain indifferent
to the knowledge of a multitude of other animals, which,
if less useful, are not less interesting, from the wonder-
ful instinct \\ it Ii which nature has endowed them.

It would then be useless to stop here, to prove that
the study of zoology is a necessary element of educa-
tion, or to establish by examples the interest presented
to us in this branch of human knowledge ; and I shall
therefore hasten to considerations more worthy to engage
our attention.

PRELIMINARY REMARKS.

GENERAL CHARACTERS OF LIVING BEINGS.

When we cast our eyes over the immense an/p^ys™!,?

i r • 1 i • l i . ^ 1 r ' C!, l characters

number or animals, which populate the surface common to an-
imals and veg-

of the globe, we are at first only struck by the etables -
enormous and innumerable differences they present ; a
man, a fish, a spider, and an oyster, for example, to a
superficial observer have nothing in common. But if
we examine with care these different beings, we shall
soon be convinced, that notwithstanding these differences,
there are a certain number of characteristics possessed
by each of them, and reproduced without exception in
all the other animals. These characteristics are of two
kinds ; some are furnished us by the material disposition
of the body, and consequently belong to anatomy ; ' the
others consist in the phenomena presented by these same
bodies during life, and they belong to physiology, 2 a sci-
ence, which treats of the actions and properties of living
bodies.

The chief distinction between animals and vegetables,
and all the other bodies of nature, is life, an interior
movement, the cause of which is unknown, but whose
effects are easily perceived.

All living beings, and these alone, possess Nutrition.
the faculty of duration for a time, and under a particular

1 Anatomy is that branch of the natural sciences, which treats of the
form, position, structure and qualities of the organs composing the bodies
of living beings. This name is derived from the Greek word hvaroula,
whose roots («>-« within and rhivsiv to cut) indicate the manner, in which
anatomical studies must be made.

2 From its etymology (<p)<ne nature and x6yog discourse) the word physi-
ology should signify discourse upon nature or science of nature, but it is
only employed in the signification given above.

4 ANATOMY AND PHYSIOLOGY.

form, by drawing constantly to their composition, appro-
priating to themselves, a part of the surrounding sub-
stances, and rendering to the exterior world a part of
their own ; in other words, these beings possess the
faculty of self-nourishment ; and, when the constant
addition of materials, of which they are composed, stops
without return, then this body dies, and is soon com-
pletely destroyed ; now, this movement has always a
limited duration, and death is a necessary consequence
of life.

With brute bodies, such as stones and minerals, it is
entirely different. Once formed, they exist, so long as
a foreign force does not destroy them ; and during this
time, not necessarily limited, they are not the seat of a
movement of nutrition : if their volume augments, it is
by the simple juxtaposition of another body similar to
themselves ; and if they lose a part of their own sub-
stance, it is by the action of a force from without, and
entirely independent of the cause of their existence.

The continual movement of composition and decom-
position, constituting the nutritive function of which
living bodies are the seat, escapes our senses ; but its
existence is revealed to us by numerous facts, very
readily perceived.

ex Kce 0fl of The desire constantly experienced by ani-
mOTement. ve mals to introduce into the interior of their
bodies foreign substances, which may serve them as
food, already suffices for the presumption, that these
beings must continually incorporate with their own
organs materials drawn from without ; and only by these
means can the increase of volume, so remarkable in all
these beings during the first periods of their existence,

PRELIMINARY REMARKS. 5

be satisfactorily explained. A new-born infant weighs
but about six pounds, and twenty-five years after, when
it has become adult, its weight exceeds an hundred ;
plainly then, at this epoch of its life, it has already de-
rived from substances, originally foreign, the greater part
of the materials of which its organs are composed. On
the other hand, the extreme emaciation, which ensues
upon certain diseases, proves that the living body may
abandon a portion of the matter, of which it was formed,
and render to the external world a part of its own sub-
stance.

The experiments of Sanctorius, who, in order to study
the phenomena of transpiration, passed a great part of
his life in a balance, prove also that the human body
constantly experiences diminutions of weight, which the
aliments are destined to repair.

But a single example can scarcely fail to remove all
doubt of the existence of the nutritive movement, even
in the hardest and deepest parts of the body. An Eng-
lish surgeon, Belchier, having by chance eaten of a hog
raised by a dyer, observed that the bones of the animal
were red, and attributing this peculiarity to the fact, that
it had been nourished on coloring matter, he conceived
the possibility of using similar means to render visible
the effects of the nutritive function ; and the experiments
undertaken by him at that time resulted in complete
success, and have since been satisfactorily repeated by a
great number of distinguished men. When animals have
been nourished upon madder for a certain time, it is
always found that the bones assume a red color ; but if,
after an animal has been thus fed, the use of the madder
is suspended, in a definite time the red matter, which

Q ANATOMY AND PHYSIOLOGY.

should have been deposited in the substance of these
organs, is no longer found, and must therefore have
been rejected. Now these facts can only be explained
by the continual movement of composition, or decom-
position, to which the name of nutrition has been
given.

^Duration and ^y e j iaye already seen, that after a certain
duration the nutritive movement is always stopped, and
that all living beings, after having existed for a time, the
extreme limit of which is fixed for each of them, must
necessarily perish. But this destruction of the indi-
vidual does not include the disappearance of the species ;
for another character, common to all these beings, is the
faculty of producing other beings like themselves, or in
other words, of perpetuating their race by the phenomena
of generation.

The origin of organic differs completely from that of
brute bodies. The latter have existed from the creation
of the world, or are formed by the combination of other
bodies in nothing resembling themselves. Living bodies,
on the contrary, always arise from a being like them-
selves, from a parent, to which they are at first united,
and from which they are separated, only when their
development is so far advanced, that they can maintain
an independent existence.

structure. All living beings have a common structure.
Their body is always formed by an union of parts dis-
similar in themselves, some of them being liquid, others
solid. It is a spongy tissue composed of lamina, or of
solid and very extensible fibres, which leave between
them interstices filled with fluid ; and this kind of struc-

PRELIMINARY REMARKS.

ture, which has received the name of organization, is
one of the essential conditions of their existence.

To give these bodies form, solid parts are evidently
necessary; and to sustain the nutritive movement, to
make penetrate into their intimate tissue the foreign
bodies destined to be incorporated there, to throw off the
particles ceasing to belong to them, fluid parts are also
requisite. The latter should be present in every part
in which life is to be sustained, should penetrate into
the substance of the solids as well as be diffused upon
their surface, and consequently these solid parts must
have a spongy and areolar texture. It is therefore im-
possible to conceive of the existence of a movement
similar to the nutritive, without a mode of structure like
that we have described ; and observation teaches us that
this organization is met with in all living beings, animal,
as well as vegetable. Thus to these has been given the
name of organic, in opposition to brute beings, which
are styled inorganic bodies.

Finally, the chemical nature of the materials, caSSSffi!
of which they are made up, is equally characteristic.
We always find in these bodies a certain number of sub-
stances also to be met with in the inorganic kingdom,
and which here offer nothing peculiar ; water for in-
stance ; but the products, which form the essential base
of all the solid parts of living bodies, belong properly to
the organic kingdom, and present very remarkable prop-
erties. The number of these substances is very con-
siderable, and although differing much in themselves
they are, for the most part, formed of the same elements
united in different proportions ; in general, compounds
of carbon, hydrogen and oxygen, or of substances

3 ANATOMY AND PHYSIOLOGY.

resulting from the union of these three elements with a

fourth principle, called azote. 1

the e c v i!arac°e f rs We see then, that there exist in nature two

of organized i r i t ,i • i i* •

beings. classes oi bodies ; the organized or living
bodies, and the brute or unorganized ; and, by reviewing
what has been said upon their properties, we shall find
that the general characteristics of the former, in which
alone we are interested, consist in their mode of struc-
ture and chemical composition, in the power they possess
of nutrition and reproduction, in their origin, and in the
limited duration of their existence.

GENERAL CHARACTERS OF ANIMALS.

coSSuon. ^ we now restrict yet closer the field of our
observations, and confine ourselves to the study of

1 Those substances are called elements, or simple bodies by chemists,
from which only particles of the same nature can be extracted : for exam-
ple, iron, gold, and sulphur ; at the present day about fifty are recognised,
and by their various combinations all (he other bodies in nature are formed.
Carbon, pure and crystalized, constitutes the diamond; while uncrystalized
and mingled with certain salts, it constitutes the ordinary charcoal ; thus,
to be convinced of the existence of this elementary principle in all organ-
ized bodies, it must be borne in mind, that when warmed by contact with
air so far as to decompose them, the residue is charcoal. Hydrogen, so
called because it enters into the composition of water, presents itself, when
isolated, under the form of a gas or aeriform fluid of extreme lightness;
combined with carbon, it forms the gas employed to give light, and is
obtained by distillation from coal, oil, etc. Oxygen is also a gas ; it forms
about the fifth part of the atmospheric mass, and produces by its combina-
tion with a great number of bodies the phenomena of combustion ; united
with hydrogen it forms water ; and united to carbon, the carbonic acid gas,
which is met with in the sparkling wines, beer, etc., and is also disengaged
from burning charcoal. It is called oxygen (which means generator of
acids) because it enters into the composition of the greater part of the
acids. Finally, azote is a gas, which, combined with oxygen, constitutes
the atmosphere.

PRELIMINARY REMARKS.

animals, we shall find that these beings have also other
characteristics, which are common to them, but not met
with in the organized bodies of the vegetable kingdom.
And first ; the chemical composition of these beings is
not the same ; the substances which constitute plants,
include little, or no azote, but have carbon as a basis ;
while in animals azote plays the principal part. 1

In these latter beings too, life is manifested JST^Zm

1 r l )• than in vegeta-

in a much more complicated form than m veg- wes.
etables. To the faculty of nutrition and of reproduc-
tion, is added that of executing, under the influence of
an inward volition, movements which tend to a deter-
mined end, and that of feeling, or receiving impressions,
and being conscious of them. Whence has arisen the
name of animated beings, given to animals in opposition
to vegetables, which are called inanimate.

To define, then, concisely, the word animal th ° word°an° f
we may say, that it is applied to every body "
endowed with the faculty of nutrition, of feeling, and of
executing spontaneous movements.

THE FUNCTIONS OF ANIMALS AND THEIR ORGANS.

The different phenomena by which life is organs.
manifested, are always the result of the action of some
part of the living body ; and these parts, which may be
regarded as so many instruments, bear the name of
organs. Thus an animal can execute movements only

1 This difference in the composition of vegetable and animal substances
is easily proved ; when the latter are burned, the azote they include, com-
bines with a certain quantity of hydrogen, and forms ammonia, which dif-
fuses a peculiar odor when disengaged. Substances not containing azote
do not possess this odor.

2

]Q ANATOMY AND PHYSIOLOGY.

by the action of certain organs called muscles, and can
obtain a knowledge of what surrounds it only through
the intervention of the organs of the senses.

Apparatus. When several organs concur to produce a
phenomenon, this assemblage of instruments is known
by the name of apparatus, and the action of an isolated
Function, organ, or an apparatus is called the function.
For example, we say locomotive apparatus, to designate
the collection of organs which serve to transport the
animal from one place to another, and function of loco-
motion, to designate the action of all these parts.

object of The functions of the animals have relation to

different func-
tions. two objects : the preservation of the individual

and the preservation of his race ; but among the first
an important distinction remains to be established ; some
serve for the support and increase of the body, others to
place the animal in relation with the beings which sur-
round him. As for the functions of reproduction, there
results from them the formation of new beings, similar
to those from which they originate.

offfSSS The functions or acts of these beings may
then be divided into three great classes, viz. ; the func-
tions of nutrition, the functions of relation, and the
functions of generation. Those of nutrition and gener-
ation, as we have already seen, are common to plants
and animals ; therefore to them has been given the col-
lective name of functions of the vegetative life ; but those
of relation exist only in the latter, and constitute what
physiologists call animal life.

Differe 'he manner in which the functions of ani-

between the

functions

different

some these acts are but few, and life is mani-

j£i.mals are executed, varies considerably. In

PRELIMINARY REMARKS. \\

fested only by a small number of faculties ; in others, on
the contrary, the most varied phenomena may be ob-
served, and the existence of a multitude of faculties,
with which the former are not endowed. Now, each of
these phenomena, as we have already seen, is the result
of the action of some part of the body ; and observation,
as well as reason, prove that the mode of action of an
organ, or instrument, depends always upon its intimate
nature, structure, and its other properties. It follows,
therefore, that the organization of different animals must
offer as little uniformity as the modes, according to which
these beings fulfil the three orders of functions already
mentioned.

In animals with the most limited faculties and simplest
life, the body every where presents the same structure.
The parts composing it are all similar ; and, the identity
of organization presupposing an analogous mode of
action, the interior of these beings may be compared to
a work-shop, where the workmen are employed in the
execution of similar labors, and where consequently their
number would influence the quantity, but not the nature
of the products. Each part of the body performs the
same function as its neighbor, and the general life of the
individual is composed only of phenomena, character-
izing the life of some one of its parts.

But in proportion as we ascend in the series thr^'nabo ^
of beings, as we approach man, the organization becomes
more complicated ; the body of each animal is composed
of parts, becoming more and more dissimilar, as well in
form and structure, as in function ; and the life of the
individual results from the accumulation of a constantly
increasing number of instruments, possessed of different

19 ANATOMY AND PHYSIOLOGY.

faculties. It is at first the same organ, which feels,
moves, absorbs from without nutritive substances, and
which continues the species ; but by degrees the differ-
ent functions are localized, they acquire instruments
proper to themselves, and the different acts, of which
they are composed, are executed in their turn by distinct
organs. Thus, the more the life of an animal is com-
pounded of different phenomena, and the more subtile
its faculties, the greater is the division of labor in the
interior of its body, and the more complicated its bodily
structure.

The principle which seems to have guided nature in
the perfection of beings, is, as we see, precisely the one
which has had the greatest influence upon the progress
of human industry : the division of labor.
of C th?s S 3! nces There is another consequence of this law,
which merits our attention, and which necessarily pre-
sents itself to the mind, however little we may meditate
upon the facts of which we have just spoken. We have
seen, that the higher an animal stood in the series of
beings, the more various were the instruments destined
to produce the collection of the vital phenomena, and
the more special and limited were the functions of each
of these organs. It results then, that the destruction of
mutt£i C ons. of any part of the body must produce trouble in
the economy, in proportion to the perfection of the facul-
ties of the animal ; and that those beings will remain
so much the less injured by mutilations, whose bodily
structure is less complicated.

Now this observation conduces to the explanation of
several facts, which, at first, appear incomprehensible,
and finds its confirmation in certain phenomena so extra-

PRELIMINARY REMARKS.

13

ordinary, that they would have been rejected as fables,
if they had not been stated by men, whose testimony is
indisputable.

Thus there exist animals, whose bodies may n J2F5lJ"J3{!
be divided into many pieces without arresting m°.
the vital movement; on the contrary, each fragment
afterwards takes on an unusual development, and soon
constitutes a new animal, similar in form to that from
which it springs, quite as perfect in its kind, exercising
the same functions, and living in the same manner.

Fig.V

The singular beings,

called
by naturalists fresh water poly-
pi, or hydrae, and which are
often found under the water len-
tils, present this queer phenom-
enon ; mutilate them as you
will, far from killing you mul-
tiply them. A naturalist of
Geneva, of the last century,
Tremblay, to whom the know-
ledge of these curious facts is due, opened one of these
little animals ; then he stretched and cut it in various
ways, completely chopping it up, and, notwithstanding
this state of extreme division, each of its fragments soon
became a complete animal.

1 la the figure 1 are represented several hydra attached to the water
lentils (a) ; these animals, as will be shown, consist only of a small gela-
tinous tube, open at one of its extremities, and surrounded by a circle of
filaments called tentacula, by the aid of which they introduce aliments into
their digestive cavities. One of the polypi (b) bears on the sides of its
body two young, which spring from it, and will soon be detached.

J4 ANATOMY AND PHYSIOLOGY.

To comprehend this phenomenon, in appearance so
contradictory to all that the higher order of animals
teaches us, we must first examine the mode of organiza-
tion of the polypi, of which we have but now spoken.
These animals are too small to be profitably studied with
the naked eye ; but when seen through a microscope,
the substance of their body is found to be every where
identical ; it is a gelatinous mass, in which no distinct
organ can be perceived, enclosing globules extremely
small.

Now, as we have already remarked, identity in the
mode of organization necessarily supposes identity in the
mode of action, of the faculties. It therefore follows,
that all the parts of the body of our polypi, having the
same structure, must fulfil the same functions ; each of
them must unite in the same manner with the rest to
the production of the phenomena, whose union consti-
tutes life ; and the loss of one, or several, of these parts
does not therefore presuppose the cessation of any of
these acts. But if this be true, if each portion of the
body of these animals is capable of feeling, motion,
nutrition, and the reproduction of a new being, we see
no reason, why, after being separated from the rest, it
may not, if placed in favorable circumstances, continue
to act as before ; and why each of these fragments of
the animal may not only continue the performance of
those functions, necessary for the support of life, but
also reproduce a new individual, and perpetuate its race ;
phenomena fully proved by the testimony of Tremblay.
Experiments Let us now apulv this same principle to

upon earth l i J i i

worms. beings, whose structure is less uniform, and
whose different acts have already instruments appropri-

PRELIMINARY REMARKS. 15

ated to each of them. Let us take, for example, the
lumbricus terrestris, or earth worm.

In this cylindrical and slender animal the localization
of the functions has already been established ; nutrition
is composed of a series of acts executed by different
instruments ; digestion is effected in a cavity, whose
walls possess particular properties ; there exists also a
system of canals, serving to conduct the nutritive
materials to all parts of the body, and an apparatus,
which has become the principal seat of the faculty of
perceiving impressions, and determining movements ;
and finally, we find instruments intended merely for
locomotion. Thus we cannot conceive the possibility of
dividing in every way the bodies of these worms, as
was done in the polypi, without death. But, if we
examine the disposition of these different sets of appa-
ratus, which concur, each in a different manner, to the
support of life, we shall find that they extend uniformly
from one extremity of the body to the other, and that
each transverse segment of the animal differs but little,
or not at all, from the others ; it is a constant repetition,
and represents to a certain extent the entire animal, for
it includes all the organs, the action of which is neces-
sary to the vital movement. We can then easily con-
ceive the possibility of detaching a certain number of
these segments from the rest of the body, without causing
either section to lose any of the vital properties enjoyed
by the entire individual ; and this really takes place. If
an earth worm be cut transversely into two, three, ten,
or twenty pieces, each of its fragments may continue to
live as the whole, and to constitute a new individual.

16 ANATOMY AND PHYSIOLOGY.

Localization But by ascending yet higher in the scale of

of the different J ~ J O

Sr'su^rior animated beings, the division of physiological

animals. i 1 * 1 i-/v t-

labor is seen to augment ; the different functions
become the appendages of so many particular sets of
apparatus ; each of the acts resulting is executed by a
special instrument, and these different sets of apparatus,
instead of being uniformly distributed through the whole
extent of the body, are lodged in different parts ; so that
the loss of each portion of the body deprives the animal
of some faculty, and produces in the economy a disturb-
ance great in proportion to the importance of the faculty
in the support of life.

be E c X hoTe P n es for I 11 studying the different functions of ani-
ti'e functions, mals, I shall be obliged to indicate the manner
in which each of them is complicated and perfected by
means of this division of labor ; but I shall only dwell
upon the most important facts, and shall confine myself
to the examination of the phenomena of life in beings,
which in this relation occupy the summit in the series of
animals. In truth, it is, when each of these phenomena
results from the action of a particular instrument, that
the different acts of which the function is composed,
may the more easily be observed, and the effects of life
be better analyzed ; consequently the most complicated
animals are the best known to anatomists and physiolo-
gists, and offer to us the greatest interest.

ORGANIC TISSUES.

Materials The bodies of these beings include a consid-

forming the

organs. erable number of different organs ; but if the
comparative structure of these different parts be exam-
ined, we shall soon be convinced that the materials, of

PRELIMINARY REMARKS. ]7

which they are composed, are far less variable than was
at first supposed. They are in truth the same tissues,
differently combined and taking upon themselves partic-
ular forms, which constitute the greater part of our or-
gans. The principal organic tissues are three, namely,
the muscular, nervous, and cellular.

The muscular tissue constitutes what is com- tissue"
monly called the flesh of animals ; it is the productive
agent of all their movements, and always consists of
fibres capable of contraction. Sometimes these fibres,
so to speak, are dispersed in the substance of our organs ;
at others, they are collected into masses and form mus-
cles ; but whatever be their arrangement, they are always
distinguished by their contractile property ; and in the
body of man, as well as of most animals, they are met
with in those situations, where there are movements to
be executed.

The nervous tissue is a soft, usually whitish Nerv s ™! tis "
matter, which constitutes the brain and nerves, and
is the seat of the faculty of perception ; when treating
of the functions of relation we shall have occasion to
study its properties and uses.

Finally, the cellular tissue, so called from its CeU sul tis "
spongy and areolar texture, is of all the materials con-
stituting our organs the most universally diffused. In
the simplest animals it appears to form almost the totality
of the body ; and in those which have, like man, the
most complicated structure, this tissue forms a layer more
or less thick between all the organs, it fills the interstices
these parts have between them, and is also met with
in their very substance, where it serves to unite the
different portions of which they are composed, as on the

3

13 ANATOMY AND PHYSIOLOGY.

surface it tends to connect the different apparatus of the
economy ; it is in a measure the link of all the organs,
and by its different modifications gives birth to the mem-
branes, and to many other tissues ; finally, in it the fat is
always deposited, but the little sacs containing this mat-
ter are completely distinct.

This tissue is a whitish, semi-transparent, and very
elastic substance, composed of filaments and small lam-
ellae more or less consistent and irregularly connected,
so as to leave between them grooves, or cellules of vari-
able size. These cellules have but incomplete walls,
and are separated from each other only by a kind of
spongy lining; thus they communicate together, and afford
a ready passage to the fluids, which traverse them ; lastly,
they are moistened by an aqueous liquor loaded with al-
buminous particles, and known by the name of serosity.

The communication of these cellules is easily demon-
strated ; if a hole be made in the skin of an animal
recently killed, and air blown into the cellular tissue,
this fluid penetrates to all parts of the body, and distends
them. Butchers do this every day to make their meat
look well ; it has also been practised by some beggars, to
deform in a most hideous manner the bodies of unfortu-
nate children, and thus excite curiosity, or public com-
miseration.

An example to the point. — A celebrated surgeon of
the sixteenth century, Fabricius Hildensis, relates, that in
1593 there was exhibited at Paris an infant from fifteen
to eighteen months of age, whose head was of monstrous
size ; the parents of the little unfortunate carried it from
city to city as an object of curiosity, and attracted a
great number of spectators ; but a magistrate, having

PRELIMINARY REMARKS.

19

suspected some fraud, caused them to be arrested and
put to the torture ; they then acknowledged, that a hole
had been made in the skin upon the summit of the head
of the child, and air blown in by means of a tube. The
operation was repeated every day, and thus in time the
head of their child had acquired this unusual aspect. In
our day we have seen this barbarous practice pursued by
a beggar of Brest.

'tab 1

The other organic tissues, which concur with mucous. &.

° brous, honytis-

the preceding to form the different parts of the sues > etc -
body, are the serous and mucous membranes, the different
varieties of the fibrous tissues, (tendons, aponeuroses,
etc.) cartilages, bones, etc. ; but to all appearance these
are only modifications of the cellular tissue. Finally,
we often see them accidentally developed from the cel-
lular tissue ; and in most of these cases the cause of
their formation is known : thus, whenever the cellular
tissue is submitted to pressure and constant friction, it is
transformed to a serous membrane ; when in contact for
some time with an irritating liquid, it puts on all the
characters of the mucous membranes ; under the influ-
ence of traction and mechanical irritation, it gives birth
to fibrous membranes : and it is to be remarked, that all
these membranes exist in a normal manner in the econo-
my, only where those causes act, which elsewhere would
have determined their formation. The more accurate
study of these tissues will naturally find its place Elementary

J J l structure of

in the course of this w T ork ; we will only add the lissues *
here, that all, both the primitive cellular, the muscular,
and the nervous tissues, appear in the final analysis to be
composed of small globules, visible only by the aid of
the microscope, and formed in circles of varying disposi-
tion.

20 ANATOMY AND PHYSIOLOGY.

THE FUNCTIONS OF NUTRITION.

Nothing certain is known of the manner in which
nutrition is effected ; and it is even probable, that for
some time yet the mechanism of this internal movement,
the existence of which has been already demonstrated,
will remain a mystery to physiologists ; but if it has
been impossible directly to observe the labor, by which
the constituent materials of the organs are constantly
renewed, greater success has attended the investigation
of the different acts, which prepare, or accompany this
curious phenomenon. We know the principal agent of
nutrition, and how it is distributed to the different parts
of the body. The manner, in which this agent, the
blood, can transport to all the organs materials not origi-
nally belonging to it, but which were deposited in a cer-
tain part of the body, or simply in contact with certain
parts, has been successfully studied. It has also been
found, that in traversing the organs the blood is deprived
of a portion of its constituent parts, gives birth to new
liquids, and changes its nature to such a degree, that it
is no longer suited to discharge its functions, until it has
been, in some sort, regenerated by the action of the air ;
lastly, it has been seen, that the nutritious liquid, thus
conducing to the support of the organs, is exhausted,
and must be renewed from foreign matters suitably pre-
pared, in organs especially appointed for this purpose.

These various phenomena of vegetative, or organic
life, give rise to the functions of circulation, absorption,
exhalation, secretion, respiration, and digestion ; acts,
which we are now about to study.

THE NUTRITIVE FLUIDS. 21

THE NUTRITIVE FLUIDS, OR THE BLOOD.

It has been shown that the nutritive function can take
place only by the intervention of fluid parts, and that
every organized body includes liquids as well as solids.

These liquids are merely water, holding in ta ££ d u {J 8 t J£ n -
solution or suspension various substances, of body-
which we shall speak hereafter. To their existence, in
the thickness even of the solid parts of the body, ani-
mals owe in a great measure their rounded form, and
from them their organs derive suppleness, and the other
qualities necessary for the exercise of their functions.
Thus by desiccation a tendon is diminished in volume,
loses its suppleness, whiteness, and pearly brilliancy, and
becomes hard, rigid, semi-transparent, and brownish ;
but if then plunged into water, it will rapidly absorb
this liquid, and retake in proportion to the absorption the
properties it had lost.

From this it might easily be concluded, that de SSattonf
the desiccation of an organized body, carried to a certain
degree, must always interrupt the vital movement, and
produce death. And this is [always observed ; u E J\™ m ™ ts
but to demonstrate in a manner yet more brio,etc
evident the part these liquids play in the animal econo-
my, I must state here the curious results obtained by
Spallanzani, Buffon, Bauer, and some other naturalists in
their experiments upon the desiccation of certain micro-
scopic animalcules. When the water, in which their
bodies are soaked, is in a great measure evaporated,
many of these extremely minute beings lose the power
of motion, and cease to afford any sign of life ; but they
do not perish at once ; they may be preserved in this

22 ANATOMY AND PHYSIOLOGY.

state of apparent death for a very long time, and to
recall them completely to life only a little water is
requisite ; this takes place in the vibrio of wheat, an
animalcule resembling a small eel, or rather the ends of
thread, and which lives in the grains of blighted wheat. 1
If placed in a drop of water, and examined by the
microscope, they are at first seen swimming with viva-
city ; but when the liquid has evaporated, they remain
immovable, and distil from their bodies a kind of var-
nish, which covers them and prevents farther desiccation.
They are then completely deformed, and resemble in
nothing living beings ; notwithstanding, by plunging
them into water they soon retake their forms, and return
perfectly to life, even after having been in this state of
apparent death for several months.

1 Wheat is subject to several maladies, such as carbon, ergot, blight,
rachitis, etc. The majority of these alterations depend upon the develop-
ment of a species of insect, called uredo, in the substance of the grain ; but
rachitis is owing to the presence of the vibrio, for this disease may be pro-
duced in ordinary wheat, by inoculating the grain with these animalcules.
The vibrio is at the most from two to three lines in length, and about the

sixth of a line in diameter.

Fig. 4.

Fig. 2.

Fig-.Z.

Fig. 2 exhibits one of these animalcules as seen through a microscope ;
and Fig. 3 a grain of wheat magnified and cut in two, to display the
vibrios lodged in it, and the alterations they have caused; lastly, Fig. 4
represents an ear of wheat, which has rachitis ; the black points are the
diseased grains. What is said by BulTon with regard to the animalcules of
ergoted wheat, must be applied to the vibrios of rachitised wheat, for in
the ergot they are not met with.

THE NUTRITIVE FLUIDS. 23

Similar phenomena have been observed upon other
microscopic animalcules, called by naturalists Rotifera,
and met with in spouts. But with most animals it is
quite different ; for to them a real death is always the
immediate consequence of desiccation to a certain de-
gree. Fishes afford us a striking example, for when
drawn from the water they soon perish, and their death
is principally to be attributed to the desiccation of their
gills.

The proportion of fluids contained in the Relative pro-

1 i portions of ttie

body of an animal is much more considerable f d u s ' lls a " d so1 "
than we should have at first imagined. The tendons,
of which we were speaking above, contain half their
weight of water, and the proportion is much greater in
the other organs. The body of a man contains about
nine tenths of its weight of fluid ; when a body, weigh-
ing an hundred and twenty pounds, had been dried in
an oven seventeen days, its weight was found to be
reduced to twelve pounds ; and mummies have been
found not weighing more than seven or eight pounds.
In other respects the proportion of fluids and solids
varies according to the animals, and individuals ; we
may generally say, that the relative proportion of the
former is greater than the latter in youth, and animals of
a simple structure.

In the animals of an uniform structure, all th fS,. of
the liquids of the economy are similar. They appear to
be merely water, more or less loaded with organic parti-
cles ; but in the beings occupying a more elevated rank
in the zoological series, the humors cease to be all of the
same nature, and there is one destined in a special man-
ner to supply the wants of nutrition : this liquid Biood.
is the blood.

24 ANATOMY AND PHYSIOLOGY.

white biood. In the majority of inferior animals the blood
is far from possessing those physical characters, by which
it is recognised in man, and the animals nearly allied to
him ; instead of being red, and thick, it consists merely
in an aqueous liquid, sometimes completely colorless,
sometimes slightly tinged with yellow, rose, or lilac. It
is therefore difficult to be seen ; and for a long time it
was supposed, that these beings were completely desti-
tute of it, hence they were called bloodless animals.

The animals with white blood, or having the blood but
slightly tinged, are very numerous : all the insects enter
into this class, and it is an error to consider flies, as hav-
ing red blood in their heads. When one of these animals
is crushed, we see, it is true, a reddish liquid exuding,
but this matter is not from the blood, it arises merely
from the eyes of these little beings. Spiders, crabs,
lobsters, and all animals resembling the latter, and which
are classed by zoologists as Crustacea, have colorless
blood ; also snails, muscles, oysters, intestinal worms,
and all other animals of the class mollusca, and of the
zoo/)hytes.

Red wood. The blood, on the contrary, is red in all ani-
mals whose structure approaches man ; such as the raam-
miferae, birds, reptiles, fishes, and even worms of the
class, annelida.

oSSSu ° f When the blood of any of these beings is
examined by the microscope, it is constantly found to be
composed of two distinct parts ; of a yellowish and
transparent liquid, to which has been given the name of
serum, and of a multitude of little solid corpuscules, reg-
ular in form, and of a beautiful red color, which swim in
the fluid just mentioned, and which arc called the
globules of the blood.

THE NUTRITIVE FLUIDS. 25

In man, and all other animals of the class g £i^. of llie
mammiferae (the dog, horse, ox, for example,) Fig. 5.1
the globules of the blood are circular ; but in
birds, reptiles, and fishes, they have constantly
an elliptical form. These corpuscules are ex- ^^.
tremely small. In man, the dog, hare, and ^^
some other mammiferae, their diameter is equal pi^ 7.
only to about the one hundred and fiftieth part |l|J||||
of a millimetre ; in the sheep, horse and ox
they are but one two hundredth of a millimetre ; in the
goat they seldom exceed the one three hundredth of a
millimetre. In birds the globules of blood are greater
than in the mammiferae : their smaller diameter is in
general one one hundred and fiftieth of a millimetre, and
their greater diameter varies according to the animals,
from the one one hundredth to the one seventy fifth of a
millimetre. In the class of fishes and reptiles, these
corpuscules are yet greater ; in the frog, for example,
their smaller diameter is one forty fifth of a millimetre,
and their larger one seventy fifth.

When these globules are attentively examined thf ^buiL**
by a powerful microscope, they are seen to be composed,
each of two distinct parts, consisting of a kind of blad-
der, or membranous sac, in the centre of which is found
a spheroidal corpuscule.

Usually this investment is depressed, and Fig. 8.*
forms around the central nucleus, a circular
rim varying in size, so that the whole pre- fty 9
sents the aspect of a lens. The exterior ^BRfatl
envelope of the globules is formed of a kind

1 Fig. 5, blood of a man ; Fig. 6, blood of a sheep ; Fig. 7, blood of a
sparrow. These globules are magnified one thousand times.

2 Fig. 8, profile view of the globule in the blood of the frog, magnified

4

26 ANATOMY AND PHYSIOLOGY.

of jelly, easily divided, and of a variable red color ; to
the presence of these vesicles the blood owes its color.
The central nucleus of the globules exhibits more con-
sistence, and is not colored.

of S flood?" In the ordinary state the blood is always
liquid, and is composed, as we have already said, of an
aqueous fluid, holding solid globules in suspension ; but
there are circumstances, in which its physical properties
are completely changed. This takes place, for example,
every time that the blood is drawn from the vessels, in
which it is contained in the interior of the body of the
living animal ; when left to itself it is transformed in a
few moments to a mass of gelatinous consistence, which
is separated by degrees into two parts ; one liquid, yel-
lowish, and transparent, formed by the serum ; the other
more or less solid, completely opaque, and of a red color,
to which has been given the name of clot, or ftbrine of
the blood. The latter is composed principally of globules
more or less changed.

The blood sometimes loses this property of coagulation.
This singular phenomenon is remarked in animals killed
by a strong electric shock, by lightning, for example, and
by the action of certain poisons, such as the bite of ven-
omous serpents. Lastly, at other times the blood may
resemble its usual mass, but afterwards it separates into
three parts, the serum, the clot, and a soft grayish layer,
which occupies the surface, and is called the buffi) coaf -
It is especially in persons affected with inflammatory
diseases, such as pneumonia, or inflammation of the
lungs, and acute rheumatism, that the blood is thus

about seven hundred times. Fig. 9, front view of the same ; the envelope
is torn so as to exhibit the central nucleus.

THE NUTRITIVE FLUIDS. 27

coated ; and the majority of physicians agree in regard-
ins; it as a certain sign of the existence of an internal
inflammation ; but recent observations prove, that the
formation of the coat may depend upon circumstances
entirely different, and which in themselves have no im-
portance, such as the size of the opening in the vein, the
form of the vessel in which the blood is received, etc.

Chemistry teaches us, that the blood contains oJJjSSn.
the greater part of the substances, which enter into the
composition of the different organs of the body which it
is destined to nourish. In man, to the hundred parts of
blood there are met with seventy-eight parts of water,
six to seven parts of albumen, 1 fourteen to fifteen parts
of fibrine and coloring matter, 2 some thousandths of fatty
matters, soda, salts, 3 finally traces of the peroxide of iron.
Under ordinary circumstances, those substances cannot
be discovered in the blood, which are found in the differ-
ent humors formed from it in the interior of the body ; but
if the action of those organs, upon which the secretion of
those humors depends, be arrested, then we find the mat-
ters in question in the blood. It must then be concluded,
that they always exist, but in too small quantity to be
appreciated by our means of analysis, and that the organs

1 Albumen is a matter, which enters into the composition of the majority
of the organic tissues of animals, and which forms almost of itself alone,
the white of the egg. It dissolves in water, but solidifies and becomes in-
soluble by heat. From the existence of the albumen in the blood, the
sugar refiners employ this liquid to clarify their syrup, as might be done by
the white of eggs.

2 Fibrine forms the basis of muscular flesh. To extract it from the
blood this liquid must be beaten with rods before it coagulates; the fibrine
attaches itself to the twigs, in the form of white, very elastic filaments.

' Chlorides of sodium and of potassium, phosphates, sulphates and alka-
line carbonates, and carbonates of lime, magnesia and iron.

ANATOMY AND PHYSIOLOGY.

we have mentioned do not form them, but separate them
from the blood as they are developed. Wherefore the
blood may reasonably be regarded, as containing all the
materials necessary for the formation, both of the solid
and fluid parts of the body, and as well meriting the
name, conferred upon it by some authors, of flowing Jlesh.
proportions The relative proportions, in which the liquid

of the serum II? T.

and globules. anc j so y l( [ p arts? or t h e g] bules and serum enter
into the composition of the blood, vary in different ani-
mals ; and as we shall soon see, there exists a remarkable
relation between the quantity of the globules, and the
heat developed by these beings. Birds are of all ani-
mals those, whose blood is richest in globules, and those
also whose temperature is the most elevated ; the glo-
bules constitute in general fourteen or fifteen hundredths
of the total weight of this liquid. The blood of the
mammiferae contains rather less, and in this connection a
difference exists among these animals ; in the carnivorous
and omnivorous classes the proportional quantity of glo-
bules seems to be greater than in the herbivorous ; in
man, the dog, and cat, they constitute from twelve to
thirteen hundredths of the total weight of the blood ;
while in the horse, sheep, calf, and hare, they form but
seven or nine hundredths. But the number of herbivo-
rous and carnivorous, whose blood has been examined, is
not so great that this result can be regarded as a physio-
logical law. Lastly, in reptiles and fishes, which are
styled animals with cold blood, on account of the little
heat they develope, the relative quantity of the globules
is much less, and hardly exceeds five or six hundredths
of the total weight of the blood.

In other respects, the proportions of the solid and

THE NUTRITIVE FLUIDS. 29

liquid elements vary in individuals of the same species,
and different circumstances may occasion modifications
in the blood of the same animal. The quantity of glo-
bules is greater, and that of the water less, in man than
in woman, and in the blood of individuals of a sanguine
temperament, than in those of a lymphatic.

It would appear, that there exists an intimate g i u b s u T es ? f the
relation between these globules, and the vital energy ;
where the phenomena of life are exhibited with the most
intensity, there it is found, that the blood is richest in
globules, and vice versa. It is even to the presence of
these particles, that this liquid owes, in a great measure,
the faculty of exciting and sustaining the vital move-
ment. The following experiment is a proof of it.

When an animal is bled to syncope, and the h eS?agI
flow of blood not arrested, in a few moments all muscular
motion ceases, respiration is arrested, and life is no longer
manifested by any exterior sign. If the animal be left
in this state, the reality soon succeeds to the appearance,
and death speedily arrives. But if blood, similar to that
which it had lost, be injected into its veins ; this Transfusion.
apparently dead body is seen with astonishment to return
to life ; in proportion as new quantities of blood are in-
troduced into its vessels, it gradually revives, and soon
breathes freely, moves with facility, resumes its accus-
tomed habits, and is completely reestablished.

This operation, known by the name of transfusion, is
surely one of the most remarkable ever made ; and
proves, better than all that can be said, the importance
of the action of the globules upon the living organs ; for
if serum destitute of globules be employed, no more
effect is produced than if cold water had been used, and

30 ANATOMY AND PHYSIOLOGY.

death is notwithstanding an inevitable consequence of
the hemorrhage.

But it is not as a simple physiological experiment, that
transfusion has become celebrated ; it is as a curative
means, that attention has been directed to it, and its his-
tory will furnish an example of the grave errors, into
which men fall, when they would apply to practice an
incomplete science, a danger, which has caused it to be
said with some truth, that " ignorance is less dangerous
than half knowledge."

About the middle of the seventeenth century, physi-
cians attributed almost all diseases to alterations in the
blood ; and they supposed that by changing this they
would be able to heal all ills ; thus, without having pre-
viously studied the conditions necessary for the success
of the operation of transfusion, they hastened to put it
in operation ; and Wren in England, Major in Germany,
Druis and Emmert at Paris, and several other physicians,
caused to be thrown into the veins of their patients
sometimes blood from a healthy man, and sometimes
from a calf.

Some of these attempts were not injurious, but others
occasioned the most unfortunate accidents, even death ;
and by an act of the parliament of Paris, passed in
1668, an end was happily put to these murderous exper-
iments.

influence of If, instead of prematurely applying the ope-
gioimics. ra tion of transfusion to the art of healing, the
question had been studied in its different aspects, as has
been done of late years, these misfortunes would have
been avoided, and a means, which in some cases is really
useful, would not have been generally proscribed. The

N

THE NUTRITIVE FLUIDS. 31

experiments published at London by Blundel, and at Ge-
neva by Dumas and Prevost prove, that by proceeding
in a certain manner the operation is always successful,
but if an opposite course be followed, it leads to an un-
fortunate result. Thus the first condition of the success
of transfusion, is the injection of blood flowing from an
animal of the same species with that, upon winch the
operation is performed. If blood be introduced, differing
from that of the animal in the volume of its globules,
and not in form ; if, for example, the blood of a cow, or
sheep, be thrown into the veins of a cat, or hare, the lat-
ter revives but imperfectly, and soon dies. Finally, if
blood with circular globules be transfused into animals,
whose blood contains elliptical globules, or vice versa,
death takes place in a short time, and is accompanied by
nervous symptoms similar to those produced by the most
violent poisons.

The result then of transfusion, as it was prac- Application.
tised in the seventeenth century, is not to be wondered
at ; for it was inferred, that because the blood of a sheep
could be introduced into the vessels of another sheep, it
might also be injected into the veins of a man. But on
the other hand, we see, that by employing only the blood
of an animal of the same species with that on which we
operate, it would not be impossible to derive a successful
result from transfusion in the practice of medicine ; and
in England it has been employed with marked success in
several cases, where death was imminent. Notwith-
standing, recourse can only be had to this operation in
extreme cases, for it is always very delicate ; and if a
certain quantity of air be introduced into the veins along
with the blood, a thing which may easily happen, the

32 ANATOMY AND PHYSIOLOGY.

death of the patient is instantaneous ; for this gas, hav-
ing arrived at the cavities of the heart, is warmed, ex-
pands, and prevents their contraction, a mechanical ob-
stacle, which stops the circulation.
influence of The influence of the blood upon nutrition is

the tilood upon L

nutrition. equally easy to be demonstrated. When the
quantity of this liquid received by any organ is dimin-
ished by mechanical means in a marked and permanent
manner, the latter is seen to diminish in size, and often
to contract, and be reduced almost to nothing. On the
other hand, the greater the functions of any part, the
more blood it receives, and the more it increases in size.
Every one knows, that muscular exercise tends to devel-
ope the parts which are the seat of it ; as in dancers, for
example, the muscles of the leg, and of the calf espe-
cially, acquire a remarkable size, while in blacksmiths,
and other men, who execute rough labor with their arms,
the muscles of the superior limbs become more fleshy
than the other parts. Now the muscles receive more
blood when they contract than when in repose, and by
this afflux of blood the nutritive labor, of which they are
the seat, is rendered active, and their volume increases.
influence of From the experiments we have related, it

the organs upon l

the biood. ma y k e seen t j iat t j ie Vj] ooc l serves not only to
repair the losses in the living organs, and nourish them,
but also to produce in certain parts an excitement, with-
out which life could not be maintained. Now by thus
acting upon the organs, with which it is in contact, this
liquid in its turn experiences from them modifications,
vrn, r ,!"'M,',"i' an d soon loses its vivifying qualities. The
blood, on arriving in the different parts of the body, is of
a red vermilion color ; while, after having traversed

CIRCULATION. 33

them, it presents a dark tint of blackish red, and in this
state does not possess the faculty of sustaining life in the
organs to which it is supplied. But blood thus vitiated,
or which has at least been used, retakes by the action of
the air its primitive properties, and then becomes adapted
to excite the vital movement.

The function, by the aid of which this important
change is effected, is that of respiration, with which we
shall soon be. occupied. Blood, which has been submit-
ted to the action of the air, and which is proper for the
support of life, is called arterial blood ; that, which has
already acted upon the organs, and which cannot con-
tinue to excite the vital movement, is called venous blood ;
it contains in general fewer globules than the arterial,
and coagulates less promptly, but its chief distinguishing-
features are, its black color, and its mode of action on
the living tissues.

CIRCULATION OF THE BLOOD.
From what has been said of the part taken Necessttyof

1 a circulatory

by the nutritive liquids in the animal economy, ninvement -
and of the influence exercised by respiration upon the
physiological properties of these liquids, it is evident that
they must be the seat of a continual movement.

Since it is the blood, which distributes to all parts of
the body the materials necessary for their nutrition, and
since this liquid is also the mean, by which the particles
eliminated from the substance of the tissues are thrown
out, it cannot remain in repose, and must necessarily

5

34 ANATOMY AND PHYSIOLOGY.

traverse constantly all the organs. But in the majority
of animals these are not the sole conditions of existence,
which render the motion of the blood indispensable to
the support of life ; when the air does not penetrate into
the substance of all the tissues, (as is the case in insects)
but acts only by the intervention of the exterior surface
of the body, or of a special organ of respiration (as the
lungs), it is equally easy to see, that the blood, which
has already traversed the tissues, must pass to the respi-
ratory apparatus to be submitted to the vivifying influ-
ence of the air, before returning anew to these same
tissues.

Now this actually takes place, and this movement con-
stitutes what is called by physiologists the Circulation of
the Blood.

th^iSllm I" animals with the simplest structure, the
nutritive liquid is diffused uniformly in all parts of the
body ; it fills the spaces which the various organs, or
their constituting lamella?, leave between them ; lastly,
it presents but slow and irregular motions. But when
we examine beings more nearly allied to man, the blood
is seen to move in a constant direction, and there exists a
particular organ for the purpose of impressing upon it

Heart, this motion. This organ, called the Heart, is a
kind of contractile pocket, which receives this liquid in
its interior, and contracting upon itself, drives it in a de-
terminate course.

By ascending in the scale of beings we sec also, that
the blood soon ceases to circulate in simple spaces, but
moves in a system of canals, having walls proper to
themselves, and which arc independent of tin 1 neighbor-
ing parts. These canals bear the name of blood vessels,

CIRCULATION. 35

and, with the heart, constitute the apparatus of the circu-
lation.

The currents, of which we have just spoken, vessels.
are seen in some animals, which have not well-formed
blood vessels, and in the incubating egg they are seen
before the cavities containing the blood have acquired
distinct walls. These currents may even be regarded as
the determining cause of the formation of these vessels,
for whenever, in consequence of certain diseases, such
as fistula, a part of the body is frequently traversed by
any liquid, the accidental passage thus worn is soon
clothed with a membrane, and transformed into a canal,
having proper walls and independent of the neighboring
parts.

However, the vascular system is composed of Art v e ln S s . ana
two orders of vessels ; of centrifugal canals, which carry
the blood from the heart to the interior of all parts of
the body, and of centripetal canals, which return this
liquid from these organs to the heart — the former are
called arteries, the latter veins.

From the functions of these vessels we can judge
what ought to be their general arrangement. The arteries,
having to distribute to all parts of the body the blood issu-
ing from the heart, must necessarily be subdivided, and
ramified in proportion to their distance from this organ.
The veins, on the contrary, must present an inverse dis-
position ; they must be, at first, very numerous, and
gradually unite so as to terminate at the heart by one or
two great trunks. (Fig. 13.) The arteries, as we see,
may be compared to the branches of a tree, and the
veins to its roots ; but they differ in one very important
respect ; for in place of being separated from each other,

36 ANATOMY AND PHYSIOLOGY.

as the branches and the roots of plants, the arteries and
veins must be continuous, so as to form but a single sys-
tem of canals, and the blood must pass from one to the
other by traversing the substance of the organs. This

raSS? i s actually observed ; and the name of capillary
vessels is bestowed upon the narrow canals which unite
these two orders of ducts, and which may be considered as
being at the same time the termination of the arteries,
and the origin of the veins.

The arteries and veins, thus communicating through
one of their extremities by the intervention of the capil-
lary vessels, are united at the opposite extremity by the
cavities of the heart ; whence it results, that the vascular
apparatus forms a complete circle, in which the blood
moves, to return unceasingly to its first point of depart-
ure, and from the nature of this movement it is called
the circulation.

u»SmdaSoa! This phenomenon was unknown to the an-
cients ; the majority of the authors of antiquity supposed
that blood only existed in the veins, and thought, that
during life, as well as after death, the arteries were
empty, or contained merely air. But about the middle of
the second century of the christian era, Galen proved by
delicate experiments made upon living animals the pres-
ence of this liquid in the arteries, and thus paved the
way to the discovery of the circulation. This celebrated
man rendered to science many other important services,
and she would certainly have reaped yet greater advan-
tage from his labors, if by a fortuitous event posterity
had not been deprived of a great part of his writings :
he left five hundred manuscript rolls, containing materials
for about eighty of our octavo volumes, and they were con-

CIRCULATION.

37

sidered so precious, that for their better preservation they
were deposited in the temple of Peace at Rome ; but
this very precaution was the means of their destruction,
for they were consumed together with the edifice in the
reign of the emperor Commodus. 1

In the sixteenth century some new light was thrown
upon this important point in physiology. Michael Servet,
known as a theologian rather than physician, and cele-
brated for having been burned as a heretic in a reformed
city, and by the instigation of the reformer Calvin, 2 has
pointed out in one of his works, the direction of the
course of the blood in the pulmonary veins ; but the dis-

1 Galen, one of the greatest physicians of antiquity, was born at Perga-
mos, a city of Asia Minor, in the year 131, the fifteenth of Adrian's reign ;
he studied sometime at Alexandria, whose medical and scientific schools
were then in a most flourishing condition, and at the age of 34 years he
went to Rome, where he acquired by his public lectures a great celebrity,
and where he excited among the other physicians so great jealousy, that
he was soon obliged to quit the city, and return to Pergamos. At this
moment an epidemic broke out in Italy, and his enemies profited by this
circumstance, to accuse him of cowardice. He had, notwithstanding, the
real advantage of enjoying during his life-time all the glory his genius
could assure to him, and his high reputation remained inviolate for a long
succession of ages. At the age of 38 years we find him called to Aquilea,
by Marcus Aurelius, to combat a violent epidemic raging in the army of
Germany, and the same prince afterwards put under his charge Commodus,
his son, whose health was very delicate. Galen, however, did not delay
returning to his natal city, where he died in the year 200, at the age of 69.
He was one of the profoundest anatomists and physiologists of antiquity;
in this respect he may be compared to Aristotle ; and as a physician, he
ranks next to Hippocrates. During a long period his reputation has been
yet greater, and in the middle ages his writings were, so to speak, the sole
guide of physicians.

2 The unhappy Servet, driven by the intrigues of Calvin to fly from
France, passed through Geneva where his implacable enemy was in power;
he was arrested for his religious writings, and Calvin procured his condem-
nation to the stake. Servet was burnt alive the 27th October, 1553.

38 ANATOMY AND PHYSIOLOGY.

covery of the circulation actually dates from the com-
mencement of the seventeenth century, and the glory of
it is due to Harvey, professor of anatomy at London and
physician of the unfortunate king Charles I. In the
lectures given by him in 1619, he pointed out the me-
chanism of this function ; his ideas were immediately
attacked on all sides with virulence, and when his envi-
ous contemporaries could no longer throw doubt upon
the truth of his great discovery, they attempted to wrest
the glory of it from him, by pretending that it had been
known for a long time ; they allowed Harvey only the
merit of having propagated the knowledge of it, or, as
they said, of having circulated the circulation of the
blood : but posterity has rendered to him full justice,
and his name will always be cited as one of the greatest
of physiologists.

ex^ten f ce° f of e The existence of the circulatory movement
ti'cfn. 01 of the blood is easily demonstrated. If we

examine by the microscope a transparent part of the
body in a living animal, the membrane which unites the
claws of the hind foot of the frog, for instance, we see
distinctly sanguineous currents traversing innumerable
capillary vessels, and continuing into other canals, yet
larger. The direction of these currents is equally easy
to show ; if an artery be compressed, so as to interrupt
the course of the blood, this liquid is seen to accumulate
in that portion of the vessel situated towards the heart,
and to distend its walls, while beyond the compressed
point, the artery is in a short time more or less com-
pletely emptied ; it is then evident, that the blood tra-
verses these canals from the heart to the various parts of
the body. Now when the same experiment is made

CIRCULATION. 39

upon a vein, the contrary effect is produced ; the blood
accumulates beyond the compressed point, and does not
flow in the portion comprised between this point and the
heart ; for if the vessel be opened above and below this
same point, the blood forcibly escapes from the lower,
and not at all from the upper, opening. The common
manner of bleeding in the arm also shows, that in the
venous system the blood follows an opposite direction to*
what we have seen in the arteries, and returns from the
various parts of the body to the heart ; to swell up the
vein, and facilitate the flow of blood, the vessel is com-
pressed by means of a ligature immediately above the
point where the opening is made.

In all those animals, in which respiration is i e S e u iat? n n d
made by a special organ, such as the lungs, the sanguine-
ous vessels ramify not merely in the tissues they are to
nourish, but also in the organ in which the blood must
be submitted to the action of the air ; and this liquid
traverses two kinds of capillary vessels ; one serving for
nutrition, the other for respiration ; the circulation carried
on in the respiratory apparatus is called the less circulation,
and that of the rest of the body the greater circulation.

In other respects, the course followed by the aSvSSt 1 of
blood, and the structure of the circulatory apparatus,
vary much in the different classes of animals ; thus, in
crabs and lobsters the heart consists only of a single
contractile pocket, which sends the blood to all parts of
the body, whence this liquid passes into the venous sys-
tem to be returned to the heart by traversing the organ
of respiration. In snails, oysters, etc., the an dXn c u e s °c U a !
blood follows the same course, but there is a division of
labor in the functions of the heart ; this organ presents

40 ANATOMY AND PHYSIOLOGY.

a more complicated structure, and is composed of a cavity
called a ventricle, which serves to put the blood in mo-
tion, and of one or two pockets, called auricles, which
receive this liquid from the veins, and serve as a reservoir
to supply the ventricle.

Fishes. In fishes, the structure of the circulatory ap-
paratus is nearly the same, with this difference, that the
heart, in the place of being situated at the passage of
the arterial blood, belongs to that portion of the circula-
tory circle, traversed by the venous blood passing from
the various parts of the body to the organ of respiration,
which is expressed by saying, that these animals have a
'pulmonary heart; while in those spoken of above the
heart is aortic, or belonging to the great artery of the
body, which is called the aorta.

In all these animals, the entire mass of venous blood
traverses the organ of respiration, and is transformed into

Reptuea. arterial blood before returning to the different
parts of the body ; the vessels of the greater circulation
pass entirely into those of the less, and the circulation is
double ; but in frogs, serpents, and other reptiles, it is
more simple ; the less circulation is but a fraction of the
greater, and the venous blood is not entirely changed
into arterial, but mingles partly with the blood coming
from the respiratory apparatus, and thus returns to the
organs.

a.Ti'lnir Finally, in man and all the other animals
called by naturalists mammiferous, as well as in birds,
the circulatory apparatus is yet more complicated. The
heart presents two auricles, as well as two ventricles,
and is divided into two distinct parts; the portion situ-
ated on the left side, composed of an auricle and ventri-

CIRCULATION. 41

cle, corresponds to the aortic heart of snails and lobsters,
and serves to send the arterial blood to all parts of the
body ; while the right half of the heart, which is com-
posed in the same manner, sends the blood to the lungs,
and consequently performs the same duty as the pul-
monary heart of fishes.

The blood, arriving from the different parts of the
body by the venous system, first enters the right auricle ;
thence passes into the ventricle of the same side, from
which it is sent to the lungs by the pulmonary artery ;
after having traversed the respiratory organ it returns to
the heart by the pulmonary veins, which open into the
left auricle ; lastly, from the left auricle the blood de-
scends to the left ventricle, and this latter cavity sends it
to the arteries, by them to be conveyed to all parts of
the body, whence it returns, as we have already seen,
to the right auricle of the heart.

Thus we see then, that in animals the blood passing
through the circle of circulation, twice traverses the
heart : in the state of venous blood on the right, and as
arterial on the left side of this organ ; notwithstanding,
each circulation is in itself complete, for the pulmonary
cavities and the aortic cavities of the heart do not open
into each other, and the entire venous blood must traverse
the respiratory apparatus to be transformed into arterial
blood. 1

APPARATUS OF CIRCULATION IN MAN.

In man, which we shall take as an example Heart.
for the illustration of the apparatus of circulation, the

1 Before birth it is quite different, as will be seen when treating of re-
production.

6

42

ANATOMY AND PHYSIOLOGY.

heart is lodged in the cavity of the chest, called by ana-
tomists the thorax; its inferior extremity is directed a
little to the left and forward, and its superior extremity,
whence arise all the vessels communicating with its inte-
rior, is fixed to the neighboring parts nearly in the me-
dian line of the body. In the remainder of its extent,
the heart is completely free, and it is enveloped by a
kind of double membranous sac, the pericardium ; the
inner surface of which is in contact with itself, perfectly
smooth, and constantly moistened by an aqueous liquid,
which serves to render the motions of this organ more
easy.

Fig. 10. '

t f e

- — =>

V

a

c d b h

and an auricle. («, e, and b, d.)

The general form of
^the heart is a cone, or
irregular reversed pyra-
e mid ; its volume is about
equal to the fist, and its
substance almost entire-
ly fleshy ; it is a hollow
muscle, the interior of
which is divided by a
large vertical partition
(Fig. 11, c) into two
halves, each containing
two cavities, a ventricle

1 a, Portion of the heart occupied by the left ventricle, —b, right ventri-
cle, — c, right auricle. The left auricle is seen above the ventricle of the
same side, — (/, vena cava interior, — e, subclavian and jugular veins, ter-
minating in the superior vena cava, — /and g, carotid and subclavian ar-
teries, originating from the arch of the aorta, — h, descending aorta, — t,
trachea, — p, lungs.

I
CIRCULATION. 43

The two ventricles of the heart * p (r ^ * ,

occupy its inferior portion, and i u h k
their walls are endowed with a

strength much greater than those *iM^*v$/yi'^
of the auricles, the utility of *■*-'■
which circumstance is evident : ^^HL/^^P/ ""-"—/•

for the auricles have only to send {. ~-/vi
the blood into the ventricles

^

' a

while these latter cavities must ,••''
send it to a much more conside-
rable distance, either to the lungs, c ti
or to the other parts of the body. The left ventricle is
also much stronger than the right, and the comparative
extent of the passage, that the contractions of these
cavities must cause the blood to traverse, also explains
the cause of this difference ; for the right ventricle sends
this liquid only to the lungs, situated but a short distance
from the heart, and the left ventricle drives it to the most
remote parts of the body.

The vessels, which are to transport the arterial Aorta,
blood to all the organs, spring from the left ventricle (a)
of the heart by a single trunk, called the aorta. (See fig.
10 and 11, h.) This great artery ascends to the base of
the neck, then curves downward, passes behind the
heart, and descends vertically in front of the spine to
the inferior part of the abdomen. In its course a great
many branches are given off, the principal of which are,

1 Section of the heart to display its cavities. — a, left ventricle, — I, right
ventricle, — c, fleshy septum dividing these two cavities, — d, right auricle,
— e, left auricle, — /, valve which separates this cavity from the left ven-
tricle, — g, valve separating the right auricle and ventricle, — h, aorta, —
h\ the same after its passage behind the heart, — i, i, vense cavae, — k, pul-
monary arteries, — /, pulmonary veins.

44 ANATOMY AND PHYSIOLOGY.

the two carotid arteries, which ascend on the side of the
neck, and distribute the blood to the head ; the two ar-
teries of the superior limbs, which take successively the
names of subclavian, axillary, and brachial arteries accor-
ding as they pass under the clavicle, traverse the axilla,
or descend along the arm ; the cceliac artery, which goes
to the stomach, liver, and spleen ; the mesenteric arteries,
ramifying in the intestines ; the renal arteries, pene-
trating the kidneys ; and the iliac arteries, which termi-
nate the aorta, and convey the blood to the inferior limbs.
veins. The veins, which receive the blood thus trans-
mitted to all parts of the body, follow nearly the same
course as the arteries ; but they are larger, more numer-
ous, and in general more superficially situated. A great
number of these vessels lie directly beneath the skin,
others accompany the arteries, and at last they all unite
to form two great trunks, which open into the right auri-
cle of the heart, and which have received the names of
vena cava superior, and inferior. (Fig. 10, d, e, Fig. 11, i.)

venaporta. The veins of the intestines present in their
course a remarkable peculiarity : the common trunk,
formed by their union, penetrates into the substance of
the liver, and there ramifies ; so that the blood of these
organs does not return to the heart, till after it has circu-
lated in a particular system of capillary vessels contained
in the liver, and giving birth to canals, which open into
the vena cava inferior. This portion of the venous appa-
ratus is called the system of the vena porta.

P a u ru"ry! !iry The vessel, which conveys the venous blood
from the heart to the lungs, is called the pulmonary ar-
tery (Fig. 10 and 11, k) ; it arises from the superior and
left side of the right ventricle, ascends by the side of the

CIRCULATION. 45

aorta, and soon divides into two branches, which sepa-
rate almost transversely from each other, and ramify in
the lungs ; that of the right side passes behind the aorta
and the vena cava superior ; that of the left side passes
in front and above the arch of the aorta. The former
subdivides into three branches before penetrating into
the substance of the lungs ; the second into two ; they
both ramify upon the walls of the pulmonary cellules.

The pulmonary veins originate in the sub- Pu ve' i °". ary
stance of the lungs, from the minute capillary divisions
of the arteries of the same name, and unite in twigs and
branches, which follow the same course with the latter
vessels ; they finally form four trunks, two from each
lung, passing to the left auricle of the heart, to which
they transmit the blood, arterialized by its contact with
the air in the interior of the respiratory organ.

The arteries and veins are lined interiorly by structure of

J J the blood ves-

a thin, smooth membrane, continuous with that sels-
lining the cavities of the heart, and analogous with those
known to anatomists as serous. In the arteries, this in-
ternal coat is surrounded by a thick sheath, yellow and
very elastic, composed of fibres of a peculiar nature, cir-
cularly disposed ; and the whole is contained in a third
tunic, formed by thick close cellular tissue. In the veins,
no distinct cellular coat can be discovered, and the inter-
nal membrane is only surrounded by a thin layer of lon-
gitudinal, loose, and extensible fibres. There must be
then a very great difference in the physical properties of
these two orders of vessels. The veins have thin flaccid
walls, which sink when they are not distended by blood,
and which quickly cicatrise, when divided. The arte-
ries, on the contrary, have walls much thicker, and pre-

46 ANATOMY AND PHYSIOLOGY.

serve their calibre even when empty, as always happens
after death. 1 Lastly, when these latter vessels are open-
ed, the edges of the wound tend to separate, on account
of the elasticity of the fibres of the median tunic, and
cicatrization is never completely effected, except by the
obliteration of the artery at the divided point ; thus to
arrest the blood, which escapes from a vein, it is suffi-
cient merely to maintain the edges of the wound for
some time in contact ; but if, on the other hand, an artery
has been opened, the vessel must either be tied, or oblite-
rated by compression.

MECHANISM OF THE CIRCULATION.

Contractions
of the heart.

It is easy to comprehend the mechanism, by
which the blood is moved in all these vessels. The cav-
ities of the heart, as we have already said, contract and
expand alternately, and thus drive the blood into the
canals, with which they are in communication.

The two ventricles contract at the same time, and
when their walls are relaxed, the auricles contract in
their turn. These contractions are called the systole?
and the opposite the diastole? They are very frequently
renewed ; in the adult man usually from sixty to seventy-
five in a minute ; in the aged their number appears to be
a little augmented ; and in very young children it gener-
ally amounts to about one hundred and fifty. Besides
the age, a multitude of other circumstances influence the

1 When death happens, the arteries contract after the left ventricle has
ceased to act, so that the blood then passes into the veins and accumulates
there, while the arteries remain empty; for this reason it was so long be-
fore the uses of these latter vessels were known.

2 2varoh), from ovaieMo), I contract.

3 dtuoTolti, from dutareXlio, I dilate.

CIRCULATION. 47

frequency and force of the pulsations of the heart ; they
are accelerated by exercise, emotions of the mind, and by
many diseases ; in swoons and syncope they are consid-
erably diminished, or even momentarily interrupted.

The left auricle, which receives the blood coming from
the lungs, communicates, as we have seen, with the pul-
monary veins on one side, and with the left ventricle on
the other ; by its contraction it expels from its cavity
the greater part of the blood, which was there ; and it is
evident, that this liquid must tend to escape by two
ways. This would take place, did not the ventricle di-
late at the same time, and thus the greater part of the
blood penetrating into its interior, very little returns into
the pulmonary veins.

Soon after, the ventricle contracts Fig. 12. '

in its turn, and drives out the blood
it had just received ; now, there is vsJ^Tv^X^//
attached around the edges on the %. ^V4Sf
upper side of the opening, by which a '"Jjprfi§ll|F

the ventricle and auricle vounuun] ' j---W^^^^fl °

cate, a membranous ibid, so arranged Y^SS^uf d

as to sink down and open when ■' ySsBp!/

driven from above downward, and N5S^

arise and shut the opening when driven in a contrary di-
rection ; 2 the result is, that during the contraction of the

1 Section of the heart to show the disposition of the valves, which sepa-
rate the auricles from the ventricles, a, Auricle opened and extended, b,
Cavity of the ventricle; tlie walls of which are supplied with a great num-
ber of fleshy fibres, irregularly disposed, so as to form a kind of cellules,
c, Valve, whose external border is fixed to the circumference of the auriculo-
ventricular opening, and the free border of which gives attachment to a
great number of little tendons, (d), arising from fleshy columns fixed to
the walls of the ventricle by their inferior extremity.

2 This species of valve has been called the mitral valve, on account of the

48 ANATOMY AND PHYSIOLOGY.

ventricle, the blood cannot return to the auricle, and is
driven into the aorta.

The measure of the force, with which the left ventri-
cle drives the blood into the arterial system, to be sent
to all parts of the body, has been the subject of much
investigation, which has given the most discordant re-
sults ; thus Borelli, guided by calculation rather than
direct experiment, was led to believe that this force must
be sufficient for the equilibrium of 180,000 pounds
(livres) ; while the physiologist, Kiel, estimates it at only
five ounces. But a young physician, M. Poiseuille, has
lately published upon this question better directed re-
searches, and from which it would appear, that the force,
with which the heart throws the blood into the aorta, is
about four pounds in the human adult, and eleven pounds
in the horse.
course of From the nature of the movements already

the blooil in J

the arteries. S p keii of, it would naturally be supposed, that
the blood could only move in the arteries by jets, each
time that the left ventricle contracted, and that, during
the dilatation of this cavity, it must remain in repose.
It is however quite the contrary ; if one of these vessels
be opened in a living animal, the blood is seen to escape
in a continuous jet, which becomes stronger at the mo-
ment of the contraction of the heart, but which is only
interrupted by the opposite movement. This depends
on the action of the arterial walls on the course of the

division of its free edge into two tongues. The mechanism, by means of
which it closes the auriculo-ventricular opening, is very simple ; small ten-
dinous cords, springing from fleshy columns fixed inferiorly to the walls of
the ventricle, are inserted into its free border, and prevent it from turning
into the auricle, while they oppose no obstacle to its opening in the oppo-
site direction. (Fig. 12.)

CIRCULATION. 49

blood. These walls are very elastic ; when a wave of
blood is projected into the aorta by the contraction of the
ventricle, they yield to the pressure thus exercised, in the
manner of a spring, but they tend afterward to return
upon themselves, and to drive out the blood, which dis-
tended them.

To demonstrate the influence of the arterial influence

of the arte-

coats upon the course of the blood, it will be mlcoats -
sufficient to expose a large artery in the living animal, and
to intercept a portion between two ligatures tightly tied,
then to make a small opening between the two points
thus obliterated. The blood in this place will be com-
pletely isolated from the influence of the movements of
the heart, and yet it will escape from the artery in a
very elevated jet, and the vessel will soon be emptied
by the simple effort of the contraction of its walls. The
portion of the artery beyond the ligature diminishes in
calibre, and sends into the veins the greater part of its
blood.

Thus through the elasticity of the arteries, the inter-
mitting movement impressed on the blood by the con-
tractions of the heart, is transformed into a continuous
movement. In the large arteries, the jets occasioned by
these contractions may be perceived ; but in the capillary
vessels, and even in the small arterial branches, they are
no longer perceived, and the blood only flows through
the influence of the pressure exercised by the elastic
walls of the arteries.

We see then, that the contractions of the heart serve
to fill continually the great arteries, and, so to speak, to
stretch the spring represented by the walls of these ves-
sels, and destined to expel in a continuous manner this
liquid into the veins.

7

50 ANATOMY AND PHYSIOLOGY.

Puise. The phenomenon, known by the name of pulse,
is only the movement occasioned by the pressure of the
blood upon the walls of the arteries at every contraction
of the heart. From the force and frequency of these
movements we may judge of the manner, in which this
organ beats, and draw from it useful inductions for med-
icine. But the pulse is not everywhere felt ; to dis-
tinguish it an artery of a certain volume must be com-
pressed between the finger and a resisting plane, a bone
for instance, and we must therefore select a vessel situ-
ated near the skin, as the radial artery at the wrist.
theSiintbl Although it be the same motive agent which
onhe e body? r drives the blood to all the parts of the arterial
system, nevertheless, it is observed, that this liquid does
not arrive at all the organs with the same rapidity. The
distance, which separates jhem from the heart, is one,
but not the only cause of this difference.
influence of Sometimes these vessels go in nearly a straight

the curvature J

of the arteries, y me ^ at others they form frequent elbows; now
whenever the column of blood, put in motion by the con-
tractions of the heart, meets one of these curvatures, it
tends to straighten the vessel, and thus loses a portion of
its motor force, which diminishes by as much the rapid-
ity of its course.
influence of It is a law of physics, that, all other things

the division of l J °

the arteries. ue j n g equal, the rapidity, with which a liquid
flows in a system of canals, is so much the greater, as
their calibre is smaller ; and observation teaches us, that
the total capacity of the various twigs of an arterial
branch, or of the various branches of a trunk, is always
superior to that of the vessels, whence they spring. It
results, therefore, that the more numerous the sub-divi-

CIRCULATION. 5 J

sions of an artery before penetrating the substance of an
organ, the slower must the blood be conveyed to the
part ; and in this respect very great differences may be
observed in the animal economy ; sometimes these ves-
sels are distributed to organs only after a great num-
ber of sub-divisions, and sometimes, on the contrary, the
arterial trunk buries itself in the substance of the part, in
which it is to ramify.

These dispositions, by the aid of which the impetuosity
of the blood is moderated at certain points of the circu-
latory apparatus, are principally remarked in the arteries
charged with conveying this liquid to organs, whose
structure is most delicate, and functions most important ;
the brain, for example. But nature with her enlightened
foresight is not confined to such precautions, to communica-

1 ' tion of the ar-

insure the arrival of the proper quantity of teries-
blood in each of the parts of the body. We can easily
conceive, that by compression, or other accidents, an ar-
tery may be obliterated at some point of its extent, and
that if the blood could not then arrive at the organ, in
which this vessel is distributed, the deafh of the part
would inevitably result, but this does not take place, for
most of the arteries have frequent communications with
each other, called anastomoses, by means of which these
vessels can receive the blood of a neighboring artery,
even if they do not communicate directly with the heart.

We have seen the mechanism, by which the blood
passes from the heart to all parts of the body ; let us
now study the means employed by nature to make this
liquid circulate in the veins, and to reconduct it to the
heart.

Again, the contractions of the left ventricle course of

° the blood in

of the heart, and the obstruction of the arterial- Uie vein3.

52

ANATOMY AND PHYSIOLOGY.

walls, contribute most to the course of the blood in the
veins.

If the passage of the blood in an artery be interrupted,
and the corresponding vein be opened, this liquid will
continue to flow from the latter vessel, so long as the
artery by its contractions has not expelled all the blood,
which distended it ; but soon after, the hemorrhage will
cease, although the vein be yet filled with blood, and the
flow of this liquid will recommence, as soon as the cir-
culation in the artery is reestablished. It is then the
impulse received by the blood at its departure from the
heart, which causes itself to be felt in the veins, and
which determines its progress in these vessels. But
there are other circumstances, which tend to favor this
movement.

In the veins of the
limbs, and of several other
parts of the body, the
membrane which lines
these vessels, forms a great
number of folds, or valves,
which open when the blood
drives them from the ex-
tremities to the heart, and
close so as to intercept
the passage, when this li-
quid is forced in a contrary
direction. Now, this ar-
rangement consequently
prevents the blood from

Fig. 13. 1
a

1 Trunk of a large vein opened to show the valves formed by the folds
of its internal membrane. — a, Superior portion of the vein, — Z>, valves,

CIRCULATION. 53

flowing back to the capillaries, and also contributes, in
an active manner, to facilitate its passage to the heart ;
for, each time that the vein by the motions of the neigh-
boring parts is compressed, the blood is driven forward,
and when the compression ceases it can no longer be
driven backward, but is replaced by a new quantity of
liquid coming from the inferior part of the limb. All
intermitting compression then of these vessels facilitates
the return of the blood to the heart.

The dilatation of the chest, produced by the respira-
tory movements in inspiration, in the manner of a pump,
facilitates also the passage of the venous blood to the
cavities of the heart, as we shall see when treating of
respiration.

Nevertheless, the blood flows much less quickly in the
veins than in the arteries, and nature has multiplied the
means proper to prevent the obstruction of one of these
vessels from arresting the return of this liquid to the
heart ; there generally are several veins destined to fulfil
the same purpose, and these vessels communicate together
by numerous anastomoses.

The passage of the blood through the cavities th ^ e s ^ ls of
of the right side of the heart is made in the SKetrtT
same manner as from the left auricle to the ventricle of
the same side.

When the right auricle is relaxed, the blood flows into
it from the two venae cavae ; and when this cavity after-
wards contracts, the greater part of this liquid passes
into the ventricle, for there is around the edge of the

the concavity of which is directed towards the heart, — c, venous twigs
anastomosing and uniting to form a large branch, (d), which opens into the
principal trunk at e.

54 ANATOMY AND PHYSIOLOGY.

opening of these vessels a valve, to oppose the reflux of
blood into the inferior vena cava, and from its weight
this liquid must tend to fall into the ventricular cavity,
rather than ascend into the vena cava superior.

The opening, by which the right ventricle communi-
cates with the auricle, is also supplied with a valve ] sim-
ilar to that of the left ventricle ; and by its contractions,
this cavity drives the blood into the pulmonary artery, by
raising other valves which surround the entrance of this
vessel, and prevent the blood from returning in the direc-
tion of the heart. 2

Le uon. rcula " Finally, the blood passes from the pulmonary
arteries into the veins of the same name, by traversing
the capillary vessels of the lungs, and enters the left auri-
cle in the same manner, in which it moves in the canals
of the great circulation.

ABSORPTION.

We have seen, that the body of a living animal must
constantly assimilate to its own substance foreign mate-
rials, derived from the exterior world, and must reject
the particles separated from its own organs, and which
can no longer serve to form them.

1 Called the tricuspid valve, because it is divided into three triangular
portions ; its arrangement is similar to that of the mitral valve.

2 These valves, to the number of three, are formed by folds of the inter-
nal membrane of the artery, and are named, from their form, semi-lunar
valves ; their arrangement is analogous to that of the valves of the veins.
(Fig. 13.) When the blood is driven from the heart into the vessel, they
are raised and applied against the Avails of the latter; but -when the blood
tends to reenter the auricle, the weight of the liquid distends and closes
them ; they then resemble considerably the little baskets in which pigeons

ABSORPTION. 55

We have also seen, that a peculiar liquid, the blood,
continually traverses the various parts of the economy to
convey these materials.

But this nutritive liquid is itself contained in cavities
within the body, which have no external opening ; the
question then arises, by what way the foreign substances,
necessary for the support of life, can penetrate into the
vessels to be mixed with the blood, and how the materi-
als existing in it can escape. These two orders of phe-
nomena constitute the functions of absorption and exhala-
tion, with which we are now to be occupied.

Absorption is the act, by which living beings Definition.
in some way suck in, and make penetrate into the mass
of their humors, the substances which surround them, or
are deposited in the interior of their organs.

To prove the existence of this absorbing fac- Proofs of the

I ~ existence of

ulty, a small number of experiments will suffice. absor P tion -
If the body of a frog be plunged into water, so that none
of this liquid can enter the mouth of the animal, never-
theless at the end of a certain time its weight is found to
have been augmented ; now, this increase, which under
favorable circumstances amounts to a third of the total
weight of the animal, can evidently depend only upon
the absorption of the water by the external surface of
the body.

If a known quantity of water be introduced into the
stomach of a dog, and by the aid of two ligatures all the
openings, by which the cavity of this organ communi-
cates with other parts, be closed, the liquid will yet dis-
appear at the end of a little while, for it will be absorbed

are hatched ; and as they touch at their free edges they close the artery.
Similar valves exist at the entrance of the aorta, where they serve to pre-
vent the blood from reentering the left ventricle, while this cavity dilates.

55 ANATOMY AND PHYSIOLOGY.

by the walls of the stomach, and thus mingled with the
blood.

of^bsorpu™. And yet there do not exist on the surface of

the skin, or stomach, any pores 1 or openings conducting

directly to the blood-vessels, and which may serve for a

passage to the liquids absorbed. But the tissues, which

form these organs, as well as those of all other parts of

the body, have a structure somewhat spongy, and are

more or less permeable to liquids.

imbibition. In the living, as well as the dead body, these

tissues always imbibe the fluids, which bathe them, and

allow themselves to be traversed with more or less facility.

Fie. 14. 2 Thus, if a current of acidula-

c h a ted water be made to traverse

a section of a vein, arranged
as in the figure, the external
surface of this vessel being in
contact with a solution of tour-
nesol, the color of the latter liquid will soon be changed
to red by the action of the acid, which has passed through
the walls of the vein. In the dead body consequently
these parts are permeable to liquids.

Now, if we expose a vein in the living animal, per-
fectly isolate this vessel, and apply upon its exterior sur-
face the extract of nux vomica, this violent poison will

1 The pores, which are perceived upon the surface of the skin, do not
traverse this membrane, but only conduct to small cavities lodged in its
interior, and serving to secrete various humors, or to form the hair ; when
treating of the touch we shall have occasion to return to the structure of
the skin.

1 o, Flask with two openings containing the acidulated water, and serv-
ing as a reservoir ; b, vase containing the blue solution of tournesol into
which is plunged the median portion of a vein, one extremity of which
communicates with the reservoir, a, and the other with the vase, c, which
receives the acidulated water flowing through the vein.

ABSORPTION. 57

soon penetrate the membranous walls of the vein, mingle
with the blood, and oceasion the terrible symptoms, which
are observed, whenever it is directly injected into the
blood-vessels. It is then evident, that, during life as
well as after death the veins are permeable to liquids.

The permeability of the solid parts of organized bodies
will at once explain to us in what manner absorption is
possible. By the aid of this property of the living tis-
sues, the liquids may have access every where ; but this
would not be enough, and, that they may penetrate into
the interior of the organs, they must be attracted by
some force.

The capillary action contributes powerfully to capillarity,
produce this imbibition ; but it is not the only force which
acts in this way ; and to form an exact idea of the me-
chanism, by means of which liquids penetrate the sub-
stance of the organic tissues, we must understand a very
curious phenomenon, recently discovered by M. Dutro-
chet, and named by him endosmosis.

This physiologist has proved, that, if a Endosmosis.
solution of gum be inclosed in a small mem-
branous sac surmounted by a tube, and sur-
rounded by pure water, the latter liquid
will penetrate into the interior of the appa-
ratus, and ascend in the tube to a consider-
able height. Here then there is a true ab-
sorption, and the force, which determines
it, acts often with such energy as to consti-
tute the equilibrium to a column of water of ^
several centimetres. If, on the contrary,
gum or sugar-water be placed without the
membranous sac, and pure water in its in-

S

58 ANATOMY AND PHYSIOLOGY.

terior, the passage takes place inversely, and the sac,
instead of filling, is emptied.

This phenomenon is very analogous to the absorption
which takes place in living beings, and the explanation
is easily given. We have seen, that the organic mem-
branes, as well as all the spongy and porous bodies, may
be traversed by liquids ; but the facility of this transport
varies with the fluidity of these liquids, and the ease
with which they imbibe the nitrations. If the two
liquids placed in the interior, and upon the exterior of
the membranous sac, could traverse equally well the
walls of this cavity, they would mingle, and the same
level be established upon either side. But if the exte-
rior liquid traverse more readily the walls of the sac than
the interior, the current from without inward will be
more rapid than the current in a contrary direction, and
the liquid will accumulate in the interior of the appara-
tus. Now, this takes place in endosmosis ; the water
surrounding the sac which contains the gum-water, fil-
trates easily through the walls of this cavity, and when it
has reached the interior, it unites with the gum, and thus
forms a new liquid, the passage of which through these
walls is difficult in proportion to the quantity of gum. It
must then accumulate, and ascend in the vertical tube,
which communicates with the membranous reservoir.

The organized bodies, which absorb the liquids by
which the} are surrounded, are placed in the same con-
ditions with the membranous sac, of which we have now
spoken ; the presumption then is, that in all these cases
the same effects arise from analogous causes, and that
the principal force, which occasions the passage of the
absorbed substances across the living membranes, is the

ABSORPTION. 59

same with that, which produces the phenomenon of
endosmosis.

In certain animals of the inferior classes, Transport

of the. abgorb-

those with the least complicated structure and cd liquids "
most limited functions, absorption consists only in the
kind of imbibition, of which I have spoken. By the
same mechanism foreign substances traverse the solid
parts, with which they are in contact, to be mingled with
the liquids, by which the areolae of these organs are
filled, and are afterwards diffused through all the body
and penetrate the interior of the tissues. But as we
ascend in the series of beings we soon see that nature
perfects the mechanism of absorption, and that to accom-
plish this, she introduces into this important function a
constantly progressive division of labor.

In the animals possessing a regular circula- ^sorption!*
tion, the absorption properly so called, or the passage of
foreign substances from without into the interior of the
economy, is always effected in the same manner as in
beings less perfect ; but from the moment when these
substances are mingled with the nutritive juices of the
body, a great change takes place ; instead of being grad-
ually diffused to the various parts by the effect of imbibi-
tion, they are taken up by currents more or less rapid,
and immediately distributed to all the points, to which
the blood penetrates. We see then, that the absorption
of these materials, and their transport to the interior of
the economy, are no longer a single act, but are com-
posed of two series of phenomena perfectly distinct ; the
first, purely local, consists in the imbibition of the tissues,
and in the mingling of the matters absorbed with the
humors of these parts ; the second, dependent upon the

(30 ANATOMY AND PHYSIOLOGY.

general circulation, consists in the transport of these same
substances to parts remote from those, at which they
originally penetrated.

sw,"ti"n. ab " I n a H these beings the principal agent by
which this transport is effected, is the blood, which trav-
erses the organs in which absorption takes place, and
which returns again to the heart, to be afterwards con-
veyed anew to the interior of the various tissues. It fol-
lows that, in animals provided with a circulatory system,
the veins perform a very important office in the absorp-
tion ; and that, in the immense majority of cases, it is
by their intervention, that the liquids, by which a circum-
scribed part of the body is surrounded, are diffused
through the whole economv.

aSpff I n ver y many animals, absorption is only
effected through the blood-vessels ; but in man, and most
animals with the more complicated organization, there
exists another system of canals, which answer the same
purpose, and which serve especially to absorb certain
substances. This is the apparatus of the lymphatic ves-
sels.

This name is given to canals, which spring from very
minute radicles in the interior of the different organs, but
afterward unite in trunks of varying size, and finally
empty into the veins near the heart. Many physiolo-
gists regard these canals as the sole agents of absorption,
and call them absorbent vessels ; but this opinion is with-
out foundation. Comparative anatomy alone would over-
throw it, and the experiments of Magendie and many
others prove it to be completely erroneous.

pmofs of th<> The absorption by the veins is as easily

venous absorp- * J

uon. proved in all animals with a system of lymph-

ABSORPTION. 61

atic vessels, as in those without. The following experi-
ments can leave no doubt in this respect.

Messrs. Magendie and Delille, having stupefied a dog
with opium, to render him insensible to the pain occa-
sioned by a laborious operation, amputated one of his
thighs, leaving only the artery and vein untouched, to
maintain the communication between the limb and the
rest of the body ; then they deposited within the paw
thus separated a violent poison {Upas Tieute). The
effects of the poison were manifested with the same
promptitude and intensity, as if the limb had not been
severed from the body ; and the animal perished in a few
moments.

It might be objected that, notwithstanding the precau-
tions taken, the untouched coats of the artery and vein
contained in their tissues the lymphatic vessels, and these
canals were sufficient to give passage to the poison.

To remove this difficulty M. Magendie repeated the
experiment upon another dog, with this modification, that
he introduced into the femoral artery a quill, to which he
fastened the vessel by two ligatures, he then divided cir-
cularly between the two the walls of the artery, and per-
formed the same operation upon the vein. The only
means of communication then, between the thigh of the
animal and the remainder of his body, were, the arterial
blood coming to the limb, and the venous blood returning
to the heart ; yet the poison then introduced into the
paw produced death with its ordinary rapidity.

This experiment leaves no doubt, but that the poison
passes from the paw to the trunk through the crural vein ;
and to render the proof yet more conclusive, it will be
sufficient to press this vein between the fingers at the

Q2 ANATOMY AND PHYSIOLOGY.

moment when the effects of the poison begin to be man-
ifested ; for by thus impeding the passage of the blood,
the symptoms of poisoning cease at once, to reappear as
soon as the vessel is again left free, and the blood allow-
ed to ascend to the heart.

In other experiments, the presence of the materials

absorbed has been directly proved in the blood of the

veins. It is then evident, that these vessels are active

organs of absorption, but it cannot be doubted, that the

proofs of the lymphatics in certain cases discharge the same

lymphatic ab- J L

sorption. duties. As we shall hereafter see, these latter
ducts are especially charged with the transport of the nu-
tritive materials, extracted from the aliments by the labor
of digestion, and in the other parts of the body they ap-
pear to fulfil analogous functions. M. Dupuytren, in
making the autopsy of a patient, who sank under an enor-
mous abcess of the thigh, found the neighboring lymph-
atic vessels distended by a liquid, having all the charac-
ters of pus. And it has for a long time been known,
that, if when dissecting a putrified body an individual
prick his finger, there often arise grave accidents from
the absorption of the substances thus inoculated, and it
is not rare to see the lymphatic vessels, which extend
from the wound to the trunk, swollen, and inflamed, as
if the passage of the poison had irritated their walls.

Moreover the absorption by the lymphatics must be
slower than that by the veins ; for the blood flows with
great rapidity in these latter canals, and tin; liquid con-
tained in the lymphatic vessels moves but slowly.

Lymph. This liquid is called the lymph. Its physical
properties are not always the same ; sometimes it is opa-
line, and of a faint rosy tint ; at others yellowish, and

ABSORPTION. (33

sometimes red ; examined by the microscope, a multitude
of small globules are seen in it analogous to those of the
blood, and when left to itself it coagulates like the latter,
and separates into two parts, a serous fluid, and a solid
clot, which exposed to the action of the air takes a red
tint. 1

The lymphatic vessels resemble the veins in L ^ff c
their structure and mode of distribution, but they are
much finer, and their walls thinner. They are met with
in nearly all parts of the body ; they form in general two
planes, one superficial, the other deep seated ; they com-
municate by frequent anastomoses, and unite in twigs
and branches like the veins. The majority of these ves-
sels thus form one large trunk (called the thoracic canal),
which ascends in front of the vertebral column, and emp-
ties into the subclavian vein of the left side ; but others
open separately into the vein on the opposite side of the
neck, or even sometimes into the different blood-vessels,
situated nearer their origin. During their course they
are seen to traverse little organs, irregularly rounded, and
situated in the axillae, groin, neck, chest and abdomen.
(See Fig. 25.) The structure and uses of these bodies
are yet but little known ; they are called ganglions, or
lymphatic glands. Finally, in the interior of the lymph-
atic vessels there exist a great number of transverse
folds, which discharge the same functions as the valves
of the veins, and which oppose the reflux of the lymph.

From what has already been said upon the circumstan-

J 1 ces influencing

mechanism of absorption, it will readily be per- absor P tion -

1 By chemical analysis the clot of the lymph has been found to be com-
posed as follows, viz. : water, 925 ; fibrine, 3; albumen, 57 ; alkaline, chlo-
rides, soda and phosphate of lime, 14 ; to the thousand parts. The propor-
tion of the clot to the serurn appears to be nearly as 1 to 300.

g4 ANATOMY AND PHYSIOLOGY.

ceived, what the principal circumstances are which influ-
ence the course of this function.
Fermeabiiity Tlius, the first condition of all absorption be-

and vasculari- l

sw»f the tis m § tne permeability of the tissues interposed
between the substance to be absorbed, and the liquids
which are to effect its transport; it is evident, that, other
things being equal, this phenomenon will be rapid in
proportion to the lax and spongy texture of this tissue it-
self, and the degree of vascularity, which is the seat of it.

In truth, the lax and spongy texture of the organic
solids is of all the physical properties, that which most
facilitates imbibition ; and with regard to the veins, since
by them principally the absorbed substances are diffused
in the economy, the influence of their number and size
is too evident to require any comments. In the major-
ity of cases, these two laws will explain to us the great
diversity, observed in the rapidity, with which absorption
is effected in the various parts of the body ; we might
even anticipate this difference from the sole consideration
of the anatomical disposition of our organs.

Thus the lungs, the structure and functions of which
will be examined hereafter, are of all parts of the econo-
my those, in which the structure is most spongy, and the
vascular system most developed. It follows, that absorp-
tion must be more rapid in these organs than elsewhere,
and to this result does experiment lead.

The soft and whitish substance, which is found be-
tween all the organs, and which is called the cellular tis-
sue, is also very permeable to liquids, but possesses far
fewer blood-vessels than the tissue of the lungs ; there-
fore absorption, although very rapid, takes place less rap-
idly than in these organs.

ABSORPTION. 65

The skin presents, on the contrary, a very dense tex-
ture, and its surface is covered by a kind of varnish,
formed by the epidermis ; in general, its blood-vessels
are small and few ; and, as might be expected from this
anatomical disposition, absorption takes place with great
difficulty. By raising the epidermis, imbibition is con-
siderably facilitated, and consequently absorption is ren-
dered more easy ; finally, when we do not confine our-
selves to simply stripping the dermis, but also excite its
vascular system, (by the irritation of a blister, for exam-
ple) this function is rendered yet more active.

In medicine, use is made of this fact to obtain the ab-
sorption of certain substances, whose irritating nature
upon the stomach is feared, and this mode of administer-
ing remedies is called the endermic method. The slight
degree of permeability of the epidermis also explains to
us how the most violent poisons may be made use of
without danger, provided the skin of the hands be un-
touched ; for in them absorption is nearly null ; while
the gravest accidents, and death itself, may result from
the contact of these same substances at any point, where
the skin has been wounded, or merely deprived of the
epidermis.

Another circumstance, which also exercises a M ^r in ° r rs the
great influence upon the rapidity of absorption, is the
state of plethora of the animal. 1

The quantity of liquid, which may be contained in
the body of a living animal, has limits as well as the de-
gree of desiccation, compatible with life. Now, the
nearer the body approaches its point of saturation, the

' The word plethora (nlrjduwa, nlifio), I fill) is employed to indicate the
state of plenitude of the vascular system.

9

(36 ANATOMY AND PHYSIOLOGY.

greater difficulty do the liquids experience in reaching its
interior.

Thus, if to two dogs equal doses of a poison be ad-
ministered, the effects of which are not manifested till
after absorption ; and if previous to this operation, the
mass of humors in one of these animals be diminished
by a copious bleeding, while in the other, the volume of
liquids contained in the body be increased by the injection
of a certain quantity of water into the veins ; the effects
of the poison will take place sooner in the former than
in ordinary cases, and in the latter those symptoms, which
denote the absorption of the poison, will not appear for
a much longer time.

These results are more important to be known, as
they meet with constant application in the healing art,
and show how much the functions of living beings are
subject to the ordinary laws of physics. The researches
of my brother, Dr. W. Edwards, relative to the influence
of physical agents upon life, have fully established this
truth, and M. Magendie has arrived at the same result
by following a different course.
Nature of the Lastlv, the nature of the substances absorbed

absorbed sub- •'

stances.

also exerts an influence upon the ease, with
which they penetrate into the interior of the tissues, and
are carried into the current of the circulation. In £ene-
ral thesis we may say, that cceteris paribus, the absorp-
tion will be so much the more rapid, as the liquids are
less dense, and readily moisten the tissues. In order that
a solid may be absorbed, we must consider in the first
place its degree of solubility, and next, the physical pro-
perties of the solutions it forms.

Thus, if water be injected into the abdominal cavity

EXHALATION AND THE SECRETIONS. 67

of a living animal, this liquid will promptly disappear ;
while oil, placed in the same condition, is not sensibly
diminished in volume for a considerable lapse of time.

Such are the most important points in the history of
absorption. Let us now study the inverse function, that,
by which a portion of the substances contained in the
general mass of the humors, and enclosed with them in
the blood vessels, can escape, either to penetrate the
cavities within the body, or to make its way externally.

EXHALATION AND THE SECRETIONS.

The passage of the fluids from the interior of the ves-
sels outward, may take place in three different ways ;
sometimes a portion of the blood itself is expelled from
these canals with all its constituent parts, which is called
a sanguineous effusion ; in others, merely a portion of
the aqueous part of the blood issues from the vessels,
carrying with it a certain quantity of the soluble mate-
rials, already existing in the liquid, and this phenomenon
is styled exhalation ; lastly, there are also times, when
there are separated from the blood new products, which
differ from it by their acidity, or greater alkaline proper-
ties, and which often contain in abundance substances,
of which but the slightest trace exists in the blood. This
labor, in some sort chemical, constitutes what is called
by physiologists a secretion.

gg ANATOMY AND PHVSIOLOGY.

TRANSUDATION. OR SANGUINEOUS EFFUSION.

The mechanism, by the aid of which the blood is
effused from the vessels to escape externally, or to flow
into the cavities within the body, is very simple. In
some parts of the economy the veins communicate with
a peculiar spongy tissue by means of openings, which in
the state of repose are not open, but which afford a free
passage to the blood, if any obstacle whatsoever, by op-
posing its ordinary course, determines its accumulation
in the veins. By such a process does the erectile tissue,
which forms various appendages around the head of tur-
keys, for example, swell, extend, and take an intense red
color.

At other times, the sanguineous effusion takes place
without any such perceptible openings to the veins ; and
then this liquid appears to filtrate through the substance
of the tissues ; this is observed but in a small number of
cases, and generally arises from a pathological condition.

EXHALATION.

Exhalation is equally a physical phenomenon, the
course of which may be modified by the action of the
vital forces, but its existence is independent of them.
JtSSSSSHf We have already seen, that the walls of the
blood vessels, as well as the other parts of the body, are
permeable to liquids ; now we can easily comprehend,
that the most fluid part of the blood must traverse them
much more readily than the solid corpuscules contained
in this liquid, and that, by acting as a filter, these mem-
branes must produce the phenomenon of exhalation.

EXHALATION AND THE SECRETIONS. gg

This actually takes place, both in the dead and living
bodj ; if there be thrown into the arteries of a dead an-
imal a solution of gelatine, colored by vermilion reduced
to a very fine powder, the injection will penetrate the
capillary vessels, and then we often see a portion of wa-
ter traversing their walls loaded with gelatine, to escape
externally, while the coloring matter is retained in their
interior.

The mechanism of exhalation is the same with that of
absorption ; all the parts, which are the seat of one of
these functions, may be of the other : in general they
take place simultaneously, and every thing, which tends
to modify the course of one, influences the other.

The degree, to which the texture is spongy, S*SS!™taSSr

i f i c I. .-,.,. enre exhala-

and ot course more or Jess iavorable to imbibi- tion.
tion, is a condition, acting equally upon absorption and
exhalation. These functions, cceteris paribus, are active
in proportion to the number of blood vessels traversing
their seat.

The variations in the mass of the liquids contained in
the body act, on the contrary, in an inverse manner upon
these two functions, the greater the quantity of liquids,
the more abundant the exhalation. In the living body
as in the dead, the tissues retain water more powerfully,
the less they contain, and by increasing the mass of hu-
mors we can at will make active the exhalation.

Finally, the pressure, which the blood supports in the
vessels, also exerts a powerful influence upon the exha-
lation ; and when the circulation in the veins is inter-
rupted, so as to cause the accumulation of this liquid,
the more fluid portion of the blood exhales in abundance
into the neighboring parts, and causes them to swell,

70 ANATOMY AND PHYSIOLOGY.

which produces the tumidity of those parts, which have
been closely surrounded by ligatures.
External and Exhalations are divided into external and in-

internal exha-
lations, ternal, depending upon the fact, whether they

take place on the general surface of the body, or in cavi-
ties, which have no free external communication.

The exterior exhalation, which must not be confounded
with the perspiration, and which takes place on the pul-
monary surface, as well as upon the skin, is also styled
insensible transpiration, because its products are dissipa-
ted by evaporation, and are not usually appreciable to our
senses. The losses experienced by man and other ani-
mals in this way are very considerable. In the state of
health, the weight of the body of an adult hardly varies,
and the losses, which he experiences by the various ex-
cretions, counterbalance the weight of the aliments daily
used by him ; now from the experiments of Sanctorius it
appears, that insensible transpiration often constitutes
five eighths of the total losses, of which we have spoken.

However, the evaporation, going on upon the surface
of the body, does not always take place with the same
intensity, and even here the influence of physical agents
is felt in nearly the same manner upon the living and the
dead. In both, the losses by evaporation are augmented
by the elevation of the temperature, agitation of the air,
(winds, etc.) by its dryness, by the diminution of the
atmospheric pressure, etc.

The internal exhalations take place upon the surface of
the walls of cavities, varying in size, situated in the
interior of the body, and they also consist of water, min-
gled with a small quantity of animal matter, and salts
contained in the blood, whence these liquids escape.

EXHALATION AND THE SECRETIONS. 7]

Such is the source not merely of the humors which con-
tinually moisten the serous membranes, 1 by which the
great viscera of the head, chest, and abdomen are envel-
oped ; but also of the serosity, which bathes the lamella3
of the cellular tissue, so abundantly diffused in all parts
of the body ; and of a part of the humors, which fill the
interior of the eye.

As these internal exhalations take place upon the sur-
face of cavities, which have no outlet, it is evident, that
the quantity of liquids contained in this species of reser-
voirs would constantly augment, if the parts, thus exhal-
ing, were not at the same time the seat of an absorption
not less rapid. In the state of health, these two func-
tions are exercised simultaneously, and counterbalance,
so as to maintain always the same quantity of liquid in
the interior of the cavity ; but sometimes this equilibrium
is destroyed, and exhalation becomes more active than
absorption ; the liquids then accumulate in the parts, and
diseases result known as Dropsies. 2

1 The disposition of the serous membranes requires attention ; they have
always the form of a species of sac, whose internal surface extremely
smooth and moistened constantly by a liquid, is everywhere in contact with
itself ; one of the halves of this sac adheres by its external face to the walls
of the cavity lodging the viscera, and the other half surrounds these viscera
and adheres to them by its external face. To make use of a trifling com-
parison, but one which perfectly represents the thing, these membranes
resemble a double night-cap, and surround the viscera as this cap the head,
the exterior surface of which should be fixed to the walls of a cavity con-
taining both the cap and the head. These membranes serve to diminish
the friction of these parts, and consequently to facilitate the*ir movements ;
therefore similar sacs are met with wherever the organs continually, or
forcibly, rub against each other, as at the articulations of the bones of the
limbs, around the intestines, etc.

2 These collections of water are variously denominated according to the
parts, which are the seat of them ; the special name of dropsy (or ascites) is

72 ANATOMY AND PHYSIOLOGY.

SECRETIONS.

The secretions differ essentially from the exhalations,
in that the liquid separated from the blood is not merely
water, or serum, but a humor, the chemical nature of
which is wholly distinct from that of the blood, or its
serum.

£erettoM. the The blood, as we have already seen, is
slightly alkaline ; the liquors secreted are sometimes very
alkaline, at others acid ; and in them we find particular
substances, not existing in the blood, or in quantities too
small to be appreciated by our means of analysis. Here
then chemical action takes place, and by comparing the
phenomena of the secretions with those produced by the
action of the voltaic pile, a striking analogy may be ob-
served. If an electric current be passed through a liquid,
holding in solution salts and albumen, serum for exam-
ple, there is formed at one pole of the pile an acid, and
at the other an alkaline liquid, and animal substances
dissolved in it are seen to change their nature. Now, it
is precisely the same with the secretory organs ; and by
admitting, that the one are seat of the positive, and the
others of the negative pole of an electric apparatus, the
greater part of the phenomena met with would be ac-
counted for very easily. But this theory, plausible as it
is, cannot be received until based upon facts, and unfor-
tunately these facts are wanting.

given to accumulations of water in the cavity of the abdomen ; and hydro-
thorax, or dropsy of the chest, to such as are formed in the pleura, the mem-
brane surrounding the lungs; dropsy of the heart, such effusions as take
place into the pericardium, the membrane around the heart; hydrocephalus,
those in the membranes covering the brain ; and cedema, those exhibited in
the cellular tissue of the various parts of the body.

EXHALATION AND THE SECRETIONS. 73

However, the secretions are not made indif- oSs. ry
ferently in all parts of the body as the exhalations ; they
always have their seat in special organs, which have
a very peculiar mode of structure. They are always
composed of a greater or smaller number of extremely
minute cavities, in the form of pockets, purses, or canals,
of very great tenacity, and which receive a great number
of blood-vessels, as well as of nerves. They are desig-
nated by the general name of glands, and divided into
perfect and imperfect, according as they are furnished with
a duct through which the product of their secretion is
poured out, or as they have the form of cavities without
openings, and from which the liquids secreted can only
issue by absorption.

The disposition of the perfect glands greatly varies ;
some are situated near the surface of various membranes,
and open directly into them, without having an excretory
canal in the form of a tube : these are called simple
glands, or crypts. Others consist of masses of crypts,
which empty the products of their secretions by several
openings ; these are the agglutinated glands. Lastly,
others still present excretory ducts in the form of rami-
fied tubes, and which unite into a small number of ca-
nals ; they bear the name of conglomerated glands, and
in the course of their excretory duct, there is sometimes
found a membranous pocket, serving as a reservoir for the
liquid secreted.

As an example of the crypts we will cite the follicles
scattered upon the mucous membrane of the digestive
canal, also those which open upon the surface of the
skin, and secrete the fatty and unctuous matter, by which
the hair is moistened ; the tonsils belong to the class of

10

74 ANATOMY AND PHYSIOLOGY.

the agglutinated glands ; and the liver, kidneys, salivary
glands, etc. to the conglomerated glands.

The imperfect glands are formed by little pouches dis-
seminated in the cellular tissue, or collected in masses of
varying volume. The organs, which secrete the fat, and
which are lodged in the interior of the cellular tissue,
present the former of these dispositions ; in very lean
persons it is difficult to distinguish them, and they are
confounded with the cellular tissue ; but when filled with
fat, they are seen to be formed of a very thin membrane,
rounded in form, without opening. 1

1 The fat is essentially composed of two particular materials, elaine and
stearine. one liquid and the other solid at the ordinary temperature; the
relative proportions of these two substances vary greatly in different ani-
mals, and hence corresponding differences in the consistence of their fat.
In general, the principal uses of this matter are all mechanical, and it
serves as an elastic cushion to protect the organs it surrounds ; this is seen
in the orbit, where the eye reposes upon a thick bed of fat, on the sole of
the foot, where it is also found in considerable quantity, and in other parts
of the body exposed to constant pressure, or friction. It may also, from its
feeble power of conducting caloric, contribute to preserve the heat disen-
gaged in the interior of the body ; finally, it may be considered as a kind of
reserve of nutritive materials deposited in certain parts of the body, in order
to serve the purpose of assimilation, when the animal can no longer derive
from without the substances necessary for the maintenance of life; when
fat persons remain a long time without eating, their fat is gradually ab-
sorbed, and appears to serve for their nutrition; it is also remarked, that
the hibernating animals, which pass a great part of the cold season in a
state of lethargy, are surcharged with fat when they become stupid, and
are on the contrary very lean when they awaken from their sleep of many
months. Fat is not deposited with the same facility in all parts of the
body; it abounds especially in the folds of the mesentery, (a portion of the
peritoneum which envelopes the intestines,) around the kidneys, and under
the skin. Repose exercises a great influence upon its formation; very
young children are usually very fat, but when they begin to take much ex-
ercise, their fat is gradually dissipated, and while the body rapidly increases
it is rarely deposited in considerable quantities.

RESPIRATION. 75

Among the imperfect and massive glands we will cite
the thyroid body, 1 and the thymus, 2 organs, whose uses
are not yet known.

The liquors produced by the secretions are, ""reted.
as we have said, acid or alkaline. The most important
alkaline humors are the bile, formed by the liver ; the
saliva, produced by the salivary glands ; and the tears,
secreted by the lachrymal glands. The principal acid
humors are the urine, elaborated by the kidneys ; the
perspiration, which distils from the follicles of the skin ;
the mucus, which lubricates the mucous membranes, and
issues from the crypts so abundant upon their surfaces ;
and the milk, which is secreted by the mammary glands.
Hereafter we shall be obliged to return to the study of
these liquids, and to point out their properties and uses.

RESPIRATION.

Having investigated the manner, in which circulation,
absorption, and exhalation take place, we may turn our

1 The thyroid body is an ovoid mass, soft, spongy, and glandular in ap-
pearance, situated at the anterior and inferior part of the neck, in front of
the trachea. It is in general larger in the infant than the adult, and exists
in all the mammiferse, but is wanting in birds, most reptiles, fishes, and
other animals of the inferior classes. The swelling of this body constitutes
the tumor called goitre.

2 The thymus is a glandiform mass enclosed within the chest between
the two folds of the anterior mediastinum, (a cavity formed by the union of
the exterior surfaces of the pleurae, and which lodges the heart.) It is ex-
tremely developed in the fcetus ; but soon after birth its volume is much
diminished, and in the adult it is completely atrophied.

76 ANATOMY AND PHYSIOLOGY.

attention to the study of another function, the history of
which is closely united with that of the blood, and in
importance not inferior to it : I mean the respiration.

We have seen, that the arterial blood, by its action
upon the living tissues, loses the qualities, which render
it proper for the maintenance of life, and that after being
thus modified, it resumes, by contact with the air, its
former properties ; this contact is then necessary to the
existence of living beings. And, if an animal be placed
under the receiver of an air pump, in which a vacuum is
created, or if it be deprived of air by any other means,
a great trouble at once arises in the various functions ;
the action of all the organs is soon interrupted, life ceases
to be manifested, and the animal falls into a state of as-
phyxia, or apparent death ; at last, life becomes entirely
extinct, and can no longer be recalled.

This phenomenon is one of the most universal in or-
ganic nature ; the contact of air is indispensable to all
animals as well as vegetables, and a living being deprived
of it always dies. Wherever there is life, air is neces-
sary.

At first one would suppose, that the animals living at
the bottom of the water, as fishes, were withdrawn from
the influence of the air, and consequently exceptions to
the law just given ; but it is not so, for the liquid, in
which they are plunged, absorbs and holds in solution a
certain quantity of air, which they can easily separate,
and which suffices for the support of life. It is impossi-
ble for them to exist in water destitute of air, for they
are asphyxiated, and die in the same manner as mammi-
fene, or birds, when withdrawn from the action of the
atmospheric air under its ordinary form.

RESPIRATION. 77

The relations of the air with organized beings form
one of the most important parts of their physiological
history, and the series of phenomena, which result from
it, constitute the act of respiration.

Air, we say, is necessary to the life of all in ^ ro ^-
animals, but this fluid is not a homogeneous p^™ the

... 1**1 oxygen con-

body ; chemistry has demonstrated m it the ex- tamed in it.
istence of very different elements, and which conse-
quently cannot take the same office in the performance
of respiration. Besides the watery vapor, with which
the atmosphere is always more or less loaded, the air
furnishes by analysis twenty-one hundredths of oxygen,
and sixty-nine hundredths of azote, as well as traces of
carbonic acid gas. The first question, which presents
itself to the mind when we enter upon the study of res-
piration, is to know, whether these different gasses act
in the same manner, or if to one in particular belongs the
property of sustaining life.

To ascertain this a small number of experiments will
be sufficient. If a living animal be placed in a vase,
filled with air, and all communication of this fluid with
the atmosphere be intercepted, at the end of a longer or
shorter time the animal will become asphyxiated, and
perish. The air, which surrounds it, has then lost the
faculty of sustaining life, and by chemical analysis it is
found to have lost at the same time the greater part of
its oxygen. If another animal be placed in a jar, filled
with azote, it also perishes ; while a third animal put
into oxygen breathes with more activity than in the air,
and presents no symptom of asphyxia. It is evident
therefore, that the atmospheric air owes its vivifying pro-
perties to the presence of oxygen.

78 ANATOMY AND PHYSIOLOGY.

The discovery of this important fact dates only from
the close of the last century (1777), and is due to one
of the most celebrated French chemists, Lavoisier, who,
notwithstanding his numerous titles to public favor, per-
ished prematurely a victim of the revolution.
oaftonic Cti Midf By the act of respiration, we have said, all
animals remove from the air, which surrounds them, a
certain quantity of oxygen ; but the changes, they thus
determine in the composition of this fluid, are not so
limited ; the oxygen, which disappears, is replaced by a
new gas, carbonic acid. The production of this sub-
stance is not less universal among animals, than the ab-
sorption of oxygen ; and in these two phenomena essen-
tially consist the performance of respiration.

To prove this fact, we have only to blow, during a
certain time, through a tube into water holding lime in
solution. The carbonic acid has the property of uniting
with this latter substance, and thus giving origin to a
body, which is insoluble, and which in its composition is
analogous to chalk ; now, in this experiment, the car-
bonic acid, which escapes from our lungs, combines with
the lime, and forms a whitish powder, which by its de-
position troubles the water, and is easily perceived. By
such means, in 1757 a chemist, named Black, first proved
the production of this gas during respiration. Carbonic
acid may also be recognised by other methods, for it
extinguishes bodies in combustion, and causes the de-
struction of animals when inspired even in small quan-
tities. 1

1 Carbonic acid, which is formed by carbon united in certain proportions
with oxygen, is produced by the combustion of charcoal, during the alco-
holic fermentation, &c, — it enters into the composition of marble, chalk,

RESPIRATION.

79

As to the azote of the respired air, its volume Azote.
changes but little, and its principal use appears to be to
weaken the action of the oxygen, which in the state of
purity excites animals too strongly, and produces in them
a kind of fever.

It has been remarked, however, that in some cases, a
part of the azote of the air disappeared during respira-
tion, and in others, its volume was augmented. It would
even appear, that animals absorb and exhale it contin-
ually, as they exhale and absorb the liquids contained in
the cavity of the pericardium, peritoneum, etc., and that
the variations observed depend upon this ; that these two
opposite functions are in general in equilibrium, so that
their result is not apparent, but that the absorption being
sometimes more active than the exhalation of the azote,
while at other times the quantity exhaled exceeds that
absorbed, occasions a diminution, or increase in its vol-

&c, and is found in most mineral waters. In the state of gas it is color-
less as air, but much heavier than this fluid, and soluble in water. From
the action of this acid upon the animal economy arises the asphyxia, pro-
duced by the vapor of charcoal, as well as most of those accidents, which
take place in mines, drains, wells, and vaults where wine or beer is fer-
menting. In a vault near Naples it is continually disengaged from the
interior of the earth, and occasions phenomena, which at first seem very
singular, and excite the curiosity of all travellers: when a man enters this
cavern he experiences no difficulty in respiration, but if accompanied by a
dog, the animal soon falls asphyxiated at his feet, and would quickly perish,
if not taken into the fresh air. This depends upon the fact, that the car-
bonic acid, being heavier than the air, does not ascend, but remains near
the ground, and there forms a layer about two feet thick. Now a dog en-
tering this grotto is necessarily entirely plunged into this mephitic gas, and
must be asphyxiated ; while a man, whose height is more elevated, has
only the lower part of his body exposed to the action of the carbonic acid,
and breathes freely the pure air above. This remarkable place is called the
Grotto of the Dog.

80 ANATOMY AND PHYSIOLOGY.

ume when compared before, or after, it has served for
respiration.

transS'ioZ Lastly, there also escapes from the body with
the products of respiration a considerable quantity of
watery vapor. This exhalation, which has received the
name of 'pulmonary transpiration, is one of the most ap-
parent phenomena of respiration, when by the refrige-
rating action of the surrounding air these vapors are con-
densed on their departure from the body, and form a
thick cloud.

Refill! While the respired air undergoes the changes
already indicated, the blood, which passes over the mem-
branes in contact with this fluid, also experiences impor-
tant modifications ; it is rendered proper for the support
of life, and changes from a blackish color to a lively and
sparkling red. To observe this fact, we have only to
open an artery in the living animal, and to compress at
the same time its neck, so as to prevent the air from
penetrating into the lungs ; the blood flowing from the
artery will at first be of a lively red, but will soon be-
come dark, and of a venous color. If a new access of
air to the lungs be then permitted, this liquid is seen to
change its color, and take the tint proper to the arterial
blood.

r^'i'h.'.uon. Such are the principal phenomena of the respi-
ration of animals. Let us now seek for an explanation
of them.

And first, what becomes of the oxygen, which disap-
pears, and what is the origin of the carbonic acid pro-
duced during the exercise of this function ?

When charcoal is burnt in a vase filled with air, oxy-
gen is found to disappear, and its place to be supplied

RESPIRATION. ft]

by an equal volume of carbonic acid gas ; at the same
time a considerable disengagement of heat takes place.
Now, during respiration, the same phenomena take place,
and a remarkable relation may always be observed be-
tween the quantity of oxygen employed by the animal,
and that of the carbonic acid it produces : under ordinary
circumstances, the volume of the latter is but little below
that of the former, and animals, as will be shown, all
produce more or less heat.

There exists then the greatest analogy between the
principal phenomena of respiration, and those of the
combustion of charcoal : and this similarity of result has
given rise to the idea, that the cause of the two might
be the same.

And in truth one can hardly suppose the respiration of
animals to be other, than the combustion by the oxygen
of the air of a certain quantity of carbon, furnished by
the bodies of these beings.

But where does this combustion take place ? JSKlS!
Is it the blood, which furnishes to the air the carbon thus
consumed, and does this combustion take place on the
surface of the respiratory organ ? or, is the oxygen ab-
sorbed, and conveyed by the blood into the interior of all
the organs, and the carbonic acid thus formed in all these
parts, to be afterward expelled by the same way, which
afforded a passage to the absorbed oxygen ?

The majority of physiologists have adopted exclusively
one or the other of these opinions ; but neither of these
hypotheses is alone sufficient for the explanation of all
the facts observed, and it would really appear, that the
transformation of oxygen into carbonic acid takes place,
both at the expense of the blood, at the moment of con-

11

82 ANATOMY AND PHYSIOLOGY.

tact of this liquid with the air, and in the substance of
the tissues, which compose our various organs : the fol-
lowing experiments may be adduced in proof.

If venous blood be enclosed in a flask filled with oxy-
gen, and agitated, it is seen to change its color ; a part
of the oxygen disappears, and carbonic acid is produced.
All the chemical phenomena of respiration, consequently
take place independently of life, and by the simple fact
of the contact of the blood with the oxygen. Now in
the bodies of respiring animals the blood is separated
from the air only by very thin membranes, which do not
at all oppose the contact. If phosphorus dissolved in oil
be injected into the veins of a dog, this substance, when
traversing the capillary vessels of the lungs, will combine
with the oxygen of the air, burn, and be driven out as a
thick white smoke. The blood must then evidently be
submitted in the respiratory organ to the contact of the
air, and furnish carbon to the oxygen of this fluid, as in
the experiment previously related ; and consequently it
must be acknowledged, that the direct combination of
the oxygen of the air with the carbon of the blood is
the source, at least of a part, of the carbonic acid pro-
duced.

But on the other hand, if an animal capable of resist-
ing asphyxia for some time, a frog, for instance, be placed
in a vase containing no oxygen, and filled with azote, it
will continue to exhale carbonic acid, as if respiring air.
Now, in this case, it is impossible to attribute the forma-
tion of this gas to the direct combustion already spoken
of, for this combustion must cease as soon as the respired
air is deprived of its oxygen ; wherefore the carbonic
acid lias simply been exhaled from the respiratory organ,

RESPIRATION. #Q

and formed elsewhere, from the oxygen already existing
in the interior of the body of the animal.

The vapor, which escapes from the body at Jj£7mSii!K
the same time with the carbonic acid, also arises from
the blood, and is simply exhaled from the surface of the
respiratory organ. Some authors think, that this liquid
is always formed during respiration, and that, a part ol
the oxygen employed, by direct consumption of the hy-
drogen furnished by the blood, gives origin to the water ;
and thus they imagine that they can explain the cause of
pulmonary transpiration, as well as the disappearance of
a volume of oxygen superior to that of the carbonic acid
formed. But experiment overthrows this hypothesis, for
pulmonary transpiration continues, when the respired air
no longer contains oxygen ; and the quantity of vapor
thus exhaled may be augmented at will, by the injection
of water into the veins of a living animal.

x\ll the volatile substances contained in the blood, are
also expelled from the body by the exhalation from the
respiratory organ. If camphor, or spirit of wine, be in-
jected into the veins of a dog, they will soon escape with
the vapor issuing from the lungs, and be recognised by
their odor : the same result follows the injection of hy-
drogen gas in small quantities into the veins.

We have elsewhere seen, that the same organs also
absorb with great rapidity the matters with which they
are in contact ; and this absorption is exercised upon the
gasses, as well as upon the liquids ; for an example take
the following.

In one of the experiments made upon himself by the
physiologist, Linning, he found, that his body had in-
creased in weight eight ounces, without having made use
of any aliment, and solely because he had respired an air

34 ANATOMY AND PHYSIOLOGY.

charged with thick fog. Now, phenomena analogous to
those thus accidentally manifested, take place normally in
the ordinary performance of respiration.
Recapitulation. By a review of what has been said upon the
nature of the respiratory function, it is found to consist
in these four particulars, viz. :

1st. In the direct combustion of a certain quantity of
the carbon of the blood by the oxygen of the air ;

2nd. In the absorption of oxygen, and exhalation of
carbonic acid ;

3d. In the absorption and simultaneous exhalation of
a small quantity of azote ;

4th. In the exhalation of water furnished by the blood,
as are all the other expelled products.
th^relpimtufn. We have seen, that respiration is necessary
for the support of life in all beings ; but the degree of
activity of this function varies much in different animals.

Birds. Birds are of all animated beings the most ac-
tive in their respiration ; in a given time they consume
more air than any other class of animals, and therefore
yield more readily to asphyxia.
Mammifera. The mammiferse have also a very active respi-
ration ; and a great number of experiments have been
made, to estimate the quantity of oxygen that one of
them, man, thus employs in a given time. This quan-
tity varies with the individual, age, and various other cir-
cumstances ; but the average appears to be about seven
hundred and fifty litres or cubic decimetres a day. Now
oxygen forms only the twenty one hundredths (in vol-
ume) of the atmospheric air ; it follows then that man
consumes, during this space of time, at least three thou-
sand five hundred litres or cubic; decimetres of the latter
fluid,

RESPIRATION. 35

Animals of the inferior classes have, in gene- ^'SK.™ 1
ral, a respiration much more limited, especially those liv-
ing in the water. But yet when we reflect upon the
enormous quantities of oxygen, that all these beings must
consume daily, it is evident that the atmosphere would
soon be deprived of it, and all animals perish asphyxia-
ted, if nature did not employ certain means for the con-
stant renewal of the quantity of this gas, diffused around
the surface of the globe.

This she accomplishes by the respiration of ^*™™*f&
plants ; and it is worthy of observation, that the JEWSiJE

■ - , £ .1 sition of the

mean employed is a phenomenon ot precisely atmosphere.
the same order with that, whose effects it is intended to
counterbalance.

Vegetables absorb the carbonic acid diffused in the
atmosphere, and under the influence of the solar light
they extract from it the carbon, and give out oxygen.
Thus the vegetable kingdom supplies animals with the
oxygen necessary for them, and the respiration of ani-
mals constantly furnishes vegetables with the carbonic
acid necessary for their growth.

We thus see, that it is in a great measure upon the
relation existing between animals and vegetables, that
the nature of the atmosphere depends ; and that in its
turn the composition of the air must in some sort govern
the relative proportion of these beings. 1

1 From this it might be supposed, that in cities, where a great many men
are collected, and where there are very few plants, the atmosphere must be
less rich in oxygen than in the country, but it is an error. Chemical anal-
ysis demonstrates that the air has everywhere the same composition, and
this uniformity must be attributed to the currents, by which the atmosphere
is continually agitated.

86 ANATOMY AND PHYSIOLOGY.

Delation be- There always exists a remarkable relation

tween the ac- ^

SElIndS between the quantity of air consumed by each
motion! animal in a given time, and the vivacity of its
motions. Animals, whose motions are slow and rare,
have, all other things being equal, a respiration much
less extensive than those which move with rapidity, and
remain but a short time at repose. A frog, or toad, for
example, consumes far less air than certain butterflies,
although its body be much larger than that of these in-
sects ; but these reptiles move seldom and slowly, while
the butterflies constantly execute the most lively motions.
circumstances The activity of respiration varies also in the

infhiencinfi the J 1

respiration* 6 same animal according to the circumstances, in
which it is placed ; and it may be established as a gene-
ral proposition, that everything, which tends to diminish
the energy of the vital movement, determines a diminu-
tion either in the absorption of the oxygen, or in the rel-
ative proportion of the carbonic acid exhaled ; while, on
the other hand, everything, which augments the force of
the animal, produces a corresponding change in the
extent of the respiration.

Thus in the young this function is less extensive than
in the same beings at the adult age.

During sleep the extent of respiration is also dimin-
ished. Fatigue, abstinence, the abuse of spirituous
liquors produce the same effect. Moderate exercise and
the taking of food exert on this function a contrary influ-
ence.

Finally, heat augments the extent of respiration and
cold diminishes it.

It appears, that there exist, also variations in the quan-
tity of carbonic acid produced at different parts of the

RESPIRATION. 87

day, and, from some facts, it would seem that the pres-
sure of the barometer exercises a very marked influence
upon this phenomenon.

APPARATUS OF RESPIRATION.

Hitherto we have been occupied merely with the phe-
nomena of respiration, considered in themselves, and
without regard to the organs, which are the seat of them.
Let us now see what are the instruments of this impor-
tant function, and how they are modified in different ani-
mals.

In those with the simplest organization, respi- skin,
ration is not assigned to any special apparatus, but is ef-
fected in all the parts, which are in contact with the ele-
ment, in which these beings live, and from which they
derive the oxygen necessary to their existence.

The general envelope of the body, or the skin, is like-
wise the seat of a respiration more or less active, in the
greater part of animals of the more elevated classes, and
especially in man ; but in all these beings a determined
part of the tegumentary membrane is more especially
destined to act upon the air, and is so modified in its
structure, as to better fulfil this function.

In the animals, in whom respiration once be- ^f^
gins to localize itself, it has for its instrument a certain
number of membranous appendages, which are raised
upon the surface of the skin in some part of the body,
and assume the form of tubercles, folds, or fringes.

In other animals, in whom respiration is more active,
the portion of the general envelope of the body to which
is assigned the performance of this act, in place of rising
upon the surface, folds inward and constitutes sacs or
canals, into which the air penetrates.

88 ANATOMY AND PHYSIOLOGY.

General char- Whatever be the form, that the respiratory

actors of the *■ J

gHn P s. ratory or " apparatus assumes, it is remarked, that the part
thus modified to act upon the air, presents a soft, spongy,
and fine texture ; that it receives a great quantity of
blood ; and that it is arranged so as to offer, under a vol-
ume comparatively small, an extent of surface propor-
tioned to the activity of the respiration. It may be
established, as a general proposition, that this organ will
be an instrument of so much the greater power, as its
organization differs from that of the general envelope of
the body, and that the respiration, which takes place by
the skin, will be less active in proportion as that by these
special organs is extended.
Differencea The structure of the respiratory organs varies,

with regard to 1 •/ o '

Sspira tion? f according as they are to be in contact with the
air in the state of gas, or to act upon water holding in
solution a certain quantity of this fluid.

In all animals living under the water, and respiring by
the intervention of this liquid, the special instruments of
respiration are salient, and bear the name of gills ; while
in animals with aerial respiration there arc no gills but
interior cavities answering the same purposes, and which
arc called the lungs, or tracheee.

Giiis. The gills, in their simplest form, consist merely
of a few tubercles with a texture a little softer than that
of the rest of the skin, and which receive a slightly in-
creased quantity of blood ; but they are very far from
being the sole instruments of respiration, and the rest of
the skin takes an active part in its performance.

Several marine worms possess this mode of organiza-
tion ; but when these organs are to be the seat of a more
active respiration, their structure is complicated, and they

RESPIRATION. 89

take the form of lamelke very thin and numerous, or of
simple, or ramified membranous filaments.

The former of these modes of structure is met with in
most of those animals, which, with the crabs and lob-
sters, constitute the group to which the name of Crustacea
has been given, and in a great number of those inhabit-
ing the interior of shells, and which constitute the class
mollusca ; oysters, for example. The second modifica-
tion of the gills is found in fishes, &c.

The interior cavities, which serve for the aerial respi-
ration, sometimes take the form of tracheae, sometimes of

lun°;s.

The trachea are vessels, which communicate Tracheae.
with the exterior by openings called stigmata, and ramify
in the interior of the various organs. They convey to
them the air, and consequently respiration is effected in
all parts of the body. This mode of structure is peculiar
to insects and some of the arachnidce.

The lungs are sacs more or less divided into i^n gs .
cellules, which receive the air into their interior, and the
walls of which are traversed by the vessels containing
the blood to be submitted to the vivifying influence of
the oxygen.

Lungs exist (but in a state of great simplicity,) in
most spiders, in some of the mollusca, such as snails.
Reptiles, birds, and the mammiferae, are also provided
with them.

In man, (as well as in all the mammiferse,) Lungs of man.
the lungs are lodged in the cavity called the thorax, which
occupies the superior part of the trunk, and which is
separated from the abdomen (or belly) by a transverse
partition, formed by the diaphragm. These organs are,

12

90

ANATOMY AND PHYSIOLOGY.

Fig. 16.
a

so to speak, suspended in this cavity, and are enveloped
by a thin, close membrane, which also lines the thorax,
and which is called the pleura* They are in number
two, one upon either side of the body, and they commu-
nicate externally by means of a tube, the trachea, which
ascends along the anterior part of the neck, and opens
into the posterior fauces.

This duct is formed by a se-
ries of small cartilaginous bands
placed across, in the form of in-
complete rings : their interior is
lined by a mucous membrane of
the same nature with that of the
mouth, and continuous with it.
Finally, at its inferior part the
trachea divides into two branches,
which take the name of bronchi,
d and which ramify into the inte-
rior of each lung, as the roots of
a tree in the soil.

The lungs, as we have already

1 The disposition of the pleura is analogous to that of the other serous
membranes, of which we have spoken (page 71). It forms a sac without
opening, which is folded upon itself, and the external half of which adheres
to the walls of the thorax, while the other half is fixed upon the surface of
the corresponding lung: the internal face of the pleura is consequently
every where in contact with itself, and as it is extremely smooth, and con-
tinually lubricated by serosity, it slides very readily, and essentially favors
the respiratory motions.

2 This figure represents the trachea and the lungs ; one of these organs
has been left untouched (</), but on the other side the substance has been
destroyed to expose the ramifications of the bronchi (e). a, Larynx and
superior extremity of the trachea ; — b, trachea ; — c, divisions of the bron-
chi ; — e, bronchial twigs ; — d, one of the lungs.

RESPIRATION. 91

said, present in their interior a multitude of cellules, into
each of which a small branch of the corresponding bron-
chus opens. The walls of these cavities are formed by
a very fine, soft membrane, pierced by numerous capillary
vessels, which receive the venous blood coming from the
pulmonary artery, and expose it to the action of the air.

Within the same volume, the smaller the size of the
cellules of which the lungs are formed, the greater is the
surface, upon which respiration will act, and the more
numerous are the points where the blood comes in con-
tact with the air. There consequently exists a direct
relation between the size of the pulmonary cellules, and
the activity of the respiration ; for example in frogs, in
whom this function is exercised only in a slow and feeble
manner, the lungs have the form of sacs, merely divided
by a few partitions ; while in the mammiferre and birds,
in whom respiration is most active, these organs are di-
vided into cellules so small, that by the naked eye it is
difficult to perceive them.

In man and the other mammiferae, the bronchi all ter-
minate in the pulmonary cellules, and these latter are
always terminated in a cul-de-sac ; wherefore the air,
which enters the lungs of these animals, can advance no
farther. But in birds, in whom respiration is yet more
active, some of these canals traverse the lungs completely,
and open into the cellular tissue which surrounds them,
and which in the rest of the body fills the spaces between
the different organs ; the cavities contained in this tissue
all communicate together, and the air, which arrives in
them also penetrates into all parts of the body, even into
the substance of the bones.

92 ANATOMY AND PHYSIOLOGY

MECHANISM OF RESPIRATION.

From what has been said of the alterations, which the
air undergoes from respiration, it is evident, that this
fluid must be unceasingly renewed in the interior of the
lungs ; which is effected by the movements of inspiration
and expiration, that we momentarily execute.

The mechanism, by which the air is drawn into the
lungs, or expelled from them, is very simple, and resem-
bles in all points the play of a bellows, except that in
the former the fluid penetrates into and escapes from the
organ by the same outlet. The walls of the thorax
being movable, its cavity may be alternately enlarged
and contracted, and the lungs will follow all their move-
ments ; thus in inspiration, the column of air pressed by
the whole weight of the atmosphere, is driven into the
chest through the mouth, nasal fossa?, and trachea, and
fills the pulmonary cellules, in the same way that water
ascends in the body of the pump when the piston is
raised. In expiration, the air contained in the lungs is,
on the contrary, compressed and driven out by the same
way, which served for its entry.

To understand how the thorax of man dilates and
contracts, it is necessary to examine its structure.

RESPIRATION.

93

Fig. 17

a

<? i

Structure of
thorax.

This cavity f h "
lias the form of a cone
with the apex above and
base below, and its walls
are chiefly formed by a
kind of bony cage, re-
sulting from the union of
the ribs with a portion
of the vertebral column
(or spine,) behind, and
with the os sternum in
front.

The spaces between
the ribs are filled by
muscles, which extend
from one of these bones
to the other ; muscles also pass from the first rib to the
cervical portion of the vertebral column ; lastly, the in-
ferior wall of the chest is formed by the diaphragm,
which is attached to the inferior border of the bony case
just mentioned.

The dilatation of the thorax may take place D t he ta u!orax? f
in two ways, by the contraction of the diaphragm, or
elevation of the ribs.

1 Thorax of a man. The muscles of the left side are removed, those on
the right entire.

a, Cervical portion of the vertebral column ; — a\ lumbar portion of the
column ; the dorsal portion, which enters into the formation of the thorax
is concealed by the sternum, &c. ; — i, sternum ; — c, c, ribs ; — c', false
ribs ; — d, clavicle ; — e, intercostal muscles ; — /, lower false rib, concealed
by the insertion of the diaphragm ; — g, arch formed in the interior of the
thorax by the diaphragm ; on the right side the continuation of this arch
is indicated by the dotted line ; — h, pillars of the diaphragm inserted into
the lumbar vertebrae; — i, levator muscles of the ribs.

94 ANATOMY AND PHYSIOLOGY.

SKjK^ The diaphragm in the state of repose forms
an elevated arch, which ascends into the interior of the
chest (£-) ; and it is easy to perceive, that the contrac-
tion of this muscle must diminish the curvature of the
arch, and thus proportionately enlarge the cavity of the
thorax.

The action of the ribs is a little more complicated ;
these bones, (c and c') to the number of twelve on a side,
describe each a curve, the convexity of which is turned
outwards and a little downwards ; their anterior extrem-
ity, which is united to the sternum (b) by means of in-
tervening cartilages, is much less elevated than the pos-
terior, and the articulation of the latter with the vertebral
column, permits them to ascend and descend. The for-
mer of these motions is determined by the contraction of
the muscles at the base of the neck, (/.) When the ribs
ascend, their tendency is to form a horizontal line ; for
at the same time that their anterior extremity ascends,
carrying with it the sternum, they turn a little upon
their axis, so that their curve is no longer directed down-
ward, but outward ; wherefore the lateral and anterior
walls of the thorax are removed to a greater distance
from the vertebral column, and the capacity of the chest
increased.

Sffiimi ln tne movement of expiration the diaphragm
is relaxed, and the lungs, by reason of the elasticity of
their tissue, contract, and draw with them this muscular
partition, till it ascends like an arch. When the muscles,
which have produced the elevation of the ribs and ster-
num, cease to contract, the weight of these bones, and
the traction made by the elasticity of the lungs causes
their depression ; but there are also other forces, which

RESPIRATION. 95

may contribute to the diminution of the capacity of the
thorax, and the expulsion of the air from the lungs : such
are the contractions of the muscles, which form the walls
of the abdomen, and which are fixed to the inferior part
of the chest.

Several degrees may be remarked in the ex- things. of
tent of these movements, and in ordinary respiration, the
quantity of air aspired by the thorax, or driven from the
lungs, scarcely exceeds the seventh part of what these
organs can contain. The quantity of air, contained in
the lungs under ordinary circumstances, has been estima-
ted at nearly 4580 cubic centimetres, and that which
enters the chest, or issues from it, at each inspiration, or
expiration, at 655 cubic centimetres.

The number of the respirations varies with Frequency

J- ot trie rcspifti-

the individual and the age ; in infancy they are tions -
more frequent than in the adult, and in the latter there
are about twenty inspirations to the minute.

Thus we see, that in the ordinary state there must
enter the lungs of a man about 13,100 cubic centimetres
of air in a minute, making about 786 litres to the hour,
and the daily consumption nearly 19,000 litres of this
fluid.

Sighing, gaping, laughing, and sobbing, are j^ 6 ™ 1 '™ 3
but modifications of the ordinary movements f torymolions -
respiration. Sighing is a long and deep inspiration, in
which a great quantity of air gradually enters the lungs ;
thus this phenomenon does not depend solely upon the
moral affections, which are its most frequent cause, but
the need of sighing is felt whenever the respiratory func-
tion is not effected with sufficient rapidity.

Gaping is an inspiration yet deeper, accompanied by

96 ANATOMY AND PHYSIOLOGY.

an almost involuntary and spasmodic contraction of the
muscles of the jaw and velum palati.

Laughing consists in a succession of slight interrupted
expiratory motions, varying in frequency, and chiefly de-
pendent upon the almost convulsive contractions of the
diaphragm. The mechanism of sobbing differs but little
from that of laughing, although the former expresses
very different affections of the mind.

THE INFLUENCE OF RESPIRATION UPON THE OTHER FUNCTIONS.

In concluding our remarks upon respiration, we will
add a few words upon the influence of its various move-
ments on the other functions, the history of which has
already been given.

SiStloS! 6 cir " It i s evident, that the dilatation of the thorax
must produce upon the blood, contained in the great ves-
sels emptying into this cavity, the same effect as upon
the air contained in the trachea. By the movements of
inspiration, that portion of the venae cavae, comprised
within the thoracic cavity, is swollen by the access of
blood thus aspired ; and from the same cause the veins,
which enter this cavity, but are situated externally, and
consequently under the influence of atmospheric pressure,
are more or less completely emptied.

This kind of suction contributes to aid the course of
the blood in the venous system, and is felt even in the
arteries, with which the former vessels are continuous
through the intervention of the capillaries.

The motions of expiration, on the contrary, momenta-
rily suspend the course of the blood in the great veins,
and accelerate it in the arteries, which originate from the
heart, and are thus compressed.

RESPIRATION. 97

To these two phenomena must be attributed the swell-
ing of the veins, (especially those of the head and neck),
during expiration. In the interior of the cranium this
swelling is so marked, that at each respiratory movement
the vessels, situated at the base of the brain, elevate this
viscus, and produce a kind of pulsation.

The dilatation of the chest appears also to v £SaS. ab "
exercise a remarkable influence upon the absorption ; in
fact it acts like a pump upon all which surrounds the
thorax, and must tend to force from without inwards, all
the fluids which communicate with its interior ; but this
action is felt only in the immediate neighborhood of the
chest.

Finally, the abundant exhalation, which al- upon the P ui-

J ' ' monary exlia-

ways takes place upon the surface of the pul- latlon -
monary cellules, is determined in a great measure by the
degree of suction, which accompanies each movement of
inspiration, and which acts upon the liquids, by which
the walls of these cellules are moistened, as it acts upon
the blood of the venae cavse, and primarily upon the air
of the trachea. We have already seen, that in the nor-
mal state, all the volatile substances met with in the
blood are thus exhaled ; but if the thorax of a living ani-
mal be opened, and artificial respiration performed, so
that there is no suction upon the surface of the pulmo-
nary cellules, this exhalation is almost entirely arrested ;
and then camphor injected into the veins does not escape
more rapidly in this way, than from the surface of every
other membrane, whose tissue is as vascular and permea-
ble to liquids.

13

98 ANATOMY AND PHYSIOLOGY.

ANIMAL HEAT.

There exists another phenomenon, the history of which
is closely united to that of the respiration, and the im-
portance of which is so great that we must necessarily
devote some time to it, viz. : the faculty of producing heat.
Difference This faculty appears to be common to all ani-

in the temper- J i i ^

niais! of ani " ma ^ s '•> out tne majority develop so little caloric,
that it cannot be appreciated by our ordinary thermome-
ters ; while in the remainder the production of heat is so
great, that we are not required to make use of scientific
instruments to prove its existence. To compare this dif-
ference, we have only to place a hare and a fish, having
about the same volume, in two calorimeters, and to sur-
round them with ice at the temperature of 0° ; the
quantity of this body melted in a given time will be pro-
portional to the quantity of heat developed by these two
animals. Now, in the instrument containing the fish,
the quantity of ice melted in the space of three hours,
for example, will not be appreciable ; while in that con-
taining the hare, we shall find, after the same lapse of
time, more than a pound of liquid water ; and to melt
this quantity of ice would require as much heat, as to
warm from melting ice to boiling water about three
fourths of this weight of water ; this heat could only have
been furnished by the animal under experiment.

This enormous difference in the production of heat
occasions corresponding differences in the temperature of
the different animals. A thermometer placed in the
body of a dog or bird, for example, will always ascend to
36 or 40 degrees, (centigrade,) while in the body of a

ANIMAL HEAT. 99

frog or fish, it will indicate a temperature nearly equal
to the atmosphere at the time of the experiment.

These are called animals with cold blood, which do
not produce a sufficient degree of heat, to have a tem-
perature of their own and independent of the atmospheric
variations ; those are animals with ivarm blood, which
preserve a temperature nearly constant through the ordi-
nary variations of heat and cold, to which they are ex-
posed. Birds and mammiferae are the only beings inclu-
ded in the latter class ; all others are animals with cold
blood.

The temperature of man and most of the Temperature

1 of the in a in mi-

other mammifera3 scarcely varies from 36 to 40 ferajandbijrds -
degrees ; that of birds ascends to about 42 degrees, cen-
tigrade.

But the faculty of producing heat varies in ^S"" 8
the different animals of these two classes, and also in the
same individual, according to age and circumstances.
Thus most mammiferae and birds produce a sufficient de-
gree of heat, to preserve the same temperature in sum-
mer and winter, and to resist the ordinary effects of cold,
though it be very severe. But there are others, which
produce only heat enough to raise their temperature 12
or 15 degrees above that of the atmosphere ; wherefore,
during summer, their temperature is nearly the same
with the warm-blooded animals, but in the cold season it
is much diminished ; and whenever this cold reaches a
certain limit, the vital movement is rendered slower, and
the animal experiencing it falls into a state of torpor, or
lethargic sleep, which lasts till the temperature again as-
cends. The beings, which present this singular phe-
nomenon, are called hibernating animals, and in this re-

100 ANATOMY AND PHYSIOLOGY.

spect they are in some sort intermediate between the
warm-blooded animals non-hibernating, and the animals
with cold blood,
influence of In the early periods of life, all warm-blooded

nge upon the J - 1

he^. uction of animals are more or less nearly allied to the
cold ; these, as well as the latter, do not produce in gen-
eral sufficient heat to preserve their temperature, even
when exposed to very slight degrees of cold. But the
decrease of temperature, which is without inconvenience
for the cold-blooded animals, acts upon the others in a
very different manner, for always, if carried beyond a
certain degree, or lasting a determined period, death is
the result. With regard to the faculty of producing heat,
the young of warm-blooded animals, which are born with
their eyes open, and which immediately after birth can
run and seek their nourishment, differ far less from the
adults, than the mammiferse, which are born with their
eyes closed, or birds, which on issuing from the egg, are
not yet covered with feathers. If, for example, new
born cats and dogs are taken away from the parent, and
exposed to the air, even in summer, they arc chilled to
the very point of death.

Infants produce also much less heat in the first days
following birth, than at a more advanced period of their
life ; their temperature then decreases very readily, and
the influence of cold is very injurious to them ; therefore
a greater number die in winter than during the rest of
the year.

Everything, which acts as an excitant and which aug-
ments the energy of the vital movement, tends also to
augment the faculty of producing heat, and everything,
which weakens the animal economy, exercises a debili-
tating influence upon this function.

ANIMAL HEAT. 101

Thus the action of a moderate cold tends to t hJ n temperature.
augment the faculty of producing heat, and in conse-
quence during winter we can better resist the causes of
chill than in summer.

The influence of heat, when not prolonged for too
long a period, is excitant and increases the faculty of
producing caloric ; but, if long continued, it weakens the
body and diminishes the energy of this faculty. For this
reason, persons, who have resided for some time in tropi-
cal regions, are so sensible to the cold of our winters.

Finally, exercise ever augments the produc- exerdse, ce &c!
tion of heat, and the acceleration of the respiratory move-
ments is followed by the same effect. During sleep, this
faculty appears to be, on the contrary, less powerful than
when awake ; thus when men, exposed to a very low
temperature, have the imprudence to fall asleep, they
yield to its effects more rapidly than if awake and in
motion. The disastrous retreat from Russia furnishes
numerous examples of the bad effects of sleep upon the
soldiers, weakened by fatigue and privation of all kinds,
and exposed to a most intense cold.

The cause of the production of heat in the cause of the

1 production of

body of animals appears to be the action of the heat-
arterial blood upon the tissues, under the influence of the
nervous system. There exists an evident relation be-
tween the faculty of producing heat, the intensity of the
nervous action, the richness of the blood, and the more
or less rapid transformation of the venous to arterial blood.
Experiment has proved, that every thins;, influence of

1 A j a> the nervous

which tends considerably to weaken the action systetn-
of the nervous system, tends also to diminish the produc-
tion of heat. Thus if the brain or spinal marrow of a

]Q9 ANATOMY AND PHYSIOLOGY.

dog be destroyed, and the respiration be imitated by ar-
tificial means, the life of the animal is indeed sustained,
but the production of heat ceases, and the body becomes
cold as rapidly as a dead body would do, if placed in
similar circumstances. If the action of the brain be
paralyzed by certain energetic poisons, such as opium,
the same effect is produced, and these experiments varied
in different ways have firmly established the fact, that
one of the conditions necessary to the development of
animal heat is, the influence exercised by the nervous
system upon the rest of the body.

^hebiood.^ On the other hand, the action of the blood
upon the organs appears to be equally indispensable to
the manifestation of this phenomenon ; for, the suspen-
sion of its circulation in any part of the body is followed
by coldness of the part ; and, moreover, a remarkable
relation exists between the faculty of producing heat in
different animals, and the richness of their blood. Birds,
which have the highest temperature of all animals, are
also those whose blood is the most loaded with solid par-
ticles (in general fourteen or fifteen parts to the hundred) ;
the mammiferso, whose temperature is not quite so ele-
vated, have more aqueous blood, in general the weight of
the globules constituting only the nine or twelve hun-
dredths of the total weight of this liquid ; lastly, in the
cold-blooded animals, such as frogs and fishes, we find
barely six parts of globules and ninety-four of serum.
the"espirat e ionf But the action of the nervous system, and of
a blood more or less rich in globules, are not the only-
circumstances, which influence the production of animal
heat ; in order that the nutritive liquid may exercise upon
the economy the necessary action, it must possess all the

ANIMAL HEAT. 103

properties, which characterize the arterial blood ; and as
it acquires these only from respiration, the development
of caloric must also depend upon this latter function.
All the causes, which render the transformation from ve-
nous to arterial blood less complete, or less rapid, tend
also to diminish the production of the heat, and there
always exists an intimate relation between it and the
activity of the respiration.

The formation of cabonic acid, which is one of the
most remarkable phenomena of the respiration of ani-
mals, may also explain to us the cause of the production
of the greater part of the heat developed by these beings.
If the oxygen absorbed during respiration is employed to
form this gas by its union with the carbon, arising from
the blood or from the living tissues, as we have every
reason to suppose, this combination must be accompanied
by a disengagement of heat as from the combustion of
charcoal in the air.

Numerous experiments, made with an extreme preci-
sion, demonstrate that the heat, which would be pro-
duced by the combustion of the carbon contained in the
carbonic acid gas exhaled by warm-blooded animals, is
equal to more than half the quantity of caloric disengaged
by these beings. And if we admit, that the absorbed
oxygen, without being replaced by the carbonic acid,
combines in the interior of the body with the hydrogen
to form water, we see, that the heat produced by this
combustion taken with that of the carbon already men-
tioned, would be equivalent to nine tenths of that devel-
oped by the animal. The motion of the blood, and the
friction of the different parts of the body probably pro-
duce the remainder.

|04 ANATOMY AND PHYSIOLOGY.

As a last analysis we see then, that the respiration is
the principal cause of the production of animal heat ;
and that the kind of combustion, occasioned by the ac-
tion of the oxygen upon the blood and living organs, is
effected solely through the influence of the nervous sys-
tem.

of '5£'t This important function is not, however, ex-
body. c e ercised with the same energy in all parts of
the body ; those, in which the blood circulates, with
greater abundance and rapidity (and in which, conse-
quently, life is the most active), are also those, in which
the most heat is disengaged ; and therefore the organs
more distant from the heart, must, cceteris paribus, produce
less heat, and consequently be more readily chilled.
This is the true state of the case ; the temperature of
our limbs being less elevated than that of the trunk, if
we are exposed to the action of an intense cold, these
parts are the first to freeze.

s'istinj heSt" The faculty of producing heat explains to us,
why animals with warm blood have a temperature, which
can sustain itself above that of the surrounding atmos-
phere. But how happens it, that these beings can pre-
serve the same temperature, when they are placed in air
hotter than their body ? A man, for example, can re-
main during a certain time in a dry hot-house, where the
air is heated to a degree approximating boiling water,
without any perceptible increase of the temperature of
his body except two or three degrees.

The power of thus resisting heat depends upon the
evaporation of water, constantly going on at the surface

DIGESTION. ]05

of the skin, or in the apparatus of respiration, and which
constitutes the cutaneous and pulmonary transpiration ;
for the transformation of water into vapor, withdraws
caloric from every thing surrounding it, and the body is
chilled as fast as warmed by the external heat. For the
same reason water placed in the porous vases, called alcar-
azas, cools so promptly even in mid-summer. 1 Now the
quantity of water thus evaporated, increases with the tem-
perature of the air, and the cause for the cooling becomes
more powerful, the greater the heat of the atmosphere.

DIGESTION.

We have already seen, that all living beings are obliged
continually to seek in the exterior world for nutritious
substances, and to assimilate to their organs new mate-
rials. We have also seen how this absorption is effected,
and the study of respiration affords us examples of these
substances thus penetrating into the nutritive liquid, and
being carried by it into the interior of the organs, with-
out having undergone any previous modification.

In vegetables, all nutritive substances penetrate di-
rectly into the organs. But, in animals, the greater part
of the materials necessary for the support of life, are not

1 These vases allow the water they contain to filter through, and thus
have a constantly moist surface, from which a rapid evaporation takes
place, which cools the liquid contained in their interior. From the same
cause, do we experience so lively a sensation of cold, when ether is poured
upon the skin, and the part thus moistened blown upon.

14

1Q6 ANATOMY AND PHYSIOLOGY.

absorbed until they have undergone a certain preparation,
by means of which their properties are changed, and
their composition modified ; or, in other words, till after
they have been digested.

Aliments. The name of aliments may be given to all
substances, which, introduced into the body of a living
being, serve for its increase, or to repair the losses it con-
stantly undergoes ; but in general, the sense of this word
is more restricted, and is only applied to the materials
which are not absorbed, and may not serve for nutrition,
till after they have been digested. For the sake of per-
spicuity, we shall only employ it in the latter accepta-
tion.

den?™!™™™ Aliments are not less necessary to life, than
Simente! ck of the air we breathe, or the water which our
body continually absorbs, either in the liquid state as
drink, or in the form of vapor. When animals are de-
prived of them, their body diminishes in volume, their
powers are weakened, and death arrives after sufferings
more or less prolonged.

Hunger. The want of aliments first makes itself known
by a peculiar sensation, which has its seat in the stomach,
hunger. It is increased by exercise, by the stimulating
influence of a moderate cold, and by the action of cer-
tain bitter substances, as the cashew nut, upon the sto-
mach. On the contrary, everything, which retards the
vital movement, immobility, sleep, &c, also tends to
render this want less imperious. Hibernatm" animals
take no food during the season of their lethargy, and
cold-blooded animals, such as fishes and frogs, can sup-
port a very long abstinence, when the exercise of their
functions is retarded by the influence of a very low tern-

Death from
inanition.

DIGESTION. 107

perature. But the animals, whose nutritive movement is
very rapid, such as man and most mammiferae, soon perish
for the want of food. The herbivorous, whose blood is
less rich in globules than the carnivorous, yield sooner
than the latter ; and young animals, whose nutrition is
much more active than in the adult (since the volume of
their body is constantly increasing, in the place of re-
maining stationary), also die of hunger sooner than the
latter. Dante, in the famous episode of Count Ugolino,
has but depicted in lively colors the truth, as it would
occur, if a man, already having reached the period of
his growth, and children of a tender age, should at the
same time be deprived of all nutrition.

Prolonged abstinence occasions very remarka-
ble phenomena, which may be ranked under three heads.
In the first period, hunger makes itself frequently felt,
and occasions a greater or less degree of weakness, with
considerable alteration of the features. In the second
period, the intellectual faculties are troubled ; in man, as
well as in animals, inquietude, or even fury arises, and
sometimes mental alienation is manifested by visions.
Lastly, in the third period, this exaltation gives place to
a state of depression or complete stupidity, and it is to
be observed, that often when abstinence has been pro-
longed beyond a certain period, the use of aliments can
no longer save the life of the individual. In this latter
case death almost always ensues, whether the animal
continue to fast, or retake its ordinary regimen.

The aliments are all furnished by the organic p JJ^« an d f
kingdom, and life is maintained in man and all "- alimeflts -
other animals from substances, which have themselves
made part of a living being.

]Q8 ANATOMY AND PHYSIOLOGY.

All alimentary substances do not possess the nutritive
property in the same degree, and very curious experi-
ments have established the fact, that in most animals at
least, the union of a certain number of different sub-
stances is indispensable to the wants of life. Thus hares,
nourished upon a single substance, such as cheese, cab-
bages, oats, or carrots, die in the space of about fifteen
days, with all the appearance of inanition, while if nour-
ished with these same substances, given together, or suc-
cessively at short intervals, they live and do well.

The diversity and multiplicity of the aliments, is then
an important rule of hygiene ; and in this, the precepts
of science agree perfectly with our instinct, and with the
variation, brought by the seasons in the alimentary sub-
stances offered us by nature.

Experiment has also proved, that substances, such as
sugar, gum, oil, and fat, into the composition of which no
azote enters, cannot suffice for the nutrition of animals,
in whatsoever order they may be given. The use of a
certain quantity of azoted aliments, such as muscular
flesh, the gluten found in the grain, albumen, &c, ap-
pears to be indispensable to the support of the life of all
animals.

When we compare the nutritious qualities of the differ-
ent alimentary substances, we must also take into con-
sideration the quantity of water they contain ; by deduct-
ing this from the weight of the mass employed, Ave arrive
at the knowledge of the really nutritious matter. Thus
our ordinary bread contains, to the 1000 parts, 250 of
water; beef about 700; potatoes 750; turnips and
cabbages 950.

But the different substances, which may serve as

DIGESTION. 109

aliments to animals, vary with the nature of these beings ;
and these differences, as we shall see, are always in rela-
tion to other differences in the organization. From an
investigation of the digestive apparatus, we can under-
stand why one animal is nourished upon vegetables, and
another upon flesh. But one thing, for which we cannot
account, but which is notwithstanding very true, is the
faculty possessed by certain animals of nutrition upon
substances, which, to others, are violent poisons. Thus,
goats and sheep may eat with impunity hemlock, while
a very small quantity of this plant is sufficient to destroy
man and many other animals.

Digestion, or the process by which animals Modification

o ' i J of the aliments

modify the aliments so as to render them proper by di s esti °»-
for absorption and nutrition, consists essentially in the
action of certain humors upon these matters, in conse-
quence of which they undergo various alterations, and
are separated into two parts ; one destined to penetrate
the interior of the body, and supply the wants of the
animal, called chyle, the other improper for this purpose,
and ultimately expelled under the form of fceces.

From the nature of this process, it is evident, seat of the

1 digestive pro-

that digestion must always take place in an in- cess -
terior cavity of the body, which may serve as a reservoir
for these humors, and for the aliments they are to act
upon. All animals are provided with a digestive cavity,
and the existence of this organ is one of the characters
distinguishing them from vegetables, in which the alimen-
tary substances are absorbed without any previous pre-
paration.

In some animals with very simple structure, this sac is
but a fold of the skin which penetrates deeply into the

110

ANATOMY AND PHYSIOLOGY.

Fig. 18. 1
can

body, and terminates in a cul-de-sac. This is the case
with the hydrae or fresh water polypi, of which we have
already spoken : thus one of these animals can be turned
like the finger of a glove, without changing its manner of
livinp;. The surface, which was exterior, then becomes
interior and forms the cavity, in which the aliments are
digested, while the surface which originally lined this
cavity, becomes external, and no longer acts upon these
substances.

SgSSS. The digestive ca-
vity of man and most an-
imals has the form of
a long canal, extending
from one extremity of the
trunk to the other, with
alternate dilatations and
contractions, so as to con-
stitute several kinds of
chambers or pockets, uni-
ted by ducts more or less §
narrow. This tube is
formed by a membrane,
called mucous, analogous
in structure to the skin,
with which it is continu-
ous ; differing however in
its greater degree of soft-

m

1 Digestive canal and its appendages.

a, ./Esophagus, — b, stomach, — c, pylorus continuing with the duode-
num, or first portion of the small intestine, — d, d, small intestine, — e,
cecum, or first portion of the large intestine, in which the small intestine
terminates, — /, vermiform appendix of the cfecum, — g, ascending colon,

DIGESTION. HI

ness, the greater number of its capillary vessels and se-
cretory follicles, and in the almost complete absence of epi-
dermis. Surrounding this membrane is a fleshy envelope,
formed of muscular fibres, somewhat abundant, and by their
contractions driving the alimentary substances from the
mouth to the anus, or arresting them in their course, and
impeding their progress for a certain time in one, or anoth-
er part of the digestive apparatus. Lastly, in a great part
of its extent, this tube is also enveloped by a serous
membrane, thin, and transparent, called the peritoneum,
which serves both to fix it, and to facilitate its move-
ments.

The digestive apparatus is composed of this alimen-
tary tube, of the organs destined to divide the aliments,
of the various glands serving to form the humors neces-
sary for digestion ; and of the vessels charged with the
duty of conveying the nutritive materials thus elaborated,
from the digestive cavity into the interior of the appara-
tus of circulation.

The alimentary tube takes, in various parts, different
names. Its anterior part, enlarged, and filling the pur-
pose of a sort of vestibule, is called the mouth, the cavity
continuous with it is called the pharynx ; the third part
of the canal constitutes the (Esophagus ; the fourth the
stomach ; the fifth the small, and the sixth the large in-
testines, which terminate at the anus.

In man, and the animals nearly allied to him, the
organs which effect the mechanical division of the ali-
ments, are situated in the mouth, and are called the teeth.

— h, transverse colon, — i, descending colon, — /, rectum, — /.', extremity
of the rectum, — /, liver, — m, gall bladder, — n, pancreas, a great portion
of this gland is concealed behind the stomach, — o, spleen.

] ]2 ANATOMY AND PHYSIOLOGY.

But in certain animals this process is confided to other
parts, to the stomach, for example, as in birds.

The principal glands of the digestive apparatus are ;
the salivary glands, the gastric follicles, the liver, and
pancreas.

Lastly, the vessels which serve for the absorption of
the products of digestion, are in man, as well as all other
mammiferse, birds, reptiles, and fishes, special canals
called chyliferons, or lacteal vessels.

All these organs, with the exception of the mouth, sal-
ivary glands, pharynx, and sesophagus, are lodged in a
large cavity, which occupies the inferior two thirds of the
trunk, and is called the abdomen, or belly. It is separa-
ted from the thorax by the diaphragm, and terminated
inferiorly by a basin, formed of a large bony circle, the
centre of which is occupied by a kind of fleshy wall.
Behind, it is bounded by the spine, and in front, as upon
the sides, its walls are formed by large muscles, which
extend from the thorax to the basirt, (pelvis,) of which
we have just spoken. The internal surface of this cavity
is lined by the peritoneum, and this membrane moreover
forms various turns, between the folds of which are con-
tained the stomach, intestines, liver, pancreas, and spleen.
These folds, called mesenteries, all originate from the
posterior part of the abdomen, and some among them are
prolonged much beyond the organ they are to cover, and
thus form veils or aprons called epiploons.

JtoSEKt? The introduction of the aliments into the
digestive canal is effected in various ways ; and its me-
chanism is varied according as the substances are liquid,
or solid ; but it is always performed either by the move-
ments of the mouth, or by means of the superior extrem-
ities.

DIGESTION. 1]3

With anatomists, the mouth does not consist Mouth.
in the opening which separates the two lips, but in the
oval cavity, formed above by the upper jaw and palate,
below by the tongue and lower jaw, laterally by the
cheeks, behind by the velum palati, and in front by the
lips. Its external communication may be enlarged or
closed at will, either by the movement of the lips, or sep-
aration or approximation of the jaws. It is then easy
to understand, how it may serve for the prehension of
aliments. These organs act as pincers, and seize the
bodies which are to be introduced into the mouth. In
most animals, these organs are situated anteriorly, to
seize the aliments ; but in man, and some other animals,
this function is discharged by other members. The hand
places the aliments in the mouth, and the jaws approxi-
mate only to retain them there.

Liquids are taken in two ways ; sometimes the liquid
is turned into the mouth, and falls by its own weight ;
at other times, it is sucked in, either by the dilatation of
the thorax, which thus determines the entry of air into
the lungs, or by the movements of the tongue, which by
retreating backwards, acts in the manner of a piston ;
the latter constitutes the phenomenon of sucking.

Fluids do not ordinarily remain in the mouth, stoppage of

J the aliments

but descend at once into the stomach ; while in the mouth -
the solid aliments remain in it a certain time, and are
submitted to mastication and insalivation.

Mastication, or the mechanical division of the Mastication.
aliments is effected by the teeth.

These organs are bodies of an extreme dura- Teeth.
bility, implanted in the border of either jaw, so as to act
upon each other. They greatly resemble bone, but dif-

15

j]4 ANATOMY AND PHYSIOLOGY.

fer in one important respect ; for bones are living parts,
and constantly nourished, as shown by the experiments
upon their coloration, while the teeth do not live ; they
are not the seat of a nutritious movement, and the mate-
rials of which they are composed, are not renewed. In
this they resemble the hair, nails, and all the products se-
creted by the glands, such as the saliva, bile, and urine.
Only in the place of being always liquid, as the latter,
they soon become solidified, and acquire an extreme
durability.

Modeof forma- ^ teeth are f igm 1 9 .'

ft P

formed by secretory organs
contained in the interior of
the jaws, (d, fig. 19). These d
organs are small membranous
sacs, (capsules, or matrices of i-- y
the tooth,) at the bottom of which is a small pulpy
nucleus, called the germ, and in which ramify many ner-
vous filaments, and a great number of blood-vessels, (fig.
20). The bulb, or germ, (b,) permits a gelatinous humor
to transude, which fills the capsule, (a,) and there is soon
deposited upon its superior surface some grains of a stony
substance, (d, d,) which enlarge by the exudation of a
new quantity of matter, and unite so as to envelop the
pulpy nucleus, from which they originate. The solid
envelope, resulting from this species of crystalization, is
moulded exactly upon the germ, and as this is to con-

1 This figure represents the lower jaw of a very young infant; the greater
part of the exterior surface of the bone has been removed to expose the cap-
sules of the teeth in its interior; a, gum ; b, inferior border of the jaw; c,
angle of the jaw ; d, capsules of the teeth ; c, coronoid process ; /, condyle
of the jaw.

DIGESTION. 1J5

stitute the tooth, the form of these bodies Fig. 20. '
must depend upon that of the germ itself.

In proportion as this organ allows a new « /^nS&\

(jnaiitit \ of stony material to exude, the (1111111)

latter is gathered to that previously formed, ^W^
and constitutes a new layer, situated upon c

the preceding. The tooth thus enlarges by the addition
of successive and concentric layers, and the germ is at
last found contained in a canal, occupying the middle of
this body, and which diminishes as new materials are
interposed between this organ and the substance of the
tooth. When the germ adheres to the bottom of the
capsule only by a single point, the tooth can terminate
only by one prong, or root ; but if this organ adhere by
several points, the stony matter secreted by it, penetrates
between the peduncles, envelops the part beneath the
germ, and by its prolongation forms as many prongs, or
roots, as there are points of adherence.

Thus is the body of the tooth formed, and B l K e 53h!! r
developed ; but while the stony matter is thus being de-
posited by layers on its interior, the surface becomes en-
crusted by a still harder substance, which is formed by
the capsule, and is called the enamel, while the central
part secreted by the germ is called the ivory. Upon the
superior part of the sac, enveloping the germ, a multitude
of very minute vesicles may be observed, which are ar-
ranged with much order, and which secrete a peculiar
liquor, which expands by minute drops upon the tooth,

1 Section of the capsule of a tooth magnified to show the disposition of
the germ, and the manner, in which the stony matter is deposited upon its
surface ; a, capsule ; b, bulb or germ ; c, blood-vessels and nerves, which
penetrate to the bulb ; <7, d, first rudiments of the tooth.

compo:
the teeth.

HQ ANATOMY AND PHYSIOLOGY.

thickens and forms the kind of varnish already men-
tioned.

In man and the carnivorous animals, the teeth are
formed solely of these two substances, the ivory and the
enamel ; but in the herbivorous mammiferae, some of
these bodies present a third substance, which covers the
enamel, and is therefore called the cortical ; it is secre-
ted by the capsule, and much resembles the ivory.

chemical The ivory of the teeth is composed of gela-

nposition of J ± o

tine, mixed with the phosphate of lime, (in the
proportion of about sixty parts to the hundred in the
adult man,) and containing also a small quantity of the
carbonate of lime (ten to the hundred parts of ivory).
The enamel contains only twenty to the hundred of ani-
mal matter, and eight of the carbonate of lime. Accord-
ing to some chemists there is also a florate of lime ; but
the existence of this material does not appear to be con-
stant, and in any case it is only met with in small quan-
tities. But the enamel is particularly distinguished from
the ivory, by its compact and fibrous tissue, its color, and
its hardness, which is so great that sparks may be elicit-
ed by collision with steel, like the flint.

oMiieTeth' As the tooth increases by the addition of
new layers, either of ivory, or enamel, it approaches the
edge of the jaw, then traverses it, issues from the gum
with which this border is furnished, and appears exter-
nally ; but the inferior part of the tooth which is of later
formation, remains in the jaw and serves to fix it there.
The name of alveolcc is given to the bony cavities in
which the teeth arc implanted, and that of roots to the
parts enclosed : that part which appears above the gum
is called the crown, and the neck is the connexion of the
crown and root.

DIGESTION. U7

The roots differ also from the crown of the teeth by
the absence of enamel, with which the latter is, on the
contrary, covered ; and the cause of this difference evi-
dently resides in the position of the part of the capsule,
which secretes the stony varnish : it is in relation with
the superior part of the teeth, but does not descend to
the peduncle of the bulb, where the roots are formed.

The teeth present different forms, and their Fo t r ™ t ^ the
uses vary with the nature of these differences ; some ter-
minate by a thin sharp edge, serving to cut the substan-
ces introduced between the jaws, and have received the
name of incisors, (fig. 21, a, b,). Others are conical,
and in most animals advanced beyond the neighboring
teeth ; they do not serve to cut the aliments as the inci-
sors, but to lay hold and tear them ; they are called the
canine teeth, (c,). Lastly, others terminate by a broad,
unequal surface, and present the most favorable condi-
tions for crushing and grinding the aliments ; these are
the molar teeth, or grinders, (d, e,f, g, h,).

In the study of animals, the disposition of the teeth is
found to vary, according as these beings are to be nour-
ished upon animal or vegetable substances, soft flesh, or
little animals hid under a coriaceous or horny coating, as
insects, tender herbs, or firm wood ; and to such a de-
gree that by the mere inspection of these organs, one may
obtain with much certainty a knowledge of the regimen,
manners, and even general structure, of most mammi-
ferse.

The mouth of man is furnished with the three kinds
of teeth already mentioned, and the manner in which
they are planted in the jaw varies as much as the form
of their crown. The incisors, (a, b,) whose action tends

118

ANATOMY AND PHYSIOLOGY

to bury them in their alveolae, rather than tear them out,
have but a single root quite short. The canine teeth,
(c,) extend into the jaws more deeply than the incisors,
and the molars, (d, e,f,g, h,) which must support the
greatest efforts, present two or three diverging roots, to
augment the solidity of their insertion.

Fig. 21. 1
h g f e deb

a

First denti-
tion.

At the period of birth, the development of the
teeth is but little advanced ; it is very seldom, that any
of these bodies have yet pierced the gum, and their evo-
lution does not commence till the age of six months, or a
year. The teeth, which then form, are destined to fall
out at the end of a few years, and to give place to others.
They are called milk-teeth, or of the first dentition, and
are twenty in number, viz. : in each jaw, four incisors,
which occupy the front of the mouth, two canines, situa-
ted one on each side next the incisors, and four molars,
placed at the bottom of the mouth, two on each side.

Se t C ition. den " The teeth of the second dentition are more
numerous than those of the first ; the complete number
of these bodies is thirty- two, viz. : to each jaw, four in-
cisors, two canine, and ten molars, the two first of which
on each side have but two roots, and are called small

1 Teeth of an adult : a, first incisor ; b, second incisor ; <•, canine; d and
e, small molars ; /', g t /i, large molars.

DIGESTION. H9

molars, (fig. 21, d, e,) while the three next, situated at
the bottom of the mouth, arc provided with three roots,
and called large molars, (f, g, h,).

In extreme old age, these teeth fall out as the milk-
teeth of infancy, but are not replaced, and their alveolae
are obliterated.

The teeth, the development and structure of Scation f
which we have been studying, are the passive instru-
ments of mastication : they are moved with the jaws in
which they are planted. The upper jaw does not move
upon the rest of the head, but the lower, whose form
resembles a horse shoe, articulates with the cranium only
by the extremity of its two branches, and may be sepa-
rated from, or approximated to the upper jaw. A great
many muscles are fixed to this bone, and impress upon
it their motions. Its depression is determined by the
contraction of those which extend from its inferior border
to the os hyoides. The contrary effect
is produced by the action of the mus-
cles, extending from the different points
of its surface to the temples, and the
neighboring parts of the head. 2 The
power of the levator muscles of the jaw

1 a, Inferior jaw, — b, articulation of the lower jaw with the cranium,
— c, masseter muscle, — d, zygomatic arch, — e, temporal muscle, — /,/,
orbicular muscle of the lips, — g, orbicular muscle of the orbits, — h, occi-
put, or posterior part of the cranium.

2 The principal levator muscles of the lower jaw, are, 1st, the temporal
muscle (e, fig. 22), which springs from the coronoid process of this bone
(see fig. 19, e), passes under the zygomatic arch (d), and extends upon the
sides of the head to which it is fixed ; 2nd, the masseter muscle (c), which
extends from the external face of the angle of the jaw to the zygomatic
arch (d) ; 3d, the two pterygoid muscles, which occupy on the internal face
of the jaw the place corresponding to that of the masseter, and are fixed to

]20 ANATOMY AND PHYSIOLOGY.

is very great, and by their contraction, the substances in-
troduced between the teetli are compressed the more
forcibly, when placed near the bottom of the mouth, and
consequently near the fixed points of these muscles.

The aliments are continually thrown between the
teeth by the contractions of the cheeks, or by the mo-
tions of the tongue ; and thus pressed between two sur-
faces, hard, very unequal, and whose asperities are
adapted to each other, these substances are soon divided
into small portions, and crushed.
influence of The importance of this operation is verv great,

mastication up- l *■ J °

on digestion. f or ^ e more complete the mastication the more
easy is the digestion : which is as easily proved as un-
derstood. If an animal be made to swallow pieces of
meat of various sizes, and after a certain time it is killed
and the stomach opened, the smallest fragments will be
the most advanced in digestion, and the superficies of the
greater will hardly have been touched, while the smaller
portions will be completely softened. Now this happens
when fragments unequal in size, of any body susceptible
of being dissolved in this liquid, are plunged into water,
sugar, for example.

of SfiuESSl While the aliments are submitted to the me-
chanical division, they imbibe saliva, and are sometimes
even dissolved in it.

sauva. The saliva is a colorless liquid, transparent,
slightly viscous, which continually flows into the mouth,
the lower parts of which it occupies. Chemical analysis
has demonstrated, that it is composed of about 993 parts
of water to the 1000 ; the other seven thousandths are

the base of the cranium on each side of the posterior opening of the nasal
fossae.

DIGESTION. 121

formed as follows ; of a peculiar animal matter about three
thousandths, of mucus 1.4; chloride of sodium (or ma-
rine salt), chloride of potassium, tartrate of soda, and a
small quantity of free soda, which gives to this liquid its
alkaline properties, make up the remainder.

The mixture of the saliva with the aliments is a cir-
cumstance of more importance, than would at first be
supposed. It facilitates mastication, aids powerfully de-
glutition, and, as we shall hereafter see, appears to per-
form an important office, in the digestion of these sub-
stances.

The glands, which form the saliva, are situated a ffZ
around the mouth, and are composed of small agglomer-
ated granulations. In man, there are three pairs, placed
symmetrically upon each side of the head : the parotid
glands situated in front of the ear, and behind the lower
jaw ; the submaxillary glands, lodged under the angle of
the jaw (m, fig. 23), and the sublingual glands (I) placed
beneath the tongue, in the space between the two sides
of the jaw.

Each of these glands communicates with the mouth
by a peculiar excretory duct, and pours into it the saliva
in variable quantities. With a tolerable appetite, the
sight of aliments is sufficient to determine a more con-
siderable afflux, and the presence of a foreign body in
the mouth, even if it be completely insipid, always ex-
cites the secretion of this liquid : it would appear, that
upon mastication it becomes more alkaline than usual.

So long as mastication is unfinished, the pos- JfJi''
terior opening of the mouth is closed by the velum palati,
which descends and rests upon the base of the tongue.
The aliments cannot then penetrate farther into the di-

16

122

ANATOMY AND PHYSIOLOGY

gestive canal : but when this operation is terminated,
this movable separation of the mouth from the pharynx
is raised, and deglutition goes on.

Fig. 23. 1 This name is given to the

passage of the aliments from

the mouth to the stomach,

through the pharynx and

> a oesophagus.

■j» jro£t\ i The pharynx, or posterior

4|*#iPRiiS[ fauces, is a cavity continuous

;s^fey# j with the mouth, and which is

h) mJ. m placed at the superior part of

*3-~ d the neck (Jig. 23 and 24.)

W... .. e By its summit it communi-

cates with the nasal fossae ;
71 and above and in front, it is
separated from the mouth
f only by the velum palati.

Below and in front, the larynx (e), opens into it ; lastly,

h

1 This figure represents a side view of a vertical section of the mouth
and pharynx ; — a, the nose, — b, the upper lip, placed in front of the arch
of the palate, which extends horizontally backwards, and separates the
cavity of the mouth from the nasal fossae, — r, the tongue, the base of
which is fixed to the os hyoides (<•/), — e, the larynx suspended to the os
hyoides, and opening into the pharynx, — /, portion of the trachea, a tube,
which continues with the larynx at one end and at the other communicates
with the lungs, — g, portion of the base of the cranium, to which is sus-
pended the pharynx (h), — t, commencement of the oesophagus, — /,-, section
of the velum palati; above this partition is the posterior opening of the
nasal fossre, and below are two kinds of pillars, between which are situated
the tonsils, — /, sublingual gland placed beneath the tongue, and com-
municating with the mouth by a small excretory duct, directed forward, —
m, submaxillary gland, placed behind and below the preceding, — n, thyroid
body, a kind of imperfect gland, placed in front of the inferior part of the
larynx.

DIGESTION.

123

Fig. 24.'

a

below and behind, it continues into the oesophagus (i) ;
a long and narrow tube, which descends the whole length
of the neck, traverses the thorax, passing between the
lungs, behind the heart, and in front of the vertebral
column, perforates the diaphragm, and at last terminates
at the stomach.

The velum palati, which
separates the mouth from
the pharynx, is a movable
partition, suspended trans-
versely from the posterior
border of the palate, and free
at its inferior border, which
is prolonged in the middle f-
to a point, called the uvula
{fig. 23, k, and 24, d). It is
formed by a fold of the mu-
cous membrane, which lines
the whole digestive canal,
and contains in its interior a h

1 The pharynx seen from behind, and opened to display the relative po-
sition of the posterior openings of the nasal fossa?, of the velum palati,
base of the mouth and opening of the larynx ; — a, base of the cranium, —
b, mastoid process of the temporal bone, situated at the side of the
base of the cranium behind the ear, — c, vertical partition of the two
nasal fossa?, the termination of which may be seen at the superior part of
the posterior fauces, — d, velum palati, making part of the arch of the
palate; in the middle of its inferior border is found a prolongation, called
the uvula, and on each side of this appendix is seen the buccal cavity, — e,
base of the tongue, — /, extremity of the os hyoides; on the opposite side
this bone is entirely concealed by the portion of the posterior wall of the
pharynx, which is turned outwards, — g, opening of the larynx or glottis ;
conducting to the lungs by the trachea, a kind of valve, called epiglottis,
opens upwards and in front of this opening ; it is here applied against the
base of the tongue, — h, portion of the trachea, — i, commencement of the
aisophagus, — A, one of the levator muscles of the pharynx.

|24 ANATOMY AND PHYSIOLOGY.

great number of muscles, which allow it to execute
many motions ; to descend and rest upon the base of the
tongue, to be raised and carried obliquely backwards
toward the posterior wall of the pharynx, so as to inter-
cept more or less completely the passage between this
cavity and the nasal fossae.

ofdegSo™ Deglutition appears to be very simple, and
yet it is really the most complicated of all the operations
of digestion. It is produced by the contraction of a great
number of muscles, and requires the concurrence of
several important organs. All the muscles of the tongue,
velum palati, pharynx, larynx, and sesophagus take part
in it.

When it is to commence, the aliments are collected
upon the back of the tongue, which is raised, and presses
them from before backwards against the velum palati ;
this partition then rises to a horizontal line, and thus per-
mits the aliments to issue from the mouth ; if it did not
oppose the motion impressed upon these substances by
the movements of the tongue, the aliments would pene-
trate the nasal fossa 1 ; but the direction it occupies,
obliges them to descend into the pharynx. This first
period of deglutition is under the direction of the will ;
but not so with the remainder of this operation, and the
motions, by means of which the aliments arrive at the
inferior part of the pharynx, are involuntary and in some
sort convulsive. The alimentary bolus (for thus each
mass of the aliment swallowed is called), then passes
over but a very small space ; but it must avoid the open-
ing of the larynx, and that of the nasal fossa?, where its
presence would be injurious, while its passage must be
so prompt as to offer but a momentary interruption to the
free communication of the larynx with the external air.

DIGESTION.

125

Let us see how nature accomplishes this important result.

The alimentary bolus no sooner touches the pharynx,
than every thing is called into action. This cavity con-
tracts and embraces the alimentary bolus, while on the
other hand the larynx ascends and passes in front of this
body, to render more rapid its passage over the opening
of the glottis. Finally, during this movement, the edges
of the opening close exactly, and the epiglottis, pressed
against the base of the tongue, descends so as to cover
the entrance of the larynx. Thus the alimentary bolus,
continually pressed by the contraction of the pharynx,
slides upon the surface of the epiglottis, and arrives
at the sesophagus, the cir-
cular fibres of which, by
successive contractions,
drive it into the stomach.

The stomach (fig. 18,
6), is an enlarged portion
of the alimentary canal,
which is continuous with
the oesophagus, and which
is the seat of the most
remarkable phenomena of
digestion, the transforma-
tion of the aliments into
chyme. It is a membra-
nous sac placed across the
superior part of the abdo-
men, and in form resem-
bling a bag-pipe. 1 It

1 In fact, the bag-pipe is constructed from the stomach of those animals,
in whom this organ most resembles man.

126 ANATOMY AND PHYSIOLOGY.

gradual]) diminishes from left to right, and curves upon
itself, so that its superior border is concave and very
short while its inferior border (called the great curvature
of the stomach) is convex and very long. Toward either
third of the stomach there exists, especially during di-
gestion, a contraction which divides the organ into two
parts ; that situated to the right called the cardiac por-
tion of the stomach, that to the left called the jnjloric
portion. The opening, by which this viscus communi-
cates with the esophagus, is also called the cardiac ori-
fice, because it is situated on the side of the heart. That
which conducts from the stomach to the intestines is
called the pylorus, 1 and is situated at the extremity of
the pyloric part.

The walls of the stomach are very extensible : when
its cavity is not filled with aliments they contract, and
there are upon its internal face a multitude of folds, the
number of which diminishes in proportion to the disten-
tion of the organ. We also remark upon the surface of
the mucous membrane which lines the stomach, a very
considerable number of small secretory cavities, called
gastric follicles, which pour out upon the aliments the
liquid they secrete.
Gastric juice. This liquid, which is called the gastric juice,

1 The word pylorus is derived from the greek nvlovobg, gate keeper,
{nvhj a gate and ovqoq a keeper), and has heen given to the intestinal ori-
fice of the stomach, to signify the functions it fulfils; while the aliments
are as yet not sufficiently digested to allow of their passage into the intes-
tine, the pylorus remains contracted and does not open to them a passage;
hut when the aliments are converted into chyme, this opening relapses and
allows them to pass. The name of valve of the pylorus is given to a circu-
lar fold, which surrounds this opening, and which is formed by a fold of the
mucous and muscular tunics of the stomach.

DIGESTION.

127

is, as we shall hereafter see, one of the most important
agents of digestion, as by its action the aliments are con-
verted into chyme. When the stomach is empty, it is
formed in very small quantities ; but when the walls of
this cavity are excited by the contact of food, and espe-
cially of solid food, the gastric juice flows in abundance,
and has always very marked acid properties. This acid-
ity appears to be due in part to the free hydrochloric
acid, and partly to the presence of a peculiar substance,
which is also met with in the milk, and is called the lac-
tic acid. Some salts may also be detected in it, such as
marine salt, phosphate of lime, etc., and about ninety-
eight hundredths of water.

The alimentary substances, which accumulate Delay of the

J food in the

in the stomach, are strongly pressed upon by st01uach -
the action of the muscular walls of the abdomen, and
would remount into the aesophagus, if the portion of this
duct near the cardia were not closed by the contraction
of its muscular fibres. Sometimes this resistance is over-
come, and the food reascends to the mouth, or is even
thrown out, which bears the name of regurgitation, or
vomiting.

On the other hand, the food cannot simply traverse
the stomach, and then at once enter the intestines, for
the opening of the pylorus is completely closed by the en-
ergetic contraction of the muscular fibres, by which it is
surrounded. The food must therefore remain in the
stomach, where it accumulates principally in the cardiac
part, or great cul-de-sac of this organ. Some of the in-
gesta are there simply absorbed by the walls of the sto-
mach, and penetrate into the blood without any previous
alteration ; this is the case with water, diluted alcohol,

128 ANATOMY AND PHYSIOLOGY.

and some other liquids. Other substances pass into the
intestine, and are even expelled as excrements without
any alteration ; but the aliments are here digested, and
thus transformed into a pulpy and semi-liquid mass, called
chyme.

ti!e rn ci!ym n e. of The fragments, placed towards the surface of
the alimentary mass, and near the walls of the stomach,
early imbibe the gastric juice, become acid as is this
liquid, and gradually soften from the superficies towards
the centre. The whole mass of the food finally under-
goes the same alteration, and in consequence of this soft-
ening, these substances are transformed into a soft, pul-
taceous, grayish matter, of a faint and peculiar odor,
which is chyme mixed with the remains of the food. A
white substance is formed upon the walls of the stomach,
resembling the white of an egg partially cooked, and
which mingles with the other products of the stomachic
digestion.

These alterations take place with more rapidity in the

portions of the stomach near the pylorus than in the

great cul-de-sac, and are propagated from the superficies

of the alimentary mass to its centre.

peristaltic While chymification is «oinp on, the walls of

movements of J °

the stomach. t j ie s t mach become the seat of circular contrac-
tions, which at first proceed from right to left, so as to
propel the chyme by which the alimentary mass is cov-
ered towards the great cul-de-sac of the stomach ; but
after a certain time, all these vermicular motions, which
are called peristal tic, take place in an opposite direction,
and convey the chyme to the pylorus, and then into the
small intestine.

DIGESTION. |29

All alimentary substances are not transformed Duration „ f

J the digestive

into chyme with equal rapidity. The observa- p |ocess -
tions and experiments, which have been made upon this
subject, demonstrate that muscular flesh is much easier
of digestion than most herbaceous substances ; that cook-
ing exerts a great influence upon it, and that boiled veal,
for instance, is two thirds more digestible than roast ;
that the skin and tendons resist a long time the action of
the stomach, etc. Great differences however exist in
different individuals : the size of the pieces swallowed
also influences their transformation into chyme, as might
easily be inferred from the nature of the digestive pro-
cess.

In general, the aliments remain several hours in the
stomach before they are completely transformed into
chyme.

A great number of experiments have been cause of the

° J- transformation

made with the view of ascertaining what passes lXc%me. nts
in the stomach during digestion. The most remarkable
are those of Spallanzani, a celebrated physiologist of
Modena. At the time when he entered upon his re-
searches, it was thought that this phenomenon was only
a species of trituration, and that the chyme was merely
the food bruised till reduced to pulp : but Spallanzani
showed this not to be the case. He caused birds to
swallow articles of food contained in tubes, and little
metallic boxes, the walls of which were pierced with
holes, so as to preserve these substances from all friction,
but not to withdraw them from the action of the liquids
contained in the stomach, and he found that digestion
took place as under ordinary circumstances. He there-
fore justly concluded, that the gastric juice must be the

17

130 ANATOMY AND PHYSIOLOGY.

principal cause of the chymification of food, and to be
more completely assured, he had recourse to very inge-
nious experiments. He made crows and other birds
swallow little sponges attached to a thread, by means of
which he withdrew these bodies from the stomach after
they had remained there for some minutes, and had im-
bibed the liquids contained in this cavity. Thus he pro-
cured a considerable quantity of the gastric juice, which
he placed in small vessels with the food suitably divided ;
he took care at the same time to raise the temperature,
so as to imitate as nearly as possible the circumstances
under which chymification takes place ; and at the end
of some hours he found the alimentary mass, submitted
to this artificial digestion, transformed into a pulpy mat-
ter, similar in all respects to that which would have been
formed in the stomach by a natural digestion. Thereby
proving that the action of the gastric juice upon the food
is the principal cause of its transformation into chyme.

intestines. That portion of the alimentary canal, into
which the food penetrates after its digestion in the sto-
mach, bears the name of intestine (fig. 18, c, d). It is a
membranous and convoluted tube, small in diameter, but
very long, in man being about seven times the length of
the body.

In animals nourished exclusively upon flesh, the intes-
tines are, in general, shorter than in man, and other om-
niverous animals; while in the herbivorous, their length
is much more considerable. Thus in the lion it is only
about three times that of the body, and in the rain it
often equals twenty-eight times this length. The reason
of this difference is obvious, for it is evident that herba-
ceous substances, which are very slow of digestion, and

DIGESTION. 131

which contain but a really small portion of nutritive ma-
terials, must be taken in greater quantities, and must
remain a longer time in the alimentary canal than mus-
cular flesh, the digestion of which is very prompt, and of
which nearly the whole mass is composed of nutritive
materials.

The intestines, as we have already said, are lodged in
the abdomen, and enclosed by the folds of the perito-
neum, which fix them to the vertebral column. They
are divided into two distinct parts, the small and the
large intestine. The small intestine makes the Sni u ne ! ntes "
continuation of the stomach, and in its interior digestion
is finished. It is very narrow, and constitutes about
three fourths of the whole length of the intestines. Its
exterior surface is smooth ; the muscular fibres which
surround it, are placed side by side; and the mucous
membrane, lining the interior, presents upon its surface
many small follicles, and a great number of prominent
appendages, called villosities, also a great number of
transverse folds called valvules conniventes. The follicles
secrete a viscous humor very considerable in quantity ;
the villosities, as we shall afterwards see, appear to serve
especially for the absorption of the products of digestion ;
and the valvulae conniventes to retard the course of the
chyme.

Anatomists distinguish in the small intestine three
parts, the duodenum, so called because its length is about
equal to twelve fingers, the jejunum, because in the dead
body usually found empty, and the ileum, (from eihuv to
turn, to twist), but this distinction is of little importance
in physiology.

The alimentary matters which enter this in- F| « ids «m*

J taineu in the

testine, are mixed with the humors secreted by ™e" ,ntes "

]32 ANATOMY AND PHYSIOLOGY.

its walls, and with two peculiar fluids, the bile and
pancreatic juice, each formed in distinct glandular organs
situated in the neighborhood of the stomach.

The nver. The liver (fig. 18, /,) which is the productive
organ of the bile, is the largest viscus of the bodv. It
is situated at the superior part of the abdomen, princi-
pally upon the right side, and descends to the lower bor-
der of the false ribs. Its superior face is convex, and its
inferior irregularly concave. It is divided into three
lobes, the largest of which is situated to the left, and
separated from the right by a fissure, and the smallest
(called the lobule) is placed under the others. The
color of this organ is reddish brown upon the surface,
and yellowish in the interior. Its substance is soft and
compact, but traversed by a multitude of canals, and
when torn it appears to be formed by the agglomeration
of small solid granulations, into which the blood vessels
empty, and from which originate the excretory ducts
carrying off the bile.

These excretory ducts successively unite to form twigs,
branches, and lastly a 'trunk, which issues from the infe-
rior face of the liver in the direction of the duodenum;
and which, in its course communicates with a membra-
nous sac adherent to the liver, habitually distended with
bile, and called the gall-bladder. The termination of
this canal may be seen in the duodenum, at a short dis-
tance from the stomach. 1

The liver presents a very remarkable peculiarity. The

1 The excretory duct immediately from the liver is called the hepatic duct,
and that from the Madder the cystic duct. Finally the common trunk,
formed by the union of these two vessels, is called the ductus choledochus
(from %ohj, bile and do/dc, the container.

DIGESTION. 133

greater part of the blood, which circulates in this organ,
is not arterial, as in the other parts of the body. The
venous blood coming from the intestines enters it by the
vena porta, which ramifies like an artery, and it would
even appear, that the formation of the bile depends prin-
cipally upon this liquid.

The bile is a viscous, ropy liquid, greenish, and Biie.
of a very bitter taste. Its chemical composition is very
complicated, for we find in it water, albumen, resinous
matter, a yellow coloring principle, various fatty matters,
several salts, and free soda. It is always alkaline, and
has some analogy to soap.

The bile is constantly flowing into the intestine, but
the flow appears to be increased in quantity during diges-
tion ; for when the stomach is empty the gall-bladder is
full, and when digestion is terminated, this reservoir is
nearly empty.

The pancreatic juice is very analogous to the
saliva, both in physical properties and chemical com-
position ; the pancreas, 1 which forms it, resembles the
salivary glands. It is a granular mass, divided Pancreas.
into a great number of lobes and lobules, of firm consist-
ence, whitish gray color bordering upon red, placed
crosswise between the stomach and the vertebral col-
umn (fig. 18, n). From each of its granulations there
originates an excretory duct, all of which unite together
as the veins, and thus form a canal opening into the
duodenum near the mouth of the ductus choledochus.

We have already seen how the peristaltic move- ^^*£ [^
ments of the stomach propel the chyme into the '

Pancreatic
juice.

intestine.

1 The word pancreas signifies all of flesh (from nav, all, and xgwg, flesh),
and was given to this gland by the ancients.

134 ANATOMY AND PHYSIOLOGY.

duodenum through the pylorus. This opening is supplied
with a valve, which opposes the return of this material
to the stomach, and the presence of the chyme in this
intestine causes in it contractions analogous to those of
the stomach, and which exactly resemble the movements
of a crawling worm. By the aid of these movements
the chyme accumulates in the intestine, and gradually
advances farther in the tube. During this passage it
mixes with the bile, and the other humors in its course,
and gradually changes its properties ; it becomes yellow-
ish, bitter, loses its acidity, then becomes alkaline, and
at the same time there is separated from it a matter more
or less thick, sometimes white, sometimes gray, according
to the nature of the aliments, from which it arises, which

chyie. is attached to the surface of the intestinal mucous
membrane, and which bears the name of chyle. This
matter, as we shall afterward see, is absorbed, and toward
the inferior third of the small intestine is no longer met
with ; the paste formed by the residue of the chyme, by
the bile, and the other humors already mentioned, ac-
quires in this portion of the alimentary tube more con-
sistence, takes a deeper color, and passes into the intes-
tine to be rejected as excrement.

Agassi"! 1 Digestion then is finished in the small intestine,
and during its performance various gasses are disengaged
from the alimentary mass, which more or less dilate the
intestine. These gasses are principally carbonic acid
and pure hydrogen ; sometimes too azote is found with
them.

L Tne intes " The large intestine, (fig. 18, e, g, h, i,) which
is the continuation of the small, and which receives the
residue left by digestion, may be easily distinguished by

DIGESTION. J35

the numerous dilatations of its walls between the col-
lections of its muscular fibres. It is divided into the
ccecum, colon and rectum. The ccecum, 1 which is coecum.
situated near the haunch bone of the right side, is pro-
longed into a cul-de-sac beyond the point of insertion of
the small intestine, and presents at this extremity a ver-
miform appendix. Folds arranged as valves supply the
opening from the small intestine, and prevent the matters
driven into the ccecum from reentering the ileon, and re-
turning to the stomach.

The colon, (derived from xtolto, I stop, because colon.
this intestine retains for a long time the excrementitial
matters in its folds), is continuous with the ccecum, re-
mounts towards the liver, traverses the abdomen directly
beneath the stomach, and redescends on the left side to
gain the pelvis, where it continues into the rectum, which
terminates at the anus.

The residue, arising from the digestion of the Progress of

r i •» i • i-i r 1 tne remainder

food, is driven by degrees from the ccecum to ^ Question in

J ° the large in-

the rectum, so called because straight, where it testine -
accumulates, and remains for a longer or shorter period.
By thus traversing the large intestine these matters ac-
quire greater consistence, and a peculiar odor. There is
developed at the same time in this intestine a considera-
ble quantity of gas, differing essentially from the gases
of the small intestines by the almost constant presence
of carbonated hydrogen, and sometimes also by the pre-
sence of a little sulphureted hydrogen.

The fleshy fibres around the anus, and which form the

1 Anatomists have named the first portion of the large intestine the coe-
cum, because it is prolonged inferiorly in the form of a cul-de-sac (from cce-
cus, blind).

]36 ANATOMY AND PHYSIOLOGY.

sphincter muscle of this opening, are continually con-
tracted, and consequently oppose the exit of matters ac-
cumulated in the large intestine. In general, the con-
traction of the muscular fibres around the intestine does
not suffice for the expulsion of their contents, the dia-
phragm and the other muscles of the abdomen concur to
the same end, by compressing the mass of the viscera
contained in this cavity.

dSron°. f Such are the principal phenomena of digestion.
Let us now inquire, if, in the present state of science, it
is possible to explain in a satisfactory manner the differ-
ent changes experienced by the food during the perform-
ance of this function.

The experiments of Spallanzani and of some other
physiologists show, that the principal agents of digestion
are the various liquids, which moisten the food in the
different parts of the digestive canal. These juices are
of three kinds: 1st, the saliva, always alkaline: 2nd,
the gastric juice, which is acid : 3d, the bile an'd pan-
creatic juice, which are alkaline as the saliva.

By the action of the saliva the food is sometimes dis-
solved, in most cases, however simply softened, and often
without much change in its physical properties. It
would appear that this liquid plays an important part in
digestion, as may be seen from what takes place in ru-
minating animals.

In these animals there are four distinct cavities, to
discharge the functions of the single stomach of man.
The food is at first introduced into a large sac called the
paunch, when it remains a certain time, and then passes
into the second stomach (the reticule), and is thrown up
from the latter into the mouth, to be bruised by the teeth

DIGESTION. ]37

and moistened with saliva ; it next descends into the
many-plies or third stomach, and thence into the reed.
The experiments of Prevost and Lerojer of Geneva
show, that the aliments contained in the paunch and the
reticule are moistened with an alkaline juice, and that
by its action the albumen and some other substances,
of which they are in part composed, are dissolved. If
by pressure this liquid is forced out, and acid thrown
upon it, there is immediately formed a flaky precipitate,
similar to the white of an egg half cooked. Now pre-
cisely the same takes place, when the alimentary mass
passes into the many-plies : it meets there an acid juice,
and deposits upon its walls a whitish layer, which is no-
thing but chyme.

On the other hand the experiments of Spallanzani,
which we have already had occasion to mention, show
that the food may also be directly attacked by the gastric
juice. This liquid may dissolve substances, on which
the saliva is inert, and the principles thus dissolved must
in their turn be precipitated as solid globules, when the
alkaline juices contained in the small intestine are
mingled with the acid products of the stomachic diges-
tion.

Digestion seems then to be the result of the chemical
action of the saliva, gastric juice, and bile, upon the ali-
ments, and upon the materials extracted from these sub-
stances by the action of the digestive liquid, to which
they have been submitted before meeting either of these
two latter agents. This phenomenon would then essen-
tially consist in the solution of the alimentary matters,
and their subsequent precipitation in the globular state ;
but it must be confessed, there are very many points yet

18

138

ANATOMY AND PHYSIOLOGY.

to be elucidated relative to the theory of digestion, and
this question, the interest and importance of which every
one can appreciate, demands a new investigation.
of1hfchy°e n f ^° terminate the study of this function, it re-
mains for us to examine how the nutritious matter, ex-
tracted from the food by the digestive function, can pass
from the intestinal canal into the mass of the blood,
which it is destined to renew.

C vei f ™ Some of the liquids introduced into the sto-
mach are directly absorbed by the veins in the w T alls of
this cavity, and in those of the small intestine ; but the
chyle follows another route, and penetrates into a partic-
ular set of canals, destined to effect its transport. These

vessels called chylif-

f

Fig. 25. 1
e d

h -

!•

h

erous (or lacteals,
from the appearance
they take when fill-
ed with chyle) be-
long, as we have
already said, to the
lymphatic system.
They arise from im-
perceptible orifices
on the surface of
the villosities of the
intestinal mucous
membrane, and unite
like veins into larger

1 A portion of the small intestine with the chylifcrous vessels originating
in it and the commencement of the thoracic canal.

a, portion of the intestine, — 5, mysentery which fixes the intestine to the
posterior wall of the abdomen,— c, radicles of the chylifcrous vessels

DIGESTION. 139

or smaller branches, which proceed between the two
folds of the mysentery to the vertebral column. During
this course the lymphatic vessels traverse a number of
small bodies, irregular in form, and of a pale rose color,
which are called the mesenteric glands (d), and after
issuing from these glands they unite into a common
trunk, called the thoracic duct (f). This canal also re-
ceives the lymphatic vessels from almost all other parts
of the body. It traverses the diaphragm, and mounts in
front of the vertebral column to the base of the neck,
where it finally terminates in the left subclavian vein.
There are in its interior, folds similar to the valves of the
veins, so arranged, as to permit the passage of the liquids
towards the subclavian vein, but to prevent their return
to the intestine.

If an animal is fasting, these vessels are nearly empty,
but when the intestinal digestion is in full activity, they
are soon gorged with chyle.

The physical properties of this liquid vary with chyie.
the nature of the food, from which it arises, and the ani-
mals in which it is observed. In man and most mammi-
ferae, the chyle is usually a white liquid, opaque, having
nearly the aspect of milk, of a salt alkaline taste, and of
a peculiar odor. Examined by the microscope, it pre-
sents a multitude of globules, analogous to those forming
the central nucleus of the globules of the blood. When
at rest, it soon forms a mass, like the blood, and after the

creeping upon the intestine, — d, mesenteric glands, — e, chyliferous vessels
after their passage across the mesenteric glands, — /, thoracic duct, — g,
enlarged portion of the thoracic duct called the reservoir of Pecquet (better
known as the receptaculum chyli), — h, h, lymphatic vessels of the inferior
limbs going to the thoracic duct, — i, i, portion of the aorta, by the side of
which the thoracic duct ascends to gain the subclavian vein.

140 ANATOMY AND PHYSIOLOGY.

expiration of some time it separates into three parts ; a
solid clot, which occupies the bottom of the vessel, a
liquid analogous to the serum, and a very thin layer,
which swims upon it, and which appears to be of a fatty
nature. The chyle also takes during coagulation, a lively
rosaceous tint, and if agitated with oxygen the phenom-
enon is yet more marked.

Chyle, arising from articles of diet, which do not con-
tain fatty substances, is much less opaque than that fur-
nished by matters containing fat or oil, and the layer
which forms upon the surface after coagulation is much
less thick. The solid clot, which is principally com-
posed of fibrine and coloring matter, is very small in
quantity in the chyle arising from the digestion of sugar,
gum, etc., while from the chyle furnished by muscular
flesh is formed a considerably large one.
Mechanism The villosities, with which the surface of the

of t lie chylous

absorption. mucous membrane of the intestines is supplied,
appear to be the special agents of the absorption of the
chyle. As soon as it commences, we find them swollen
and saturated with this liquid, as sponges which have
imbibed milk ; some anatomists have imagined they
could distinguish in this species of fringe, very small
openings communicating with the radicles of the lym-
phatic vessels ; and if this be the case, we can easily
comprehend, how the chyle may penetrate into these
vessels without being absorbed by the veins. This liquid
contains, as we have already said, globules too large to
pass through the simple porosities of the venous walls,
while they would find an easy access into the chyhferous
vessels through the holes, with which the villosities ap-
pear to be pierced.

DIGESTION. 141

However, the chyle penetrates into these latter ves-
sels, and flows with considerable rapidity the length of
the thoracic duct to the left subclavian vein ; if this canal
be tied in the living animal, the passage of the chyle into
the circulatory system is completely cut off, and this
liquid accumulates in the thoracic duct. The cause of
its movement of ascension in this canal, and in the nu-
merous chyliferous vessels, which represent the roots of
this trunk, is not known. It is found to continue some
time after death, and it has also been ascertained, that
the course of the chyle is favored by the respiratory
movements, the beating of the arteries, and all the move-
ments, which compress in an intermitting manner the
thoracic duct, and which can be readily comprehended,
by reason of the valves already mentioned, and the action
of which has been explained when treating of the venous
circulation.

The chyle thus mingling with the blood serves Us chyfe. the
to repair the losses experienced by this liquid in its action
upon the organs nourished by it. But how is this hcema-
tosis, or transformation of chyle into blood, effected ?

We have already said, that these two liquids are much
alike, and that by the action of the air upon the chyle,
this resemblance becomes yet closer, because the color of
this liquid is rendered very analogous to that of the blood.
From which it might be concluded, that a part of the
modifications necessary to change the chyle into blood,
take place in the interior part of the lungs, and by the
act of respiration.

Still there exists between these two liquids an import-
ant difference, not to be thus accounted for. The glo-
bules of the chyle do not appear to be contained in a

|42 ANATOMY AND PHYSIOLOGY.

colored vesicle, like those of the blood, and therefore
the question arises, where are these latter globules
formed ?

This question is not yet completely determined ; but
from some acknowledged facts, the liver would seem to
be the agent in effecting this important change.

URINARY SECRETION.

One portion of the foreign substances absorbed by the
human body and of the materials eliminated from the or-
gans by the exercise of nutrition, are expelled from the
economy, either by the respiration, pulmonary exhalation,
and cutaneous transpiration, or by the secretion from the
surface of the intestines and the other mucous mem-
branes ; but substances, which are useless or injurious to
the economy, may be rejected by another way, the urin-
ary excretion.

U paratus. ap " This function is that of the kidneys, which are
two voluminous glands situated in the abdomen, on cither
side of the vertebral column, between the muscles of the
lumbar region of the back and the peritoneum, and ordi-
narily surrounded by much fat ; their color is reddish
brown, and their form like that of a hancot or kidney-
bean. The panenchyma appears to be formed of two
substances ; one superficial, called the cortical or glan-
dular ; the other interior, named tubular or mamellated.
The cortical substance is formed of extremely small
granulations, and a multitude of capillary canals twisted

URINARY SECRETION. 143

upon themselves, and united in clusters ; the mamellated
is composed of canals, which spring from the cortical,
and, converging towards the middle of the interior border
of the gland, form by their union a certain number of
cones, with a rounded base, surrounded by the cortical
layer. These canals all empty at the summit of these
pyramids into other and greater ducts called the calices,
which in their turn supply the pelvis, a small membrane-
ous pouch situated in the fissure of the internal border
of the kidneys.

These glands receive a considerable quantity of blood
from a large artery, which ramifies upon the cortical sub-
stance, where is effected the secretion of a peculiar liquid,
the urine.

This liquid descends by the canals composing the
mamellated substance, and by the calices to the pelvis,
and thence passes into the bladder through a long mem-
braneous tube of the size of a writing quill, which passes
transversely from the pelvis to the bladder, and is called
the ureter. The bladder is a conical pouch, which fulfils
the functions of a reservoir for the urine, and is situated
at the inferior part of the abdomen, behind the anterior
portion of the pelvis, called the arch of the pubis. It is
formed of a mucous membrane, surrounded by fleshy
fibres, and continues inferiorly with a narrow canal, open-
ing outwards, and which is called the urethra.

The urine is a yellowish and acid liquid, which, urine.
in man, is composed in the normal state of nearly ninety-
three hundredths of water, three hundredths of a peculiar
matter, called urea, of a thousandth of uric and a small
quantity of lactic acid, and of several salts (the chloride
of sodium or marine salt, phosphate of lime, &c.) In

]44 ANATOMY AND PHYSIOLOGY.

the carnivorous mammifene its chemical composition is
nearly the same as in man, except that we do not find
the uric acid ; but in young children and herbivorous an-
imals, there is a very peculiar substance contained in it,
namely, the hypo-uric acid ; and in birds, as well as in
most reptiles, (lizards, serpents, &x.) it scarcely contains
any thing but uric acid ; finally in frogs and turtles, we
find both urea and albumen : its composition appears to
be nearly the same in fishes, but in insects there is uric
acid. In certain diseases, its composition, however, is
considerably changed.

So \7rhi° e f . the The rapidity, with which fluids introduced
into the stomach pass into the bladder and are expelled
by the urinary passages, is very great. Every one has
made the remark, and the experiments upon living ani-
mals also prove it. But yet there exists no direct com-
munication between these two organs, and the liquids
can only pass to the bladder after having been absorbed,
mingled with the mass of the blood, thus conveyed to
the substance of the kidneys, and separated by the se-
cretory exercise, of which these glands are the seat.

It is evidently from the blood that the kidneys derive
all the aqueous portion of the urine ; and if certain sub-
stances, easily recognised, (such as rhubarb, or the yel-
low cyanuret of potassium or iron,) be introduced into
the current of the circulation, (either by injection or ab-
sorption,) they are soon found to be expelled in the
urine.

The blood, then, furnishes to the kidneys the materials
necessary to form the urine ; and the knowledge of this
fact must naturally lead physiologists to inquire if the
several principles contained in the latter existed, com-

URINARY SECRETION. J45

pletely formed, in the blood, and were merely separated
by the action of the kidneys, or whether these organs
produced them, by their action upon other substances con-
tained in the blood.

Water and most of the matters expelled by the urinary
passages, exist in quantities more or less appreciable in
the blood ; but, under ordinary circumstances, chemical
analysis does not reveal to us the presence of urea and
the other principles essentially characterizing the urinary
secretion. It might therefore be supposed, that these
materials were formed directly by the kidneys ; but it is
not so ; these organs only separate them from the blood
gradually, as they appear ; and an infallible proof will
be found in the extraction of the kidneys in the living
animal ; for then, the urinary secretion being interrupted,
we find urea in the blood.

Therefore it is a legitimate inference, that the urinary
glands actually derive from this liquid the substances
which compose the urine, and that they find them ready
formed.

But different circumstances influence the ac- SSSSSJSS

. . r . . r . -i -■•,. lii activity of the

tivity or this function, and may moony both the secretion.
mass of the liquids expelled by the urinary passages, and
the quantity of solid materials, separated from the blood
by the action of the kidneys, and held in solution by the
aqueous part of the urine.

The quantity of water expelled by the urinary secre-
tion depends, in a great measure, upon that of the fluids
taken into the stomach.

Water introduced into the mass of the blood by ab-
sorption separates from it more or less rapidly, so that
after a certain time the equilibrium is established in the

19

]46 ANATOMY AND PHYSIOLOGY.

economy, however great the quantity of fluids introduced
into the stomach. This liquid escapes from our bodies
in two distinct ways, namely, by pulmonary and cutane-
ous exhalation, and by the urinary secretion ; and these
two functions are in a measure mutually dependent, and
the mass of fluids in circulation remaining the same,
every thing which tends to diminish the one, tends to
augment the other.

For example, the action of heat upon the body tends
to augment the transpiration, and, consequently, to di-
minish the urinary secretion : thus the latter function is
more active in winter, than in summer, 1 and if any one
take a considerable quantity of drink, he can almost vol-
untarily determine its expulsion, by one or other of these
means, according as he is placed in circumstances favor-
able for transpiration, or the urinary secretion.

The quantity of solid substance expelled by the kid-
neys, and held in solution by the aqueous portion of the
urine, depends, in a great measure, upon the nature and
abundance of the aliments taken.

It has been proved by M. Chossat, that when nour-
ished upon the same aliments, the only variation being
in quantity, the secretion of urea and the other different
principles, with the exception of water, expelled by the
kidneys, varies in the same proportion. It diminishes
with rigorous abstinence, and augments with the increase
in the quantity of food, always provided this quantity be
not too great for digestion.

1 The curious experiments of M. Chossat demonstrate, that in the cold
season the mass of urine surpasses that of the fluids taken into the sto-
mach. In the months of spring, when the temperature is mild, this rela-
tion is sensibly diminished, and in the hot season the proportion of the
urine to the drink is only about nine tenths.

URINARY SECRETION. 147

This physiologist has also proved, that the secretion of
these matters increases in the ratio of the quantity of
annualized substances taken, that is, substances which
contain a considerable proportion of azote. Thus by
nourishing himself upon bread alone, or upon flesh alone,
he found, that for an equal weight of food (abstracting
the water contained), the quantity of solid principles
expelled under the form of urine was four times as great
in the latter case, as in the former.

If we compare the quantity of carbon, azote, hydro-
gen, and oxygen, which enter into the composition of
the aliments employed by man, with that of the same
elements expelled under various forms, either by the
lungs and skin, or by the kidneys, we find almost all the
carbon, thus introduced into the body, escapes from the
lungs under the form of carbonic acid, while the azote
is almost entirely expelled by the urine, as urea, uric
acid, &c.

But the state of the animal's system also exercises
great influence upon the results of the urinary secretion ;
as every thing which tends to weaken, appears to retard
this secretion, and to diminish the exhalation of carbonic
acid by the respiration.

The urine sometimes deposits in the interior ^^cateS!!
of the urinary passages various substances, which may be
held in solution, but which when deposited as solids are
styled gravel and urinary calculi.

The gravel is almost always formed of uric acid, and
depends upon its too great secretion ; thus this malady is
increased by every thing which tends to augment the
proportion of solid substances held in solution by the
urine, as the diet of the animal, the too constrained use

]48 ANATOMY AND PHYSIOLOGY.

of aqueous drinks, &c. In general this deposit forms in
the kidneys and is passed out with the urine.

The urinary calculi are larger concretions, which also
sometimes form in the kidneys, but more generally are
developed in the bladder where they reside. They
gradually enlarge by the addition of new matter from
the urine, and owing to their formation present concen-
tric layers, more or less distinct.

The substances entering into their formation are very
various. Some are always existent in the urine, but in
quantities so small, that they are ordinarily held in solu-
tion. Others are produced, or rendered insoluble by the
chemical action experienced by the urine when long ex-
posed to the air, or confined in the bladder. Finally,
others are the result of an abnormal action of the se-
cretory organ itself.

The first are of uric acid, the second urate of ammo-
nia, the phosphate ammoniaco-magnesian, the phosphate
of lime, the third the oxalate of lime, the cystic oxide, etc.

Calculi of the first class are the most common, and it
often happens that their presence in the bladder deter-
mines the deposition of the salts, that we have ranged in
the second category. It is rare to see these latter sub-
stances form the nucleus of a calculus ; but nothing is
more common, than to find a nucleus of uric acid or oxa-
late of lime encrusted with earthy phosphate.

REVIEW.

Having now gone over the different series of phenom-
ena, by means of which the nutrition of the body of ani-
mals is effected, to embrace at a glance the operation of
all these functions, it is thought proper to give their enu-

URINARY SECRETION. ^49

meration in an order varying from that adopted in their

study.

It has been shown, that all living beings must contin-
ually draw to the interior of their bodies water, oxygen,
and various other alimentary matters derived from the
exterior world, and deposit these new materials in the
tissue of their organs.

The name of absorption has been given to this passage
from without inwards, and to the combination of the
materials, thus sucked in by the living organs with the
mass of the nutritive fluid.

In plants, all nutritive substances are absorbed at once,
and penetrate directly into the parenchyma of the organs,
without having undergone any previous preparation. In
animals, certain substances, as water and the oxygen of
the air, are absorbed in the same manner, either by the
skin, or by the internal tegumentary surface lining the
aerial and digestive passages ; but with most nutritive
materials, it is quite otherwise, and the food cannot serve
for the support of the body, and penetrate into the inte-
rior of the organs, until it has first been transformed into
a peculiar liquid, called chyle, a transformation, which
constitutes the phenomena of digestion.

The chyle, absorbed by the lymphatic vessels, mingles
with the blood, and furnishes the materials of which this
liquid is composed.

The blood circulates in all parts, and conveys to them
the materials necessary for their support. By the aid of
the nutritive principles, which are furnished them by this
liquid, the living tissues continually incorporate with
their own substance new particles, and while this exer-
cise of assimilation is going on, they abandon other mole-

]50 ANATOMY AND PHYSIOLOGY.

cules, which entered into their composition, and the
renewal of which has therefore become necessary.

This continual movement of the composition and de-
composition of the solid parts of the body, constitutes
the exercise of the function of nutrition. When the quan-
tity of foreign materials, thus assimilated to the substance
of the organs, exceeds that of the matters eliminated
from these same organs, the body increases ; in the oppo-
site case, it becomes lean ; and if these two phenomena
are equally active, the weight of the animal remains sta-
tionary, although the materials of which its body is com-
posed are unceasingly renewed.

The excrementitial matters, separated from the sub-
stance of the living organs by the exercise of nutrition,
must be thrown out, — and this actually takes place.
They are at first mingled with the blood, which con-
veys them along with it far from the parts where they
were detached, and in its turn this liquid is freed from
them, either by the simple exhalation which takes place
from all tegumentary surfaces, exterior as well as inte-
rior, or by the secretion from the glands, the parenchyma
of which it traverses.

The water thus expelled from the body, escapes prin-
cipally by the insensible transpiration of the lungs and
of the skin, and by the urinary secretion.

The greater part of the azoted principles and of the
materials not volatile, are in general excreted by the
kidneys.

On the contrary, from the lungs are exhaled carbonic
acid and the other volatile principles which may be found
mingled with the blood.

Respiration is consequently, at the same time a func-

FUNCTIONS OF RELATION. ]5J

tion of assimilation and of excretion, as it serves as a
means for the entrance of the oxygen necessary to the
support of life, and for the exhalation of the carbonic
acid produced by the nutritive decomposition of the
organs.

With regard to the nature of the movement of nutri-
tion, of which all living parts are the seat, we again re-
peat, nothing certain is known : we can only presume,
that it must resemble the secretory exercise, and that it
must depend upon the action of an analogous cause,
which cause appears to be the nervous influence, and
which seems to have a great analogy to the physical
force which produces the electro-chemical phenomena.
Recent experiments by M. Becquerel upon the influence
of electricity on the vegetation of plants, come to the
support of this opinion.

FUNCTIONS OF RELATION.

In the enumeration of the different faculties, with
which animals are endowed, we found that some were
exclusively destined to confirm the existence of these
beings, while others served to convey to them a knowl-
edge of surrounding objects. The former constitute the
functions of nutrition, which we have already studied ;
the latter, the functions of relation, with which we are
now to be occupied.

If we examine what takes place in an animal contractility.
of the simplest structure and most limited powers, the
first thing we notice is its motion, and that the move-

]52 ANATOMY AND PHYSIOLOGY.

ments which it executes are determined and directed by
a cause acting internally. Among these movements,
some are repeated in the same manner, whatever be the
circumstances in which the animal is placed, and over
which it has no actual control.

volition. But there are others, which vary according to
the wants of the animal, and are under the direction of
an intelligent power, known as volition.

These two orders of phenomena constitute two of the
most important functions of relation, to wit : contractility
or the faculty of executing spontaneous movements ;
and volition, or the faculty of exciting contractility, and
varying its effects with a view of arriving at a result
foreseen by the animal.

sensation. There is yet another property inherent in all
animated beings, and which is still more remarkable ; it
is sensation, or the faculty of receiving impressions from
external objects, and being conscious of them.

instinct. These three faculties are common to all ani-
mals, but they are not the only ones observed. It is re-
marked, that in all there exists an inward power, which
causes them to perform certain acts useful for their pre-
servation, but the result of which they cannot certainly
presage, and the cause of which depends upon no appa-
rent need. Thus a multitude of animals construct with
the most admirable art dwellings, destined to lodge their
offspring, and calculated to supply all their wants, and
they always do this in the same manner, and with the
same skill, even when they have been separated from
others of their kind from birth, and have never seen
analogous labors. Others at a determinate season of the
year emigrate to far countries, where the climate will

FUNCTIONS OF RELATION. ]53

be more favorable to them, and they direct themselves
thitherward as certainly, as if the end of their voyage
were before their eyes.

The name instinct has been given to the cause, which
thus constrains animals to execute certain determinate
acts, which are neither the effect of imitation, nor yet
the result of reasoning. These inclinations vary, so to
speak, in every species of animals, and the phenomena,
which result from them, are sometimes extremely simple,
and sometimes of an astonishing complication.

Other animals more highly privileged, enjoy intelligence.
the possession of the intellectual faculties, or the power
of recalling to the mind the ideas primarily produced by
the sensations, of comparing them, of drawing from them
general ideas and deducing motives of conduct.

Finally, there are also some animated beings, Expression,
which enjoy the faculty of imparting their ideas to their
fellows, either by certain movements, or by the produc-
tion of various sounds.

The various phenomena, by which animals are put in
relation with surrounding objects, may therefore, as we
have seen, be referred to six principal faculties ; sensation,
contractility, volition, instinct, intelligence, and expression.
The four first exist in all animals, the two latter only in a
small number, and the manner in which they are execut-
ed varies almost to infinity.

In some animals of very simple structure, the polypi
for instance, the various faculties of relative life are not
the appropriation of any particular organ : each separate
portion can feel and move without the concurrence of
another portion ; but in man and the immense majority
of animals, the exercise of all these functions is dependent

20

]54 ANATOMY AND PHYSIOLOGY.

upon the action of a determinate part of the body, which
is called the nervous system.

NERVOUS SYSTEM.

Nervous tissues. This system is formed of a peculiar substance,
soft and pulpy, which is almost fluid in the early periods
of life, but which acquires consistence as man approaches
the adult age.

It is worthy of observation, that in this respect, the in-
ferior animals resemble more perfect beings whose devel-
opment is not completed. In frogs the cerebral pulp
affords no more consistence than in the human foetus, and
in crabs it is almost liquid. There is in nature a tendency
of which we shall often have occasion to speak, viz., that
of causing the superior order of animals to pass through
transitory stages, analogous to the state which is perma-
nent for beings of a less perfect structure.

The aspect of this substance, which is named the ner-
vous tissue, varies greatly ; sometimes it is white, at others
gray and ashy ; sometimes it is gathered into consider-
able masses, at others it forms long ramified cords. The
latter organs are named nerves, and the former ganglions
or nervous centres, for they serve as a point of union for
all the filaments in question.

In man, and all the animals nearly allied to him, the
nervous apparatus is composed of two parts, called ner-
vous system of animal life or cerebrospinal, and the ner-
vous system of organic life or ganglionar}/ ; and each of
these systems, in its turn, is composed of two parts ; one
central, formed of nervous masses more or less consider-
able, the other a periphery, formed of nerves going from
these centres to various parts of the body.
Encephajojj. The central portion of the cerebro-spinal ner-

FUNCTIONS OF RELATION.

155

vous system is often designated as the cerebro-spinal axis,
or the encephalon. It is essentially composed of the brain,
cerebellum and spinal marrow, and it is lodged in a bony
sheath formed by the cranium and vertebral column, or
spine.

The cavity of the cranium occupies all the su- Pansprotect-

•f r 111? the encc-

perior and posterior part of the head. It is of pl,al0 " -
an oval form, and presents, on its inferior surface, a great
number of holes, which give passage to the nerves pass-
ing out, and to the blood-vessels which serve for the nu-
trition of the parts contained in its interior. Lastly, in the
point where the head articulates with the vertebral col-
umn on which it rests, there exists a great opening called
the occipital hole, through which the cavity of the cranium
is continuous with a canal, which extends the whole
length of the median line of the back.

This canal is formed by a succession of bony SSS?
rings, called vertebrce (fig. 26), which joined Fig. 26. 1
together in a solid manner, constitute a kind of
stalk, which occupies the whole length of the
body, and is called the spinal or vertebral col-
umn (fig. 27). On each side there exists a
series of holes, through which the nerves pass
to the different parts of the body.

Several membranes also surround the ence-
phalon, and serve to fix or to protect this organ,
whose structure is very delicate, and import-
ance very great.

The first of these tunics is called the JX.
dura mater ; it is a fibrous membrane, firm, thick,
whitish and moist, which adheres by several
points of its exterior surface, to the walls of the

1 Fig. 26. The superior surface of one of the vertebras of the back. Fig.
27, a profile view of the vertebral column.

Fig. 27.

j 56 ANATOMY AND PHYSIOLOGY.

cranium and vertebral canal, and forms around the ner-
vous system a very resisting sheath. Upon its interior
surface are many folds, which bury themselves in furrows,
more or less deep, of the encephalic nervous mass, and
form a kind of division, which prevents these parts from
being displaced, and sustains them so that they do not
press against each other in any position of the body.
There also exist between its internal and external sur-
face, very large venous canals, which are called sinuses of
the dura mater, and which serve as reservoirs for the blood
coming from the different parts of the encephalon.

Arachnoid. Within the dura mater we find a second cov-
ering, the arachnoid, so called from its tenacity and trans-
parence, which have caused it to be compared to a spi-
der's web. It belongs to the class of serous membranes,
and represents a sac without an opening doubled upon
itself, which envelops the encephalon, and lines the walls
of the cavity of the dura mater, in the same way that the
pleura envelops the lungs, and the peritoneum the intes-
tines. Its interior surface, every where in contact with
itself, is lubricated by a serous humor, and its internal
plate penetrates into the different cavities, of which we
shall hereafter have occasion to speak, in the interior of
the brain. Its principal use is to furnish a liquid which
bathes this organ and facilitates its movements.

pia mater. Finally, we find beneath the arachnoid a third
cellular membrane, which is wanting in certain parts, and
which is called the pia mater. It is not a membrane, pro-
perly so called, but a cellular layer destitute of consist-
ence, in which are ramified and interlaced, in a thousand
different directions, a multitude of blood vessels, more or
less fine and tortuous, which come from the encephalon,

FUNCTIONS OF RELATION.

157

or are scattered in its substance ; the circulation of the
blood in the encephalon being in a very peculiar manner.
The arteries before penetrating into this organ, the texture
of which is very delicate, are reduced to capillary ves-
sels, the purpose of which is to moderate the force with
which the blood reaches the organ.

Fig. 28. 1

/'--

The cerebro-spinal axis, Encephalon.
which is protected by these different
envelopes, is composed, as before
mentioned, of several distinct organs;
but all these parts are intimately
united together, and may be consid-
ered as a continuation of each other.
Its anterior or superior part is very
voluminous, and occupies the interior
25 of the cranium : to this belongs
1 the special name of encephalon. It
is divided into two parts, the brain
(cerebrum), and the cerebellum, both
33 continuous inferiorly with a large
nervous cord lodged in the spinal
column, and called the spinal mar-
row.

The brain (fig. 28, a, and fig. 29,
A, B, C,) is the most voluminous
portion of the encephalon ; it occu-
pies all the superior part of the cra-
nium, from the forehead to the occi-
put. Its form is oval, with the large

1 Cerebro-spinal system seen on its anterior face (the nerves being divided
at a short distance from their origin), — a, brain, — b, anterior lobe of the
left hemisphere of the brain, — c, median lobe, — (/, posterior lobe, almost

158

ANATOMY AND PHYSIOLOGY.

extremity behind, its superior face is quite a regular arch,
and at the sides it is a little compressed, while below it

no 10 g

entirely concealed by the cerebellum, — c, cerebellum, — /', medulla ob-
longata, — /, spinal marrow, — 1, nerves of the first pair, or olfactory, —
2, optic, or nerves of the second pair, — 3, nerves of the third pair, which
originate from behind the interlacing of the optic nerves in front of the
pons varolii, and above the peduncles of the brain, — 4, nerves of the fourth
pair, — 5, trifacial or nerves of the fifth pair, — 6, nerves of the sixth pair
lying upon the pons varolii, — 7, facial or nerves of the seventh pair, and
acoustic or nerves of eighth pair, — 9, glossopharyngeal, or nerves of the
ninth pair, — 10, pneumogastric, or nerves of the tenth pair, — 11, nerves
of the eleventh and twelfth pairs, — 13, suboccipital, or nerves of the thir-
teenth pair, — 14, 15, 16, three first pairs of cervical nerves, — g, cervical
nerves forming the bracbial plexus, — 25, a pair of the dorsal nerves, — 33,
a pair of the lumbar nerves, — h, lumbar and sacral nerves forming the
plexus, from which arise the nerves of the lower extremities, — i, and j T
termination of the spinal marrow called the cauda equina, — k, great sciatic
nerve going to the lower extremity.

1 Vertical section of the cerebrum, cerebellum, and medulla oblongata ; —

FUNCTIONS OF RELATION. J 59

is somewhat flattened. At first, we distinguish two late-
ral halves, named hemispheres of the brain, and separated
by a deep fissure, in which is buried a partition, formed
by a fold of the dura mater, and called from its form the
■cerebral falx. From before backwards, this fissure divides
the brain in its whole extent ; it does not however ex-
tend completely through from above downward, but is
bounded inferiorly by a medullary plate, which extends
from one hemisphere to the other, and is called the cor-
pus callosum (fig. 29, f). The surface of the hemi-
sphere is divided by a great number of tortuous and
irregular furrows of various depths, which separate the
rounded eminences upon its exterior, convoluted upon
themselves, and having some resemblance to the folds of
the small intestine, in the abdomen. These eminences
are called the convolutions of the brain ; and the furrows,
which separate them, and lodge the folds of the internal
plate of the arachnoid, are called anfractuosities. They

A, anterior lobe of the brain, — B, median lobe, — C, posterior lobe, — D,
cerebellum, — E, spinal marrow, — /, section of the corpus callosum, situ-
ated at the bottom of the fissure which separates the two hemispheres of
the brain ; below this transverse band of white matter are found the lateral
ventricles of the brain, — g, optic lobes concealed below the anterior face
of the brain, — 1, olfactory nerves, — 2, the eye, in which terminates the
optic nerve, the root of which may be followed upon the sides of the annular
protuberance to the optic lobes ; behind the eye we see the nerve of the
third pair, — 4, nerve of the fourth pair, which is distributed like the pre-
ceding to the muscles of the eye, — 5, superior maxillary branch of the
nerve of the fifth pair, — 5', ophthalmic branch of the same pair, — 5", in-
ferior maxillary branch of the same nerve, — 6, nerve of the sixth pair
going to the muscles of the eye, — 7, facial nerve, below the origin of this
nerve we see a section of the acoustic, — 9, glossopharyngeal or nerve of
the ninth pair, — 10, pneumogastrie, — 11, hypoglossal, or nerve of the
eleventh pair, — 12, spinal or nerve of the twelfth pair, — 14, and 15, cer-
vical nerves.

I GO ANATOMY AND PHYSIOLOGY.

vary in depth, and it is worthy of remark, that in the
child and in most animals, even those nearest to man, the
convolutions are but little developed. On the inferior
face of the brain we find in each hemisphere three lobes,
separated by transverse furrows, and designated as the
anterior, median, and posterior lobes ; we also observe
in this part of the brain two round eminences, placed
near the median line (mamillary eminences), and two
large peduncles which seem to issue from the substance
of this organ to continue with the spinal marrow (com-
missures or penduncles of the brain). Also from this part
of the brain issue the nerves, to which this viscus gives
origin.

The surface of the brain is almost entirely formed of
a gray nervous substance ; but its interior is composed of
a white substance. When this organ is cut into, we
find that there exist in its interior several cavities, which
communicate externally, and which are called the ventri-
cles of the brain. (Fig. 29, f).

cerebellum. The cerebellum is placed beneath the poste-
rior part of the brain (fig. 29, D, and fig. 28, e,) and has
not one third the size of this organ, even in the adult,
where it is larger in proportion than in the infant. It is
divided like the brain, into two hemispheres, or lateral
lobes, separated by a fissure, and a median lobe, situated
behind and below, in a depression already mentioned.
The surface of the hemispheres and of the median lobe
is formed of a gray material, and presents no convolution,
but a great number of furrows nearly straight, and placed
parallel one by the side of the other, so as to divide this
organ into a multitude of plates, arranged like the leaves
of a book. Inferiorly the brain is continuous with the

FUNCTIONS OF RELATION. \Q\

spinal marrow, by means of two short thick peduncles,
and at the same point, it surrounds this latter organ with
a band of white substance, which extends transversely
from one hemisphere to the other, passing in front of the
spinal marrow, with which it is closely united, and which
bears the name of annular protuberance, or pons Varolii ;
so called in honor of a celebrated anatomist, Varolius.

When the posterior lobes of the brain are OpUc lobes.
raised, there may be seen between this organ and the
cerebellum, four small round eminences, placed a pair
on either side of the median line (fig. 29, g). They are
raised upon the superior face of the medullary prolonga-
tions going from the brain to the spinal marrow, and
constitute what anatomists call the optic lobes, or tuber-
cula qnadrigemina, to be noticed hereafter.

The spinal marrow (fig. 28,/, and 29, E,) is n f a p r ^..
in some sort a prolongation of the cerebrum and cerebel-
lum. It has the form of a thick cord, and presents in
front, as well as behind, a median and longitudinal fur-
row, which divides it into two lateral and symmetrical
halves. At its superior extremity (to which anatomists
have given the name of medulla oblongata), several en-
largements may be observed, called olivary, pyramidal,
and restiform bodies, and from either side of which issue
a great number of nerves, at first directed outward but
afterwards descending more obliquely, so that the spinal
marrow appears to terminate by dividing into a great
number of longitudinal filaments, arranged as the hairs in
the tail of a horse, (fig. 28, j), a resemblance, which has
secured to this part the name of the object to which it
has been compared. On a level with the origin of the
nerves distributed to the thoracic members, the spinal

21

162 ANATOMY AND PHYSIOLOGY.

marrow presents an evident enlargement ; afterwards it
contracts, and again enlarges in volume at the origin of
the nerves supplying the abdominal muscles; its lower
extremity is very small, and is found toward the superior
part of the lumbar region of the vertebral column.

The spinal marrow is composed, like the brain and
cerebellum, of two medullary substances different in
color; but here the gray matter, in place of being upon
the surface, occupies the interior of the organ, and is
covered by the white material. There is no pia mater
around the spinal marrow, and the sheath formed by the
dura mater, is not entirely occupied by this organ, but is
distended by a considerable quantity of liquid, in the
midst of which it is suspended ; an arrangement admi-
rably adapted to preserve it from the pressures or com-
motions, which might result from too violent movements
of the vertebral column, or from any other cause, and
which would produce upon this part of the nervous sys-
tem consequences more serious than upon the brain.

enc r epha[on he We have said, that the substance forming the
cerebro-spinal axis was soft and pulpy ; yet in the white
matter fibres may be distinguished, and the study of their
course leads to the explanation of many remarkable phe-
nomena.

The spinal marrow presents, then, two halves, united
by bands, formed principally of transverse medullary
fibres ; on either side we find also, in the white sub-
stance of this organ, a great number of longitudinal fibres,
which, at the superior part, are united in six principal
portions. Four of these portions occupy the anterior
face of the medulla oblongata; they constitute the en-
largements known as the anterior pyramids, and olivary

FUNCTIONS OF RELATION. 163

bodies, and they penetrate into the brain. The fibres
of the pyramids present a very remarkable peculiarity ;
those of the right side branch to the left, and those on
the left to the right : not till after this interlacing are
they buried in the annular protuberance, and, continuing
their course forward they constitute the peduncles of the
brain. These fibres afterwards diverge and expand in
the inferior, anterior and superior convolutions of the
anterior and median lobes of the brain. The longitudi-
nal fibres from the olivary eminences ascend, like those
of the pyramidal, across the annular protuberance, and
go to form the posterior and internal part of the pedun-
cles of the brain ; they traverse, like those of the pyra-
midal bodies, various masses of the gray substance, in-
crease in volume and number, and by following different
directions form several parts of the brain, as the thalami
of the optic nerves, and the corpora striata; finally,
they expand into the convolutions, the entire mass of
which constitutes the cerebral hemispheres ; by the in-
tervention of other transverse fibres the two halves of the
brain communicate together, and these fibres constitute
the corpus callosum already mentioned, as well as several
other transverse bands, designated by anatomists under
the general name of commissures.

The longitudinal fibres of the posterior pyramids of
the spinal marrow are united to some fibres coming from
the neighboring parts of the medulla oblongata, and thus
constitute the peduncle of the cerebellum ; they plunge
to the very centre of the corresponding hemisphere of this
organ, and send to its circumference a multitude of plates
which subdivide and form by their ramifications, as it
were, branches enveloped in the gray material, and called

](34 ANATOMY AND PHYSIOLOGY.

by some anatomists the arbor vitce (fig. 29, D). The
communication of the two hemispheres of the cerebellum
by means of transverse fibres may also be seen, a part of
tt liich surround the medulla oblongata in front and form
the annular protuberance.

Nerves. The nerves, which spring from the encephalon,
and which establish the communication between this svs-
tern and the different parts of the body, are in number
forty-three pairs (fig. 28, and fig. 29). They all arise
from the spinal marrow or base of the brain, and are dis-
tinguished, from their position, by regular numbers from
before backward. Most of them are at first formed by
several roots, or collections of isolated fibres, and present
near their origin an enlargement called a ganglion (fig.
Fig. 30. ' ^O, c). The twelve first pairs spring from
a the encephalon, and issue from the skull by

the various holes in the base. The suc-
ceeding thirty-one pairs arise from that por-
tion of the spinal marrow which is contained
in the vertebral canal, and issue from this
osseous covering by holes situated on each
side, between the vertebrae. (Fig. 27.)
Finally, these nerves, with very few exceptions, soon
divide into a multitude of branches, which in their turn
are subdivided into twigs, and terminated by filaments
extremely tenacious, in the substance of the different

1 Section of the spinal marrow to show the disposition of the nerves
originating from it, — a, spinal marrow, — b, the anterior root of one of the
spinal nerves, — c, ganglion, situated in the course of this root, — d, posterior
root of the same nerve, united to the anterior root beyond the ganglion, —
e, common trunk formed by the union of these two roots, — /, small branch
anastomosing with the great sympathetic nerve.

FUNCTIONS OF RELATION. Jg5

organs. Often, too, some of these nervous branches are
united, and form an anastomosis 1 or a plexus. 2

All the spinal nerves originate by two roots, composed
of several fasciculi of fibres ; one from the anterior, the
other from the posterior part of the spinal marrow (fig.

30).

The ganglionic nervous system, called also the ^£ 1C
great sympathetic, or nervous system of the organic life, is
composed of a certain number of small nervous masses,
perfectly distinct, but united to each other by medullary
cords and various nerves, which anastomose with those of
the cerebro-spinal system, or are distributed to the neigh-
boring organs. These nervous centres are called gang-
lions ; they are found in the head, neck, thorax, and ab-
domen. Most of them are placed symmetrically upon
either side of the median line in front of the vertebral
column, and thus form a double chain from the head to
the pelvis ; but they are also found in other parts, near
the heart and in the neighborhood of the stomach.

The nerves of the cerebro-spinal system go to the
organs of the senses, to the skin, muscles, &c. ; those
which make a part of the ganglionic system are distrib-
uted to the lungs, heart, stomach, intestines, and sheaths
of the blood vessels. In a word the former belong spe-
cially to the organs of relation, the latter to the organs
of nutrition.

1 The nerves, having been regarded by some anatomists as canals to con-
duct the nervous fluid, the name of anastomosis has been given to the
union of their branches, or twigs ; this word, as we have already said, sig-
nifies really an emptying or a communication between two vessels.

2 Plexus (from plecto, I interlace) is the name given to a kind of union
of several nerves or vessels. The principal nervous plexi are those formed
by the nerves of the limbs, soon after issuing from the vertebral column.

Fig. 28, g and h.)

]QQ ANATOMY AND PHYSIOLOGY.

Such are the various parts which compose the nervous
apparatus of man ; let us now see its uses, beginning
with the study of sensation.

SENSATION.

Sensation we have defined to be the faculty of receiving
impressions, and being conscious of them. It belongs to
all animals, but the degree in which it is developed varies
with each of them. As we ascend in the scale of ani-
mal life, and approach man, the sensations are much
more varied. The animal acquires the power of taking
cognizance of a greater number of the properties pos-
sessed by surrounding objects, and of better appreciating
slight shades of difference. The impressions produced
become more lively, and as the faculty of sensation is
thus perfected, the structure of the organs of the life of
relation, become more complicated ; for here, as well as
in all the other functions, by the division of labor does
nature obtain increasingly perfect results.

Wherever the sensations produced by external objects
are a little varied, there exists a distinct nervous system,
and upon its action depends the faculty of perception.
Its structure is at first very simple, and then all the parts
composing it appear to fulfil nearly the same function.
In the earth worm, for example, it is a knotty cord ex-
tended the length of the body, all the parts of which
possess the same properties ; for if the animal be divided
transversely into several sections, each of these fragments
will continue to move and feel as before ; but in beings
of a more complicated organization, and more perfect
faculties, this apparatus is composed, as in man, of sev-
eral dissimilar parts, each of which then acts in a man-

FUNCTIONS OF RELATION. 1£7

ner different from the rest, and discharges special func-
tions.

The most general phenomena, of those de- sense of tact.
pendent upon the action of the nervous system, is the
perception of a sensation from the contact of a material
object with one of the organs of the animal. These are
not the sole sensations that may be experienced, and to
be more precise in our language, we must distinguish by
a particular name the faculty on which they depend, and
we therefore call it the sense of tact.

All parts of our body are not equally endowed sensible and

1 •' x J insensible

with this sense ; some organs enjoy a most ex- parts -
quisitely delicate sense of tact, while others may touch
foreign bodies, and even be cut and torn by them, with-
out the least sensation to the animal. Now, the most
sensible parts are most abundantly supplied with nerves,
and where there are no nerves there is no sensation. If
an incision be made in the paw of a living animal, and
the nerve of this part be exposed, it will be found that
this cord is endowed with an extreme sensibility ; how-
ever slightly it is pinched or pricked, the animal displays
all the signs of most acute pain, and the muscles, to
which the nerve thus injured is distributed, are agitated
by convulsive contractions.

From this it may be supposed, that to the aS^m

i m .I. -i upon sensa-

nerves our organs owe their sensibility; and to uon.
prove this it is only necessary to destroy one of these
cords. For if the experiment be performed upon the
limb of a living animal, all the parts supplied by the
nerve are immediately paralyzed, or deprived of the fac-
ulty of sensation and motion.

But is this nerve, whose action is indispensable to the

1(58 ANATOMY AND PHYSIOLOGY.

exercise of these functions, itself charged with determin-
ing the motions, and perceiving the sensations ? Or
does it merely play the part of a conductor, and is it
destined only to transmit to the muscles the influence of
volition, and to convey to another organ, which may be
the seat of the perception of sensations, the impressions
resulting from the contact of an external object with the
surface of the body ?

To solve this question physiologists have had recourse
to experiments upon living animals.

If, in any point of its extent, the nerve going to the
posterior claw of the frog, for example, be divided, and
the extremity thus separated from the rest of the ner-
vous system, be pinched or pricked, it is found to be
completely insensible, while the part situated above the
section preserves all its sensibility ; the parts of the
limb, which receive branches from the inferior fragment
of the nerve, are likewise paralyzed.

A nerve, separated from the system of which it made
a part, ceases then to discharge its functions ; it cannot
consequently continue to be the seat of the perception of
sensation, and the conclusion must necessarily be drawn,
that it serves to transmit to the organ charged with this
function, the impressions received by the parts endowed
with the sense of tact.

This has been clearly demonstrated by all the re-
searches made relative to this end. The impression
produced by the contact of a body with the nerve itself,
or with the part in which the nerve is ramified, cannot
be perceived, and cannot consequently produce a sensa-
tion, if it is not transmitted by the nerve to other organs.

This fact once established, we are naturally led to

FUNCTIONS OF RELATION. \Q$

ask, to what part must the sensations be conveyed to
render the animal conscious of them, or, in other words,
what is the organ charged with perceiving them ?

The nerves, the functions of which we have rf JJfgg
now been studying, all end in the spinal mar- marrow-
row, and the latter terminates in the brain ; it is then
evident, that this faculty must reside in some part of the
encephalon. Let experiment decide for us, whether it
is in the spinal marrow, cerebellum, or cerebrum.

When experiments are made upon the spinal marrow,
similar to those already performed upon the nerves origi-
nating from it, the first observation is, that this organ is
extremely sensible : the slightest prick produces an acute
pain and convulsive motions ; and if cut across, a com-
plete paralysis of all parts supplied by the nerves origi-
nating below the section is the result, while those, whose
nerves arise from that portion of the spinal marrow yet
in communication with the brain, continue to enjoy the
faculty of sensation and motion.

By care to maintain artificial respiration, so as to pre-
vent the animal thus experimented on from perishing
with asphyxia, in consequence of paralysis of the respira-
tory muscles, it may be proved, that all parts of the spi-
nal marrow and medulla oblongata lose the faculty of
determining voluntary movements, and of giving birth to
sensations, as soon as they are separated from the brain,
and therefore the conclusion must be drawn, that the
faculty of perceiving sensations, or of determining volun-
tary movements, does not reside in them.

But with the brain it is quite otherwise. If byt h a e rt bra!n™

. i*i r 1 • • tne perception

we expose the two hemispheres or this organ in ( .r sensations.
a living animal (a pigeon for example), and irritate their

22

J 70 ANATOMY AND PHYSIOLOGY.

surface with the point of a cutting instrument, we shall
be struck with their insensibility ; we may cut and tear
the substance of the brain, and the animal will not betray
the slightest sign of pain, not even appearing to be aware
of the mutilation going on ; but if, as in the experiment
of M. Flourens, this organ be removed, the animal falls
into a state of stupidity, from which it cannot be roused.
Its whole body becomes insensible, its senses no longer
act, and if it moves, it is because impelled by some out-
ward power, and apparently the will is not concerned in
the determination of any of its movements.

From this experiment it may be learned, that the ac-
tion of the brain is indispensable to the perception of
sensations and manifestation of the will ; and that the
impressions, received by the nerves, must be conveyed
to this organ that the animal may be conscious of them.

Review. In the function of sensation there is then a
very remarkable division of labor. The parts, which by
their contact with foreign bodies are susceptible of giving
birth to sensations, cannot themselves perceive these
impressions ; and on the other hand, the organ, which
has for its exclusive function the perception of these im-
pressions, cannot itself directly receive them ; it is insen-
sible, and can be excited only by the impressions trans-
mitted by the intervention of the nerves.

Three properties then may be distinguished in the
apparatus of the sense of tact ; viz. : 1st, the faculty of
receiving by contact with a foreign body such an impres-
sion, as will give birth to a sensation ; 2nd, the faculty
of transmitting these impressions from the point of their
production to the organ charged with perceiving them ;
3d, that of giving to the animal the consciousness of their
existence, or of perception.

FUNCTIONS OF RELATION. J7|

From the experiments of M. Flourens, and some other
physiologists, it would appear, that in man and animals
approaching him, such as the mammiferae and birds, this
latter faculty resides essentially in the hemispheres of the
brain.

The faculty of transmitting to this organ the Nerves ° f

* ° ° sensation and

impressions produced by the contact of a foreign mot,on -
body belongs to the nerves of the cerebro-spinal system
and to the spinal marrow, though all nerves do not pos-
sess this property. All those which originate from the
spinal marrow, possess at the same time both the power
of transmitting to the muscles the influence of the will,
and of transmitting to the brain the impressions alluded
to: consequently, they are nerves of motion Functions

1 j > j ot'tlie anterior

and sensation. But the roots which fix them ■SJ B p S? p tS>
to the spinal marrow, do not present the same spui
properties. All these nerves, as we have seen, originate
by two orders of filaments, one from the anterior, the
other from the posterior portion of the spinal marrow,
and the interesting experiments of M. Magendie have
shown, that the latter serve for the transmission of sen-
sations, and the former for the influence determining the
voluntary movements.

If the posterior roots of a spinal nerve are divided, this
cord is immediately deprived of the faculty of transmit-
ting impressions ; the part of the body to which it goes
becomes insensible, but the movements remain under the
influence of the will : while the section of the anterior
roots, the posterior being untouched, causes the loss of
motion without destroying the sensation.

By the division of the posterior roots of all the spinal
nerves, the animal is not prevented from executing vol-

|72 ANATOMY AND PHYSIOLOGY.

untary motions, but its whole body, (except the head,
the nerves of which originate in the interior of the cra-
nium) is rendered completely insensible. The posterior
roots are then nerves of sensation, and the anterior of
motion, and by their union the cord thus resulting enjoys
at the same time the two faculties.

c n e ^.gs C Among the nerves from the cephalic portion
of the encephalon, some possess the same property with
the spinal ; these are the facial or nerves of the fifth pair;
the pneumogastric or tenth pair ; and the suboccipital
or twelfth pair. All these nerves originate by roots, one
of which presents a ganglionic enlargement and belongs
to sensation, and the other has no ganglion and belongs
to motion.

The other cephalic nerves are but little or not at all
sensible, and serve either for motion, or for the transmis-
sion of certain peculiar impressions, produced by light,
sounds, &c, and to which we shall have occasion to re-
turn.

poterlo'r 01 lot The different parts of the spinal marrow do not
sptoai marrow, possess in an equal degree the faculty of trans-
mitting sensations, or of exciting motions ; sensation is
very delicate on the posterior face of this organ, and
much more feeble on its anterior.

flSfc at ne™e?" Finally the ganglionary nervous system is but
little, or not at all, sensible : these ganglions may be
pinched or cut, as well as the nerves proceeding from
them, without producing pain, or occasioning muscular
contractions. It is also worthy of remark, that, in the
state of health, the internal organs receiving these nerves
transmit to us very feeble and confused sensations, and
their sensibility is only developed in certain diseases.

FUNCTIONS OF RELATION. J 73

In this case it is to be presumed, that the sensations ar-
rive at the brain only by the intervention of the branches,
which unite the nerves of the ganglionary system to each
of the spinal nerves. But this point in physiology calls
for new investigations.

Till now we have been occupied only by the special senses.
sensations produced by the contact of a material body
upon our organs and with the function which permits us
to recognise the existence of objects, which resist our
movements, and to judge of the consistence, degree of
polish, temperature, and, to a certain point, form of these
objects. But these are not the only sensations these ob-
jects awaken in us, and we also enjoy the faculty of ap-
preciating several of their qualities, which completely
escape the sense of touch, such as their taste, odor, colors,
and the sounds they produce.

These faculties constitute the special senses of man
and most animals. For the perception of these sensa-
tions, as in the exercise of touch, the concurrence of the
brain must be obtained to judge of them, and of a nerve
to transmit to this organ the sensation produced ; but the
division of labor is here carried yet farther, for this nerve
is not fitted itself to receive the impression : the latter
must be received by a special instrument and transmitted
by the nerve of this organ to the brain. Thus the light,
to produce upon us any sensation, must necessarily strike
upon a determined part of the body, the sensibility of
which is modified, although the nerve which conducts to
the brain the impression thus received, is itself insensible
to this agent. The nerves of the special senses all ori-
ginate from the brain, or the neighboring part of the me-
dulla oblongata, and enjoy but in a very limited degree

J74 ANATOMY AND PHYSIOLOGY.

the sense of touch. The optic nerve may be pinched
and cut without producing pain. But the organs, which
are the seat of these special senses, and are all lodged in
the head, receive branches from the trifacial nerve, which
give to them their sensation.

These different modifications of the faculty of sensation
constitute the five senses, by means of which we acquire
all the ideas we have of surrounding objects.

Let us now examine in a particular manner how each
of these faculties is executed, and let us study the instru-
ments, which serve both for touch, taste, smell, hearing,
and sight.

THE SENSE OF TOUCH.

All animals enjoy a sense of touch more or less deli-
cate, which is executed by means of the membrane cover-
ing the surface of the body. To study it we must first
examine the structure of the skin.

S the Ct s lI kTn. of I 11 man tne exterior surface of the body and
the cavities in the interior which communicate externally,
such as the digestive canal, &c, are covered with a teg-
umentary membrane varying in thickness, and very dif-
ferent from the substance of the parts covered ; which is
continuous throughout, and really forms but one whole.
Its properties however, are not always the same, and it
is known by different names, as it is folded inward to
line the different cavities, or spread upon the exterior
surface of the body. The internal portion of this gene-
ral tegumentary membrane is called the mucous mem-
brane, and the external the skin.

The skin is composed of three layers : the dermis or
chorion, the rete mucosum (mucous net work), and the
epidermis.

FUNCTIONS OF RELATION. J 75

The dermis forms the deepest and thickest layer nermis.
of the skin. It is a white, supple membrane, but very
elastic and resistent. It is composed of a great number
of fibres and lamella? interlaced in a very serrated man-
ner. Its internal face is united to the neighboring parts
by a layer, varying in thickness, of cellular tissue, and
at some points giving attachment to the muscular fibres,
which serve to move it. Lastly, upon its surface are a
great number of small reddish prominences, very sensible,
and arranged in pairs, forming in certain parts of the
body, such as the palm of the hands and extremities of
the fingers, regular series. These bodies are known as
the papilla of the skin, and the dermis of the skin of
certain animals, when prepared by tanning, constitutes
leather.

The rete mucosum is a plexus of vessels, soft m „e„ e s t L.
in consistence, covering the dermis, and filled with a
pulpy granulated material, to which the skin owes its
color, and the tint of which, of course, varies in the dif-
ferent races, and even in different individuals. In ne-
groes this coloring matter is black ; in Europeans, it is
white. When the rete mucosum forming it has been
destroyed, it is not reproduced, and for this reason the
cicatrices in the skin are white, even in negroes.

Finally, the epidermis is a kind of semi-trans- Epidermis.
parent varnish, covering the surface of the skin, to which
it is moulded ; it is not a sensible part, nor even living,
but a matter secreted by the skin, and only takes a cer-
tain degree of solidity when dry. Thus, in those parts
of the body, which are withdrawn from the action of the
air, it is soft and indistinct ; and in animals living in the
water it is not solidified, except when converted into
stony matter, as in lobsters and most Crustacea.

^76 ANATOMY AND PHYSIOLOGY.

pores. Upon the surface of the epidermis may be found
a multitude of little openings, called pores of the skin.
They correspond to the summit of the papillae already
Perspimtion. mentioned, and open a passage to the perspiration,
which is an acid liquid formed by secretion, and not to
be confounded with the moisture continually exhaled
upon the surface of the skin, and which constitutes in-
sensible transpiration. These pores are extremely small,
and do not traverse the dermis, and must be considered
as the secretory ducts of the organs secreting the sweat. 1
Hair. We also find upon the surface other and larger
openings, some of which give passage to the hairs, the
mode of the formation of which we shall hereafter inves-
tigate ; and from others, there distils a fatty matter se-
creted by follicles lodged in the thickness of this mem-
Nans, brane ; lastly, at some points of the surface of the
body, we find issuing from the substance of the skin
horny plates called nails, in nature similar to the hairs.

S s e e a nsa°tion he The sense of touch resides in the dermis, and
seems to belong especially to the papillae covering its
surface. All parts of the skin are not equally sensible,
which depends not merely upon the number of nerves
distributed to them, but also upon the thickness of the
epidermis covering them.

The principal use, then, of the epidermis is to oppose
the evaporation of the liquids contained in the body, and
to protect the skin, properly so called, from the immedi-
ate contact of foreign bodies, so as to moderate the im-

1 The perspiration is an acid liquid, as the urine and the gastric juice.
To be convinced of it apply upon the skin, moistened by this secretion, a
piece of paper colored blue by toumesol ; its color will be changed to red,
as always results from the action of an acid.

FUNCTIONS OF RELATION. J 77

pressions produced by this contact. We have already
seen, that this solid covering is insensible, and as it is
always interposed between the dermis and external ob-
jects, by contact with which upon this membrane sensa-
tion is caused, it will be easy to understand, that the
thicker the epidermic layer, the more is the dermis with-
drawn from the action of foreign bodies, and the more
obtuse the impressions it must receive. Now, in some
parts of the body, the heel for example, the epidermis is
very thick ; while in others, the extremity of the fingers,
the lips, &c, it is extremely thin. Wherever too the
skin is exposed to friction, its epidermis is thickened.
Every one knows that the layer formed in the hands of
blacksmiths and similar workmen becomes thick, hard,
and wrinkled. Lastly, in some animals the epidermis is
encrusted with calcareous matter, and becomes entirely
inflexible ; in this case, the surface of the body is ren-
dered completely insensible.

The sense of tact, as it exists in all parts of T ?* c ™ d
the surface of our bodies, is sufficient to make us ac-
quainted with the consistence, temperature and some
other properties of the bodies in contact with it. This
sense is then only exercised passively, and may therefore
be designated as tact ; but at other times the part pos-
sessed of this sensibility is actively impressed ; muscular
contractions directed by the will multiply and vary the
points of contact with an external object, and then we
give to this sense the name of touch.

Touch is then only tact perfected and made active ;
but it can be exercised only by organs arranged so as to
be moulded in some sort upon the objects to be handled.

In man, the hand is the special organ of touch, „ f p ^,

ratua
touch.

23

]78 ANATOMY AND PHYSIOLOGY.

and its structure is very favorable to the exercise of this
sense. Its epidermis is thin, smooth, and verv supple,
its chorion is abundantly supplied with papillae and nerves,
and reposes upon a thick layer of very elastic fatty cellu-
lar tissue. Finally, the mobility and flexibility of the
fingers are extreme, and the length of these organs is con-
siderable ; now these circumstances are the more advan-
tageous, in that they tend to increase the sensibility of
the part, and permit it to be applied to all bodies, what-
ever be the irregularity of their figure. But another or-
ganic disposition, which no less contributes to the per-
fection of our touch, is the power possessed by man of
opposing the thumb to the other fingers, so as to be
able to enclose small objects between the parts of the
hand, which are precisely those in which the sensation is
the most exquisite.

In most animals the organs of touch are arranged in a
manner much less favorable. In the mammifera?, for ex-
ample, this sense becomes obtuse as the fingers become
inflexible, and are enveloped in nails, by which they are
armed. Sometimes, however, the place of the hands is
supplied by other organs of no less perfect structure, as
the trunk of the elephant ; and finally, some animals
employ the tongue as an instrument of touch, while others
are provided with particular appendages, answering the
same purposes, and which are called tentacular, palpse, &c.
th^sense. Touch enables us to appreciate more or less ex-
actly most of the physical properties of the bodies, on
which it is exercised ; their dimensions, form, tempera-
ture, consistence, polish, weight, movements, &c. This
sense is so perfect, that several philosophers of antiquity,
as well as of modern times, have considered it as more

FUNCTIONS OF RELATION. J79

useful than sight or hearing, and as being even the source
of our intelligence. These opinions are evidently ex-
aggerated, for the touch has really no prerogative over the
other senses ; and in some monkeys, whose intelligence
is incomparably less developed than that of man, the or-
gans of touch are as perfect as in the human body.

SENSE OF TASTE.

The sense of taste, like that of touch, is excited by
the contact of external objects upon certain surfaces of
our body ; but it acquaints us with properties, which
escape the touch, to wit, the tastes of bodies.

All substances do not act upon the organ of T b a df eg of
taste. Some are very sapid, others but slightly so, and
many are completely insipid. The cause of this difference
is unknown, but it is found, that generally those bodies
which cannot be dissolved in water, have no taste, while
most of the soluble are more or less sapid. Their solu-
tion appears even to be a necessary condition of their
action upon the organ of taste ; for when this organ is
completely dry, the sensation of taste is no longer impart-
ed ; and there are substances, which, being insoluble in
water, are insipid in their ordinary state, but which acquire
a strong taste when dissolved in some other liquid, such
as spirits of wine.

The knowledge of the taste of bodies serves Se t a a S "l the
principally to direct animals in the choice of their food :
and therefore the organ of taste is placed always at the
entrance of the digestive tube. The tongue is the prin-
cipal seat of it, but the other parts of the mouth may also
experience the sensation of certain tastes.

The mucous membrane covering the tongue fh t o u t C o t n g r ue? f

j§q ANATOMY AND PHYSIOLOGY.

is abundantly supplied with blood vessels, and presents
on its superior surface many eminences of various forms,
which render it rough. These eminences, or papillae, are
of various kinds ; some lenticular, and few in number,
consist of a collection of mucous follicles ; others, fungi-
form or conical and very numerous, are vascular or ner-
vous ; the last cover the terminations of the lingual nerve,
and appear principally to serve for the sense of taste.

Ne t r onlu°e f . the Trie tongue, the substance of which is formed
by many muscles interlaced, receives the branches of sev-
eral nerves ; some serving to excite motion, others to con-
duct to the brain the sensation of the tastes. The trifacial
nerve or the nerve of the fifth pair, which springs from
the superior extremity of the spinal marrow, and separates
from the encephalon near the anterior border of the annu-
lar protuberance, (see fig. 29) supplies these latter func-
tions. It issues from the cranium behind the orbit, and
divides into three principal branches, to wit ; the opthal-
mic nerve supplying the apparatus of vision, etc., the
superior maxillary nerve, which is distributed to the
upper jaw and cheek, and the inferior maxillary nerve,
one of the principal branches of which bears the name of
the lingual nerve, and terminates in the mucous mem-
brane of the tongue.

If the lingual nerve be divided in a living animal, the
motions of the tongue are not paralyzed, but the organ is
rendered insensible to tastes ; and if the trunk of the trifa-
cial nerve be divided in the interior of the cranium the
sense of taste is destroyed, not merely in the tongue, but
in all the other parts of the mouth.

The section of the nerves of the ninth and eleventh
pair, which also go to the tongue, does not deprive the

FUNCTIONS OF RELATION. ]g|

animal of the faculty of perceiving tastes, but occasions
the loss of motion in the tongue and the other parts, to
which these nerves are distributed.

It follows then that the lingual branch of the fifth pair
is the special nerve of taste.

SKNSE OF SMELL.

Certain bodies possess the peculiarity of exciting in us
sensations of a particular nature, which cannot be per-
ceived by the aid of the sense of touch or taste, and
which depend upon the odor they exhale.

Odors are produced by particles of an extreme odors.
tenuity, which escape from odoriferous bodies, and are
diffused in the atmosphere, as vapors. All volatile or
gaseous bodies are not odoriferous ; but, in general, those
which may be easily transformed into vapor, diffuse little
or no odor, and in most cases we find, that odoriferous
substances become more so when the circumstances in
which they are placed favor volatilization. But yet the
quantity of matter thus diffused in the air, to produce
even the strongest odors, is extremely small. A particle
of musk, for example, may perfume the air of an apart-
ment for a long time, without any sensible change of
weight. A multitude of bodies, such as water, clothing,
etc., may imbibe these vapors, and in their turn become
odoriferous ; but other substances, such as glass, com-
pletely oppose their passage. We may perceive the odor
of bodies at a great distance from us ; but to arouse our
olfactory sense, odoriferous particles, emanating from
these bodies, must arrive in contact with the oman des-
tined to receive them. And in this the mechanism of

182 ANATOMY AND PHYSIOLOGY.

smell is analogous to the taste and touch, while with
sight and hearing, as we shall soon see, it is quite other-
wise.

aSiScs. The air is called the vehicle of odors; by this
fluid they are transported to a distance, so as to reach us.
It is then plain, that the organ destined to perceive them
must always be placed so as to receive their contact, and
experience teaches us, that to have this organ discharge
its functions, the membrane touched by the odors must
be continually moistened and covered by a liquid proper
to absorb the odoriferous particles, and to fix them for -a
certain time upon its olfactory surface. If this surface
were exterior, the former of these conditions would be
fulfilled, but not the latter; the odors would strike it, but
it would soon dry up, and become insensible to their con-
tact. Smell must consequently reside in the walls of a
cavity within the body, communicating freely externally ;
and the more rapidly and regularly the air, conveying to
us the odors, is renewed, the more favorable are the con-
ditions to the exercise of this sense.

This actually takes place, not merely in man, but also
in all the other mammiferse ; in birds and reptiles also
the sense of smell has its seat in the nasal fossae, and
these cavities are constantly traversed by the air, going
to the lungs to supply the requisitions of the respiration.
They communicate outwardly by the nostrils, and open
posteriorly into the pharynx, at a short distance from the
glottis. (See fig. 23.) Thus whenever the mouth is
shut, the air must pass through them to reach the latter
opening, and they may be considered as the anterior
portion of the aerial tube.

d -

FUNCTIONS OF RELATION. 133

The nasal fossae are sepa- pia-. 31.'

rated from each other* by a m k I e i

vertical partition, directed
from before backward, and
occupying the median line
of the face ; their walls are
formed by various bones of n
the face, and by the carti-
lages of the nose, and their
extent is very considerable. Upon the external surface
may be remarked three projecting plates curved upon
themselves, and called the ossa turbinata (g, i, k,). They
increase the surface of this wall, and are separated from
one another by a longitudinal furrow, called a meatus
(f, A,). Lastly, these fossae communicate with sinuses
hollowed out in the os frontis, 2 ossa maxillaria superiora,
etc. The mucous membrane, lining the nasal fossae, is
called the pituitary membrane ; it is thick, and prolonged
beyond the borders of the ossa turbinata, so that the air
can traverse the olfactory cavities only by narrow and
long routes, and the least swelling of this membrane
renders the passage of this fluid difficult, or even impos-
sible. The surface of the pituitary membrane presents
many little projections, which give it a velvety aspect ;

1 This vertical section of the nasal fossfe represents the exterior wall of
one of these cavities; — a, mouth, — i, nostril, — c, posterior opening of
the nasal fossae, — d, portion of the base of the cranium, — e, forehead, —
/, inferior meatus, — g, inferior turbinated bone, — h, median meatus, — i,
median turbinated bone, — k, superior turbinated, — I, frontal sinus, — m,
spheroidal sinus, — n, outlet of the eustachian tube.

2 The frontal sinuses do not exist in infancy, but are developed by age
and acquire very considerable dimension; these cavities cause the projec-
tion of the inferior part of the forehead above the root of the nose.

}84 ANATOMY AND PHYSIOLOGY.

lastly it is continually lubricated by a liquid more or less
viscous, called the nasal mucus', which appears to be
formed in a great measure in the sinuses already men-
tioned, and it receives a very great number of nervous
filaments, some from the fifth pair, and others from the
olfactory or first pair.

rf 1 ft?£3E The mechanism of smell is very simple ; it is
only necessary, that the nasal mucus should imbibe the
odoriferous particles, diffused in the air traversing the
nasal fossae, and that these particles should be thus ar-
rested upon that part of the pituitary membrane which
receives the filaments of the olfactory nerve. From this
it can easily be conceived, how important is the nasal
mucus to the sense of smell, and how the changes in the
nature of this liquid, which take place during coryza or
cold in the head, may cause, for a time, the loss of this
sense.

In the superior part of the nasal fossae the branches of
the olfactory nerve are most numerous, the nasal mucus
most abundant, and the routes followed by the air most
contracted. In this part, therefore, are the odors most
easily and vividly perceived. It would even appear, that
the principal use of the nose is to direct the inspired air
to the vault of the nasal fossee ; persons losing this organ
at the same time lose the sense of smell, and cases have
occurred, where it was sufficient, to adjust an artificial
nose upon the face of the patient, in order to restore this
sense.

N wneii. of The olfactory nerve has generally been consid-
ered as the nerve destined to convey to the brain the im-
pressions produced by odors ; but the nerve from the fifth
pair appears to be of important service in the discharge

FUNCTIONS OF RELATION. J 35

of this function, for M. Magendie has proved that its
section rendered the pituitary membrane insensible to the
strongest odors.

With regard to the uses of the sinuses which ^nSJ/ -
communicate with the nasal fossae by narrow openings,
and which are lined by a thin membrane, nothing positive
is known. It has been remarked, however, that animals,
in whom these cavities are more vast, are also those in
whom the sense of smell is the most delicate.

SENSE OF HEARING.

Hearing is the function which makes us acquainted
with the sounds produced by vibrating bodies.

The apparatus of hearing is very complicated ; a ppaS.
the different parts of which it is composed are for the
most part extremely small ; thus it occupies but a very
small space, and is almost entirely contained in the inte-
rior of a bony prominence, which from either side of the
head, advances into the interior of the cranium, and con-
stitutes that part of the temporal bone called, from its
hardness, the petrous portion. (Fig. 32, e.)

It may be divided into three portions, namely, the ex-
ternal, middle, and internal ear.

The external ear is composed of the pavilion External ear.
of the ear, and auditory canal.

The pavilion of the ear (a) is a fibro-cartila- P tf£i of
ginous plate, supple and elastic, which is perfectly free
in the greater part of its extent, and which adheres to
the edge of the auditory canal. The skin covering it is
thin, dry, and very tense ; its surface turns in several
ways, and presents various eminences and depressions,
the most considerable of which is the concha (d). It

24

186

ANATOMY AND PHYSIOLOGY

Fig. 32. l

h g e n e m f

A duct°. ry forms a sort of tunnel very open, and continuous
with the auditory duct, which is buried in the temporal

1 This figure represents a vertical section of the auditory apparatus with
the interior parts slightly magnified, that they may be better seen, a, Pa-
vilion of the ear, — b, lobule of the pavilion, — c, small eminence called the
antilragus, — d, concha, the bottom of which is continuous with the audi-
tory duct, — e, e, portion of the temporal bone, called the petrous, in which
is lodged the auditory apparatus, — c', mastoid portion of the tempo-
ral bone, — e", portion of the glenroid fossa in which the lower jaw is
articulated, — e'", styloid process of the temporal serving for the insertion
of the muscles and ligaments of the os hyoides, — c"", extremity of the
canal traversed by the internal carotid artery before entering the cavity of
the cranium, — /, auditory duct, — g, tympanu n, — h, cavity from which
has been taken the chain of bones, — i, openit gs from the cavity of the
tympanum into the cells (j) of the petrous portion, — on the internal wall
of the cavity we find two openings, fenestra ovalis, and rotunda, — A-, the
eustachian tube conducting from the cavity to the summit of the pharynx,
— /, vestibule, — m, semicircular canals, — v, cochlea, — o, acoustic nerve.

FUNCTIONS OF RELATION.

187

bone, and curves upward and forward. The skin lining
this duct terminates abruptly at its internal extremity,
and beneath it, we find many small sebaceous follicles,
which furnish the yellow and bitter matter known as the
cerumen.

The middle ear is composed of the cavity of Middle ear.
the tympanum and the parts dependent upon it.

Fig. 33. ' The cavity (fig. 32, cavity.

h), is of an irregular form,
hollowed in the petrous sub-
stance of the temporal bone,
e and making part of the audi-
tory duct, from which it is
separated by a membranous
f partition, very tense and elas-
tic, called the tympanum (b).
Opposite the opening, in
which the tympanum is, as it were, set, (that is, upon the
internal portion of the cavity), may be found two other
holes, which are covered in the same manner by a tense
membrane ; they are called from their form, the oval and
the round fenestra. Upon the posterior wall of the cavity

a

1 This figure represents the external wall of the cavity, the tympanum,
the bones of the ear, and their muscles, all enlarged, a, a, Frame of the
tympanum, — b, tympanum, — c, handle of the mallet, its end resting upon
the middle of the tympanum, — d, head of the mallet articulating with the
anvil, — e, process, which springs from below the neck of the mallet, and
buries itself in the glenoidal fissure of the temporal bone; its extremity
gives attachment to the anterior muscle of the mallet, — /, internal muscle
of the mallet, — g, anvil, a vertical branch of which rests upon the walls
of the cavity, and a vertical branch articulates with the os orbiculare (h), —
i, stirrup, the summit of which articulates with the os orbiculare, and the
base of which rests upon the membrane of the fenestra ovalis; — k, muscle
of the stirrup.

]gg ANATOMY AND PHYSIOLOGY.

is a hole conducting to the cells of the mastoid portion
of the temporal bone, and on its inferior wall may be seen
the opening of the eustachian tube, a long and narrow
duct, with an outlet to the posterior part of the nasal
fossae, and which thus establishes a communication be-
tween the cavity of the tympanum and the external air.
Finally, this cavity is traversed by a chain of little bones,
which extends from the tympanum to the membrane of
the fenestra ovalis, and which leans, by means of a branch
directed to the side, upon the posterior wall of the cavity.
(Fig. 33.)

Fis: 3V These bones are four in number, and

a b are called the mallet, or malleus (fig.

34, a), the anvil, or incus (6), os lenti-

HD £jv culare (c), and stirrup, or stapes (7/).

/ yf A small stalk, which may be compared

c to the handle, and which belongs to the
malleus, rests against the tympanum, and
I the base of the stapes thus reposes upon

d the membrane of the fenestra ovalis.

Finally little muscles fixed to these bones, impress upon
them movements, by means of which they press more or
less strongly upon these membranes, and consequently
augment or diminish their degree of tension.

internal ear. The internal ear, as well as the middle, is en-
tirely contained within the petrous portion. It is com-
posed of several cavities, which communicate together,
and which are called the vestibule, semicircular canals,
and the cochlea. The vestibule occupies the middle

1 Bones of the ear separated, — a, malleus or mallet, — b, incus or anvil,
— c, os orbiculare, — d, stapes or stirrup.

FUNCTIONS OF RELATION. Jgg

part, and communicates with the cavity by the fenestra
ovalis. The semicircular canals project upon the supe-
rior and posterior part of the vestibule; they are three
in number, and have the form of rounded canals swelled
at one extremity, like a flask. Lastly, the cochlea is a
very singular organ, spirally twisted like the shell of the
animal whence it takes its name. Its cavity is divided
into two parts by a longitudinal partition, semi-osseous,
semi-membranous ; it communicates with the interior of
the vestibule, and is separated from the cavity only by the
membrane of the fenestra rotunda. This latter cavity is
filled with air; the internal ear, on the contrary, is filled
with an aqueous liquid, and the membrane lining the ves-
tibule, as well as the semicircular canals, is not applied
to the bony walls of the cavity, but is in a manner sus-
pended in their interior.

The nerve of the eighth pair, which arises A ^i c
from the medulla oblongata near the restiform body, and
which departs from the encephalon between the pedun-
cle of the cerebellum and the annular protuberance, enters
the petrous portion through a bony passage called the in-
ternal auditory canal, and terminates in the interior of
the membranous sacs of the vestibule, and semicircular
canals, and also in the cochlea. Upon it depends the
sensibility of the organ of hearing, and therefore it is
called the acoustic nerve.

Such are the principal parts of the auditory JftSj
apparatus. Let us now see the part taken by each in the
exercise of the sense of hearing.

Hearing, we have said, is to make us acquainted with
sounds.

Sound results from a very rapid vibratory mo- ^3.°'

190 ANATOMY AND PHYSIOLOGY.

tion of the particles of sonorous bodies. To be assured
of this, it will suffice, merely to sprinkle some fine sand
upon a plate of glass, or the table of a violin, and to pro-
duce on this plate or instrument any sound whatever.
The grains of sand are at once agitated, and thrown into
the air with a force proportioned to the intensity of the
sound. The undulations experienced by the sonorous
body are communicated to the air in contact with its sur-
face, as they were communicated to the grains of sand in
the preceding experiment ; and thus from step to step
are sounds propagated to a distance. To perceive these
sounds, the vibrations now spoken of, must reach the
internal ear, and by their influence the liquid, which im-
mediately bathes the acoustic nerve, will itself be thrown
into undulation. To point out the rationale of the mecha-
nism of hearing, we must then follow the course of these
undulatory motions through the various parts of the audi-
tory apparatus, interposed between the external air and
the acoustic nerve,
use of the The sonorous vibrations of the air first strike

pavilion of

the ear. ^ e p av jij on f the ear. In animals, where this
part has the form of a horn, it serves to reflect the vibra-
tions, and to augment the intensity of the sounds at its
contracted extremity, as experiment easily proves. Every
body knows that persons a little deaf hear with much
more facility when they use a similar horn, and if a thin
membrane be stretched over the open summit of a paper
cone, and its surface be sprinkled with fine sand, the
movements of the sand will be found much more intense,
when the sound arrives at the membrane by the broad
outlet of the tunnel, than when coming from the opposite
side.

FUNCTIONS OF RELATION. J9|

In man, the concha and the auditory duct discharge
the same functions ; but the other parts of the pavilion
are not so arranged as to reflect sounds to the tympanum,
and they also appear to have other uses. When sonorous
vibrations fall perpendicularly upon an elastic surface, the
undulatory motions, excited in the latter, are much more
intense than when the sound arrives obliquely; and it may
be concluded, that the varied directions of the surface of the
pavilion of the ear, are destined to present to the sonorous
waves, whatever be the direction in which they strike us,
a plane thus arranged, and, consequently, they serve to
augment the vibratory action of this elastic appendage.
The pavilion of the ear is not, however, of very great
utility, and the loss of it does not much affect the hear-
ing.

The vibrations, thus excited in the pavilion of a ^- t l r y { dua.
the ear, are communicated to the walls of the auditory
duct, and thence to the deeper seated parts of the appa-
ratus of hearing; but these movements can only be very
weak, and principally by the intervention of the air con-
tained in this duct the sounds penetrate into the interior
of the ear. Thus, if the tube be plugged with cotton or
any other soft body, which opposes their passage, the
perception of them is rendered indistinct.

The tympanum serves principally to facilitate VympaLm?
the transmission of sonorous vibrations from the external
air to the acoustic nerve. The experiments of one of
our most skilful physicians, M. Savart, prove that sounds,
by striking upon a thin and moderately tense membrane,
excite in it, very easily, vibrations. If a leaf of paper
be stretched upon a frame, and its surface powdered with
sand, the latter is readily agitated, and collected so as to

J92 ANATOMY AND PHYSIOLOGY.

form varied lines, as soon as a sonorous body in vibration
is brought near. If the same experiment be made with
a plane of wood, or a leaf of paper, no such movement
will result, unless the sound employed be extremely
intense. But if to these latter bodies there be adapted
a membranous disc, similar to the tympanum, they will
readily vibrate under the influence of sounds, "which be-
fore would have produced no appreciable efTect.

It is plain, then, that the tympanum must readily vi-
brate, when sounds strike upon it, and that its presence
must augment the facility with which the other parts of
the auditory apparatus experience similar motions.
sionlf^mds The vibrations are transmitted from the mem-
vity!' 8 brane of the tympanum to the bones of the ear,

to the walls of the cavity, and especially to the air, with
which this cavity is filled : they thus arrive at the poste-
rior wall of the cavity, where there are membranes
stretched upon openings conducting to the internal ear,
nearly as the tympanum is stretched between the audi-
tory duct and the cavity. These membranes must act in
the same manner as the latter, that is, easily be made to
vibrate, and transmit these motions to the neighboring
parts.

internal ear. The posterior face of these membranous discs
is in contact with the aqueous liquid, which fills the in-
ternal car, and in this liquid are suspended the membra-
nous sacs, 1 which, in their turn, are distended by another
liquid, into which are plunged the terminal iilaments of

1 They are called the memhrane of the vestibule, and the tubes of the
semicircular canals, according as they occupy the vestibule or the semicir-
cular canals; in the cochlea there is nothing similar, and the liquid by which
it is filled, is the same which bathes the membrane of the vestibule.

FUNCTIONS OF RELATION. 193

the acoustic nerve. The vibrations executed by these
membranes must then be transmitted to this liquid, after-
wards be communicated to the membranous sac of the
vestibule, and finally arrive at the nerve, upon which their
action produces the sensation of sound.

From the preceding observations, it will be .uses of the

i o ' air contained

seen, that the air contained in the cavity plays in the cavity *
a very important part in the mechanism of hearing ; now,
if this cavity did not communicate externally, this air
would soon be absorbed and disappear, and the vibrations
of the tympanum could be transmitted to the internal
ear, only by the osseous walls of the cavity, and then
with difficulty. This accounts for the use of the eusta-
chian tube, and explains to us in what way the obstruc-
tion of this duct may become a cause of deafness.

The tympanum is not indispensable to hearing, t he tiIl cavity.
for when this membrane is torn, the vibrations of the air
contained in the auditory duct are communicated without
interruption to the air of the cavity, and thus arrive at
the membranes of the fenestra ovalis and rotunda. It
might then be asked, what is the use of this, and what
disadvantage could arise, if, the cavity not existing, the
membranes of the fenestra ovalis and rotunda were placed
externally ? To reply to this question it must be borne
in mind that the manner in which the membranes vibrate
under the influence of the same sound, varies with their
degree of dryness or humidity, their temperature, etc.
Now it is probable, that two sounds make upon us the
same impression whenever they cause the liquid, in
which the acoustic nerve terminates, to vibrate in the
same manner ; and, consequently, in order that the same
sound may always act upon us in an identical manner,

25

J 94 ANATOMY AND PHYSIOLOGY.

the membranes, which communicate directly their vibra-
tions to this liquid, must constantly be at the same tem-
perature, and the same degree of dryness ; and this is
precisely the case with the membranes of the fenestra?
of the internal ear. The air of the cavity being renewed
but very gradually is always completely charged with
moisture, and at the same temperature, while if the cavity
did not exist, or had free external communication, the
condition of these membranes would be changed at every
instant, according as they were exposed to the action of
air, hot or cold, dry or moist.

^tSff™ This also explains to us, why the eustachian
duct is long and narrow in all warm-blooded animals,
while in the cold-blooded, such as the lizards, it is short
and very large. In the former, the air must have time to
ascend to the temperature of the body before penetrating
the cavity, while in the latter this temperature being the
same with the atmosphere, the speedy renewal of the air
contained in the cavity has no bad results.

use 9 of the We learn, therefore, that the chain of bones

bones of the

ear " traversing the cavity, and which rests upon the

tympanum and the membrane of the fenestra ovalis, may
execute certain movements, by means of which the pres-
sure it exercises upon these membranes may be increased
or diminished. The utility of this arrangement is easily
understood ; if sand be sprinkled upon a membrane made
tense by a frame, and a sonorous body in vibration be
approximated to it, it will be found, that without in the
least changing the intensity of the sound, the violence
with which the sand is thrown into the air will be increased
or diminished, as the tension of the membrane is increased
or diminished. In the former case, it will execute under

FUNCTIONS OF RELATION. 195

the influence of a sound of the same intensity vibratory
movements much more extensive, than when the tension
is increased. From this we may infer, that the pressure
more or less strong of the malleus upon the tympanum,
and of the stapes upon the membrane of the fenestra
ovalis, will prevent these membranes from vibrating too
strongly under the influence of very intense sounds, with-
out depriving them of the faculty of vibrating, when a
feeble sound strikes them. The pressure exercised upon
the membrane of the fenestra ovalis is thus communicated
to the membrane of the fenestra rotunda, by the inter-
vention of the liquid with which the internal ear is filled ;
and the result is, that the bones of the organ of hearing,
by leaning upon the two membranes to which they are
fixed, prevent the sonorous vibrations arriving at the
acoustic nerve, from being so intense as to injure this
delicate organ.

The loss of the malleus, incus, or os orbiculare dimin-
ishes the hearing, but does not destroy it ; that of the
stapes is, on the contrary, followed by deafness, for this
bone, adhering to the membrane of the' fenestra ovalis, by
its fall tears the partition, and thus, the liquid contained
in the vestibulum being lost, the acoustic nerve can no
longer discharge its functions.

We see then, that all the parts composing the vbm^a
external and middle ear serve to perfect the apparalus -
hearing, without, however, being absolutely necessary to
the exercise of this sense. Thus they gradually disap-
pear, as we depart from man, and study the structure of
the ear in animals gradually descending in the scale of
beings. In birds there is no pavilion of the ear ; in rep-
tiles the external auditory duct is also wanting, the tym-

]9(j W ATOMY AND PHYSIOLOGY.

panum becomes external and the structure of the cavity
is simplified ; finally, in most fishes there is neither
concha, external, nor middle ear.

In animals placed yet lower in the series of beings, it
is the same with the cochlea, and the semicircular canals,
parts, the uses of which are not well known; 1 but the
membranous vestibule is an organ never wanting; wher-
ever there exists an auditory apparatus, there is always
found a small membranous sac filled with liquid, in which
the acoustic nerve terminates, and this vestibule is always
an instrument indispensable to the exercise of the sense
of hearing.

SIGHT.

Sight is that faculty, which makes us sensible of the
action of light, and which acquaints us through this
agent, with the form of bodies, their color, size and
position.

Ap v"?on S ° f The apparatus Fig. 3.5. 2

charged with this function ch s' s a- b

is composed of the nerve of
the second pair, of the eye, r
and the several parts destin-
ed for the protection or mo- %
tion of this organ.

g*£ The globe of the eye, l
with which we shall first be s 1 r u pc b

occupied, is a hollow sphere, a little swollen in front, and

1 From the experiments of M. Floureus it would appear, that the destruc-
tion of the semicircular canals does not destroy hearing, but renders it con-
fused and painful.

' Interior of the eye, — c, transparent cornea, — s, sclerotica, — .<', portion
of the sclerotica, turned outward to display the membranes situated beneath,

FUNCTIONS OF RELATION. 197

filled with humors more or less fluid. Its exterior en-
velope is composed of two very distinct parts, one white,
opaque, and fibrous, called the sclerotica (s) ; the other
transparent and similar to a plate of horn, therefore called
the cornea (c). The latter occupies the front of the eye,
and is, as it were, set in a circular opening of the sclero-
tica. Its external surface is more rounded than that of
the latter membrane, and it resembles a watch-glass ap-
plied upon a sphere, and projecting beyond its surface.

At a short distance behind the cornea, in the w s .
interior of the eye, is a membranous partition (■«'), which
is stretched transversely, and fixed to the anterior border
of the sclerotica, quite around the cornea. This kind of
diaphragm, which varies in color with the individual, is
called the iris, and presents in its middle a circular open-
ing named the pupil (p). Muscular fibres may be de-
tected in the tissue of this organ, directed like rays from
the edge of the pupil towards the circumference of the
iris, and other fibres of the same nature, which are circu-
lar and surround this opening like a ring. When the
former contract, the pupil dilates, by the action of the
latter, it is contracted.

The space comprised between the cornea and SSS.
the iris constitutes the anterior chamber of the eye (ca).
By the opening of the pupil it communicates with the
posterior chamber, a cavity situated behind the iris, and
which is filled, as well as the former chamber, by the

— ch, choroid, — r, retina, — n, optic nerve, ca, anterior chamber of the eye
placed between the cornea and iris, and filled with the aqueous humor, —
i, iris, — p, pupil, — cr, crystalline lens placed behind the pupil, — pc, ciliary
processes, — v, vitreous humor, — b,b, portion of the conjunctiva which,
after having covered the anterior part of the eye, is detached from it to line
the eyelids.

]98 ANATOMY AND PHYSIOLOGY.

aqueous humor, a perfectly transparent liquid composed
of water, holding in solution a little albumen and a small
quantity of salts, such as are met with in all the secre-
tions of the animal economy. This humor is supposed
to be formed by a membrane behind the iris, which pre-
processL. sents a great number of radiated folds, called cil-
iary processes (pc).

crystalline. Almost directly behind the pupil is a transpa-
rent lens, called the crystalline (cr). It is lodged in a
diaphanous membranous sac (the capsule of the crystal-
line lens), and appears to be the product of a secretion
from it ; for when taken from the eye of the living ani-
mal without destroying its capsule, a new lens is found
to take the place of the old. It is also remarked, that
this body is composed of a great number of concentric
layers, constantly increasing in hardness from the circum-
ference to the centre, which agrees with our remarks
upon the mode of its formation. Its posterior face is
also much more convex than its anterior.

V humor. s Behind the crystalline lens we find a large ge-
latinous diaphanous mass, resembling the white of an egg,
and enveloped in a membrane of extreme tenuity, a great
number of lammelke from which extend inward, so as to
form partitions or cells. This membrane is called the
hyaloid, and the humor found in it the vitreous humor (y).

Retina. Every where, except in front, where are the
crystalline lens and the iris, the vitreous humor is sur-
rounded by a soft white membrane called the retina (r),
which is only separated from the sclerotica by another

choroid, membrane, equally thin, which is called the choroid
(ch). The latter is principally formed by a net-work of
blood vessels, and is stained with a black matter, which

FUNCTIONS OF RELATIOTST. J 99

gives to the bottom of the eye that deep color, which is
seen through the pupil, and which is wanting in those
persons and animals called albinos.

The globe of the eye receives several nerves, optic nerve.
The most remarkable for its size and functions is the op-
tic nerve (n), which traverses the posterior part of the
sclerotica, and is continuous with the retina, which ap-
pears in fact but an expansion of it. The other nerves
of the globe of the eye are extremely small, and ™™l
are called the ciliary nerves : they spring from a small
ganglion, formed by the union of some branches of the
nerves of the third and fifth pairs (see fig. 29), and are
distributed to the iris and the proximate parts of the in-
terior of the globe of the eye.

By the intervention of light, we have said, ^y'lsfow™ of
bodies placed around us act upon our sight. Those which
emit light, the sun and bodies in ignition, for example,
are visible of themselves ; but others become so, only
when the light striking upon them is reflected in such a
way as to meet our eyes.

This agent moves with an extreme rapidity ; it can
act upon our senses only to the extent it strikes upon the
retina, situated at the bottom of the eye. Opaque bodies
reflect or absorb it, but transparent bodies, such as the
atmosphere and water, afford it a free passage.

The first condition, then, for the exercise of vision is
the absence of every opaque body between external ob-
jects and the bottom of the eye. Therefore the cornea,
which covers the anterior part of this organ, like a watch
glass, is completely transparent, and the light, which
traverses it, and passes through the opening of the pupil,
readily arrives at the retina ; for it only encounters on

200 ANATOMY AND PHYSIOLOGY.

the way the crystalline lens, which is diaphanous, and
the humors, which are equally so.

But in some diseases it is quite different, and this loss
of transparency always causes blindness. In the affec-
tion known as the cataract, for instance, the crystalline
lens becomes opaque, and thus opposes the passage of
light : and when white spots or pellicles are formed upon
the cornea, this membrane becomes a kind of screen,
which prevents the luminous rays from penetrating to the
eye, and thus entirely destroys vision.

The diaphanous parts of the globe of the eye do not
serve to give passage to the light merely. Their princi-
pal use is to change the direction of the rays which enter
this organ, so as to collect them upon some point of the
retina. The interior of the eye resembles exactly the
optical instrument known as the camera obscura, and the
image of the objects seen by us is painted upon the re-
tina, as upon the curtain placed behind the latter. To
understand this phenomenon, it is necessary to examine
the course of luminous rays through transparent bodies
in general, and to apply the knowledge thus acquired, to
the study of the mechanism of vision.

Light ordinarily advances in a straight line, and the
different rays, which start from any one point, are dis-
persed according to the direction in which they travel,
and the distance of the space traversed. When these
rays fall perpendicularly upon the surface of a transpa-
rent body, they traverse it without any change in direc-
tion ; but if they strike it obliquely, there is always more
or less deviation from their primitive course. If the body,
into which they penetrate, be more dense than that from
which they issue, if they pass from air into water or

FUNCTIONS OF RELATION. 201

glass, for example, they then form an elbow and approach
the perpendicular at the point of immersion. If, on the
contrary, they pass from a dense to a rare medium, they
depart from this perpendicular, and these deviations are
greater in proportion to the obliquity, with which the ray
strikes the surface of the transparent body.

This phenomenon, which is known as the refraction of
light, is easily understood. It is owing to this change in
the direction of the luminous rays, in their passage from
water into air, that a straight stick, plunged half its
length into the former liquid, always appears as if bent
at the point of immersion ; and Fig. 36.'

if a piece of money (a) be placed

at the bottom of an empty vase, / /° ^

and the edge of the latter be / Xv^

raised just high enough to pre- ^ //;'.

vent the eye of the observer from jj§j^jj *
perceiving this object, to render ^ff 1 ^
it visible, it will be sufficient, to fill the vase with water.
For the ray of light coming from the money, instead of
always advancing in a straight line, will be refracted in
its passage from the water into air, and will depart from
the perpendicular ; and by this change in direction, the
rays, which before passed above the eye of the observer,
will strike upon it.

1 From the position of the eye it is evident that if the light travelled in
a straight line, the observer could perceive the piece of money (a) only so
long as the ray a, c, reached his eye ; but the walls of the base being opaque
this ray and all others situated below the line a, b, and a, c, are intercepted.
Now when the vase is filled with water the rays are refracted in passing
from this liquid into the air, and consequently, one of the rays which before
passed above the eye, the ray a, d, for example, will be deviated so as to
reach the observer.

26

202

ANATOMY AND PHYSIOLOGY.

Fi<f. 37.

The luminous rajs, we have observed, approach the
perpendicular at the point of contact, whenever they pen-
etrate obliquely a body denser than that from which they
issue. Therefore, the form of bodies exerts a great in-
fluence upon the course of the light traversing them ;
and as their surface is convex or concave, these rays will
be collected or dispersed.

Some examples will render this proposition easy to be
understood. Let us suppose three diverging rays to set
out from the point a, traverse the air, and fall upon a lens
with a convex surface, represented by the line b. The

ray a c, will strike
perpendicularly up-
on this surface, and
consequently will
/ traverse the lens
without experienc-
ing any deviation ;
but the ray a d, fall-
s' ing obliquely upon
h & this surface, will be

refracted, and approach the perpendicular drawn to the
point of immersion ; now this perpendicular will take the
direction of the dotted line e, by approximation to which,
the luminous ray, instead of following its course towards
the point d, will follow the line /. The same will be
the case with the ray a g, which in continuing its course
will approach the perpendicular A, and be directed towards
the point /, instead of continuing in a straight line towards
the point g. The other rays, which strike upon the lens,
will be refracted in an analogous manner, and, conse-
quently, in the place of being dispersed, they will be

FUNCTIONS OF RELATION.

203

ft

collected and may even unite in one point, which may be
called the focus of the lens.

If the surface of the crystal, in place of being convex,
is concave, the luminous rays will not approach the
axis of the bundle, p- oo

as in the preced- j e

ing case, but, on ^^^

the contrary, will ^-~-~~~-^\^~~~'

greatly diverge. n ~—-~ ' ~~~ ' i

The ray a d, for ~~~ -~-____^ J

example, must y ^xr^-

approach the per-
pendicular at the
point of contact, which will have the direction of the
dotted line e, and by this deviation the ray will take the
direction of the line f.

The refraction of the luminous rays, in thus traversing
convex or concave lenses, is greater in proportion to the
curvature of the surface of these bodies, and the mere
inspection of the figures we have made use of will be
sufficient to make us comprehend it must be so. For the
greater the curvature of the surface upon which the di-
verging rays strike, the more will the perpendiculars, at
the point of immersion, depart from these same rays.

Physics also teach us that transparent bodies refract
the light more powerfully in proportion to their density,
(that is to say when under the same volume they have a
more considerable weight), and when formed of more
combustible materials.

The light which strikes a transparent body does not
entirely traverse it ; a considerable portion is reflected,
and owing to this property, bodies answer more or Jess
perfectly the purpose of mirrors.

2Q4 ANATOMY AND PHYSIOLOGY.

Course of the
lislit in the eve.

From what precedes, we see that when a col-
lection of luminous rays falls upon the cornea, one part
must he reflected while the other traverses it. It is the
light thus reflected, which gives to the eyes their bril-
liancy, and which causes our own image in the eyes of
others. The rays, which penetrate into this transparent
plate, pass into a body much denser than the air ; they
are, consequently, refracted and approximated to the per-
pendicular or axis of the collection, the more forcibly in
proportion to the convexity of the cornea ; for the greater
the projection of this membrane, the more acute will be
the angle formed by the diverging rays striking upon its
surface.

aqueous hunwr! If> an:er having traversed the cornea, the lu-
minous rays entered the air, they would be refracted to
the same degree as upon their entrance into this mem-
brane, but in a contrary direction ; they would conse-
quently retake their primitive direction. But the aque-
ous humor which fills the anterior chamber of the eye,
possesses a refracting power much greater than the air,
so that on entering it the rays are less dispersed, than
they were approximated by their passage through the
cornea ; the action of these parts therefore renders them
less divergent than before their entry into the eye, and
causes a more considerable quantity of light to pass into
the opening of the pupil.

Us pV,',ii lhc A great part of the light, which arrives at the
bottom of the anterior chamber of the eye, meets the iris
and is absorbed or reflected outwardly by it : that only,
which falls upon the pupil, penetrates to the bottom of
the eye, and the quantity is in proportion to the size of
the opening. Thus when but a small quantity of light

FUNCTIONS OF RELATION. 205

reaches the eye, the pupil is dilated, while it contracts
under the influence of a brilliant light ; the iris, as we
see, regulates the quantity of light reaching the retina.

The rays of light having traversed the pupil, SgSwftS!
fall upon the crystalline lens, which is diaphanous, and
which changes anew their direction, causing them all to
converge to one point, called the focus, where they unite.
Now this focus is precisely upon the surface of the retina,
and it is thus that the luminous rays, sent to the eye
from different points of a body placed at a distance, are
collected upon this nervous membrane so as to paint upon
it, in miniature, the object from which they emanate.

It is easy to be convinced by experiment that „. Formation

J i of images upon

images are thus formed in the bottom of the the retina "
eye. Take the eye of a hare or pigeon, the sclerotica
of which is nearly transparent, or better yet, the eye of
an albino, and place in front of the cornea a very brilliant
object, a lighted candle, for example, and the image of
the latter will be seen depicted upon the retina.

These images are al- Fig- 39-

ways formed upside down, &.
and the cause of this phe-
nomenon is easily shown.
When we consider the course the luminous rays, origi-
nating from the two extremities (a, c,) of an object, must
take to reach the retina, it will be seen they must cross
before reaching it, and that consequently the ray coming
from the superior extremity (a), of an object will be at
the lower part of the space occupied upon the retina by
the entire collection of rays forming the image (6), while
that coming from the inferior extremity of the object (c)
will occupy the top of the same space (d). The same

206 ANATOMY AND PHYSIOLOGY.

will take place with all the other rays, and therefore the
object will appear reversed at the bottom of the eve.

U ctoroM. ,ie 1^ ie bl ac k matter, which is situated behind
the retina, and which lines the whole bottom of the eye
as well as the posterior face of the iris, serves to absorb
the light immediately after it has traversed the retina.
If this light were reflected in other points of the mem-
brane, it would considerably trouble the sight, and pre-
vent the clear formation of images on the bottom of the
eye. Thus in albinos, whether man or animal, where
this pigment is wanting, vision is extremely imperfect ;
during the day they can scarcely see at all.

Per theeye. of The globe of the eye serves to conduct the
light and to concentrate it upon the retina. It discharges
the office of a kind of spectacle-glass, but it is an optical
instrument far more perfect than any of those ever yet
constructed by scientific men : for at the same time that
it is perfectly achromatic and presents no aberration of
sphericity, its capacity may vary considerably.

Achromatism. By achromatism is meant the property of turn-
ing light from its course without developing any color,
and, consequently, the achromatic lenses are those which
form in their foci colorless images, or possessing only the
colors of the object represented. The white light results
from the union of the seven colored rays of the solar
spectrum, and these different rays are not equally refran-
gible. Wherefore, when light is passed through a re-
fracting body, it is more or less completely decomposed,
and the objects whence it proceeds, appear to have the
color of the solar spectrum. Achromatic telescopes are
obtained by combining several glasses, some of which
correct the dispersal of the light produced by the others,

FUNCTIONS OF RELATION. 207

so as to unite in one locus all the rays. It is probable
the achromatism of the eye depends upon a similar ar-
rangement, but physicians have not yet agreed upon the
explanation of this phenomenon ; some think it depends
upon the different humors of the eye, others attribute it
to the difference of density in the different layers of the
crystalline lens.

The aberration of sphericity consists in the A ^ e h r eric°ty. of
union of rays which fall upon different parts of a lens,
into foci sensibly different, whence results a want of
clearness in the images. When the lenses are very con-
vex, the rays which pass near the edges do not unite in
the same focus with those which traverse the central
part of the instrument, and to obtain clear images, the
passage of the former must be intercepted by placing in
front of the lens a separating medium pierced by a hole.
Now, the images formed behind the crystalline lens of
the eye are never diffused, and this want of aberration of
sphericity has been attributed to the iris, which answers
the purpose of the divisions in the interior of telescopes.
Every one knows that objects may be seen with the
same clearness when placed a few inches from the eye,
as when at a considerable distance from this organ. In
our optical instruments, on the contrary, the image
formed in the focus of a lens advances or recedes, ac-
cording to the distance of the object. It has, therefore,
been supposed that to give to our sight such varying
capacity, the crystalline lens must approach or recede
from the retina as necessity required, or else the globe of
the eye must change its form. But direct observation
does not confirm these hypotheses, and this peculiarity
has never found a satisfactory explanation.

208 ANATOMY AND PHYSIOLOGY.

However, the eye does not always possess in the same
degree this precious faculty ; some can see distinctly
only at the distance of some feet; nearer all images are
confused. With others, on the contrary, the sight be-
comes clear only when the objects are brought within a
few inches of the eye, and every thing beyond seems
enveloped in a cloud.

Presbytia. The former of these infirmities, known as
presbytia, depends upon a want of convergence in the
collections of rays traversing the humors of the eye.
The rays which arrive at this organ from a very distant
object, diverge very little and may be collected at one
point of the retina, although the refracting power of the
eye be small ; but those which come from a near object
diverge greatly, and the refracting power of the eye is
too weak to collect them upon a determinate point of
the retina. Those thus afflicted have usually a con-
tracted pupil, as if they were continually making an effort
to prevent any other rays from entering the eye than
those falling upon the centre of the crystalline lens, and
which do not require great deviation from their course to
be collected together behind it upon a fixed point of the
retina. This want of refracting power in the eye ap-
pears, in general, to belong to a flattening of the cornea
or crystalline lens, which circumstance must tend to
produce presbytia, and which may be found in nearly all
old men.

Myopia. Myopia is the result of a contrary effect. The
rays which traverse the eye are then so forcibly deviated
from their course, that in place of diverging they even
converge before reaching the retina. This imperfection
of the visual organ depends, in general, upon too great a
convexity of the cornea or crystalline lens.

FUNCTIONS OF RELATION. 20'J

It is remarked that short-sighted persons become less
so by age, which happens in consequence of a diminution
in-the secretion of the humors of the eye always occur-
ring in old age, which, by rendering the cornea less con-
vex, renders the sight longer; in most cases, it causes
presbytia, but here it only serves to correct the errors of
the eye and to give to the sight its usual character.
Therefore the vision of short-sighted persons is improved
by age, while in others it is usually weakened ; but as
this diminution in the abundance of the humors of the
eye always continues, there is a moment when the eye of
the short-sighted individual becomes also too much dimin-
ished in the power of refraction, and his sight, conse-
quently too long.

To correct these natural faults of the eye, recourse
must be had to means, the efficacy of which confirms the
explanation just given of the cause, whether of myopia
or presbytia. Glasses are therefore placed before the
eyes with surfaces so directed as to augment or diminish
the divergence of the rays traversing them. Short-sighted
persons make use of concave glasses, which give diverg-
ence to the rays of light, and the far-sighted employ con-
vex, which, on the contrary, collect the rays diverging
from the axis of the bundle.

The contact of light with the retina, we have u Tethm. the
said, causes vision, and when this membrane is paralyzed
(a condition which constitutes the disease known as gutta
serena), this sense is completely destroyed. But the
sensibility of the retina is entirely limited, and can only
be excited by this subtile agent. This nervous mem-
brane enjoys little or no sensibility to the touch, and it

27

210 ANATOMY AND PHYSIOLOGY.

may be touched, pinched, or even torn upon the living
animal without the slightest manifestation of pain.

However, this peculiar sensibility of the retina has its
limits : too feeble a light does not act upon it, and too
strong a light injures it and renders it incapable of action.
But, in this respect, the influence of habit is extreme ;
when a person has remained sometime in obscurity, a
light, although very feeble, dazzles the eyes, and renders,
for some instants, the retina incapable of discharging
'its functions, while those accustomed to the light of day
experience the same effects only when looking upon the
most brilliant objects, in seeking, for example, to take the
sun's altitude.

When w r e look for a long time upon the same object
without a change of position, the point of the retina re-
ceiving the image is soon fatigued, and this fatigue, car-
ried beyond a certain limit, deprives for some time, the
part, experiencing it, of its usual sensibility. Thus, if we
look for some time at a white spot on a black ground, and
then change our sight to a white ground, we think we see
a black spot, because the point of the retina already fa-
tigued by the white light has become insensible to it. 1

The fatigue experienced by the retina in the exercise
of its functions depends in part upon the efforts made to
fix the attention upon the object placed before the eyes.
If we endeavor to examine attentively bodies in a feeble
light, we soon experience a painful sensation in the orbit,
and also in the head.

1 The black color depends upon the absence of light, and the bodies which
afford it to us are those which absorb all the light falling upon them ; we
perceive them only because they are surrounded by bodies which reflect
them.

FUNCTIONS OF RELATION.

211

All points of the retina are adapted to receive the im-
pression of light ; but the central part of this membrane
enjoys a more exquisite sensibility than the rest, and it is
only when the images of external objects are formed upon
this part, that we see them distinctly. Thus, when look-
ing at any object, we take care to direct toward it the
axis of our eyes.

We might attain the same end by means of the various
movements of which the head is susceptible ; but, in or
der to render these changes in the direction of the eyes
more easy, nature has provided these organs with muscles
destined especially for their motion.

These muscles are fixed to the sclerotica by 'SKjJ?
their anterior extremity, and inserted by their opposite
behind the globe of the eye
(to the bottom of the orbit),
and, since this organ reposes
upon fatty cellular tissue, with-
out intimately adhering to it,
each of these muscles by
contracting, turns the eye to 5','.'-<x\ ^jj
its own side.

d

Fig

in number : four of them
called recti muscles, inserted

1 Vertical section of the orbit to show the position of the eye and its
muscles. — a, Cornea, — b, sclerotica, — c, optic nerve, the opposite ex-
tremity of which enters the globe of the eye, — d, rectus inferior muscle of
the eye, — e, rectus superior muscle, — /, portion of the rectus externus
muscle of the eye; at the bottom of the orbit we see the other extremity
of this muscle, of which the entire middle part has been removed to dis-
play the optic nerve situated behind it ; — g, extremity of the small oblique
muscle, — h, large oblique, the tendon of which passes into a small pulley
before it is fixed to the sclerotica, — ?', elevator muscle of the superior eye*
lid, — /«•, lachrymal gland.

212 ANATOMY AND PHYSIOLOGY.

in the four opposite points of the circumference of the
sclerotica and proceed directly backward, so that they can
direct the eye upwards, downwards, to the right or left,
depending upon the muscles called into action. Lastly,
two of these muscles which are called the oblique muscles,
(//, g,) are so arranged as to cause this organ to execute
movements of rotation, which direct the pupil downwards
and inwards, or upwards and outwards.
neSSTa? theeye. The nerves, which give motion to these mus-
cles, belong exclusively to the apparatus of vision. They
are furnished by the third, fourth and sixth pairs. (Fig.
29). The recti muscles are entirely under the direction
of the will ; the oblique often act independently of it,
and from their contraction arises the rolling up of the eyes
in syncope.

The optic nerve, which, by its expansion on the bot-
tom of the eye, forms the retina, transmits to the brain
the impressions produced upon this membrane by the
contact of light : its section therefore produces total blind-
ness.

In order that the retina may discharge its functions re-
quires not merely the consent of the optic, but also of the
nerves of the fifth pair, which we have already seen exer-
cises the greatest influence upon taste and smell. If the
section of this nerve be made between the brain and the
point of origin of the branches to the eye, vision is de-
stroyed. The animal appears to distinguish light from
darkness, but is really blind ; and singular though it be, at
the end of some time the cornea becomes opaque, ulce-
rates, the eye is emptied and atrophied.

JnmlK The hemispheres of the brain appear to be the
seat of the perception of these sensations, as of all others ;

FUNCTIONS OF RELATION. 213

for when they are destroyed the animal becomes at once
blind. But there are other parts of the encephalon which
also exercise great influence upon this sense ; these are
the optic lobes, or tubercula quadrigemina (fig. 29, g,).
When destroyed in a bird (where these parts are much
developed), blindness will also ensue ; and it is worthy of
observation that animals in whom the retina is most de-
veloped and the optic nerves the largest, are also those in
which these lobes acquire the most volume and have the
most complicated structure. These organs may even be
considered as depending upon the optic nerve, and as
beins; the uniting; bonds of these nerves to the cerebral
hemispheres.

But the most striking result of our experiments upon
the encephalon is to find, that the destruction of the
cerebral hemisphere or optic lobe of one side does not
occasion the loss of sight of the same side : the eye of
the opposite side becomes blind, and anatomy explains
this fact ; for the optic nerves soon after their separation
from the brain, unite and interlace so that the one fur-
nished by the right lobe goes to the left eye, and vice
versa.

We judge of the form of bodies by that of the F J-" cl ^
image they produce upon our retina; therefore, when,
from any cause, the form of the luminous pencil of rays
sent by them to this membrane, is changed before reach-
ing the eye, we fall into great errors in our judgment.
The experiment already cited of a stick half plunged
into water and then appearing bent, although actually
straight, is an optical illusion of this kind.

We judge of the position of surrounding ob- P 3j2jJ*
jects by the direction of the luminous rays they send to

214 ANATOMY AND PHYSIOLOGY.

us, and we always see them in the extension of the
straight line followed by these rays at the moment they
penetrate the eye. For this reason, when the pencil of
rays sent by one of these objects upon a polished surface
(a mirror, for example,) is reflected by the latter so as to
make a greater or less angle and arrive at the eye, we
see the object as if it were placed behind the mirror, in
the prolongation of the straight line pursued by the ray
meeting the eye from this instrument. Judgment may
rectify the consequences we draw from this sensation ;
but it always exists.

This accounts for our using but one eye when we wish
to be certain that bodies are in an exact line with each
other. When this condition is actually fulfilled, and one
of our eyes placed upon the prolongation of the line
occupied by these objects, the luminous ray which is
directed from the more distant body towards our eye
cannot arrive to it, being intercepted by the intervening
body, and so of the rest, consequently the nearest body
conceals from us entirely or in part all the others ; when
if regarded by both eyes, the same thing happens only
when the objects are so far distant from us that the rays
sent to our eyes are almost parallel, or when the inter-
vening object is very large in comparison with the more
distant or very near to it, and even then the coincidence
is much less plain than if the observer uses but one of
his eyes.

™b™ct s e . of To estimate the distance, which separates us
from objects, the simultaneous action of the two eyes is,
on the contrary, of great assistance : the following experi-
ment will convince us of the fact. Suspend a ring by
a thread, and try to introduce a pointed instrument fixed

FUNCTIONS OF RELATION. 215

to the end of a long stick ; by making use of both eyes
you will easily succeed at every trial ; but if one eye be
closed you will find the greatest difficulty in threading
the ring : the instrument will go beyond or stop short,
and only by chance or after repeated trials will you suc-
ceed in introducing it into the ring.

Thus when an individual has lost one eye he generally
remains some time unable to judge correctly of the dis-
tance of bodies situated near him, and this privation ren-
ders the appreciation always much more difficult.

But the utility of the two eyes in this case is easily
explained upon physical laws. When an object is only
a short distance from us, it is requisite, in order that its
image may fall upon the same point of the retina of the
two eyes, that the axis of these organs should converge
toward the point looked at, and this inclination, of which
we are conscious, is great according to the proximity of
the object. But when objects are so far distant that in
beholding them the optic axes of the two eyes become
sensibly parallel, we have no longer a sure rule to deter-
mine their distance, and we can only form our judgment
from data more or less deceptive, such as the degree of
light, the clearness with which we distinguish the minu-
tiae, the size of the object itself, our previous acquaint-
ance with it, etc. When we can compare this distant
object with those intervening, this appreciation becomes
much more certain ; every one knows how difficult it is
to judge of the distance of a light seen in the middle of
the night, when the obscurity prevents surrounding ob-
jects from being seen.

The concurrence of the two eyes is moreover essential
in that it makes objects appear plainer. If we regard a

216 ANATOMY AND PHYSIOLOGY.

strip of white paper with one eye, and place before the
other an obstacle which will conceal half the object, the
portion seen by both eyes, at the same time, will appear
much more brilliant than when seen by one alone.

size of objects. The manner in which we judge of the size
of bodies depends much more upon intelligence and cus-
tom, than upon the action even of the apparatus of vision.
Our first guide is really the size of the image formed at
the bottom of the eye ; but as the distance between us
and an object increases, this image diminishes, so that to
judge of the dimensions of the former, the distance at
which we suppose it must always be considered. When,
therefore, the distance is not exactly appreciated, it is
difficult to judge of the size of a body seen for the first
time. A mountain, which we see afar off for the first
time, appears to us, in general, much smaller than it
really is, because we imagine it near us, when it actually
is at a considerable distance.

M obje n cts of The estimation of the motion of bodies is
sometimes made from the change of direction of the light
which arrives at the eye, whence results the displacement
of the image upon the retina, sometimes from the varia-
tion in size of this same image. In order to follow the
motion of a body its displacement must not be too rapid,
for then we do not perceive it unless it project a very
great quantity of light, and, in this case, the same effect
is produced upon our eyes as if it instantaneously occu-
pied the whole length of the line traversed. On the con-
trary, we generally recognise with great difficulty, and
sometimes we even cannot recognise the motion of bodies
the image of which is very slowly displaced, either from
the actual slowness of their motion, as in the hand of a
watch, or from their great distance, as in the stars.

FUNCTIONS OF RELATION. 217

From the remarks made with regard to the Education of

the sense of

manner in which we judge of the distance and S1{!ht
size of bodies, it is easy to see that the sense of vision
has need of a kind of education, and that under some
circumstances it will always lead us into error.

It is by making use of these errors, known in physics
and physiology by the name of optical illusions, as well
as of the laws of the animal economy on which they de-
pend, that the arts are able to produce them at will, to
make plane surfaces appear round and prominent, and to
make near objects more or less distant.

That sight may give us the valuable information it is
susceptible of communicating, this sense must undergo
long exercise and a thorough education. The new-born
infant distinguishes only the light from the darkness ; and
although its eye already presents all the physical qualities
necessary to vision, 1 it does not begin to see till after some
weeks of existence. At first its eyes are only directed to
the most brilliant objects, such as the sun, etc., without
distinction. The first things which attract it are those of
a red color ; it soon, however, begins to distinguish the
other brilliant colors, but has, as yet, no idea of distance
or size, and it will extend its hand to seize upon remote
objects, without the least regard to their dimensions. By
degrees vision is perfected, and it is principally in correct-
ing, by the aid of the other senses, the errors to which
the former is exposed that the infant acquires the faculty
of judging rightly of what he sees around him.

1 In the fcetus prior to the seventh month, it is otherwise; the iris has
not yet been perforated ; but at this period the pupillary membrane, which
occupies the place of the pupil, breaks and is absorbed so as to give access
to the light.

28

21 g ANATOMY AND PHYSIOLOGY.

To give some idea of the kind of education necessary
to vision, it will be sufficient to read the curious history
of a man blind from his birth, to whom Cheselden, a
celebrated English surgeon, restored sight at a sufficiently
mature age to enable the young man to analyze all his
sensations, and give an account of them.

" When he first saw, he was so far from making any
judgment about distances, that he thought all objects
whatever touched his eyes (as he expressed it) as what
he felt did his skin, and thought no object so agreeable
as those which were smooth and regular, though he could
form no judgment of their shape or guess what it was in
any object that was pleasing to him. He had during his
blindness such feeble ideas of colors as he could distin-
guish by a strong light, but they did not leave sufficient
traces to be recognised ; when he did see them he said
the colors he perceived were not the same he formerly
saw. He knew not the shape of any thing, nor any one
thing from another, however different in shape or magni-
tude : but upon being told what things were, whose form
he before knew from feeling, he would carefully observe,
that he might know them again ; but having too many
objects to learn at once, he forgot many of them ; and
(as he said) at first he learned to know and again forgot
a thousand things in a day. More than two months
elapsed after the operation, before he could be made to
comprehend that pictures represented solid bodies, when
to that time he considered them only as party-colored
planes, or surfaces diversified with a variety of paint ;
but even then he was no less surprised, expecting the
pictures would feel like the things they represented, and
was amazed when he found those parts, which by their

FUNCTIONS OF RELATION. 219

light and shadow seemed round and uneven, felt only flat
like the rest, and asked which was the lying sense, feel-
ing, or seeing ?

" Being shown his father's picture in a locket at his
mother's watch, and told what it was, he acknowledged
a likeness, but was vastly surprised ; asking how it could
be, that a large face could be expressed in so little room ;
saying, it should have seemed as impossible to him, as to
put a bushel of any thing into a pint.

" At first, he could bear but very little light, and the
things he saw he thought extremely large ; but upon
seeing things larger, those first seen he conceived less,
never being able to imagine any lines beyond the bounds
he saw. And now being lately couched of his other eye,
(more than a year after the first operation), he says, that
objects at first appeared large to this eye, but not so large
as they did at first to the other ; and looking upon the
same object with both eyes, he thought it looked about
twice as large as with the first couched eye only, but not
double, that we can any ways discover."

When we began the study of vision it was EjawS^"
with the remark, that the apparatus charged with the ex-
ercise of this sense was composed of an essential part,
the globe of the eye and optic nerve, and of various
accessory parts destined to move or to protect the former.
Enough has been said upon the structure and functions
of the eye itself, and also of the muscles which are fixed
to it : to close the history of this function, we have only
to describe the protecting parts of this organ.

The first objects of interest are the bony cavi- orbit.
ties, which lodge the eyes and are called the orbits.
These are deep holes hollowed in the face and bounded

220

ANATOMY AND PHYSIOLOGY.

V

by the several bones of the
head. They are very large
and have nearly the form
of a cone, with the base di-
rected outwards, and apex
towards the brain, which is
pierced by a hole for the
passage of the optic nerve.
In man and monkeys the or-
bits are directed forward,
and their external wall separates them completely from
the temporal fossa? ; but if we examine animals gradually
differing in an increased ratio from these, the orbits will
be found to become more and more lateral, and to be
more intimately confounded with the above mentioned
fossa?.

But the globe of the eye is separated from the bony
walls of the orbit by its muscles, and by a great quantity
of fatty cellular tissue which surrounds it, as an elastic
couch.

In front, the eye is protected by the eyebrows, eyelids,
and by a peculiar liquid, the tears, with which its surface
is always bathed.

Eyebrows. The eyebrows are transverse eminences formed
by the skin, which in this point is supplied with hair and
provided with a special muscle of motion. They serve
to protect the eye against external violence, to prevent
the perspiration flowing from the forehead from irritating
the surface of this organ, lastly, to protect it from the im-
pression of too strong a light, especially when the latter
comes from an elevated place.
Eyelids. The eyelids in man, and all other mammiferae,

FUNCTIONS OF RELATION. 221

are two in number situated one above the other, and for
this reason divided into superior and inferior. They are
a kind of movable veil placed in front of the orbit and ac-
commodated in form to the globe of the eye, so that being
closed they completely cover the anterior face of this
organ. Exteriorly, they are formed by the skin which at
this place is very fine, semi-transparent, and sustained by
a fibro-cartilaginous plate (the tarsal cartilages). Their
internal face is lined by a mucous membrane, called the
conjunctiva, which is reflected upon the globe of the eye,
covers the whole anterior part of the sclerotica, and is
confounded with the transparent cornea. The free bor-
der of the eyelids is supplied by a range of hairs, having
behind them a series of holes which communicate with
the glands of Meibomius, follicles lodged within the tarsal
cartilages and secreting a peculiar humor, which, when
thickened and dried, as often happens in sleep, is known
as the wax. Finally, there are within the eyelids muscles
of motion ; one of them surrounds the opening like a ring,
and contracts them with more or less force (fig. 32, h) ;
the other extends from the superior eyelid to the bottom
of the orbit, and serves to raise this veil, (fig. 40, i).

The eyelids serve to prevent the access of light to the
eye during sleep. When awake, they approach or sepa-
rate so as to allow only the quantity of light necessary to
vision to pass, but not enough to injure the retina. They
also protect the eye from the contact of foreign bodies
which are in motion in the air, preserve it from shocks,
by their almost instantaneous occlusion, and oppose the
effects of the prolonged contact of the air by continual
motions, which return at nearly regular intervals.

One of the uses of the conjunctiva is to facilitate winking.

222 ANATOMY AND PHYSIOLOGY.

the operation of ivinking. This membrane, with an ex-
quisite degree of sensibility, secretes a humor which
increases the polish of its surface, and renders the con-
stant friction of the pallebral, upon the occular portion of
the conjunctiva, much more easy ; but this liquid is not
alone sufficient for this effect, and in order that the con-
junctiva may properly discharge all its functions, its sur-
face must be lubricated by the tears.

Tears. This humor, composed of water, holding in
solution some thousandths of animal matter, and of salts
met with in all the liquids of the animal economy, is
formed in a large gland, situated in the vault of the orbit,
behind the external part of the border of this cavity and
above the globe, (fig. 40, k).

appnrTu^ 1 This lachrymal gland sheds the tears upon the
surface of the conjunctiva by six or seven small canals,
which open upon this membrane, on the superior and ex-
ternal part of the upper lid. The tears afterward spread
over the whole surface of the conjunctiva, preventing its
desiccation and forming a uniform layer, which gives to
the eye its polish and brilliancy. They must also serve
to prevent the evaporation of the humors of the globe of
the eye, and that of the liquids moistening the cornea ;
and it is actually the case, that when after death tears
cease to be diffused upon the surface of the eye, the latter
soon becomes flaccid, and the cornea loses its transpa-
rency.

The tears, which do not evaporate or are not absorbed
by the conjunctiva, pass into the nasal fossrc by means of
canals, the openings of which may be seen in the free
border of either lid, near the internal angle of the eye, at
the point where these organs quit the globe of the eye to

FUNCTIONS OF RELATION. 223

pass to the caruncula lachrymalis, a projecting body of a
rose color, principally formed by a collection of small folli-
cles. These two openings, styled lachrymal points, are
extremely narrow and communicate with very fine canals,
which are lodged in the interior of the lids and directed
inward to empty into the nasal duct. This latter duct
extends from the internal angle of the eye to the inferior
meatus of the nasal fossae, and to reach it traverses a bony
canal hollowed between the orbit and the nose.

In the ordinary condition, the absorption of tears by the
lachrymal points takes place but very slowly ; but when
the latter become very abundant and roll in the eyes,
their passage into the nasal fossae becomes so rapid, that
the handkerchief is requisite at every instant. Sometimes,
in certain lively emotions of the mind, for example, the
secretion of tears becomes so very abundant that this
liquid runs over the eyelids and falls upon the cheeks.

Weeping may, also, depend upon another cause. Some-
times there occurs an obstruction of the nasal canal which
prevents the tears from reaching the nasal fossae ; this
liquid then flows upon the cheek and accumulates with
so much rapidity in the superior part of the obstructed
canal, that a considerable tumor may result, or even its
walls be ruptured and a fistula lachrymalis formed.

The structure of the apparatus of vision and Apparatus

11 of vision in

the mechanism of sight, are nearly the same in anima!s -
man and all the mammifera?, as in birds, reptiles and
fishes. The eye of some of the mollusca, such as the
poulpe 1 also resembles ours a little ; but in most animals

1 This term is applied to such of the mollusca, belonging to the class
cephalopoda, as inhabit chambered shells ; the Nautilus, some of the
polypi, etc., are examples.

224 ANATOMY AND PHYSIOLOGY.

of this class and in the arachnida, the Crustacea and
insects, these organs have scarcely any points of resem-
blance with the eyes of the superior animals.

OF THE INTELLECTUAL AND INSTINCTIVE

FACULTIES.

We have already seen how, in order that man may
have the knowledge of the impression produced by the
bodies acting upon his senses, it is not alone sufficient
that these parts be endowed with the faculty of feeling,
and that the sensations of which they are the seat be
conveyed to the brain by the intervention of the nerves :
but that, in order to have the impression thus received by
the brain become a sensation of which we are conscious,
this organ must not remain passive, but must perceive
and acquaint us with it. And in very many cases a mul-
titude of impressions are received by the brain without
any consciousness on our part. In sleep, for instance,
we are ignorant of noise at our ears, or odors acting upon
the organ of smell. When awake, custom also renders
us insensible to a great number of these impressions,
and when several strike us at the same time, we may
even, sometimes, by the mere effort of volition, abstract
ourselves from some of them, and only really perceive
those to which we wish to direct our attention.
Perception. This faculty of perception, which, when excited
and directed by the will, takes the name of attention, is
one of the attributes of the brain, and exists only when

INTELLECTUAL FACULTIES. 225

this organ is in activity. The experiments, in which the
two hemispheres of the brain have been removed in liv-
ing animals, have already demonstrated, that the loss of
these parts rendered these beings insensible to all im-
pressions received by the organs of the senses, and when
the brain is prevented from discharging its functions,
either by eompression or the administration of certain
poisons to the animal, as opium, the same effect is pro-
duced. Different diseases of the brain, also, render it
unsuited to perception, and when it has been for some
time in a state of continual activity, it presents the same
phenomena with all our other organs ; it becomes fa-
tigued and cannot continue to discharge its functions, till
it has remained, for a longer or shorter time, in repose.

The brain does not merely possess the faculty Memory.
of perceiving sensations and thus producing what are
called ideas, it is also capable of recalling ideas already
acquired. This new faculty bears the title of memory,
and it is independent of perception ; for, in certain cere-
bral affections, we find it completely lost without de-
priving the patient of the faculty of knowing what sur-
rounds him. It is remarked that the memory preserves
the clearest idea of the most lively impressions, and that
this faculty, extremely developed in the early period of
life, is weakened with the progress of age. In the aged,
memory is sometimes entirely lost, and in the adult it is
weaker than in the adolescent or child. Therefore, at a
tender age, such knowledge is acquired as does not de-
mand great reflection, such as the languages, history, the
descriptive sciences, etc., exercise tends also to render it
stronger.

But memory can hardly be considered a single faculty,

29

226 ANATOMY AND PHYSIOLOGY.

and a multitude of facts go to show that there are, so to
speak, as many distinct memories as there are orders of
different faculties of the mind. There is a memory of
words, of forms, of places, of music, etc., and it is very
rare that a man possesses them all in the same degree ;
in general one of these faculties predominates, and in cer-
tain cases of mental disease, one of them has been com-
pletely lost, while the other kinds of memory were not
sensibly weakened.

Reasoning, etc. Acquired ideas do not remain isolated in the
mind : we possess the power of comparing them, of
seizing upon their respective relations, of drawing from
them conclusions, and, in a word, of exercising our judg-
ment upon all we perceive. The faculty of forming a
succession of judgments which are chained to each other,
or of reasoning, is one of the most precious attributes of
man. But the peculiar characteristic of human intelli-
gence, and, that which permits him to acquire the prodi-
gious development manifested by him in civilized nations,
is the faculty of generalization, which consists in creating
signs to represent ideas, to think by means of these signs,
and to form abstract ideas.

instincts. Finally, it would appear that, upon the action
of the encephalon depend the inclinations or instincts,
which induce man and animals to execute certain deter-
minate actions, and to prefer certain sensations to those
of another order.

Relation be- it j s remarked that an orsran acts powerfully

twnni t lie di' <-> i J

J'hr'bni'i'l'i'SiiHi m proportion to its volume. It might then be
faculties. ' supposed, that there would be a certain relation
between the development of the encephalon and that of
the intellectual or instinctive faculties, which appear to

INTELLECTUAL FACULTIES. 227

have their seat in it ; and when man is compared with
other animals, his brain is generally found to be propor-
tionally more voluminous. It is, also, remarked, that an-
imals which display the most intelligence, monkeys for
instance, have this organ very large, while in the more
stupid, as fishes, it is always extremely small.

These facts have led to the inference that we Facial angle.
might judge of the degree of intelligence of animals, and
even of man himself, by the greater or less development
of their brain ; and to appreciate these differences, vari-
ous methods have been resorted to, the most celebrated
of which is the measure of the facial angle, proposed by
Camper, a skilful Dutch naturalist.

These measures serve to point Fig. 41.

out the relation existing between «
the volume of the cranium (which \ x^* ( ^\/
is filled bv the brain and cerebel- P ''g0T^X \^-
lum), and that of the face, and are ]
taken in the following manner. A c
horizontal line (c, d), is drawn on
a level with the auditory hole and
floor of the nasal fossae, so as to follow nearly the direc-
tion of the base of the cranium ; a second line is then
let fall upon this (a, b), which touches the most promi-
nent point of the forehead and the extremity of the upper
jaw. Now, it is evident that this latter will be inclined
upon the former, and will form with it an angle so much
the more acute, as the face is more developed and the
forehead retreating, and that, consequently, the measure
of the facial angle (for so the angle of which we have
just been speaking is called), may indicate with sufficient
accuracy the relation sought.

228

ANATOMY AND PHYSIOLOGY.

Fisr. 43.

Man is of all animals the one
with the facial angle most open, and
in this respect there exist great
differences among the different hu-
-d man races. European heads are
usually about 80° (fig. 41), and ne-
groes about 70° (fig. 42) ; in the
different monkey tribes it varies from 65° to 30°, and
becomes yet more acute as we depart from man and de-
scend in the series of mammifene ; in the horse, for ex-
ample, the forehead is so retreating that it becomes im-
possible to draw a straight line from the extremity of the
superior jaw to the cranium, on account of the projection
of the nose, as any one will soon be convinced by casting

his eyes upon the an-
nexed figure ; finally, in
birds, reptiles and fishes,
the facial angle, when it
can be measured, is more
acute than in the mam-
mifcrpc.

The greater or less coincidence which exists in gene-
ral between the inclination of the facial line and the ex-
tent of the intellectual faculties, does not appear to have
escaped the observation of the ancients ; not only have
they truly remarked that the open angle was a sign of a
more generous nature and one of the characteristics of
beauty, but in the figures of their heroes and gods, they
have advanced the facial line more than it is in man, and
in some statues (that of Jupiter Olympus, for example,)
they have inclined it a little forward. 1

1 It is possible, however, that this manner of representing the Divinity
arose from another cause, and was independent of any idea of a relation

INTELLECTUAL FACULTIES.

229

Most persons are accustomed to attribute stupidity to
men and animals with retreating foreheads, or projecting
snout ; and when by any circumstance the facial line is
raised, even without augmenting the capacity of the cra-
nium, we find, in animals which present this disposition,
a peculiar air of intelligence, and we are induced to at-
tribute to them qualities they do not actually possess.
The elephant and owl are examples, and this is caused
by the great extent of the frontal sinuses giving to their
forehead a considerable prominence. The owl, as every
one knows, was with the ancients an emblem of wisdom,
and the elephant bears in the Indies a name which sig-
nifies that he partakes of reason, and yet neither of these
animals is actually remarkable for the development of its
intellectual faculties.

However, we must beware of attaching too much im-
portance to these measures ; they can give at the most
but a proximate idea of the development of the brain,
and as yet there is no proof that the extent of the intel-
lectual faculties is proportional to this material develop-
ment of the encephalon.

We have already seen that the brain is the D s y c to e r m Gan.

between the development of intelligence and the opening of the facial angle-
All people attach ideas of beauty to the exaggeration of peculiarities of
structure characteristic of their race; negroes esteem the blackest skins
the handsomest; the inhabitants of Oceania, with remarkably flat noses,
think their beauty is increased by augmenting the width of this part; and
the Caraibs, with extremely retreating foreheads, compress the heads of
their children, to exaggerate yet more this characteristic disposition. Now
one of the peculiarities of the Cossack race, and more especially of the
Greek nation, is the slight inclination of the facial line, and consequently
from the tendency just observed the Greeks might naturally regard this
disposition as a condition of beauty, and think that to represent beings su-
perior to ourselves, it must be exaggerated.

230 ANATOMY AND PHYSIOLOGY.

seat of many very distinct functions, and when we ex-
amine the manner in which the intellectual faculties and
feelings are exercised in different men, we soon observe
that a more or less increased development of one is not
always accompanied by an equal development of the rest.
A man, who shall be remarkable for the instinctive love
to his offspring, may have but very feeble intellectual
faculties ; and another, endowed with a most happy dispo-
sition for the sciences of calculation, may yet lack com-
pletely imagination, or power of observation.

These considerations and many similar facts, have led
some philosophers to consider the brain as a single organ,
all parts of which concur in the same manner to the pro-
duction of the phenomena of instinct and intelligence,
but that nature has established in the functions of the
encephalon the same division of labor that we find in
the other apparatus of the animal economy, when the
faculties of the latter are perfected. They have regarded
the feelings as having their seat in a determinate part of
the brain, the intellectual faculties in another, and, in a
word, each kind of function executed by the brain as
the result of the action of an instrument or particular
organ, and that these special organs were different por-
tions of the nervous mass of the encephalon.

Upon this hypothesis of the localization of the various
functions of the encephalon is founded the phrenological
system of Dr. Gall.

He considers each of these functions to be the appen-
dage of a determinate part of the brain or cerebellum, and
that the greater or less activity of each of them depends
in a great measure upon the development of the part
which is their seat. Now in man and most of the supe-

INTELLECTUAL FACULTIES. 231

rior animals, the encephalon fills the whole cavity of the
cranium, and the walls of this osseous case are in some
sort moulded upon the nervous mass, so that one may
judge of the proportional size of the different parts of the
brain by the prominence of the corresponding parts of the
head. And admitting these suppositions to be correct,
we may consequently judge by mere inspection of the
cranium, of the inclinations and faculties of every indi-
vidual.

Phrenologists admit that the feelings which give to ani-
mals their inclinations or excite their desires are situated
in the posterior and inferior parts of the encephalon ; the
instinct of propagation resides therefore in the cerebellum ;
the love of offspring would depend upon that part of the
third cerebral lobe which is seen immediately above this
orsan : the instinct which renders animals more or less
social would result from the action of a neighboring part ;
courage would depend upon that part of the brain situated
above and behind the ear ; the love of destruction on that
directly above the ears ; finally, the inclination which in-
duces to the employment of stratagem and the desire of
acquisition would occupy neighboring parts. The feel-
ings on which depend the sentiments of self-love, of van-
ity, circumspection, benevolence, firmness, justice, etc.,
would have their seat in the superior and anterior parts of
the brain ; lastly, the different intellectual faculties have
been assigned to the parts corresponding to the forehead.

A great argument in favor of this hypothesis may be
drawn from the peculiarities to be observed in the config-
uration of the heads of men, remarkable for certain quali-
ties of mind, or the force of certain inclinations, and the
variations observed in the form of the cranium of animals

ANATOMY AND PHYSIOLOGY.

of the most opposite instincts. What has already been
said with regard to the facial line applies especially to the
more or less considerable development of the anterior
part of the brain, and the existence of a depressed and
retreating forehead will give the whole head an aspect of
stupidity. It is also remarked, that in carnivorous ani-
mals living by the chace and which display the most
courage and ferocity, the width of the cranium, at the
ears, is much greater than in the herbivorous, with mild
and timid manners. It must also be allowed that in almost
all animals the posterior part of the head, where phrenolo-
gists place the love of offspring, seems to be more devel-
oped in females than males, and we all know that the
tenderness of a mother for her young is a much stronger
passion, than in the father.

But if some of the suppositions which form the basis of
phrenology appear to be really quite plausible, others are
not founded upon any conviction and must even appear
absurd to all persons accustomed to analyze the phenom-
ena of intelligence. Thus some phrenologists admit a
particular faculty for the appreciation of weight, another
adapted to judge of length and so on.

But we repeat, no fact is yet known suitable to prove
that this division of labor really exists in the brain, and
some experiments of M. Flourens would even lead to the
idea that it does not.

MOTIONS.

The various modifications of the faculty of perception
which have been noticed in the preceding pages, render
man and animals capable of knowing surrounding objects ;
but their relations with the external world do not merely

motions. 233

consist in these phenomena, in some sort passive. These
beings may also act upon foreign bodies, make changes
in them, move, and often express in a manner, more or
less precise, their sentiments or ideas.

This new series of functions, with which we contractility.
are now to be occupied, depends essentially upon a prop-
erty not less general among animals than sensibility, to
wit, contractility.

This name is given to that faculty possessed by certain
parts of the animal economy, of alternate contraction and
extension.

In some animals of an extremely simple structure, Musdes.
such as the hydree, all parts of the body appear susceptible
of this contraction ; and however little we ascend in the
series of beings this faculty soon becomes the property of
particular organs, called muscles. These muscles, which
are the active instruments of all our motions, form the
greater part of the mass of the body and constitute what
is commonly called the meat, or flesh of animals. Their
color is generally whitish. In some animals they are, on
the contrary, of a more or less intense red ; this color does
not necessarily belong to them, but simply depends on
the blood they contain.

Each muscle is formed by the union of a certain num-
ber of muscular bundles, which are united by cellular tissue
and composed of smaller bundles. These in their turn
are formed of bundles less in volume, and, from division
to division, we finally arrive at fibres of an extreme tenuity,
which are straight, ranged parallel-wise, and which, seen
by a powerful microscope, appear to be formed each by a
series of small globules of about one three hundredth of a
millemetre in diameter. After death the muscular tissue is

3U

234 ANATOMY AND PHYSIOLOGY.

soft and easily torn, but during life it is very elastic and
resisting. Finally, it is essentially composed of a material
already met with in the blood and called by chemists
fibrine. We also find albumen, osmazome and some
salts.

comrac't'ons. Under the influence of certain exciting causes,
the muscular fibres are contracted, and at the same time
the bundles they form become larger and harder than in
the state of relaxation. Any one can observe this phe-
nomenon upon himself, if he executes any movement
and observes the changes which take place in the muscles
called into action in producing it. Let any one forcibly
bend the fore-arm upon the arm, for example, the muscles
of the anterior part of the arm will be found swollen and
hardened.

Fig. 44. 1 By t ne aid f the microscope we can

. a . : easily distinguish the manner in which

a4 this contraction is made. When the

B c muscular fibres are in a state of relaxa-

jl c tion, they are extended in a straight line

■ (fig. 44) ; but when they contract, they

a suddenly take a zigzag course and pre-

sent many angular and regularly opposite undulations
(fig. 45). By repeating this experiment we are soon able
to recognise that the flexions of each fibre take place in
certain determinate points, and never otherwise. When

1 Fig. 44. Portion of a muscle, in the state of repose, seen by the micro-
scope to demonstrate the disposition of the fasciculi of muscular fibres and
the mode of distribution of the nervous filaments, — a, nerve ; b b, fasciculi
of muscular fibres arranged parallel and in a straight line ; — c, nervous
filaments which separate from the nerve a, and traverse perpendicularly
the muscular fasciculi at equal distances.

MOTIONS. 235

the contraction is feeble, these flexions are slightly marked,
and in the stronger contractions they never advance be-
yond angles of 50°.

Thus by contraction the two extremities
of the fibre are approximated without in
any respect changing its total length. Now,
these extremities are fixed to the parts the
muscles are to move, and by the displace-
ment of the former, the latter are drawn
with them. b 'a

This insertion of the muscles into movable parts is not
made directly, but takes place by means of an interme-
diate substance of a fibrous texture, which penetrates
into the substance of these organs, so as to send a pro-
longation to each of the fibres composing them. Some-
times this fibrous tissue, which is white and pearly, takes
the form of a membrane and then it is called an aponeu-
rosis ; at other times it resembles a cord of varying
length and then constitutes what anatomists call tendons. 2

We said above that contractility appertained oJSSwif
exclusively to the muscular fibres : these are actually the
only parts of the animal economy which possess the faculty
of contraction ; but this property they owe to the ner-
vous system.

Each muscular bundle receives one or several nerves.
These nerves, which are surrounded by a sheath called
neurilemma, are composed of many longitudinal filaments
and these filaments are scattered throughout the whole

1 The same muscle at the moment of contraction ; the letters a, b, c, in-
dicate the same parts as in the preceding figure.

2 The tendons and ligaments are vulgarly called the nerves, although
they have nothing in common.

236 ANATOMY AND PHYSIOLOGY.

muscle, passing nearly parallel between and transversely
upon the muscular fibres, precisely in the points corres-
ponding to each of the angles, formed by the zig-zag
folds, upon which contraction depends. After having
thus continued their course during a certain time, these
nervous fibres are seen to curve, bend, and return to the
brain, so that they appear to form with this organ a con-
tinuous circle.

Now, if a nerve, which is thus distributed to the mus-
cles, be divided, and thus separated in a manner from the
central mass of the nervous system, its fibres are pre-
vented from contraction ; they are paralyzed. It is suf-
ficient, merely to compress the brain in a living animal,
to cause it to lose the faculty of executing motions.
expellments. Many researches have been made to ascertain
the nature of the influence exercised by the nervous sys-
tem upon the muscles, when it determines their contrac-
tion. The most celebrated are those of a physician of
Bologna, Galvani ; and at the same time that they have
thrown new light upon this delicate question, they have
conducted to one of the greatest discoveries of the past
century, that of galvanic electricity.

The labors of Galvani, A^olta, and of some other dis-
tinguished men, have demonstrated that when certain
bodies of different natures, copper and iron, for example,
touch, they develope electricity, and this electricity passes
with great rapidity through certain bodies, such as the
nerves and the metals, which for this reason are called
good conductors of electricity, while it is arrested by
others, such as glass and resin.

When a muscle is paralyzed by the section of the
nerve goin^ to it, we may, during some time, supply the

MOTIONS. 237

want of nervous action by electricity ; and by means of
this agent cause contractions similar to those which, under
ordinary circumstances, take place from the influence of
the will.

The most convenient manner of making these experi-
ments is to deprive a frog of its skin, and divide the ani-
mal on a level with the loins, then to seize the lumbar
nerves and envelop them in a small sheet of tin foil ;
then the abdominal members are to be placed upon a
plate of copper, and every time that the foil touches this
latter metal, the muscles are seen to contract, the legs
bend and are agitated, and this half of the frog seems to
be leaping, as when alive. These singular effects may be
produced sometime after the death of the animal, and
are also observed in man ; for by passing an electic cur-
rent through the bodies of some criminals, they were
thrown into violent convulsions.

An analogous phenomenon takes place, when upon di-
viding a nerve in a living animal, the portion adherent to
the muscles is pinched or burned, the latter immediately
contract, but yet this effect appears to depend upon the
same cause with the convulsions produced in the preceding
experiments, for it has been proved that in all these cases
there is a production of electricity.

From the preceding statements we learn that Tlie °ry of

1 o muscular con-

the electric currents act upon the muscles in the traction -
same manner as the nervous influence, and the knowl-
edge of this fact has led to a very plausible explanation
of muscular contraction.

Physics teach us that when an electric current traverses,
in a contrary direction, two parallel branches of a con-
ducting rod, an iron wire, for example, they will be found
to approach each other.

238 ANATOMY AND PHYSIOLOGY.

We have also seen that the nervous fibres in their dis-
tribution to the muscles, form elbows. It must then be
supposed that the electric fluid, which has traversed them
in all the preceding experiments, follows the course of
these curved fibres, and consequently descends by one
branch to ascend by the other parallel branch. If this be
so, these nervous fibres must be found in the same condi-
tion with the metallic conductor just mentioned ; they
must approximate, and by approximating, they must draw
with them and fold the muscular fibres they traverse.

Now, the same phenomena may be observed in the
muscular contractions produced by means of the nervous
influence, and in those caused by electricity ; it may
therefore be supposed that in the two cases, the cause
which produces them is, if not the same, at least very
analogous, and that in the normal state these contractions
depend upon the passage of a fluid having, in this respect,
the same properties with the electric fluid.

In this hypothesis, which is due to Messrs. Prevost
and Dumas, the muscular fibres would be mere passive
instruments in the phenomena of contraction, and these
nervous turns would be the true motor agents. A cir-
cumstance in support of this opinion, which has been
established by many delicate experiments, is the constant
relation already mentioned between the point in which
these nervous fibres traverse the muscular fibres, and
that in which the latter bend in contraction ; the nerves
are always found at the summit of the angles formed by
these folds, and this is really the place they should
occupy, if their approximation were the cause of these
curves.

However, we see that contraction can take place only

motions. 239

in the muscular tissue, and that the action of the nervous
system is its determining cause. Let us now inquire
what are the parts taken by the several portions of this
system, in the production of this important phenomenon.

The muscles present in themselves very great differ-
ences ; some contract only under the influence of voli-
tion, others are equally under the empire of this force,
but their contraction may also take place independently
of it ; finally, there are yet others on the motions of
which volition has no influence. The muscles of the
limbs, etc., belong to the former of these three classes,
those of the respiratory apparatus to the second, and the
heart, etc., to the third.

All those muscles whose motions can be Nerves of

voluntary

caused by volition receive nerves from the inotion -
cerebro-spinal system. But all the nerves of this sys-
tem do not discharge these functions ; some, as we have
already seen, belong exclusively to sensation. The cere-
bral nerves of the third, fourth, sixth, seventh, ninth, and
eleventh pairs, (fig. 29) appear, on the contrary, to be
exclusively assigned to motion ; finally, the cerebral
nerves of the fifth and tenth pairs, and all the nerves
which arise from the spinal marrow, discharge these
functions at the same time that they serve for sensation.
Their anterior root, as already seen, gives them the fac-
ulty of transmitting sensations to the brain ; and by their
posterior the nervous influence necessary for voluntary
motion is propagated from the brain to the muscles.

In fact, when the posterior roots of the spinal nerves
are divided in the living animal, the parts to which they
are distributed are deprived of the power of contraction,
exactly as if both roots had been divided.

240 ANATOMY AND PHYSIOLOGY.

Functions When the spinal marrow is divided, the move-

of the spinal * '

marrow, nieiits of all the parts whose nerves originate
below the section are suspended, while those whose
nerves are yet in communication with the brain, continue
Brain. to be moved. But if instead of thus experi-
menting upon the spinal marrow, we act upon the brain,
by removing or compressing it so as to prevent the dis-
charge of its functions, all the muscles of voluntary mo-
tion are paralyzed at the same time.
oft bod!es. ated It would also appear that certain parts of the
nervous system exercise a different influence over the
motions. Thus M. Magendie has proved that if the por-
tion of the brain, called by anatomists the corpora striata,
be cut into, the animal thus mutilated is no longer master
of his movements, but seems driven forward by some in-
ternal force which he cannot resist; he leaps forward,
runs with rapidity, and finally stops, but seems unable to
cerebellum, move backward. If, on the contrary, the two
sides of the cerebellum be wounded in one of the mam-
miferae or in a bird, 1 it will walk, swim, or even fly back-
ward, without being able to advance.

When these lesions are only practised on one side,
other phenomena will be observed, which at first sight
appear much more singular, but which are consequences
of the effects already mentioned. Thus, if one side of
the cerebellum or of the annular protuberance be cut ver-
tically, the animal begins at once to roll on its side, turn-
ing from the wounded part, and sometimes with such
rapidity, that it makes more than sixty revolutions in a
minute.

1 From the experiments of M. Magendie it would appear that the same
effects were not observed in reptiles and fishes.

MOTIONS. 241

From these curious experiments, and the researches
upon the same subject by Flourens and some other physi-
ologists, the cerebellum and neighboring parts of the
encephalon have been found to possess, among other
properties, that of regulating the movements of locomo-
tion.

The movements which, although under the S3.
direction of the volition, are also independent of its in-
fluence appear then to depend upon the action g^Sniif
of the medulla oblongata. In fact, when the obl ? n s ata s
brain no longer discharges its functions, and when con-
sequently there can be no volition, the muscles of the
respiratory apparatus continue to act as if their move-
ments were under the direction of the will ; but when
this portion of the medulla is destroyed, although the
brain be left intact, they are immediately arrested.

Those muscles, whose contractions are entirely rn 3^f
independent of the will, receive their nerves from the
ganglionary system, and in this system resides their prin-
ciple of action ; for if respiration be maintained by arti-
ficial means, the whole encephalon may be destroyed, as
well as the spinal marrow, without arresting the beating
of the heart, or the peristaltic motion of the intestines.

The contraction of the muscular fibre is a ifv*uwxm-

cular contrac-

phenomenon essentially intermittent. The mus- tion -
cles cannot remain in a state of permanent contraction,
and at the end of a longer or shorter time they are neces-
sarily relaxed. Thus the heart, whose action only ceases
with life, alternately contracts and reposes ; but in the
muscles of voluntary motion, these same contractions,
interrupted by longer or shorter intervals of repose, can-
not be continued beyond a certain time, for they produce

31

242 ANATOMY AND PHYSIOLOGY.

a feeling of lassitude which increases till at last these
movements become impossible, which is only relieved by
a period of inaction or repose.

The ease with which muscular fatigue is manifested
varies greatly according to the individuals ; but, ceeteris
paribus, it is in the ratio of the intensity of the contrac-
tions, the duration of each of them, and the rapidity with
which they succeed each other.

The force displayed by the contraction of a muscle
depends upon the texture of this organ ; and the nervous
energy of the individual. The large, firm, and red mus-
cles, are capable of contracting with more power than
the small, flabby, and pale ; but only when these condi-
tions are united to a very strong volition, can these organs
produce the greatest effects, and almost always they are
in an inverse ratio. The energy of the muscular con-
tractions may be carried to an extraordinary degree by
the sole influence of the action of the brain. We ac-
knowledge the power of an angry man and of a lunatic ;
and when, in the ordinary state of the economy, a simi-
lar nervous energy is united to a great material develop-
ment of the muscular system, astonishing effects result ;
of such the ancients have transmitted us recitals in speak-
ing of their athlete, and the buffoons of our own day are
also sometimes examples.

Muscular contraction is an important office in several
of the functions, the history of which has already been
given ; but the subject to which we shall now turn our
attention is more directly connected with it, for we are
about to enter upon the study of the general and partial
movements of the body, upon which depend attitudes,
locomotion, and many other phenomena entirely mechan-
ical.

MOTIONS. 243

In the inferior animals the muscles are all in- ^moff"
serted into the tegumentary membrane, which is soft and
flexible ; and by acting upon it they so modify the form
of the body as to impress on it motion entirely or in part ;
but in animals of a more perfect structure, the apparatus
of motion is more complicated, and is composed not
merely of muscles, but also of a system of solid pieces
which serve to increase the precision, force and extent of
the motions, at the same time that it determines the gen-
eral form of the body and protects the viscera against
external violence.

This solid frame, to which the muscles are at- skeleton.
tached, bears the name of skeleton. In certain animals,
such as insects and lobsters, it is situated externally, and
consists merely in a modification of the skin ; but in man
and all animals nearly allied (namely, the other mammi-
ferae, birds, reptiles and fishes,) it is situated in the inte-
rior of the body, and is composed of parts peculiar to
itself.

In some fishes (the rays, for instance,) the skel- cartilages.
eton is formed of a white substance, opaline, compact, to
appearance homogeneous, very resistant and elastic, which
is called cartilage. It is the same with the skeleton of
man and other animals at the early period of life; but
this state, which is permanent in the fishes spoken of, is
in the other animals but transitory, and the cartilages of
the skeleton become encrusted with stony materials of a
calcareous nature, which render them stiff, brittle, and
very hard, and which transform them to the state Bone.
of bone.

To be convinced that bones are but cartilages, har-
dened by the deposition of calcareous salts into their

G)hh ANATOMY AND PHYSIOLOGY.

substance, it is only necessary to macerate them for some
time in a particular liquid, called muriatic or hydrochloric
acid. This liquid has the property of dissolving the stony-
materials contained in the bones without attacking the
cartilages, so that the latter may thus be separated from
the salts which masked its properties. 1

?rthl°bS The ossification of the skeleton commences
by an infinity of points which are constantly extending ;
therefore the number of distinct osseous pieces is at first
immense ; but by the progress of ossification several
among them are united, so that in the adult there are
fewer distinct bones than in the infant ; and in extreme
old age, several bones are often united in one, and parts
originally cartilaginous are encrusted with calcareous
matter. The utility of this mode of development can
be at once comprehended ; in order that the solid frame
of the body may not oppose its motions, the former must
always be composed of a great number of movable pieces,
but this division is especially necessary when all these
parts must yield to the increase of the organs situated in
its interior.

s Kon e es of The surface of the bones is always covered
by a membranous layer, to which is given the name of
periosteum, and their substance is composed of fibres or

1 From the analysis of M. Berzelius the bones of the human skeleton,
completely deprived of fat, are composed to the hundred parts, as follows:
of cartilage, 32.17: vessels, 1.13; neutral phosphate of lime, with a small
portion of the fluoride of calcium, 53.01; carhonate of lime, 11.30; phos-
phate of magnesia, 1.1 G ; soda, with a small proportion of chloride of so-
dium, 1.20. In the hones of the ox this chemist found the same proportion
of animal matter, but less of the carbonate of lime. The cartilaginous
part of the bones is composed of gelatine, and is therefore used in the arts,
and in domestic economy, for the manufacture of glue and the preparation
of economical broths.

MOTIONS. 245

lamella, easily distinguished. When these organs are to
occupy a small space and present great solidity, as is the
case with the flat bones, which cover the majority of the
most important and delicate viscera, the osseous tissue is
extremely compact. But when the bones arc to occupy a
long space, the motions would be injured if their weight
were considerable, their tissue is dense and close only upon
the surface, and in their interior exist large cellules or even
canals, called medullary, because they are filled with
marrow.

The bones vary greatly in form, and from this Form.
variation they are divided into long, short and flat bones.
The former simply present a medullary cavity and are
always nearly cylindrical. We often find in all of them
eminences which give attachment to the muscles or to
other parts, and which, when they form a considerable
prominence, are designated as processes. The bones
also present upon their surface depressions more or less
shallow, and which serve to lodge the soft parts or to re-
ceive other bones which are to move in these cavities,
and in many places, are holes which afford a passage to
the blood vessels or nerves.

The name of articulation is given to the union Articulation.
of the various bones together. The means of conjunction
employed by nature for this purpose vary much, according
as the bones are always to preserve the same relation
and remain fixed, or to execute motions of greater or
less extent.

When the articulation of the bones is not destined to
permit motion, it may take place in three ways : by jux-
taposition, by suture, or by implantation. The articula-
tions by simple juxtaposition of the articular surfaces are

946 ANATOMY AND PHYSIOLOGY.

only seen in certain parts of the skeleton, where the po-
sition of the bones is such that they cannot be displaced.
In the articulations by suture, the articulating surfaces
present a series of asperities and angular projections,
which are reciprocally received ; thus these articulations
may have great solidity with but small extent of surface.
Finally the articulations by implantation are those, in
which a bone is set into a cavity hollowed in the sub-
stance of the bone which serves as its base : these are
the most solid but are rare. 1

In the movable articulations, the bones are not directly
united together, but are maintained in contact by bonds
extending from one of these bones to the other.

Sometimes these articulating surfaces are united by an
intervening cartilaginous or fibro-cartilaginous substance,
strongly adherent to both of them, and which only allows
them to move by reason of its elasticity, (this is called the
articulation by continuity) : at other times the articulating
surfaces slide upon each other, and are only kept in con-
tact by ligaments? which surround them and are so ar-
ranged as to limit their motions. The latter mode of
conjunction constitutes what anatomists call articulation
by contiguity, and is met with in all cases of very ex-
tended motion. The surfaces thus articulating are always
extremely smooth and surrounded by a cartilaginous layer,
which highly increases their polish ; but these are not the
only means employed by nature to diminish the friction
in the joints : for she has placed in them a sort of mem-

1 The teeth, which are not true bones, are the only parts thus articulated.

2 The name of ligaments is given to collections of fibres similar to those
of the tendons, very resisting, round or flat, and of a pearly white, which
fasten together the bones.

MOTIONS. 247

branous pocket, called the synovial sac, which is similar
to the serous membranes, and is filled with a viscid
liquid, which permits these surfaces to slide readily upon
each other.

All the muscles destined to produce the great ^cgm of the
movements of the body, are fixed to the skele- thebunes -
ton by their two extremities. Therefore, by contrac-
tion, they must displace the bone which presents to them
the most feeble resistance, and draw it towards the one
which remains immovable, and which serves as a fixed
point to move the former. Now, in the majority of in-
stances, the bones are more movable as they are at a
greater distance from the central part of the body ; con-
sequently, the muscles which are fixed to two of them
act in general upon the more distant, and the muscles
destined to move a bone always extend from this organ
to the trunk. Thus the muscles serving to bend the fin-
gers occupy the palm of the hand and the fore-arm ;
those which bend the fore -arm upon the arm occupy the
arm, and those which move the arm upon the shoulder
occupy the shoulder.

In certain circumstances, however, these muscles dis-
place the bones which in ordinary cases answer the pur-
pose of a fixed point. When we attempt to raise the
body hanging by the hands, the flexor muscles of the
fore-arm not being able to displace the latter, approxi-
mate the arm to it, and thus draw up the whole body.

The kind of movement caused by the contraction of a
muscle generally depends on the one hand, upon the na-
ture of the articulation of the bone displaced, and on the
other, upon the position of the muscle with regard to this
bone : it always draws it to its own side, and approxi-

248 ANATOMY AND PHYSIOLOGY.

mates it to the point where its opposite extremity is fixed.
Thus the muscles which flex the fingers occupy the pal-
mar face of the hand and fore-arm, while those for their
extension are upon the opposite side of the limb.

Several muscles are often so arranged as to concur in
the production of the same motion. They are then said
to be allied ; and the antagonist of a muscle is the one
which causes the opposite motion.

The muscles are also designated, from their uses, as
flexors and extensors, adductors and abductors, rotators,
etc.

F mu!-ck-s"' e The force with which a muscle contracts depends
upon its volume, the energy of the will, and some other
circumstances already mentioned ; but the effect produced
by this contraction depends, also in a great measure, upon
the manner in which it is fixed to the bone to be moved.
Thus, all things being equal, the motion caused by the
contraction of a muscle will be more powerful in propor-
tion as the muscle is less obliquely inserted upon the bone
to be moved : when inserted at a right angle its whole
force is employed in displacing the latter ; but in the op-
posite case, a more or less considerable part of its force is
lost.

Fig. 46. Thus if the muscle m, the

n a force of which we suppose
equal to ten, is fixed perpen-
dicularly to the bone /, the ex-
tremity of which a, is movable
upon the fulcrum point r, it will
d h l only have to overcome the

weight of this bone, and will carry it from the position a b,
in the direction of the line a c, causing the point of its

MOTIONS.

249

insertion to describe a space which we will also represent
by 10. But if this muscle acted obliquely upon the bone,
in the direction of the line n b, for example, it would then
be quite different ; for it will tend to carry it in the direc-
tion b n, and consequently to approximate it to the artic-
ular surface r, upon which the extremity of the bone re-
poses, but the latter being an inflexible stem this displace-
ment cannot take place ; the bone can only turn upon
this point r, as on a pivot, and the contraction of the mus-
cle n, without any loss of the energy we have attributed
to it will only be able to carry this bone in the direction
a d, and consequently to produce a displacement for which
one fourth of the force would have been sufficient in its
first position perpendicular to the bone.

The muscles are inserted for the most part very oblique-
ly into the bones, and consequently in a manner very
little favorable to the intensity of the result of their con-
traction. There often exists, however, a disposition which
tends to diminish the obliquity of Fig. A7. Fig. 48.
these insertions : this is the swelling m
met with at the extremities of most
of the long bones, and which princi- *■-
pally serves to give their articulations
greater solidity. The tendons (i), of the muscles (in)
situated above the articulation are generally inserted di-
rectly below this swelling, and thus arrive at the movable
bone (o), by following a direction more nearly approach-
ing the perpendicular, as any one may convince himself
by comparing the disposition of muscle m in figure 48,
where these swellings exist, with figure 47, in which the
articulating extremities have been represented without any
such swelling.

32

250 ANATOMY AND PHYSIOLOGY.

The distance separating the point of attachment of the
muscle from the fixed point on which the bone moves,
and from the opposite extremity of the lever represented
by this organ, also exerts a very great influence upon the
effects produced by its contraction. To explain this
fact we must have recourse to Mechanics.

Levers. The bones we say represent levers, a name
given in physics to every inflexible rod which moves
upon a fixed point, called the fulcrum. The force which
puts the lever in motion is called the power, and that
which opposes its displacement is called the resistance.
The distance which separates the fulcrum point from the
point to which the power or resistance is applied, is
called the arm of the lever.

The length of the arm exerts a very great influence
upon the force necessary to constitute an equilibrium to
a given resistance. For proof let us observe the mecha-
nism of the Roman balance, as it is called. The beam
Fig- 49- is divided into two parts of un-

equal length by the fulcrum (a).
At the extremity of one of the

branches (r), which is very short,
is found the resistance (or object
to be weighed), and upon the other (p) slides a weight,
which makes the equilibrium to a resistance so much the
more considerable as it is farther removed from the ful-
crum and consequently the arm of the power of the lever
lengthened, that of the resistance remaining always the
same.

Every one knows too how great the difference is in
the power a man can employ when he seeks to raise any
burden with his arm bent or extended. In these mo-

r~\

MOTIONS. 251

tions, the same muscles are called into action, and the
lever-arm of the power remains the same, it is only the
lever-arm of the resistance, represented by the distance
from the shoulder to the hand, which is lengthened.

The science of mechanics teaches us, that to consti-
tute an equilibrium on any lever whatever, the resistance
and the power must be proportional to the length of the
arms of the lever, that is, when multiplied by their re-
spective arms, they must both give the same product.

Thus, to make an pfe 50.

equilibrium to a resist- Q> f\

ance (/), equal to 10, | |» [ j

applied to the extremity a & <£> c

of a lever (a b) of the «p JL r

m cj)

length 20, the power
(j?), if applied at the same point and consequently at an
equal distance from the fulcrum (a), must also be equal
to 10. But if applied at the point c, to produce the same
effect, the power must be equal to 20, for the resistance,
which we have supposed equal to 10, being multiplied
by the length of its arm of the lever (20), will give as a
product 200, and on the other hand, the power arm of
the lever (c a) being only equal to 10, the latter must be
multiplied by a force equal to 20, to give the same pro-
duct 200. Finally, if the power be placed yet nearer
the fulcrum, at the point d, it must have a force equal to
100 ; for its lever arm will be only 2, and 2 x 100 = 200.
The disposition of the levers exerts as great influence
over the rapidity of the motions produced, as over their
force ; and if, by employing a power comparatively feeble,
a much greater resistance can thus be overcome, a slower
or more rapid movement may also be obtained with the

252

ANATOMY AND PHYSIOLOGY.

aid of these instruments, by the employment of a motor
force of a certain rapidity.

Thus let us suppose the
power J7, to act upon the
lever a r, so as to cause the
point of insertion c, to de-
scribe a space of 5 in a
second, it will displace at
the same time the extremity
r, of the lever and cause it to arrive at b, with a rapidity
equal to 25, for the distance described at equal periods
by this point will be five times as great as that described
by the point c. The application, then, of a force whose
rapidity is only 5 to the point c, produces the same result
as if there had been directly applied to the point r, a
force whose rapidity is equal to 25.

But from what has been already said we see, that what-
ever is gained in rapidity is lost in force, for such results
are obtained by making the resistance arm of the lever
longer than that of the power.

Now, in the animal economy, nearly all the levers
represented by the bones are so arranged, as thus to
favor the rapidity of motion at the expense of the force
necessary to produce them. Thus when the extended
arm is brought down to the side, if the rapidity with
which the muscles contract is such that their insertion
be displaced three inches in a second, the extremity of
the limb will be removed, from its primitive position,
with the rapidity of nearly three feet in a second.

Having made these preliminary remarks upon animal
mechanics, we may now undertake the study of the
different parts of the apparatus of motion, which we shall
first examine in man.

MOTIONS.

253

Vertebral
column.

Fig. 27.

The skeleton, as we have already said, is skeleton.
composed of a great number of bones united together ;
it is divided like the body, into three parts, the head,
trunk and limbs.

The most important part of the skeleton, which serves
for the support of all the others, and differs least in the
different animals, is the vertebral or spinal column.

This name is given to a kind of osseous stem extend-
ing the whole length of the trunk, and which is com-
posed of a great many small bones called vertebrae, which
are placed one upon the other and solidly united together.

This column (fig. 27), also called the spine,
occupies the median and posterior line of the
body, and supports on its anterior extremity
the head, which may be considered as its con-
tinuation. In man we reckon thirty-three ver-
tebrae, and they are divided into five portions,
viz. : a cervical portion composed of seven ver-
tebrae, a dorsal of twelve, a lumbar of five, a
sacral also of five, and a coccygeal of four. It
presents several curves and increases in size
from its anterior or superior extremity to the
commencement of the sacral portion. At birth, c d
all the vertebrae are perfectly distinct, and are simply
articulated with each other ; but in a short time the five
sacral are united and form but one bone, called the
sacrum (s).

The essential character of the vertebrae is
to be traversed hy a hole, which, by uniting
with those of the other vertebrae, forms a canal,
extending from the cranium to the extremity
of the body, in which the spinal marrow is

d

Fig. 28.

254

ANATOMY AND PHYSIOLOGY.

Fig. 52. — Skeleton of Man.

Frontal bone. Parietal bone.

Tibi i
Fibula

Temporal bone.

Clavicle.

Dorsal vertebrae.

Iliac bone.

MOTIONS. 255

lodged. In man the vertebra? of the coccyx present no
such canal, for they are reduced to a rudimentary state
and merely consist of so many solid nuclei. On the
sides, this vertebral canal communicates externally by a
series of holes, called holes of conjugation, because they
result from the union of two grooves in the superior and
inferior borders of each vertebra, so as to correspond
when these bones are united. These holes, as already
shown, give passage to different nerves which arise from
the spinal marrow, and are distributed to the several
parts of the body.

Each vertebra is divided into a body and several pro-
cesses. The body of the vertebra (fig. 28, a,) is a thick
disc, situated in front of the vertebral canal (or below, if
the column is in a horizontal position, as in most animals),
and serving to give solidity to the articulations of these
bones with each other. The two faces of this disc are
nearly parallel, and each of them is united to the corres-
ponding surface of the neighboring vertebra, by a thick
layer of fibro-cartilage which adheres to each, over the
whole extent of the articulating surfaces, and only per-
mits them to be separated so far as its elasticity will allow.
The articulation of the vertebrae is also strengthened by
the existence of four small processes, situated on the sides
of the vertebral canal, and which interlock with those of
the neighboring vertebrae. Finally, behind this canal,
there exists a process called spinous (6), which assists in
the same purpose, by limiting the flexion of the column
backward ; and fasciculi of aponeurotic fibres extend,
also, from one bone to the other so as to fasten them to-
gether.

The articulation of the vertebrae is thus rendered ex-

256 ANATOMY AND PHYSIOLOGY.

tremely solid, and the motions of each of these bones are
in general very limited ; but the addition of these slight
motions to each other, gives sufficient flexibility to the
whole column without injuring its strength. But this
mobility varies greatly in the different parts of the spine ;
in the lower part it is almost null, in the loins, on the con-
trary, it is quite marked, but it is the greatest in the cer-
vical portion of the column ; therefore, in these parts, the
fibro-cartilaginous layer, in order to allow of these move-
ments, is thicker than in the back, and the spinous pro-
cesses are farther removed from each other, so as to allow
of a considerable curvature of the column before they
meet.

The weight of the body tends constantly to curve the
vertebral column forward. To resist this flexion and
straighten the column, powerful muscles were requisite,
which are inserted the whole length of its posterior face ;
and to render their action more powerful, nature has so
arranged their point of attachment as to allow them to
draw perpendicularly upon quite a long arm of a lever.
In fact, most of them are fixed to the extremity of the
processes called spinous, which form a prominent crest
the whole length of the spine, and others take their ori-
gin from two other processes (c), which are equally promi-
nent and are named from their direction, transverse pro-
cesses.

It must, also, be observed that in the portions of the
column where these muscles are to employ the most
power, as in the loins, these processes are much longer,
and consequently form a lever far more powerful than in
the parts where all this force is not necessary, as in the
neck, for example. In animals with a heavy head, situ-

MOTIOiNS. 257

ated at the extremity of a long and horizontal neck, these
processes have an extreme length on the back, where
they serve for the attachment of the ligaments and mus-
cles intended to sustain these parts and support the neck.

The motions of flexion of the column forwards require
scarcely any force, and the muscles employed to produce
them, and situated in front of the body of the vertebras,
are, consequently, small and few in number.

The first vertebra of the neck, called the atlas, is much
more movable than any of the rest ; it has the form of a
simple ring, and turns upon a kind of pivot formed by a
process which ascends from the body of the next verte-
bra (or axis). Upon this articulation are effected nearly
all the motions of rotation of the head. The bonds
which unite these two vertebras are far less strong than
those of the other vertebrae ; and in fact, in the ordinary
position of the body, the weight of the head pressing
upon the atlas, tends rather to maintain them in contact
than to separate them. When, however, the head sup-
ports the entire weight of the body, as in those who are
hung, the case is altered ; these two vertebras then sepa-
rate easily, and their luxation produces almost instantane-
ous death in consequence of the compression of the spinal
marrow, precisely at the point whence originate the prin-
cipal nerves of the respiratory apparatus. It was with
the view of causing this dislocation of the neck, and, con-
sequently, of abridging the sufferings of criminals con-
demned to perish on the gallows, that hangmen were
formerly accustomed to rest one foot upon the shoulder of
the criminal at the moment he was thrust from the ladder
with the cord around his neck. And from the same

33

258

ANATOMY AND PHYSIOLOGY.

cause, sudden death may happen in those imprudent
plays where a child is raised from the ground by the ears.
The vertebral column, as we have already said, sup-
ports in a measure all the other parts of the body. By
its superior extremity it articulates with the head, each of
the dorsal vertebrae articulates with a pair of ribs, and the
sacrum is wedged between the two haunch bones.

Head. The head is composed of two principal portions,
the cranium and face.

cranium. The cranium is a kind of
osseous box, oval in form, occupy-
ing the whole superior and posterior
part of the head, and lodging as
before stated, the brain and cere- na
bellum. Eight bones are united to m c s
form the walls, namely, the frontal
or coronal in front (f), the two pa- ■»./ a» c ta

rietal (p), above, the two temporal (t), upon the sides,
the occipital (o), behind, and the sphenoid (s), and ethmoid
below. All these bones, with the exception of the last,
have the form of large thin plates and are of a very com-
pact texture, and all articulated together so as to be com-
pletely immovable and to give the cranium great solidity.
These articulations are very remarkable in that they vary
in form in the different parts of the cranium, for the pur-
pose of better resisting external violence which might
tend to disunite these bones, and would produce different

1 /, Frontal bone, — p, parietal, — /, temporal, — o, occipital, — s, sphe-
noid, — n, nasal, — m s, superior maxillary, — j, malar or cheek bone, —
m t, inferior maxillary, — n a, anterior opening of the nasal fossae, — t <z,
auditory foramen, — a :, zygomatic arch formed by a part of the temporal
and malar bones, — a, b, c, <I, lines indicating the facial angle.

MOTIONS. 259

effects, according to the point on which it acts. Thus
when a blow falls upon the summit of the head, the
movement is propagated in all directions, and tends to
separate the parietal bones by driving forwards or back-
wards the frontal and occipital bones; therefore, all these
bones are united by closely serrated sutures. But when
the cranium receives a blow upon the side, the effort
acting upon the temporal tends to drive in this bone, to
prevent which accident, nature has united the temporal to
the neighboring bones, not by means of sutures, merely
adapted to prevent disunion, but by a very oblique articu-
lating border, so as to render this bone externally much
larger than the space in which it is set.

The vault of the cranium presents nothing remarkable;
but, at its base, we find a number of holes which serve
for the passage of the blood vessels of the brain and of
the nerves, which arise from the encephalon. Through
one of these holes, hollowed in the occipital bone and
much larger than the others, passes the spinal marrow,
and there exists near its border upon each side, a large
convex process called the condyle, which serves for the
articulation of the head upon the vertebral column. The
head is nearly in equilibrio upon this kind of pivot, but
yet the portion in front of the articulation is more volu-
minous than that behind, and tends to counterbalance the
first. Therefore, the muscles which extend from the
vertebral column to the posterior part of the head, and
which serve to raise the latter, are much more numerous
and powerful than the flexor muscles, p'aced in the same
manner in front of the column; and when the former are
relaxed, as happens during sleep, the head usually leans
forward and rests upon the chest.

260 ANATOMY AND PHYSIOLOGY.

Upon the sides of the base of the cranium, we also
observe two very large processes, called mastoid, into
which are inserted two muscles, which descend obliquely
to the chest at the anterior part of the neck, and serve to
turn the head upon the vertebral column. 1 Finally, di-
rectly in front of these processes, is the opening of the
external auditory duct, which, together with the several
parts of the middle and internal ear, is hollowed into that
portion of the temporal bone called, from its hardness, the
petrous.

Face. The face is formed by the union of fourteen
bones of very different forms, and presents five great
cavities for lodging the organs of sight, smell and taste.
All these bones, except the lower jaw, are completely
immovable, and are articulated together or with the bones
of the cranium. The two principal are the superior max-
illary bones (ms), which constitute almost the whole of
the upper jaw, and which articulate with the frontal so
as to aid in the formation of the orbits and nasal fossa?.
On the outer side they are articulated with the malar
bones (j), and behind with the palate bones, which in
their turn are joined to the sphenoid.

The orbits, as we have elsewhere seen, are two conical
fossa? or pits, the base of which is directed forward : the
arch of these cavities is formed by a portion of the frontal
bone and their floor by the superior maxillary bones.
On the inner side, the ethmoid and a small bone, called
the lachrymal, complete their walls, and on the outer,
they are formed by the malar and the sphenoid ; the latter
also occupies the bottom of the orbit, and in it are found

1 Called, from their attachment, stemo-mastoid muscles.

MOTIONS. 261

the openings for the passage of the optic nerve, and the
other nervous branches of the apparatus of vision. In
the vault of the orbit may be seen a depression which
lodges the lachrymal gland, and on its exterior wall is
found a canal which descends vertically into the nasal
fossae and gives passage to the tears.

The nose is formed in a great measure of cartilage;
thus in the skeleton the anterior opening of the nasal
fossae (iia) is very large, and the bony portion formed by
two small bones, called nasal (n), is but slightly promi-
nent. The nasal fossae are very extensive ; superiorly,
they are excavated in the ethmoid bone, the whole interior
of which is filled with cellules ; inferiorly, they are sepa-
rated from the mouth by the arch of the palate, which is
formed by the superior maxillary and two palate bones;
finally, they are separated at the median line by a vertical
septum formed superiorly by a plate of the ethmoid, and
inferiorly by a particular bone called the vomer. In the
interior of these fossae may, also, be found two distinct
bones which are called the inferior turbinated and also
the opening of the frontal, sphenoidal, and maxillary
sinuses, cavities more or less extensive, hollowed in the
bones from which they take their names.

All the teeth of the upper jaw are implanted into the
superior maxillary bone. In early life it is formed of sev-
eral pieces, and in most animals we find an anterior por-
tion which is called the intermaxillary bone.

The lower jaw, in man, is composed of a single bone,
for the two halves of which it is formed in many animals
are early united and completely consolidated. This
bone, called inferior maxillary, much resembles a horse-
shoe, the curved ends of which are greatly raised. It is

262 ANATOMY AND PHYSIOLOGY.

articulated with the temporal bones by a projecting con-
dyle situated on each extremity, and received in a cavity
called the glenoid (e) ; finally in front of these condyles
there rises upon either side a process called coronoid,
which serves for the insertion of one of the levator mus-
cles of the lower jaw (the temporal muscle) ; these mus-
cles (t) are all fixed to the angle of the jaw, and at a
short distance from the fulcrum point on which this lever
moves. In the majority of instances, on the contrary,
the resistance to be overcome by this same lever during
mastication, is applied to the anterior part of the jaws ;
therefore, these muscles, although very powerful, can pro-
duce but very feeble effects, and to crush between the
teeth the hardest bodies, they must be carried as far as
Fig. 22. possible to the bottom of the mouth, so

z t

as to shorten the resistance arm of the
lever and render it equal or even shorter
than that of the power. These muscles
are fixed on the internal, as well as ex-
e ternal face, of the jaw, and make their

fulcrum point upon the sides of the head, as high as the
temples, passing between the lateral walls of the cranium
and a bony arch called the zygomatic (c), which extends
from the malar bone to the ear, and also serves for the
insertion of these organs.

The head, as before shown, is essentially composed of
twenty-two bones ; but their number is actually greater;
for in the interior of each temporal bone, there are, as
elsewhere stated, four little bones belonging to the appa-
ratus of hearing, and the hyoid bone may also be consid-
ered a dependence of the head. This bone is suspended
from the temporal bones by ligaments and is placed across

MOTIONS. 2£3

the upper part of the neck, where it bears the tongue
and sustains the larynx.

The cervical vertebras only articulate with each Thon*.
other, or with the head and the first dorsal vertebra ; but
each of the twelve dorsal vertebrae supports a pair of
very long and flat arches which curve around the trunk,
so as to form a kind of osseous cage to lodge the heart
and lungs. These arches are the ribs, the num- ***
ber of which is consequently twelve on each side of the
body; their posterior extremity is articulated with the
body of the corresponding vertebra and with one of the
transverse processes ; the other extremity is continuous
with a cartilaginous shaft, which, in certain animals (birds,
for example,) is always ossified, and is then called the
sternal rib. The cartilages of the seven first pairs of ribs,
which are called the true ribs, are united to the sternum,
which is a single bone, occupying, in front, the median
line of the body and serving to complete the walls of the
thoracic cavity ; the five last pairs of ribs do not reach
the sternum, but are joined to the cartilages of the pre-
ceding ribs, these are called the false ribs, (fig. 17).

Upon the bony cage just mentioned are fixed s S or
the superior limbs. In each of them may be distinguished
a basilar portion, which may be compared to a pedestal
upon which is inserted the essentially movable portion of
the limb, which itself represents a lever, to which the
former serves as a fulcrum. This basilar portion is com-
posed of two bones, the scapula and clavicle.

The scapula is a large flat bone, occupying the scapula,
superior and external part of the back : its form is nearly
triangular, and it presents, on the upper and outer side,
an articulating cavity quite large, but rather shallow, which

2g4 ANATOMY AND PHYSIOLOGY.

receives the extremity of the bone of the arm (glenoidal
fossa of the scapula). At its superior border we find a
projecting process called the coracoid, and on its external
face a very prominent horizontal crest, which terminates
above the articulation of the shoulder by a process called
the acromion, at the extremity of which the clavicle is

ciavicie. articulated. This latter bone is small and cylin-
drical ; it is placed across the superior part of the chest
and extends, like an arch, from the sternum to the scap-
ula. Its principal use is to keep the shoulders separated :
and, therefore, it is very often broken, when, by falls upon
the side, this part is driven with violence toward the ster-
num ; and in those animals which bring the arm power-
fully to the breast (as birds in flight), this bone is greatly
developed, while it is completely wanting in those who do
not execute such motions, and only move their limbs lon-
gitudinally, as in horses, etc.

theshouuie^ Numerous muscles fix the scapula to the ribs.
One of the principal is the serratus magnus, which extends
from the anterior part of the thorax to the posterior border
of this bone, passing between it and the ribs. In man it
is not much developed ; but in quadrupeds it is extremely
strong and constitutes with that of the opposite side a
kind of girth, which supports the entire weight of the trunk,
and which prevents the scapula? from ascending toward
the vertebral column. In man, the trapezius muscle, which
extends from the cervical portion of the vertebral column
to the scapula, has, likewise, very important functions : for
it raises the shoulder and sustains the weight of the entire
thoracic extremity, therefore it is greatly developed.

The portion of the thoracic extremity which constitutes
the lever to which the scapula serves as a fulcrum, is
composed of the arm, fore-arm, and hand.

MOTIONS. 265

The arm is formed by a single long cylindrical Humerus.
bone called the humerus. Its superior extremity (or
head) is large, round, and articulated with the glenoid
cavity of the scapula, in which it can roll in any direction.
The muscles which move this bone are inserted into its
superior third and attached by their opposite extremity to
the scapula or thorax. The three principal are the great
pectoral, which carries the arm inward at the same time
it depresses it ; the great dorsal, which carries it backward
and downward, and the deltoid, which raises it.

The inferior extremity of the humerus is enlarged and
has the form of a pulley, upon which the fore-arm moves
as on a hinge.

Two long bones, placed parallel, form this por- L jj$ia£ d
tion of the thoracic extremity ; the ulna situated on the
inner, and the radius on the outer side. They are united
by ligaments and an aponeurotic septum, which extends
from one to the other, their whole length : but yet they
are movable, and the radius, which bears at its extremity
the hand, can turn upon the ulna, which serves for its
support. From the different uses of these two bones it
might be foreseen what would be the principal differences
in their general form. The ulna, to articulate in a solid
manner with the humerus, must present at its superior
extremity a certain size, and an extensive articulating sur-
face, while at its inferior extremity, where it serves as a
pivot to the radius, it must be small and rounded. The
radius on the contrary must be, for the same reason, small
at its superior, and very large at its inferior extremity, to
which the hand is suspended. This is actually the case,
and we also observe that these two bones only touch at

34

2(36 ANATOMY AND PHYSIOLOGY

their two extremities, which renders more easy the mo-
tions of rotation of the radius upon the ulna.

The ulna which carries with it the radius, moves upon
the radius in only one direction ; it only executes motions
of flexion and extension, and in the latter it can only
form, with the humerus, a straight line, for it presents be-
yond its articulating surface a process, called the olecra-
non, which in that situation rests upon the humerus and
affords an invincible obstacle to any farther extension.
The extensor and flexor muscles of the fore-arm extend
from the shoulder, or superior part of the humerus, to the
superior part of the ulna : wherefore they are arranged in
a manner favorable to the rapidity of motion of the fore-
arm, but very unfavorable to the employment of a great
force ; for the power-arm of the lever, represented by the
space comprised between the articulation of the elbow
and their insertion, is very short, while the resistance-arm
of the lever, which is equivalent to the entire length of the
limb from this same articulation, is, on the contrary, very
great.

The rotation of the radius and of the hand upon the
ulna are effected by muscles situated on the fore-arm, and
which extend obliquely from the extremity of the hume-
rus, or ulna, to one or other of these parts.

Hand. The hand is divided into three portions, carpus,
metacarpus, and fingers.

carpus. The carpus or wrist is formed by two ranges of
little short bones, united very closely together, so that the
whole of this part enjoys a degree of mobility ; although
each of the bones composing it can scarcely be displaced,
an arrangement which is adapted to give their articula-
tions a very great solidity. They are in number eight.

MOTIONS.

267

Four of these bones, viz. : the scaphoid, semi-lunar, pyri-
midal and pisiform compose the first range ; the four
others, which are called trapezium, trapezoid, os magnum,
and os unciforme, form the second. It must be remarked
that these different bones are arranged so as to protect
the vessels and nerves passing from the fore-arm to the
hand ; for this purpose they form, with the ligaments,
a canal which is traversed by these organs and which
can support, without flattening, the strongest pressure.

The metacarpus is composed of a range of little Metacarpus.
long bones, placed parallel-wise, and equal in number to the
fingers with which their extremities articulate. Four of
these bones are united by their two ends, and are scarcely
movable ; but the fifth, which bears the thumb, only artic-
ulates with the carpus and moves freely upon the latter.

Finally, the fingers are formed each by a series Phalanges:
of small, slender bones, joined end to end, and called
phalanges. The thumb presents only two, but the fingers
have three. The last phalanx bears the nail. The fingers
are all very movable and may all move independently of
each other. Their flexor and extensor muscles form the
greater part of the fleshy mass of the fore-arm, and termi-
nate by extremely long and small tendons, some of which
are fixed to the first phalanges, and others to the last.

When we examine the united thoracic extremities, we re-
mark that the several levers joined end to end to form them,
diminish progressively in length. The arm, for instance,
is longer than the fore-arm ; the latter is longer than the
wrist, and each phalanx is shorter than the preceding.
The utility of this arrangement is readily comprehended.
The numerous and close articulations at the extremity of
the limb, permit the latter to vary its form in a thousand

2(38 ANATOMY AND PHYSIOLOGY.

ways, and to accommodate Itself to the body to be seized ;
while the long levers, formed by the arm and fore-arm,
permit us to carry the hand rapidly to considerable dis-
tances. The motions of the humerus upon the scapula
principally determine the general direction of the limb ;
the articulation of the elbow is specially designed to per-
mit it to be lengthened or shortened.

members. The structure of the inferior members is very
analogous to that of the thoracic, and the principal differ-
ences are those necessary for their greater solidity at the
expense of their mobility, and to render them organs of
locomotion rather than of prehension. They also have a
basilar portion, which is the counterpart of the shoulder,
and is called the haunch, and an articulated lever formed
of three parts, the thigh, the leg and the foot, which
answer to the arm, fore-arm and hand.

mac bone. The haunch, or basilar portion of the abdominal
extremity, is formed by a large flat bone, called the iliac
(from the latin word ilia, flank) or coxal bone (from the
word coxa, which in Greek signifies haunch). This bone
results from the union of three principal pieces, always
distinct in foetal life, which may be compared to the body
of the scapula, its coracoid process and the clavicle. The
iliac bones have not bases corresponding to the bones of
the shoulder,, ribs and sternum, to rest upon ; being des-
tined to sustain the entire weight of the body they must,
however, be fixed in the most solid manner to the trunk ;
thus they are articulated behind with the portion of the
vertebral column, called the sacrum, and in front they
unite and form an arch, called the pubis. They are per-
fectly immovable, and from the union of these two bones
and the sacrum results a large osseous cincture, which

MOTIONS.

269

inferiorly terminates the abdomen, and which, from its
open form, is called pelvis (fig. 52). This kind of ring is
closed inferiorly by muscles and gives passage to the in-
testine called rectum, and to the genito-urinary organs.
Upon the sides, externally, we observe upon each iliac bone
an articulating cavity, nearly hemispherical, which serves
to lodge the head of the thigh bone. Finally, most of
the muscles which move the thigh and leg, are inserted
into the pelvis, and the muscles, which enclose, as we
have elsewhere seen, the abdominal cavity, are fixed to
it, and reach from it to the thorax.

The thigh, as the arm, is composed of a single Femur.
bone, which is called the femur. Its superior extremity
is inclined inwards, and its head, which is rounded, is
separated from the body of the bone by a contraction,
called the neck of the femur. At the lower end of this
neck, and at the point where it joins the body of the
bone at an open angle, are several large tuberosities
which may be felt through the flesh, and which give in-
sertion to the principal motor muscles of the thigh ;
finally, its inferior extremity is very large and presents
two condyles laterally, compressed and rounded from be-
fore backward, which slide upon the articulating face of
the principal bone of the leg and only permit the latter
to be bent, or extended, while the femur itself may move
upon the pelvis in any direction.

The difference of the leg and fore-arm is much T *h ? b n Iar
greater. Besides the fibula and tibia, which are the two
principal bones of which this part of the limb is com-
posed, as the fore-arm of the ulna and radius, we find in
front of the knee a third bone called the patella, which
may be regarded as analogous to the olecranon process of

270 ANATOMY AND PHYSIOLOGY.

the ulna, and which principally serves to elongate from
the knee the tendon of the extensor muscles of the leg,
and to render its insertion more oblique, an arrangement,
which as already shown, must increase the power of its
action. The foot not being required to execute motions
of rotation as the hand, but requiring, to support the
whole weight of the body, that it should present great
solidity in its articulation, the two bones of the leg do
not move upon each other, and the one which articulates
with the femur and which represents the ulna (the tibia),
is also the one to the extremity of which the foot is at-
tached. The fibula, which is small and situated on the
external side of the tibia, only serves, so to speak, to
maintain the foot in its natural position and to prevent it
from turning inward. Its superior extremity is applied
against the head of the tibia, and its inferior constitutes
the outer ancle.

Foot. The foot is composed, as well as the hand, of
three principal parts, namely, the tarsus, metatarsus, and
the toes.

Tarsus. There are seven bones in the tarsus, and it only
articulates with the leg by one of them, the astragalus,
which ascends above the others and presents a head in
form of a pulley, adapted to the cavity formed by the
articulating surface of the tibia and the two malleoli. 1
The astragalus rests upon the calcaneum which is pro-
longed farther behind and constitutes the heel ; lastly a
third bone, called scaphoid, terminates the first range of
the bones of the tarsus, and the second range is com-
posed like the hand, of four small bones, three of which

1 The inner malleolus, or ancle, is a process of the tibia ; the outer is
formed by the fibula.

MOTIONS. 271

have received the name of cuneiform bones, and the
fourth, placed in front, is called the cuboid.

The bones of the metatarsus, to the number Metatarsus.
of five, exactly resemble those of the metacarpus : only
they are stronger and less movable, especially the inner,
which is arranged in the same manner as the rest. Phalanges.
It is the same with the toes ; we reckon the same num-
ber of phalanges as in the fingers of the hand, but they
are shorter and not so easily moved. The great toe is
not detached from the others and cannot be opposed to
them, as the thumb to the other fingers.

Upon the internal side of the foot, the bones of the
tarsus and metatarsus form a kind of arch to lodge and
protect the nerves and vessels, which descend from the
leg to the toes. When this arrangement does not exist,
and the sole of the foot is flat, as sometimes happens,
these nerves are compressed by the weight of the body,
and walking cannot be long continued without pain.
The whole extent of the foot, however, rests M £ S e C \ e e 8 g. of
upon the ground, and forms a large and solid base of
support ; it can be moved upon the leg only in the direc-
tion of its length, and the muscles serving for this pur-
pose surround the tibia and fibula. The extensors of the
foot, which form the calf of the leg, are fixed to the cal-
caneum by a long tendon, called the tendon of Achilles,
and are arranged in the manner most favorable to their
action ; for their insertion is nearly at a right angle and
farther removed from the fulcrum than the resistance to
be overcome, when the weight of the body, pressing up-
on the astragalus, is raised by the foot.

All the mammifera?, birds, reptiles, and fishes, Animals with

' ' i. ' ' an internal

have an internal skeleton, more or less nearly skeIeton -.

272 ANATOMY AND PHYSIOLOGY.

resembling that of man, composed of nearly the same
bones, and likewise moved by muscles placed between
this solid frame and the tegumentary envelope. This
skeleton gives to their body its general form, and upon
its disposition and the action of the muscles fixed to its
various parts, depend the attitudes as well as motions of
these animals.

standing. A small number of these beings lie with the
whole length of their bodies upon the ground, and only
move by undulations of the trunk ; but others are ordi-
narily sustained upon their limbs, and the name of stand-
ing is given to the state in which an animal thus supports
itself on the ground by its legs.

That the limbs may remain firm and thus sustain the
body, their extensor muscles must be kept in a state of
contraction, for, without it, these organs would bend
under the weight they support and thus occasion its fall.
We have already seen that the muscles are more quickly
fatigued the longer each contraction continues ; thus in
most animals, standing for a long time is more fatiguing
than walking, in which latter case, the extensor and
flexor muscles mutually relieve each other.

This condition is not the only one indispensable to
standing ; that the body may remain upright on the limbs
thus stiffened, it must be in equilibrium.

An equilibrium is established, not only when a heavy
body rests upon a resisting object with the whole extent
of its largest surface ; but also, when it is so placed, that
if one part of the mass be depressed toward the earth,
an opposite part, equally heavy, would be raised in the
same degree ; the weight of one part serves then to
counterbalance that of the other, and the point around

MOTIONS. 273

which all these parts are reciprocally in equilibrium and
where support must be given to keep in place the entire
mass, is called the centre of gravity. To support this
centre, it is requisite that the base of support (that is to
say, the space occupied by the points by which the mass
leans upon a resisting object, or that comprised between
these points), be situated vertically beneath it.

That the body of an animal may remain in equilibrium
upon its paws, the vertical line passing through its centre
of gravity must consequently fall within the limits of the
space left between the feet, or covered by them : and
the larger this base of support is in relation to the height
at which the centre of gravity is found, the more stable
will be the equilibrium, for the more it may be displaced
without throwing the line of gravity, just mentioned,
beyond the limits of this base. It is also deserving of
note, that the more difficult the equilibrium to be pre-
served, the more intense must be the muscular contrac-
tion to maintain it, and the more fatiguing the position of
the animal.

From this reasoning it might be inferred, that when an
animal rests upon all-fours, its standing will be more
firm, solid, and less fatiguing than when it only rests
upon two, and that in this latter case, its equilibrium will
be more stable than when it only rests upon one leg :
for the extent of the base of support is thus constantly
narrowed. When an animal is supported upon four legs,
the space comprised between them is very considerable,
and can be but slightly modified by the larger or smaller
extent of the surface of these organs. To render
them very large would then have increased their weight,
without adding to the solidity of the base of support :

35

274

ANATOMY AND PHYSIOLOGY.

Fig. 5 1.

Fig. 53.

therefore, in most quadrupeds, the
members touch the ground only
by an extremity, hardly dilated ;
and we find the number of fingers
constantly diminishing, without
injury to these organs as instru-
ments of locomotion : the foot of
the stag and horse are cases in
point (fig. 53 and 54) ; but when
the animal only rests upon two of
its feet, whatever be their dis-
tance apart, the base of support
can have no solidity from before
backwards, only in as much as these organs touch the
ground in a considerable extent, as in the foot of man ;
and when an animal readily supports itself upon one
paw, as birds, nature must have given their feet more
width, as well as length.

To allow an animal to put itself in equilibrium upon
a single leg, the foot on which it rests must also be
placed vertically below the centre of gravity of its body,
and its muscles so arranged as to permit it. to keep this
limb inflexible and immovable. Man can do this ; for
the centre of gravity of his body is about the centre of
his pelvis, and when placed in a vertical position it is
enough for him to lean a little to the side not supporting
the weight, in order that the line of gravity may fall
upon the sole of the foot of the opposite side ; but with
most quadrupeds the thing is impossible.

Most of these latter animals cannot even remain erect
upon their hind paws, on account of the direction of the
members relatively to the trunk ; and if they do succeed

MOTIONS. 275

for an instant, it is impossible for them to remain so, be-
cause their base of support is very narrow, the centre of
gravity of their body is placed very high (toward the chest),
and the muscles called into action in this attitude must
be contracted with a violence requiring immediate repose
In man and a small number of other mammiferse, the
vertical position upon the two abdominal limbs, is, on the
other hand, more or less easy ; for these members may
readily be placed in the direction of the axis of the body,
the centre of gravity is situated very low, and the base
of support formed by the feet is very large. In man
especially, is this attitude rendered solid by the width of
the pelvis, the form of the feet, and several other corres-
responding peculiarities of organization.

In the vertical position, the muscles of the posterior
part of the neck are contracted to keep the head in equi-
librium upon the vertebral column, the extensor muscles
of which are also called into action, to prevent it from
yielding under the weight of the thoracic members and of
the viscera of the trunk, which tend to curve it forward.
The whole weight of the body is thus transmitted by the
vertebral column to the pelvis, and from the pelvis to the
femur. Left to themselves, these latter bones would bend
upon the pelvis, and the trunk would fall forward, did not
the contraction of their extensor muscles keep them ex-
tended. The extensor muscles of the leg, at the same
time, prevent the knees from bending, and the extensors
of the foot keep the leg in a vertical position, so that the
weight of the body is transmitted from the thigh to the
leg, from the leg to the foot and from the foot to the
ground.

The seated position is less fatiguing than standing, be-

276 ANATOMY AND PHYSIOLOGY.

cause the weight of the body being then directly trans-
mitted from the pelvis to the base of support, it is not
necessary for the extensors of the abdominal extremities
to contract in order to maintain the equilibrium. Finally,
when man is laid upon his back or belly, the weight of
each movable portion of his body is directly transmitted
to the ground, and consequently, to continue so, he is not
required to contract a single muscle.

Locomotion. The progressive motions by which man and
animals are transported from one place to another, require
a determinate rapidity in a certain direction to be im-
pressed upon the centre of gravity of their bodies. This
impulse is given to it by the employment of a certain
number of articulations, more or less bent, and the posi-
tion of which is such that upon the side of the centre of
gravity their employment is free, while in the opposite
direction it is confined, or even impossible, so that the
totality or greatest part of the motion produced, takes
place in the first of these directions. The same thing
then takes place, as in a spring with two branches, one
extremity of which is applied against a resisting obstacle,
and the two branches of which, after being approximated
by a force from without, are restored to their former lib-
erty ; by reason of their elasticity they would tend to
separate equally, until restored to their position before
they were approximated ; but that applied against the
obstacle, not being able to overcome it, the movement
will take place in an entirely opposite direction, and the
centre of gravity of the spring will be repelled from this
obstacle with a greater or less degree of rapidity. In the
body of animals, the flexor muscles of the part employed
in oneh kind of motion, represent the force which com-

MOTIONS.

277

presses the spring, the extensors represent the elasticity
which tends to separate the branches, and the resistance
of the ground, or fluid in which these beings move, repre-
sents the obstacle which opposes the extension of one of
the branches.

Walking is a motion upon a fixed plane, in Progression.
which the centre of gravity is alternately moved by one
part of the locomotory organs, and sustained by the others,
without entirely preventing at any time the body from
resting upon the ground. This latter circumstance dis-
tinguishes it from leaping and running, motions in which
the body quits momentarily the ground, and throws itself
into the air.

In walking upon two feet, in man and the other animals
to whom this mode of locomotion is possible, one of the
feet is carried in front, while the other is extended upon
the leg ; and as this latter leans upon a resisting plane,
its elongation displaces the pelvis and projects the whole
body forward ; the pelvis turns at the same time upon
the femur of the opposite side which sustains it, and the
leg, which previously remained behind, is bent and car-
ried in front of the other, then straightens, and in its turn
serves to sustain the body while the other limb, during
its extension, gives a new impulse to the centre of gravity.
By these alternate motions of extension and flexion, each
limb bears, in its turn, the weight of the body, as in
standing upon one foot, and at every step the centre of
gravity is pushed forward ; but we see that it must, at the
same time, be carried alternately to the right and to the
left, to be directly above each of its bases of support.

The majority of quadrupeds in walking make use prin-
cipally of their hind legs to propel their bodies forward,

278 ANATOMY AND PHYSIOLOGY.

and of their anterior legs to sustain themselves in the new
position given by each step. When these motions are
made by all four feet at the same time, the animal is for
an instant suspended above the ground, and this mode of
locomotion constitutes the gallop. In walking, two feet
only contribute to the formation of each step, one in front,
the other behind ; in general, those upon opposite sides
are raised simultaneously, at others, those on the same
side; this latter gait is the amble.

Leaping is performed by the sudden employment of
various articulations of the limbs, which are at first more
flexed than usual. The extent of space the animal thus
passes through in the air, depends principally upon the
rapidity impressed upon its body at the moment of de-
parture, and this rapidity, in its turn, depends upon the
proportional length of the bones of these members and
the force of their muscles. Therefore, animals which leap
the best, have the hind legs and thighs very long and
very muscular.

£5flyi3 Swimming and flying are motions analogous to
those of leaping ; save that they are effected in fluids, the
resistance of which takes the place, to a certain degree,
of that of the ground in the preceding phenomena.

The members, which by extending and bending back-
wards drive the body forward, are applied in this case
against the water or air, and tend to crowd together the
particles of which these media are composed with a
greater or less rapidity ; but if the resistance, which the
air or water presents in this way, is superior to that which
opposes the motion of the animal in a contrary direction,
these fluids will furnish to the limb a fixed point, and the
motion produced will be the same as if this spring, touch-

MOTIONS. 279

ing by its posterior extremity an invincible obstacle, only
expanded with a force equal to the difference existing
between the rapidity employed and that impressed by it
upon the surrounding fluid in bending backwards. Now,
the less dense the fluid in which the animal moves, the
less resisting will be the fixed point furnished by it ; and
the greater the force necessary to overcome, in rapidity,
this displacement of the fixed point, and propel the body
forward. Thus, flying requires a much greater motor
power than swimming, and neither of these movements
could be effected by the force requisite for a leap upon a
solid surface. But this great employment of the motor
force is not the only condition necessary for aerial or
aquatic locomotion ; as the animal plunged in a fluid, finds
upon all sides an equal resistance, the rapidity acquired
by striking upon this fluid behind, would soon be lost by
that which it would be obliged to displace in front, if it
could not diminish considerably the surface of the locomo-
tory organs immediately after having made use of them to
give the blow. This is the actual case, and one of the
characteristics of every organ of flight, or even of swim-
ming, is the power of changing its form and presenting,
in the direction perpendicular to that of the movement
produced, a surface alternately very large and very
narrow.

With regard to the structure of the organs of aerial, or
aquatic locomotion, we will only say that in the superior
animals the thoracic almost always alone serve for flight,
and that their transformation into wings takes place either
by the extreme elongation of the fingers, and the exist-
ence of a membrane which extends between these appen-
dages, and is also fastened to the sides (as in the bats,

280 ANATOMY AND PHYSIOLOGY.

fig. 55), or by the implantation of long and stiff feathers
upon the whole extent of the limb, which then becomes
Fig. 55. long and narrow (as in birds). The

abdominal and thoracic members may
also serve for swimming, and when they
are completely transformed into fins we
find, in general, that their terminal part
Fig. 56. becomes very large, and that the por-

tion which represents the arm and fore-
arm is shortened, so that the portion an-
alogous to the hand seems to spring
directly from the trunk: this is easily
proved in the phocae and cetacea (fig. 56).

THE VOICE.

In concluding the history of the functions of relation, it
it remains for us to treat of the production of sounds, a
faculty which in man is of extreme importance, as upon
it depends voice and speech.

In the lower animals there is no trace of this faculty,
and in insects, the monotonous noise which is called the
hum of these little beings, merely results from the rubbing
of their wings, or some other parts of their tegumentary
envelope, against each other ; but the superior animals
nearly all can utter sounds more or less varied, the pro-
duction of which depends upon the passage of the air into
a determinate part of the respiratory duct, so arranged as
to impart vibration to this fluid.

Larynx. In man and the other mammiferse, this phe-
nomenon takes place in that portion of the air passage
which is situated at the top of the neck, between the
pharynx and the trachea, and called the larynx (fig. 16,

THE VOICE. 281

a ; fig. 23, e ; fig. 24, g). In fact an opening made in
the trachea below this organ, by permitting the expired
air to escape outwardly without traversing it, completely
prevents the production of sounds. Examples are cited
of persons who with such an opening in the neck, pro-
duced either by a wound or some disease, have lost the
voice, but recovered the faculty of speech by putting a
close cravat around the neck so as to stop the wound,
and, consequently, force the air to follow its usual course.
On the other hand, a similar opening above the larynx
does not destroy the voice ; whence we may with cer-
tainty conclude, that the production of sounds takes
place in this organ.

The larynx is a large and short tube, p- ^ i
which is suspended to the os hyoides, i

(h) and continues inferiorly into the tra- /fi^^g-.
chea. Its walls are formed by various F^T^l
cartilaginous plates, designated as the a ..U'l 1
thyroid cartilage (t), the cricoid cartilage %— Jl
(c), and the arytenoid cartilages ; m front HaB

we see the projection usually known as tr

Adam's apple (a) ; and in the interior, the mucous mem-
brane lining it, forms, about its centre, two great lateral
folds, directed from before backwards and arranged like the
lips of a button-hole. These folds are called vocal cords,
or inferior ligaments of the glottis ; they are very thick ;

1 Profile view of the human larynx ; h, os hyoides ; — I, body of the hy-
oid bone, to which is attached the base of the tongue; — t, thyroid carti-
lage ; — a, projection formed by the thyroid cartilage in front, and commonly
called Adam's apple ; the thyroid canilage is united to the os hyoides by a
membrane ; — c, cricoid cartilage ; — tr, trachea ; — o, posterior wall of the
larynx in relation with the aesophagus.

36

282 ANATOMY AND PHYSIOLOGY.

F'o- 58 ' their length is in proportion with the

ft projection of the anterior part of the
thyroid cartilage (or Adam's apple), and
a by the aid of the contractions of a small
ZZ V muscle lodged in their interior, and of
the movements of the arytenoid carti-
lages to which they are fixed posteriorly,
they may be approximated in a greater or less degree, so
as to enlarge or diminish the space of the fissure (the
opening of the glottis), which separates them. A little
above the vocal cords, arc found two other similar folds
of the mucous membrane of the larynx; they are called
superior ligaments of the glottis, and the two depressions
Fa- 59 a which divide them from the inferior
a a ligaments, are named ventricles of the
±1 _ larynx. The space comprised between
these four folds is called the glottis ;
r ™!™J&f~Y finally above this opening is a kind of
~" c fibro-cartilaginous tongue, the epiglot-
tis, fixed by its base beneath the root
& b of the tongue, and which ascends
obliquely into the pharynx, but which can be depressed so
as to cover the glottis, as was exemplified when treating
of deglutition, (fig. 58, e).

In the ordinary state, the air expelled from the lungs

1 Vertical section of the larynx ; — h, os hyoides ; — t, thyroid carti-
lage ; — c, c, cricoid cartilage ; a, arytenoid cartilage; — v, ventricle of the
glottis, formed by the space left between the vocal cords and the superior
ligaments of the glottis ; — e, epiglottis.

2 Front view of the larynx; the shape of the internal wall is indicated
by the lines a, a, b, b ; — li, inferior ligaments of the glottis or vocal cords ;
— h, superior ligaments. The other parts are indicated by the same letters
as in the preceding figures.

THE VOICE. 283

traverses freely the larynx and produces no sound in it ;
but when the muscles of this organ contract and the
passage of the air becomes more rapid, the voice may
be heard. An experiment by Galen demonstrates the
necessity of these contractions for the formation of
sounds.

He divided in living animals the nerves supplying the
muscles of the larynx ; x and this operation, which occa-
sioned paralysis of these organs, also involved the loss of
the voice. Other experiments also prove that the pro-
duction of sounds depends especially upon the action of
the ligaments of the glottis. When the superior folds
are divided, the voice is considerably weakened, and when
the inferior, or vocal cords, it is destroyed.

Most physiologists consider the larynx as act- , Mechanism

i J ° J of the produc-

ing in the production of the voice upon the prin- tion of sou " ds -

ciple of a reed instrument : they think, that the air ex-
pelled from the lungs rushes out, in a continual stream,
from the lips of the glottis, until these elastic cords re-
turn upon themselves and momentarily close the respira-
tory passage, to be separated anew, so as to produce
movements of vibration sufficiently rapid to give birth to
sounds, nearly the same things that transpire in blowing
upon the reed of a hautboy. But from the recent obser-
vations of M. Savart it would appear, that the production
of the vocal sounds does not depend upon a mechanism
similar to that of the reed instrument, but rather takes

1 The pneumogastric nerves, which arise from the lateral portion of the
medulla oblongata, issue from the cranium, descending one upon each side
of the neck, and penetrate into the thorax and abdomen. Immediately
after their entrance into the former of these cavities they give origin to a
branch, which ascends on either side of the neck and ramifies upon the
larynx ; it is called the recurrent nerve, from its direction.

234 ANATOMY AND PHYSIOLOGY.

place in the same manner as in the little instruments used
by sportsmen to imitate the song of birds.

These instruments, called bird-calls, are ordinarily
constructed of wood or metal, and consist of a small
cylindrical canal, very short and closed at each end by a
thin plate, pierced in its centre by a hole. To elicit
sounds, the sportsman places the call between his teeth
and aspires the air through the two openings by which it
is pierced. The current, which thus traverses the instru-
ment, draws with it a part of the air contained in its
cavity, and the latter, being rarefied, soon ceases to be in
equilibrium with the pressure of the atmosphere, which
by its reaction crowds upon and compresses it, until, by
its own elasticity and by the influence of the current, it
undergoes a new rarefaction, followed by a second con-
densation, and so on. The small mass of air contained
in the call thus enters into vibration, and gives origin to
sonorous waves, which scatter themselves in the atmos-
phere. By moderating, or accelerating the rapidity of
the current, we produce grave or acute sounds, and they
are varied yet more by enlarging or contracting the open-
ings of the instrument, varying its form, rendering its
walls more or less elastic, and adapting to it tubes of va-
rying length.

It would appear that, by similar modifications of the
larynx, the sounds produced by this organ become grave
or acute. As the voice ascends, the lips of the glottis
become tense and contract so as to diminish, to a great
extent, the size of the opening left between them.
The contraction of the muscular fibres upon the walls of
the ventricles of the larynx, and of the muscles of the
posterior fauces, give at the same time to all these parts

THE VOICE. 285

a degree of tension favorable to the development of the
sound produced, and we find that the larynx itself as-
cends as the sounds are more acute, a circumstance,
which is explained by the laws of acoustics, for it causes
the shortening of the passage traversed by the sounds in
making their exit, and we know perfectly well that in
our ordinary instruments of music the length of this pas-
sage has the greatest influence upon the rapidity of the
sonorous vibrations ; when we wish to draw from the
reed of a clarinet, or hautboy, for examp