Outlines of physiology: with an appendix on phrenology

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OUTLINES

PHYSIOLOGY:

AN APPENDIX

PHRENOLOGY

BY P. M. ROGET, M.D.,

SKCRETAHT TO THE KOTAI SOCIETY, PHOFESSOR OF PHTSIOLGGT IBT THE ROTAL

INSTITUTIOK OF GREAT BRITAIIf,

ETC. ETC.

FIRST AMERICAN EDITION,
REVISED, WITH NUMEROUS NOTES.

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PHILADELPHIA

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LEA AND BLANC M(^^yL,r ^^1\V>^

(successors to CARET AND CO.)*

1839.

lYt^

Entehed, according to Act of Congress, in the year 1839, by Lea and Blan-
cHARD, in the Clerk's office of the District Court for the Eastern District of Penn-
sylvania.

Printed by Haswell, Barrington, and Haswell.

AUTHOR'S PREFACE.

So great and so numerous are the improvements which Phy-
siology, in all its departments, has received since the period of
the publication of the former edition of the Encyclopesdia Bri-
tannioa, that it was deemed necessary by the Editor to give, in
the present edition, an entirely new Treatise on that subject.
When I engaged, at his request, to write this Treatise, I was far
from sufficiently Estimating either the magnitude of the under-
taking, or the space to which, in endeavouring to comprehend
all its branches, the subject would extend. The limited time
which was assigned me for its completion, and my distance from
the place of pubHcation, will, I trust, be admitted in extenuation
of whatever errors may be discovered to be still uncorrected.

In revising the article Cranioscopy, which had been published
in the Supplement to the last edition of the Encyclopaedia, and
which the Ediltor purposed introducing in the present edition
under the title of Phreivology, making such additions to it as I
might think were requisite, I have availed myself of this per-
mission to reply to some of the criticisms which had been made
upon it by Mr. G. Combe and Dr. A. Combe: it was, accord-
ingly, thought desirable to reprint the former essay, with no
other alterations than a few verbal corrections, and the intro-
duction of a few sentences descriptive of some modifications and
additions to the system of Gall and Spurzheim contained in
Mr. Combe's System of Phrenology. In the remarks which I

4 PREFACE.

#

have subjoined to that essay, the reader will perceive that I have
refrained from entering into the discussion of the numerous ob-
jections that might be urged against the metaphysical part of the
modern system of Phrenology, having neither the leisure nor the
inclination to engage in controversies of this nature.

P. M. R.

London, Oct. 20, 1838.

PREFACE

THE AMERICAN EDITOR,

The contents of the present volume — as will be seen by the
Author's Preface — form the articles "Physiology" and "Phre-
nology" in the seventh edition of the Encyclopaedia Britannica.
These articles have been recently pubHshed separately in Edin-
burgh, in two handsome volumes, and from these the present
edition has been printed.

Of the Author's qualifications as a physiological writer, it is
scarcely requisite to speak. The fact, of his having been selected
to compose the Bridgewater Treatise on Animal and Vegetable
Physiology, is sufficient evidence of the reputation which he then
enjoyed ; and the mode in which he executed the task amply
evinces that his reputation rested on a solid basis.

The present volume contains a concise, well-written epitome
of the present state of Physiology — human and comparative —
not, as a matter to be expected, the copious details and devel-
opments to be met with in the larger treatises on the subject ;
but enough to serve as an accompaniment and guide to the phy-
siological student.

The attention of the American Editor has been directed to the
revision and correction of the text; to the supplying, in the form
of notes, of omissions ; to the rectification of some of the points
that appeared to him erroneous or doubtful; and to the furnishing

1*

PREFACE.

of references to works in which the physiological inquirer might
meet with more ample information.

In Phrenology, the Author is a well-known unbeliever, and his
published objections to the doctrine have been regarded as too
cogent to be permitted to pass unheeded. It will be seen, that
farther examination in the interval of many years, which has
elapsed since the publication of the sixth edition of the Ency-
clopaedia, has not induced him to modify his sentiments on this
head. On the contrary, he appears to be as satisfied, at this
time, of the fallacy of the positions of the Phrenologist, as he was
at any former period.

Philadelphia, July 1, 1839.

CONTENTS

CHAPTER I.
General Views of Physiology . . . , Page 13

1

CHAPTER n. \

Application of Physiology . . . . . . 34

CHAPTER HI,
Arrangement of Functions , . , . • . 47

CHAPTER IV,
The Vital Powers , , , , . . , . 5?

CHAPTER V.

The Mechanical Functions — Organization in general — Comhina--
of Textures — The Cellular Texture — Adipose Texture — Membra'

8 CONTENTS.

nous Structures — The Osseous Fabric — Cartilage — Fibro-Cartila-
ginous Structures — Ligamentous Structures — Mechanical Connex-
ions— Articulation — Package of Organs — The Integuments — The
External Integuments — Of the Internal Integuments, or the Mucous
Membranes — Muscular Action — Structure of Muscles — Muscular
' Contractility — Functions of the Osseous Fabric, or Skeleton — The
- Cranium— The Face— The Thorax— The Spine— The Pelvis— The
Limbs in general — The Lower Extremities — The Upper Extre-
mities .......... 66

CHAPTER VI.

Assimilation — Chemical Constitution of Organized Matter — Ne-
cessity of Aliment — Chemical Conditions of Organized Matter —
Proximate Animal Principles — Gelatin — Albumen — Fibrin — Ar-
rangement of the Functions of Assimilation — Properties of Food
, — Animal Food — Vegetable Food — Condiments — Appetites —
Hunger — Thirst — Preparation of the Food for Digestion — Mastica-
tion— Insalivation — Deglutition — Digestion or Chylification 130

CHAPTER VIL

Chylification — Properties of Chyle — Functions of Intestines — Pro-
perties of Bile — Functions of the small Intestines — Functions of the
Spleen — Functions of the large Intestines — Lacteal Absorption —
Sanguification . . 16^

CHAPTER Vm.

Circulation — Apparatus for Circulation — Cardiac Apparatus — San-
guiferous System in general— Arterial System — Venous System—

CONTENTS. 9

Capillary System — Phenomena of Circulation — Course of the Blood
in its Circulation — Proofs of Circulation — Powers concerned in the
Circulation — Action of the Heart — Actions of the Arteries — Action
of the Capillaries — Action of the Nerves — Pulmonary Circula-
tion . . . . • . . . . . . 187

CHAPTER IX.

Respiration — Mechanism of Respiration — Chemical Effects of Res-
piration— Animal Temperature . • » • • 2iQ

CHAPTER X.

Secretion — Apparatus for Secretion — Glandular Apparatus — Ar-
rangement and Properties of the Secretions — The Aqueous Secre-
tions-^ The Albuminous Secretions — Mucous Secretions — The
Fibrinous Secretions — Oleaginous Secretions — The Resinous Se-
cretions— The Saline Secretions — Theory of Secretion . 217

CHAPTER XI. , - ^

Absorption — Structure of the Absorbent System — Function of Ab-
sorbents— Venous Absorption — Effects of Absorption — Function
of the Lymphatic Glands 233

CHAPTER XII.

Excretion — Excretory Function of the Lungs — Excretory Func-
tion of the Skin — Excretory Function of the Kidyieys — Excretory
Function of the Liver . ..... . 240

10 CONTENTS.

CHAPTER XIII.

Nutrition — Ossification — Dentition — Nutrition of the Softer Tex-
tures— General Phenomena of Nutrition . . . 244

CHAPTER XIV.

The Sensorial Functions — General Views — Organization of the
Nervous System — Organization of the Brain and Spinal Cord —
The Nerves — Ganglia 251

CHAPTER XV.

The External Senses — Touch — Sensation of Pressure— Sensations
of Temperature — Anomalous Sensations — Sensation of Pain — The
Muscular Sense. Taste — Organs of Taste — Function of Taste.
Smell — Organs of Smell — Function of Smell. Bearing — Acoustic
Principles — Organ of Hearing — Function of Hearing. Vision-
Internal parts of the Eye — External parts of the Eye — Optical Prin-
ciples— Formation of Images in the Eye — Adjustments for the Cor-
rection of Aberration ....... 259

^ CHAPTER XVI.

Physiological Laws of Sensation — Phenomena of Sensation —
Specific endowment of the Nerves of Sensation — Modifications of
Impressions — Conditions necessary for Sensation — Theories of
Sensation 287

CHAPTER XVII.

Locality of the Sensorium — Requisite conditions of the Sensorium

CONTENTS. 1 1

—Laws of Recurrence and the Association of Impressions—
Volition and Voluntary Motion— Automatic Motions— Instinctive
Motions—Involuntary Motions— Psycological relations of the Sen-
sorium — Sleep •••..... 294

The Voice

CHAPTER XVIII.
31S

CHAPTER XIX.

Generation— General Views— Unimpre gnat ed Ovum— The Male

, System— The Female System— Theories of Generation— Utero-

Gestation— Parturition— Lactation— Fcetal Evolution . 326

CHAPTER XX.

Progressive Changes in the Animal Economy . . 35©,

CHAPTER XXI.

Temperaments

359

CHAPTER XXII.
Varieties of the Human Species 354

CHAPTER XXHI.

Comparative Vii\siOhOGX— Comparative Physiology of Mammalia
—Peculiarities of the Human Conformation— Peculiarities in the
Conformation of other Mammalia — Quadrumana—Chiroptera—
Insectivora — Plantigrada—Digitigrada— Amphibia— Marsupialia —
Rodentia— Tardigrada— Monotremata— Pachydermata— Solipeda—

12 CONTENTS.

Ruminantia— Cetacea. Comparative Physiology of Birds— Gene-
ral Description— Peculiarities in particular Families and Genera of
Birds. Comparative Physiology of Peptiles—Ue^iWes in General
— Chelonia— Sauria— Ophidia— Batrachia. Comparative Physi-
ology of Fishes. Comparative Physiology of Mollusca—QeY>\i^-
lopoda — Gasteropoda— Acephala. Comparative Physiology of
Jlrticulata — Annelida —Crustacea- Arachnida— Insects. Compa-
rative Physiology of Zoojj/tyfes— Echinodermata— Entozoa— Aca-
lepha— Polypi— Infusoria 368

CHAPTER XXIV.

History of Physiology . . • ' .' , / ' ^^^

kv^mmx— Phrenology ^55

PHYSIOLOGY.

j:!!"^ \

CHAPTER I

GENERAL VIE w"^ r*

1. Physiology, or the science of animal life, has been variously
defined by different writers. If the term were interpreted strictly
according to its etymology, it would carry a meaning much more
extensive than is warranted by common usage ; for being derived
from ?ua-(f, nature, and Koyai, discourse, its proper signification
should be, the science of nature. It might accordingly be under-
stood to comprehend inquiries in every department of nature,
both animate and inanimate ; and might indeed be regarded as
synonymous with physics, or natural philosophy, which are
othei' expressions of corresponding import, but ^yhich at present
are themselves restricted in their meaning to a special depart-
ment of nature. There can be no doubt, indeed, that such must
originally have been the real signification of these terms ; but it
is npedless now to inquire by w4iat gradual transitions they have
at length come to bear such different and even, in some respects,
opposite significations. If we were desirous of substituting a
a term which would accurately express the idea now associated
with the word physiology, we should adopt that of biology, from
/S'of, life, first introduced by Treviranus, who has written a Ger-
man work on this subject, which bears that title.

2. Natural philosophy, or physics, is now understood as desig-
nating that class of sciences, wliich have for their object the
examination of the properties of lifeless matter ; whilst physio-
logy, in its modern acceptation, is in like manner limited to the
consideration of the properties which are peculiar to organized
and living bodies. The former is conversant only with nature in
her dead or inanimate condition; the latter with nature endowed
with life, and in all its various forms and modifications. '

14 PHYSIOLOGY.

Thus mechanics, hydrostatics, and pneumatics, wholly relate
to the general phenomena exhibited by matter in its solid, liquid,
and gaseous forms ; optics, which relates to the phenomena of
light, together with electricity, magnetism, and the science of
heat, which regard other classes of phenomena produced by
peculiar agents, are all considered as branches of natural philo-
sophy. Chemistry, which is concerned with the changes of
composition in bodies, resulting from the mutual action of their
particles at insensible distances, ranks also with the sciences
relating to the properties of inorganic matter, and of which the
assemblage constitutes what are more correctly termed in the
present day, the physical sciences.

3. On the other hand, the study of animated nature does not
admit of the same extent of 'subdivision. Nature has indeed
traced a broad and obvious line of demarcation between the
vegetable and the animal kingdoms ; the first being the province
of botany, the second of zoology ; both of which departments
offer us a wide field of inquiry, and inexhaustible subjects of
speculation. But it is in the animal world, more especially, that
the busy and ever-changing scene is calculated to awaken the
most lively curiosity, and inspire the deepest interest. The
multiplied relations which connect us with the lower animals, the
obvious analogies which subsist between them and our own
species, and the striking evidences of power, intelligence, and
benevolent design displayed in all the phenomena they present to
our observation, confer on the study of animal life a degree of
importance which belongs to scarcely any other study.

4. But the foundations of all science must be laid by drawing
accurate distinctions among the objects which come within its
cognizance ; by making a strict analysis of the ideas it compre-
hends, and by establishing precise definitions of the terms it
employs. As in all the other departments of human knowledge,
we can arrive at general facts, or comprehensive laws, only by-
submitting to the previous task of ascertaining and collecting
individual facts; so in natural history we find it necessary to
subdivide our labours into that which takes cognizance of indi-
vidual objects only, and that which inquires into their more
general relations with one another. The first is properly the
history, {he second the philosophy of nature; and this distinction
we may observe to run through all the branches into which the
subject is divisable. It applies even to astronomy, in which the
mere physical history of the phenomena forms a preliminary
body of knowledge, yet subordinate to that higher range of
inquiry which establishes connexions between these phenomena,
and uni'es them into comprehensive laws or theories. Minera-
logy, again, must be studied as the foundation of geology ; the
former being the history of the actual appearances ; the latter,

^ GENERAL VIEWS., 15

the theory of the series of changes which have led to these
observed phenomena. Thus, also, the external forms, and more
obvious habitudes of plants, and their classifications in conform-
ity w^ith those forms and properties, constitute the subjects of
botany, properly so called; whilst the study of their internal
structure and economy, with relation to the more general phe-
nomena of vegetation, is comprised under the head ot ph,ylology,
or the physiology of vegetables.

5. In like manner, the proper objects of zooIos;y are to trace
the external forms of animals, to distribute and arrange them in
systematic order, and to record the particular facts relaling to
their history ; that is, to the more obvious phenomena which they
present to our observation. Physiology embraces a wider field
of research, inquires into the connexions between the phenomena,
and investigates the causes from which they spring, and the laws
by which they are governed. The zoologist is content with
collecting observations on the visible actions of animals, on their
peculiar habits, modes of life, and the manifestation of those
faculties with which they are respectively endowed by the Author
of nature; a pursuit which aflx)rds inexhaustible sources of amuse-
ment, and furnishes abundant matter of admiration and of wonder.
But the physiologist aims at far higher objects ; and considering
the external phenomena presented by animals as lying merely at
the surface, seeks for information relative to the causes of all the
facts which are furnished to him by zoology, by examining the
interior structure of their bodies, by inquiring into the movements
of that interior mechanism, and the sources of those various
actions which give rise to all the complicated phenomena of life.
An extensive and even boundless region of knowledge opens to
his view in these highly curious and interesting subjects of
research, constituting one vast science, which, although consider-
able progress has been made in it by the labours of our prede-
cessors, is yet destined to occupy, for an incalculable period of
time, the unremitting elfbrts of succeeding generations.

6. The phenomena of living beings have a totally different
character from the changes which take place in inanimate
matter; and are with more difficulty subjected to the severe ana-
lysis required by inductive philosophy. The properties of inor-
ganic bodies are of a simpler and more definite nature, and
however variously they may be combined in their effects, admit,
in general, of a reduction to general laws. This is most effec-
tually accomplished by means of experiments, varied in such a
manner as to reduce each class of phenomena to its simplest
conditions, and afterwards combined in such a way as to allow
of a comparison of their results "with the appearances presented
by nature, and of thus verifying their identity.

But it is hardly possible to pursue the same process of investi-

16 PHYSIOLOGY.,

gation to any extent in the diversified phenomena of organization.
So comphcated is the mechanism, and so fine the minute struc-
ture of animal and vegetable bodies, that they elude the cogni-
zance of our senses, even when assisted by the utmost refinement
of optical and mechanical art. All that chemistry has yet
achieved in disclosing to us the properties of different species of
matter, and of their various combinations, falls infinitely short of
that knowledge which could enable us to follow and to under-
stand the curious and elaborate series of chemical changes which
take place in the interior of the living body. Far less are we
competent to trace the operation of those more subtle and myste-
rious principles, which are the springs of motion, and which
regulate the actions of the machine, and connect the whole of its
movements into one harmonious system. Judging from their
more obvious effects, indeed, these principles appear to be quite
of a different nature from those which produce the phenomena
of the inorganic world. The series of changes which are exhi-
bited by an animal or a vegetable, from the first moment o-f its
separate existence, through all the stages of its growth, maturity,
and decline, to the period of its death, are far too complicated
and multifarious to admit of being reduced to one single princi-
ple, in the same way as the movements of the heavenly bodies,
for instance, are reducible to the simple law of gravitation.

7. Physiologists, indeed, not deterred by these difficulties,
which are inherent in the subject of their researches, have in all
ages attempted generalizations of this kind. They have consi-
dered all the actions and phenomena which are pecuhar to living
beings, and which differ from those exhibited by the same bodies
after death, as resulting from the operation of a single principle
of life. Different designations have been given to this power by
different theorists ; thus, some have called it fhe vital principle,
others the spirit of animation, the archcBUS, the organic force ;
and many other appellations have been given to it, according to
the particular taste or fancy of the writer. Nothing, indeed, can
be more specious than this reference to unknown facts, which
have a manifest connexion with one another, to a common prin-
ciple of action, or in other words, to a vital power. The only
idea we can form of life appears to imply the unity of such a
principle. This idea, as is well remarked by Cuvier, is suggested
hy the observation of a certain class of phenomena, succeeding
each other in an invariable "order, and having certain mutual
relations with one another : yet it is but a vague, and indistinct
idea. We are ignorant of the nature of that link which unites
the whole of these phenomena : but the existence of sdme such
link forces itself upon our belief, and we are compelled to give it
a particular designation, and speak of it as if it were something
more than a mere fiction of the intellect.

GENERAL VIEWS. 17

8. Those who are unaccustomed to philosophical reasonings,
may be, indeed, and often are, decciv^ed by the employment of
these abstract terms, and regard them as the expressions of a
simple law of nature, of the same comprehensive, yet definite
character, as those of gravitation, cohesion, heat, and electricity.
A more careful and profound analysis, however, will convince
us that the power inherent in organization, upon which its infi-
nitely diversified actions depend, is not a simple agency, but a
combination of several powers, not only different from the phy-
sical agents which actuate the inorganic world, butdifl^ering also
very widely 'amongst each other. In order to arrive at this con-
clusion, however, it will be necessary to take a review of the
phenomena themselves, and we shall therefore defer the consider-
ation of this subject to a future chapter.

9. Although the peculiar nature of the phenomena which phy-
siology embraces has hitherto baffled all our endeavours to obtain
results of the same general and comprehensive nature as those
which have rewarded our efforts in the purely physical sciences,
yet other resources are open to us, capable of conducting us to a
still more ample and inviting field of inquiry. Living nature is
impressed with a character, which at once raises it to a higher
order among the objects of human intellect, and invests the
science which regards it with a more lofty and ennobling senti-
ment. Life is peculiarly characterised by the manifestation of
INTENTION. Adaptation of means to an end is visible throughout
the whole of this animated scene. Express design is palpably
discernible in every formation, in every arrangement, in every
series of changes which this vast theatre of nature displays.
Utility is the governing principle of all ; intelligence and power
far exceeding the utmost stretch of our imagination, are revealed
to us in language not to be mistaken, and carrying with it irre-
sistible conviction. Thus, while the sciences of inorganic matter
are founded on the relations of cause and effect, physiology takes
cognizance more especially of the relations of means to ends,
which the phenomena presents to our view. Hence we obtain a
new principle of arrangement among these phenomena ; hence
also arises a new source of interest, of a kind very superior to
that which mere physical relations can ever inspire.

10. The purposes to which, pursuing the new principle of ar-
rangement, we can perceive the different structures which com-
pose an animal body, are subservient, are termed, in the language
of physiology, the functions of those parts. Life results from
the exercise of these functions, and consists in the continued
accomplishment of their respective objects. The principal object
of physiology, then, is the study of the functions of life ; that is,
the investigation of the changes occurring in the living system
with reference to their respective objects, and in their subser-

2*

18

PHYSIOLOGY.

vience to the maintenance of life, and the various purposes for
which Hfe was bestowed. We shall now proceed to take a
general review of these functions, in order to establish a founda-
tion for the divisions of (he science we are now treating.

11. The most cursory view that we can take of the phenomena
of life will be sufficient to show that the functions to which they
are referable are of different degrees of importance with relation
to the objects of life. Some are so closely connected with these
objects, that their continued exercise is indispensable to the very
existence of life, which would cease if they were for a moment
interrupted. Others, which are less immediately concerned in the
actual maintenance of the vital actions, are yet essential to its
preservation, and cannot, with safety, be suspended but for a
very short interval. Some are only occasionally called into play,
and others are so remotely useful, as to admit of lying dormant
for a considerable period, or even of being dispensed with
altogether. Some functions require for their performance the
concurrence of others, and these, again imply the exercise of
many more. Some are of a more isolated nature, and have less
connexion with the general system of functions. By studying
these relations, we are enabled to trace a certain plan in the
designs of nature, and a certain subordination of functions suffi-,
cient to guide us in our studies, and to enable us to trace out a
tolerably connected order of subjects.

1 2. It will be useful, before proceeding to the details of the subject,
to pi'esent our readers with a general sketch of the system of the
animal economy, which may serve, indeed, the same purpose, as
a map does to a traveller, imparting a general notion of the
bearings and relations of the several objects of interest ih the
country he is about to traverse. We shall for this purpose,
embrace in one view that assemblage of functions which con-
stitutes animal life in its most complete and perfect form, and in
the attainment of its full development.

13. All the functions of the animal economy, all the mechanical
dispositions of the 'system, and all the movements of its parts, are
subordinate to two great objects ; first, the preservation and wel-
fare of the individual being which they compose; and, secondly,
the continuance of the race to which it belongs. It is evident
that the first great purpose to be accomplished is the conferring
of the powers of sensation and perception, these being the essen-
tial attributes of animal nature, and the characteristics which
distinguish it from the mineral or vegetable world. Next to
these is the power of voluntai^y motion, by which the animal is
enabled to change its place, to procure for itself those objects
which are necessary for its subsistence or gratification, and to
repel those which are noxious or painful.

14. The power of being affected by external objects, or of

GENERAL VIEWS. 19

receiving impressions of which we are conscious, is con-
nected, in the more perfect animals, with a part of the body
having a more pecuhar organization, and very remarkable pro-
perties. It is a soft and pulpy substance, of a whitish colour, with
different shades of gray, opaque, and exhibiting slight traces of
a fibrous structure. It is termed medullary or nervous substance.
Of this substance are composed the hrain, which is a large
mass of medullary matter ; and also the nerves, which have the
appearance of white cords, extending from the brain to almost
every other part of the body. The nerves establish a communi- •
cation between these parts and the brain, so that impressions
made upon the former, are communicated, along the nerves, and
by their intermedium, to the brain, where they excite their appro-
priate sensations, corresponding to the nature of the impression,
and to the structure of the organ that originally received it. By
what agency, or in what way affections of the brain, thus in-
duced, are instrumental in producing sensation, or how the sen-
tient principle is connected with the physical constitution of the
brain, are subjects of which we have no knowledge; nor have
we, in our present state, the smallest ground of hope that the
mystery in which it is involved, will ever be dispelled. Sufficient
let it be for us that such is the fact ; and resting on this as an
ultimate fact, let us proceed in our inquiries, as to the occasions
on w^hich this power, assuming it to exist, is called into action.

15. Experience shows that the impressions conveyed by each .
nerve, or class of nerves, are of different kinds, for they are
capable of being readily distinguished from one another by the
percipient being whose brain receives them. Hence he acquires
a knowledge of the presence, of the situation, and of the different
properties of external bodies, which are the source of those im-
pressions. The nature of that power with which the nerves are
endowed is such as to convey the impressions from which this
knowledge is derived, from the external organ to the brain, with
a velocity that exceeds all imagination. This instantaneous
transmission is evidently a provision of the highest importance
both for the welfare and preservation of the individual.

16. The different powers of perception, corresponding to dif-
ferent qualities of external objects, constitute the external senses;
and each has its appropriate organ, furnished with its separate
system of nerves. The skin, which is the organ of touch, receives
the largest share of nerves, as it is evidently of the greatest con-
sequence that the surface of the body should receive impressions
from every substance with which it may happen to come in
contact. The nerves, of the skin are also susceptible of various
impressions, besides those of mere impulse or resistance from
solid bodies. They are affected, for instance, by variations of
temperature ; and when acted upon in any way that may be inju-

20 PHYSIOLOGY.

rious to the part impressed, or to the system generally, they give
suitable warning to the individual, by exciting a sense of pain.
Hence he is admonished of impending evil, and is incited to the
prompt adoption of the means of averting it.

17. Next in importance to the sense of touch are those of sight
and oi hearing ; but for the communication of distinct impres-
sions relating to these senses, a much more refined apparatus is
requisite than for that of touch. The structure of the eye is
calculated to combine, upon a thin expansion of nervous sub-
stance, the retina, the rays of light proceeding from distant
objects, so as to form a picture of these objects, and thus convey
to the mind an exact knowledge of the relative situation of all
their parts that are within the sphere of vision. Hence are
derived the perceptions of their distance and position with respect
to the observer.

18. In like manner are the sonorous undulations of the air col-
lected into a kind of focus by the structure of the ear, and im-
pressed upon the sensitive expansions of nervous matter in the
inner regions of the organ. Thus an important avenue of com-
munication is opened with the external world, highly useful in an
infinite variety of ways.

19. The existence and properties of various objects at a dis-
tance are also recognized by the sense of Smell, which enables
us to appreciate the presence of the subtle effluvia which they
emit, and which affect thie atmosphere often to a considerable
distance around. The olfactory nerves are adapted to the im-
pressions of this kind, and are situate on the surface of those
passages destined for the transmission of the air in subservience
to another function hereafter to be noticed, namely, that of respir-
^ation.

20. The sense of Taste is exercised on ' the substances em-
ployed as aliment, and has its' seat at the entrance of the passages
appropriated to the reception of food, and which are subservient
to another class of functions presently to be described.

21. The faculty of Sensation consists merely in the excitation
of a simple mental change, known to every one, although inca-
pable, in consequence of this very character of simplicity, of
either analysis or definition- With reference to its physiology,
we know that it is efiected through the intermedium of certain
nerves, connected, on the one hand^ with the organs on which
impressions of various kinds are made by the physical action of
external objects, and on the other, with those parts of the brain,
of which the physical affections are, by some inscrutable link,
connected with the affections of the soul, or sentient principle.
These simple and preliminary phenomena, composed of both
physical and mental changes, are to be carefully distinguished
from those subsequent operations that constitute perception.

GENERAL VIEWS. 21

thoug"ht, volition, and the whole series of psychical phenomena,
which v^'e are in the habit of referring to a distinct branch of
human knowledge, and which is generally denominated Meta-
physics, Psychology, or the Philosophy of Mind ; in contradis-
tinction to Physics, Somatology, or the Philosophy of Matter.

2iJ. There can be little doubt that these operations, which we
are naturally accustomed to consider as being purely of a mental
character, are, in some unknown degree, connected with physical
changes taking place in the cerebral substance ; but as we are
utterly unconscious of these changes, and as we are totally pre-
cluded from arriving at any knowledge of their nature, or even
of conceiving the manner in which a connexion between mind
and matter has been established, we are compelled, in this branch
of the inquiry, to direct our attention exclusively to the mental
phenomena, to study their laws by the evidence of our own con-
sciousness, and to resort to processes of analysis and methods of
inductive investigation, in many respects different from those
which are successfully employed in the more arable fields of
physical science.

Whenever w'e are fortunate enough to trace some portions of
the mysterious but broken thread which unites the material
changes occurring in our bodily organs, with the operations of
the intellect, or the affections of the soul, we may then occasion-
ally re-enter the territory of Physiology ; and while the two
sciences are thus capable of being studied in conjunction, they
will derive mutual advantage and illumination.

23. Yet, with regard to the mere physiological study of the
animal functions, it cannot escape our observation, that a vast
variety of phenomena in the economy have a direct reference to
the mental constitution of our nature, and are to be studied, with
relation to final causes, in immediate connexion with these
objects. Thus, although the special purposes served by the mul-
tiplicity, the curious arrangement, and intricate structure of the
parts of the brain, are as yet wholly unknown, and we still are,
and shall probably ever remain, in utter darkness as to the mode
in which they perform their respective ofiices as instruments of
perception, thought, and volition, yet when we return to the
observation of the bodily actions consequent on these mental pro-
cesses, as well as contributing to their performance, we are ena-
bled to resume our physiological inquiries, and trace the con-
tinuity of design in the exercise of the faculties of voluntary
motion, by which the mind exerts a power of reacting on matter,
employs its properties for beneficial ends, and exercises that par-
tial dominion over nature, which has been granted to it Ijy the
Divine Author of its being. The possession of voluntary motion
is directed, first, to enlarge the sphere of our perceptions, by
directing our organs of sense to their respective objects ; secondly.

22 PHYSIOLOGY.

to bring the objects themselves within the reach of chose organs
by which they are to be exannined ; thirdly, to alter their forms
and combinations, and modify them in various ways, so that the
mind may, from these different modes of examination, derive
accurate and extensive information of their properties, and apply
these properties to use; and lastly, to effect the locomotion of
the whole body, and thus extend widely the range of its opera-
tions, and spread the dominion of man over every kingdom of
nature, and over every region of the globe.

24. But the relations of man with the external world compre-
hend a much larger and more important field, since they are not
limited to the sphere of the material world, but embrace the in-
tellectual and moral existence of other percipient and sentient
beings. Through the intermedium of signs, the results of move-
ments of our bodily organs acting on the senses, communications
are established, not merely between mind and matter, but be-
tween mind and mind. Mutual interchanges take place, of
thoughts, of opinions, of feelings, and of affections ; and the value
of existence is, to an incalculable degree, augmented by the
operations of sympathy, the impulse of benevolence, and all the
potent and benign influences of social^ union. Hence, physiolo-
gically considered, the function of the voice, and its modulation
into articulate sounds, ranks as an important part of the animal
economy.

25. The faculty of Voluntary Motion, like that of Sensation,
is derived from the peculiar properties of the nervous substance.
In the instance of sensation impressions are conveyed by means
of the nerves from the external organs of sense to the general
centre of the sensitive faculty, the brain. A similar power, we
find, is exercised, though in a contrary direction, in transmitting
the actions arising from the determinations of Volition, and which
produce the first effects on the brain, towards those parts which
are capable of executing these determinations. Modern discove-
ries have shown, that for this latter purpose sets c)f nervous
fibres are employed different from those instrumental in convey-
ing sensitive impressions from the organ of sense to the brain.
Hence a distinction is established between the Nerves of Sensa-
tion, and the nerves of motion, or the Motor Nerves.^ While the
nerves of sensation should properly be considered as commencing
at the organs of sense, and terminating in the brain, the nerves
subservient to volition have their proper origin in the brain, and
proceed thence to the organs of motion. Let us next examine
in what these organs of motion consist.

* We would suggest the propriety of designating these two classes of
nerves respectively, by the terms Sensiferous and Voluntiferous, as more dis-
tinctly expressing their proper functions.

GENERAL VIEWS. 23

26. The principal source of motion, in the animal body, resides
in the Muscles^ which taken altogether, usually compose by far
the largest part of the bulk of the animal. Muscles consist of a
collection of fleshy fibres, proceeding for the most part in parallel
directions, and extending from the two points in the limb, or
parts of the body, which are designed to be brought nenrer to
each other. The fibres of which the muscles are composed are
endowed with the remarkable property of contracting, under
certain circumstances, with prodigious power, so as to move the
parts to which they are attached with sudden and enormous
force. The impulse given to them by the nerves of volition, by
which they are connected with the brain, in every effort of
volition, excites them to contraction, antl produces those move-
ments of the body which are the objects of that volition.

27. The movements required for the purposes of animal life,
are of course infinitely diversified in their kind, and scarcely
admit of any distinct classification. Amongst the objects of
these movements, however, we may notice two, which are of
essential importance; the first is that of Locomotion, the second
that of Prehension.

28. Locomotion is one of the faculties more particularly dis-
tinctive of animal life in opposition to that of the vegetable.
Plants are more or less rooted to the soil where they originally
sprung: animals, destined to a wider sphere of action, are en-
dowed wiih the power of transporting their bodies from place to
place, on the one hand, of pursuing, and on the other, of flying
from pursuit; of choosing their habitations, or of changing re-
gions and climes according to their wants or necessities. •

29. The power of detaining and laying hold of olijects, is
another mode in which the faculty of voluntary motion may be
highly advantageous to the animal possessing it. With these
may be associated the various actions requisite for defence or
attack, rendered necessary by the conflicts incident to their
condition.

30. For the performance of all these actions, there is required,
in the first place, a solid and unyielding structure, capable of
sustaining the weight of the body, and of furnishing to the mus-
cles or agents of motion, fixed points of attachment. The hones,
the union of which constitutes the skeleton, are pr^ided for
these objects. They are formed into separate pieces^ with a
view to their being moveable upon one another. Their extre-
mities are connected together by smooth surfaces, which are
bound together by firm bands or ligaments, bracing them on the
sides where they are exposed to the greatest strain. An appa-
ratus of this kind constitutes ^ joint.

31. The due performance of these mechanical objects, implies
a variety of subsidiary contrivances and adjustments, too diver-

24 PHTSIOLOGr.

sified in their nature and objects to admit of particular specifica-
tion. It is evident that the particular texture of each part must
be adapted to the action it has to perform. Flexibihty and com-
pressibiUty are required in one organ ; rigidity and hardness in
another. Some parts must readily yield to an extending force,
others must resist such a force with extraordinary tenacity.
Some must exert elastic power, others must be devoid of this
quality. Some textures must be permeable to fluids, others must
deny them all transmission. Hence, the variety of structures
composing the mechanical frame-work of the system.

32. But in all the variations of conformation, it would appear
that nature has employed the same ultimate structure as the^
basis of her work. All the soHd parts of the animal fabric are
formed of fibres, variously united and interwoven ; in some cases
only loosely connected, so as to constitute a spongy or cellular
mass, flexible in every direction, and forming a medium of con-
nexion between adjacent parts of various degrees of cohesion.
This substance, which is found universally to pervade the body,
is termed the cellular substance or texture. It is eminently en-
dowed with elasticity, and thus contributes essentially to preserve
the natural figure of every organ, and to restore it to its proper
situation, after any displacement by a foreign cause.

33. When condensed into a firmer layer or sheet of animal
matter, the same substance assumes the form of Jiiemhrane, and
is extensively employed as such, to supply organs with external
coverings, or to afibrd them attachments to surrounding parts for
the purpose of protection and support. Membranes are also
used as barriers, for intercepting the communication of fluid from
one cavity to another; and they are also employed to form
receptacles for the retention of fluids, arid tubes for conveying
them from one part of the system to another.

34. The fibrous structures, comprehending ligaments, tendons,
fascice, are composed of a still denser approximation of fibres,
are endowed with a higher degree of toughness and strength,
and are capable of exerting great resistance to any stretching
force. Hence, they are extensively employed in the construction
of parts where these properties are required.

35. The organs specially appropriated to touch, are generally
also thoi^ of prehension : and progressive motion is accom-
plished by means of limbs, which act either upon the ground, the
waters, or the air, according to the element in which the animal

' resides. 'But, in order to give proper effect to these movements,
the agency of levers is required; and we accordingly find a pro-
vision made for this purpose in the construction of the bones,
which, as we have before observed, are capable of supplying the
fulcra or fixed centres of motion, and allow of the application of
the moving powers. It often happens that the actual attachment

GENERAL VIEWS. 25

of muscles to the point required to be moved, would be attended
with inconvenience. In this case, an intermediate structure is
employed, analagous to that of a ligament, but here denominated
a tendon, serving as a strap to connect the muscle to a distant
bone, or other part on which the action of the muscle is to be
exerted.

30. All the functions, which have for their object some mechan-
ical effort of the kind we have now described, may be compre-
hended under the general head of the mechanical functions.

37. The consideration of the chemical condition of the animal
system, introduces us to a class of functions of a totally different
nature from any of the preceding, yet equally essential to the
maintenance of life. The solids and fluids of which organized
structures are composed, differ materially in their chemical con-
stitution from the products of the mineral kingdom. Their
elements are combined by a much more complicated arrange-
ment, and united by less powerful affinities ; or rather the balance
of affinities, by which they are held together, is more easily
destroyed, and thus, proneness to decomposition is constantly
present. One of the most remarkable and important of the
operations of the vital functions, is to repress this tendency to
decomposition ; for no sooner is life extinct, than we find both the
solids and fluids of the body hastening to assume new forms and
combinations of their elements ; and nothing can now prevent the
final disorganization of that fabric which so lately delighted the
eye with its beauty, and in which dwelt the genial warmth of
fife, and the elastic vigor of youth. If we watch the progress of
those dangers which take place in the body, we shall find it
characterised by a perpetual renovation of materials, continual
losses of substance on the one part, being compensated by an
equally constant supply on the other. From an atom of imper-
ceptible minuteness we trace its gradual increase of size, by the
reception of nutritious matter from without, by the incorporation
of this matter with that which had before existed, by the conso-
lidation of the fluid, by th^ extension of the solid parts. We see
all the organs expanding by a slow, but uniform increase, and in
regular proportion, till they arrive at a certain limit. Having
attained this limit, the body remains stationary for a certain
period ; that is, the waste of substance is exactly compensated by
the supplies furnished by the food received into the body. At
length, however, the compensation is less perfectly maintained ;
the powers which carry on the functions begin to decline, the
solids dry up and harden, and a general torpor gradually pervades
the system. Life is sooner or later brought to a close by the
natural progress of these changes, even if its course be not sooner
arrested by causes of an accidental nature.

38. The functions of nutrition embrace a class of operations,

3

26 ' PHYSIOLOGY.

destined to supply the materials wanted for the growth of the
body, and for the supply of those materials which either may
have been expended in the natural exercise of the other functions,
or lost in various ways, or else employed in the reparation of
injuries, which the organs may have accidentally sustained. The
nutritive, or as they may also be termed the chemical functions,
since they relate to the chemical condition of the body, compre-
hend a long series of processes, which, in order to be studied
successfully, require many successive subdivisions.

The first division includes all those functions which contribute
to the reduction of the food to a substance of similar chemical
composition with the materials of which the body already con-
sists ; pi'ocesses which are comprehended under the general term
of Assimilation.

The second and third divisions relate to the collection of the
nutriment thus prepared, or assimilated, into a general reservoir;
and its subsequent distribution throughout the body, so as to
admit of being applied to use whenever it may be wanted. These
objects are attained by the functions of Absorption and of Circu-
lation.

A fourth division refers to the purification of the general mass
of nutritious fluid existing in the great reservoir of the body, by
the separation of its superfluous combustible portion, and more
especially of its carbon ; a change which is effected by the func-
tion of Respiration.

The last division of this class of functions comprehends the
several processes by which certain materials are separated from
the blood in a solid or fluid form ; some wdth a view to their
final expulsion from the system, some to answer purposes con-
nected with other functions, and the remaining part being
expended in repairing the waste which the solids of the body
undergo in the exercise of their respective offices. To the former
of these functions the term Secretion is applied: whilst the last
is more especially regarded as the proper and final process of
Nutrition,, We shall examine each of these divisions more par-
ticularly.

39. Assimilation is effected by a long series of processes, which
are partly of a mechanical and partly of a chemical nature. The
food taken into the mouth is first masticated by the action of the
teeth and jaws, so as to break down the cohesion of its parts, and
prepare it for the chemical action of the fluids to which it is after-
wards to be subjected. There is at the same time added to it a
quantity of liquid, termed the saliva, prepared by a set of glands,
to be hereafter specified, and poured out into the mouth in large
quantities during the act of mastication. By these means the
food is softened in its texture, and reduced to the form of a pulp,
in which state it is swallowed, by the organs of deglutition, and

GENERAL VIEWS.^ 27

conveyed through a tube called the cesophagus into the stomach.
The stomach is a capacious bag, or receptacle, capable of holding
a considerable quantity of food, and of retaining it for a certain
period. The inner niembrane which lines the cavity of the
stomach prepares a fluid termed the gastric juice, w^hich acts
chemically upon the food in that cavity, while this food is at the
same time subjected to a degree of pressure from the action of a
set of muscular fibres which are interposed between the interior
and exterior coats of the stomach. The food is also slowly
moved by the successive contractions of these muscles, so that
every part of it comes in its turn to be acted upon by the gastric
juice, until the whole is converted into a soft and smooth mass of
uniform consistence which is termed chij?ne ; the operation itself
by which this conversion is effected being termed digestion.

40. The aliment thus digested, or reduced to the state of chyme,
passes onwards from an orifice at the farther end of the stomach
into a tube of great length, several^ portions of which have received
different names, but which are comprised under the general term
of the intestines. In the first portion, the duodenum, the aliment
undergoes still further changes ; it is mixed with two fluids, the
one called the bile, which is prepared by a large glandular organ,
termed the liver ; and the other called i\\Q pancreatic juice, pre-
pared by another gland, the pa7icreas. Secretions also take
place from the inner membrane of the intestines themselves, and
the result of the united action of all these fluids, aided by the
movements imparted to the aliment by the contractions of the
muscular fibres contained in the coats of the intestines, is gradu-
ally to convert part of what was chyme into a new substance
called chyle, which is the most nutritious portion of the aliment,
and has the appearance of a milky fluid. The chyle is received
into a set of very minute tubes called lacteals, which are ex-
ceedingly numerous, and arise by open mouths from the inner
surface of the duodpnum and its prolongations, the jejunum and
ileum. They collect the chyle together, and pour it into an
intermediate receptacle, whence it is conveyed along a large tube
called the thoracic duct, into other cavities, of which we shall
presently speak. That portion of the chyme which is not con-
verted hito chyle, descends into the lower portions of the intestinal
canal, is collected in the larger intestines, of which the colon is
the principal one, and is finally 6jected from the body.
, 41. The next step in the assimilatory process is the conversion
of the chyle into blood, a change which has been termed sangui-
fication. It is in the great system of vessels which contained
the blood already formed, and in the course of the passages through
which the blood is moved, that this gradual change is effected.
The great reservoir of this important fluid, on which the nutri-
tion of every part of the body, and its maintenance in a state of

28 PHYSIOLOGY.

action, immediately depend, is the heart. The thoracic duct
opens into one of the veins or tubes leading directly to the heart ;
the chyle is therefore immediately conducted into this reservoir,
and thoroughly mixed with the general mass of food.

42. The heart is a powerful muscular organ ; from its cavity
arise the trunks of large tubes, called arteries, which subdivide
and ramify as they proceed in their course to every part of the
body, being distributed in abundance to every organ, with a very
few exceptions. No sooner are the cavities of the heart distended
with blood, than the muscular structure which surrounds their
cavities contracts with enormous force, and propels their fluid
contents through the system of arteries, sending it in one great
wave, even to the extremities of its minutest ramifications. From
these extremities of the arteries it passes into corresponding
branches of another set of vessels, the veins, which proceed in
the opposite direction, towards the heart, uniting in their course
into larger and larger trunks, till they reach the heart, to which
they deliver back the portion of blood that has thus percolated
through every part of the body. No sooner has it again filled
the cavities of the heart, than it is again sent with renewed force
into the same arterial channels, and again brought back by the
veins. The functions by which this circular course is given to
the blood, is termed the circulation.

43. The blood, in the course of its circulation, furnishes to all
the organs the materials which are necessary for their growth,
for the renovation of their powers, and for the supply of those
iiuids and other animal products which are wanted in various
parts of the economy. The separation of these fluids, and the
formation of these peculiar animal products, are the objects of
another function, that of secretion. Particular organs are in
most cases provided for the purpose of eflfecting these processes.
These^are the glands, which are variously constructed, according
to the particular offices they have to perform ; each is furnished
with an elaborate apparatus pf vessels ; and the fluid which is
formed by them, is generally conducted to its place of destination
by a pipe, or excretor^y duct, as it is termed.

44. The fluids which are thus separated from the blood are,
for the most part,' applied to useful purposes in different parts of
the economy; some for the repair of that loss of substance in
the part of the body incident to the exercise of their respective
functions, others for different subsidiary purposes related to those
functions. The substance of the bones, for example, undergoes
a gradual change during the whole of life ; each particle is re-
moved in succession and is replaced by others, so that iii the
course of time the whole substance of the body undergoes reno-
vation. Two important functions are called into action for the
completion of these processes ; the first of these is concerned in

GENERAL VIEWS.

d9

the removal of the old and decayed materials ; the second in the
due application of those which are to replace them.

45. The removal of those particles which have become useless,
and W'hose presence might be injurious, is effected by a distinct
set of vessels, called lymphatics. The lymphatics are met with
in almost every part of the body ; and resemble, both in structure
and mode of distribution, the lacteal vessels already described.
The mode of their origin is not well ascertained, but, like the
lacteals, the smaller branches successively unite into trunks,
which terminate either in the thoracic duct, or into the larger
veins leading directly to the heart. Through these channels,
then, it is that all the particles which require removal are con-
veyed away, and deposited in the general mass of circulating
fluids. The function thus performed by the lymphatics in com-
mon with the lacteals, is termed absorption.*

46. The function having for its object the reparation of the
substance of the different organs, is designated by the general
name Nutrition. It includes the development and growth of
the parts, and their maintenance in the healthy state, — that is,
the state in which they are fitted for the exercise of their several
functions ; as well as the restoration of what they may have lost
from accidental causes, such as mechanical injuries.

When a bone is broken, for instance, a solid union is by de-
grees effected by the deposit of new ossific materials, consisting
chiefly of phosphate of lime, which is secreted or separated from
the blood by the irritated vessels in the neighbourhood of the
injury. In all these cases, the absorbents are also at work in
modelling the shape of the part to be restored, in removing all
roughnesses or angular projections, and making room for the
new formations which are to take place. The functions of ab-
sorption and nutrition are thus, in some respects, opposed to each
other, producing contrary effects, though both co-operating in
the accomplishment of one final purpose, and balanced and ad-
justed to one another with that manifest intention. The general
bulk of the body, and of its parts, varies according to the predo-
minance of the one or the other of these actions of absorption
and nutrition; wasting when the former is in excess; thriving
and enlarging when the latter prevails.

47. There is one peculiar mode in which superabundant nutri-
tion manifests itself When the supply of nutriment is greater
than what the wants of the system require, the superfluous por-
tion is converted into an oily fluid, which is laid up in store for
future use. The fluid is the/<2^ ; and it is accumulated in various

* [Absorption is not, however, effected exclusively by the lymphatics. It
will be seen, hereafter (549), that when substances possess the necessary
tenuity, they readily pass through the parietes of the veins under favourable
circumstances, and enter the circulation.]

'A*

30 PHYSIOLOGY.

parts of the body, and especially between the skin and the mus-
cles, and in other places, where it may also serve a subsidiary
purpose of mechanical protection against inequalities of pressure.
The fat is thus useful as a soft cushion on which deUcate organs,
such as the eye, may move in security ;, and also as a convenient
material for filling up hollows in various unoccupied situations.
The chief use, however, of large accumulations of fat, is to serve
as a magazine ,pf nutriment, out of which the body may be sup-
ported in those seasons when the supply of food is deficient, and
more particularly du)i-ing those periods which are, by some ani-
mals, passed in a state of complete inactivity. This is the case
in those animals which are said to hyhernate, or continue during
the whole of winter in a perfectly torpid state.

48. Whilst some of the products of secretion are thus employed
in nutrition, others are subservient to the functions of particular
organs. Thus, the tears are useful in washing away from the
surface of the eye, dust, and other materials which might obstruct
vision ; the gastric juice is subservient to digestion ; and the
mucilaginous secretion of the wind-pipe and nostrils defend those
passages from the acrimony of the air. But, in other, cases, the
secreted matters have noxious qualities ; and it is the object of
their separation from the blood, to get rid of them altogether.
This is the case with the secretions from the kidneys, and from
the skin, and perhaps, also, partly with that from the liver.
These are termed the excretions, in contradistinction to the pro-
per secretions, and the organs which separate them are termed
the emunctories.

49. The organs which, in this sense of the term, must be con-
sidered as the principal emunctory of the body are the lungs. It
would appear that the blood, from which the animal solids and
fluids derive their nourishment, contains a larger proportion of
carbon than what is required for the formation and reparation of
these soHds and flyids ; the elements abstracted from the blood
by the process of secretion and nutrition, being principally oxy-
gen, hydrogen, and nitrogen. \

The continuance of these processes must tend, therefore, to
produce an accumulation of carbon in the blood ; and accord-
ingly we find. that this fluid, in the course of its circulation, gra-
dually acquires a darker colour. From being of a vivid scarlet
hue in the trunks of the arteries, it has changed to a dark purple
by the time it has reached the veins. It is returned to the heart,
therefore, in a state unfit for the purposes of nutrition, and not
proper to be again circulated through the vessels of the body.
In order to restore it to its original state, it is necessary to de-
prive it of the ingredient it contains in excess, that is, of carbon,
which, when thus present in the blood, is found to exert a posi-
tively deleterious power on the parts to which it is applied.

GENERAL VIEWS. 31

For this purpose the blood is transmitted by an appropriate
system of arteries, to the lungs, where it is exposed to the influ-
ence of atmospheric air, alternately received into, and expelled
•from that organ. By a process which appears to be analogous
to slow combustion, the superfluous carbon of the blood combines
with the oxygen of the atmospheric air, and is expelled, in the
form of carbonic acid gas, along with the air expired. The blood
thus purified, and restored to its salutary qualities, is conducted
back again, by a corresponding set of veins, to the heart, and is
again sent, by the contractions of that organ, into the arteries of,
the body, and performs the same round of circulation as before.
Respiration, which is the title of the function we have now been
describing, completes this class, which we have termed the che-
mical functions of the economy.

50. The three classes of functions we have been reviewing,
namely, the mechanical, the chemical, and the sensitive, relate
only to the preservation and welfare of the individual. But as
nature has assigned a limit to the duration of Hfe, it became ne-
cessary that a provision should be made for the multiplication of
individuals, and the conservation of the race. Such, then, is the
object of a fourth class of functions, namely the reproductive
functions, including the process oi fecundation, of evolution, of
gestation, and of parturition, and the auxiliary function of
lactation, provided for the supply of the new-born infant with
nourishment adapted to the tender condition of its organs of
assimilation.

51. Having studied the phenomena and the circumstances
which lay the foundations of individual existence, the physiologist
has next to occupy himself with the consideration of the long
series of changes which intervene between the cradle and the
grave, and constitute the " strange eventful history" of the phy-
sical life of man. He follows the rise and development of the
several organs, and the occasions on which their functions are
called forth : he notices their entry on the stage of life, in which
they are destined to play more or less important parts; he
watches their progress, maturity, and decay, till they finally
disappear from the scene, when their functions have successively
declinfed, and passed away, the vital spark becomes extinguished,
and the curtain drops on the fleeting drama of our probationary
existence. A multitude of interesting subjects press on his atten-
tion in tjiis division of his subject, so replete with wonder, and
so calculated to impress us with exalted ideas of divine presci-
ence, and of the unbounded resources of creative power.

To this department of physiology properly belong, first, the
history of the changes which take place in the organs, during
their natural course of development, in what has been styled
their normal condition, such as the formation of the vital organs,

32 PHYSIOLOGT.

the process of ossification, the general growth of the body, the
changes occurring at the period of puberty, the slow but sure
progress of consolidation attending the decline of life, and the
successive decay and obliteration of the faculties which precede
death ; and, secondly, the study of phenomena exhibiting the
operation of those powers of repair and renovation, which exist
in the constitution, and which are called forth only on certain
occasions, when the organization has been injured or destroyed,
or when the functions have been deranged or suspended, by
various accidental causes.

52. These topics introduce to our notice the varieties which
are observable in different classes of individuals in the general
mode in which the functions are performed with reference to
their balance, or relative preponderance : conditions which con-
stitute the different temperaments, as they are called, and which
are severally characterised by peculiar external indications.

53. Physiology, lastly, comprehends within the scope of its
inquiries, those more strongly marked diversities that are met
with in the inhabitants of different regions of the globe, and
which appear to form separate races of mankind. These con-
stitutional peculiarities, as shown by diffei-ences both in external
conformation, and in the internal endowments of an intellectual
and moral nature, are of so distinct and permanent a character,
as to have suggested the hypothesis;, of their indicating, in a
zoological sense, not merely varieties of a single species, but
several different species of the genus Man.

54. The present treatise is intended to exhibit a condensed
viqw of the actual state of our knowledge on all the subjects com-
prised in the above outline, and to conclude with a review of the
progressive history of the science from the earliest periods to the
present time.

55. It is hardly necessary to remark, that the province of
Physiology, is restricted to the consideration of the phenomena
of the living body in its perfectly normal or healthy state: while
those which are presented when these hmits of healthy action
are passed, and when the abnormal, or diseased state commences,
are the subjects of another branch of science, denominated Pa-
thology, no less interesting and important than the former, as
furnishing the principles by which the art of medicine derives all
its powers; but which, it must be obvious, must have its founda-
tions laid in an extensive and correct knowledge oi physiology.

56. It is evident that the foundation of all physiological know-
ledge must be laid in a thorough acquaintance with the structure
or internal mechanism of animals. The study of anatomy,
indeed, derives its chief interest from its connexion with physi-
ology ; for unless viewed with reference to their uses or sub-
serviency to particular purposes, the examination of the forms

GENERAL VIEWS. , 33

and properties of the parts of a machine would be a barren and
an irksome task. Let us imagine, for example, a person, who
had never seen a ship, and had no idea of the object for which it
is intended, to visit it for the first time, and to be at liberty to
examine at his leisure every part of its rigging and internal con-
struction. A restless curiosity might indeed lead him to handle
the ropes and blocks, and climb upon every mast ; to descend
between the decks, and minutely inspect every part of its fabric ;
to explore, in a word, the whole anatomy of this most stupendous
product of human ingenuity. But his labour would avail him
nothing. The most complete survey would afford him no
instruction, or leave any distinct impression as long as he had no
principle to connect them in his mind. But let him review the
same objects with an experienced guide, instructing him, as he
proceeds, on the general purposes of the whole machine, and the
particular uses of every part, as well as on the mode in which
they operate and concur in the production of the intended effect.
Then it is that he will feel a real interest in the examination :
then it is that he will attach due importance to each part of the
inquiry. Perceiving the relations which connect the objects, and
understanding the functions of the- several instruments he sees, he
is no longer perplexed and bewildered ; individual facts arrange
themselves in a natural order, and the whole forms in his mind
one connected system of knowledge, readily retained and easily
communicated.

The case is perfectly similar with regard to the body of an
animal, of which anatomy lays open to us the structure. Dissec-
tion can only show us that it consists of various parts, some
hard, some soft, and others fiuid. The harder parts, such as the
bones, are of various forms, perforated by numerous apertures,
and joined together in different ways. The soft parts are found
to be composed of various kinds of textures, of which the ele-
ments appear to be collections of fibres or plates, curiously dis-
posed and interwoven, so as to constitute a cellular or spongy
tissue, and, occasionally, more extended layers of membrane.
In every part we find innumerable tubes and passages branching
out, and again uniting, in an infinite variety of ways. We arrive
at cavities of different forms and extent, enclosing organs of
various 'descriptions, or containing fluids which pass through
appropriate channels of communication to very distant parts ;
composing altogether a vast and complicated system of mechani-
cal and hydraulic apparatus. Thus,, whilst we confine our atten-
tion to the mere anatomy, all is perplexity and confusion ; we
are overwhelmed by the multiplicity of objects, and lost in the
immense, mass of unconnected detail. But no sooner do we study
the parts of the animal frame with reference to their uses, and
their subserviency to the several functions of the living body,

34 PHYSIOLOGY. ,

than the whole appears under a new aspect. Aided by the Hght
of physiology, we trace order and connexion in every part, and
gather increasing delight and instruction as we proceed. The
requisite adaptation of the organs to their respective offices, and
the correspondence established between these offices, by which
they concur in the same ultimate object, must ever excite our
most profound admiration, and exalt our ideas of that infinite
intelligence which planned, and that transcendent power and
beneficence which executed the vast and magnificent system of
creation.

CHAPTER II.

APPLICATIONS OF PHYSIOLOGY.

57. Physiology claims our attention, not merely as an orna-
mental branch of speculative knowledge, but as a science of
immediate and vast practical utility. Numerous are the occa-
sions on which a scientific knowledge of the structure of our own
bodies, and of the operations that are carried on within us, is
highly valuable to its possessor ; and more especially if combined
with the more enlarged views derived from the study of compa-
rative physiology. It may be useful here to point out some of
the most important appUcations of physiological knowledge.

58. It is scarcely necessary to dwell on the utihty of know-
ledge of anatomy, enlightened by physiology, in its application to
the art of medicine; for the very foundations of that art must be
laid by these sciences. It is, however, proper to advert to the
limited advantage which would accrue from such application if
those sciences were confined to the human structure and the
human functions, instead of comprehending within its range the
whole of the animal creation. All the important discoveries of
modern times with regard to the economy of the human body
have been derived from observations made on the lower animals.
That of the circulation of the blood, for instance, which has im-
mortalized the name of Harvey, was obtained principally from
this source. John Hunter, one of the greatest benefactors to the
healing art in modern times, was so deeply impressed with the
necessity of an extended study of comparative physiology, that
he devoted his whole life to its cultivation, with an ardour and
a perseverance that have been rarely equalled, and never sur-
passed; as is attested by the unrivalled museum of preparations
in every department of comparative anatomy, which he formed

APPLICATION TO ZOOLOGr. 35

by his own unaided exertions, and which will ever remain an
imperishable monument to his fame.

59. The various combinations of faculties, which are met with
in the different tribes of animals, exhibit in a most striking man-
ner the mutual dependence and relations of the animal and vital
functions. As if with the express intention of assisting us in our
physiological researches on the attributes of that vitality which
eludes our experimental investigations, nature offers to our view,
in the diversified structures of each successive order of animals,
a series, as it were, of varied experiments ; and exhibits the
several organs under every degree of simphcity and complication
of structures, and every possible mode of combination. The
application of all this knowledge comes home to our own bosoms ;
for the human race is then viewed as composing a member of
the great family of nature: and we ourselves, as well as all the
individuals of that race, are placed under the governance of those
general laws which regulate all animated beings. Our deepest
interests, our future comforts and enjoyments, our powers of
action, our intellectual existence, our capacities of feeling and of
reasoning, all that renders life desirable, nay, that very life itself,
are wholly dependent on the operation of those laws, and on the .
minutest results produced by their varied combinations. In a
word, we ourselves are animals, and nothing that relates ever so
remotely to animal life can be to us a matter of indifference.

60. Although researches into comparative physiology neces-
sarily imply a knowledge of the forms and history of the different
races of animals, it tends to reffect, in its turn, the most important
light on the science of zoology; and more especially on that de-
partment which relates to the classification of animals. All
scientific knowledge must be founded on correct classification;
but in zoology a methodical arrangement is indispensable ; for
scarcely any progress could be made without it. The number
of animals in the habitable globe is immense, while our faculties
and means of observation are extremely limited. Of insects
alone, the number of distinct species, which have been already
determined, considerably exceeds one hundred thousand. Of the
other classes of animals, though less numerous, the catalogue of
known species is af least half as great. Each of these races of
beings has its distinct and characteristic form, its peculiar orga-
nization, habits, and faculties. It is obvious that if, at the outset
of our inquiries, we were to attempt describing, or even taking
an inventory of all the living objects that presented themselves
to our notice without regard to any principle of order, our atten-
tion would soon be distracted, and our memory overwhelmed by
the confused accumulation of details ; and it would not be possi-
ble to deduce from them any useful result. Classification affords
the only clue, which can extricate us from this intellectual laby-

36 PHYSIOLOGY.

rinth, which can resolve this state of chaos, and reduce this
crude and indigested mass of materials into the form of regular
science. It is only by a methodical arrangement of objects that
we can arrive at the perception of the more extended relations
which subsist among them, or establish general propositions, em-
bracing a multitude of subordinate facts, and capable of an inde-
finite number of useful applications.

61. In framing a system of classification of the animal king-
dom, there are two objects which we have in view ; first, that of
being able readily to ascertain the name of any animal which
may present itself to our notice, and of recognising its identity
with a species already known and described ; or, secondly, that
of becoming acquainted with the general nature and character
of the animal in question ; with the affinities which it has with
others of the same class, and with the rank which it holds in the
scale of animation. The first of these objects is attained by what
are called artificial methods of classification ; the second by
what are called natural methods. Much error and confusion
have prevailed in the reasonings of naturalists from their ne-
glecting to discriminate the respective objects of these two
kinds of methods, which nevertheless are perfectly distinct from
each other.

62. In endeavouring to accomplish the first of these objects,
we take, as it were, an inventory of nature, we record all her
productions, and follow her in all her variations ; we collect the
fullest and most faithful description of every known species, and
assign to each a particular name.

The end we have in view being simply to devise a ready me-
thod of identifying animals, we follow a process of this kind.
We first unite those species which are most nearly allied to each
other into one genus. We observe, for example, several species
which have much resemblance to the stag ; such as the rein-
deer, the elk, the roebuck, the fallow-deer,'the axis, the muntjac,
and several others : we assemble all these into one genus, which
we call the deer kind. By a similar process we form another
genus of animals resembling the bull ; such as the buffalo, &c.
The genus antelope will, in like manner, comprehend the gazelle,
the chamois, the nylghau, the oryx, the saiga, the gnu, and a
multitude of others. In the same way, the camelopard, the
goat, sheep, camel, and musk, may be regarded as so many
generic terms, each including a number of different animals,
distinct in race, but similar in appearance. Having thus consti-
tuted the genera, we may apply to them the same principle of
generalization that we did to the species ; uniting them, accord-
ing to their simiUtudes, into more comprehensive assemblages.
Thus, the genera above mentioned, having many features of re- '

APPLICATION TO ZOOLOGY. 37

semblance, are considered as composing a tribe or order, to
which Linna3us has given the name />ecora.

63. We may continue this process till we have gone through
the whole animal kingdom; but it will then be necessary to
adopt in some respects a contrary method ; and instead of
ascending as we have done from particulars to generals, to de-
scend from generals to particulars. Reo;ardin2[ the animal kincr-
dom as one entire suoject, we must partition it into provinces,
and again subdivide these into smaller portions. All these divi-
sions and subdivisions must be founded upon distinct variations
of external organs, and must be characterised by concise defini-
tions, enumerating the leading circumstances common to all the
animals they comprehend, and by which they may be contrasted
with those included in the collateral divisions. The great pri-
mary divisions of the animal kingdom are the classes; the
subdivisions of these form the orders; these comprehend the
genera, which again include the separate races t)r species ;
while the ultimate ramifications of the system, expressive merely
of diversities arising in the same race, constitute what are called
varieties. By thus confining our attention to a small number of
essential characters, we are enabled to ascertain, by a sort of
analytical process, the name of any animal that we may wish to
examine or identify. We have converted our rude inventory
into a convenient dictionary of nature, where every object may
be found at its appropriate place. The characters of the classes
resemble in their office the initial letter of a word ; the charac-
ters of the subsequent divisions that of the succeeding letters,
conducting us with certainty and precision to the place we seek.
The full development of this method, and of the logic which
should regulate it, and its successful application to natural his-
tory, we owe to the genius and industry of Linnasus, to whom
the science will ever have to record a lasting obligation.

64. But however perfectly we may have accomplished the
purpose we had in view in these artificial arrangements, it is
impossible not to perceive that we have obtained them by the
sacrifice of that order which nature herself points out. A strict
adherence to any arbitrarily assumed principle of classification,
is, in truth, incompatible with the preservation of the natural
affinities of animals. Thus, in the system of Linn;cus, the order
primates, among the mammalia, presents the incongruous asso-
ciation of man with monkeys, lemurs, and bats. In the order
bellucs, the horse is placed by the side of the hog. The ferce
offer us the unnatural association of the seal, the dog, the bear,
the opossum, the hedgehog, and the mole, merely because these
animals, in most respects totally dissimilar, happen to agree in
having the incisor teeth of a conical shape. The continual
violation of natural analogies, which is yet necessarily incident

4

88 PHYSIOLOGY.

to all artificial systems, has exposed them to much censure and
ridicule, from those who forget that the purpose for which they
are framed, is that of convenient reference, and that it is essential
to arrangements adapted to that end, that they should be arbi-
trary. As well might it be made the subject of complaint, that,
in a dictionary, w^ords having very different m,eanings, are found
placed in juxtaposition.

65. Cuvier has justly remarked that a perfect natural method
should be the expression of the science itself, that is, of its most
general propositions. By assembling animals in groups, accord-
ing to their general resemblances in the more important circum-
stances of their organization and functions, we are enabled to
connect them under one description, and afterwards apply to each
individual species ail the particulars comprised in this description,
and thus we obtain more or less comprehensive statements, or,
as it were, zoological laws, enabling us both to acquire and to
retain the facts wuth greater facility, and to apply them with
readiness in every case ; in a word, it gives us the entire com-
mand of that knowledge, by imparting to it the form of science.
The tribe oi pecora, formerly mentioned, may be taken as an ex-
cellent example of a natural family of animals; for they consist of
species which bear a striking resemblance with another in form,
organization, and manners. If we meet with a new animal hav-
ing one or two of the leading characters of this tribe, we deduce at
once all the most important features of its history. We know, for
instance, from its possessing a double hoof, that it belongs to
this tribe, and consequently that it feeds on herbage, that it has
four stomachs, and that it ruminates its food ; that it belongs to
a species disposed to assemble in flocks or herds, and that it has
a disposition to be domesticated. We may pronounce that its
upper jaw has no incisor teeth, and so forth.

66. It is evident that from the discovery of these analogies, on
which the arrangement into nat-ural families is founded, we must
resort to the aid of comparative physiology. It is this science
alone that can teach us to discriminate the circumstances which
are of real importance in the animal economy, and on which
their very nature and character depend. The immense progress
which has been made in this branch of knowledge, since the
lime of Linnaeus, has enabled us to determine with much greater
precision the relative affinities of animals, and the rank which
each tribe is entitled to hold in the natural system of classifica-
tion.

67. Attempts have often been made to combine these two
methods into one, by a sort of mutual compromise between them ;
that is, by an arrangement partly natural, and partly artificial, to
obtain the principal advantages of both. The most perfect speci-
men of this union of the two methods is that of Dumeril, which

APPLICATION TO ZOOLOGY. ' "39

he has published under the title of Zoologie Analyiique. The
characters on which his divisions are founded are distributed
in a strictly analytical order, and they conduct us to classes
much more natural than those of Linnajus. Thus, he divides the
Linnffian class of insects into two, namely, Crustacea, and insects
properly so called. The very miscellaneous class of vermes, in
which animals very dissimilar in their nature had been thrown
together, as it were in a lumber closet, compose in this system
the more natural assemblages of moUusca, vermes, and zoophytes.
Dumeril has pursued this plan throughout the whole of the ani-
mal kingdom, reducing all the characters which lead to the deter-
mination of classes, orders, families, and genera, to the form of
synoptic tables.

68. The arrangement which makes the nearest approach to a
natural distribution is that adopted by Cuvier in his celebrated
work, entitled Le RSgne Animal Distribid cTaprls son Organi-
zation ; as it is founded chiefly on the structure of the organs most
essential to life, and having most influence in determining the
intelligence, sensibilities, activity, habits, and manners of animals.
Physiology is, in fact, the basis of Cuvier's classification, for it
proceeds on the following principles.

69. The powers of sensation and of voluntary motion being
the chief attributes of animal life, it follows that the organs of
primary importance in the economy are those which are imme-
diately subservient to the performance of these functions. They
are, as we have seen, the organs composing the nervous system ;
and the general form and distribution of the nervous system,
therefore, should lay the foundation of the primary divisions of
the animal kingdom. There appear to be four general types or
models of structure of these organs presented in the animal crea-
tion. The first consists of a brain, or large mass of nervous
substance, from which a cylindrical process, called the spinal
marrow, is continued ; and these are protected respectively by
the bones of the skull, and by a series of bones, called vertehrcB,
which form a jointed column along the whole length of the back.
Animals formed on this construction are called vertehrated
animals, a division which comprehends all the higher classes of
the animal kingdom, namely, mammalia, birds, reptiles, a.nd fishes.

In the second form of the nervous system, there is properly
but one central mass of nervous substance, or brain, without any
spinal marrow, and from this mass filamients of nerves proceed,
in various directions, to be distributed to all the other parts.
This division comprehends all the molliisca, including both the
mollusca and testacea of LinnoBUs.

The third form is that of a longitudinal series of masses con-
nected together by lateral filaments, and sending out, as from so
many centres, ramifications of nerves. This structure is the dis-

40

PHYSIOLOGY.

tinctive mark of articulated animals, and may be recognised in
insects, and worms properly so called.

The fourth and last division of Cuvier, he denominates
radiated animals, in which, wherever nerves are found, they
appear as a number of equal masses disposed in a circle, and
sending out fibres, which diverge hke rays from a common
centre. Hence the whole body of the animal, or at least some of
its principal organs, has a radiated or starlike form. This is the
case with the asterias, medusce, polypi, and all the other animals
comprehended under the name of zoophytes.

As frequent reference will be made, in this treatise, to the
zoological classification of Cuvier, we shall here give a table of
the principal divisions which it comprises, together with examples
of animals included in each order.

I. VERTEBRATA.

1. MAMMALIA.

1. Bimana Man.

2. Quadrumana Monkey, ape, lemur.

3. Cheiroptera Bat, colugo.

4. Insectivora Hedgehog, shrew, mole.

6. Plantigrada Bear, badger, ^glutton.

6. Pigitigrada ^"S-, l^on, cat, martin, weasel, otter.

7. Amphibia Seal, walrus.

8. Marsupialia Opossum', kanguroo, womlat.

9. Rodentia Beaver, rat, squirrel, porcupine, har".

10. Edentata Sloth, armadillo, anteater, pangolin, ornithorliynchus.

11. Pachydermata .... Elephant, hog, rhinoceros, tapir, horse. •

12. Ruminantia Camel, musk, deer, giraffe, antelope, u,oat, sheep, ox.

13. Cetacea Dolphin, whale.

2. AVES.

1. Acclpitres Vulture, eagle, owl.

2. Passeres Thrush, swallow, lark, crow, sparrow, urren,

3. Scansores Woodpecker, cuckoo, toucan, parrot.

4. Gallinae Peacock, pheasant, grouse, pigeon.

5. Graliae Plover, stark, snipe, ibis,Jlatningo.

6. Pahnipedes Jluk, grebe, gull, pelican, swan, duck.

3. REPTILIA. »

1. Chelonia Tortoise, turtle, emys.

2. Sauria Crocodile, lizard, gecko, chameleon.

3. Ophidia Serpents, boa, viper.

4. Batrachia Frog, salamander, newt, proteus, siren.

4. PISCES.

1. Acanthopterygii , . . Perch, mackerel, sword-fish, mullet.

2. Malacopterygii . , . . Salmon, herring, pike, carp, silurus, cod, sole,rcmora, eel.

APPLICATION TO ZOOLOGY. 41

3. Lophobranchii . . . . Pipe-fish, pegasus .

4. Plectognathi Sun-fish, trunk-fish.

5. Chondropterygii . . . Lamprey, shark, ray, sturgeon.

II. MOLLUSCA.

1. Cephalopoda Cuttle-fish, calamary, nautilus.

2. Pteropoda Clio, hyalsea.

3. Gasteropoda Slug, snail, limpet, whelk.

4. Acephala Oyster, muscle, ascidia.

5. Brachiopoda Lingula, terebratula. • ,

6. Cirrhopoda Barnacle.

III. ARTICULATA.

I. ANNELIDA.

1. Tubicola Serpula, sabella, amphitrite.

2. Dorsibranchia .... Nereis, aphodrite, lob-worm.

3. Abranchia Earth-worm, leech, nais, hair-worm.

2. CRUSTACEA.

1. Malacostraca

Decapoda Crab, lobster, prawn.

Stomapoda Squill, phyllosoma,

Amphipoda Gammarus, sand-hopper.

Lsemodipoda' Cyamus.

Isopoda Wood-louse.

2. Entomostraca Monoculus.

3. ARACHNIDA.

1. Pulmonalia Spider, tarantula, scorpion,

2. Trachealia Fhalangium, mite.

4. INSECTA.

1. Aptera Centipede, podura.

2. Coleoptera Beetle, glow-worm.

3. Orthoptera Grasshopper, locust.

4. Hemiptera Fire-fly, aphis.

5. Neuroptera Dragon-fly, ephemera.

6. Hymenoptera Bee, wasp, ant.

7. Lepidoptera Butterfly, moth.

8. Rhipiptera Xenos, stylops.

9. Diptera Gnat, house-fly.

IV. ZOOPHYTA.

1. Echinodermata .... Star-fish, urchin.

2. Entozoa Fluke, hydatid, tape-worm.

3. Acalephse Actinia, medusa.

4. Polypi Hydra, coral, madrepore, pennatula.

6. Infusoria Brachionus, vibrio, proteus, monas.

4*

42 PHYSIOLOGY.

It has long been a favourite notion with speculative naturalists,
that organized beings might be arranged in a continued series,
every part of which, like the links of a chain, should be con-
nected with that which preceded and that which followed it.
Linneeus was even impressed with the idea that nature, in the
formation of animals, had never passed abruptly from one kind
of structure to another. But the idea of a chain, or continuous
gradation of being, was cherished with enthusiastic ardour by
Bonnet, who, assuming man as the standard of excellence,
attempted to trace a regular series, descending from him to the
unorganized materials of the mineral world. Many other writers
have adopted this speculation; but none have carried it to a
more extravagant length than Lamarck, who blends it with the
wildest and most absurd hypothesis that was ever' devised, to
account for the diversities of animal structures. He conceives
that there was originally no distinction of species, but that each
has, in the course of ages, been derived from some other less
perfect than itself, by a spontaneous improvement in the race.
He believes that the animalcula of infusions gave birth, by suc-
cessive transformations, to all other animals ; aquatic animals
acquiring feet and legs, fitting them for walking on the ground,
and, after a time, being converted into wings, merely from the
long continued operation of a desire to walk or to fly.

70. In support of the theory of continuous gradation many
anomalous animals are produced as instances of links of con-
nexion between different classes of animals. The bat has been
regarded as one of these intermediate links between mammalia
and birds. The cetaceous tribe, including the wliale, cachalot,
dolphin, and narwhal, though properly belonging to the class
mammalia, make an apparently near approach to the tribe of
fishes. The ornithorhyncus is allied both to quadrupeds and
to birds. Many similar examples might be produced among
the inferior classes of the animal kingdom. A little attention,
however, will soon enable us to perceive that they occupy but
small portions of the wide spaces intervening between different
orders of animals. Even in the best arranged systems, such as
that of Cuvier, we discover innumerable chasms wholly unoccu-
pied, between adjacent orders ; and in many instances animals,
which are scarcely in any respect allied to each other, are placed
in immediate sequence. This defect, as I have already observed,
is unavoidable, because it is inherent in the very nature of the
subject. Instead of a single continuous line, nature presents us
with a multitude of partial series, with innumerable ramifications,
and occasionally a few insulated circles. If metaphor must be
employed, it would be better to say, that instead of being a chain,
the natural distribution of animals ofi^ers the idea of a complicated
net-work, where several parallel series present themselves, and

APPLICATION TO GEOLOGY. 43

are occasionally joined by transverse or oblique lines of connexion.
The great divisions of Cuvier represent these principal parallel
scries. The last, however, or that of the radiata, appears to be
the least perfect of these series, and might with advantage be
farther divided.

On the subject of natural classification Mr. Macleay* has ad-
vanced a hypothesis, which he supports with some ingenuity,
namely, that the real types or niodels of structure may be repre-
sented by a circular or recurring arrangement ; and he gives a
number of instances in which this principle appears very happily
to apply. But speculation on these subjects can lead to satisfac-
tory conclusions only on the supposition that an extensive com-
parison of organs has been instituted throughout the whole of the
animal kingdom.

71. A scientific knowledge of the organization and functions
of animals is valuable, not only in its application to zoology, but
also in reference to many other sciences, such as geology, wath
which it might at first view appear to have but little connexion.
By attending to the arrangement of mineral bodies as they occur
in nature, we have sufficient proofs that the earth has undergone
frequent and considerable changes prior to the existence of any
living beings. But we find, besides, a great number of strata,
which contain unequivocal remains of vegetable and animal
bodies. A large proportion of these are shells, exuviae of zoo-
phytes, and other marine animals. We also find, in other strata,
a multitude of fossil bones, and teeth of various quadrupeds and
reptiles ; and occasionally, but more rarely, of birds and fishes.
Whole mountains and extensive districts appear to be composed
entirely of these animal remains. It is by the aid of comparative
anatomy and physiology alone that we are enabled to compare
these relics of antiquky with similar facts of hving or recent
animals, to discover their difTerences or identity, and to deduce
certain conclusions with regard to the nature, habits, and charac-
ters of the animals to which they had belonged; and by studying
their relation with the strata in which they are found, to draw
inferences with regard to the changes which must have taken
place in those parts of the earth, inferences which are of the
highest importance towards estabhshing a correct theory of those
changes. ' The difficulties attending researches of this nature
were of course exceedingly great ; but they have been at length
surmounted by the persevering zeal and industry of modern
naturalists. In these arduous investigations Cuvier stands pre-
eminent; and his labours have been rewatded with a number of
highly interesting results. The great principle which he has as-
sumed as the foundation of his researches, is that every organized'

* Macleay, Horx Entomohgicse, or Essays on Annulose Animals, 1821.

44 PHYSIOLOGY.

individual constitutes a system of itself, of which all the parts are
connected to each other by certain definite relations. In passing
from each of these structures to that of other animals in the
natural series, we find that all the changes of form which take
place in any one organ are accompanied by corresponding altera-
tions in the form of every other organ ; so that by the careful
application of certain rules, deduced from this observed recipro-
cal dependence of its functions, we are enabled to ascertain with
considerable certainty the forms and habits of animals, of which
only small fragments have been preserved. We have already
given an instance of this mode of reasoning as applied to rumi-
nant animals. By following this guide Cuvier ascertained and
classed the fossil remains of nearly 100 different quadrupeds in
the viviparous and oviparous classes. Of these above seventy
were distinct species, hitherto unknown to naturalists.

It appears from these researches that the earth has sustained
more numerous convulsions than had before been suspected, and
that these must have been separated by considerable intervals of
time; that the ocean has deposited various strata in regular suc-
cession ; that the species of animals whose remains are found in
these strata change with every variation in the nature of the
deposit, and become more and more analogous to the living
animals of the present day, in proportion as the deposits have
been of more recent date. It appears from an examination of
these fossil remains, that the sea must have retired at intervals
from the districts it had formerly covered, and left dry land,
affording habitation for large quadrupeds ; and that after a certain
unknown space of time, the sea has suddenly returned to the same
spot, has destroyed all the terrestrial animals, and has formed
subsequent deposits of shells and other marine productions.

These sudden irruptions and recessions of tfie ocean, which
have occurred several times in the same district, must have been
attended with extensive destruction of animal life. Whole races
have perished irretrievably, and are known to us only by the
durable memorials they have left behind of their own existence,
and of the several epochs of antediluvian chronology.

72. The study of the fossil remains of animals has also extend-
ed our views of the animal kingdom ; it has in many instances
supplied chasms which had occurred in the natural series, and
has enlarged our ideas of the extent of creative power. Another
important conclusion which has resulted is, that the human race
has been the last created ; for nowhere do we find any vestiges
of human bones. These researches tend also to throw fight
on the history of mankind, and to refute the pretensions to
high antiquity which have been arrogated by certain nations,
and particularly the Chinese, &c. which Voltaire and other mo-
dern philosophers had so zealously defended. All that science

APPLICATION TO NATURAL THEOLOGY. 45

has brought to h'ght, indeed, is in conformity with the testimony
of the sacred writings, when rationally interpreted, and may
even be adduced as^'illustration of their truth. Geology and
comparative physiology concur with these writings in teaching
us that man was the last act of creative power ; that a great
catastrophe took place on the surface of the globe a few thousand
years ago, during which the sea covered for a time every part
of the land; and that the subsequent diffusion of the population
of the earth is of comparatively recent date. It is pleasing to
see conclusions, derived from such different sources, converging
to the same points, and affording each other that reciprocal
confirmation which is the invariable concomitant and surest test
of truth.

73. The enlarged views to which we are conducted by the
study of comparative physiology afford us a glimpse of some of
the plans or models of structure which appear to have been
followed in the formation of the animal world. The analogies of
form discernible in corresponding organs, throughout a very ex-
tensive series of tribes, have been lately traced and developed
with extraordinary care by the modern naturalists of the French
and German schools, and especially by Cuvier, Blainville, Sa-
vigny, Geoffroi St. Hilaire, Oken, Carus, and Milne Edwards.
The conclusions they have drawn from their labours, though
sometimes overstrained, are always ingenious, and in general
satisfactory; and they strongly tend to prove, that several dis-
tinct types, or standards of figure, have been adhered to in all
the multiplicity of forms with which it has pleased the Author of
nature to diversify the animal creation.*

74. These inquiries, however, suggest still higher subjects of
contemplation. They illustrate the connexion and relationship
of every part with the rest of the system. They prove the unity
of design with which the system has been planned and executed.
They demonstrate the perfection with which all its parts are
mutually adjusted, and the harmony which pervades the whole.
The evidences of express design and contrivance are so distinct
and palpable, and they so multiply and accumulate upon us as
we advance, that they may almost be said to obtrude themselves
on our notice; and we cannot avoid being impressed with the
notion of its being intended that we should observe them. Whilst
the purpose to be answered continues the same, the means are
varied in every possible manner, as if designedly to display to
us the exhaustless resources of inventive power, and the supreme
intelligence wdth which that power is wielded. Nor is it possible
to overlook the general object to which every thing so manifestly

* See the Bridgewater Treause on Animal and Vegetable Physiology,
where this subject^is enlarged upon, and especially the chapter on " Unity of
Design." ii. 625. [American Edition, ii. 437.]

46

PHYSIOLOGY.

tends in the system of animal existence. Every element in every
part of the habitable globe, teems with life, and that life is replete
with enjoyment. Happiness is unquestionably the great object of
animal existence. The benevolence which pervades the whole
system of creation, is no less conspicuous than the power and
intelligence from which it emanated. Revealed religion is thus
in unison with the theology derived from the contemplation of
nature, and the lights of modern science.

75. The facts derived from comparative physiology which
more especially support the arguments of natural theology have
been collected by authors who have written professedly on the
subject. Derham's work, entitled Physico-Theology, has been
deservedly held in estimation ; but since the time it was published,
which is now above a century, the sciences have been prodigi-
ously, extended. Dr. Paley, in his Natural Theology, has pro-
duced a great multitude of facts and observations in support of
the same arguments, has applied them with singular felicity, and
impressed them with the most fascinating perspicuity and elo-
quence. But his object being purely theological, he has not
professed to adhere to any scientific order in stating them. The
design of the Bridgewater Treatise, already referred to, is to
supply this desideratum, by presenting the details of animal and
vegetable physiology, arranged according to the functions to
which they relate, or in other words, in reference to final causes.
As theological arguments, the value of these facts cannot fail to
be better appreciated when they are studied in all their bearings,
and as forming a part of the science to which they belong. It
is by the aid of genuine science alone, that we can avoid the
dangerous error of building arguments, on so momentous a sub-
ject, upon equivocal or unstable foundations, and of injuring a
cause already established upon incontrovertible grounds, by
weak and inconclusive evidence.

76. It has been too hastily inferred, from the abuse which has
too often been made of philosophical inquiries, that they are to
be avoided as dangerous, and even pernicious ; and that of the
fountain of philosophy, as of the Pierian spring, we should "drink
deep," or abstain from tasting. Superficial knowledge has often
been decried as mischievous, and extremely liable to abuse.
The hackneyed maxim of Pope, that " a little knowledge is a
dangerous thing," has furnished a ready text for those who de-
claim against all attempts to render science popular, and to
include it as a branch of general education. Willing proselytes
to this doctrine will always be found among those whom indo-
lence or frivolity render averse to mental exertion, when bestowed
on subjects not immediately connected with the common concerns
of life, as well as among those who, already enjoying some of the
advantages of knowledge, are desirous of securing to themselves

ARRANGEMENT OF FUNCTIONS. 47

the monopoly of those advantages. But their sophistry is soon
detected when we examine inio the real meaning of the expres-
sions they employ. What is commonly denominated superficial
knowledge, may certainly be useless, or even dangerous; but the
mischief or danger arises, not because it is superficial, but be-
cause it is incorrect. It is error, under the guise of knowledge
that alone deserves such reprobation. The value of information
is to be estimated much more by its accuracy, than by its extent.
Although it may be true that there is no royal road to science,
it is equally true that many are the roads that lead astray; and
that much fruitless labour may be spared by having that one
pointed out which leads directly to the object we wish to attain.
Though the distance we have to travel cannot be abridged, yet
the path may be rendered smoother, and the velocity of our pro-
gress accelerated, by availing ourselves of such guidance as may
be afforded by concise treatises, which, however superficial in
appearance, or popular in their garb, are yet, as far as they go,
perspicuous, accurate, and comprehensive.

CHAPTER III.

ARRANGEMENT OF FUNCTIONS.

77. The general review we have taken, in our introductory
chapter, of the objects and mutual connexions of the functions
of the animal economy, will furnish us with the principles on
which the methodical arrangement and classifiation of those
functions should be established. Various attempts have been
made by different systematic writers on physiology towards the
accomplishment of that object ; but they have generally been
deficient in that logical precision, which alone can ensure entire
comprehensiveness of every branch of the subject, and at the
same time convey clear perceptions of the bearings of every part
to one another. Some physiologists have limited their views to
the human economy, or that of animals which most nearly resem-
ble man ; others have framed their systems so as to embrace the
whole animal kingdom, and even all beings endowed with life.
Some have been wholly governed by anatomical considerations,
regarding mere structure as the basis of physiological distinctions ;
others, overlooking the unity of purpose in each function, and
pursuing their subdivisions to an excessive degree of minuteness,
have overloaded the subject by needless multiphcation and super-

48 PHTSIOLOGr.

fluity of detail. Many have introduced confusion by a loose and
villous nomenclature, derived from partial or hypothetical views;
which were often tinctured with mysticism, and which, by biass-
ing their judgments, have betrayed them into a wide field of de-
lusion and of error.

78. Another source to which the greater part of the mistakes,
pervading all the systems of physiological arrangement that have
been hitherto framed, may be traced, is inattention to the essen-
tial distinction which exists between physical and final causes.
The study of the phenomena of life differs from all the other
branches of philosophical inquiry, by its involving considerations
relating to both these kinds of causes ; the latter of which introduces
a totally new principle of arrangement, wholly inapplicable in
those sciences which concern the physical properties of inert and
inorganic matter. The rules of a strictly philosophical induction,
which alone can guide our steps in the pursuit of these sciences,
must be greatly modified, and in some measure superseded, by
those derived from another department of, human knowledge, —
namely, psychology. The knowledge of those general facts,
which, when once estabhshed, and the conditions on which they
depend ascertained, constitute what are called the laws of nature,
is obtained first, by comparing together phenomena, and uniting
in one class such as are of the same kind, and carefully separa-
ting them from others which are essentially different ; and next,
by endeavouring to remove all extraneous influences, so as to
reduce each class of phenomena to its simplest conditions ; an
object to be attained by experiments, that is, by varying the cir-
cumstances under which they occUr, and also by combining
them in different ways, so as to enable us to verify our theories,
by comparing their results with the actual observation of nature.
But the attempt to apply the same process of induction to
the physiology of organised beings, is attended with peculiar dif-
ficulty; for while the changes v/hich occur in their organic world
exhibit the operation of forces or agents characterized by their
simplicity, their constancy, and their uniformity, the phenomena
presented to our view by living beings, so prodigiously varied in
their form, so extensively spread throughout every element, every
clime, and every habitable region of the globe, and so infinitely
diversified in their nature, and complicated in their connexions,
are calculated to baffle the efforts of the most cautious reasoner,
and elude the penetration of the most sagacious inquirer after
truth. The resources of experimental research are here ex-
tremely narrowed, in consequence of the simultaneous and con-
nected operation of a great number of powers, which prevent
us from studying the influence which each would exert when
isolated from the rest, and ascertaining the laws which are pecu-
liar respectively to each. Hence it is, that we have hitherto

ARRANGEMENT OF FUNCTIONS. 49

made but very imperfect approaches to the determination of those
laws.

79. Some compensation is, however, afforded us, while strug-
gling with the obstacles which impede our progress in the direct
and thorny path of science, by the abundant resources accessible
to us in the psychological considerations, which everywhere arise
in this vast field of contemplation. All the phenomena of organic
beings reveal to us so palpably the indications oi design, that we
cannot resist the impression thus created in our minds; nor can
we avoid recognising the connections, which are so established
between the objects and the changes they present, as being those
of means employed for the accomplishment of certain ends. Thus,
then, the relation of means to ends becomes a leading principle of
association among the facts of physiology: giving a new aspect to
the science and creating an interest of a different and much higher
kind, than could ever be inspired by the study of mere physical rela-
tions. So deep has been this impression, and so completely has
the principle of final causes been interwoven with the pursuits of
physiologists, that the study of the functions of life, that is, of
the purposes to which the actions constituting life are subservient,
has been almost universally regarded as the principal, if not the
sole object of the science. It has, accordingly, been assumed as
the basis of arrangement, in all systematic treatises of Physiology:
and likewise in framing theories for explaining the phenomena
of life, physiologists have generally been satisfied with pointing
out their final, rather than their physical causes.

80. This natural proneness to substitute final for physical
causes has been a frequent source of delusion, by insensibly lead-
ing to the belief that we have reached the physical law which
regulates the phenomena we are viewing, when we have, in fact,
done nothing more than traced their relation to the intelligent
agency by which they have been each adjusted to their respective
objects, and given that law a name with reference to that agency;
thus, in our eagerness to grasp at hidden knowledge, mistaking
the shadow for the substance,

81. Frequent instances of this confusion of ideas occur in the
writings of the older physiologists; but at all times the predominant
tendency has been to refer the phenomena to their final causes ;
that is, to the purposes which they answer in the animal economy.
The functions were arranged by the ancients into three classes,
designated by the titles of animal, vital, and natural ; the first
comprising those powers of sensation and of voluntary motion ■
which are more especially characteristic of animal, as contra-
distinguished from vegetable life ; the second, those powers, the
coniinued exercise of which are immediately necessary for the
maintenance of life, such as respiration and the circulation of
the blood ; and the third, those which are directly concerned in

5

50 PHYSIOLOGY.

the continuance of its vital actions, but which are yet indispensable
in preserving the organs in the conditions enabling them to perform
their respective ofKces, by supplying the materials requisite for
their nutrition, and for counteracting their tendency to decom-
position ; in this class were included digestion, secretion, and
absorption. To these were added by many, o. fourth class, the
generative, comprehending all the functions which have for their
object the continuance of the species by the reproduction of in-
dividuals similar to the parent animal. The principal objection to
this arbitrary division of the functions is, that the line cannot be
drawn with sufficient distinctness between what are called the vital
and the natural functions, their connexion with the maintenance
of life being one of degree only, and not of kind ; as is evident from
their being united together in the lowest tribes of the animal
kingdom. This classification appears also to be defective, inas-
much as it omits all notice of those functions which have immediate
reference to the mechanical condition of the frame ; conditions
which are the foundation of their physical capabilities of executing
the operations assigned them in their respective places in the
general system. It is also liable to the imputation of employing
terms to designate the classes which are obviously incorrect, and
bear not the meaning they are intended to convey. In one sense,
and that which would first present itself to the mind, the term
animal functions would comprehend all the others, for there are
none in which powers peculiar to animal life are not called into
play ; and, on the other hand, the strictly animal functions are
equally entitled to the appellation of vital, as being directly es-
sential to the support of life; and no specific meaning can attach
to the term natural, as applied to any description of functions.

82. Vicq D'Azyr proposes to estabhsh a preliminary division
of the functions into two great classes ; the first, comprising those
concerned in the preservation of the individual; and the second,
those concerned in the preservation of the species. The former
class he divides into two orders ; the first having for their object
the assimilation of food into the substance of the body, and de-
signated as the interior assimilative and nutritive functions ; and
the second, establishing the relations of the individual to sur-
rounding objects, and denominated the exterior or relative func-
tions.

The first of these orders comprises six genera; namely, 1st,
digestion, by which the nutritive particles are extracted from
the food ; 2d, absorption, by which this nutritive matter is con-
veyed into the blood ; 3d, circulation, by which it is carried to
all the organs ; 4th, respiration, by which it is exposed to the
influence of atmospheric air; 5th, secretion, by which it is made
to undergo various modifications ; 6th, nutrition, by which it is
applied to the organs for the purposes of growth and nourish-
ment.

ARRANGEMENT OF FUNCTIONS. 51

The second order of the first class comprehends three genera;
namely, 1st, the sensations, which give to the individual notice
of the presence of surrounding objects; 2d, the motions, which
bring him towards, or remove him from them ; 3d, voice and
speech, which enable him to communicate with his fellows with-
out transporting his body to a diflerent place.

The second class, or the generative functions, likewise com-
prise two orders; the first, including the functions of conception
diXid generation, recimnng \he concourse of both sexes; the se-
cond, \nc\\yA'mg gestation, parturition, and lactation, performed
exclusively by the female. To these were subjoined by Vicq
d'Azyr, as a kind of supplement to his system, the several facts
relating to the progressive changes taking place during the ad-
vance of life from infancy to decrepitude, through the ages of
growth, of maturity, and of decay, and to those which attend
the absolute extinction of life, and the subsequent decomposition
of the organs.

The arrangement of Vicq d'Azyr is entitled to much commen-
dation, and has been followed in all its essential features by
Dumas,* Richerand,-|- and other systematic authors on physiology,
with the exception of Haller^J who adopted a classification of
functions founded altogether on the anatomical relations of the
organs by which they are performed.

83. Bichat,§ whose original genius led him to disregard the
opinions of his predecessors, and to strike out for himself new
paths of inquiry, aimed at giving greater simplicity to physiolo-
gical classification, by pursuing a more rigid analysis, and in-
fusing a more philosophical spirit into tlie methods of research.
With this view he distributed the functions into two classes,
which he denominates respectively the animal and the organic ;
the former coinciding nearly with those already known by that
title ; and the latter comprehending both the vital and the natural
functions of preceding writers. Impressed, however, with the
necessity of drawing distinction among the powers of life, he has
perplexed his system by intermixing with those final causes,
which he takes as the basis of his divisions, the results of a
philosophical analysis of those powers. He is thus led to make
continual eftbrts to establish a distinction between muscular con-
tractibility — which is one of the simple and elementary powers
of life — when that power is employed in subservience to the
animal functions, and when it is subservient to the functions of
organic life ; a distinction which regards only the final, and not
the physical causes of the phenomena. Dumas has been guilty
of a still more palpable error in deeming it necessary to add to

* Principes de Physiologie. X Elemens de Physiologie.

f Primffi Lineee Physiologiae. § Anatomie Generale.,

52 PHYSIOLOGY.

his catalogue of principles, consisting of the acknowledged
powers of sensibility and contractility, a third power, which he
terms " the force of vital resistance ;" thus associating a final
cause in the same rank with causes that are strictly physical.

84. To the animal and vital functions of Bichat, Cuvier has
added, in his physiological arrangement, a third class, the gene-
rative, which cannot, indeed, be, with any propriety, included
in any of the former. He still, however, falls into a similar mis-
take as that of Dumas, which we have just now pointed out ; for
he describes sensibiUty and muscular contractility not as primary
principles, but both of them as functions of the nerves. Adelon*
distinguishes the following eleven actions as being the functions
of life ; namely, sensibility, locomotion, language, digestion,
absorption, respiration, circulation, nutrition, calorification,
secretion, and generation. Bourdonf reduces them to seven,
which are as follows: caloricit^, nutrivit^, absorptiviti, exkala-
tivite, durabilite, reproductivite, et resistabilit^ ; -thus presenting
a strange jumble between physical principles of action, and
actions referred to definite purposes. The same confusion may
be remarked in the classification of the functions by Bec]ard,J who
has arranged them into six classes, viz. nutrition in its most
extended sense, generation, muscular action, sensation, nervous
action, and the functions of the intellect. But it would be need-
less to multiply examples of this error, since it will be found to
pervade almost every physiological system that has yet been
framed, not excepting even that adopted by Dr. Bostock, in his
valuable Elementary System of Physiology.

85. Dr. Bostock regards contractility and sensibility as the
two primary attributes of animal life, each equally characteristic
of it, and peculiar to it, and each performed by its appropriate
organs. " The functions," he remarks, " depend on the exercise
of these powers, and although probably, in all cases, they are
both of them exercised, yet generally one of them seems to be
the principal agent, or the prime cause of the ensuing operation ;
we may consequently divide them into the contractile and sen-
sitive functions, or those which more directly belong to contrac-
tility and to sensibility, and which, of course, serve respectively
for motion and sensation, and to these two classes must be added

* Physiologie de I'Homme. [The arrangement of Adelon is adopted from
Magendie, and has been embraced by Dr. Dunglison. The functions are
divided into three classes. 'Vhe first class, X\\e functions of relation, or animal
functions, includes those that establish our connexion with the bodies surround-
ing us ; — the sensations, voluntary motions, and expressions. The second class
— \he functions of nutrition — comprises digestioii, absorption, respiration, circu-
lation, nutrition, calorification, and secretion ,- and the third class, the functions
of reproduxtion, — generation. — Duno-lison's Human Physiology, 3d edit. i. 51.
Philad. 1838.]

f Elemens d'Anatomie. X Pnncipes de Physiologie Medicale.

ARRANGEMENT OF FUNCTIONS. 53

a third class of the intellectual functions." Anaong the contrac-
tile functions, the essence of which consists in motion, Dr. Bos-
tock considers the circulation as being the first in point of
importance, and the one which may be regarded as the most
necessary to the direct support of life, and to the indirect main-
tenance of all the rest. Next in importance is respiration, which
modifies the blood so as to adapt it to the maintenance of life.
After these two functions, by the former of which the blood is
carried to all the parts of the body, and by the latter of which it
acquires its vital properties, Dr. Bostock places those of calorifi-
cation, secretion, digestion, including assimilation and sanguifica-
tion, and absorption, functions which contribute, he observes, to
the continuance of the motion of the animal machine, and which
preserve all its parts in their proper condition, without, however,
being essential to the immediate support of life. In this class he
places the function of generation, which, although one of the
most inexplicable of all the operations that are performed by the
animal powers, and acting in a specific manner, of which we
have no other example, may be considered as essentially consist-
ing in secretion.

The sensitive functions are divided by Dr. Bostock into
two classes ; first, those which originate in the action of the
external agents on the nervous system ; and, secondly, those
of a reverse kind, which depend on the reaction of the nervous
system on these agents. In the first of these divisions are
included what are called the external senses, the sight, hear-
ing, taste, smell, and touch ; and in the same division must
be placed the sensation of hunger, that of -temperature, and
some others, which have not been correctly discriminated from
general feeling, but which possess specific characters. In the
second class, — those functions which depend on the reaction of
the nervous system on external bodies, — he places volition; and to
the same class he also relers instinct, association, sympathy,
habit, and some other faculties of a similar kind, which appear
to hold an intermediate rank between the corporeal actions and
those of a purely intellectual nature. As the functions, which
compose the first of these classes, may be all referred to a species
of perception, so the latter may be considered as more or less
analogous to volition ; in the former, the effect on the nervous
system, whatever it may be, is propagated from the extremities
to the centre ; in the latter, it proceeds in the opposite direction,
from the centre to the extremities of the body.

The intellectual functions compose, in this arrangement, the
third class. These, Dr. Bostock observes, are a less direct object
of physiology than the two former, yet many of them are so
closely connected with the physical changes of the body as

5*

54 PHYSIOLOGY.

to require being included in a complete view of the animal
economy. Among those intellectual operations which possess a
decided action on the corporeal frame, he places the passions ;
and also refers to this class that compound of mental and physi-
cal influence, from which results what are called temperament
and character. These lead to the consideration of functions of
a more purely and intellectual kind, which as they recede from
the corporeal, and advance towards the mental part of our frame,
are less within the province of the physiologist, and belong moie
to the metaphysician or the moralist.

86. Dr. Alison* has adopted a principle of arrangement, which,
though differing in some of its applications, is essentially the same
as that of Dr. Bostock, as it is derived from the analysis of the
phenomena of life into certain powers; or if these phenomena be
considered as the results of a single principle, which we may
denominate vitality, the study of physiology will resolve itself
into an inquiry into the conditions under which the various phe-
nomena of life take place, that is, into the laios of vitality. These
laws are ranked by Dr. Alison under three heads : 1. Those of
vital contractions, by which the visible movements of living
animals are chiefly effected : '2. Those of vital affinities, by
which the chemical changes peculiar to living animals are deter-
mined, and their physical structure maintained: 3. Those of
nervous actions, by which the physical changes in living animals
are placed in connection with mental phenom.ena, and subjected
to the control of mental acts. The first and third of these divi-
sions correspond to those of Dr. Bostock, which he has denomi-
nated the contractile and the sensitive functioils. The second
division of Dr. Alison is founded on the principle pointed out by
the author in a treatise on Physiology which appeared many
years ago in the last Supplement to the Encyclopgedia Britannicaj,
and to which he gave the designation of the organic affinities.

Dr. Alison considers that the movement of the fluids, in all the
higher classes of animals, is in a great measure dependent on
vital contractions in certain of their solids, and may accordingly
be regarded as the first and most important consequence of the
exercise of the vital power. This subject he divides into two
parts; first, the movement of the mass of blood in the heart, ar-
teries, and veins, or the function of circulation ; and, secondly,
the continual evolution of matters from, and absorption of matters
into, the mass of blood ; or the functions of nutrition, exhalation,
secretion, and absorption, to which the circulation is subservient,
and on which all the other functions are dependent. The study
of these nutritive functions naturally introduce the consideration
of the properties of the dilferent textures and secretions which

* Outlines of Physiology and Pathology, Edinburgh, 1833.

ARRANGEMENT OF FUNCTIONS. 55

are formed from the blood, and which are the materials combined
in the construction of the organs themselves.

The nervous system has been endowed with peculiar proper-
ties or powers, in order that it may be the seat, and the instru-
ment, of mental acts. These mental acts, and all the functions
in which they bear a necessary share, constitute, according to
Dr. Alison, the animal life, or animal functions. As in all ani-
mals the reception of food into the digestive organs, and as, in
all vertebrated animals, and many of the inferior orders, in the
adult, the reception of air into the respiratory organs is accom-
plished by movements which are excited through the intervention
of sensations and of instincts and volitions ; he considers the
commencement of the processes of respiration and digestion in
them as belonging to the province of animal life, and as dependent
on the nervous system. Dr. Alison, thei'cfore, commences his
account of the animal functions, with the consideration of res-
piration, animal heat, and digestion, which he refers to that
class : proceeding afterwards to notice the physiology of the
external senses, of the mental faculties, voluntary and instinctive
motion, the involuntary action of the mind on the body, sleep and
the analogous states of somnambulism, reverie, and other irre-
gular actions of the nervous functions. The subjects of genera-
tion, and the pecuharities of age, sex, and temperament, occupy
the concluding chapters of his work. <;

87. The order in which Mr. Mayo has treated of the func-
tions,* differs but little from that adopted by Dr. Alison.

88. The author has given, in his Bridgewater Treatise,-] an
arrangement of the functions founded altogether on the basis of
final causes: and corresponding therefore with the views, which
have been explained in the preceding chapter, of the relative
subordination of purposes which the functions are designed tO'
answer in the economy; and not limited to human physiology,
but embracing all the difierent forms and modifications which
those functions present in the animal kingdom. Taking them in
the order of their increasing complexity, he has distribuied them
into the four following classes; namely,

FirsUX\\Q mechanical functions, which include the€onsideration
of all the circumstances relating to the mechanism of the frame
and of its different organs ; the arrangements provided for pro-
curing the pi'oper cohesion, strength and mobility requisite for
the drtferent actions they have to perform ; and also for the pre-
servation of their connexions, support, security and other me-
chanical conditions adapted to the exercise of their respective

* Outlines of Human Physiology, 3d edition, London, 1833. [4th edit.
Lond. 1837.]

I Roget, Animal and Vegetable Physiology, considered with reference to
Natural Theology, 2 vols. London, 1834. [Philad. 1836.]

56 PHYSIOLOGY.

functions. To this head are also referred the operation of the
moving powers, derived principally from muscular contractility,
by which the various parts of this system of machinery are set
in motion.

Secondly, the nutritive, or chemical functions, corresponding
to w|iat has been formerly denominated the vital functions ; and
the object of which is the preservation of the organs in those
states of chemical composition, which enable them to sustain
life, and to perform their destined offices in the economy. The
functions by which, in the higher orders of animals, this object
is accomplished, may be arranged under the following heads ;
each, however, admitting of further subdivision. 1. Assimilation,-
including the processes which prepare the food for digestion —
chymijication, which is the office of the stomach, and chylijication,
which is performed in the intestines. 2. Lacteal absorption, by
which the chyle, so prepared, is collected into the heart and
blood-vessels. 3. Circulation, by which the blood, or nutrient
fluid, is regularly diffijsed over the system. 4. Respiration, or
the aeration of the blood. 5. Secretion, by which the properties
of that fluid are modified. 6. Excretion, by which various
chemical principles are separated from the blood, and discharged
from the system. 7. Absorption, by which substances are con-
veyed from different parts back again into the general mass of
circulating fluids. 8. Nutrition, by which the nutritive matter
is applied to the growth or restoration of the various organs of
the body, so as to maintain them in the state which enables them
to discharge their proper functions. 9. For effecting all these
various processes, the agency of a peculiar power, derived from
the properties of the nervous system, is requisite. This may be
termed the nervous jjower, in contradistinction to those actions
of the same system, which have reference to mental phenomena,
and which come under the next class of functions.

Thirdly, the sensorial functions comprehend all those corporeal
changes in which the mind is concerned ; and consequently in-
clude those of sensation, of perception, of volition, and all those
intellectual functions, which employ for their agency the physical
organization of the body.

Fourthly, the reproductive functions, which have for tfieir
object the continuance of the species, and the multiplication of
its numbers. This subject is naturally connected with the pro-
gressive development of the organs, the growth of the body from
infancy to manhood ; and the stages of its decline, till all the vital
phenomena cease by the death of the individual.

THE VITAL POWERS. 57

CHAPTER IV.

THE VITAL POWERS.

89. We have already remarked, that there are two ways in
which the assemblage of phenomena presented to us by living
beings may be studied. We may, in the first place, view these
as mere physical phenomena, applying to them the same methods
of induction which have been employed with so much success
in other departments of natural science. The object of philo-
sophical induction is the reference of the events occurring in
nature to their proper causes. This is accomplished by compar-
ing the phenomena together, observing in what they agree, and
in what they differ, classing them in the order of their agreement ;
and distinguishing them according to their differences. The
result of this process, when it has been carried as far as the
extent of our mass of facts will allow, is the establishment of
certain general relations between these facts, orconditions, under
which they occur, and which we may consider as so many laios
of nature ; and any appearance we may afterwards meet with
which corresponds in its character to any single law, or com-
bination of these laws, is at once referred to them, and considered
as a particular instance or exemplification of these laws. When
we can succeed in tracing these coincidences with a previously
established law or general fact, we are said to have discovered
its cause. Philosophy, in this sense, then, comprehends the col-
lection and comparison of phenomena, their classification, the
establishment by careful induction of general laws; the verifica-
tion of these laws by experiment; and lastly, the subsequent
reference of particular phenomena to their appropriate laws.

90. In the sciences which relate to the laws of matter in its
inorganic state, this inductive method of philosophising admits of
being pursued to an indefinite extent, and v^'ith comparative
facility. The phenomena themselves, which are the subjects of
induction, are of a simple and more definite character than those
of animal or vegetable life ; they are generally more under our
control; and more easily subjected to the test of experiment.
The endless variety of the forms of life, the extent and intricacy
of the connexions between the different parts of the animal system,
introduce a degree of complexity in the phenomena, incomparably
greater than is ever met with in the combinations of inorganic
matter. We shall accordingly find that the knowledge we have

58 PHYSIOLOGY.

hitherto acqmred of the physical laws which govern the vital
phenomena, is as yet exceedingly imperfect.

91. In entering upon the philosophical study of the phenomena
presented to us in the living body, and carefully arranging them
according to the rules of induction, and without reference to the
final causes that connect them, (a subject which forms a totally
different branch of inquiry,) we easily recognize the operation of
many of those powers and principles to which inorganic matter
is also subjected. The living system, with all its complicaied
apparatus of solids and fluids, is obedient to the universal laws
of gravitation, of cohesion, of elasticity, of capillary attrac-
tion, &c., as well as toHhe ordinary principles of mechanics,
hydrostatics, hydraulics, and pneumatics, which result from com-
binations of these laws ; and we may pursue the application of
these laws to the mechanism of the body, as far as no other
causes intervene, without danger of error.

92. The laws of chemistry apply also, to a certain extent, to
the changes which are going on in the living system : but in
tracing the operation of these laws, we soon become sensible of
the apparent interference of other principles which seem to control
the ordinary chemical aflinities which the same kinds of matter
are found to exert when deprived of life. Here, then, we per-
ceive a sensible deviation from the course of phenomena exhibited
by inorganic matter ; and we are forced to recognize the exist-
ence of new and unknown powers pecuhar to, and characterizing
the living state. We discern the operation of such powers in the
processes of digestion, of sanguification, of nutrition, of secretion,
of the growth and organization of the various structures that
compose the fibres of the body. Powers of a similar kind are
exhibited in the phenomena of vegetation: they seem, therefore,
to attach to vitality in all its forms. In order to distinguish them
from the ordinary chemical affinities to which they are so fre-
quently opposed, we shall designate them by the name of Or-
ganic Affinities, although, as we shall afterwards attempt to
show, they probably do not differ in their kind, but only in the
circumstances and conditions of action, from the ordinary inor-
ganic affinities.

93. Another power which more peculiarly appertains to animal
fife is Contractility. This is especially a property of those fibres
which compose the muscles. It is often denominated Irritability,
a name originally given to it by Glisson, but which has justly
been objected to by Dr. Bostock as a term employed in many dif-
ferent senses, according as it is applied in physiology, pathology,
or ethics. Haller speaks of it frequently under the designation
of the Vis insita. The term Contractility, adopted by Dr. Bos-
tock,* and sanctioned by many other eminent physiologists, is in

* Elementary System of Physiology, third edition, pp. 91, 92.

THE VITAL POWERS. 59

itself unobjectionable, and has the advantage of being a simple
expression of the fact itself. It consists in the spontaneous short-
ening of muscular fibres, in consequence of the impression of
certain agents termed stimuli, by a power residing in the fibres
themselves, and which operates with a force greatly superior to
any of the ordinary mechanical sources of motion.

94. The remarkable property which the nerves possess of con-
veying with electric celerity impressions made on one of their
extremities, or even on any part of them, to the opposite ex-
tremity, and to other parts in the line of their course, the influ-
ence of which impressions are rendered apparent by certain
etiects, such as the contraction of the muscles, increased or
modified action of the blood-vessels, absorbents, and organs of
secretion, and the evolution of animal heat. All these effects
may take place from impressions, or irritations, (by which term
is meant impressions of a certain degree of intensity,) which do
not excite sensation, or volition, or any other mental change;
and they even occur after the destruction or removal of those
parts of the nervous system which are connected with affections
of the mind. A power of the same kind is also possessed by
those nerves which are connected with the sensorium, on the
parts in immediate connexion with the sentient principle.

95. It is by the exertion of this power that impressions made
on those nervous filaments which are instrumental in sensation,
and especially if made on their extremities which are distributed
to the organs of the external senses, are instantly transmitted to
the sensorium, in which they may be said to terminate, and the
changes produced in which are attended by the mental affection
termed sensation. In like manner, certain other changes in the
sensorium, consequent on volition, which is a mental affection,
are followed by the contraction of certain muscles, by means of
some unknown influence communicated through the medium of
certain other nervous filaments having their origin in the senso-
rium, and their termination in those muscles. The nature of the
power by which these transmissions are effected in the course of
each of these sets of nervous filaments, judging from the simi-
larity of the circumstances under which it takes place, especially
in the instantaneousness of the effect, is probably the same in
every case ; the only perceptible difference in the mode in which
it is exerted consisting in the direction of the transmission. This
remarkable power, which is totally distinct from any mental
effort that may accompany its exertion, we shall distinguish by
the name of the nervous jjower.

96. A fourth power, perfectly distinct from any of the former,
although it also belongs to a portion of the nervous system, is
that from which the corporeal changes which take place in those
parts immediately connected with sensation, volition, and the

60 PHYSIOLOGY.

intellectual operations, proceed. To this specific property, which
should be carefully distinguished from the mere faculty of trans-
mission possessed by the fibres of the nerves, the name of senso-
rial poioer has been given. We are indebted to Dr. Wilson
Philip for the establishment of this important distinction in the
specific powers of the nervous system, and for having bestowed
upon it the above appropriate designation. The same term had,
indeed, been employed by physiologists in a different and much
more extended sense, as including muscular irritability, which
had been regarded as in some way or other analogous to nervous
power. In the sense in which we shall use the term, it is meant
to apply exclusively to those physiological changes occurring in
certain parts of the nervous system, which produce or accom-
pany changes or affections of the mind.

97. It is evident that the astonishing properties belonging to
the refined organization of the brain, which constitute sensorial
power, and which are, in a manner utterly incomprehensible to
us, connected with the affections of the sentient and intelligent
principle, present subjects of far higher interest than even the
organic, muscular, or nervous powers, and are infinitely more
remote from the ordinary attributes of matter.

98. Thus we may perceive that the system of the living body
exhibits not only a multiplicity of new powers, which we no
where meet with in unorganized matter, but also presents us
with a gradation of powers ascending from those of a mecha-
nical nature, but yet derived from a highly artificial arrangement
of particles, to those of a refined and elaborate chemistry silently
at work in the secret laboratories of the body ; rising again to
principles of a still more elevated order, acting through the me-
dium of the nerves ; till we lose ourselves in the more lofty con-
templation of those mysterious agencies, which confer on the
central portions of the nervous system the power of exciting
sensation ; which render them instruments of thought and of
volition, and which stamp on the being they compose the distinc-
tive character of individuality.

99. Viewed with reference to their subserviency to final causes,
it is to the sensorial powers, which confer the capacity of enjoy-
ment, that the supreme rank in point of importance must be as-
signed. The faculties of sensation, of voluntary motion, and of
enjoyment, are the only ultimate ends for which, as far as we can
judge, the animal has been created and endowed with life. Those
ultimate ends of its being are attained primarily by the sensorial
powers ; and to the maintenance of these are the muscular and
the nervous powers subservient. Of these latter powers it is
also evident that the muscular is placed in obedience to the
nervous, in the same manner as the nervous is obedient to the
sensorial power. Thus, the views now presented of the classifi-

THE VITAL POWERS. 61

cation and distribution of the physical powers which operate in
producing the phenomena of hfe, are in strict accordance and
harmony with the results obtained from the consideration of final
causes, which we have already presented in our preliminary
chapter.

100. If the analysis we have here offered of the vital powers,
that is, of powers peculiar to the phenomena of life, and the dis-
tinctions we have endeavoured to establish between them be
correct, we shall be enabled at once to detect the fallacy of those
views of life, and of those definitions of the vital principle which
are generally received ; and which, we apprehend, have been
laid down in violation of the just rules of philosophical induction.
The truth is, disguise it how we may by a vain parade of words,
the real state of the science is not sufficiently advanced to authorise
that degree of generalization which these definitions would imply.
We are certainly not warranted, by the phenomena already
known, in regarding life as the effect of any sins;le power. The
attempt of Brown, of Hunter, and of Bichat to reduce the science
to this state of simplification, though highly ingenious, are yet
premature ; and have, it is to be feared, had rather the effect of
retarding than of advancing the progress of real science.

101. Many of the older physiologists entertained the notion of
a principle, endowed with qualities in some measure partaking
of intelligence, and as if it were a spirit presiding over and
governing the vital actions. Such was the idea attached by
Van Halmont, and by Stahl, to the principle which they termed
the archceus, or anima, and which, they conceived, regulated the
operations of the different powers of the system ; an assumption
which, however, naturally suggesting itself to the mind, while
contemplating the harmonious adjustments that pervade every
part of the animal economy, is in no respect a philosophical ex-
planation of the phenomena, and is even utterly irreconcilable
with some of these phenomena. In like manner, the vis medi-
catrix natures, which Hoffman and Cullen have so largely
employed in their pathological theories, and which supplied them
with ready solutions of every obscure morbid change that em-
barrassed them, was, in fact, nothing more than a branch of the
same doctrine. Nor have the more sober theorists of modern
times been sufficiently on their guard against this illusion. In
the attributes which John Hunter ascribes to his mtal 'principle,
we may continually trace the same want of discrimination between
that intelligence, by which the conditions of organization were
originally adjusted to a variety of contingent circumstances, and
those physical agents, by the instrumentality of which the intended
objects are attained. When it is said, for example, in the language
of this school, that the coagulation of the blood is occasioned by
" the stimulus of necessity," it is clearly the final cause alone

6

62 PHYSIOLOGY.

which is indicated, while the real physical cause is not assigned;
and it is also evident that no advance is thereby made towards
its discovery. This pi^inciiole of life, with which organized
beings are endowed, is represented as a new power, which
modifies and controls the operation of those simpler physical
laws, to which the same matter, in its unorganized slate, is sub-
jected; a power which imposes new cohesive and repulsive forces
on the solid materials of the animal or vegetable structures, which
imparts to the fiuids a new property of coagulation, which alters
the order of chemical affinities between their elements or primary
compounds, retaining them, contrary to their natural tendencies,
in a certain state of equilibrium, and resisting the agency of
causes usually tending to destroy that state : and, lastly, which
produces, in a degree corresponding with the wants of the system,
either an evolution or an absorption of caloric. All these, it
must be admitted, are purposes of manifest utility, being directly
conducive to the welfare of the individual, and indeed essential
to its continuance in the living state. In as far as they are
means conducive to specific ends, the reference of all these
phenomena to one class cannot be objected to. The fallacy lies
in regarding it as a philosophical generalization of effects of a
similar kind, resulting from the operation of a simple power in
nature ; for between many of these effects, considered as mere
physical phenomena, there exists not the remotest similarity.
But it is the fundamental principle of the method of induction,
that similar effects alone are to be ascribed to the agency of the
same physical cause. Judging, therefore, from the observed effects,
which differ widely in their nature from each other, we ought
to infer the operation of several distinct powers, the concurrence
of which is requisite to produce the complex phenomena in ques-
tion. We are, no doubt, unavoidably led to view these phenomena
as conjoined, because we witness their existing combinations,
and perceive that they are tending to the accomplishment of a
specific purpose ; namely, the preservation and welfare of the
being to which they relate. But this unity of design is an at-
tribute, not of matter, but of intellect, and does not necessarily
imply the unity of the agent employed in their production.

102. We m.ay take, as an example, the phenomena of the cir-
culation of the blood, which, when viewed with relation to that
function, form together so beautiful and harmonious a system.
These phenomena, taken abstractedly, are ultimately resolvable
into such as result from a few general powers, as muscular con-
tractility, membranous elasticity, the hydrauhc properties of the
blood, &c. The phenomena of digestion, in hke manner, when
subjected to analysis, are found to be results of the combined
agencies of the muscular action of the stomach and intestines, of
the chemical powers of the gastric juice, the bile, &c. of the

THE VITAL POWERS. 63

organic powers of secretion, and so forth ; all of which concur
in the production of a definite object, namely, the conversion of
the aliment into chyle. The combined processes subservient to
this purpose, constitute, when viewed in their relation to final
causes, the function of digestion.

103. However the laws which regulate the vital phenomena
may appear, on a superficial view, to differ from those by which
the physical changes taking place in inorganic matter are gov-
erned, still a more profound investigation of their real character
will show that, when viewed abstractly from the consideration of ,
final causes, there is really no essential difference between
them, either as to their comprehensiveness, their uniformity of
action, or the mode in which they are to be established by the
generalization of particular facts.* The difficulty of effecting
these inductive generalizations is undoubtedly incomparably
greater in the former than in the latter; but this difficulty is
similar to that which impedes our progress in-all cases wfiere the
existing combinations which are the objects of study, are too
numerous and too complicated to yield to our powers of analysis.
We have examples of this difficulty in many branches of physical
science ; in meteorology, for example, where no one can doubt that
the phenomena are the results of the ordinary physical powers,
of the laws of which we are tolerably cognisant ; but the opera-
tions of which, in effecting the daily and hourly changes of atmos-
pheric phenomena, have hitherto bafffed the most persevering and
penetrating inquiries directed to this highly important branch of
physics. There is, in like manner, no distinct evidence of the
material particles, which compose the organized and living fabric
being actuated by any powers or principles different from those
which are inherent in them, in their ordinary or inanimate state.
They are, in both cases, obedient to certain definite physical laws,
the operation of which is determined by the peculiar circumstances
of their mode of combination, and the peculiar conditions under
which they are brought into action.

104. It may, in like manner, be contended, that the affinities
which hold together the elements of living bodies, and which
govern the elaboration of organic products, are the same with
those which preside over inorganic compounds; and that the
designations of organic and vital affinities are expressive only of
peculiarities attending the circumstances and conditions under
which they are placed, but do not imply any real difference in
the nature of the powers themselves. If our knowledge of these
circumstances and conditions were complete, their identity would
be at once revealed to us ; but until that period, which must be

* See an Essay by Mr. Carpenter on the difference of the Laws regulating
Vital and Physical Phenomena, Edinburgh New Philosophical Journal, xxiv.
337.

64 PHYSIOLOGY.

very far distant, has arrived, we must be content with gathering
a few indications, which occasionally break out from the clouds
of mystery in which the subject is obscured, of the similarity of
operation between these two apparently contending powers, the
ordinary cl emical, and the extraordinary vital affinities. Every
fresh discovery in animal and vegetable chemistry, by showing
the mutual convertibility of many of the proximate principles of
organic compounds, adds to the number of those indications.
Hence it becomes every day more and more probable that the
forces immediately concerned in the, production of chemical
changes in the body, are the same as those which are in constant
operation in the inorganic world ; and that we are not warranted
in the assertion that the operations of vital chemistry are directed
by distinct laws, and are the results of new agencies.

105. We are therefore led to the conclusion, that the vital
properties are not, as' it is commonly expressed, superadded to
matter in the process of organization, but are the result of the
material constitution, that is, of the peculiar combinations and
arrangement of the ultimate molecules of the organised tissues,
which call out and develop the properties previously existing
in those molecules, but which cannot be effective unless these
circumstances exist.

106. However natural it may be to conceive the existence of
a single and presiding principle of vitality, we should recollect
that this in the present state of our knowledge, is only a fiction
of the mind, not warranted by the phenomena themselves, in
which we perceive so much real diversity, and therefore inadmis-
sible as the result of philosophical induction. We find, that
vitality ceases in different textures, at different periods, prior to
the total extinction of life ; a phenomenon which appears scarcely
compatible with the unity of any such power.

107. It is w^ell known that attempts have, in like manner, from
time to time been made to reduce the phenomjcna of the inorganic
world to a single primordial law ; instead of being content to
refer them to 'the Operation of distinct laws, such as those of
gravitation, cohesion, elasticity, light, heat,^electricity, magnet-
ism, and chemical affinity. The phenomena usually ascribed to
these great powers of nature have, for instance, been considered
as resolvable into one universal principle of attraction. By other
philosophers they have been regarded as the effects of a general
and sole power of repulsion. None of these simplifications are
as yet warranted by facts ; and equally vain, in the present state
of the science, is the endeavour to reduce all the vital phenomena
to one single law. It is possible, or perhaps even probable, that
future researches may be successful in establishing the identity
of some of the powers we now conceive to be distinct, with
other powers already known. Thus, in the physical sciences,

THE VITAL POWERS. 65

the recent discoveries that have taken place in electro-magnetism,
have satisfactorily established the identity of the magnetic and
electric agencies. The same may possibly be accomplished in
future times, with regard to heat and light, which are already
connected together by so many analogies. But no such approxi-
mation can yet be attempted with any prospect of success,
between the muscular, the nervous, the sensorial, and the ofganic
powers. No speculative ingenuity can reduce them to a single
physical power; nor can we establish any kind of association
between them, but by the consideration of another and a totally
different class of relations, namely, those they bear to the general
object which they combine to produce. This, however, is to
substitute final for physical causes ; a mode of procedure, which,
we have seen, is totally at variance with the principles of philo-
sophical induction. Physical causes only are the legitimate
objects of philosophical analysis, and the true bases of the physi-
cal sciences.

108. We shall now proceed to give an account of each sepa-
rate function ; taking them in the order of their respective
simplicity, with reference not only to their objects, but also to
the powers which are concerned in their accomplishment.

109. We shall accordingly begin with the consideration of the
mechanical functions, as being more simple in their character,
and implying the operation of the simpler powers of organiza-
tion; together with the peculiar faculty of muscular contractihty,
which is the great source of mechanical power provided for
carrying on the greater movements of the machine. We shall,
in the second place, review that class of functions which depend
more especially on the operation of the organic affinities, and
which have for their objects the nutrition and, extension of the
organs, and their maintenance in that state of chemical, as well
as mechanical condition, which fits them for the performance of
their respective offices. We shall then be properly prepared for
the study of that higher class of functions, which appertain to sen-
sation,^nd all the other faculties connected with mind; functions
which imply, in addition to all the powers concerned in the prece-
ding functions, others of a superior order, but which, although
in the highest degree interesting and important, are incompara-
bly the most obscure and complex of all. Our attention will, in
the last place, be directed to the functions relating to reproduc-
tion, the study of which requires a previous knowledge of every
other department of physiology.

6*

66 MECHANICAL FUNCTIONS.

CHAPTER V.

THE MECHANICAL FUNCTIONS.

Sect. I. — On Organization in general.

110. If we analyze the ideas attached to the term organiza-
tion, we find that it implies, as its essential condition, a specific
arrangement of parts, adapted to some particular purpose, and
composing by their assemblage, an individual system endowed
with life. It seems impossible, therefore, to attach the idea of
organization to a mere fluid, because the mechanical condition
of the particles of a fluid is such as to preclude the capability of
any permanent arrangement. It appears to be essential to every
organized structure, that there shall be solid parts provided for
containing those which are fluid. All animal bodies accordingly
are composed of solids and fluids ; the former being more perma-
nent in their nature and arrangement, and constituting the basis
by which the general form of the body is determined ; and the
latter, being lodged in appropriate cavities formed by the solids,
but capable by their mobility of undergoing more rapid changes
of place, and of chemical composition.

ill. It may in -general be said, that the solids bear but a
small proportion to the fluids, which enter into the composition
of the body. It is difficult, however, to determine the exact pro-
portion which they bear to one another ; in the first place, be-
cause this proportion is not fixed, and admits of variation in
different agents, circumstances, and conditions of the system ;
and, secondly, because it is scarcely possible to effect the com-
plete separation of these two constituent portions ; partly from
the ready conversion of the solids into fluids, and vice versa,
and partly from the tenacity of their mutual adhesion. Some
estimate of this proportion has been attempted to be formed, by
carefully drying the dead body in a stove, or oven ; and the re-
sult of some experiments has been, that in an adult man, the
weight of the fluids is to that of the solids, as six to one, or,
according to other experiments, as nine to one. From the exa-
mination of an adult Egyptian mummy, which may be supposed
to contain nothing but the dry fibres of the body, a still lower
proportion has been assigned to the solid part; since this mummy
weighed only seven pounds and a half.*

* See Beclard, Elemens de Anatomic Generale, p. 77.

ORGANIZATION IN GENERAL. 07

112. The possibility of reducing all the organic textures of the
human body to one elementary material, which might be regard-
ed as the basis of the whole, was long a favourite subject of
speculation among anatomists: and Haller has devoted it to the
first section of his great work on Physiology.* He conceives
that all the solid parts of the frame are ultimately composed of
fibres ; the animal fibre being the simplest form of organized
matter, and being to the physiologist, what the line is to the
geometrician, that from which all other figures are produced-
This simple fibre, he observes, is invisible, even with the assist-
ance of the microscope ; it is only by the union of the primary
fibres, that visible fibres are constituted ; and from the assem-
blage and lateral adhesion of these, again, thin plates of animal
substance are formed, while the grosser substance of the organs
themselves, is composed of a complicated contexture of these
plates and fibres.f This supposed basis, or essential constituent,
of all animal textures, has been by some termed the animal
■parenchyma, and, by others, has been designated by the general
name of animal membrane.

1 13. Besides this spongy or areolated texture, which composes
by far the greater bulk of the organs of the body, Haller has
also admitted two other constituent parts, namely the muscular,
and the nervous substances. These views have since been gene-
rally adopted by physiologists, with some slight modifications.
Many have thought it necessary to introduce, in addition to the
preceding, an element which they consider as of a tubular form,
constituting vessels fitted to contain fluids. This was the fa-
vourite doctrine of Boerhaave, who supposed that the simple
fibres, or the smallest into which they can be conceived to be
divisible, formed by their lateral adhesion, a membrane of the
first order, which, when coiled up into a tube, would constitute
a vessel of the first order. These vessels, again, when interwoven
together, composed a new order of membranes, by the duplica-
tion of which a second order of vessels was formed. Successive
series of membranes and vessels were thus constructed, until
they acquired a magnitude sufficient to be visible to the eye.
According to this hypothesis, therefore, all the parts of the body
might ultimately be resolved into a congeries of vessels, arranged
in these ascending orders. This hypothesis, which evidently
rested on the most visionary basis, has been ably refuted by
Albinus, and by Haller. It has, however, left some traces in the

* Elementa Physiologriaj Corporis Humani.

t [The notion of Haller must be regarded as a mere abstraction; for as
different animal substances are found to be composed of different proportions
of carbon, hydrogen, oxygen, and azote, it is fair to infer that the elementary
fibre must differ also in the different structures. See Dunglison's Physiology,
ij. 36.]

68 MECHANICAL FUNCTIONS.

opinions expressed by many subsequent anatomists, who still
cherished the idea of the universal vascularity of the animal
fabric, and of this vascularity being essential to organization.
The skilful injections of Ruysch, who succeeded in introducing
coloured fluids into vessels, the contents of which are naturally
transparent, had long ago shown that there exists an order of
vessels too minute to be otherwise detected. Dr. William Hunter
has, even in later times, adopted the opinion that every living
part is necessarily vascular; and that where there is no circula-
tion, there can be no life. Mascagni was also a strenuous advo-
cate of the hypothesis of the universal vascularity of the animal
textures ; but he conceived that every part is made up of a
congeries of minute lymphatic vessels. We shall have occasion
afterwards to point out the fallacy of these views.

114. Although the analysis of animal tissues, into the three
primitive elements we have pointed out, namely, into the mevi-
hranous, the muscular and the nervous fibres, be founded on the
most prominent and well marked features of distinction which
they exhibit, yet there are perhaps other kinds of texture also,
which possess sufficiently characteristic properties to entitle them
to rank as elementary tissues ; these are the alhugineous fibre
of Chaussier, and the epidermoid substance ; and to these we
might also add, in order to make the analysis complete, the car-
tilaginous and the osseous structures.

115. But this analysis of animal textures, has, by some later
anatomists, been carried, in another point of view, still farther.
With relation to the forms assumed by the elementary tissues,
they have been referred to three kinds, the fibrous, the lamellar,
and the granular, or globular. The two former are exemplified
in the structure of the cellular substance, which composes the
greatest portion of the animal fabric ; the fibrous is characteristic
of the muscular and ligamentous structures; the fibrous, united
with the granular, is exhibited in the texture of the glands, and
in the medullary substance of the nervous system; and the globu-
lar is most perfectly shown in the composition of the chyle, the
blood, and several of the secretions.

116. Anatomists have sought for still more general results, by
means of microscopical investigations. When very high magni-
fying powers are employed, both the muscular fibre, and the
nervous or medullary matter, appear to be resolvable into a mass
of globular particles, analogous to those which compose the
opaque portion of the blood. Meckel has founded upon these
observations the following system : He conceives that every
animal structure is ultimately resolvable into two kinds of sub-
stance, the one formed into minute, but solid spherular masses,
or globules ; and the other, being an homogeneous, but amorphous
matter, either uniting together these globules in the way of a

COMBINATIONS OF TEXTURES. 69

cement interposed between them, or constituting by itself, what
has been termed the cellular substance, membrane, and the
various structures derived from membrane. Dr. Edwards, on
the other hand, has carried this notion to the utmost possible
length; for he represents the cellular and membranous substances,
as being themselves composed of globules ; so that, according
to his views, the whole structure of an animal body will consist of
globules.

But the later, and more careful investigations of Dr. Hodgkin
and Mr. Lister,* appear to have established, that the globular
appearance of the different organized textures, when viewed
with microscopes of high magnifying power, is altogether an
optical deception. A similar conclusion, indeed, was, many years
ago, deduced by Dr. Monro, from his microscopical researches,
detailed in his work on the Nervous System.

Sect. II. — Combinations of Textures.

H7. Such being the results of the general analysis of animal
textures, into a few primary elements, we are next to consider
the combinations of these textures, which are actually presented
to us by nature, in the various organs of the body ; and in order
to possess the most comprehensive views on this subject, it will
be proper to study these organs as forming systems of which the
several parts are related to each other by similarity of composi-
tion and properties. The most elaborate arrangement, founded
on this principle, is that of Bichat, who distinguishes the constitu-
ent textures of the body into twenty-one different kinds.f But it
may be objected to his classification, that it is founded on dis-
tinctions of function, as well as on those of structure. We
therefore prefer following, on this subject, the arrangement of
Beclard, which proceeds on one uniform principle — namely,
that of mechanical conformation. Taking this principle as our
guide, we shall find that the systems of organs may be easily
reduced to eleven different classes: namely, 1, the Cellular;
2, the Adipous ; 3, the Membranous ; 4, the Dermoid ; 5, the
Ligamentous ; 6, the Cartilaginous ; 7, the Osseous ; 8, the
Muscular; 9, the Medullary or Nervous; 10, the Vascular;
and, 11, the Glandular systems of structures. The properties
of these several tissues will come under our review in connexion
with the functions to which they are more immediately subser-
vient. The three first of these, however, claim our immediate
attention, as being the simplest, and most generally diffused over
the body.

* Philosophical Magazine, and Annals of Philosophy, vol. ii. p. 136 ; and
also in the appendix to their translation of Dr. Edwards's work,
f See his Anatomie Generule.

70 MECHANICAL FUNCTIONS.

1. The Cellular Texture.

118. This is the simplest form in which the animal substance
presents itself to our observation ; and it appears to be not only
the real basis of the structure of all the other organs, but also the
general medium which unites their several parts together, as well
as the bond of connexion between adjacent organs. It is, accord-
ingly, of all the simpler textures, that which is the most exten-
sively diffused over the body; not only pervading the substance
of the' organs, but also filling up all the intervening spaces, and
preserving them in their proper relative situations. Haller found
it to consist of an irregular assemblage of plares and fibres, cros-
sing one another in all manner of directions ; so that when
stretched or expanded by the insinuation of any fluid between the
plates, the whole presents a cellular structure. These cells, which
are produced by the separation of the plates from each other,
are of no regular shape, but communicate freely with one
another throughout the whole extent of the substance in which
they are met with.

119. As there is a continuity of the cellular substance in every
part of the body, where it exists in this form, there must, in like
manner, be a continuity in the cavities of these cells ; and the
consequence of this structure is, that any fluid, such as air, or
water, which may happen to be introduced into any one part,
will readily find its way into adjoining parts, and will thus
gradually be diff'used over the whole body. If the fluid be water,
as happens in dropsies, it will, by its gravity, tend to accumulate
in the most depending parts of the body, as the ankles, while a
person is standing or sitting; and it will leave these parts, and
be more generally distributed, after he has remained for some
time in a horizontal posture.

The cellular texture may easily be inflated by air ; and this
may happen in consequence of injury, even during life; in which
case the air gradually insinuates itself into every part of the
frame, pufling up the skin to an extraordinary degree, so as
totally to obliterate the features of the face, and disfigure the
whole body. If measures be not taken to let the air escape, the
patient is at length destroyed by suflfocation. A remarkable
instance of this disease, which is termed Emphysema, is given
by Dr. William Hunter, in an essay on the properties of the
cellular texture, contained in the second volume of the Medical
Observations and Inquiries,^ and which also deserves particular
notice, as presenting the best account of this branch of general
anatomy.

* Page 26, et seq.

ADIPOSE TEXTURE. 71

120. The cells, or rather intervals between the plates and
fibres of this substance, contain in the natural and healthy state,
a quantity of aqueous fluid, which has been termed the cellular
serosity, and which serves the purpose of lubricating the surfaces
of the plates, and thus, by diminishing friction, of facihtating
their relative motions on each other. To this circumstance we
may also trace many of the mechanical properties of the cellular
texture ; such as its perfect flexibility, and its great extensibility
in various directions ; while it exerts, at the same time, consi-
derable powers of cohesion. The combination of these two latter
properties is the source of another, which it possesses in a very
eminent degree, that of Elasticity, or the power of recovering
its original form, when the disturbing force, whether producing
compression or extension, has ceased to act. It is evident that
by possessing all these properties, the cellular texture is eminently
qualified to fulfil the important offices assigned to it, of serving as
the elastic scaffolding or canvas for sustaining all the other
parts, and retaining them in their proper situations ; and whilst
it is tlie universal mechanical cement, or medium of connexion
between them, it is at the same time admirably adapted to faci-
litate their relative movements and mutual actions, which are
required for the performance of their respective functions.

121. Another property, besides elasticity, has also been ascribed
to the cellular substance and other textures derived immediately
from it. It consists in a peculiar kind of contractility, attended
by a sudden corrugation and curling up of its substance. As
this property has been supposed to bear some relation to muscular
contractility, we shall defer its consideration till w^e come to treat
of that property.

2. Adipose Texture.

122. This texture contains the oily secretion which is known
by the name of fat. The adipose matter, or fat, is lodged in par-
ticular portions of the cellular texture, appropriated to this office.
It consists of very minute grains of globules, distinguishable only
by the aid of the microscope. Each of these globules is con-
tained in a separate investment, or sac, constructed of an ex-
ceedingly fine and delicate membrane, formed out of the consti-
tuent plates of the cellular substance, and having no external
opening. The size of these vesicles is stated to be from the
eight-hundredth to the six-hundredth part of an inch in diameter.
They are collected together in small rounded masses, united by
vessels, and presenting an appearance under the microscope, not
unlike that of a bunch of grapes. They are lodged in the cells
of the cellular substance in various situations throughout the
body, and contribute to fill up the hollows which occur in difier-

' 72 MECHANICAL FUNCTIONS.

ent places between the bones and muscles, and other organs.
They are very abundant immediately under the skin ; and in
some parts are evidently interposed as cushions for the protec-
tion of organs exposed to injury from pressure or other mecha-
nical violence.

It is evident that the cells in the cellular substance which are
occupied by the fat, are different from those which are the seat
of dropsical accumulations of fluid ; and that they do not, like
the latter, communicate with one another; for it is found that
each portion of fat always remains stationary in the same cell in
"which it was originally lodged.

12.3. The fat varies considerably in its consistence in diflferent
. parts of the body, according to the purpose it is intended to serve.
At the usual temperature of the living body, however, it is retained
very nearly in a state of fluidity. The quantity accumulated in
the body is very different at different periods of life ; and varies
also according to the state of health, and the peculiar habit and
constitution of the individual. It is whiter in its colour, and more
firm in its consistence, during the earlier periods of life, and be-
comes more soft, and acquires a yellow tinge as age advances.

124. The fat of animals has been resolved by Chevreul, who un-
dertook an elaborate analysis of this substance, into two proximate
principles, to which he gives the names, stearin and elam.
The former, derived from the Greek word o-reag, signifying tallow,
is of a much more solid consistence than the latter in ordinary
temperatures, and does not melt under a heat of from 110° to
120° of Fahrenheit. It is obtained from fat by digesting it in
alcohob in the form of white crystalline needles, which are de-
posited as the fluid cools. It is a white brittle substance, void of
taste or odour, and resembling wax in its appearance. If, after
the stearin has been deposited, heat be applied to the remaining
solution, so as to drive off the alcohol, there remains an oily
matter, which continues fluid at 59° of Fahrenheit, and is called,
by Chevreul, elam, from the Greek term for oil, Imiov.

The consistence of the fat of different animals, and in different
parts of the same animal, admits of considerable diversity, ac-
cording to the proportions in which these two ingredients are
contained ; the abundance of stearin is the principal cause of the
hardness of tallow or suet, whilst an increased proportion of elain
characterises the composition of marrow, which is one of the
most fluid kinds of fat.

125. The marrow which occupies the central cavities of the
cylindrical bones, and which also exists in small quantities in the
canals that pervade the substance of the denser portions of the
bones, is perfectly analogous in its composition and structure to
the fat in other parts of the body. The oily pai'ticles are con-
tained in membranous vesicles, which are themselves connected

MEMBRANOUS STRUCTURES. 73

together, and retained in their places by a fine net- work of plates
and fibres, corresponding to the general cellular structure of
other parts, but of a peculiarly delicate contexture.

3. Membranous Structures.

127. When the texture of cellular substance becomes consoli-
dated by the intimate adhesion of the plates and fibres of which
it is originally composed, which, of course, produces the complete
obliteration of its cells, it constitutes the difl^erent varieties of
membranous structures. These structures are of diffei'ent degrees
of thickness, and compose masses of different degrees of density.
When expanded into a continuous sheet or plate, it forms what
is more properly termed a membrane. These membranes, when
sufficiently thin, are semi-transparent, and have a smooth and
uniform surface. Haller found that all membranes are resolvable,
by long maceration in water, into a flocculenf spongy substance,
in which the original cells of the cellular texture from which
they were formed, could be rendered apparent by inflating them
with air.

128. Membranes retain almost all the mechanical properties
belonging to the cellular substance from which they are derived ;
for they are equally flexible and elastic, although possessing
superior strength and firmness. But in one respect they exhibit
a marked difference, while the simple cellular texture, as we
have seen, allows of the general communication of fluids intro-
duced into its cells, from one part to another; membranes are
for the most part impermeable to fluids, and are in consequence
employed with the express design of preventing their ditTusion.

129. The property possessed by membranes of contracting
in their dimensions by the evaporation of the water they contain,
and which is united vwith the animal material by a very weak
affinity, constitutes what may be termed the hygrometric jiro-
perty.

All the membranes are capable of being dried by the continued
apphcation of a moderate heat, and may be kept in this dry state
for a great length of time without undergoing any change. But
if a dry membrane be immersed in water, it absorbs a consider-
able quantity, recovers its softness and flexibility, and expands in
all its dimensions. These effects are greater when the action of
warmth is combined with that of moisture, A membrane will
absorb moisture even from the atmosphere, and again part with
it, according to its different states of humidity. Philosophers
have availed themselves of this property in the construction of
an hygrometer, or instrument for indicating these varying states
of the atmosphere with respect to dryness or humidity. Any
long slip of dried membrane, suspended in the air, and stretched

7

74 MECHANICAL TUNCTIONS.

by a moderate weight, may be made to act on a moveable index
by any mechanical contrivance rendering the variations in its
length visible on a large scale, and v\'ill serve the purpose of an
hygrometer. The menjbrane will be found to lengthen by expo-
sure to a humid atmosphere, from which it imbibes moisture, and
again to contract by the evaporation of this moisture in a drier
air.

A piece of catgut, which is prepared from the membrane of a
sheep, will answer the same purpose. We find, accordingly,
that the state of the weather has a considerable effect upon the
tone of a musical instrument made of catgut. A violin, or harp,
may be in perfect tune in one situation, and yet become quite
out of tune when placed in an atmosphere of greater humidity,
as in that of a room filled with company.

The principle of which these facts are illustrations, is to a
certain extent applicable to the animal body. The doctrine of
the animal fibres being braced or relaxed, which was formerly
a rtiore fashionable language than it is at present, may perhaps
have been carried too far, but it has certainly a foundation in
truth. Warmth and moisture have a powerful influence on the
body, £fnd their efi'ect is partly mechanical ; and this operation,
which is primarily exerted on the skin, renders them' efficacious
in the relief of inflammatory action, by diminishing the tension of
the inflamed parts. This effect is not merely temporary, but may
become the permanent habit of the system. Thus, we find that
the inhabitants of elevated countries where the air is peculiarly
dry, are more hardy, and possess more of the vis tonica in their
frames, than those who dwell in a humid climate, or in low and
swampy plains. The Swiss, and other inhabitants of mountain-
ous tracts, may in this respect be contrasted with the Dutch and
Flemish, who have in general a constitutional laxity of fibre; and
similar differences have been observed in the lower animals
among varieties of the same race.

130. All these properties of membrane, taken together, adapt
them for being employed in various useful ways in the animal
economy. Membranes in general are employed to establish re-
lations not only between adjacent, but also between distant parts ;
they strengthen their connexions, and, whilst in some they allow
of relative motions in certain directions, and to a certain extent,
in others they restrain them and limit their degrees. Almost
every organ is furnished with a firm covering of membrane,
which gives it protection and support. For all these purposes,
a looser and more yielding cellular tissue would not have posses-
sed adequate strength.

131. As the cellular substance is the basis of membrane, so
membrane, in different modifications, constitutes the essential
portion of many other parts of the body ; such as all those re-

MEMBRANOUS STRUCTURES. 75

cipient organs, having the form of sacs cr pouches, hke the
stomach, and especially those which are provided for the retention
of fluids, as the gall-bladder, and urinary bladder. Membranes
are also formed into tubes of various kinds, destined to transmit
their fluid contents to various parts. These tubes, known under
the name of vessels, canals, or duels, are also frequently furnished
with a valvular apparatus, likewise composed of membrane, al-
lowing of the passage of the fluid only in one direction.

132.' The structure and properties of every description of
membranes have been minutely investigated by Bichat, who, in
his Anatomie Gin^rale, has given us an elaborate classification
of the animal textures. He establishes two general divisions of
membranes, namely, the simple and the covrpound. Of the
former he makes three classes; first, the mucous membranes, the
surface of which is defended by a mucous secretion ; secondly,
the serous membranes, characterised by the serous nature of the
fluid with which their surface is constantly moisiened; and,
thirdly, the fibrous membranes, which are distinguished by their
peculiar structure, as being composed of dense and inelastic
fibres. The compound membranes are formed by the intermixture
of two or more of the simpler membranes, and exhibit a combi-
nation of the characters of each.

133. Serous, membranes are universally met with wherever
there are internal cavities in the body, which are closed on
every side, that is, have no communication, by any channel,
with the external air; such cavities being always lined by serous
membranes. This is exemplified in the cavities of the chest,
which are three in number ; namely, one on each side, containing
the right and left lung, and the intermediate cavity, occupied by
the heart. The membranes lining the former are called the
pleurcE ; and the membrane lining the latter, the pericardium.
The great cavity of tha abdomen, in which are situate the organs
of digestion and chylification, is lined by the peritoneum, which
is also a serous membrane. The same, also, applies to the cavites
in the interior of the brain, which are called ventricles, and also
the external surface of the organ, which are lined by the dura
mater, the arachnoid coat, and pia mater. The serous mem-
branes, after lining their respective cavities, are extended still
farther, by being reflected back upon the organs inclosed in their
cavities, so as to furnish them with an external covering. If it
were possible, therefore, to dissect these membranes from off" the
parts which they invest, they would have the form of a sac
without an opening, the organ invested by one of their folds,
being altogether external to the cavity of that sac ; just as happens
when a double night-cap is worn, of which the part immediately
covering the head is analogous to that portion of the serous
membrane which adheres to, and invests the organ ; whilst the

76 MECHANICAL FUNCTIONS.

external portion of the cap represents the lining of the cavity in
which that organ is said to be contained.

134. Hence it will readily be understood, that the serous
membranes never open, or allow of any perforation, for the pas-
sage of blood-vessels, nerves, or ducts, to or from the enclosed
organs ;* but that they are always reflected over those parts,
forming a sheath round them, and accompanying them in their
course. It also follows, as a necessary consequence, that their
free surfaces completely isolate the parts between which they
intervene. The great viscera, suspended in the bags formed by
their serous coverings, can have no communication with the
adjacent parts, except ai the points where their vessels enter ; in
ali other situations there is no continuity of parts, although there
may be contiguity.

135. In every serous memjbrane we may distinguish two sur-
faces having very different characters : the external surface, or
that by which they adhere to the surrounding organs, and the
internal surface, which is in immediate contact with another
portion of the same membrane, but without adhering to it. This
interior surface is remarkable for its perfect smoothness and
polish ; and it is continually preserved in a state of moisture by
a serous fluid, which exudes from it.f This fluid has been
termed the liquid of surfaces, and consists almost entirely of
water, with a very minute proportion of albuminous matter. Its
presence is evidently of the greatest use in facilitating the mo-
tions of the parts contained within the cavities, with relation to
their sides, by diminishing friction, preserving the smoothness of
the surfaces applied to each other, and preventing their mutual
adhesion. When the internal surface of these membranes is
exposed to the air in living animals, or immediately after death,
this fluid exhales in the form of vapour, to which formerly great
attention was paid, and which was dignified with the name of
halitus. In consequence of disease, this fluid of surfaces some-
times accumulates in one of these cavities, and thereby produces
a dropsy of that respective cavity : a fact which proves the
pov/er of serous membranes to retain these fluids, and not, as
in the case of the cellular substance, to allow of their diffusion
into the adjoining organs.

136. The serous membranes constitute the simplest form of
condensed cellular substance ; they are not divisible into any

* [The only exception to this is in the case of the peritoneuna, on which
the ventral extremities of the fallopian tubes terminate.]

f [Rudolphi (^Grundriss der Fhysiologie, 113) asserts, that some membranes
are incapable of inflammation, are not vascular, and do not secrete, buttliatthe
secretions of shut sacs take place from the subjacent parts and transude the
serous membranes proper, which, in his view, are, consequently, a kind of
epidermis.]

OSSEOUS FABRIC. 77

regular layers ; although cellular portions may be removed from
the outer surface by which they are attached to the surrounding
parts. In the natural state they are exceedingly thin and trans-
parent; but become thicker and opaque by disease. Although
perfectly flexible, they possess considerable strength ; they are
exceedingly extensible ; but they are not in the same proportion
elastic : for after they have been stretched, they give but feeble
indications of a power of retraction.

4. The Osseous Fabric.

137. For the purpose of thoroughly understanding the whole
mechanism and operations of any complicated engine, or system
of machinery, the best and most natural course is to commence-
with the study of the solid framework, which gives stability to
the whole fabric, and affords fixed bearings from which the
powers, regulating the movements of its different parts, exert
their respective powers. This purpose of procuring mechanical
rigidity and support, is the appropriate function of the osseous
system, or skeleton ; which is composed of a connected series of
solid structures, called hones, deriving their mechanical proper-
ties from their peculiar chemical composition, and almost crys-
talline hardness, and which constitute one of the most important
of the constituent textures of the body. Our first object of atten-
tion, therefore, in considering the mechanical functions, is the
study of this system of structures.

138. The bones, then, are to be viewed as the densest and
most solid parts of the animal frame; constituting the basis of
support to the softer textures, affording protection to all the vital
organs, and furnishing those powerful levers which are essential
to the advantageous action of the muscles concerned in locomo-
tion, and in the various movements of the limbs. With reference
to their form, they have usually been divided into three classes :
\he long cylindrical hones; the broad and fat bones; and the
sho7^t or square bones, which include those of a more irregular
form, and not referable to either of the other two heads. To
the first class belong the principal bones of the upper and lower
limbs, which are adapted more especially to the purposes of
motion. Under the second may be ranked the bones of the skull,
which serve for the protection of the brain ; and the third include
the vertebras, the bones of the face^ and the small bones which
concur in the formation of the wrist and the ankle. There are,
besides, other bones, such as the ^ibs and the bones of the pelvis,
of a more anomalous description, which are rather distinguished
by their irregularity than by any definite character.

139. On examining the mechanical structure of bones, we
find that their external surface is generally their hardest part,

7*

78 MECHANICAL FUNCTIONS.

and that it consists of a solid plate, or layer of bony matter, of
different thickness in different bones, and in different parts of the
same bone. In the cylindrical bones this firm and compact sub-
stance extends only to a certain depth, and within this the struc-
ture is spongy and cellular. To the latter part the name cancelli
has been given. In the middle of the long bones the central
parts are occupied by the marrow ; but as we continue our
examination, by taking different sections across the bone,
in proportion as we approach the extremities, we find the
dense external substance diminishing in thickness, while the
proportion of the spongy part increases, and encroaches upon
the space in the centre occupied by the marrow, which at
length disappears, so that at the very extremity of the bone,
nearly the whole area of the section is filled by the cancelli,
while the outer covering of solid bone is merely a thin superficial
plate. In the ffat bones, having, of course, an upper and under
surface, the plates of bone forming each of these surfaces, are
termed the two tables, and the cellular portion which is found
between them is called the diploe. In many of the more irregu-
larly shaped bones, neither cancelli nor diploe are found, the whole
substance being compact. Dr. Bostock observes, that the transi-
tion from the compact to the spongy part of a bone is not marked
by any decided limit ; but they pass into each other by insensible
degrees, so as to show that there is no essential difference between
them.*

140? Bones present the appearance of fibres on their surface.
This is seen particularly in all bones that have been long
exposed to the weather, or that have been long boiled. In the
cylindrical bones most of these fibres are longitudinal ; but in the
flat bones they generally run in a radiated direction. In the
short bones their course is much more iiTegular and diflficult to
trace. In the compact part of the section oi a bone, the appear-
ance of plates is not very distinguishable ; but certain cavities
are discovered which, for the most part, run in a longitudinal
direction, and nearly parallel to one another. They are of
various lengths ; and their diameters are exceedingly small.
They have transverse or oblique canals, which establish communi-
cations between them ; and some of which also open into the larger
cancelli in the middle of the bone. These cavities have been
called the canals of Havers,f who first discovered them. Their
existence, however, was for a long time considered dubious ; but
it has been lately verified by Mr. Howship,J who, with the help
of the solar microscope, oblaiijed distinct views of them, and was

* Elementary System of Physiology, third editicn, p. 61.

f Osleologia nova, §35, 37.

X Medico-Chirurgical Transactions, vii, 393.

OSSEOUS FABRIC. 79

enabled to trace their course. He ascertained the diameter of
these canals to be about the 400th of an inch; and farther disco-
vered that they are lined with an extremely fine vascular mem-
brane, and that they are filled with marrow.

141. The intimate structure of bone was first minutely investi-
gated by Malpighi, who discovered that its basis consists of an
animal membrane having an areolated, or cellular form. Duha-
mel* next ascertained that this membranous matter was fre-
quently disposed in plates or laminae ; and he described these
plates as forming concentric rings, analogous to those which
compose the trunk of a tree ; but there is no other foundation
than mere fancy for this analogy. We owe to Herissantf the
important fact, that the chief properties of bone are derived from
the presence of an earthy ingredient, which is deposited in the
animal basis, or parenchyma of the bone.

142. The analysis of a bone into its two constituent parts is easily
effected by the agency either of acids or of heat. By macera-
ting a full-grown bone for a sufficient time in diluted muriatic
acid, the earthy portion of the bone, amounting to nearly one-
third of its weight, is dissolved by the acid ; the animal portion
only remaining. This animal basis retains the bulk and shape
of the original bone, but is soft, flexible, and elastic; possessing,
in a word, all the properties of membranous parts, and corres-
ponding in its chemical charaoSer to condensed albumen.J A
•portion of this solid animal substance affords gelatin by long
boiling in water, especially under the pressure, admitting of a
high temperature, to which it may be subjected in Papin's digester.
On the other hand, by subjecting a bone to the action of fire, the
animal part alone will be consumed, and the earth left untouched,
preserving, as before, the form of the bone, but having lost the ma-
terial which united the particles, presenting a fragile mass which
easily crumbles into powder. This earthy basis, when chemi-
cally examined, is found to consist principally of phosphate of
lime, which composes eighty-two hundredths of its weight ; and
to contain also, according to Berzelius, minute portions of fluate
and carbonate of lime, togethei: with the phosphates of magnesia
and of soda.

Dr. G. O. Rees, who has lately made exact analyses of different
hones taken from the same individual, in a state of perfect dry-
ness, and quite free from fat, periosteum, or cartilages, deduces
from his researches the following conclusions :§ 1. The long
bones of the extremities contain more earthy m.atter than those
of the trunk. 2. The bones of the upper extremity contain

* Memoires de TAcademie des Sciences, pour 1739, 17-11, 1742-, and 1743.
flbid. 1758.

:j: This was first satisfactorily shown by Mr. Ilatchelt. Phil. Trans, for 1800.
§ Medico-Chirurgical Transactions, xxi. 409.

80 MECHANICAL FUNCTIONS.

somewhat more earthy matter than the corresponding bones of
the lower extremity ; thus the humerus more than Jthe femur, and
the radius and ulna more than the tibia and fibula; this difference is,
however, small, being about one-half per cent. 3. The humerus
contains more earthy matter than the radius and ulna, and the femur
.more than the tibia and fibula. 4. The tibia and fibula contain,,
as nearly as possible, the same proportions of animal and earthy
matter, and the radius and ulna may also be considered alike in
constitution. 5. The vertebrae, ribs, and clavicle, are nearly
identical as regards the proportion of earthy matter; the ileum
contains somewhat more of the earth, the scapula and sternum
somewhat less ; the sternum contains more earthy matter than
the gcapula. 6. The bones of the head cqntain considerably
more earthy matter than the bones of the trunk, as observed by
Dr. J. Davy ; but the humerus and other long bones are very
nearly as rich in earths. 7. The metatarsal bones may probably
be ranked with those of the trunk in proportional constitution.
8. The cancellated structure (at least in the rib) contains less
earthy matter than the more solid parts of the bone ; this dif-
ference, however, is not considerable. 9. The bones of the trunk
of the foetal skeleton are as rich in the proportion of earthy matter
as those of the adults ; at least the difference is too small to be
material. 10. The bones of the foetal extremities, on the other
hand, are deficient in earthy matter, which is a fact simply ex-
plicable from the circumstance that such an excess of earths as
appears necessary to very great strength of bone is not needed
at birth, and therefore only appears in after life.*

The existence of a general law, regulating the proportion of
earthy deposit in the different bones, (which is shown by the
curious agreement of relative proportions observed between the
foetal and adult skeletons,) adds one more to the many proofs of

* [Professor Miescher, of Basel, in Switzerland, who has published an excel-
'lent account of the general anatomy of bones, with which he has favoured the
Editor, gives the following as the proportions of the animal and earthy parts.

Infants. Adults. Aged.

Animal matter, . . . 47.20 20.18 12.20

Earthy matter, . . . 48.48 74.84 84.10

95.68 95.02 96.30

The proportions, however, differ in the different bones : According to Thilenius,
in a dissertation on the chemical composition of bones, published at Got-
tingen, in 1823, the bones of the extremities of the new-born infant, freed
from animal matter by burning, left 57.59 per cent. ; the vertebra of the neck
and back, 47.41 ; the clavicle of a boy, 63.26; the os frontis and os parietale,
65.21; the petrous bone of the adult, 68.72; the bones of the extremities,
66.66; the ribs, 63.37; the frontal, femoral, occipital, and inferior maxillary
bone of an old person, 66.79. — Miescher, De Injlammatione Ossium eorumque
Anatome Generali, p. 48 : Berol. 1836. See, also, Pancousfs Edition of Wis-
tar's Anatomy^ i. 29. Phil ad. 1838.]

OSSEOUS FABRIC. 81

the regularity and perfection of design wiiich nature evinces in
her operations.

143. It appears evident, then, from these and other facts, that
the basis of the osseous structure is essentially the same as that
of membranous parts, being composed of fibrous laminae or plates,
which are connected together so as to form, by their intersection,
a series of cells analogous to those of the cellular texture. In
the interstices of these plates, or in the cells themselves, the par-
ticles of phosphate of lime are deposited ; the particles being held
in union by the interposed membrane, which performs the office
of a cement. Hence there is no necessity for admitting the
hypothetical explanation of Gagliardi,* who maintained, that the
bony plates are held together by small processes, like nails, which,
rising from the inner plates, pierce through the adjoining ones, and
are fixed into the more external plates. Of these processes, or
claviculi,as he called them, he described four different kinds, the
perpendicular, the oblique, the headed, and the crooked. But
no subsequent anatomist has been able to verify these observa-
tions ; and the account given by Gagliardi remains on record as
a curious instance of the extent to which an observer of mere
appearances is liable to deceive himself by the influence of too
vivid an imagination. Monro^ states, that in bones fitly prepared
he could only see numerous irregular processes rising out from
the plates. . Duhamel, trusting to a fancied analogy between the
process of ossification, and the growth of trees, imagined that a
bone is composed of a series of regular concentric laminae. But
this hypothesis has been refuted by Scarpa,f who investigated,
with great care, both the mechanical structure of bone and the
mode of its formation ; and concludes that the ultimate texture
of bone is not lamellated but reticular. Raspail has indulged in
speculations of a still more questionable nature respecting the
ultimate osseous texture, which he endeavours to assimilate with
that vesicular form, which he views as the essential character
both of animal and of vegetable organization. Dr. Benson
observesj that all writers, before the time of Scarpa, considered
the structure of bone as laminated, or fibrous and laminated;
whilst, according to all later authorities, it should be regarded as
cellular. In the works of the former, however, we may notice
intimations of a reticular texture ; and in those of the latter, on
the other hand, we meet with the expressions of a tendency or
disposition to a laminated arrangement. '• If, with these opinions
before us," he continues, " we come to examine for ourselves,
we shall have no hesitionin agreeing with Scarpa that it is really
cellular. At the same time, it must be confessed > that the sides

* Anatomia Ossium. f De Penit. Structura Ossium.

X Cyclopaedia of Anatomy and Physiology, vol. i. p. 433.

82 MECHANICAL FUNCTIONS.

of the cells are, in the compact tissue, so pressed together, that
the appearance of laminas is often very striking; and, again, that
the sides of the cells have, in most places, the appearance of
fibres; whep the earthy portion is removed by an acid, we can
tear out with a pin the membranous fibres, and almost demonstrate
the fibres. But a closer examination will show that we have
torn the cells, and destroyed the true texture. The laminated
disposition supposed to be shown by exfoliation, the weather,
burnino-, &c., may all be proved to be deception ; and there can
seldom, indeed, be exhibited a plate, however small, of equal
thic4cness throughout, which has been removed by any of these
agents. There is, however, an approach to the laminated ar-
rangement, and every cell is formed of particles which approach
to the form of fibres. The longitudinal canals of Havers, Leu-
w^enhoeck, and Howship, probably result from the flattened cells,
and may be deceptive appearances in the old bone, or the chan-
nels for blood-vessels, &c."

144. Bones are invested on every part of their surface, ex-
cepting in those parts where they are plated with cartilage, with
a firm plate of membrane, termed the periosteum, which conveys
blood-vessels to the bone, and establishes mechanical connexions
between it and surrounding parts. This membrane belongs to
the class of fibrous textures, being composed of numerous in-
elastic fibres of great density and strength, passing in various
directions, and composing a kind of ligamentous tissue, interlacing
with the fibres of the ligaments which encircle the joints.

The inner surface of the periosteum is connected with the bone
by the vessels passing from the one to the other, and also by
numerous prolongations which dip down into the osseous sub-
stance. The blood-vessels of this membrane are numerous., and
easily rendered apparent by means of injections, especially in
young subjects. Besides the more obvious uses of the periosteum,
in affording protection to the surface of bones from injurious
impressions, which they might receive from the action of sur-
rounding parts, and interposing a membranous layer for the
defence of the latter, Bichat ascribes to it the more important
ofiice of affording fixed centres of support to the general system
of fibres, in its mechanical relations to the rest of the frame.
The periosteum which covers the bones of the skull has received
the name of the pericranium.

145. The internal cavities of the bones are, as is well known,
occupied by an oily secretion, termed the marroiv, contained in
a delicate structure, composed of minute vesicles which are filled
with the fluid oil, and which are connected by fine threads and
plates of fine cellular tissue. Monro describes the vesicles as per-
fectly distinct, having no communication with one another, and

CARTILAGE. 83

as presenting, under the microscope, the appearance of a cluster
of pearls.

Many have been the conjectural uses assigned to the marrow
by the older physiologists ; it was at one time very generally
imagined that it served, by its mechanical properties, to temper
the brittle quality of the earthy materials which form the chief
constituent portion of the bone ; a purpose, however, which it is
impossible it could fulfil, as, instead of being mixed up and blended
with the phosphate of lime, or diffused generally through the
substratum of the bone, it is lodged in separate cavities, and
thereby prevented from any union with bony matter, or inter-
mixture with its substance. The marrow is, in general, possessed
of little sensibility, except in a few points, where it is traversed
by the nervous filaments supplying the bone itself. It is regarded
by physiologists of the present day rather as constituting a part
of the general store of nutritious matter, which is kept in re-
serve for particular occasions of exigency, than as having any
mechanical relation with the dense texture within which it is
lodged. The circumstance of its being wholly absent in the
bones of birds is a clear proof that there is no mutual dependence
between the functions of the latter and the presence of the marrow.

146. All the internal cavities of bones occupied by the marrow
are lined with a vascular membrane, which follows all the
windings of the canals and of the cancelli, and has been called
the internal periosteum. It may easily be rendered visible by
sawing a long bone longitudinally, and plunging it ' in boiling
water, by which treatment the membrane is made to detach
itself from the bone, and contract upon the marrow which is
within it, and to which it is closely attached. It has then the
appearance of a fine cobweb.

5. Cartilage.

147. The structure which ranks next to bone in respect to its
density is cartilage, a term which expresses a firm and dense sub-
stance, apparently homogeneous in its texture, semipellucid, and
of a milk-white or pearly colour. Substances of this description
are found to enter into the composition of several parts of the
body. The surface of a cartilage is perfectly uniform, and pre-
sents no visible eminences or pores ; nor can any cavities or
inequalities of any kind be perceived in its internal texture. When
it is cut into with a sharp knife, the section exhibits a uniform
appearance, like that of a piece of glue. Yet, after exposure for
a certain time, the surface thus cut begins to contract, and a
serous fluid is perceived slowly to exude from it, proceeding
from certain invisible pores, which are in all probability minute
capillary vessels, of which the diameters are too small to admit

84 MECHANICAL FUNCTIONS.

the coloured globules of the blood. That a delicate system of
circulating passages exist in cartilages, is shown by various dis-
eased conditions, in which sometimes granulations have been seen
to arise from their surfaces, and at other times extensive absorp-
tion of their substance has taken place ; and although insensible,
on ordinary occasions, to wounds inflicted by cutting instruments,
yet in others, when sudden pressure is made on them under pe-
culiar circumstances, extreme pain arises, giving warning of
serious injury impending.

Cartilaginous structures appear to be composed of albumen
alone, with scarcely any intermixture" of gelatin. Dr. John Davy
found that they contain a small proportion of phosphate of lime,
amounting to about the two hundredth part of their weight.
Mr. Hatchett, however, does not regard the substance as an
essential, ingredient in their composition.

The mechanical property which particularly dintinguishes
cartilage is elasticity, a quality which it possesses in a greater
degree than any other animal structure, and which adapts it to
many useful purposes in the economy. Hence it forms the basis
of many parts where, contrary to the purposes answered by the
bones, phancy and resilience as well as firmness are required ;
and hence cartilage is employed when a certain shape is to be
preserved, together with a capability of yielding to an external
force. The flexibility of cartilage, however, does not extend
beyond certain limits ; if these be exceeded, fracture takes place.
Great density bestowed upon an animal structure, indeed, appears
to be in all cases attended with a proportionate degree of brittle-
ness. These mechanical properties of cartilages, as well as their
intimate structure, although nearly homogeneous in all, are
subject to modification in different kinds of cartilage. Cartilages
are covered with a fine membrane, termed the perichondrium,
analogous in its structure and office to the periosteum, which we
have already had occasion to point out among the fibrous mem-
branes, as investing the bones.

148. Cartilages are distinguished into those which are tempo-
rary and those which are permanent structures. The former
are only met with in the earlier periods of life, during the growth
of the body, and are gradually removed to make way for the
deposition of bone. When about to undergo this change, small
canals have been detected in the substance of these temporary
cartilages. The permanent cartilages are those which retain the
cartilaginous structure throughout every period of life. They
have been distinguished into three or four different kinds, such
as the membraniform, the interosseal, the articular, and the
interarticular cartilages.

149. The membraniform cartilages are included by Bichat in
the class of fibro-cartilaginous structures hereafter to be de-

CARTILAGE. 86

scribed. They furnish a basis of support to the softer parts, and
in some measure supply the place of bone, giving a determinate
shape and firmness to parts where bone would have been incon-
venient. They possess greater tenacity and less brittleness than
the other kinds of cartilage. By their elasticity they admit of
considerable variation of figure, yielding to external pressure,
and recovering their proper shape as soon as the pressure is
removed. Of this kind are the cartilages of the nose and ear,
and also those of the larynx and trachea. These cartilages are
extremely thin, and are invested with a very thick and firm peri-
chondrium, to which they are connected by means of a number
of fibres traversing their substance, and rendering their sarfaces
rough and porous. Long maceration enables us to detect these
fibres, and to resolve the whole into a cellular and albuminous
substance.

150. The interosseal cartilages pass from one bone to another,
adhering firmly by their extremities to each. They answer the
same purpose as would be attained by an increase of extent in
one or both of the bones, with the further advantage of allowing
of obscure degrees of motion, and deadening the eflJects of jars
incident to percussion. The cartilages of the ribs are of this
class. They are covered with perichondrium. When they have
been steeped in water for a great many months, they are divisi-
ble into laminas, of an oval shape, which are united by fibres
passing obliquely between them.

151. The articular, or diarthrotlial cartilages, are those
plates of cartilaginous substance which adhere firmly, and almost
inseparably, to the surfaces of those bones which are opposed to
each other in the joints, or over which tendons and ligaments
slide. In some joints the whole of the surface of the bone within
the capsular ligament is covered with cartilage ; in others, only
the parts of bones which move upon each other ; the remaining
part being covered with ligament. This latter disposition is
met with in the joint of the hip. This kind of cartilage, like the
others, appears perfectly smooth on its surface, and also w^hen a
section is made through its substance ; but by a sufficiently long
maceration, to allow of a commencement of putrefaction, its
fibrous structure may be detected. The elastic resilience of these
cartilages has a powerful tendency to lessen the shocks incident
to sudden and violent actions.

152. Cartilages of a similar kind are found in the cavities of
certain joints, and have hence been called inter articular carti-
lages. They have no immediate connexion with the bones
forming the joint, but are attached only to the inside of the
capsular ligament. They are thus rendered somewhat moveable,
and being interposed between the bones, allow them a greater
latitude of motion, while they at the same time contribute to

86 MECHANICAL FUNCTIONS.

adapt their surfaces more perfectly to each other. By long
maceration in water, a laminated structure is more distinctly
perceived in this kind of cartilage than in any of others.

6. Fibro-Cartilaginous Structures.

153. Many structures exist in the human body which appear
to be of an intermediate nature between ligament and cartilage,
in which a fibrous texture is united to a cartilaginous basis, and
which combine the characteristic properties of both these tex-
tures. They are distinguished from the purely ligamentous parts
by their high degree of elasticity, and fronri cartilage by their
fibrous texture. Accordingly we find them employed when this
combination of properties is requisite for the functions of the
parts. They form additions to interarticular ligaments, and eke
out the borders of cavities adapted to the reception of the rounded
heads of bones.

154. The principal instances of large masses of fibro-cartila-
ginous structures occur in those which unite the bodies of the
vertebree and of the bones of the pelvis. These intervertebral
substances, as they are termed, impart great elasticity to the
spine; and diminish the effects of concussion. When the body
has been long ni the erect position, the weight of the head and
upper parts of the trunk occasions the compressionof these inter-
vertebral substances, and the height of the person is diminished.
By continuance for an equal time in a horizontal posture, this
super-incumbent pressure being removed, they recover their ori-
ginal dimensions. Hence a person is taller when he rises in a
morning than after sustaining the fatigues of the day ; and the
difference of stature often amounts to a whole inch.*

7. Ligamentous Structures.

155. Structures possessing inferior degrees of soHdity, but still
exhibiting considerable density, are met with in the interior of
the body, and serve various mechanical purposes of cohesion
and support. Many of these may be regarded as mere modifi-
cations of membrane ; but yet the peculiarities of structure and
of properties, exhibited by ligamentous textures, point them out
as requiring to be classed separately. Bichat, who has viewed
them as composing a system of structures, has given to it the
title of the fibrous system ; a name which is Hable to the objection
of not being sufficiently distinctive ; since, as we shall afterwards
find, many other parts, and especially the muscles, are no less

* [Buffon asserts, that the son of one of his most zealous collaborafeurs,
M. Gueneau de Montbeillard, a young man of tail stature, lost an inch and a
half, after having danced all night.]

LIGAMENTOUS STUUCTURES. 87

fibrous than the tendons and the ligaments. As a general desig-
nation of this class of fibres, we liave therefore preferred the term
of ligamentous system, which sufficiently expresses the general
mechanical purpose which they are designed to serve in the ani-
mal economy.

156. This system includes a great number of structures, which,
although very similar in their nature and office, have received
different names, such as ligaments, tendons, fascice, aponeuroses,
capsules, &c. Fibres of a similar kind to those which constitute
these parts, also enter into the composition of other organs,
imparting to them different degrees of mechanical strength.

157. Various as are the forms and dispositions assumed by liga-
mentous fibres, they present us with two principal varieties,
according as they are expanded into thin and broad plates, or
ligamentous membranes, or collected into thick and elongated
cords. The first division includes fibrous membranes, fibrous
capsules, tendinous sheaths, and aponeuroses.

158. The jihrous membranes resemble ordinary membranes,
but have, superadded to the structure of the latter, numerous
denser fibres, which gives them greater strength, and fit them for
aflfording mechanical support to various organs. Thus, the peri-
osteum of the bones is a membrane of this description. The
internal periosteum of the skull or dura mater has a similar
structure. The external coat of the globe of the eye, or sclero-
tica; the investing membranes of many of the glands, as ol the
kidneys, belong to the class of fibrous membranes ; to which also
we may perhaps refer some of the coats of the larger blood-
vessels, and of the excretory ducts of glands. Besides envelop-
ing organs, these fibrous membranes often extend into their
interior, forming partitions, or even cells, which contribute to
their firmness and support.

159. The jihrous capsules present the form of sacs, which
surround certain joints, especially those of the shoulder and hip,
and preserve the connexion between the bones which form these
joints. These capsules, again, are fined internally by serous or
synovial membranes, supplying the fluid which lubricates the
surfaces of the parts playing upon each other.

160. The tendinous sheaths are formed by fibrous membranes
of a cylindrical shape, which surround^the tendons in those parts
where they pass over bones, and are particularly subjected to
friction, or hable to occasional displacement during the action of
the muscles which move the joint. Some of these include only
one tendon in their respective cavities, as those of the fingers
and toes : others receive several tendons, as those belonging to
the muscles of the wrist and ankle joints.

161. Aponeuroses consist of extended sheets of fibrous texture,
principally belonging to the organs of locomotion ; and disposed

88 ■ MECHANICAL FUNCTIONS.

in some instances so as to forn;i coverings of parts ; while in
others they constitute points of attachment to muscles. Thus,
they may be distinguished into aponeuroses for enveloping, and
aponeuroses for insertion. The former, which are generally
termed fasciae, either surround the muscles of the limb, forming
a general sheath for it, as the fore-arm and thigh ; or else they
invest and confine some particular muscles. The aponeuroses
for insertion either form broad or narrow surfaces, or consist of
separate fibres, giving attachment to particular portions of mus-
cles, or form arches, which both admit of their connexion with
muscular fibres, and at the same time allow of the passage of
vessels.

162. The second division compose the proper ligaments and
tendons, all of which have more or less the form of cords.

The ligaments connect together the articular surfaces of bones,
and oppose a very considerable I'esistance to any force tending
to their displacement. The fibres which enter into their compo-
sition, generally . preserve a direction nearly parallel; but fre-
quently they are extended in various ways, forming an intertexture
calculated to resist extension in different directions ; and from
their mere flattened form, bringing these ligaments nearer to the
description of fibrous membranes.

163. The tendons are generally more simple in their structure,
consisting of elongated cords; but in some instances they are
more complicated, being divided into several smaller cords.

164. Bichat* has exhibited, in the following table, a general
view of the preceding classification of what he calls the fibrous
system.

f cd [ Fibrous membranes.
-Q g I Fibrous capsules. .

1 ^ Fibrous sheaths, . j General

2 3 ! C Fnr p.nvp

fM

TFor envelop- ^ Partial.

I . J ment. ) General.

Aponeuroses, . < i^j u j r

{ r ' j f in a broad surface.

1^ [For insertion ■? In an arch.

( In separate fibres.

, r • X ^ With rpffular fasciculi.

L Ligaments, . < ^,^^^•^v, ■ i f • r

) ^ (^ With irregular fasciculi.

i m J S Simple,

f Tendons, . i n^^,.i;.

\ Complicated.

165. The structure of all these parts, as their name imports,
is essentially fibrous : the individual fibres which compose them
being exceedingly slender filaments of a very dense, firm, and
inelastic substance ; sometimes parallel to each other, as in the
tendons and ligaments, and sometimes variously interwoven, as

* See his Anatomie Generale, torn. ill. p. 142.

ARTICULATION. 89

in the fibrous membranes. In some portions of the denser struc-
tures hereafter to be noticed, the fibres are so closely united as
to present an almost homogeneous appearance ; but in all the
parts hitherto considered, the bundles of fibres admit of being
separated by maceration; and are resolvable into lengthened
filaments of extreme tenuity. It has not been perfectly ascer-
tained what is the diameter of the fibres when the subdivision
has been carried to its utmost hmit ; but they appear in this
ultimate state of division to be as fine as the filaments spun by
the silk-worm. These ultimate fibres are distinguished by their
flexibility, their extreme tenacity, and their brilliant whiteness.
They are probably in no case tubular, but soHd throughout,
although Mascagni, extending to them his general system of
organic textures, regards them as formed of lymphatic vessels.
Chaussier,* with great appearance of truth, considers them as a
peculiar and primary organic tissue, to which he has given the
name of the albugineous fibre, in order to distingush it from the
mere simple cellular or membranous fibre, which constitutes the
basis of the general substance of the body.

166. The fibres which enter into the composition of these
ligamentous textures, are united by a cellular tissue of extreme
fineness and' tenuity, which is rendered evident after maceration
when the ligamentoas fibres .are drawn asunder. Their arrange-
ment at the surface of these structures is such as to produce that
fflistenipo; and satin-like lustre which results from a surface of

111

high polish and density ; an appearance which is very character-
istic of the fibrous structures. This smoothness and resplendent
white colour is possessed in the greatest degree by tendons,
which have in general a greater extent of motion than the liga-
ments, and therefore require a higher degree of polish.

Sect. III. — Mechanical Connexions.

1. Articulation.

167. Having noticed the properties of those elementary textures
that furnish those cohesive and resisting forces which are neces-
sary for the mechanical purposes of the animal fabric, we have
next to review those combinations of structure which have been
adopted for estabhshing the connexions between the various parts
of the frame, and which adapt them to those objects. These
modes of connexion admit of great variety, according to the dif-
ferent mechanical relations which must take place between them;;
and more particularly with reference to the degrees of mobility

' Dictionnaire des Sciences Medicales. , Organization.

8*

90 MECHANICAL FUNCTIONS.

which are to result from their union. In many cases the parts
placed in juxtaposition require to be fixed in their places by the
firmest bonds which can secure their relative immobility : in
'others, the freest motion must be allowed ; while in various other
instances, we find almost every intermediate degree of flexion
allowed, and every kind of connecting mechanism employed.
But from the deep implanting of the teeth in the jaws, hke nails
firmly fixed in wood, and the mutual locking in of the bones of
the skull by indented sutures, like the dove-tailed junctions of car-
pentry, to the freely rotating joints of the limbs, as in those of the
shoulder or the hip, we may trace various modes of articulation
which are calculated to limit the extent and to regulate the kind of
movements, in subordination to particular ends. There is cer-
tainly no part of the human fabric, wonderfully and fearfully as the
whole of it has been made, which exhibits more palpable evidences
of express mechanical contrivance and adaptation to specific pur-
poses, than the construction of the joints, and of the whole of
their auxihary apparatus. It is well observed by Paley,* that
every joint is a mechanical curiosity, and a proof of contriving
wisdom. They are, indeed, as Cicero has truly expressed it,
'" mirabiles commissuras, et ad stabilitatem aptas, et ad artus
finiendos accommodatas, et ad motum, et ad omnem corporis
actionem. "f

168. There are two circumstances which determine the kind
of relative motion of which a joint, by which term is more par-
ticularly meant the connexions of adjacent bones, is capable.
The first of these comprises the form of the contiguous surfaces
of the bones themselves which are brought to play on each other,
and their mode of apposition ; the second relates to the structure
and mechanical conditions of the interjacent flexible parts, such
as the ligaments, the cartilages, and the membranes, which impart
different degrees of elastibility or springiness, and variously
modify the motions which result. With respect to the first, the
principal diversities arise from the various extent of range al-
lowed with regard to the planes of motion ; and these varieties
are naturally distributed under two heads ; the one being a semi-
rotatory motion within a considerable extent of a spherical surface,
as exemplified in what are called the ball and socket joints ; the
other, in which the angular motion is restricted to a single plane,
as is the case with what are termed the hinge-joints. It is not
necessary here to advert to the further distinctions to which a
minute examination of all the different modifications of these
kinds of mechanism, which are exhibited in the solid structures
of the body, would lead us ; which the older physiologists pursued
with great diligence, and which they were fond of dignifying

* Natural Theology. f De Natura Deorum, 1. ii. c. 35.

ARTICULATION. 91

with a formidable array of technical terms. It will be sufficient
for our present purpose to observe, in general, that the long bones
of the limbs have their extremities expanded so as to form broad
surfaces where they are in apposition with the contiguous bones,
between which a joint is formed. In the ball and socket joint,
it is the moveable bone which has the rounded head, and the fixed
bone, or that nearest to the trunk of the body, which contains
the corresponding cavity or socket. Such at least is the case in
man ; but some animals present us with examples of a contrary
arrangement ; that is, of the concave surface of the moveable,
turning on a convex projection of the fixed, bone. Bones of a
flat or irregular shape are, in general, much more limited in their
motions, when they form joints, than those of a lengthened cylin-
drical form.

169. In proportion to the extent of motion allowed in the joint,
we find provisions adapted for diminishing friction, and guarding
against injury. In all the articulations the ends of the bones,
which enter into their formation, are invested with a smooth and
polished plate of cartilage ; a substance which, by its modified
hardness, and great elasticity, is especially adapted to both these
purposes. Its limited degree of organization, also, gives it many
advantages in withstanding the influence of pressure, especially
if suddenly made, and frequently repeated. In some joints this
investing layer of cartilage is of equal thickness throughout, so
that it appears as a crust, regularly moulded over the articular
surface of the bone which it covers, and exactly preserving its
figure ; but, in other cases, it is found to be thicker at the middle
than at the marginal parts; thereby increasing the convexity of
the projecting portion, or diminishing the concavity of those
which recede ; both of which appear to be provisions for ensuring,
as the case may be, the uniformity of contact of the adjacent
parts composing the joint. These superficial cartilages, or "car-
tilages of incrustation," as they have been termed, appear to be
composed of a multitude of slender fibres, strongly adhering
together, and all of them are perpendicular to the tangential
planes of the surface of the bone they invest, like the pile of velvet,
and disposed, therefore, in a manner very similar to that of the
^bres of the enamel of the teeth, which is superimposed in nearly
the same way on the bony part of the tooth. The most complete
investigation of this structure will be found in a paper of Dr.
William Hunter's, published in the Philosophical Transactions.*
It results from this conformation, that the fibres, on the application
of pressure, yield to a certain degree, and bend in waves : just
as happens to velvet when it is compressed ; and they again
resume their perpendicular positions on the removal of the com-
pressing force.

* For 1743, vol. 42, p. 544.

92 MECHANICAL FUNCTIONS.

170. The whole of the interior surface of each joint is lined
with a smooth and glistening membrane of great tenuity, forming
a cavity closed on every side, and supplying a peculiar secretion,
termed the synovia, obviously intended for the lubrication of all
the contiguous surfaces. Similar synovial memhranes, a,s they
are called — forming, in like manner, closed sacs — are met with,
surrounding the sheaths of the tendons, and interposed between
other parts, the motions of which would expose them to con-
siderable friction. In the former case, when employed in the
articulations, they are termed capsules of the joints ; in the latter,
they have received the inappropriate name of Bursce Mucoscb.
The synovia is a transparent and viscid fluid, slippery to the feel,
and capable of being drawn out into strings by the fingers. It
has been imagined, that the secretion is principally derived from
certain fringe-like processes, chiefly visible in the knee and hip-
joints, and constituting what have been called the alar ligainents.
These membranous appendages, which project into the cavity of
the joint, and appear to be formed by folds of the synovial mem-
brane, containing some cellular substance, and small pellets of
adipose matter, present an appearance very similar to that of the
epiploic duplicatures of »*the peritoneum, and especially of the
appendices epiploiccB of the colon.

171. The motions, which a joint is capable of performing, are
often modified and extended by the interposition of detached
plates of cartilage, connected only by ligament with the synovial
capsule, and capable of shifting their position, so as to enlarge
the range and modify the mode of action. Those, which we have
already described under the title of inter articular cartilages, are
met with chiefly in joints where the motion is frequent and con-
siderable, and where the ends of the bones are subjected to great
pressure ; as^in the junction of the lower jaw with the temporal
bone, and in the knee-joint. The semilunar cartilages, in this
latter example, increase the depth of the articular cavity, and
ensure, in all the motions of the joint, a perfect adaptation of the
surfaces to one another.

172. The bones are retained in connexion, their junction
strengthened, and their relative movements farther regulated, by
the ligaments which invest the joint. Of these there are two,
kinds, the capsular, and the fascicular ; the former investing the
joint on all sides in the case of the ball and socket articulation ;
and the latter passing from bone to bone in difl^erent directions,
limiting the motion more or less to a particular plane. When, in
the hinge-joint, they are placed externally on the two sides, they
form what are called lateral ligaments ; but in the case of the
knee, additional securities are provided, by short and round liga-
ments crossing one another in the interior of the joint ; these are
the crucial ligaments. Besides these, we often find other liga-

PACKAGE OF ORGANS. 93

i;nentous bands, passing more obliquely, and dispersed in different
directions, which assist in strengthening the joint, preventing the
displacement of the bones, and thus completing the mechanical
apparatus of each articulation. The muscles, which surround
the joint, also contribute very powerfully in retaining the bones
in their proper places, and preventing the sudden dislocations
which might otherwise occur during the strains incident to rapid
and violent actions.

2. Package of Organs.

173. The great mechanical objects of adhesion and support
being provided for by the organic systems we have now consi-
dered, our attention may next be directed to purposes of a subor-
dinate and special nature, and which relate to local adaptations,
comprehending w^hat Paley has aptly termed the package of the
organs. Art and contrivance have been as manifestly displayed
in fulfilling these more limited objects, as in the more extended
designs of the general fabric. When we consider the vast multi-
plicity of parts, — requiring the study of years of patient instruc-
tion and dissection to be thoroughly acquaintedwith, — which are
closely arranged and stowed in the narrow space allotted for
them in the body, we cannot but be struck with the care that has
been taken in their disposal in the most convenient manner, and
with the greatest economy of room. The brain consists of a
prodigious number of fibres, gathered together in curious folds,
or convolutions, in order that they may occupy the smallest
possible bulk, and be contained within the circumscribed cavity
of the skull, which is to afford them protection. Within how
small a compass are lodged all the delicate parts which compose
the complex organ of hearing, and which are encased in a hollow^
space, scooped out of the most solid parts of those bones 1 Equal
care has been bestowed in the lodgment and package of the
viscera which occupy the other cavities of the body, namely,' the
thorax and abdomen. Those which are of greatest importance
to life, and whose delicate texture admit most easily of being
injured, are always placed in situations of greatest security, and
effectual care is taken to provide additional protection by means
of bones, cartilages, or other denser mechanical fabrics.* All
'the organs are tied down and secured in their places by mem-
branes, so adjusted in regard to breadth and flexibility, as to
allow of those motions which their functions require ; or, in other
cases, to retain their displacement, by tightly binding them in

* [This is true in the main ; j'et the abdominal viscera — wounds of which,
of the liver and intestines, for example, are almost always fatal — are contained
in a cavity, the anterior parietes of which afford very slender protection to
the important contents.]

94 MECHANICAL FUNCTIONS.

their situation!?. All the important viscera &,re invested with
coverings proper to themselves, composing capsules, v^^hich are
generally of great density and strength, and calculated to give
them effectual protection against pressure _or other mechanical
causes of injury. The muscles, which are in strongest and most
frequent action, are firmly braced and tied down by sheets of
fibrous tissue, inserted into the neighbouring bones, and prevent-
ing them from starting from their places when urged into sudden
and violent contractions. Lastly, all the spaces intervening
between the muscles, blood-vessels, nerves, and bones, are filled
up with a quantity of cellular and adipose substances, sufficient
to leave no vacuity. Hence arises that rounded and flowing
outline which has been given to the body, and which forms one
of the constituent elements of its beauty.

174, The provision of a general envelope to the whole of this
complex system of organs, may be regarded as another conside-
ration which appertains to the subject now before us, namely, the
package of the body ; but its importance is such as to entitle it
to be treated under a separate section.

175. This combination of structures, individually possessing
different degrees of rigidity, but cemented together by a highly
elastic medium, and bound down by a general envelope of con-
siderable strength, produces a result, which, being of considerable
importance with reference to the mechanical condition of the
fabric, is deserving of special notice. It is matter of observation
that the sum of the cohesive forces among the particles conriposing
the mass of animal tissues, is balanced, in the living body, only
by the resistance arising from the rigidity or incompressibility of
the parts opposed to them ; or, in other words, the force of elas-
ticity in the cellular and membranous textures is not in a state of
neutrality, but the equilibrium is maintained only by the mecha-
nical circumstances of situation. Thus it happens that, when
these circumstances are altered, and the equilibrium disturbed,
elasticity comes into play and produces a shrinking of the whole
mass. The result is that, in the natural- state, every part is kept
on the stretch ; but retracts as soon as its elasticity is allowed
to act by the removal of the extending cause. This will happen
whenever the contents of hollow organs are withdrawn, whenever
the parts themselves are divided transversely by a cutting instru-
ment, and also, when, by a change of position, their extremities
are brought nearer together, and the mass assumes a more
rounded figure. This property, the result of a high degree of
unbalanced elasticity, has long been known, though described
under various names. The term by which it h|as most frequently
been designated is that of tone or tonicity ; but Bicliat, who has
given a good description' of its effects, denominated it " contrac-
tu itidetissu,^ ' and " contractilitepar difaut d^ extension," whilst

EXTERNAL INTEGUMENTS. 95

he regards tonicity as anollier and distinct property not of a
mechanical, but of a vital nature. The observations we have
formerly made on the vital properties, will show that we regard
the distinction which he here makes as being founded on very
questionable grounds.

Sect. IV. — The Integuments.
1. The External Integuments.

176. The skin, which gives covering to the whole body, toge-
ther with its various prolongations and parts connected with it,
and constituting altogether the integuinents, are complex struc-
tures. They consist, in the first place, of ordinary cellular tis-
sue ; secondly, of the same substance in a more condensed and
membranous form ; and, thirdly, of a stratum of adipose sub-
stance ; but they also present us with a kind of structure which
differs totally from any of those we have hitherto had occasion
to notice. For the clear understanding of these distinctions, it
will be necessary, first to explain in greater detail the composition
of the external integuments, or the skin.

The parts of which skin consists are arranged in layers ; and
in giving an account of these we shall take them in an order the
reverse of that in which they are usually considered ; beginning
with the innermost layers, and proceeding successively to the
more external.

177. That portion of the integuments which is called the true
sJ^iny is in most parts of the body separated from the adjacent
muscles or bones, by a stratum of fat, or rather of adipose sub-
stance ; that is, as we have already seen, of a cellular and vesi-
cular structure, containing the minute globules of the fat. In
other parts, the attachment of the skin is effected merely by
interposed common cellular substance, of more or less thickness
and density in different places. The succeeding layer is that
which forms by far the largest portion of the integuments, and
has been denominated the corion, or the true skin. Its ultimate
structure is described by Haller as being analogous to that ot
membranous parts ; that is, composed of a dense intertexture of
short fibres and of plates, artificially interwoven together, and
united by the close adhesion of their surfaces. It may in this
view, therefore, be considered as merely a denser tissue of the
common cellular substance, which is, in fact, the basis of most
animal structures. The density increases gradually as we trace
the texture from the inner to the outer parts ; while at its interior
surface it passes gradually into the looser cellular texture which
is beneath it. Bichat gives a similar description of the essential

96 - . MECHANICAL FUNCTIONS.

structure of the corion, but states that, in addition to this, there
are found a great number of dense fibres, of a whiter colour than
the rest, interspersed throughout its substance, which pass in all
possible directions, so as of themselves to compose a close net-
work, and leave certain interstices or areolce. This reticulated
texture, with the interposed vacuities, may be discovered by
long-continued maceration, which loosens the adhesion of the
fibres. Small masses of fat are found occupying the intervals
between them. Thus the dense fibres of the corion may be re-
garded as the chief support or skeleton, as it were, of the whole
fabric, giving it its requisite form, consistence, and other mecha-
nical properties.

178. The external portion of the corion is more finely orga-
nized than the rest. It has been considered as forming a distinct
layer of the skin, named by Bichat, from the large proportion of
minute blood-vessels it contains, the vascular net-work ; and by
•other anatomists, corpus papillare, from its presenting on its
outer surface, when viewed with the microscope, an immense
number of little eminences or conical projections, which have
laeen termed papillce. These papilige were discovered by Mal-
pighi, and have been since described and delineated by Ruysch,
Albinus, and many other anatomists. Cheselden and others,
however, have doubted their existence, at least as a necessary
appendage of the corion ; for papillae are perfectly visible to the
naked eye on the upper surface of the tongue, where they are
presented on a very large scale. They are also easily perceived,
with a magnifying glass, at the tips of the fingers, as well as in
other organs endowed with a peculiar sensibility to impressions
of touch.* But in those parts of the body which have not the
same sensibility, and are seldom employed as the vehicles of
touch, they are so minute as scarcely to admit of detection ; and
their existence has been inferred rather from analogy than from
distinct and positive observation.

179. The external surface of the corion, or of the corpus
papillare, is covered with a thin layer of a soft substance, which
Las been termed the Rete Mucosum. It was first observed by
Malpighi, in the skin of the negro, and is hence often called after
him the Rete Malpighianum. The structure, and even existence
of this membrane have given occasion to much controversy.
Malpighi had announced it as being a stratum of soft matter,
disposed in the form of lines which crossed one another in various
directions. Blumenbach and other anatomists describe it as
merely a thin layer of pulpy matter, without any distinct reticulated
structure. Bichat, on the other hand, denies altogether its ex-

* [Breschet (^Nouvelles Recherches sur la structure de la Peau, Paris, 1835)
calls the corpus papillare the ' Neurothelic Apparatus.']

EXTERNAL INTEGUMENTS. 97

istence as a proper membrane, and supposes that what Malpighi
saw and described is merely a collection of very delicate vessels,
which, after having passed through the corion, form a net-work
on its surface. In this opinion he is supported by other anatomists
of high authority, as Chaussier and Rudolphi. Mr. Cruickshank,*
on the contrary, who bestowed great pains on the examination
of this subject, entertains no doubt of the existence of the rete
mucosum, both in the external skin, and also even in some of its
productions in the interior of the body. Dr. Gordon admits of
the presence of the rete mucosum in the skin of the negro, where
it is easily demonstrated ; but asserts that it cannot be found in
that of the European. On the whole, the positive evidence in
favour of the real existence of this membrane appears to pre-
ponderate ; and, at any rate, it seems admitted on all hands, that
the colouring matter of the skin, which is black in the negro, and
has different tints in the other varieties of the human race, is
situate in that part which has been assigned as the seat of the
rete mucosum. By some it has been stated that the rete mucosum
extends in a uniform layer over the whole surface of the true
skin ; by others that it is perforated in various parts by the papillae
of the corion, and exists only in the interstices of these papillae.*

180. The outermost layer of the skin is the cuticle or epider-
mis, which gives a uniform covering to every part of its surface,
adhering closely to it, and being accurately applied to all its
inequalities. It adheres with considerable tenacity to the subjacent
skin, through the medium of the rete mucosum, and its attachment
is perhaps also secured by fibres passing from the one to the
other. In the dead skin a separation is easily effected by macer-
ation in water, and by a state of incipient putrefaction. In the
living body the cuticle is detached by the operation of a blister,
or by scalding water, which produce an effusion of serous fluid
on the outer surface of the corion. As the cuticle is impervious
to this fluid, it is raised, and gives rise to a permanent vesicle.

181. When the cuticle is carefully separated from the corion,
after its connexion has been loosened by putrefaction, a multitude
of very slender transparent filaments are seen, stretching between
these two layers, which are torn asunder when farther extended.
Dr. William Hunter believed these filaments to be the terminations
of those vessels which exhale the perspiration, and nearly the
same views have been entertained with regard to their nature

* On Insensible Perspiration.

f [Breschet (Op. citat.') affirms, that there is a special <■' chromafngenous
apparatus'''' for producing the colouring matter, composed of a glandular or
secreting parenchyma, situate a little below the papillae, and presenting par-
ticular excretory canals, which pour out the colouring matter on the surface
of the derma.]

9

Ho MECHANICAL FUNCTIONS.

by Bichat and by Chaussier. Cruickshank, on the contrary, con-
sidered them to be processes from the cuticle, and not vessels.

182. Many erroneous notions have atdifierent times prevailed
with respect to the intimate structure of the epidermis. Lee-
wenhoeck conceived that it is composed of a number of laminae,
or scales, which he represented as having an imbricated arrange-
ment, that is, overlapping each other successively, like the scales
of a fish. But it is now generally admitted that this M'as a de-
ceptive appearance. The division of layers, which it may seem
to admit of in parts where it is of unusual thickness, is merely an
artificial separation, not warranted by any natural distinction of
textures. Although some have pretended to discover in it a
congeries of vessels, especially Ij'mphatics, yet the most accurate
and unbiassed observers declare that they cannot perceive in the
epidermis, a specific texture of any kind or any regular arrange-
ment of its parts. Dr. Gordon gives it as his decided opinion
that it is "truly inorganized, and non-vascular."*

183. Leewenhoeck imagined also that he could discern a
number of perforations, or pores, as he termed them, in the
cuticle. But later and more scrupulous inquirers have looked in
vain for these supposed pores; and it is now generally admitted
"that none such exist. Indeed, one of the most characteristic

properties 'of the cuticle is its impermeability to fluids, under
ordinary circumstances. The latest inquiries into this subject
are those of Mr. Chevalier.f who describes the cuticle as com-
posed of an infinite number of small vdamina, regularly arranged,
so as to form a bibulous and exquisitely hygrom.etrical covering.J
The mode in which the occasional transmission of fluids through
this substance takes place in cutaneous absorption, and perspira-
tion, will be the subject of future discussion. The only real dis-'
tinguishable pores in the cuticle are those which give passage
to the hairs, and to the sebaceous follicles hereafter to be noticed.
' Thus, then, there is presented to us in this layer of the integu-
ment, a kind of structure differing essentially from either the
cellular or membranous tissues which have already been des-
cribed. The epidermis is an animal texture, nearly homogeneous
in its substance, possessing but amoderate degree of extensibility,
and approaching to the nature of an inorganic substance, inas-
much as it exhibits no appearance of vascularity, and a total

* [The researches of the Investigators, referred to in the third note, have ex-
hibited that the tissue of the epidermis is complex, -and that its organization is
connected with the functions of exhalation and absorption. Its vitality, if
any it possess, has been compared to that of the vegetable.]

t Lectures on the General Structure of the Human Body, p. 133.

X [Still later investigations have been made by MM. Breschet and Roussel
de Vauzeme, {Op. citat.) by Wendt {MuUei-''s Jrchiv. 1834,) and Von
(lurlt, (Ibid. 1835.) which have thrown considerable light on its structure.
See, also, British and Foreign Med. Review, ii. 429.

EXTERNAL INTEGUMENTS. 90

absence of nerves, or other medium of connexion with the Hving
system. Bichat even considers its vitality as exceedingly ob-
scure; he doubts whether it can be said to possess life; but is in-
clined to regard it as a semi-organized, or rather inorganic body,
placed by nature at the point of communication between external
dead matter and the living skin, and serving as a gradation be-
tween them.*

184. The nails and the hair are to be classed as structures
very similar to the epidermis, of which, indeed, they are often
regarded as mere appendages. The nails, in particular, have so
intimate an adhesion to the epidermis, that both are generally
detached together, by maceration. They consist of hard, trans-
parent, and semi-elastic plates, formed of a substance analagous
to the horns of animals. They adhere to the subjacent corion,
(which is in those parts furnished with a great abundance of
minute blood-vessels, and of which the papillas are arranged in
longitudinal and parallel rows, very close to one another,) in a
manner similar to that in which the epidermis adheres to the
corion in other parts. The internal surface of the nail is soft,
pulpy, and marked with longitudinal grooves corresponding to
the lines which they cover and enclose; and by this mutual
adaptation the connexion between them is extremely intimate.
The innermost edge of the nail is received into a groove formed
of a duplicature of skin fitted for its reception. The epidermis
belonging to this portion of skin is folded back upon it, and on
arriving at the root of the nail, quits the corion, is reflected over
the external surface of the nail, and becomes identified with its
substance.

The nails, in all their mechanical properties, correspond to the
cuticle, and may be regarded as the same substance in a greater
state of condensation.

The hair consists of slender filaments, which appear to bd formed
of nearly the same substance as the nails, and may be considered,
in a mechanical point of view, as still mor^. condensed forms of
cuticle. Each hair is provided at its root, with an expanded por-
tion, or bulb, from which its extension proceeds, and which by
the intervention of its vessels, connects it with the corion, in
which it is imbedded, just as the roots of a vegetable attach it to
the soil. The strength of hair is exceedingly great, compared
with its small diameter, as has been frequently ascertained by
trying the weights which it can support without tearing. There
is no substance, indeed, which would be better adapted for making

* [Breschet affirms, that there is a special bhnnngenous apparatus for the
secretion of the mucous matter constitulinij the epidermis, which is composed
ofa glandular parenchyma or organ of secretion, situate in the substance of the
derma, and of excretory ducts, which issue from the organ, and deposite the
mucous matter between the papillae.]

100 MECHANICAL FUNCTIONS.

ropes than human hair, provided it could be procured of sufficient
length. It scarcely possesses any extensibility, and is consequently
inelastic. If exposed to moisture, it imbibes a certain quantity
of water ; and this absorption is accompanied with an increase
in the length of the hair. From its having this property, it has
been employed by De Saussure as a hygrometer, or instrument
for indicating the degree of moisture or dryness of the atmosphere.
In order to adapt it to this purpose, however, it requires to be
freed from a quantity of oily matter, which it naturally contains,
by maceration in an alkaline solution. The colouring matter of
the hair is supposed to correspond in its nature, as it does in its
appearance, to that which is contained in the rete mucosum of
the skin.

Thus we find that there is a very considerable similarity be-
tween the hair, the nails, and the cuticle, with regard both to
structure, composition and mechanical properties ; and that they
may be regarded, when once their formation has been completed,
as equally devoid of vascularity, and as possessed of the lowest
degrees of organization and vitality ; if, indeed, these latter pro-
perties can at all be attributed to them.

2. Of the Internal Integuments, or the Mucous Membranes.

185. The structure which characterises the external integu-
ments is continued in various places into the internal parts ; and is
found, with certain modifications, in all those membranes which
line the internal surfaces of cavities or channels having an exter-
nal opening. This is the case with the whole track of the alimen-
tary canal; including the mouth, pharynx, oesophagus, stomach,
and intestines. It is exemplified, also, in all the passages of the
air in respiration, as the nostrils, larynx, trachea or wind-pipe,
bronchia or air-tubes, and the air vesicles of the lungs. All those
passages which open externally, such as those of the ears, urethra,
and vagina, are like^se defended by a lining of mucous mem-
brane.

186. Bichat has considered the mucous membranes as forming
a distinct system of structure. Analogous in many respects to
the serous membranes, they present, in others, the most marked
differences. They agree in their office of affording protection to
the organs to which they are attached ; and their structure, in as
far as it is chiefly resolvable into condensed cellular tissue, is
very similar. But as they have to serve the additional office of
defending the parts which they invest against the irritating
qualities of the substances that may come in contact with them,
and which may be either the external air or the food, or extra-
neous bodies, received from without ; or else secretions formed
hy the internal organs, which are to be conducted to the surface,

INTERNAL INTEGUMENTS. 101

it was necessary that the fluid which covered them should have
properties adapted to this ohject.

187. We find, accordingly, that instead of the watery liquid
which exudes from serous membranes, the mucous membranes
prepare a secretion containing a large proportion of mucus.
Hence a more complicated structure is required in the mucous
than in the serous membranes. They are divisible into several
layers; that which connects them with the parts surrounding
the passage or cavity which they line, is of a denser structure ;
while the one which forms the inner surface of the cavity is
softer, and somewhat pulpy in its consistence. Its surface is
beset, in many parts, with numerous minute processes, or villi^
as they are termed. These have been supposed to bear some
analogy to the papillce of the corion ; and the general corres-
pondence of the structure of the mucous membrane and of the
external integuments has been farther pursued in the examina-
tion of the fine pellicle which gives a universal covering to the
pulpy portion, and which has been assimilated to the cuticle.
There can be no doubt that the cuticle belonging to the skin is
continued over the membranes which line many of the passages
above enumerated, and may be traced for a considerable way in
those passages. As wo advance farther, this cuiicular covering
becomes gradually thinner, till it ceases to be perceptible.

188. But the circumstance which more especially character-
ises the mucous membranes, is the presence of a number of small
cavities, crypts ov follicles as they are called; which have more
or less of a spheroidal shape, and which open upon the surface of
the membrane by a distinct orifice, or duct of communication.
These minute sacs or follicles are themselves lined with an
extremely fine cuticular membrane, derived from the general
covering of the surface on which they are met with. They are
found filled with mucus, and are therefore considered as the
sources whence that secretion is principally derived.

189. Follicles of a similar structure are found in the various
parts of the skin ; but the substance which they produce, and
which they effuse upon the surface of the skin, is more of an oily,
than of a mucous nature. It has been termed sebaceous matter ;
and the small cavities which prepare this matter, are known by
the name of the sebaceous glands ov follicles.

190. Thus it appears, that although the offices of the external
integuments of the internal mucous membranes are sufficiently
distinct, yet a general analogy exists between them in many
points of their structure, sufficient to justify their being arranged
under the same order, in a general classification of animal struc-
tures.

9*

102 MECHANICAL FUNCTIONS.

Sect. I V. — Muscular Action.

191. Having now considered the system which constitutes the
passive instrunnents of the fabric, it is time that we direct om'
attention to the active powers which are the sources of motion,
and the springs of animation and of energy in the Uving body.

192. As in an extensive system of machinery, economy is best
consulted by the employment of a single moving power, such as
a fall of water, the impulse of the wind, the current of a river,
or the force of steam, so, in the animal economy, nature has
provided the muscular power, and applied it in every instance
where great mechanical power was required to accomplish the
intended object. But before inquiring into the nature of this new
animal power, it will be necessary to consider the properties of
those organs, the muscles, in which this power appears to reside.

1. Structure of Muscles.

193. Muscles are organs composed of certain fibres, endowed
with a peculiar power of contracting in their length, under certain
circumstances. These fibres are generally disposed in a parallel
direction, and variously united together by intervening cellular
substance. The muscular system forms a large proportion of the
weight, and certainly the greater part of the bulk of the human
body.

194. On examining the structure of a muscle, we find the
minuter fibres are every where surrounded by a fine cellular
texture, which connects them together into bundles, which have
been called fasciculi. These bundles are connected to each other
by coarse cellular membrane, so as to form fasciculi of larger
size : these, again, are united together into still larger fasciculi
by a still more loose cellular tissue. This system of package is
continued until we arrive at large cylindrical bands of fibres,
which have been termed lacerti, and which, being applied laterally
to each other, and covered by a general investment of membrane,
compose the entire muscle. The fasciculi, as well as the cellular
membrane, are coarser in some muscles than in others. Thus
they are thicker in the large muscles of the limbs, than in the
delicate muscles appropriated to the eye, and other organs of
sense. The structure which has now been described is easily
discovered in a portion of muscle which has been cut transversely,
and then boiled for some time, or macerated in alcohol.

195. Physiologists have not contented themselves v/ith these
general views of the structure of muscles, but have been sohcitous
to ascertain the nature and dispositions of the ultimate fibres to
which muscles owe their characteristic properties. The micro-

STRUCTURE OF MUSCLES. , 103

scope has been resorted to for this purpose ; but the success of
those observers who have trusted to this instrument in establishing
any certain facts, has by no naeans corresponded with the dih-
ge'nce and zeal with which they have engaged in the inquiry.
We find in this, as in nnany other subjects where the appearances
resulting from the employment of very high magnifying powers
are the objects of research, that the greatest discordance prevails
among the accounts given by different observers. Leewenhoeck,
who was one of the first who applied the microscope to the in-
vestigation of the intimate structure of organized bodies, but
who was too often led away from the truth by the ardour of his
imagination, describes the ultimate muscular fibres, or those
which admit of no further mechanical division without a separa-
tion of their substance, as being almost inconceivably minute.
He states them to be many thousand times smaller than a fibre
which would only be just visible to the naked eye. He represents
them as cylindrical in their shape, and parallel to each other, but
pursuing a serpentine course. He remarks that they are of the
same figure in all animals, although differing considerably in their
diameter in difierent animals, and that without any relation to
the size of the animal. He observed, for example, that the fibril
of the frog was larger than that of the ox.

196. Muys, a Dutch anatomist, who was engaged for a period
of twenty-five years in the most laborious researches on this sub-
ject, arrived at a very different result from Leewenhoeck ; for
he concludes that the real ultimate fibrils of muscles are in all
cases, even when the comparison was extended to animals,
exactly of the same size.

197. Among the more modern anatomists, Prochaska* has
bestowed the greatest care in the examination of this subject;
and his account has every appearance of being entitled to our
confidence. He states expressly that the muscular fibrils are
not all of the same diameter, but differ in different animals, and
even in different parts of the same animal. Each individual
fibril, however, when carefully separated from all extraneous
matter, is of uniform thickness throughout its whole extent, and
perfectly continuous, even in the longest muscles, from one end
to the other. He confidently asserts that they are solid ; and
instead of being cylindrical, that they have a prismatic, or poly-
hedral shape, generally flattened, or thicker on one side than on
the other ; a transverse section of the muscle thus presenting the
appearance of basaltic columns in miniature. Their diameter is
stated to be about the fiftieth part of that of the globules of the
blood. Their surface was found to present a number of depres-
sions or wrinkles ; a circumstance which gives them a serpentine

''^De Came Musculari.

104 MECHANICAL FUNCTIONS.

appearance. These transverse lines he attributes to the numerous
blood-vessels, nerves, and membranous bands which cross the
fibrils at different points.

198. According to Hooke and Swammerdam, the muscular
fibrils are composed of a series of globules. Other physiologists,
such as Cowper and Stuart,* whose observations appear to have
been influenced by preconceived theories,' imagined that they
were cellular. Borelli,t who was also biassed by his favourite
hypothesis, believed them to be composed of a series of rhomboidal
vesicles. The Abbe FontanaJ in general agrees with Prochaska
in his representation of muscular fibrils. He remarks that they
are furnished with transverse bands at regular intervals, and that
they may always be distinguished by their parallel disposition
from the fibres of membrane, which are more or less contorted.

Sir Anthony CarUsle§ states that a muscular fibre duly pre-
pared, by washing away all adhering extraneous substances, and
viewed by a powerful microscope, appears to be a solid cylinder,
the covering of which is a reticulated membrane, and the con-
tained part, a dry pulpy substance, irregularly granulated and of
little cohesive power when dead.

199. Mr. Bauer,|| who is one of the latest authorities on this
subject, represents the ultimate muscular fibrils, as composed
of a row of globules, exactly corresponding in size to those of
the blood when deprived of their colouring matter ; that is,
about the five-thousandth part of an inch. By long maceration
in water, he finds that the mutual coesion of these globules is
loosened, and the fibre is consequently broken down and resolved
into a mass of globules. The general results of Mr. Bauer's
observations were confirmed by various observers an France,
such as Dr. Edwards, and by Messrs. Prevost and Dumas, Beclard
and Dutrochet.

200. On the other hand, the more recent, and apparently ac-
curate researches of Dr. Hodgkin and Mr. Lister,1[ and subse-
quently those of Mr. Skey,** have clearly shown that the supposed
globular structure of the muscular fibre is a mere optical decep-
tion, arising from deficient defining power in the microscope
employed ; and that the fibre is continuous throughout its whole
length, and sometimes marked by transverse stri^, which occur
at intervals much smaller than the diameter of the fibre itself
They have also pointed out this circumstance as constituting a
remarkable distinction between the muscles of voluntary and

* Dissertatio de Structura et Motu Musculari.

t De Motu Animalium. X ^"'' ^^s Poison?.

§ Philosophical Transactions for 1805. _ || Ibid, for 1818, p. 164.

"if Appendix to Dr. Hod^kin's translation of Dr. Edwards's work, " De
I'lnfluence des Agens Physiques sur la Vie."

**Philosophical Transactions for 1837, p. 371. t

MUSCULAR CONTRACTILITY. 105

those of involuntary motion, with regai'd to this striated struc-
ture; for it is only the fibres of the former which are charac-
terized by innumerable very minute, but clear and fine parallel
lines, or strias, which cross the fibre transversely. Mr. Skey
concludes from his researches, that these fibres in man have an
average diameter of one four-hundredth of an inch, and that
they are surrounded by transverse circular striae varying in
thickness, and in the number contained in a given space. He
describes these stria) as constituted by actual elevations on the
surface of the fibre, with intermediate depressions, considerably
narrower than the diameter of a globule of blood. Each of these
muscular fibres, of which the diameter is one four-hundredth of
an inch, is divisible into bands of fibrillse, each of which is again
subdivisible into one hundred tubular filaments, arranged parallel
to one another in a longitudinal direction, around the axis of the
tubular fibre which they compose, and which contains in its
centre a soluble gluten. The partial separation of the fibrillce
gives rise to the appearance of broken or interrupted circular striae,
which are occasionally seen. The diameter of each filament is
one sixteen-thousandth of an inch, or about a third part of that
of a globule of the blood. On the other hand, the muscles of invo-
luntary motion, (or as Bichat would term them, of organic life) are
composed, not of fibres similar to those above described, but of
filaments only; these filaments being interwoven with each other
in irregularly disposed lines of various thickness, having for the
most part a longitudinal direction, but forming a kind of untrace-
able net-work. They are readily distinguishable from tendinous
fibres, by the filaments of the latter being uniform in their size,
and pursuing individually one unvarying course, in lines parallel
to one another. The fibres of the heart appear to possess a
somewhat compound character of texture. The muscles of the
pharynx exhibit the character of the muscles of voluntary mo-
tion ; whilst those of the oesophagus, the stomach, the intestines,
and the arterial system, possess that of the muscles of involuntary
motion. The determination of the exact nature of the muscular
fibres of the iris, presented considerable difficulties, which Mr.
Skey was not able satisfactorily to overcome.

2. Muscular Contractility.

201. The proper muscular fibre is so completely surrounded
by cellular membrane, and is of so small a diameter, that it is
scarcely possible to determine with accuracy its physical proper-
ties, independently of those of the tissue in which it is imbedded.
The contractile power with which it is endowed, can be studied
only as its effects are exhibited by collections of fibres, such as
those which constitute the muscles ; although in these it must

106 MECHANICAL FUNCTIONS.

obviously be combined with the elastic power of the cellular
texture entering into its composition.

202. It will soon be evident, however, that the property by
which the muscular fibre is eminently characterised, is that of
suddenly contracting in its length, and thus of bringing the two
ends of the muscle, and the parts to which those ends are
attached, nearer to each other. This contraction is produced
with astonishing quickness and force, overcoming considerable
resistances, and raising enormous weights. It is generally the
effect of the will of the animal to move the parts to which the
muscle is attached ; but it may also be excited by other causes.
The agent which thus produces muscular contraction is called a
stimuhts.

203. Under the appellation of stimuli, are included many things
which seem scarcely to have any property in common, except
that of acting upon the muscular fibres, either directly, or through
the medium of the nerves which supply them. The contact of
many bodies will produce this efi'ect by mere mechanical impulse,
independently of any other quality they may possess. Whatevet
occasions a mechanical injury to the texture of the muscle or
nerve, or an actual breach of substance, such as the puncture,
division, or laceration of the fibres, will immediately excite mus-
cular contraction. This effect also results from tlie application
of any substance exerting a chemical action on the part; a class
of stimuli which comprehends a great variety of agents, such as
acids, alkalies, and most of the salts which they form by their mutual
combinations, as also the earthy and metallic salts, alcohol, the
volatile oils ; and above all, oxygen, either in the form of gas, or
when contained in substances that part with it readily. Even
water itself seems to have some corrugating power when it is
applied directly to the muscular fibre ; its action, however, is
much increased by minute quantities of salt which it may hold in
solution. Thus it is found that hard water promotes the contrac-
tion of the muscles of fish that have been crimped more than
fresh water; and a similar difference of eflect is often observed
in boiling meat in soft or in hard water.

204. But besides these, there are several of the vegetable and
animal products which, when applied to the body, produce mus-
cular contraction by an agency which cannot clearly be traced
to any chemical property they possess. This class of stimuli
includes a variety of substances which are denominated acrid,
and others which are called narcotics, because when largely
applied they destroy altogether the power of contraction, and soon
extinguish life. As an example of this latter class, we may take
opium and hydrocyanic acid.

205. Some particular muscles have a disposition to be acted on
more especially by particular kinds of stimuli. Each stimulus

MUSCULAR CONTRACTILITY. 107

applied to the body generally, appears to exert a particular in-
Huencc upon certain parts of the system which are predisposed to
be affected by it, while on other parts it appears to be wholly inert.
Thus, emetic substances act principally on the stomach, even
wdien applied to a diHcrent part of the system ; and cathartic sub-
stances act specifically on the intestines. The muscular fibres of
the heart are more particularly excited to contraction by the in-
flux of blood into the cavities of that organ ; and in like manner,
every system of muscular fibres concerned in carrying on the
vital functions has a specific disposition to be affected by its
appropriate stimulus.

206. All the muscles which move the joints of the limbs, aiad
the several parts of which the skeleton is composed, together
with several muscles attached to the softer parts, such as the
eye, tongue, and throat, are excited to contract by the stimulus
of the will, and are therefore called voluntary muscles. They
compose a class, by themselves, as distinguished from^ those
muscles which are not under the control of volition, and which
are therefore involuntary muscles, such as the heart, stomach,
intestines, and blood-vessels. The nature of this distinction, and
of the different laws under which each class of muscles act, will
be afterwards pointed out, when we come to treat of the physi-
ology of the nervous system,

207. The natural state of a muscle, or that in which it exists
when not acted upon by any external cause, is relaxation. When
contracted, its surface, from being smooth, becomes furrowed,
its middle portion swells out, and grows exceedingly hard and
firm, while the extremities are drawn nearer to each other, so
that the muscle is now both thicker and shorter than it was before.

208. It has been frequently made a question whether the
increase of thickness exactly compensates for the diminution of
length. This point might be determined by ascertaining whether
the specific gravity of a muscle undergoes any alteration during
this change. Glisson had inferred from some experiments which
he had made on this subject, that the bulk of a muscle is, on the
whole, diminished when it is in a state of contraction. Sir Gilbert
Blane,* on the contrary, inferred from experiments which he
made on fishes confined in a glass vessel with a very slender
neck, that the absolute bulk, and of course the specific gravity,
of their muscles remains the same whether they are contracted
or relaxed; for the level of the water in the narrow stem of the
vessel was observed to be unafl'ected by the muscular exertions
made by the fish. Mr. Mayo, by an experiment of this kind on
the heart of a dog, found the bulk of that organ unchanged during
its contraction or relaxation.f

* Phil. Trans, for 1805, p. 22, 23.

f Anatomical and Physioligical Comnnentaries, p. 12. [See, on the whole
of this subject, DungUsoii' s Fhysiolugy, 3d edit., 1. 341.]

108 MECHANICAL FUNCTIONS.

209. The long- continued, or frequent application of a stimulus
■to a muscle, tends to impair its power of contracting, or in other
words, to exhaust its irritability. This liability to exhaustion is
exemplified by all the muscles that are under the control of the
will. We cannot continue to exert the same muscle, or set of
muscles with the same degree of power beyond a certain time,
however strong may be the motive to continue that action, and
whatever mental effort we may make to persevere. If, for
•example, we extend the arm in a horizontal hne, with a weight
held in the hand, we shall find, in the course of a few minutes,
that the sense of fatigue becomes intolerably acute ; and the arm
at length drops from mere exhaustion, in spite of every voluntary
•eflfort.

210. The contraction of a muscle ceasing on the removal of
-the stimulus that produced it, relaxation succeeds, and the muscle
becomes again elongated ; not, however, in consequence of any
inherent power of elongation, but from the operation of causes
which are extraneous to it. The elasticity of surrounding parts
is often -sufficient to produce this effect; but in most cases the
elongation of the relaxed muscle is the consequence of the action
of other muscles, which produce motion in a contrary direction.
Almost every muscle has another corresponding muscle, or set
of muscles, which are antagonists to it. If the one, for instance,
binds a joint, the antagonist muscle unbinds or extends it ; and
.by this action must elongate the former muscle.

211. The swelling of the muscles of the limbs, when they are
in strong action, is matter of familiar observation. It is this cir-
cumstance, above all others, which renders a knowledge of ana-
tomy so essentially necessary to the painter and the sculptor. In
•every attitude and in every movement of the body some particular
set of muscles are in action, and consequently swelled and pro-
minent, while others are relaxed and less conspicuous ; and unless
these differences were accurately noted and faithfully expressed,
it would be impossible to give a correct representation of the
living figure.

212. Although the fibres which compose the smaller portions
of a muscle are arranged in parallel directions, yet the disposition
of the mass of fibres, relatively to the whole muscle, varies con-
siderably according to the action which the muscle is intended to
perform. We find them, in some cases, radiating from, or con-
verging to a particular point; and sometimes we even find that
the different portions of a muscle having this structure can act
independently of the rest. The temporal muscle is an instance
of a muscle of which the fibres converge from the circumference
to a central point, where they are inserted into the coronoid pro-
cess of the lower jaw. In other cases, the fibres composing the
muscle pass in a circular direction so as to close upon some organ

MUSCULAR CONTRACTILITY. 109

which they surround, or to compress the bodies they enclose.
Thus the eye and the mouth are closed each by a circular or
orbicular muscle. In other parts, muscles of this description are
called sjMncters. Some parts, as the iris, are provided with both
radiating and circular fibres, the one used for dilating, and the
other for contracting the central aperture. We meet with a
circular arrangement of muscular fibres in the coats of the various
pipes and canals of the body, such as the blood-vessels generally,
and also the alimentary passages; and together with these cir-
cular fibres are also often found bands of longitudinal fibres,
which shorten the tube, while the former tends to contract its
diameter, and press upon its contents. The several hollow re-
ceptacles for fluids, such as the heart and the stomach, present
us with a still greater complication in the arrangement of their
muscular fibres, in which we may sometimes trace layers of fibres
having a spiral course.

213. But it very frequently happens that the action of a muscle
is wanted when its presence would be exceedingly inconvenient.
The common medium of connexion employed by mechanicians,
when the object to be moved is at too great a distance to admit
of the direct application of the power, is that of a rope or strap.
In the animal machine the same purpose is effected by means of
tendons, which are Ions; strings attached at one end to the mus-
cle, and at the other to the bone, or part to be moved. If the
muscles by which the fingers are bent and extended, for instance,
had been placed in the palm or back of the hand, they would have
enlarged that part to an awkward and clumsy thickness, which
would not only have destroyed the beauty and proportion of the
organ, but have impeded many of its uses as an instrument.
They are therefore disposed at the arm, even as high up as the
elbow, and their tendons pass along the joints of the wrist, to be
affixed to the joints of the fingers they are intended to move.

214. The employment of tendons also reduces the space which
would have been necessary for the direct insertion of the muscu-
lar fibres into a bone, so that the same bone may be acted upon
in a great variety of ways, by means of the tendons attached to
it proceeding from a great number of muscles.

215. Another advantage resulting from the employment of
tendons is, that by their intervention a great number of fibres are
made to act in concert, and their united power is concentrated
upon one particular point. In this respect, also, they resemble a
rope, at which a great number of men are pulling at the same
moment, by which means their combined strength is brought into
action. These tendons are variously disposed with respect to
the muscular fibres to which they are attached. It is but in a
few muscles that the fibres are arranged in a perfect longitudinal

10

110 MECHANICAL FUNCTIONS.

direction. We often find them covered on both sides with a ten-
dinous investment, the muscular fibres proceeding obliquely from
the one to the other. This arrangement forms what is called a
penniform muscle, which may be either single or double. The
structure is frequently even more complex than this, a number
of tendinous layers being interposed among the fleshy fibres. By
means of tendons a different direction may also be given to the
moving power, without altering its position. There are many
instances of this employment of tendons, in which they are made
to pass through a loop, which serves as a pulley, an expedient
which is adopted in one of the oblique muscles of the eye.

216. We have already seen, that wherever friction takes
place by the motion of tendons over bones, or other hard parts,
a bursa mucosa is interposed, which obviates in a great measure
the injurious effects that would otherwise result from the rubbing
of the parts.

217. But although it be true that the force with which mus-
cles contract is very great, yet the extent to which they are
capable of exerting that force is in general very limited, and
would be insufficient for most of the purposes their contraction
is intended to serve, unless it were very considerably enlarged
by mechanical expedients. In the practice of mechanics we
find a variety of contrivances had recourse to for attaining this
object; namely, the production of a great extent of motion, by
a power acting through very limited space. But most of these
devices would not answer in the human body, from the incon-
venience which would attend their application. We find that
nature has solved this problem in the simplest possible manner.
In the first place, the tendons are inserted, into the bones they
are designed to move, very near to the centres of motion, so
that a small extent of contraction in the muscle will produce a
great range of motion at the other extremity of the limb. The
principle is here obviously that of what mechanicians have
termed a lever of the third class, namely, that in which the
power is applied at some point intermediate between the fulcrum
and the weight to be raised, or resistance to be overcome.
Secondly, the direction of the power so applied, with reference to
the line connecting the point of application and the centre of
motion, or what is termed the radius of rotation, is oblique ; that
is, it forms with it an acute angle. Here again we may perceive
another cause of the increase of motion, obtained by a smaller
extent of contraction above that which would have resulted if
the power had been applied at right angles to the radius of rota-
tion, which is obviously the most advantageous mode of employ-
ing that power, when the object is to economise it, by giving it
the greatest mechanical advantage. It must happen, indeed, by

MUSCULAR CONTRACTILITY. Ill

such a disposition of the force, that a large portion of it is lost,
being spent on a fixed obstacle, namely, on the bone of the joint,
against which the pressure is exerted ; but the quickness and
velocity of the motion that results are undoubtedly increased.
Thirdly, the muscular fibres are theiioselves obliquely disposed
with respect to the tendons, so that the same cause operates in a
similar manner here also. Lastly, pairs of muscles are placed
so as to form an obtuse angle with one another, and are made to
contract at the same time. Their actions, therefore, will partly
concur, and partly oppose one another. They will conspire to
produce a movement in the parts to which their extremities are
attached, in a direction intermediate to that of the muscles them-
selves ; for it is a fundamental law of dynamics, that when a
body is urged by two forces inclined to each other at any angle,
it will move as if it were ura-ed bv a force in the direction of the
diagonal of a parallelogram, having for its sides lines corres-
ponding in their direction and their lengths to the directions and
relative intensities of the two component forces.

218. In all these cases it is^ evident that there must be a great
loss of force ; but when the muscular power is concerned, we
almost always find that strength is sacrificed to convenience, and
that construction adopted which unites on the whole the most
advantages. We must allow, that the muscular power is turned
to the best account when it is made to perform in the completest
and quickest manner the intended motion. We find, in following
the mechanism not only of the joints of the limbs, but of the
whole system of organs, both internal and external, that the mode
in which this force is applied is diversified in every possible way.
Its combinations are varied, and its action modified beyond calcu-
lation, though the original power be still essentially the same,
and observe the same laws in its action.

219. The source of that enormous mechanical power, which
seems to be an inherent property of the muscular power, has
long been sought for by physiologists ; but it has always conti-
nued to elude their most patient and laborious researches. It
was at one periqd a favourite subject of speculation to devise
hypotheses as to mechanical arrangements of particles capable
of producing results similar to those of muscular contraction.
Borelli* conceived that each muscular fibre might be composed
of a series of minute bladders, or vesicles, of a rhomboidal figure.
Stuart supposed that these vesicles were I'ound. But, on either
hypothesis they were conceived to be empty while the muscle
remained in its natural state of relaxation. On the sudden intro-
duction of a fluid of some kind into these vesicles, their sides
would be separated, they would become distended, and, assuming

* De Motu Anirnalium,

112 MECHANICAL FUNCTIONS.

a more spherical form, would consequently be shortened in their
longitudinal diameter ; and as this shortening would take place
simultaneously in all the vesicles, the whole muscle would be
contracted in its length, and at .the same time proportionally
dilated in its breadth. The contrivance had certainly the merit
of ingenuity, inasmuch as it explained the swelling of the muscle
as well as its shortening, in the act of contraction. But it evi-
dently will not bear the test of serious examination. No such
structure as is implied in the hypothesis has ever been rendered
visible to the eye, however dexterously the microscope may have
been applied to the muscular fibre ; nor can we find any power
sufficient to propel so large a quantity of fluid as would be re-
quired for the distension of the vesicles ; an effect also which, in
order that the theory may correspond wdth the phenomena, must
be produced almost instantaneously. The resistance that would
be opposed to the entry of a fluid so propelled would be incalcu-
lable, and incomparably greater than that exerted by the muscle
itself, which latter force, it may be observed, it is the professed
object of this theory to explain. The hypothesis itself, therefore,
on which the theory is built, involves a greater difficulty than
the simple fact. Such, indeed, was a very common mistake in
the speculations of the earlier philosophers, who were ever prone
to theorize without having any legitimate basis for the formation
of a theory ; their foundations being often more in need of sup-
port than the superstructure they attempted to raise upon it. It
I'erainds us of the Indian fable of the world being carried on the
back of an elephant, whilst the elephant was supposed to require
a tortoise for its own support.

220. The hypothesis that the fibres of muscles have a spiral
shape, and pass in a contorted line from one end of the muscle
to the other, like the turns of a corkscrew, a form which readily
admits of elongation or contraction, according as it is more or less
contorted, is quite as unsatisfactory as the former; and equally
open to the fundamental objection, that it leaves the original
source of motion still unexplained. Muscular power, indeed,
does not appear, from what we hitherto know of its laws, to bear
any close analogy to any of the other great principles in nature,
which we recognize as original sources of mechanic force ; and
until such analogy can be traced, all our gndeavours to explain
the phenom.ena of muscular contraction must be fruitless.

221. It was a favourite notion with the physiologists of the
seventeenth century, that an eflfervescence was excited in the
interior of the muscle, by some chemical operation ; such as a
mixture of acid and alkali. Willis and others ascribed muscular
contraction to a fermentation occasioned by the union of the
particles of the muscle, with a supposed nervous fluid, or ethereal
spirit contained in the blood.

MUSCULAR CONTRACTILITY- 113

222. But in fact, the only power in nature to which irritability
can be compared in the quickness and suddenness of its variations,
as well as in its dependence on peculiar qualities of matter, is
electricity, and more particularly that form of electricity which
constitutes galvanism. Attempts have accordingly been often
made, since the phenomena of galvanism have engaged so much
attention in the philosophic world, to explain muscular contrac-
tion by means of this principle ; and endless have been the fanciful
hypotheses invented for this purpose. Each muscular fibre was
at one time considered as performing the office of a separate
Leyden jar, charged with opposite electricities on its exterior and
interior ; whilst the filament of nerve which penetrated into its
substance was the conducting wire, that occasioned the discharge
of the jar. After the discovery of the voltaic pile, it was im-
mediately conceived that an arrangement corresponding to the
plates of the pile, existed among the particles of nerve and muscle,
thus composing a galvanic apparatus, ready to discharge itself
when the proper communications were affected. The latest
hypothesis of this kind, is that of Prevost and Dumas, who con-
ceived that the muscular fibre was thrown, during its contraction,
into serpentine flexures, in consequence of the attractions of
electrical currents, passing in similar directions through minute
filaments of nerves,* the directions of which were at right angles
to the axis of the fibres. But in the present state of the science,
all these analogies are far too vague and- remote to serve as the.
foundation of any solid theory .f

223. It has been the fashion among some physiologists to con-
sider muscular contraction as only a particular mode of attrac-
tion, and as included in the general law of attraction which
subsists among all the particles of matter; but this is a generali-
zation totally unwarranted by the phenomena. Others have
maintained that contractility is to be ascribed to the attraction
of life, and to be merely a modification of vitality. Thus, Gir-

* [Dr. Rog-et, himself, was at one time disposed to think, that light might
be thrown upon the subject of muscular contraction by investigations of this
nature. A slender harpsichord wire, bent into a helix, being placed in a vol-
taic circuit, instantly shortened itself whenever the electric stream was sent
through it, but recovered its former dimensions the moment the current was
intermitted. (Electro-Magnetism, p. 59, in Vol. 11. of Natural Philosophy,
Library of Useful Knowledge, Lond. 1832.) From this experiment, the
author presumed, that possibly some analogy might hereafter he found to exist
between this phenomenon and the contraction of muscular fibres. From his
silence, however, in the text, Tt would appear, that farther reflection had not
confirmed the suggestion.

A striking objection to all these hypotheses is, — that the irritability of
the muscle is lost sight of, and the nerve alone regarded to be active ; whereas,
the nervous power appears to act merely as an excitant — like galvanism — to
the irritability, and — as experiments show — exhausts it like any other ex-
citant.]

10*

114 MECHANICAL TUNCTIONS.

tanner imagined that this property resided even in the living
fluids, and was co-extensive with organized nature. This, how-
ever, is equivalent to the assertion, that the phenomena requires
no explanation at all ; for it certainly leaves the question just
where it was before. We already knew that the effects of
muscular power indicated a peculiarity in the nature of that
power, for they appeared diflerent from any other. To say that
it is a peculiar modification of the power of life, gives us there-
fore no new information, unless it be meant that it is similar in
its nature to the powers which the living organs exhibit; but it
would, in that case, convey an erroneous idea, because, the phe-
nomena themselves being different, cannot, according to the rules
of legitimate induction, be ascribed to the same physical cause.
We have already pointed out the fallacy of this mode of reason-
ing, in which final causes are confounded with physical causes,
and substituted for them as philosophical explanations of phe-
nomena.

224. There is, unquestionably, a greater degree of cohesion in
the particles which compose the fibres of muscles in their living,
than in their dead state. This cohesive power, in consequence
of the connexions of the muscle in the body, is equivalent to a
constant tendency to contraction. Hence, the fibres of muscles
are in a constant state of tension, like an elastic substance kept
upon the stretch. This property, evidently derived from, con-
tractility, has been denominated tonicity, a term which has also,
as we have seen, been applied to the peculiar state of tension of
cellular and membranous structures, derived from a particular
condition of their elasticity. (See § 175.) It produces the state
of tone in a muscle ; or that in which it is disposed to contract a
greater degree, than its connexions with the neighbouring parts
will allow. This explains why, on cutting a muscle across, the
cut edges retract to a considerable extent, leaving a wide gap at
the place of section: when, by a sudden effort, the tendo-achilles
is ruptured, the muscles in the calf of the leg to which that tendon
had been attached, being released from this stretching force,
retract to a great extent, and form a large and hard swelling high
up in the leg.

225. On minutely examining the phenomena of muscular con-
traction, it will be found, even in those instances in which the
contractile power appears to be exerted with undiminished
vigour for a certain time, that each individual fibre undergoes,
during the interval, a succession of changes of condition, con-
tracting and relaxing alternately. It is only a certain number of
the fibres that are in action at the same moment; their power is
soon exhausted ; and until recruited by repose, other sets of fibres
are thrown into contraction, so as to supply their place. They
thus relieve one another in succession, until by frequent action

FUNCTIONS OP THE OSSEOUS FABRIC. 115

the exhaustion becomes more general, and the restoration less
complete. In this state, the whole muscle is fatigued, its con-
tractions become irregular and unsteady in proportion as they
are more feeble, and the whole action is tremulous, and incom-
petent to the production of the desired effect. These tremulous
movements are very obvious when the muscles are weakened
from any cause, as well as when exhausted by excessive action.
Dr. Woilaston,* with his usual acuteness, detected, by a very
simple experiment, the minute oscillations consequent upon these
continual and rapid alternations of contraction and relaxation in
the fibre. When the finger is inserted in the ear with a moderate
degree of force, and the pressure is continued with as much
steadiness as possible, a peculiar vibratory sound is heard, similar
to that of a carriage rolling on the pavement. This must evi-
dently proceed from a corresponding vibratory action of the
muscular fibres. It appears, therefore, as Dr. Woilaston remarks,
that the voluntary effect in this case, although it may seem to us
to be perfectly continuous, consists in reality, of a great number
of vibrations repeated at extremely short intervals.

226. There is a peculiar kind of contractility possessed by
membranous structures, v^^hich has often been supposed to bear
an analogy to muscular contractility, or even to be some modi-
fication of this property. It is called into action by the applica-
tion of a certain degree of heat, and also by some powerful
chemical agent, such as the concentrated mineral acids; and the
effect produced is a sudden corrugation, or curling up of the
membranous part. This phenomenon was noticed by Haller,
and was termed by Bichat racornissement. Alcohol, and many
of the neutral salts produce, but more slowly, effects which are
similar in kind, though much inferior in degree; but in this case
the corrugation continues to increase, if the agent continues ap-
plied, which does not happen when the more powerful agents, as
the acids or boiling water, are employed; for the continued
operation of these latter agents is to dissolve and disorganize the
animal substance. Bichat took considerable pains to investigate
these phenomena, and has pointed outf several circumstances by
which this property may be distinguished from mere membra-
nous elasticity. From muscular contractility, indeed, it differs
much more considerably, and depends, therefore, in all proba-
bility, on principles totally different from that remarkable animal
property.

Sect. V. — Functions of the Osseous Fabric or Slieleton.

227. The general basis for the mechanical support of all the
softer organs of the body, both in their states of quiescence and

* Philosophical Transactions for 1810, p. 3.
f Anatomie Generale.

116 MECHANICAL, FUNCTIONS.

of motion, is the osseous fabric, or skeleton ; composing a con-
nected frame-work of solid and unyielding structures, fitted for
the threefold purposes of giving protection to the more im-
portant organs which perform the vital functions, of sustaining
the weight of the several portions into which the body may be
conceived to be divided, and of furnishing fixed points of attach-
ment to the muscles or moving powers, and thus supplying them
with the mechanical advantages of levers in the execution of the
more powerful movements of the frame, and especially in the
progressive motion of the whole body from place to place.

228. The organs, more especially defended from external
injury by a bony covering, are the brain, the principal organs of
the senses, and the organs of circulation and respiration.

1. The Cranium.

229. The bones of the°lskull are contrived with singular artifice
and skill to afford protection to the brain, an organ, as we have
seen, of peculiarly soft and delicate texture, and of which the
functions are so refined as to require for their accomplishment
the most perfect freedom from external pressure, and even from
any harsh vibration or concussion of its parts. It is evidently
with this view, that the bony covering of th^ brain, or skull-cap,
as it has been called, is constructed in the form of a vault or'
dome, as being the best calculated to resist external pressure, on
the well-known mechanical principle of the arch. But pressure
applied vertically to an arch necessarily gives rise to an outward
horizontal thrust at the two ends of the arch. In architecture,
various expedients are resorted to for opposing this force. In a
bridge it is resisted by the solid abuttnents where the arch takes
its rise on each side. In the higher arches of ornamental archi- '
lecture it is counteracted by the weight of a buttress placed over
the origin of the arch, and in harmony with the design of the
whole. For the support of the roof of a building, which has to
rest upon perpendicular walls, either these walls must be built
of a strength equal to withstand this horizontal pressure, or,
what is generally resorted to, a tie-beam must be attached to
the base of the roof, which tie-beam will resist by its cohesive
strength the force which tends to stretch it, derived from the
outward pressure of the roof

230. In the architecture of the skull we find the exemplifica-
tion of these methods, and their strict conformity with the refined
principles of mechanics. The two parietal bones on the sides,
the frontal bone before, and the occipital bone behind, may be
considered as the four great stones which compose the convex
part of the dome. If we first consider the parietal bones, view-
ing them as constituting a single arch, we find that their lower

' FUNCTIONS OP THE OSSEOUS FABRIC. 117

edges are bevelled off at an acute angle, so as to be overlapped
on each side by the upper edge of the tennporal bone, which con-
tinues the curvature as far as the basis of the skull. Thus, the
two parietal bones are effectually wedged in between the two
temporal bones, and any pressure applied on the top of the head,
which would of course tend to thrust their lower sides outwards,
is resisted by the temporal bones. But these lemporal bones are
themselves locked into the irregularly-shaped sphenoidal bone,
which, as we have seen, forms the central piece of the basis of
the skull, being in actual contact with every one of the bones
which compose it, as well as the face, in which the organs of all
the senses, except that of touch, is contained. The os sphenoides
thus performs the office of a great tie-beam to the lower part of
the arched roof of the skull : and the same principles will be found
to hold gpod when the section of the skull is taken in the longi-
tudinal direction ; the os frontis before, and the os occipitis behind,
which sustain their share of any pressure made on the upper
parts of the head, being so locked in, by the bending inwards of
their lower processes, with the sphenoid bone, as effectually to
prevent their starting outwardly.

231. Another circumstance in the architecture of the skull is
particularly deserving of notice, as it exhibits the most marked
instance of provident design. It relates to the structure of the
bones themselves, which is the best calculated to resist fracture
on the one hand, and on the other to prevent the transmission of
vibrating concussions to the brain. It is manifestly with this
view that it is composed of two plates of bone, the external one
fibrous, tough, and not easily broken ; the inner one more dense
and rigid, offering the most powerful resistance to simple direct
pressure ; yet, on that very account, more fragile in its nature,
and partaking therefore in the quality of brittleness, which belongs
to all the harder bodies, such as glass or flint. It was on account
of its possessing this property that it was named the tabula
vitrea by anatomists. But while it is evident that such an acci-
dent would have been of frequent occurrence if that part of the
bone had been directly exposed to every casual blow, this ^vil
has been carefully guarded against by the interposition of a
spongy intertexture of bon\^ fibres, the canceUaied stnccture, as
it is termed, which forms a thick layer between the two laminas
of bone, or as they have been called, the outer and the inner
tables of the skull. This intervening layer operates as a cushion,
arresting the progress of the vibrations from the external to the
internal plate of bone, and preventing fracture.

232. Even when the impetus is so great as to penetrate
through this resisting medium, still the force with which it im-
pinges on the subjacent parts must be very considerably mode-
rated, and the danger of injury to the brain diminished. It is

118 MECHANICAL FUNCTIONS.

witFi a similar design of giving protection that a soldier's helmet
is lined with leather or covered with hair ; a provision which we
even find in the head-piece of the Roman soldiers, in whose
equipment utility alone was consulted, and nothing was admitted
that served the purpose of mere ornament. Wherever the bones
of the skull are more particularly exposed to blows, we find a
greater thickness of bone provided for the sake of additional
power of resistance.

233, The sutures, or joinings of these bones, are also admirably
contrived to stop the transmission of vibrations, arising from per-
cussion from extending to any distance round the skull. These
sutures, externally, where the tough and fibrous plates of bone
are united, present a serrated line ; the fibres at the edges of
each being mutually inserted between those of the contiguous
bone. But this dove-tailed joining is not met with in the inner
table ; there the edges of the bone are smooth and placed in
simple contact. This is evidently done in order to prevent the
chipping off of the minute parts of a brittle structure, had they been
interlaced together as the fibres of the outer table are. But still
the interruptions afforded by the suture tend in a great degree to
check the progress of fracture.*

2. The Face.

234. The organs of the principal senses, the eye, the ear, the
nostrils, and the mouth, are protected by the bones of the face,
which likewise form part of the skull. The eyes are exceedingly
well defended by the superciliary ridge of the frontal bone above,
and also by the orbital plate which supports the anterior lobes of
the brain ; anteriorly, they are protected by the projection of the
nasal bones, and outwardly by the arched process which divides
them from the temples ; while the prominent cheek bones below
guard them from injury in that quarter. No part of the body
has so effectual a protection from bone as the internal organ of
hearing : nor is there any part of the osseous system so hard as
the portion of the temporal bone in which this organ is lodged.
The nasal cavities, in like manner, which are occupied by the
membranes receiving impressions from odorous effluvia, are
formed in deep recesses of bone. The organ of taste is also pro-
tected by the jaws, though less completely, because the same
parts are required to enjoy extensive power of motion.

* [This is questionable. Observation has shown, that the sutures do not
possess much, if any, effect in puttingr a limit to fractures. In all cases of
severe blows, the skull appears to resist, as if it were constituted of but one
piece.]

FUNCTIONS OP THE OSSEOUS FABRIC. 119

3. The Thorax.

235. The heart and lungs, -which are lodged in the cavity of
the thorax, are defended before and behind by the spine and
sternum ; and laterally by the ribs, which form bony arches, the
shape best calculated for resisting pressure applied externally.
They are formed of separate pieces, with intervals between, in
oi-der to admit of motion : for the cavity of the chest requires to
be alternately enlarged and contracted in the performance of
respiration, which is a function of primary importance in the
animal economy.

4. The Spine.

236. The support of the trunk and upper parts of the body,
including the head, is entrusted to a column of bones, the assem-
blage of which constitutes the spine. The spine is that part of
the skeleton of all animals composing the four superior classes,
namely, the mammalia, birds, fishes, and reptiles, which is most
constantly found, and which exhibits the greatest uniformity of
structure. The individual bones which compose the spine are so
intimately united and so firmly secured by ligaments on every
side, that they appear in the living body as one continued bone,
and the whole assemblage is known, in ordinary language, by
the name of the hack-hone. The purposes answered by this
complex fabric are numerous and important. It is the great
central beam of the fabric, and furnishes the basis of support to
all other bones of the skeleton. It serves, in particular, to unite
the bones of the limbs with the trunk, so that they form with the
latter one connected frame-work. It is the axis of their princi-
pal motions, the common fulcrum round which they all revolve.
It has an intimate mechanical relation wdth all the parts of the
body. It affords attachment to the great muscles which move
the trunk and the principal joints of the extremities. It contains
and gives protection to that important organ, the spinal cord,
from which, as we have seen, almost all the nerves of the body
take their origin, and which is unquestionably, next to the brain,
the most essential organ in the economy. Whilst the spinal
column performs these offices, it is at the same time capable of
considerable flexion, both laterally and longitudinally; and admits
also of some degree of twisting motion, in a plane perpendicular
to its axis.

237. No where has art been more conspicuously displayed
than in the construction of an apparatus adapted to fulfil such
opposite and apparently incompatible functions. To secure the
firmness and strength which are required in the basis of support
to the whole body, in the key-stone, as it were, of its various

120 MECHANICAL FUNCTIONS.

arches, whilst it is at the same time rendered capable of so great
a variety of motions, objects "which seem utterly at variance with
its also affording protection to a tender and delicate organ, in
which the least pressure would be attended with fatal conse-
quences, must be allowed to be a most difficult problem of
mechanism. And yet these various, complicated, and apparently
inconsistent ofhces, we find executed by one and the same instru-
ment. Flexibility is obtained by subdividing it into a great num-
ber of small portions, each of which is separately allowed but a
small degree of bending upon the next; and thus a considerable
motion is obtained in the whole column, with but a very incon-
siderable one at each joint. Each bone, as was described in the
account of its anatomy, is connected with its neighbour by a
broad basis of attachment; and the slight relative motions of
which they are susceptible are chiefly entrusted to the lateral
articulations. Whilst these broad bones give the whole chain
its requisite firmness and stability, they are so constructed as to
afford a passage, without any diminution of their strength, to the
substance of the spinal marrow. For this purpose each of the
bodies is hollowed out so as to form a continued groove all down
the back; and over this groove a broad arch is thrown from
each side, converting it into a complete canal. In order to pre-
serve the continuity of this canal, and prevent the vertebrae from
shifting upon one another so as to spread upon the spinal cord
within, during the various movements of the body, further securi-
ties are provided. They are severally connected together by
their projecting processes, which lock into one another, and are
still more firmly secured by the ligaments that bind them down
on every side. Thus, the bodies of the vertebrae are guarded
against the danger of accidental slipping, but they are defended
also from displacement by any force short of what would break
the bone.

238. But besides all these provisions the vertebral column is
protected from injury arising from violent jolts or jars by having
interposed between each adjoining vertebrae, the peculiar springy
substance known by the name of the intervertebral cartilage or
ligament ; for it in reality partakes of the nature of both these
textures. It is a substance quite peculiar to this part of the frame.
Its compressibility and the elastic force with which it recovers
its shape when relievedfrom the compressing power, must greatly
lessen the quantity of motion required of each bone during the
flexion of the column, as well as soften all the concussions inci-
dent to violent motion. No chasm is left by their separation
when the spine is bent ; and the unity of the whole column, and
of the channel in its centre, is preserved unbroken. A passage is
at the same time allowed between each contiguous vertebra for

FUNCTIONS OP THE OSSEOUS FABRIC. 121

the nerves which issue in pairs from the spinal cord, to distribute
their branches and filaments to every part of the body.

239. The natural curvatures in the line of the vertebral column
also contribute materially to the elasticity of the whole frame-
work. On receiving any shock in the direction of its length, the
impulse, instead of being propagated the whole length of its line,
is diverted from its course and taken off by the flexures of the
column; and the maintenance of its natural position is effected
more by the power of the muscles attached to the spine, than by
its inherent elasticity.

' 5. The Pelvis.

240. The broad expansion of bone which extends on each side
of the pelvis, and the extremities of which form the hips, are
evidently designed as a basis of support for the viscera of the
abdomen. The lower portion of the bones of the pelvis is at the
same time rendered light by being formed into several arches ;
strengthened at the points where it is exposed to the greatest pres-
sure, and at the same time affording room for the articulations of
the thigh bones.

8. The Limbs in General.

241. The third office of the skeleton is to furnish levers for
accomplishing the progression and other movements of the body,
which require great force, great extent, and great precision of
motion. These objects are attained by the limbs, which, as is
well, known, are divided into separate portions, obviously for the
purpose of increasing the facility of adaptation to a great variety
of movements and of actions which the individual may be called
upon to perform.

242. The principal bones of the extremities have the shape of
lengthened cylinders, and compose a system of levers adapted to
the regular and accurate appUcation of the moving force, and for
the execution of rapid, extensive, and powerful movements. The
circumstance of their hollow and cancellated structure is a pal-
pable instance of provident adaptation to the office for which
they are framed. It may be mathematically demonstrated, that
if the quantity of materials assigned for the construction of the
bone be given, there is no mode in which those materials could
have been more advantageously disposed for resisting a trans-
verse force ; that is, a force tending to break it across, than the
form of a tube, or hollow cylinder, which is that actually given
to them by nature. If, for instance, the same quantity of matter
had been collected into a solid cylinder of the same length, it
would have been subject to fracture by a much smaller force than

11

122 kECHANICAL FUNCTIONS.

that which it bears without injury in its actual tubular form.
This remark was long ago made by the elder Dr. Monro,* who
observes that the resistance opposed by a body of cylindrical
shape to a force applied transversely is in the direct ratio of its
diameter ; hence the same number of fibres disposed round the
circumference of a circle in such a way as that their sections
would present the appearance of a ring, will resist with greater
force than if they had been united at the centre, so that their section
would present a circle of much smaller diameter than the ring.
The hollow cylindrical bones are accordingly found in those
situations where the power of resisting external force is princi-
pally wanted, while it is at the same time an object of importance
not to add unnecessarily to the weight. A simple experiment
will illustrate in a very striking manner this proposition. Let a
cylindrical glass rod and a glass tube be taken of the same length
and also of the same weight, so that they may both contain the
same quantity of materials. If each be then supported at their
two ends, on a frame adapted to the purpose, it will be found that
the same weight which, when hung from the rod, will break it
asunder, will, when transferred to the tube, be sustained without
even bending it in any sensible degree. Dr. Porterfield has given
an elaborate mathematical demonstration of the general proposi-
tion.!

243. There are few subjects' in physiology v^'hich present so
many interestirrg points of inquiry, or afford more abundant proofs
of intelligence and design than the mechanical properties of the
osseous fabric. From the account we formerly gave of the
composition of bone, it appears that it is constructed of two
principal materials, an earthy basis, which is the phosphate of
lime, and an animal or membranous substance, which possesses
considerable tenacity. To the first of these ingredients the bones
owe their solidity and hardness. No inorganic matter, not even
the metals, has so great a cohesive power, with a given weight
of materials, as the earthy bodies ; and this is probably the reason
why the phosphate of lime has been selected as the substance
employed to give the necessary solidity and hardness to bones.
But these qualities, if carried to excess, would be accompanied
with brittleness. To guard against this evil, the cohesion of the
inorganic earth is tempered by the interposition of an elastic
organic material ; this is the cellular tissue, within the cells of
which the bony matter is deposited, and which acts the part of
a cement, binding them more strongly together, and at the same
time obviating the excessive brittleness which a substance of more
uniform hardness would have possessed. Thus, by the admirable

* Anatomy of the Bones and Muscles, p. 21.
f Edinburgh Medical Essays, vol. i. p. 95.

FUNCTIONS OF THE OSSEOUS FABRIC. 123

blending of these two elements, two qualities— which, in masses
of homogenous and unorganized matter are scarcely compatible
with one another — are happily united.

244. The manner in' which'the cylindrical bones are connected
together is also highly deserving of attention. There are, indeed,
few parts of the mechanism of ajiimals more peculiarly fitted to
excite our admiration than the structure of the joints. Every
provision seems to have been made for facilitating their motion,
and every precaution taken to enable them to act with safety.
Their ends are enlarged for the purpose of affording a broader
surface of junction, and for procuring greater firmness and
security of connexion. The rough and hard substance of bones
would have been particularly exposed to injury if they had been
allowed to grate upon one another without some intervening
smooth surface. In all the joints, at the places where the ends
of the bone would have suffered from this cause, we find them
tipped with a white, smooth, and elastic cartilage. Dr. Paley*
has very aptly compared this expedient to the plating of a naetal-
lic instrument with a different metal. Detached portions of car-
tilage, are, as we have seen, frequently placed between the bones,
which thus, instead of working upon each other, work upon the
intermediate cartilages. This is analogous to the contrivance
practised by mechanics, who interpose a loose ring where the
friction of the joints of any of their machines is great, and who
particularly resort to it where some strong and heavy work is to
be done. It is precisely under similar circumstances that the
same contrivance is employed in the human body; and the ana-
logy is a striking evidence of that art and foresight which are
manifested in the plan of its conformation. The lubricating
quality of the synovia is also an /exquisite provision designed to
diminish friction. i

245. The ligaments which bind the ends of the bones together,
and restrain the direction of their motions, are admirably cal-
culated to perform the offices assigned to them. Like the bones,
they unite qualities which are rarely met with in conjunction.
They have all the properties we can desire in a rope ; namely,
perfect flexibihty, with great power of resisting extension. It is
hardly imaginable how great a force is required to stretch, or
rather to break asunder a ligament, for it will not yield in any
sensible degree until the force is increased so as at on,ce to tear
it to pieces. Yet with all this toughness, it is so flexible as to
oppose no impediment to the suppleness of the joint. " Every
joint," says Dr. Paley, " is strictly a mechanical instrument, and
as manifestly contrived, and as accurately defined as any that
can be produced out of a cabinet maker's shop. Their durability

* Natural Theology.

124 MECHANICAL FUNCTIONS.

is no less astonishing. A limb shall swing upon its hinge, or play
in its socket, many hundred times in an hour, for sixty years to-
gether, without diminution of its agility."*

7. The Lower Extremities.

246. The three portions into which the lower extremities are
divided, namely the thigh, leg, and foot, being united by joints,
and moveable upon one another, are calculated to serve the double
purpose of firm columns of support to the body while standing,
and of facilitating and regulating its movements while advancing.
It might, on a superficial view of the subject, be supposed that,
in standing in the erect posture, the weight of the body would
be more firmly and effectually supported had the whole Jimb
consisted of a single straight column. But, independently of the
greater strain to which such a structure would be exposed, in
consequence of the great length of bone required, it would, in
fact, have had less stabiHty than it now possesses. A marble
statue of a man resting merely on the feet in a natural attitude,
would be overthrown by a small impulse; and even in the living
body, it is an infalHble consequence of the laws of mechanics, that
if ever the perpendicular line drawn from the centre of gravity
happen to pass beyond the base of support, the body must in-
evitably fall in spite of every muscular exertion that can be made.
The only way to prevent such an accident is to bring back the
centre of gravity nearer to a point above the centre of the base
before it has actually passed it ; and this we instinctively do when
we feel ourselves in danger of falling to one side, by extending
the arm horizontally on the opposite side.

247. But the limb being divided into joints, these joints would
give way under the weight of the body, were they not prevented
from bending by the constant action of the , muscles. Th6 con-/
tinual muscular effort required in standing is nearly as great an
expenditure of muscular power as the act of walking. Soldiers
on parade, remaining in the same attitude, experience even more
fatigue than they would suffer by a march during an equal time,
because the same muscles are constantly in action. The posture
of a soldier under arms, with his thighs and legs in the same
straight line, is one which requires a painful effort to preserve.
The moment the word of command is given him to " stand at
ease," the muscles on one side immediately relax, the right knee
is slightly bent, the tension of the ankle-joint is relieved, and the
body, sinking upon the left hip, has its height diminished by above
an inch and a-half. The weight of the trunk is sustained more
directly by the column of bones of the left limb, which support

f Natural Theology.

FUNCTIONS OP THE OSSEOUS FABRIC. 125

that weight at a greater mechanical advantage than before ; for
the oblique direction of the neck of the thigh bone, with regard
to the bones of the pelvis, which is very great in the perfectly
erect position, is now diminished. Bui the great source of relief
is that a diflerent set of muscles is called into play on every
change of posture ; those which were before fatigued have time
to recruit their energies, and become prepared afterwards to
afford in their turn the same relief to others by resuming their
exertions.

248. Strictly speaking, it is quite impossible for even the
strongest man^ remain for even a very short interval of time
in precisely the same position. The fatigue of the muscles which
are in action soon become sensible, and relief is instantly given
to them by varying the points of support. Thus we may observe,
that in standing, the weight of the body is naturally thrown al-
ternately from one foot to the other. The action of standing must
be considered as a series of perpetual, but obscure movements,
by which the centre of gravity is continually shifted from one
part of the base to the other ; the tendency to fall in any one ,
direction being perpetually counteracted by small and insensible
movements in the contrary direction. Long habit has rendered
us unconscious of these exertions, and inattentive to the sensations
which prompt them. But a child, when acquiring the art of
walking, is sensible of all these difficulties, and does not learn to
walk but by reiterated lessons, and by the experience of many
falls. It is by a practice of the same kind, and continued during
a longer period, that the rope-dancer learns to support himself
on a narrower or more unstable base than that which nature has
provided. This he effects, not by keeping his centre of gravity
precisely in the mathematical perpendicular to the rope, but by
continually shifting it from side to side ; never allowing it to fall
above a certain very minute distance, and immediately correcting
the vacillation by a movement, which gives it an impulse in the
contrary direction.

249. The flexures of the joints of the lower extremities, it may
be observed, take place alternately in opposite directions. Thus
the thigh is bent forwards upon the pelvis; the leg is bent back-
wards upon the thigh; and the foot, again, is bent forwards upon
the leg. This arrangement is obviously the one best adapted to
convenience, both as regards the folding of the parts when bent,
and the commodious disposition of the muscles, which perform
the opposite motions of flexion and extension. As the weight
of the body occasions the flexion of the joints, so it is that flexion,
which the muscles are chiefly required to counteract; and this is
the duty of the extensor muscles. We accordingly find, that
in each joint the latter are much larger, and more powerful than
the flexors. They are enabled also to act with greater mechan-

126 MECHANICAL FUNCTIONS.

ical advantage, in consequence of their being inserted into pro-
jecting processes of the bones, evidently provided with this express
intention. This is the purpose of the trochanter of the thigh
bone, and the projecting bone of the heel. The same object is
accomplished, in a still more artificial manner, in the knee-joint,
by an additional bone, the jpatella, or knee-pan, into which the
great extensor muscles situate in the fore part of the thigh are
inserted, and which renders their action much more efficient, both
by diminishing its obliquity, and by removing it farther from the
centre of rotation. It acts, therefore, as a pulley, which is a
species of lever; and it is so contrived, that while the knee is
bent, and the muscles at rest, as when we are sitting, this bone
sinks down, concealed in a hollow of the knee. When the
extensor muscles begin to act, they draw out the patella from this
hollow; and in proportion as they contract, and their strength
diminishes, the patella gradually rising, gives greater mechanical
advantage to their action, which is greatest of all when, by their
complete contraction, their power is most expended.

250. The structure of the feet is also admirably contrived, as
a secure basis for their support of the whole superincumbent
weight of the body, and of all the additional burdens which the
body may be made to sustain. The arrangement of the bones is
in as strict conformity to the principles of the arch as those of the
skull. The bones of the tarsus constitute what may be called a
double arch ; that is, an arch in two different places at right
angles to one another. There is, in the first place, one great
longitudinal arch, springing from the point of the heel to the ball
of the great toe ; and there is, in the second place, a transverse
arch formed among the tarsal bones themselves, one within
another. Near the heel this arch is composed of the astragalus,
OS calcis, and naviculare; and farther on, by the cuneiform or
wedge-like bones, the name of which expresses their office,' ana-
logous to that of the stones at the crown of an arch of masonry.
The elasticity, as well as security, resulting from all these arches,
imparts that ease and spring so remarkable in the step, and
obviates the injurious jar that would be otherwise inevitably com-
municated to the body by leaps, by falls, or other accidents.

251. In walking, the first action consists in fixing one foot
firmly on the ground, by transferring to it the whole weight of
the body ; the other foot being then at liberty to move, is with
t^e leg carried forwards. This projection of the limb is neces-
sarily attended with a corresponding advance of the centre of
gravity, which proceeds to move forwards till it arrives beyond
the basis of the foot on which the body is resting. Whenever
this happens, the body, being unsupported, begins to fall, and
would continue to fall, wei'e not the other foot in advance, and
ready to receive it, and stop its further descent. This is the

FUNCTIONS OF THE OSSEOUS FABRIC. 127

reason why we experience so disagreeable a jar, if in walking
inattentively, the foot we had advanced Ijappens to arrive at a
lower level on the ground than had been expected ; as when, for
instance, we meet with a descending step for which we were
not prepared. The body on these occasions, falHng through
greater space than usual, acquires a certain velocity of descent,
and this unusual velocity being suddenly checked, communicates
a shock to the whole system.

252. While the weight of the body is thus transferred alter-
nately from one foot to the other, the centre of gravity of the
body, while it is continually carried forwards, is at the same time
alternately raised and lowered, so as to describe at each step a
small arch; and its whole motion may be represented by a
waving line, having lateral as well as longitudinal inflexions, and
composed of a succession of short curves. In taking long steps,
we are obliged to raise the centre of gravity through a longer
arch, and therefore to a greater height. This is consequently
more fatiguing than a shorter step. If, however, we go into the
contrary extreme, and take too short steps, the advantage ob-
tained in lessoning the height of the arches described by the
centre of gravity, is more than compensated by the greater
quickness required in the motions necessary for keeping up the
same rate of walking.

253. The lateral undulation of the body during walking is
iiever performed with precise equality on both sides ; and the
amount of the accumulated deviations would be considerable,
did we not avail ourselves of the assistance of the sense of sight
in counteracting it. This will appear from the well-known fact,
that it is impossible for a person who is blindfolded to continue
to walk in a straight line for any considerable distance. Even
on a perfectly level plain, we unavoidably inchne to the right or
to the left ; and the want of consciousness that we are doing so,
prevents us from rectifying the error; so that while we imagine
we have undeviatingly pursued a straight course, we may per-
haps, when the bandage is removed from our eyes, find ourselves
near the very spot from whence we had commenced our circum-
ambulatory excursion.

8. The Upper Extremities.

254. The upper extremity, though exempt from the ofiice of
supporting any part of the weight of the trunk, and intended for
a variety of very different uses, presents us with exactly the same
number of divisions as the lower extremities ; excepting that in
the skeleton, if we compare the scapula to the bones of the pelvis,
there is an additional bone provided in the clavicle, or collar
bone, by means of which the bones of the arm are articulated

128 MECHANICAL FUNCTIONS.

with those of the trunk. The extremity of the clavicle, indeed,
by which it joins the sternum, is the pivot on which all the great
motions of the arm are performed. The interposition of the
scapula is evidently for the purpose of giving a more extended
surface for the attachment of the strong muscles destined to act
upon the arm and upper part of the trunk, and which also lend
their aid in performing the movements necessary for respiration.
It also contributes its share in the defence of the back part of the
chest.

255. The joint of the shoulder is of the ball and socket kind,
and admits, therefore, of the greatest latitude of motion. That
of the elbow is a simple hinge-joint, and restricted consequently
to mere flexion and extension. A rotatory motion was here unne-
cessary ; for the free rolling of the arm at the shoulder answ^ers
every purpose that can be desired, and the elbow -joint is rendered
more secure by this limitation of its motion ; for it will always
be 'found, that whenever a hinge-joint is sufficient for the pur-
poses required, it is employed in prefei^ence to that of the ball and
socket, which, from its very extensive range of motion, must
necessarily be looser in its structure, and more liable to disloca-
tion.

256. In the wrist, which is the great centre of all the motions
of the hand, a construction was called for which might allow of
the utmost latitude of motion. The following were the three
kinds of movement required ; first, simple flexion and extension;
secondly, lateral flexions ; and, thirdly, twisting, or rotation of
the hand, as when it is employed in turning a screw. If all
these different motions had been entrusted to a simple ball and
socket joint, they could not have been well performed without
great strains and hazard of dislocation. This danger is admira-
bly obviated by distributing the motions among several articula-
tions. No part of the bony system is more complex than the
wrist, which consists of eight small bones crowded into a very
narrow space, and lashed together by many strong ligaments,
that form bands crossing one another in every possible direction.
While they are together fitted to the bones of the fore-arm in the
manner of a hinge-joint, their mutual connexions allow at the
same time of considerable lateral flexion.

257. But still the rotatory or twisting motion of the hand,
which is perhaps the most useful of all, is not provided for by this
mechanism. For the accomplishment of this object there is
employed a contrivance to -v^hich the rest of the system presents
nothing similar. The wrist is connected not so much with the
principal bone of the fore-arm, as with a subsidiary bone of equal
length with it, and placed in a parallel position, termed the i^adius ;
and its peculiar mode of junction is such as to enable it to
describe round the former a complete semicircle. In these

FUNCTIONS OP THE OSSEOUS FABRIC. 129

rolling motions the radius carries along with it the hand, which
thus turns in perlect security; for it is difficult to conceive how
a force could well be applied, so as to separate bones having so
long a lever of resistance. Thus, while the wrist is exempt from
the weakness incident to circular joints, it possesses all the pro-
perties which we find in the most moveable.

258. The manner in which the fingers are disposed in the
hand, like radii from a common centre, is such as to allow them
very free play, and to extend their sphere of action. But the
chief perfection of the hand, as a mechanical instrument of
prehension, consists in the structure of the thumb, which is fur-
nished with muscles of so great a strength, compared with those
of the fingers, as to enable it to oppose and balance their united
power. Hence the hand is capable of grasping a spherical body,
and of keeping firm hold of a variety of objects, which it would
otherwise have required the concurrence of both hands to retain.

259. The passage of the tendons, by which the fingers are
bent, is particularly deserving of notice, and has often been
appealed to as a signal instance of express contrivance. As the
uses of the hand require the beading of each joint of the fingers
independently of the others, it was necessary that separate muscles
and separate tendons should be provided for each. The muscles
are most advantageously placed high up in the arm, and
convenience requires that those muscles which bend the last
joints should He beneath those that bend the middle joints.
Had the tendons proceeding from the latter been directly inserted
into the middle of the second bone of the finger, they would have
been exactly in the way of the tendons which are underneath,
and which are proceeding to a more distant insertion. They
are therefore split into two branches, each being inserted into the
side,of the bone; and the lower tendon is thus allowed to pass on
securely between them. This structure has also this further advan-
tage, that it procures a morereadyflexionof the last joint than of the
other joints ; a provision, the pui'pose of which is manifest, since
it tends effectually to prevent the escape of the object we wish
to lay hold of " There is nothing," says Dr. Paley, " in a silk
or cotton mill, in the belts, straps, or ropes, by which motion is com-
municated from one part of the machine to the other, that is more
artificial, or more evidently so than this perforation." " Let a
person observe his own hand while he is writing, the number of
muscles that are brought to bear upon the pen, how the joint and
adjusted operation of several tendons is concerned in every stroke,
yet that five hundred such strokes are drawn in a minute. Not
a letter can be turned without two or three tendinous contractions,
definite both as to the choice of the tendon, and as to the space
through which it moves. Yet how correctly does the work pro-
ceed ; how faithful have the muscles been to their duty; how
true to the order which endeavour or habit has inculcated. Let

130 NUTRITIVE FUNCTIONS.

US watch the hand while playing upon a musical instrument.
All the changes produced, though extremely rapid, are exactly
measured, even when most minute ; and display on the part of
the muscles an obedience of action alike wonderful for its quick-
ness and its correctness."

260. To specify all the instances of express contrivance in the
mechanical conformation of the hand would fill a volume. As
an organ of touch it is admirably formed. No instrument is bet-
ter adapted to the practice of the mechanical arts ; none could be
better fitted for examining the properties of bodies, and the laws
of the material world, of which none of the other senses, unassisted
by that of touch, could impart to us any accurate knowledge.
So great are the advantages which the possession of this organ
has conferred upon the human race, that many philosophers, prone
to paradox, have ascribed to this circumstance alone the whole
of the intellectual superiority which he enjoys over the brute
creation.

CHAPJ^ER VI.

ASSIMILATION.

Sect. I. — Chemical Constitution of Organized Matter.

1. JVecessity of Aliment.

261. A coivsTANT supply of nutritive matter is necessary for the
continuance of life, a necessity arising from a variety of causes.
In the first place, the substance of which the body is formed is
exposed to various sources of waste and dissipation, and is con-
tinually verging to a state in which the organs become unfit for
the performance of their functions. The chemical affinities, by
which the elements of organized substances are retained in that
peculiar mode of combination which constitutes their living state,
are, as we shall presently see, very nicely balanced, and would
be unable to preserve them in that condition were not some
means provided for counteracting their natural tendency to
decomposition. By the active exercise of their respective func-
tions all the organs, but more especially the muscular and nervous
systems, experience a deterioration of their component parts, and
suffer decay and waste. Fresh materials are required for sup-
plying this continual expenditure. A certain degree of tempera-
ture must also be kept up, otherwise the muscles would lose their

CHEMICAL CONDITIONS OF ORGANIZED MATTER. 131

faculty of contracting, and the nerves their power of conveying
impressions to and from the sensorium. Materials are therefore
necessary to be employed as fuel for keeping up the vital warmth.
The daily consumption of combustible materials, apparently used
for this purpose in the animal economy, is, we shall afterwards
find, very large, and forms a considerable proportion of the food
received into the body.

262. All that we have now said refers to the body in its adult
or mature state, when it has attained its full dimensions, and when
all that is required is its preservation in that state. But during
all that period of life when the body is increasing in its size, it is
evident that its growth can only take place in consequence of the
addition of new particles to those already composing the sub-
stance of the body ; and some parts, such as the hair and nails,
continue to grow even to the latest period of life. At every age
some part is liable to be injured or destroyed, and a provision is
in most cases made for the reparation of that which has been
injured, or even for the replacement of that which has been de-
stroyed. These objects can be effected only by the supply of
new materials derived from external sources.

The changes effected by the long series of assimilatory pro-
cesses being essentially chemical, it becomes necessary to insti-
tute a particular inquiry into the chemical constitution of organized
substances in their successive stages of mutation, from the most
simple to the more complex conditions in which they are found
to exist in the composition of an animal body.

2. Chemical conditions of organized matter.

263. The parts, which by their assemblage constitute an
organized body, when compared with unorganized matter, ex-
hibit in ther chemical, as well as in their mechanical characters,
the most well marked and striking contrast. Complexity, variety,
and difficulty of analysis, are the leading features as much in the
former as in the latter of these subjects of consideration. Com-
binations equally artificial, equally the result of design, and of
refined elaboration, are exhibited both in the mechanism of orga-
nic structures, and also in the chemical constitution of organic
substances. Compared with the latter, all the bodies which are
presented to us in the mineral kingdom, are extremely simple ;
and their study presents no difficulties of an insurmountable na-
ture. The number of primary or elementary substances, or of
those at least which we regard as simple, is, indeed, greater in
the mineral kingdom, than that of those which enter into the
composition of animal or vegetable bodies ; but they are for the
most part found united in binary combinations, or arc, at least,
easily resolvable into a small number of such binary compounds.

132 NUTRITIVE FUNCTIONS.

In the products of animal or vegetable systems, we find a less
variety of ultimate principles ; but this is more than compensated
by the infinitely greater diversity of modes in which they are
combined. The same elements, instead of forming with each
other mere binary combinations, generally exist in more compli-
cated states of union; three, four, five, or even a greater number
of constituent substances, having their affinities nicely balanced,
and harmonized into one individual combination.

264. From this diversity in the mode of union, there arise
remarkable diflTerences in the properties of different organized
products, formed from the same ultimate principles : nor can we,
as in bodies belonging to the mineral kingdom, with an exact
knowledge of the nature and proportions of the component sub-
stances, proceed, by any artificial arrangement, to the actual
formation of the compounds themselves. No approach has yet
been made by human ingenuity, to the imitation of nature in
these refined operations of vitality.

265. Another consequence resulting from this difference in
constitution between organized products and the inorganic bodies
of the mineral kingdom, is that the affinities by which the ele-
ments of the former class of bodies are held in union, being nicely
balanced, are more subject to change. The equipoise is easily
disturbed and subverted. The principles have a constant ten-
dency to react on each other, so as to give rise to a new order
of combinations; which readily take place by slight alterations
of circumstances.

266. All organic products are susceptible of decomposition by
heat alone ; they are readily acted upon by various agents, as
water or atmospheric air ; and they are generally liable to spon-
taneous changes, to fermentation, and putrefaction.

267. Such, then, are the distinguishing features of the chemical
properties belonging to the products of organization; simplicity
as to the number of ultimate elements ; complication in the mode
and order of combination ; unsteadiness in the balance of affinities
retaining them in union, and consequent proneness to decomposi-
tion, and impracticability of their artificial formation by a reunion
of their principles.

268. Whilst the products of the animal kingdom participate
with vegetable bodies in these common characters, which dis-
tinguish them from inorganic materials, they differ from the
former in several subordinate circumstances of chemical relation.
The constituent principles of animal substances are somewhat
more numerous, and their affinities more nicely adjusted, and
more easily disturbed. Their chemical constitution is the result
of still more delicate processes, and of a more elaborate organi-
zation. The three great component elements of all vegetable
bodies, are oxygen, hydrogen, and carbon ; but animal substances

CHEMICAL CONDITIONS OF ORGANIZED MATTER. 133

generally contain, besides these, a considerable proportion of a
fourth element, namely nitrogen, the presence of which has a
considerable influence on the changes they undergo when sub-
jected to the operation of foreign agents, or left to the spontaneous
operation of internal causes of decomposition. P/iosphorus and
sulphur must also be enumerated among the com,ponent parts of
the greater number of animal substances; and the affinities ex-
erted by these elements also tend to modify the results produced
by these various causes. The greater the number of elementary
ingredients present in any assemblage, the greater will be the
tendency to form binary or ternary combinations ; and the more
will the affinities be divided between difierent elements, and pass
easily from one mode of arrangement into another. Hence the
greater susceptibility to decomposition whichcharacterises animal
products when compared with vegetable.

269. In addition to the substances already mentioned, we must
also reckon among the constituents of animal substances, /m^,
potash, sdda, and iron ; but these exist only in small quantities.

270. Some of the most important qualities distinguishing animal
substances are owing, in particular, to the predominance of
nitrogen in their composition. This substance is disengaged from
them in large quantities by the action of the nitric acid. This
acid, indeed, itself contains nitrogen; but it has been ascertained,
that in producing this effect, the acid does not undergo any
decomposition ; so that the nitrogen is furnished not by the acid,
but entirely by the substance subjected to its action. Ammonia
is evolved both during the putrefaction of animal substances, and
also by the application of a heat sufficient for their decomposi-
tion ; and this ammonia results from the combination of the nitro-
gen W'ith hydrogen during these processes. Cyanogen, or prussic
acid, is also a frequent product of these operations ; and is known
to consist chiefly of nitrogen. Under these circumstances, also,
the phosphorus enters into new combinations, particularly with
the hydrogen and azote, and forms compound gases, w^hich are
extricated both during the putrefaction and destructive distillation
of animal substances. By becoming acidified by its union with
oxygen, it enters into combination with earths, alkalies, and oxide
of iron, and forms a variety of neutral salts. The same obser-
vations also apply to the sulphur which is found in certain quan-
tities in several animal substances.

271. Another general difference in the chemical composition of
animal and of vegetable substances, is that the former contain a
smaller proportion of carbon, and a greater proportion of hydro-
gen than the latter. Carbon may be regarded as the base of
vegetable matter, to which oxygen and hydrogen are attached;
while hydrogen appears to be the principal component part of
animal matter, and is there combined with nitrogen, oxygen,

12

134 KUTRITIVE FUNCTIONS.

carbon, and phosphorus. Hence during the decomposition of
animal substances by heat, the chief products are ammonia and
empyreumatic oil, in both of which hydrogen is a principal con-
stituent. In general animal matters contain less oxygen than
vegetable, and hence afford less acid by their decomposition ;
and the coal which remains differs from vegetable charcoal in
being much less combustible.

'&

3. Proximate Animal Principles.

272. In the numerous and diversified products of the animal
kingdom, we may trace different degrees of complication in the
composition of their elements. Several substances present the
appearance of greater simplicity, and appear to result from the
more direct union of a few elements, and to preserve among
various shades of modification the same general properties, and
the same distinctive characters. The more compound products
often admit of an intermediate analysis into these comparatively
simpler constituents, which are distinguishable from each other
by a certain uniformity of character, and which we may pre-
sume are obtained in the same state as that in which they existed
in the compound subjected to the analysis. These form what are
termed the intermediate or proximate principles of animal bodies,
in contradistinction to the elementary principles, which are the
result of the ultimate analysis of the substance. These proximate
principles may be considered as forming by their mixture, or
combination, all the varieties of animal matter; and they are
therefore the more immediate object of attention to the chemist
in his analysis of animal substances.

273. The only method resorted to by the earlier chemists, in
the infancy of science, for ascertaining the composition of ani-
mal substances, was that of subjecting them to the process of
distillation at a high temperature, by which their proximate prin-
ciples were entirely destroyed, and either converted into new
compounds, or resolved into their ultimate elements. Many of
these, being gaseous, were sufl^ered to escape, and were totally
disregarded. Scarcely any light could be thrown upon the com-
position of animal bodies by such an imperfect mode of exami-
nation. Successive improvements were afterwards introduced
into this branch of chemical research, consisting chiefly in the
application of various re-agents, from which instructive results
were derived.

274. The modern art of animal analysis may be considered
as comprising three different kinds of operations, which however
admit of being variously combined. The first consists in observ-
ing the spontaneous changes resulting from various natural
circumstances in which the substances may be placed ; the second

PROXIMATE ANIiMAL PRINCIPLES. 135

depends on the application of chemical agents, employed either
as tests to indicate the existence of particular elements or proxi-
mate principles, or as menstrua, which by their specific affinities
may separate the elements or primary compounds from each
other ; while the third set of operations, reverting to the original
plan of destructive analysis, effects the complete decomposition
of the substance, but carefully collects all the volatile and gaseous
matter, and deduces an accurate estimate of the nature and pro-
portions of the ultimate elements. We obtain, for example, a cer- "
tain quantity of water, carbonic acid, and ammonia ; and knowing
the proportions of oxygen, hydrogen, and carbon, which they re-
spectively contain, we are able to ascertain the precise amount
and relative proportion qf the elements which entered into the
constitution of the substance analysed.

275. The general result of the investio-ations which have been
conducted by the last of these methods is, that the simple bodies
of which animal substances consist are comprised in the following
Hst:

1. Oxygen. 2. Nitrogen. 3. Carbon. 4. Hydrogen. 5. Lime.
6. Phosphorus. 7. Sulphur. 8. Soda. 9. Potass. 10. Chlorine.
11. Magnesia. 12. Iron. 13. Silica. 14. Manganese.

276. Of these, the first six may be considered as the principal
elementary ingredients of animal substances. Magnesia and
Silica are found only in very minute quantities, and may there-
fore be in a great measure considered as foreign bodies. The
soft parts of the body are composed almost entirely of oxygen,
nitrogen, carbon, and hydrogen ; while lime and phosphorus form
the basis of the hard parts.

277. The proximate principles most generally met with in
animal substances are. 1. Gelatin. 2. Albumen. 3. Fibrin.
4. Mucus.

278. To these have been added some others, such as urea,
picromel, stearin, elain, osmazone, and several saccharine and
acid principles, which being more limited in their extent, will
fall more properly under consideration in the review we shall
give of the substances which chiefly contain them. We shall
first then present an account of the properties of the four essen-
tial principles above enumerated.

4. Gelatin.

279. Gelatin may be extracted by long continued boiling in
water from almost all the hard and solid parts of the body, such
as the skin, membranes, ligaments, cartilages, and even the bones
themselves. By the slow evaporation of the water which thus
holds it in solution, the gelatin may be obtained in a state of
purity, when it appears as a hard, brittle, and semi-transparent
substance, which breaks with a glassy fracture. It varies some-

136 NUTRITIVE FUNCTIONS.

what in its appearance, according to the source from which it
has been obtained. Glue may be taken as an example of dried
gelatin, in which, however, a few impurities are contained.
Isinglass may be considered, on the whole, as the purest form
under which gelatin is met with, and it exhibits most con)pletely
the characteristic properties of that proximate animal constituent.

280. One of the most striking characteristics of gelatin is the
property it exclusively possesses, when united to a quantity of
water, of dissolving slowly, but completely, forming a solution
of an opaline colour, which is perfectly fluid when warm, but
becomes concrete on cooling, assuming the tremulous appear-
ance so well known as belonging to jelly. In this state it readily
again becomes liquid, by the application of a gentle heat, and
mav, by the continuance of that heat, be brought back to the
state of dryness. These alternate solutions and d'esicca'tions may
be repeated for any number of times, without any change being
produced in the chemical constitution of the gelatin. The pro-
portion in which gelatin forms a solution capable of concreting
by cooling, has been ascertained by Dr. Bostock in the follow-
ing manner. One part of dry gelatin to 100 parts of water gave
a solution which completely stiifened by cooling. But when the
proportion of water was 150 parts to one of gelatin, a compound
was produced, which, though evidently gelatinous, did not as-
sume the concrete form.

281. Solid gelatin undergoes no change if it be kept perfectly
dry; but when united with water, either in the form of solution
or of jelly, it very soon becomes putrid; an acid first makes its
appearance, a fetid odour arises, and ammonia is afterwards
formed.

282. The most ready and convenient test of the presence of
gelatin in any fluid is a solution of tannin; the addition of which
immediately occasions, by the combination of these two princi-
ples, a copious precipitate, which assumes a solid form. This
precipitate collects into an elastic adhesive mass, which soon
dries in the open air, and forms a brittle resinous-like substance,
very similar in appearance to over-tanned leather. It is per-
fectly insoluble in water, and is not susceptible of putrefaction.
It is this combination of tannin with gelatin that constitutes the
preservative part of tanned leather, and which enables it to re-
sist the transmission of moisture. The solutions of tannin most
conveniently appKcable as tests of gelatin, may be prepared by
an infusion of an ounce of gall-nuts in a pint of water ; or, as
Dr. Bostock has proposed, the extract of rhatania, digested in
hot Vv^ater, and filtered after it becomes cold. A considerable
precipitate is produced by these infusions, when the proportion
of gelatin to the water is so small as to compose only the five
thousandth part of the solution. The precipitate afforded by
tannin is not, however, to be considered as a decisive test of the

PROXIMATE ANIMAL PRINCIPLES. 137

presence of gelatin ; for, as we shall presently find, it also occurs
in consequence of the presence of albumen. In order to pre-
vent any confusion from this cause, it will be necessary to have
recourse also to another test, that of corrosive sublimate, which
is found to precipitate albumen, but not gelatin. If, therefore, by
adding corrosive sublimate, we obtain no precipitate, we may be
certain of the presence of albumen.

283. Gelatin is insoluble i» alcohol, but when already in solu-
tion in water, it is not precipitated by that fluid. Acids dissolve
it with great facility, even when much diluted, especially when
aided by heat. The nitric acid eftects its decomposition, during
which nitrogen, and then nitrous gas, are disengaged in consider-
able quantities ; and oxalic and malic acids are evolved, and
may be obtained from the residuum. Sulphuric acid, with the
assistance of heat, partly converts it into a substance resembling
sugar. Chlorine combines with gelatin, forming a white sub-
stance, which assumes the form of filaments.

The pure liquid alkalies dissolve gelatin very readily. The
solution is a brown viscid substance, which possesses none of the
properties of soap, and is not precipitated by acids. This pro-
perty of remaining dissolved after acids are added to the alkaline
solution, distinguishes gelatin from albumen, fibrin, and other
animal products, and is therefore a valuable mode of discrimi-
nating its presence, and of separating it from them in analysis.

284. Gelatin is precipitated by several of the metallic salts
and oxides, but not so unequivocally as to aflx)rd satisfactory
tests of its presence. Like all the other constituents of animal
bodies, gelatin, while it preserves its essential properties, is sus-
ceptible of many shades of variation, and appears therefore
under a diversity of forms, such as glue, size, isinglass, &c. ; but
although many valuable remarks on this subject are contained in
Mr. Hatchett's Observations on the Component Parts of Animal
Membrane, published in the Philosophical Transactions for 1800,
we are still very much in the dark as to the circumstances w^hich
occasion the differences in the several kinds of animal gelatin.

5. Albumen,

285. The proximate principle, which, from its composing the
greater part of the white of eg^, has been termed albumen, is
most abundantly met with in almost all the parts of animals,
whether solid or fluid. It is the chief basis of several of the
more solid textures of the body, such as the membranous and
fibrous structures, and the parenchymatous substance of the
glands and viscera; and it also forms a large proportion of the
blood and of the secreted fluids.

In the white of egg, albumen exists in a state of solution in

12*

138 NUTRITIVE FUNCTIONS.

water, and combined with a small quantity of soda. By agita-
tion with a still larger quantity of water, the two fluids unite, and
form a viscid liquid, the component parts of which do not sepa-
rate by standing.

286. The characteristic property of albumen is its capability
of coagulating, or passing from a liquid to asohd form, by the
action of heat, of acids, and of alcohol, and several metallic
salts and oxides. This change tak^ place in undiluted albumen,
at a temperature of 160° Fahrenheit. After it has been once
coagulated, albumen is no longer soluble in water, unless by long
boiling, aided by pressure. By a long cojitinued gentle heat,
CQagulated albumen gradually has its moisture dissipated, and
the solid matter, amounting to about one-fifth of the original
weight is left behind, in the form of a hard brittle transparent
substance.

287. If the albumen be much diluted, it appears to be incapa-
ble of coagulation by the usual means; but still it was found by
Dr. Bostock, that a solution containing only one tjiousandth
of its weight of albumen, ahhough not properly coagulated, was
rendered perceptibly opaque by a boiling temperature ; so that
heat may be considered, for all practical purposes, as a suf-
ficiently accurate test of its presence in any fluid. During coagu-
lation there is no absorption of oxygen; nor is any gas extricated:
and hence there appears to be no reaction of the principles of the
albumen upon each other. The nature of the change, which
takes place during this transition from the fluid to the solid form,
is by no means well ascertained. Dr. Thomson supposed the
fluidity of albumen to depend on the presence of alkaline matter;
and its coagulation to the removal or neutralization of this alkali;
and some experiments which were devised by Mr. Brande tend
strongly to support this theory. He found that a rapid and abun-
dant coagulation took place in the white of an egg subjected to
the action of a galvanic battery, around the negative pole, where
the alkah must have been separated ; while a thin film only col-
lected round the positive pole. He discovered also, by these
experiments, that galvanic electricity may be applied succes-
sively to the detection of very minute quantities of albumen,
which would not be rendered sensible by any other test.

288. Another agent which immediately effects the coagulation
of albumen, unless it be previously much diluted, is alcohol.
Ether also produces the same effect.

289. Acids in general occasion the coagulation of albumen;
but several of them afterwards redissolve the coagulum if assisted
by heat. This is at lea»t the case with the three mineral acids.
The coagulum formed by acids always retains in combination a
portion of the acid which has been employed. That produced
by nitric acid is the least soluble; and hence nitric acid occa-

PROXIMATE ANIMAL PRINCIPLES. 139

sions a precipitate from solutions of albumen, which are so dilute
as not to bo affected by other acids. Thenard remarks that the
coagulum produced by acids, is re-dissolved by pure alkalies,
and even by ammonia, which does not dissolve albumen that has
been coagulated by heat. ]\itric acid, when concentrated, de-
composes albumen, extricating from it azotic gas, and during its
solution, nitrous gas. Oxalic and malic acids are formed, and a
thick oily matter, soluble in alcohol, appears on the surface. On
the other hand, when coagulated albumen is subjected to the
action of dilute nitric acid, it is after some time converted into a
substance having the properties of gelatin. For this highly curious
fact we are indebted to Mr. Hatchett.* Alum, probably in con-
sequence of its excess of acid, coagulates albumen, provided the
solution be not very dilute. One part of albumen in five hundred
of water is rendered slightly turbid by a solution of alum, but
without any formation of a precipitate.

290. The triple prussiate or ferrocyanate of potass is, accord-
ing to Dr. Henry, an extreinel}^ delicate test of the presence of
albumen, and may be used to discover it in fluids to which other
tests are inapphcable. To enable it, however, to produce a pre-
cipitate, a very shght excess of acetic acid should be previously
added, either to the test, or to the hquid suspected to contain
albumen.

291. Another dehcate test of the presence of albumen is a
solution of corrosive sublimate ; and it is the more valuable,
inasmuch as it has no effect on solutions either of gelatin or of
mucus. Dr. Bostock found that a single drop of a solution of
corrosive subhmate, added to a hquor containing one-thousandth
of its weight of albumen, renders it visibly mdky, and at the end
of some hours a flocculent precipitate falls to the bottom of the
vessel. The same re-agent produces a sensible effect on a liquid,
containing only half that quantity, or one two-hundredth of albu-
m.en.

292. Many other metallic sahs, throw down a precipitate from
solutions of albumen, — as the acetate of lead, the nitro-muriate
of tin, the nitrate of silver, and the nitro-muriate of gold ; but as
they produce a similar effect on other species of animal matter,
they are scarcely deserving of confidence as tests of any one in
particular. A solution of tannin, which, when added to albumen,

» occasions, after some time, a precipitate, may sometimes afibrd
useful indications in analytical inquiries, for it may be distinguished
from that produced from gelatin by its want of density, and
cohesion.

293. Albumen is readily dissolved by the pure liquid alkalies,
which disengage ammonia from it, and form with the residue a

* See his paper already quoted from the F hilosophical Transactions fox
1800.

140 NUTRITIVE FUNCTIONS.

saponaceous compound. * This soap, when dissolved in water, is
precipitated by acetic or muriatic acids.

6. Fibrin.

294. The proximate animal principle, known by the name of
fibrin, or animal gelatin, eid'&is in large quantity in the blood, and
forms the basis of the muscular flesh of animals. When properly
prepared, and freed from the admixture of extraneous matter, it
presents a substance of a white colour, destitute of taste or smell,
of a fibrous texture, and of a soft and elastic consistence. When
dried it- is brittle, and has a certain degree of transparency ; it
undergoes no change from the action of either air or water.

295. When exposed to heat, it contracts very considerably,
and exhibits movements like horn, exhaling at the same time the
smell of burned feathers. When subjected to great heat, it yields
the usual animal products of water, oil, ammonia, carbonic acid,
and carburetted hydrogen, with a large carbonaceous residuum.
This charcoal is very difHcult to incinerate, owning to the presence
of phosphoric salts, which are fused by the heat employed for
that purpose, and form a glassy coat on the surface. A consider-
able quantity of carbonate of Ume is found in the residual ashes.

296. The acids exert a considerable action upon fibrin. Con-
centrated acetic acid renders it soft and transparent ; and the
whole mass is converted by heat into a tremulous jelly. By the
addition of water, and the continued application of heat, a complete
solution is effected, attended with the evolution of nitrogen. Fibrin
combines with muriatic acid in two proportions; the one gives a
neutral compound soluble in water; the other, containing an excess
of acid, is insoluble, but becomes soluble by the action of pure
water. Concentrated sulphurjc acid decomposes and carbonizes
fibrin. Diluted with six times its weight of water, this acid ac-
quires a red colour by being digested with fibrin, but scarcely
dissolves any sensible portion ; but part of the acid is absorbed
by the remaining mass,.which becomes a compound of fibrin and
an excess of sulphuric acid. Water deprives it of this excess,
and a neutral combination is obtained, which is soluble in water,
and has the same characters as neutral muriate of fibrin. The
action of nitric acid upon fibrin is much diversified, according to
its dilution or state of concentration. When the acid is diluted '
with a large quantity of water, a great abundance of nitrogen
gas is disengaged. This gas is entirely derived from the fibrin,
and not from the acid, which, as Berthollet ascertained, has suf-
fered no decomposition during the process. The residuum, in
this, case, is principally oxalic acid, with a small quantity of
malic and acetic acids, and a portion of fatty matter. When
the nitric acid is undiluted, on the other hand, it undergoes de-

PROXIMATE ANIMAL PRINCIPLES. 141

composition, and nitrous gas, mixed witli nitrogen gas, is dis-
engaged. When fibrin is digested for twenty-four hours in nitric
acid of the specific gravity 1.25, it is converted into a pulverulent
mass, of a pale citron colour, which is deposited at the bottom
of the liquid. By washi-ng it in water, the excess of acid is
carried otf', and the colour gradually becomes of a deep orange.
Fourcro}'- and Vau(iuelin considered this yellow matter to be a
peculiar acid, which they distinguished by the name of the yellow
acid. But Berzelius has shown that it is merely fibrin combined
with nitric and malic acids. When the action of nitric acid on
fibrin is very slow, it is gradually converted into a state somewhat
analogous to gelatin.

297. Fibrin, when subjected to the action of caustic alkali, in-
creases in bulk, becomes transparent and gelatinous, and at length
is entirely dissolved, forming a yellowish green solution. From
this solution it is precipitated both by acids and alcohol, but seems
to have undergone some change ; for it is not, as before, soluble
in acetic acid. Fourcroy had asserted, that the compound of
fibrin and alkali resembles soap ; but it does not, in fact, appear
to have any analogy with saponaceous bodies.

298. Alcohol of the specific gravity of 0.81, converts fibrin into
a kind of adipocirous matter, which is soluble in alcohol, and
precipitated by the addition of water. It has a strong and un-
pleasant odour. The alcoholic solution leaves, on evaporation,
a fatty residue, which did not pre-exist in the fibrin, but which,
like the origio^al substance, is soluble in acetic acid. By the
action of ether, fibrin is converted into the same kind of adipocire,
but which has a more ofl^ensive odour, and is in larger quantity.

299. After the account we have given of the three proximate
principles which enter so largely into the composition of animal
matter, namely, gelatin, albumen, and fibrin, it will be useful to
take a comparative view of the analogies they present, and of
the differences by which they are distinguished, both in their
properties and composition. ,They are apparently composed of
the same ultimate elements, combined in proportions which are
not widely different. They admit accordingly of mutual con-
version into one another, by processes which produce a slight
alteration in the proportion of their constituents. By the action
of the nitric acid, fibrin is converted into a kind of gelatin, and a
similar change has been effected on albumen by the same re-
agent. All these substances are presented both in the liquid and
sfJid forms, and pass readil}'- from the former to the latter of
these states, without any apparent change in their chemical
constitution. They are all of them indestructible when perfectly
dry, but readily undergo putrefaction when united with water.
Yet the modes in which they are respectively acted upon by
water are different, and this affords an easy character of distinc-

142 NUTRITIVE FUNCTIONS.

tion bjetween them. Gelatin is soluble in cold water ; the solu-
tion when evaporated becomes gelatinous ; and if this jelly be
dried, it is still again soluble. Albumen is likewise soluble in
water; but whenever the temperature is raised to 170°, it sepa-
rates by coagulation, and this coagulum is not again soluble.
Fibrin is clearly distinguished by its total insolubility in water at
any temperature, at least under the common atmospheric pres-
sure.

300. Then these principles likewise differ in their composition ;
for though they seem to consist of the same ultimate princi-
ples,— nitrogen, hydrogen, oxygen, carbon, phosphorus, and
sulphur, yet these differ somewhat in their proportions. The
most accurate analysis of these substances into their ultimate
elements, are those of MM. Gay ]jussac and Thenard, the results
of which are exhibited in the following table :

Gelatin. Albumen. Fibrin.

Carbon, - - - 47-881 - 52-883 - 53-360

Oxygen, - - - 27-207 - 23-872 - 19-685

Nitrogen,- - - 16-988 - 15-705 - 19-934

Hydrogen, - - 7-914 - 7-540 - 7-021

100. 100. 100.

It appears from the above analysis, that the principal difference
of composition occurs in the proportion of nitrogen. Gelatin
contains the least of this element ; albumen more ; and fibrin a
quantity considerably larger than either of the others. The last
substance appears therefore to be the most animalized product.
It also contains the largest quantity of carbon, as appears indeed
from the greater residuum of charcoal, which it leaves after
destructive distillation. Sulphur is perhaps peculiar to the com-
position of albumen. On the other hand, the proportion of oxygen
is considerably greater in gelatin than in either of the other two
substances. This predominance of oxygen, together with the
less compactness of its mechanical composition, are probably the
causes of the greater tendency which gelatin shows to pass into
the acid fermentation. In this respect, also, gelatin shows itself
to be less completely animalized than the other proximate prin-
ciples, and to partake more of the chemical character of vegeta-
ble substances, which are well known to evolve an acid in the
progress of spontaneous decomposition. There are indeed some
vegetables, as the tribe of fungi, that become alkaline by their
putrescence ; and these are found to contain nitrogen ; so that
gelatin on the one hand, and the fungi on the other, may be
regarded as forming, on each side, the connecting links between
these two great kingdoms of nature.

301. It is a curious subject of speculation to reduce the pro-

PROXIMATE ANIMAL PRINCIPLES. 143

portions resulting from tlie analysis of the French chemists, to
those which are most reconcileable to the atomic theory. They
will then stand as follows ;

Number of atoms of

In Gelatin.

In Albumen.

In Fibrin.

Carbon,

-

15

-

17 -

- 18

Oxygen, -

- -

6

,. -

6 -

5

Nitrogen, -

-

2

-

2 -

3

Hydrogen,';

- -

14

- -

13 -

- 14

The weights, both absolute

1 an

d relative, of the atomic elements,

are shown in the foll(

awing table :

Gelatin.

Albi

imen.

Fibrin.

Absolute.

Relative.

Absolute.

Relative. ,

Absolute.

Relative.

Carbon, - - 90 -

50-00

-

102 -

53-40 .-

108 -

52-94

Oxygen, - - 48 -

26-67

.

48 -

25-13 -

40 -

19-61

Nitrogen,- - 28 -

15-55

-

28 -

14-67 -

42 -

20-59

Hydrogen - 14 -

7-78

-

13 -

6-80 -

14 -

6-86

180 100- 191 100- 204 100-

In the conversion of albumen into jelly, by the slowly continued
action of nitric acid, we may conclude that the acid imparts a
portion of its oxygen to the albumen, and perhaps adds also a
small quantity of nitrogen ; thus constituting the proportions
assigned to gelatin by Gay Lussac and Thenard.

7. Mucus.

302. The term mucus has been employed in very different
senses by different writers. Some have applied it vaguely to al-
most every animal substance which was not referable to any other
class. Fourcroy and Vauquelin, while they include under this
term the viscid secretions which lubricate the alimentary and
other passages that open at the surface of the body, have admit-
ted its claim to be considered as a peculiar proximate principle,
but regard it as analogous to vegetable gum, from which they
suppose it to differ only by containing a portion of nitrogen. Their
descriptive account of its properties, however, is deficient in the
precision which the subject seems to require, and which has been
aimed at by subsequent chemists. Berzelius, it is true, refuses
to allow, that there is any such common principle as mucus,
and founds his opinion on the ground that the chemical characters
of the fluids, which bear that name, are very various in different
parts of the body, and are modified in different situations, ac-
cording to the particular purposes they are intended to fulfil.
Mr. Hatchett, in his interesting paper on the Component Parts of
Animal Memhrane, has attempted to fix the meaning of the term
more definitely. Viewing mucus as extremely analogous in its

144 NUTRITIVE FUNCTIONS. '

properties to gelatin, he considers these two substances as mere-
ly naodifications of each other; the former characterized by its
incapability of being gelatinized ; the latter by possessing that
property ; while both are soluble in water.

Dr. Bostock. in his excellent papers on the Analysis of Animal
Fluids, has endeavoured to establish definite characters as belong-
ing to this fluid, when existing in a state of purity. He states,
that if the solid matter, obtained from the evaporation of saliva
to dryness, be re-dissolved in water, and filtered, the solution will
consist of mucus alone, or with scarcely any extraneous sub-
stance. ^Y a careful evaporation he found that the solution
contained one two-hundredth part of its weight of mucus. He
also obtained a similar principle by macerating an oyster in
water, and evaporating the liquid. It thus appeared that the water
had dissolved about one-fiftieth of its weight of animal matter.
Mucus thus obtained resembles gum-arabic, excepting that it is
somewhat more opaque. Like it, it has scarcely any taste, dis-
solves readily in water, and forms an adhesive solution. Alcohol
added to this solution has no tendency to coagulate it. No ap-
pearance of coagulation is produced by exposing the fluid for
some time to the heat of boiling water ; nor is there any tendency
to gelatinize, by evaporating and afterwards cooling the fluid.
No distinct effect is produced on the solution of mucus, either by
the nitro-muriate of tin, corrosive sublimate, or the infusion of
galls. The subacetate of lead, or Goulard's extract, occasions '
an immediate opacity, and, after some time, a flaky precipitate.
' 303. Dr. Bostock concludes that a decided and essential dif-
ference is thus established between mucus and jelly, by the
different effects produced by tannin, and by subacetate of lead.
Tannin is a most delicate test of jelly, but does not in any degree
affect mucus. Goulard's extract, on the other hand, is a dehcate
test of mucus, but does not in any degree aflTect jelly. The bi-
chloride of mercury (corrosive sublimate), on the contrary, which
is one of the most accurate tests of albumen, does not appear to
affect either jelly or mucus.

Notwithstanding the attempts, which Dr. Bostock made to de-
vise a method of directly determining the proportion of mucus
in a compound fluid, he was not able to succeed, in consequence
of the facility with which Goulard's solution decomposes the dif-
ferent extraneous ingredients, both animal and saline, which are
almost always present in substances that contain mucus, even in
a state the nearest approaching to purity. The salts are particu-
larly liable to act upon the metallic solutions employed as tests;
so that it is impossible to say how much of the effect is owing to
each of these separate causes. The precipitates thrown down
from mucus by subacetate of lead, and nitrate of silver, were
found by Mr. Brande to consist both of the muriates and phos-

FUNCTIONS OF ASSIMILATION. 145

phates of those metals. Mr. Brande also attempted to obtain
mucus free from neutral salts, by subjecting it to the action of
galvanic electricity. He thus detected a small quantity of al-
bumen in saliva, which was not discoverable by the ordinary
tests.

304. A great resemblance has frequently been noticed between
the mechanical properties of animal mucus and vegetable gum ;
and Dr. Bostock found that they strongly resemble each other
also in their chemical qualities. A solution of gum-arabic, con-
taining one grain of gum or two hundred grains of water, was
not affected either by the bichloride of mercury, or by tannin.
With the nitro-muriate of tin, and with the nitrate of silver, there
was only a slight degree of opacity ; but with the subacetate of
lead there was a dense precipitate instantly formed.

305. On the whole, however, animal mucus in its chemical
relations appears to be most nearly allied to albumen ; and the
constituent upon which its characteristic properties principally
depend, would seem, as Dr. Bostock remarks, be a mere modifi-
cation of this substance.

306. We shall conclude our account of this substance by the
following direction as to the order in which it will be most con-
venient to conduct our analytical inquiries of a fluid, which may
be supposed to contain either albumen, jelly, or mucus. The
first step is to observe the effect of the bichloride of mercury ; if
this produce no precipitate, we may be certain that the fluid in
question contains no albumen. We should next employ the in-
fusion of galls, and if this also occasion no precipitate, we may
conclude that the animal matter held in solution consists of mucus
alone. Such being the chemical properties of the chief proximate
principles of animal organization, we have next to examine the
mode in which these substances are produced in the economy.

Sect. II. — Arrangement of the Functions of Assimilation.

307. The means provided by nature for meeting the various
demands of the system, by converting materials derived from
without into the proximate principles of animal organization, the
properties of which we have now examined, constitute a separate
class of functions distinct from all the others. They might not
unaptly be termed the reparatory functions ; but as the changes
which are effected in the materials receiv^ed into the body ibr its
conversion into nutriment are wdiolly of a chemical nature, we
thought they might, with still greater p^ropriety, be termed the
chemical functions, in contradistinction to those the objects of
which are entirely of a mechanical nature, and which have already
passed under our review.

308. The reparatory, or chemical functions, may be divided

13

l46 KtTRITlVE PtlNCTIONS.

into two great orders ; the first consisting of those -which effect
all the changes that the food undergoes during its conversion into
blood ; the second, of those which apply the blood, or nutriment
thus properly prepared, to the various purposes for which it is
wanted, and which effect in it those chemical changes that are
required for those objects.

309. The first order may again be subdivided into several
subordinate processes, including, 1st, the preparation which the
food undergoes in the mouth by mastication, or mechanical divi-
sion. 2d, Its admixture with saliva and other secretions, which
is generally termed in salivation. 3d, Its deglutition, or convey-
ance into the stomach. 4th, Its digestion in that cavity, and
conversion into chyme, which may properly be termed c/iymifi-
cation. .5th, The subsequent changes it undergoes in the intes-
tines, by the influence of various agents, such as the bile, the
pancreatic and intestinal secretions ; and its ultimate conversion
into chyle, and separation from the excrementitious portion,
comprising the process of chylijication. 6th, Its absorption by the
lacteals, its transmission to the heart, and its sanguification, or
conversion into blood. To the above functions the title of
natural functions was given by the older physiologists, and the
name is retained in many modern works in medicine.

310. The second order comprehends, in like manner, a number
of most importatit functions, which, from their immediate influ-
ence on the continuance of life, have been emphatically denomi-
nated the tj/te/ /Mwci!w??s. They consist, 1st, of the Circulation
of the blood, by means of the heart, arteries, veins, and capillary
vessels. 2d, Bespiration, by which every portion of the blood is
subjected in its turn to the chemical action of the air respired ; is
freed from its excess of carbon, an-d becomes oxygenated, or
arterialized, and fit to be applied to the purposes of the system.
3d, Secretion, a term which expresses a variety of changes effected
in the blood, by passing through glands and other secreting or-
gans, adapting it to different purposes in different cases. Closely
allied in its object to secretion is the function of (4th) Nutrition,
whereby the several parts of the body receive accessions to their
growth, and are maintained in the condition requisite for the
perfect performance of their requisite offices. 5th, Absorption
by the lymphatics, for the removal of all superfluous or decayed
particles in the body. 6th, The last function in this order, which
completes the series of chemical changes going on in the living
laboratory of the body, is Excretion, or the separation of useless
or noxious materials from the blood, and their rejection from the
system. We shall proceed to the consideration of these func-
tions in the order in which they have been enumerated. But for
the proper understanding of the subjects they involve, it will be

PROPERTIES OF FOOD. 147

necessary to premise an inquiry into the chemical nature of the
substances which are received into the body as'-food.

Sect. III. — Properties of Food.

311. The food of man is more various in its kind than that of
any other animal; for it comprehends a great multitude of arti-
cles both of animal and vegetable nature. Hence man has been
regarded as entitled to the appellation oi" an omnivorous animal.
His powers of digestion, however, though capable of being exer-
cised upon a great variety of materials, are yet inadequate to the
assimilation of many substances, wh^ch form the exclusive food
of several of the larger quadrupeds whose structure and economy
are not very remote from those of man. The human stomach
and intestines are incapable of extracting nourishment from the
fibrous or membranous parts of vegetables, like the ox, the sheep,
and other herbivorous animals; nor have they the power of
digesting hard and solid bones, like the hyasna, the dog, and
other highly carnivorous quadrupeds. Neither the leaves of
trees nor the grasses, have ever, in any age or country, been
used as the food of man. Many savage races of the American
continent, though possessing vast tracts of country abounding in
trees and grass, have frequently been visited by the extremes of
famine, by which whole districts have been depopulated. When
Australia was first visited by Europeans, the native inhabitants
were found only occupying the sea-coast, gathering up a scanty
and precarious subsistence from the shell-fish casually thrown
upon the shore ; but the settlements which have since been made
have occasioned their retirement into the interior, and their
numbers have rapidly diminished. It is obvious that, had the
leaves of the vegetables which grow wild in those regions been
capable of affording the sniallest sustenance, they would have
necessarily been resorted to in these extremities of hunger. But
no authenticated instance of the kind occurs in the history of the
human race.

312. Man, however, seems to enjoy the exclusive privilege of
having organs of digestion equally adapted to the assimilation of
both animal and vegetable aliment of certain kinds; and the range
which is allowed him in this respect is most extensive. Hence
we find, that in most countries where there prevails a high degree
of civilization, and where religious scruples do not interfere, both
animal and vegetable food is indiscriminately employed by all
who can procure them. In many parts of the globe, indeed,
necessity compels a restriction to certain kinds of diet; and in
some the same restriction is imposed as a religious duty. Thus
the Gentoos live entirely on the vegetable produce of the earth,

148 NUTRITIVE FUNCTIONS.

to which, however, they add the i highly nutritious article of milk.
The Birmans, who are a remarkably active and robust race, are
said to Hve exclusively upon vegetable food. On the other hand,
the inhabitants of the mouths of many of the African rivers, live
wholly upon the produce of the ocean. The flesh of the rein-deer
constitutes the principal food of the Laplander. In general it
would appear that the inhabitants of cold climates consume a
larger proportion of animal food than those of the torrid zone-
Whence it has been, with much probability, inferred, that less
combustible matter is required by the system in situations where
the external temperature is habitually high ; a remark which, if
well founded, is conformable to the principle already laid down
in our statement of the purposes to which a portion of the food is
applied, namely, that of keeping up the animal temperature. In
the ruder periods of society, when the arts of civilization had not
yet diffused their beneticial inflqence over mankind, it is probable
that men were more carnivorous than in the present state of the
world. The introduction of the use of corn, and other grains
of the same class, has effected in this respect an important change
in the condition of the species ; but it would appear that the
introduction of this great benefit was very gradual, and must
have required a long succession of ages before the cultivation of
the gramina had attained any degree of perfection.

1. Animal Food:

313. The parts of animals which is chiefly consumed as food
is the muscular flesh; but milk, and the different products ob-
tained from milk, together with eggs, also compose articles of
diet. The animals from which these aliments are derived, are
principally the herbivorous mammalia, different tribes of birds
and fish, a small number of the class of reptiles, and several
species of raollusca and Crustacea. The flesh of the mammalia
and of birds consists principally of fibrin and gelatin, intermixed
also with fat. Milk may be considered as an emulsion of albu-
men, oil, and sugar, suspended in a large quantity of water.
The two former ingredients, when obtained separately, constitute
respectively cheese and butter. The eggs of birds chiefly contain
albumen, together with a smaU quantity of oil. Fish contains
less fibrin, but a larger portion of albumen and gelatin than the
flesh- of either quadrupeds or birds; and in some fish there is
joined to these constituents a large; quantity of oil. This also is
the case with those Crustacea and moUusca which are used as
articles of diet. When we come, therefore, to analyze the
proximate principles from which animal nutriment is derived,
we find them reducible to the following: namely, fibrin, albumen.

PROPERTIES OF FOOD. 149

oil, gelatin, and sugar; together with a few others, such as
ozmazome, M'hich are of minor importance.

2. Vegetable Food.

314. The parts of vegetables most frequently consumed as
food, are the seeds, seed-vessels, fruits, stalks, .roots, and tubera,
and more commonly the leaves. The most nutritious amongst
the proximate principles resulting from the analysis of these
vegetable materials, are gluten, farina, mucilage, oil, and sugar.
The seeds of cerealia or of rice constitute the chief bulk of the
food in those countries where civilization has made any consider-
able progress. Of all these kinds of grain, wheat appears to
contain, in proportion to its bulk, the greatest quantity of nutri-
ment ; and this arises from its abounding in gluten, which of all
the vegetable principles appears to be best adapted to the human
organs of digestion. In its properties it bears a strong resem-
blance to animal substances ; and it appears, indeed, by chemical
analysis, to contain a large proportion of nitrogen. Hence it may
be considered as the most animalized of the vegetable products.
Gluten is contained in most vegetables which afford farina, and
is also found in the leaves of many esculent vegetables, such as
the cabbage.

315. Farina is found in great abundance in wheat and other
grains, and also forms a large proportion of the nutritive por-
tion of rice, and of certain tubers, among which the principal is
the potatoe. The leaves, stalks, and seed-vessels of plants are
rendered nutritious by the mucilage which they contain, which is
generally united with a portion of sugar.

316. The saccharine principles contained in vegetables, and
blended with other elements, contributes greatly to render them
nutritious ; though in its pure state, as extracted from the sugar-
cane, or the beet, it is rather used as a grateful addition to other •
articles of diet than as a separate source of nutriment. Sugar
may be extracted from a great variety of plants besides those
above mentioned. The maple, the birch, the parsnip, the cocao-
nut, walnut, maize, and carrot, contain it in great abundance, as
is the case, indeed, with every species of grain used as food.
Almost all fruits are more or less saccharine. Figs, grapes, and
dates, which contain it in large quantity, form a very consider-
able proportion of the food of the inhabitants of the south of
Europe, and the African nations on the borders of the Mediter-
ranean. All fruits contain a basis of mucilage, and in many this
mucilage is combined with oil as well as with sugar. ,

317. Attempts have frequently been made to reduce all nutri-
tious substances to a single principle common to all of them, and
to establish accordinglv a scale of nutriment, the place which

13*

150 NUTRITIVE FUNCTIONS.

any substance should occupy on that scale being regulated by
the proportion in which this essential principle existed in it. Hal-
ler conceived that jelly might be considered as fulfilling this con-
dition, and as being the essentially nutritive substance in nature.*
Cullen thought that this property appertains to two substances,
the nutritous matter being either of an oily or saccharine nature,
or consisting of these two qualities combined.f Richerand con-
siders alimentary matter as either gummy, mucilaginous, or sac-
charine.J Dr. Fordyce referred all nutriment to the presence of
mucilage.§ All these, and many other attempts at generaliza-
tion, made by different physiologists at different times, are
premature and unphilosophical, since they associate in the same
class substances having properties totally dissimilar, although
they concur only in that of affording materials for the support of
the animal system. Perhaps the most exact classification of the
kind is that of Magendie, who refers all alimentary substances,
whether animal or vegetable, to the following heads, namely,
farinaceous, mucilaginous, saccharine, acidulous, oily, caseous,
gelatinous, albuminous, and fibrinous.

318. Prout, in a paper published in the Philosophical Transac-
tions,\\ thinks that all the articles of food used by man may,
according to their chemical relations, be arranged under three
heads, namely, tlie saccharine, the albuminous, and the oily. Su-
gar, the basis of the first class of alimentary substances, he finds
to consist of carbon in different proportions, from thirty to fifty
per cent. chemicaUy combined with water. The basis of albu-
men and oil are more compound, but are also united with water,
the proportion of carbon existing in some of the oils being nearly
eighteen per cent. He is of opinion that two at least of these
elements must be blended together in our food in order to render
it either nutritious or digestible. Milk, the food provided by na-
ture for the young animal, exhibits the most perfect union of these
three elements.

319. It must be evident, however, upon a shght consideration,
that notwithstanding all the attempts that have been made to es-
tablish an accurate scale of nutriment, more must depend- upon
the powers possessed by the digestive organs to convert the par-
ticular kind of food into nutritious matter, than upon its being able
to supply the elements requisite for composing nutriment. Thus,
there are many substances, such as oil for example, which con-
tain a very large proportion of the elements which compose the
blood, but which are extremely difficult of digestion, and conse-
quently cannot of themselves be considered as nutritious, although .
when blended with other substances which contain fewer of these

*Elementa Physiologioe, xix. 3, 2. f Physiology, § 211.

"^Elemens de Physiologie, § 3, p. 82. § Treatise on Digestion, p. 84.
For the year 1827, p. 355.

PROPERTIES OF FOOD. 151

elements, but which enable the stomach to exert a .proper action
upon the compound, they become highly nutritive. This remark
applies also to sugar, which, although adding considerably to
the nutritive qualities of those vegetable products which contain
it, would not, if used alone, be capable of supporting life. Ma-
gendie found, that dogs fed upon sugar alone soon became
unhealthy, and if that diet was persisted in, perished from inani-
tion.* Dr. Stark made numerous experiments upon himself, to
which, indeed, he ultimately fell a victim ; from these it appears,
that substances which afford most nutriment, if their use be
persevered in for any length of time, to the exclusion of other
diet, soon produce derangement of the stomach, and failure of
its digestive power. Peculiarities are often met with in the
stomachs of different individuals with respect to the power of
digesting particular kinds of food. In this respect much depends
upon previous habits ; so that it is scarcely possible to establish
any general rules with regard to the nutritious qualities of dif-
ferent species of aliment, that are not invalidated by innumerable
exceptions. The quantity of liquid that is taken in along with
the solid food is also exceedingly various in different individuals;
that'which is suited to the digestion of the one being found to
disagree with another. If we except soups, which of course
consist of the soluble parts of materials out of which they are
prepared, and also milk, the liquids received into the stomach
rarely contain any notable proportion of nutritious matter, but
seem rather to aid the digestion of more solid food, either by
supplying the place of a solvent, or by acting as a stimulus to
the stomach. They are also in many cases necessary for
supplying the loss occasioned by perspiration, which in hot cli-
mates, by regulating the temperature of the body, is essen-
tial to the peservation of health. These purposes are answered
by many vegetable infusions, such as tea and coffee, and also by
fermented liquors, although the latter contain to a certain extent
many of the materials of nutrition, such as sugar and mucilage,
besides the stimulant principle of alcohol.

3. Condiments.

320. With a view to the same stimulant effect, various sub-
stances are added in small quantities to our food, which act as
condiments. Of these the principal is common salt, a taste for
which seems to be natural to a great number of animals, and
which, used in small quantity, has the effect of promoting diges-
tion. Other condiments, such as pepper, mustard, garlic, and
various other spices and aromatics, are employed chieffy from
the agreeable impression they make upon the palate ; but they

* Physiologic, torn. ii. p. 390.

152 NUTRITIVE FUNCTIONS.

in many cases check the tendency of fermentation which many
kinds of food are Hable to undergo in the stomach. As a general
rule, to which, of course, there are many exceptions, whatever
is agreeable to the palate is adapted also to the digestive powers
of the stomach. A certain degree of variety in the articles of
diet is more conducive to the nourishment of the body than
confinement to any single article.*

Sect. IV. — Appetites.
1. Hunger.

321. Hunger is a peculiar sensation excited in the stomach by
the want of food, and by the presence of the gastric juice in that
organ conjointly. It is evidently an affection of the nerves of
the stomach, for it is a good deal dependent on the state of the
nervous system. Its periodical recurrence at stated times §hows
that it is a crood deal under the dominion of habit. Huncrer often
suddenly ceases upon the occurrence of sudden emotions of
grief or anger, and is much influenced by other causes of mental
excitation. Literary men deeply absorbed in meditation often
forget that they have occasion for nutriment, and are unconscious
of the calls of hunger. Hence such persons are often great
sufferers from disordered digestion.

322. The presence of the gastric juice appears however to be
a natural stimulus to appetite, its primary action being probably
in the nerves of the stomach. A similar efTect may be produced,
when the stomach is full, by taking spirituous liquors, or high-
seasoned dishes. Those physiologists who were inclined to refer
the phenomena of the living body to mechanical causes, ascribed
the sensation of hunger to the friction of the surfaces of the sto-
mach against one another, which they supposed took place when
it was empty ; but the anatomy of that organ, which, from its
rounded form, and from the softness of its texture, would seem
totally incapable of producing friction by any of its movements,
is totally at variance with this hypothesis. Others have conceived
that the collapse of the stomach in its empty state, by deranging

* [So much is this the case, that if, after an individual has been accustomed
to live on both animal and ve^-etable food, he be restricted to one only, his
nutrition, in course of time, becomes impaired, and scurvy is induced. There
is at this time, (June, 1839,) in the wards of the Philadelphia Hospital,
Blockley, a female, who has refused all animal food for many months, and
who is effectpd with purpura on the extremities, spontry gums, and every sign
of anaemia. It is this restriction to a single article of diet, with the confine-
ment to a small space, and the privation of wonted air and exercise, that
explains the phenomena observed in the dog fed exclusively on sugar, (§ 319)
better than the want of azote in the aliment to which it was at one time
ascribed by Magendie.]

APPETITES. 153

the position of tiie liver and spleen, drags down the diaphragm,
and thus excites irritation in the nerves of those regions ; and
they endeavour to support this doctrine by the alleged fact, that
hunger is prevented and appeased by wearing a tight girdle,
which occasions pressure on the stomach and gives support to
the neighbouring organs. But the instances already given of the
dependence of hunger on the states of the nervous system, are
sufficient to prove that it is not owing to any mechanical cause.

323. The chemical physiologists attempted to explain the phe-
nomena solely by the action of the gastric juice on the coats of
the stomach, which they imagined it tended to corrode, and
hence gave rise to an uneasy sensation. It is much more pro-
bable, however, that the impression made by -this secretion is
exclusively on the nerves of the stomach; and there is no doubt
but that this action is one of the principal causes of hunger; for it
has been found, that, if after long fasting, when there is a con-
siderable accumulation of gastric juice, and when the sensation
of hunger is extremely intense, it at once ceases if the gastric
juice be removed by an emetic; or even if it be much diluted by
taking large quantities of hot water.*

324. The effects of long abstinence from food are, great loss
of strength, emaciation, discoloration of the blood and of the
secretions, an increase of nervous susceptibility, fever, loss of
sleep, painful sensations in the region of the stomach, followed
by total loss of appetite, delirium, and death. It has been said,
that the exterior of the bodies of those who die of famine has
exhibited a shining appearance in the dark, as if they had been
impregnated with uncombined phosphorus.

2. Thirst.

325. Thirst is a sensation somewhat analo!2;ous tohunsrer with
respect to its cause and effect, and with respect of its depending
on particular states of the nervous system. It is considerably
more distressing and intolerable than hunger. The seat of the
sensation appears to be in the mouth and fauces, although its
origin is generally in the state of the stomach, or general condi-
tion of the system. In the healthy condition of the organs it is

* [These reasons are not satisfactory. The circunnstariees referred to, tend
merely to show, what we observe constantly as the effect of mental emotions —
that the sensation of hunger can be postponed for a time. An unanswerable
objection to them, l^wever, is the fact, repeatedly proved by Dr. Beaumont, and
verified, in the same case, by Dr. Dunglison, that in the fasting state there is
little if any gastric juice in the stomach. Hunger is an internal sensation
connected with the wants of the economy; instinctive, therefore, and as inex-
plicable— in the existing state of knowledge — as any other internal sensation.
— Beaumonfs Experiments and Observations on the Gastric Juice, &c. p. 57,
Plattsburg, 1833, and Dunglison''s Human Physiulugy, 3d edit. i. 493.]

154 NUTRITIVE FUNCTIONS.

a natural impulse prompting us to supply the system with the
fluids requisite for carrying on its functions ; but in the case of
fevers, and other morbid states, thirst is sometimes excessive,
and, if indulged without restriction, would prove highly injurious.
In cases where a preternatural opening has been made into the
oesophagus through the neck, the sensation of thirst is found not
to be in any degree assuaged by fluids appHed to the mouth, or
even swallowed, if they escape through the wound, and do not
descend into the stomach ; whereas, it is immediately relieved
when the same fluids are introduced into the stomach.

Sect. V. — Pre'paration of the Food for Digestion.

320. The preparatory processes to which the food is subjected
previous to its introduction into the stomach, are partly of a
mechanical and partly of a chemical nature. It is .masticated
by the teeth and jaws, and at the same time mixed with the saliva
and mu&ous secretions of the membrane hning the mouth, fauces,
and oesophagus. The effect produced by these operations is to
reduce the food to a soft and uniform pulp, which is more easil}'-
acted upon by the solvent powers of the gastric juice than if it
had been swallowed entire.

1. Mastication.

327. During mastication, a great number of muscles are called
into action. The principal of these are the powerful muscles that
elevate the lower jaw, — namely, the temporal, the masseter, and
the pterygoid, the latter of which .are capable of giving at the
same time some degree of lateral motion to the jaw, adapting it
thereby to effect a grinding action by the medium of the teeth.
The lower jaw forms a lever of the third kind with a double
angle, the fulcrum being at the condyles, which are curiously
articulated with the skull, by means of an interposed cartilage.
Its motions are almost entirely confined to those of elevation
and depression ; but it has also a more limited extent of lateral
motion.

328. The teeth, are the great agents in mastication. The
respective purposes served by each class are sufficiently evident
from their shape and position in the jaw. The incisors or front
teeth, are employed for cutting or dividing the food like a pair
of shears or scissors ; the cuspidati, or eye-teeth, placed a little
farther back in the jaw, are particularly adapted to lay hold of,
and tear asunder, fibrous textures that afford considerable re-
sistance; their action may be compared to that of pincers. Mr.
Hunter, after reviewing their different forms in the different tribes

PREPARATION OF THE POOD FOR DIGESTION. 155

of qua'drupeds, is enabled to trace a similarity in shape, situation,
and use of tiie cuspidati, from the most imperfect carnivorous
animal, which he believes to be the human species, to the most
perfect carnivorous animal, the lion. The bicuspidati and molares
compose what are called the grinding teeth, and their chief office
is the trituration of substances already torn ofi" by the cuspidati,
or cut by the meeting of the incisors. The molares especially,
being placed nearer to the articulation of the jaw, or centre of
motion, act with greater power in exerting pressure on whatever
is between them. If we wish to break a very hard body, the
shell of a nut for example, we instinctively place it between the
•backmost molares, where the resistance it opposes to fracture
acts by the shortest lever.

The bony substance of the teeth is preserved from the injury
to which it would be exposed by the friction of hard substances,
and by the contact, of corroding fluids, and the influence of the
air, by being cased in enamel, which, as we have seen, is con-
siderably harder than bone. In consequence of the peculiar mode
of its formation, the enamel is incapable of being renewed by a
fresh growth when it has been worn away by friction. When,
however, the teeth are lost by age, accident, or disease, their
alveoli close and are obliterated by absorption ; 'the gums then
acquire a degree of hardness, that renders them an imperfect
substitute for the teeth in mastication.

329. The chief agent in distributing the food so as to place
it in proper situations between the teeth for the purpose of mas-
tication, and for transferring it to the fauces, is the tongue. This
organ consists almost entirely of muscular fibres, which are
variously arranged, and interwoven together in a very intricate
manner, so as to render it capable of motion in every possible
direction. Its root is affixed to a bone which is peculiar 'to it,
called the os hyoides, from its resemblance to the Greek letter ",
which furnishes a basis of attachment to the greater number of
the muscles of the tongue, and the extremities of which, being
extended considerably backwards, serve to keep the palate ex-
panded and always prepared to receive the food. But the tongue
also contains a set of muscular fibres, which proceed longitudi-
nally through the centre of that organ, unattached to any bone,
and serving to contract its length. The tongue, is thrust out of
the mouth, not by any power of elongation in the muscles, as
might at first sight appear to be the case, but by the contraction
of that portion of the radiating fibres proceeding backwards from
the inside of the jaw and the os hyoides', and drawing forwards
the root of the tongue when they act alone. This complex struc-
ture is admirably adapted to the great variety of uses to which
the tongue is applied, not only in mastication and deglutition,
but also in speaking.

156 NUTRITIVE FUNCTIONS.

330. The muscular actions of the lips and cheeks are also
mintimately^concernedin mastication ; and ample provisionis made
for their varied movements by being furnished with so great a
number of muscles as those which cover the face, and are attached
more or less to the lips and corners of the mouth.

2. Insalivat'wn.

331. While the food is under the action of the organs of mas-
tication which effect its mechanical division, it is at the same
time mixed up with the saliva. This fluid is found, when chem-
ically examined, to consist principally of mucus and albuminous
matter held in solution in water, together with a small proportion
of saline ingredients.

332. Dr. Bostock considered that he had detected two kinds
of animal matter in the saliva, one composing the soft masses,
and giving it its consistence and physical characters, nearly
similar to coagulated albumen, the other dissolved in the water
of the fluid along with the salts, and resembling the serosity of
the blood.* Berzelius regards the former of these substances as
corresponding in its properties to mucus, and states the saline
ingredients to be chiefly alkaline muriates, with a small quantity
of lactate of soda and of pure soda.f Tiedemann and Gmehn
state the solid contents of the saliva to vary from one to twenty-
five per cent, and to consist of salts, mucus, and ozmazome, to
which are added, in some cases, a little albumen and a little
fatty matter, containing phosphorus. The soluble-salts consist
of alkaline carbonate, w^hich gives an alkaline character to the
fluid, acetate, phosphate, sulphate, muriate, and sulpho-cyanate.
The alkali in man is almost solely potass ; while, in the dog and
sheep, it consists of soda, with very little potass. The presence
of sulpho-cyanic acid, on the other hand, is almost peculiar to
the human saliva, being scarcely perceptible in that of the dog.
Some insoluble salts, namely, phosphate of lime, carbonate of
lime, and carbonate of magnesia, are also detected in the saliva,
but in very minute quantity. J Leuret and Lassaigne, whose inves-
tigations were nearly contemporaneous with those of Tiedemann
and Gmelin, represent the chemical properties of the saliva as be-
ing essentially the same in all animals, and consider the animal
matter it contains as a species of mucus.§

333. When viewed by a good microscope, the saliva is gene-
rally found to contain globules of very minute size.

* Edin. Med. Journal, ii. 44.
f Medico-Chirurgical Transactions, iii. 242.
X Recherches sur la Digestion, par Jourdan, p. 23.

§ Recherches Physiologiqnes et Chinniques sur la Digestion, p. 33. See
Bostock's Elementary System of Physiology, p. 487, note.

PREPARATION OF THE POOD FOR DIGESTION. 157

334. The saliva is secreted by the parotid and other glands in
the vicinity of the mouth> and is poured out in considerable quan-
tities during mastication. It lias been estimated that about six or
eight ounces of saliva are at each principal daily meal mixed up
and incorporated with the food. It flows much more abundantly
during a meal, and particularly if the food that is eaten possesses
stimulating qualities, and has a sapid flavour. The quantity is
augmented by the appearance, or even the idea of food, when
the appetite is keen. The influence of the nerves which supply
the salivary glands is very marked in regulating their secretions,
as we shall have occasion to observe more at length, when we
come to consider the function of secretion. The pressure of the
muscles of the cheek on the parotid gland assists no doubt in the
quick discharge of the secretion of that gland by its excretory
ducts; and the same remark applies also to the submaxillary and
sublingual glands, which also prepare saliva, and whose ducts
open into the mouth : for we find, that during mastication all the
muscles about the mouth are in continual action. The tongue
presses the food on all sides, and thrusts it between the grinding
teeth, while the muscles of the cheek, but more particularly the
buccinator, against which the food is pressed by the tongue,
forces it back again under the teeth, until it has been sufficiently
subjected to their action ; and during the whole of this time it
is gradually receiving additions of saliva, which thus become
intimately and uniformly mixed up with every portion of the
divided food. When completely chewed, it is collected together
on the surface of the tongue, which sweeps round the different
parts of the mouth for this purpose, and moulds it into the form of
a bolus ; and the point of the tongue being then raised, and its
basis depressed, an inclined plane is formed, along which the
bolus is propelled backwards, and delivered to the pharynx,
which is expanded to receive it.

3. Deglutition.

335. The action of swallowing, simple as it may appear to be,
is in reality extremely complex, consisting of a succession of
muscular contractions, nicely adjusted and balanced, so as to
co-operate harmoniously in the production of one general effect,
the descent of the food along the cesophagus. The whole exhibits
one of the most beautiful examples of mechanical contrivance
that is to be met with in the body.

336. The pharynx, as we have seen, is a large muscular bag,
shaped hke a funnel, capable of being contracted in diameter,
and of compressing its soft contents by means of the muscles
which are expanded round it, and are called the constrictors of
the pharynx. Other muscles are provided for elevating it, that

, 14

158 NUTRITIVE FUNCTIONS.

is, for bringing it nearer to the base of the tongue. While the
food is passing downwards, the velum pendulum is expanded,
thrown backwards, and raised by the muscles adapted to perform
these motions, so that it closes the posterior nostrils, and acting
as a valve, prevents any portion of what is swallowed from pass-
ing either into those cavities or into the eustachian tubes. The
bolus is thus directed towards the oesophagus, being carried
thither by the contraction of the pharynx, while the root of the
tongue being at the same time depressed, the epiglottis is turned
backwards, and being applied to the glottis, accurately closes its
■aperture, so that no part of the alimentary matter can pass into
the larynx. The mass of food, having now arrived at the upper
part of the oesophagus, is propelled towards the stomach by the
successive contractions of its circular fibres. The mucus, which
is secreted in abundance by all the surfaces along which it passes,
and continually lubricates them, very much facilitates its descent.
The longitudinal fibres of the muscular coat of the cesophagus
contribute their share in this action, by shortening and dilating
those portions of the canal into which the food is about to enter,
Dumas distinguishes four stages in this process ; first, that by
which the aliment is propelled towards the pharynx ; the second,
consisting in the dilation of that cavity, by which it receives the
bolus transmitted to it ; the third, by which the pharynx closes
upon its contents, and propels it downwards to the oesophagus ;
and the fourth, in which, by the action of the cesophagus, the
food is propelled into the stomach.*

337. When any impediment exists to the due performance of
these actions, fluids are swallowed with greater difficulty than
solids, because the particles of the former having a continual
tendency to spread themselves, it requires a closer and more
exact application of the organs to prevent their escape, while
they are compressed in giving to the fluid its proper direction.
The action of suction performed by the tongue, with the assist-
ance of the muscles of the cheeks and lips, which remove the
pressure of the atmosphere from the surface of the fluid to which
the mouth is applied, is also very complex. The tongue acts here
as a piston ; and sometimes the action is effected by the muscles
of inspiration.

Sect. VI. — Digestion or Chymification.

338. The food has now passed from the oesophagus into the
stomach, through its cardiac orifice, which has so been named
from its supposed sympathy with the heart, near which it is

' Physiologie, torn. i. p. 341.

DIGESTION OR CHYMIFICATION. 159

situate. The office of the stomach is to convert the food which
it receives into the soft pultaceous mass of a gray colour, wliich
has been denominated chyme.* These secretions do not proceed
from any glands that admit of being readily distinguished, their
existence being rather inferred from the presence of the secre-
tion. The membranes composing the coats of the stomach are
capable of great distension, so as to contain a large quantity of
food, while at other times that organ is contracted to a very
small size, partly by the elasticity of its texture, but principally
by the action of the circular and longitudinal fibres which encom-
pass its cavity, and which constitute its muscular coat. These
fibres are so disposed as to enable different portions of the sto-
mach to act separately and successively on its contents, producing
what has been termed the -peristaltic, or vermicular motion. Two
purposes are answered by these actions; in the first place, the food
contained in the stomach is asiitated and thorouarhlv mixed to-
gether, while it is at the same time exposed to the chemical action
of the gastric juice ; and secondly, the ultimate effect of this
motion is to carry the mass very gradually towards the pylorus,
through which it is transmitted into the beginning of the intesti-
nal canal.

339. While the food is thus rolled and agitated by the peris-
taltic action of the muscles, it is at the same time subjected to a
degree of pressure, the purpose of which seems to be, to bring
into closer approximation the solvent f]uids with the materials on
which they are to act, and thereby increase the chemical power
of the former, and also to repress the evolution of gas, which has
a tendency to be generated during the species of fermentation
which the aliment undergoes in the process of digestion.

340. The principal agents in effecting those changes which
constitute digestion, that is, which convert the aliment into
chyme, is the gastric juice. The important office which this
secretion performs has induced chemists to bestow great pains
in obtaining its correct analysis, and in examining all its physical
properties. When carefully collected, it appears to be a trans-
parent and colourless fluid, having a saline and somewhat bitter
taste, occasionally possessing acid properties, but probably in its
natural and healthy condition being neither acid nor alkaline.f
It contains a small proportion of albumen, together with a matter
which is either gelatin or mucus. But while it thus differs to all
appearance in so trifling a degree from many of the other sccre-

* The older authors made no distinction between chyme and chyle: the lat-
ter substance is the product of the formation of the small intestines.

f [This is more than questionable. Whenever the secretions of the stomach
have been obtained unmixed w^ith alimentary matters, as in the case, referred
to hereafter, of the man with the fistulous aperture into the organ, they were
found of a distinctly acid taste.]

160 NUTRITIVE FUNCTIONS.

tions, it yet possesses very extraordinary solvent powers over the
substances usually employed as food. Even when made to act
upon these substances in vessels out of the body, provided they
are kept in a temperature equal to that of the human body, it
will reduce them in a few hours to the state of a soft pulp, pro-
ducing apparently the very same change which is induced upon
the same species of aliment by the digestive process within the
stomach. It is evident that the chemical analysis of the gastric
juice affords as yet no clue to the explanation of this singular
property. The power which the gastric juice possesses of
coagulating milk, and other albuminous fluids, and of retarding
the putrefaction of animal and vegetable substances subjected to
its action, and even of counteracting this process when it has
already commenced, are equally involved in mystery, and baffle
all our endeavours to explain them on any of the hitherto known
chemical principles.*

341. There are three ways in which the gastric juice has been
observed to act on alimentary matter ; the -firsi is that of coagu-
lation, which is exerted on all the fluid forms of albumen, whether
existing in the serum of the blood, or the white of the egg, or in.
different secretions, more especially milk. It is by means of this
property, indeed, that cheese is obtained from the coagulation of
its albuminous portion by the addition of rennet, which is an
infusion of the digestive stomach of a calf. The object of this
coagulation appears to be to detain the substance for a longer
time in the stomach, and subject it more completely to the solvent
power of the same fluid, by previously acquiring a solid form,
which prevents its escape by the pylorus.

342. The second kind of action exerted on the food by the
gastric juice is that of counteracting the tendency to putrefaction,
and even to the ascescent fermentation. This efl^ect takes place
in a remarkable degree in many carnivorous animals, who fre-
quently take their food in a half putrid state ; and in whom the
first operation of the gastric juice is to remove from it all putres-
cence; showing that this secretion possesses the property not only
of preventing putrefaction from taking place, but also of suspend-
ing its further progress when it has actually commenced.

343. The third species of chemical action exhibited by the
gastric juice is that of solution. That this effect takes place inde-
pendently of any concurrent mechanical operation of the muscular
powers of the stomach has been very decisively proved by the

*[ Some interesting experiments have been made on the powers of acidified
mucus in effecting artificial digestion, by Eberle of Germany, Professor
Miiller and D. Schwann, and by Dr. T J. Tood. By steeping the mucous
membrane of an animal's stomach in an acid liquor a solution is obtained, to
which Eberle gave the name Pepsine. This solution has the property of
dissolving coagulated albumen, muscular fibre, and animal matters in general.]

DIGESTION OR CHYMIFICATION. 161

experiments of Reaumur, of Stevens, and of Spallanzani. Those
of Stevens, in particular, are highly valuable, from being made
on the human subject. He was fortunate enough to meet with a
man who had been in the habit of swallowing stones, which he
could afterwards, by a voluntary effort, reject by vomiting from
his stomach. Taking advantage of this power, Stevens induced
him to swallow hollow metallic spheres perforated with holes,
and filled with diflerent kinds of alimentary substances, which,
after being allowed to remain a sufficient time in the stomach,
were returned, and their contents examined. It was invariably
found that the food under these circumstances of exposure to the
gastric i^uid alone, and protection from external pressure of a
mechanical nature, was more or less completely dissolved, and
reduced to the state of a pulp. He afterwards pursued a similar
train of experiments on dogs, causing them to swallow the per-
forated spheres, and after a certain time destroying the animals,
and examining the changes effected in their contents.

344. Spallanzani has also varied and multiplied experiments of
this kind in a manner that leaves no room to doubt the truth of
the conclusion deduced from them as to the solvent power of the
gastric secretion. Dense membranes and even bones are reduced
into a pulpy mass by this fluid in many animals, while at the
same time many bodies of comparatively delicate textures, such
as the skin of fruits, and the fibres of flax or cotton, are not in
the slightest degree affected by it. This difference of action on
different subjects is analogous to the operation of chemical affinity,
and corroborates the theory that digestion is effected principally by
chemjcal agency. The results of these experiments have been
fully confirmed by experiments made on the stomachs of persons,
who, in consequence of a wound, had a permanent opening into
that organ through the parietes of the abdomen.

345. Portions of the stomach are sometimes found dissolved
after death. This takes place more especially when death has
occurred suddenly during the act of digestion. This effect can
never take place during life, because the living structures resist
the solvent power of the gastric juice, which affects only dead
animal matter. Thus it happens that worms, and the larvas of
insects live for a considerable time in the stomach, without being
acted upon by its secretions.

346. Gas is frequently evolved in the stomach during the pro-
cess of digestion ; but this W'ould appear to take place onl}' in a
disturbed or morbid condition of that process, and by no means
to be a necessary attendant upon healthy digestion.

347. Acid is also frequently developed during imperfect diges-
tion ; but it appears from the experiments of Dr. Prout, which
have been fully confifmed by other experimentalists, that this
effect is also attendant upon healthy digestion, and that it is prin-

14*

162 NUTRITIVE FUNCTIONS.

cipally the muriatic acid whicii is thus disengaged from its com-
binations, and makes its appearance in a free state. The lactic
acid, an acid which appears to be a modification of the acetic,
also is present in considerable quantity.

Professor Tiedemann and Gmelin, in an elaborate treatise on
Digestion lately published, found the acetic acid always present
in the gastric juice.* They observe that water alone, at the
temperature of the human body, is capable of dissolving many
of the substances employed as food ; and of these many that are
not soluble in water are so in the diluted muriatic and ^acetic
acids at a high temperature, and they are inclined to ascribe to
a chemical solution of this kind the principal change effected by
digestion.

348. Among the agents concerned in the digestion of the ali-
ment, the high temperature at which the contents of the stomach
and intestines is retained, must be considered as one of the most
important. The heat of the body unquestionably tends to pro-
mote the chemical action of the secretions which effect these
changes. Whilst digestion is taking place, both orifices of the
stomach are closed, and there often comes on a feeling of chilli-
ness, especially in a weakly constitution, in consequence of the
demand which the stomach makes upon it for an additional sup-
ply of heat to assist in the process that is going on. There is
also a disinclination to exertion, and frequently a tendency to
sleep while digestion is performing. Yet the indulgence in this
disposition, as well as violent exercise immediately after a meal,
lend equally to retard the formation of chyme. The circum-
stances most favorable to perfect digestion, are gentle exercise,
with cheerfulness, and moderate mental exertion.

349. It appears from Dr. W. Philip's experiments, which were
conducted chiefly on rabbits, that food recently taken is always
kept distinct and unmixed with that which has remained for some
time in the stomach, the former being introduced into the centre
of the mass previously present. The food is more digested the
nearer it is to the surface of the stomach, and is least digested in
the small curvature, more so at the larger end, and still more
perfectly at the middle of the great curvature. The state of the
food found in the cardiac portion is different from that found in

=• [In the case referred lo in a subsequent paragraph (349) Dr. Beaumont
had innumerable opportunities for obtaining the gastric secretions unmixed
with alimentary matter. These were examined by Drs. Dunglison and Em-
met, and found lo contain free muriatic and acetic acids, phosphates and mu-
riates, with bases of potassa, soda, magnesia, and lime, and an animal matter
soluble in cold water, but insoluble in hot. The quantity of free muriatic acid,
contained in them was surprising. On repeated examination, the acid charac-
ter was distinct, and the odour of muriatic acid not lobe doubted. — See a letter
from Dr. Dunglison to Dr. Beaumont, in Beaumont's Experiments, &c., on
the Gastric Juice, p. 78.]

DIGESTION OR CHYMIFICATION. 163

the pyloric portion of thO stomach ; for in the latter it is nnore
uniform in its consistence, more dry and compact, and apparent-
ly more thoroughly digested. Thus it would appear that it is at
the large end of the stomach where the gastric juice is secreted
in greatest abundance, that the first and principal operations of
digestion take place, and that from this part the food is gradual-
ly propelled towards the small end, becoming more completely
changed during its progress.

It appears from the experiments of Dr. Beaumont on an indi-
vidual, who lived many years with a fistulous opening into the
stomach, which allowed the contents of that organ to be at all
times examined, that the different kinds of aliment all require to
undergo the chemical action of the gastric juice in order to be
reduced to the state of chyle ; but that the rapidity of this pro-
cess differs considerably, according to the deUcacy of the natural
texture of the food, and the extent of its previous mechanical
division. Animal substances are found to be more rapidly con-
verted into chyme than vegetable ; and oily substances, although
containing a large proportion of nutritious elements, are compara-
tively difficult of digestion.*

Some curious evidence was afforded by Dr. Roget and Dr. P.
M. Latham, on the occasion of an epidemic scurvy which pre-
vailed in the years 1823 and 1824, among the prisoners in the
Milbank Penitentiary, that too liquid a diet, consisting of too
large a proportion of soups, although abundantly supplied, did
not furnish sufficient nourishment for the preservation of health;
probably from their not being retained in contact with the coats
of the stomach during the time requisite for their underg'oing the
process of digestion.f

350. A great number of hypotheses were devised by the older
physiologists in order to explain the process of digestion. These
we shall only briefly enumerate, without engaging in any laboured
refutation of what, in the present advanced state of science,, does
not recjuire much examination to prove the fallacy. The ancients
had generally adopted the opinion of Hippocrates, which was

* [From his experiments on this individual, Dr. Beaumont inferred, that
pig's feetsoused, rice, and tripe soused, were soonest senton into the duodenum?
but it need scarcely be said, that all such tabular results apply, in strictness, to
the individual concerned only; yet they afford useful comparative views, which,,
with exceptions depending; upon individual peculiarities, may be regarded as
approximations applicable to mankind in general'. — Beaumont, Op. di.

Dr. Beaumont's table has been copied^ — and a column indicating the ratio of
the digestibility of the various articles added — in l)iingliso7i^s Elements of Hy-
giene, p. 233, Philad., 1835, and in his Medical Dictionary, 2d edit. Philad.
1839, art. Digestible. See also. Combe's Physiology of Digestion, Amer.
ed. New York, 1836.]

■j- See an account of the disease lately prevalent in the General Penitentia-
ry. By P. M. Latham. M. D. Loudon, 1825.

164 NUTRITIVE FUNCTIONS.

enforced by Galen, that the food was digested by what was
called a process of concoction. This, however, seems_to be only
another term for digestion, instead of affording any explanation
of its nature. Some physiologists considered digestion as result-
ing from a degree of putrefaction ; a process which is in reahty
of a totally opposite nature, although agreeing in some minor
points, such as the breaking down of the cohesion of the particles,
and the occasional disengagement of gas.. Others, reasoning
from the analogy of the stomachs of granivorous birds, which
are provided with a strong muscular apparatus for the purpose
of grinding, conceived that a similar process took place in the
human stomach, and that digestion was the effect of mechanical
trituration. But the experiments of Stevens and Spallanzani, the
results of which have been already stated, are alone sufficient to
overturn this hypothesis.

351. The earher chemical physiologists ascribed digestion to
a species of fermentation. This term, however, appears to have
been misapplied, in as far as digestion is conceived to be identi-
cal with either the acetous or vinous fermentatipn ; and if it were
meant to convey the idea of a peculiar species of chemical change
taking place in the stomach, and in no other situation, then no-
thing is gained by the substitution of the term ernployed for that
of digestion, which must express precisely the same idea. More
modern writers have imagined they were giving an explanation
of the phenomena of digestion, by referring them simply to the
action of the vital principle, or the vital powers, or the prin-
ciple of life, or by whatever name they chose to designate an
imaginary agent which gave rise to all those phenomena, not
referable either to mechanical or chemical principles. But after
the remarks we have elsewhere made on this radical error of
substituting final for physical causes, and of prematurely general-
izing the principles which actuate the living system, it is needless
farther to insist upon the fallacy of this mode of reasoning.

352. A doctrine has lately been advanced, with greater sem-
blance of truth, that digestion is essentially a nervous function ;
that is, one which is directly dependent on nervous power. A
variety of facts unquestionably prove that the functions of the
stomach are very much influenced by the states of the nervous sys-
tem. The section of the par vagum, or eighth pair of nerves, in the
neck of an animal, is followed by the almost total interruption
of digestion; whence we may infer that the influence conveyed
by these nerves is necessary both for the secretion of the gastric
juice, and perhaps also for the muscular actions of the stomach.
It is exceedingly remarkable, however, that where the galvanic
influence is sent through the mutilated nerves, by means of a
voltaic battery, digestion maybe renewed, and goes oil for a con-
siderable time; whence it has been inferred by Dr. W. Philip,

CHYLIFICATION. 16&

that the nervous power, or the agency which is conveyed through
the nerves, and which influences secretion, is itself identical with
the electric or galvanic fluid.*

353. The pyloric orifice of the stomach is furnished with a
circular bund of fibres, covered by a fold of the nervous coat;
and acting as a sphincter muscle, which closes the passage
during the earlier stages of digestion, so as not to suffer the
escape of the food until it has undergone the requisite changes
which constitute its digestion. The aliment is conveyed to the
pylorus in proportion as it has undergone these changes. There
appears to exist in this part of the stomach a peculiar and ex-
tremely delicate sensibility, and a power of selecting those por-
tions of the food that are properly digested, and of allowing
them to pass, while those which are undigested are retained in
the stomach.

A portion of aliment often passes, however, unchanged through
the pylorus along with the chyme. We observe, for instance,
that many hard substances, such as the stones of cherries and
plums, find their way through the pylorus without much diffi-
culty. The seeds of many plants are only softened by their
detention in the stomach, and passing with no other change
through the intestinal canal, are prepared for germination in the
soil to which they may be transferred. Thus many species of
plants and trees have been known to grow at places very remote
from each other in consequence of their seeds having been con-
veyed by birds that had swallowed them.

CHAPTER VIT.

CHYLIFICATlOiV.

354. The aliment, now converted by the process of digestion
into chyme, after passing the pylorus, enters into the duodenum,
which is the first of the small intestines. In the duodenum the
chyme undergoes further changes, which are quite as great and

*[ Dr. Prout {Bridgewater Treatise, Amer. edit. p. 268, Philad. 1834)
conceives, that tlie source of the muriatic acid in the stomach is the common
salt existinnj' in the blood, which he conceives is decomposed by sjalvanic
' agency ; and Drs. Purkinje and Pappenheim (^M idler'' slrclilv. 1838, and British
and Foreign Med. Rev. Oct. 1838, p, 527) announce a similar opinion. From
their galvanic experiments, they think it results, that the juices mixed with
the food in the natural way, — the saliva, the mucus, and the portions of chloride
of sodium generally present therein; and still more, the gastric mucous mem-
brane itself, — develop as much chlorine as is required.]

16G NUTRITIVE FUNCTIONS.

as essential to its proper assimilation, as those which the food
experienced in the stomach, and they are at the same time in-
volved in equal obscurity. Almost all that is known respecting
the nature of these changes, is, that soon after the chyme has
been received into the intestines, it begins to separate into two
parts; the one a white milky fluid, which is termed the chyle;
and the other, residual matter, which afterwards becomes /ceces,
and is eventually ejected from the body.

355. Previously to our examining the processes by which this
separation is effected, it will be proper to consider the chemical
properties of the chyle.

1. Properties of Chyle.

356. Chyle is the fluid which is prepared from the food taken
into the stomach, and which, being the last process of digestion,
is formed in the intestinal canal. It is only of late years that we
have acquired any accurate knowledge of its chemical proper-
ties. It is evident that experiments on this fluid can only be
instituted on quadrupeds, and that it is only by reasoning from
analogy that we can extend the knowledge so obtained to the
human economy. If chyle be taken from the thoracic duct of
an animal a few hours after it has taken food, it has very much
the appearance of cream, being a thick fluid of an opaque white
colour, without smell, and having a slightly acid taste, accom-
panied by a perceptible sweetness. It restores the blue "colour of
litmus, previously reddened by acetic acid ; and appears, there-
fore, to contain a predominance of alkali. When subjected to
microscopic examination, chyle is found to contain a multitude
of globules, of smaller diameter than those of the blood, and cor-
responding in size and appearance to those of milk. In about ten
minutes after it is removed from the thoracic duct, it coagulates
into a stiff jelly, which in the course of twenty-four hours sepa-
rates into two parts, producing a firm and contracted coagulum,
surrounded by a transparent colourless fluid.

357. The coagulated portion, according to Vauquelin, is a
substance of a nature intermediate between albumen and perfect
fibrin, marking the transition from the one to the other. It has
perhaps, indeed, a closer resemblance to the caseous part of milk
than to fibrin. It is rapidly dissolved both by pure and sub-
carbonated alkalies, forming pale brown compounds. Its solu-
tion in ammonia has a reddish hue. The acids throw down a
substance intermediate between fat and albumen, which an ex-
cess of nitric acid re-dissolves in the cold; and sulphuric, muriatic,
oxalic, and acetic acids, by boiling for a short time, also dissolve
it. Diluted sulphuric acid also very readily effects its solution.
Very dilute nitric acid gradually converts it into adipocire ;

CHYLIFICATION. 167

when the acid is more concentrated, the coagukim assumes the
appearance of gelatin ; and when heat is applied, oxalic and
carbonic acids are evolved. It is insoluble either in alcohol or
ether.

358. That portion of chyle which retains the liquid form con-
tains a portion of albumen, which may be coagulated by heat,
alcohol, or acids. The clear liquid, reduced by evaporation to
half its bulk, deposits crystals, which were found by Mr. Brande
to bear a strong resemblance to those of sugar of milk.

359. A few saline bodies, similar to those existing in most
animal fluids, were found by Dr. Marcet, to be present in chyle.

360. The principal ingredients in chyle, are, thepefore, accord-
ing to Vauquelin, 1st, a large proportion of albumen; 2d, a
smaller one of fibrin; 3d, a fatty substance which gives to the
chyle the appearance of milk ; 4th, several salts, such as carbo-
nate of potass, muriate of potass, and prophosphate of iron.

361. Berzelius is strongly inclined to distrust the supposed
analogy betvi^een chyle and milk, as having but little foundation
in their real chemical nature.

362. It would be exceedingly interesting to ascertain the differ-
ences which exist in the properties of chyle taken from different
orders of animals, that we might be able to trace the influence of
different kinds of food upon this fluid. Dr. Marcet and Dr. Prout
have made comparative experiments with this view upon the
chyle taken from different dogs, some of which were fed exclu-
sively on animal, and others on vegetable food. The chyle in the
former case was found to be much whiter, contained more solid
matter, and yielded more albumen than in the latter. The general
results of these experiments are contained in the following table.
Some faint traces of oily matter and of sugar of milk were
obtained, but in quantities too minute to be estimated.

Chyle from
vegetable food.

Chyle from
animal food.

Water - - 93-6 < -

89-2

Fibrin - - -6 -

•8

Incipient albumen 4-6

4-7

Saline matters - -8 -

•7*

363. When both kinds of chyle were submitted to destructive

* [The difference between the chyle from food of such opposite character as
indicated by these results is trifling, and exhibits the great uniformity in the
action of the agents of chylous absorption. More recent researches by
MM. Macaire and Marcet {Mem. de la Societe de Physique, &c. de Geneve, v.
389,) tend, indeed, to establish the fact, that the chyle and the blnod of her-
bivorous and carnivorous quadrupeds are identical in their composition, in as
far, at least, as regards their ultimate analysis. There must, consequently,
be an action of selection at the very extremities of the chyliferous vessels, to
occasion this striking uniformity in the composition of the chyle.]

168 NUTRITIVE FUNCTIONS.

distillation, the vegetable chyle produced three times as much
•carbon as the animal chyle ; the latter, therefore, probably con-
tained a greater proportion of hydrogen and nitrogen. The chyle
of a horse, derived of course from vegetable food alone, v^^as
found by Vauquelin to be in a more animalized state than that
which Dr. Marcet procured from dogs. Dr. Prout, also, com-
paring the chyle as prepared from vegetable and from animal
food, found the former to contain more water and less albuminous
matter, while the fibrin and the salts were nearly the same in
both, and both exhibited traces of oily matter. On the whole,
he states the difference between the tvvo kinds of chyle to be less
considerable than had been observed by Dr. Marcet. On tracing
the successive changes, which the chyle undergoes in its passage
along the vessels, he found that its resemblance to blood increases
in each of these successive stages of its progress.*

2. Functions of the Intestines.

364. At the part of the duodenum where the separation of the'
chyme into chyle and residual matter takes place, the ducts from
the pancreas and the liver terminate, so that the chyme is sub-
jected to the action of the secretions from these two important
glands, namely the paMc?-eaizcjMZce, and the 6z7e, which slowly
distil into the duodenum. Sir Benjamin Brodie concluded, from
experiments which he made upon living animals, that the forma-
tion of chyle is the immediate result of the admixture of bile with
the chyme.t In studying the changes which occur in this proi-
cess, it will be necessary first to examine the chemical properties
of these secretions.

365. The secretion from the pancreas, which flows into the
intestine, and is mixed with the digested food almost immediately
on its exit from the stomach, has, no doubt, some share in the
process of chylification ; but as it appears to be exceedingly
analogous, both in its sensible properties and chemical composi-
tion, to the saliva, it is difficult to understand the mode of its
operation, independently of mere dilution. As it is found, how-
evef, to contain a large quantity of albumen, a great portion of
this substance may perhaps go to the formation of chyle.

* Annals of Philosophy, xiii. 29.

f [These experiments consisted in tying the choledoch duct in animals ;
but similar experiments by M. Voisin (^Nouvel Apercu sur la Physiologie du
Foie, &c., Paris, 1833) show, that the ligature of the choledoch duct does not
prevent the formation of chyle, provided the passage of the pancreatic fluid
is not at the same time obstructed. The bile, consequently, although an im-
portant, is not an essential, agent in digestion effected in the duodenum. Bun-
■glison''s Physiology, i. 539.]

CHYLIFICATION. 160

3. Properties of Bile.

366. Tlie bile, a secretion prepared by the liver, is poured into
the same part of the intestine as the pancreatic juice. Its great
importance in the animal economy induced physiologists from the
earliest times to pay much attention to its chemical properties.
Its analysis has been attempted by Boyle, Boerhaave, and Baglivi,
and more recently by Fourcroy, Cadet, Thenard, and Berzelius.*
But it unfortunately happens, that in several important particulars
the accounts given by these diflerent chemists do not accord
with one another. These discrepancies, as Mr. Brande observes,
seem partly to arise from the extreme facility with which
chemical reagents react on this secretion^ so that many of the
supposed educts, or component parts which have been enumerated
by different chemists, are probably products of the different
operations to which it has been submitted, or, at all events,
modifications of its true proximate elements.! The bile of the
ox, from the facility of preserving it, has been that chiefly selected
as the subject of experiment, and made the standard of comparison
with that of man and other animals.

367. The substances to which this fluid owes its specific pro-
perties are, according to Thenard, fi7\^t, a peculiar inflammable
resin, soluble in alcohol; secondly, picromel, a substance insoluble
in water and in alcohol, incapable of being crystallized, but form-
ing, with resin and a small portion of soda, a triple compound
which is soluble in water ; and it is in this state that it exists in
bile ; and, thirdhj, a yellow matter, distinct from either of, the
former. In addition to the soda, which is combined with the
resin and picromel, bile contains a small quantity of phosphate,
muriate ahd sulphate of soda, as also phosphate of lime, and a
minute trace of iron.

368. Berzelius denies the correctness of the distinctions which
Thenard has endeavoured to draw between the three animal
ingredients of bile above mentioned. He gives to its character-
istic principle, the name, of biliary matter; and describes it as
being of a resinous nature, and precipitable by acids ; the preci-
pitate, or pier 07nel, or the gallenstoff o{ Berzelius, being a com-
pound of the acid employed and this biliary matter. According
to Thenard, human bile differs from that of the ox chiefly in

* [The latest analysis is by Muratori (Bulletino Medicke di Bologna, p. 160,
Agosto et Settembre, 1836.) He assigns it the following constituents : —
Water 832 ; peculiar fatty matter 5 ; colouring matter 11 ; cholesterine com-
bined with soda, 4; picromel of Thenard, 94*86; extract of meat {^Estratto
di Came) 2-69 ; mucus, 37 ; soda, 5'14 ; phosphate of soda, 3*45 ; phosphate
of lime, 3; and chloruret of sodium, 1.86.)

f Cyclopaedia of Anat. and Phys., art. Bile.

15

170 NUTRITIVE FUNCTIONS.

containing no picromel. M. Raspail considers bile to be essen-
tially a saponaceous substance, with a base of soda.*

369. The peculiar matter of hile is found in the residual matter,
and does not enter into the composition of chyle. The chief
uses of the bile appear to be those of a chemical agent, promoting
the decomposition of the chyme, and also stimulating the secre-
tion of mucus, and the peristaltic motion of the intestines.
Digestion may, however, go on to a certain degree, and imper-
fectly, although the flow of bile into the intestines be entirely
prevented.

4. Functions of the Small Intestines.

370. Professors Tiedemann and Gmelin found, from their expe-
riments, that the upper part of the small intestines contains a
considerable quantity of uncombined acid, which is principally
the acetic, mixed with a little butyric, and rarely with the mu-
riatic. On proceeding to the lower parts of the small intestines,
they found the fluids had alkaline instead of acid properties. This
gradual disappearance of acid is probably in part the effect of
its neutralization by the free alkali contained in the bile. The
following, according to these physiologists, are the changes
which take place in the contents of the small intestines. The
chyme, which is acid, mixes with the bile, the pancreatic juice,
and the mucous secretion from the coats of the intestine. The
muriatic acid combines with the soda of the bile, and at the same
time disengages from it the acetic or carbonic acids with which
it had been previously united. It also separates the mucus and
cholesterine of the bile in the form of white flakes, which have
often been mistaken for chyle. The pancreatic juice and the
intestinal mucus contribute, in some unknown manner, to this
effect. The chemical changes are promoted, and the contents
of the intestines successively propelled forwards along the whole
tract of the canal, by the peristaltic actions of the muscular coat,
the effects of which are analogous to those we have already
described as taking place from a similar action in the stomach.

5. Function of the Spleen.

371. It is probable that the spleen is an organ subservient to
some purpose connected with digestion ; but what that precise
purpose can be is a question involved in great obscurity. A vast
number of hypotheses and conjectures have been hazarded on
this subject ; but they are, for the most part, devoid of even the

* [This was the view of Cadet, upwards of seventy years ag^o — Experi-
ences siiM' la Bile des Hommes^ &c, in Memoir, de I'Academ. de Paris, 1767.]

CHYLIFICATION. 171

slightest probability. Any theory that assigns a very important
office to the spleen will be overturned by the fact, that in many
animals the removal of this organ, far from being fatal, or inter-
rupting in any sensible manner the continuance of the functions,
seems to be borne with perfect impunity. Sir E. Home has ad-
vanced an opinion, for which there appears to be some proba-
bility, namely, that the spleen serves as a receptacle for any
superfluous quantity of fluid taken into the stomach, and which,
if not removed, might interfere with the regular process of diges-
tion. This excess he supposes is transmitted directly to thq
spleen by communicating vessels, and lodged there until it is
gradually removed, partly by the veins, and partly by the ab-
sorbents.

372. It appears, indeed, from the observations of Bichat, Leu-
ret, Lassaigne, and others, that during digestiori, and even after
copious draughts of liquids, the vessels of the spleen become ex-
ceedingly turgid with blood. Hence the opinion has arisen, that
the chief use of the spleen is to relieve the stomach and intes-
tines from that congestion which would otherwise take place in
their blood-vessels during digestion. The very vascular, ap-
proaching to a cellular structure of the spleen, which very readily
admits of dilatation, would seem to countenance this hypothesis.*

6. Functions of the Large Intestines.

373. The functions of the large intestines are not confined to
the mere conveyance and expulsion of feculent matter, altjiough
the exact nature of the changes which take place in their con-
tents, and the subserviency of those changes to the object of
nutrition, have never been clearly determined. It would appear
that some important changes are effected in that enlarged por-
tion of the canal which is termed the coicum, and which has by
some been regarded as a kind of supplementary stomach, in
which fresh chyme is formed, and fresh nutriment extracted from
the materials that have passed through the small intestines. This
chymous product is supposed to be converted, as in the former
case, into a species of chyle, which, from containing a greater
proportion of oil, bears a resemblance to fat, and is in this state
absorbed from the inner surface of the great intestines. The
capability of the great intestines to extract nourishment from
their contents is proved by the fact, that nutritious matter inject-
ed into them has been known to support life for a certain time,
and also from their being able to eilcct the coagulation of* milk.'

* [One of the latest views is that of MM. Tiedemann and Gmelin, who
regard the spleen as a ganglion of the absorbent system, which prepares a
fluid to be mixed with the chyle to effect its animalization ; thus regarding its
functions to be identical with those of the mesenteric glands.]

172 NUTRITIVE FUNCTIONS.

374. A certain quantity of gas is almost constantly present in
the intestinal canal, and often also in the stomach. Magendie
and Chevreul, who have analysed these gases, found that what
the stomach contained consisted of a mixture of oxygen and
nitrogen; but that in the lower intestines the oxygen had wholly
disappeared, as also a great part of the nitrogen, and that, in-
stead of these, the component parts of the gas were carbonic
acid, hydrogen, carburetted hydrogen, and a little sulphuretted
hydrogen.

375. The time required for the completion of the 'processes
we have described as taking place in the stomach, the small, and
the large intestines, varies much, not only according to the
nature of the food, but according to the conditions of the organs
and of the general health, and to constitutional peculiarities.
The digestion of food in ttie stomach is usually considered as
requiring three or four hours. Animal food is longest retained,
and undergoes the greatest alteration in the stomach. Vegetable
food, on theother hand, passes more quickly and with less altera-
tion, out of the stomach, and undergoes more change in the
intestines than animal food.

Sect. VIII. — Lacteal Absorption.

376. The chyle, which has been prepared in the duodenum,
and along the whole course of the small intestines, in the man-
ner we have described, is received by absorption into the lacteals,
and by them conveyed to the thoracic duct, which transmits it
to the great veins in the vicinity of the heart. The lacteal ves-
sels may be considered as forming part of the great system of
absorbents which, as we shall afterwards find, are extensively
distributed throughout the body. We shall therefore reserve
their description until a general account is given of this system,
in treating of the function of absorption generally.

377. The discovery of the lacteals was made in the year 1622
by Aselli, in the mesentery of a dog, which he bad killed a few
few hours after the animal had made a plentiful meal. Their
termination in the thoracic duct was discovered by Pecquet in
1651. They originate by open mouths from the villi of the inner
coat of the small intestines, in the form of very minute tubes,
which soon unite into one common vessel proceeding from each
of the villi ; and these vessels afterwards joining successively
form larger and larger branches, which ascend along the mesen-
tery, generally following the course of the veins, till they are
collected at the root of the mesentery, and, after passing through
numerous glands, terminate at the lower end of the thoracic duct,

LACTEAL ABSORPTION. 173

where there is aa enlargement which has been called the reccpta-
culum chyl.i.

378. Uncertainty, however, still exists respecting the minute
anatomy of the lacteals, at their origin from the intestine, many
anatomists having in vain sought for the appearances above
described. Their open orifices can only be seen when the lac-
teals are distended with chyle, and they are more readily detected
in fishes where they have no valves, and where therefore the
branches admit of being injected from their trnnks.* Their
coats, although thin and perfectly transparent, yet possess con-
siderable strength, so as to allow of being distended by injections
without being ruptured ; and even afford decisive indications of
having the power of contracting and propelling, forwards their
contents.' The utility of the numerous valves with which they
are provided in every part of their course, in preventing any
retrograde motion of the fluid they transmit, is sufficiently
obvious.

379. The power by which the chyle is made to enter the open
orifices of the lacteals, is by no means easily determined. It has
been referred generally to capillary attraction. But the applica-
tion of the laws wdiich govern the ascent of fluids in rigid inor-
ganic tubes, to the elastic vessels of the living system, is liable
to much fallacy. The phenomena appear to indicate that the
lacteals exercise, in the exclusive absorption of chyle, a power
of selection somewhat analogous to that of chemical or electric
attraction. It has been supposed, accordingly, that there is a
specific attraction between chyle and the lacteal vessels, which
causes that fluid to enter into them; while other fluids which are
presented to the same vessels are rejected. This obscure subject
has given rise to various speculations, which are more curious
and ingenious than leading to any satisfactory conclusion. It is
now generally agreed among physiologists, that the power which
the lacteals pos'sess of admitting the absorption of extraneous
substances, if it exist at all, is exceedingly hmited, and is exerted
only on rare occasions.

Various experim.ents made on animals fully warrant the con-
clusion, that by far the greater portion of the nutritive matter
imparted to the system is conveyed into the blood-vessels through
the channels we have been describing, namely, the lacteals and
the thoracic duct. On the other hand, there appears to be evidence
that a large portion of the thinner fluids received into the stomach
passes at once into the veins by the immediate absorption of these
veins ; for they always disappear rapidly from the stomach, in
whatever quantity they are introduced. It is probable also, that

* [The doptrine of open mouths has been contested by Mascatrni, Rudol-
phi, Meckel, Mojon and others, and it must be admitted, that we know nothing
definite regarding the extreme radicles of the lacteal or chyliferous vessels,]

15*

174 NUTRITIVE FUNCTIONS.

some admixture of tte contents of the lacteals with those of the
blood-vessels takes place in the mesenteric glands, and that part
of the chyle finds its way into the mesenteric veins by more direct
channels than that of the general circulation.

380. An elaborate series of experiments was undertaken by
Tiedemann and Gmelin, with a vievv^ to ascertain whether there
exists any direct communication between the digestive cavities
and the blood-vessels, exclusive of the known channel through
the lacteals and thoracic duct. The experiments consisted in
mixing with the food of certain animals various odorous, colour-
ing, and saline materials, the presence of which might be easily
detected by their appearance, odour, and other sensible or chemical
properties ; and in comparing, after a proper interval of time, the
state of the chyle with that of the blood in the mesenteric veins.
The odorous substances employed were camphor, musk, alcohol,
oil of turpentine, and assafoetida. These were generally disco-
vered to have found their way into the system, by their being
detected in venous blood, in the urine, but not in the chyle. The
colouring matters were sap-green, gamboge, madder, rhubarb,
alkanet, and Htm us ; these appeared. Tor the most part, to be car-
ried off without being absorbed ; while the salts, namely potass,
the sulphate and the prussiate of potass, muriate of barytes,
muriate and sulphate of soda, acetate of lead and of mercury, and
prussiate of mercury, were less uniform in their course. A con-
siderable portion of them seemed to be rejected, while many of
them were found in the urine, several in the venous blood, and a very
few only in the chyle. Hence the authors conclude, that the odo-
rous and colouring substances never pass into the lacteals, and that
saline bodies do so occasionally only, or perhaps incidentally ; the
w^hole of them are, however, found in the secretions, and they
must, therefore, have entered into the circulation by some other
channel than the lacteals.*

381. There appears not, as far as we know, to be any thing
specific in the action of the thoracic duct, which, as it appears,
transmits its contents into the subclavian vein, as it receives it
from the absorbents.

Sect. IX. — Sanguification.

382. The chyle consists, as we have seen, of alimentary
matter, reduced to a certain state, which may be regarded as the
first stage of animalization, having already made a near approach

m
* Edin. Med. Journal, xviii. p. 455, &c. The above analysis ;.of these ex-
periments is that given by Dr. Bostock in his worli on Physiology, p. 617,
note.

SANGUIFICATION. 175

to the nature of that blood into vviiich it is afterwards to be con-
verted. This conversion of chyle into blood takes place after its
introduction into the sanguiferous system of vessels, and while it
passes round in the course of circulation. During this course, it
necessarily traverses the minute vessels of the lungs, where it is
subjected to the chemical action of atmospheric air, and its con-
stituents gradually acquire the characteristic properties which
they possess as the ingredients of the blood. The chief changes
experienced are, first, that the fibrin of the chyle obtains a
greater cohesive tendency, and a power of spontaneous coagula-
tion; and, secondly, that the white globules of the chyle receive
an addition of red colouring matter, and are invested with an
external vesicle, by which their size is increased. But' in order
correctly to estimate their changes, it will be necessary to take
a general review of the chemical and other physical properties
of the blood.

383. The nature and properties of the blood have attracted a
verv large share of the attention of physiologists in all ages; and
immense labour has been devoted to the investigation of its che-
mical constitution.

384. When examined immediately on its being drawn from
the vessels, the blood appears as a smooth and homogeneous
fluid, of an unctuous adhesive consistence, of a slightly saline
taste, and of a specific gravity somewhat exceeding that of
water. It exhales a vapour which has a peculiar smell -, but
which, when condensed and collected, affords a liquor not differ-
ing sensibly from water. Much importance was formerly
ascribed to this vapour, which was dignified with the name of
Halitus.

As the blood does not preserve the same consistence at differ-
ent times, its density is hable to variation. Haller states the
specific gravity of human blood to be at a medium, 1.0527. Dr.
Milne Edwards says that it varies from 1.052 to 1.057. Dr. Davy
states that the specific gravity of arterial blood is 1.049, and of
venous blood, 1.051. Although it appears homogeneous, it is
found by microscopical examination to contain a large proportion
of minute globular particles, difilised through a liquid.

385. In a few minutes alter its removal from the body, a thin
film appears on the surface, and after a short time, which on an
average is about seven minutes, the whole mass becomes cohe-
sive, and what-is termed its coagulation has taken place. After
it has remained for some time in this gelatinous state, a separa-
tion of the mass into two distinct parts gradually takes place. A
yellowish liquid oozes out from beneath the surface of the mass,
and at length the whole is resolved into a clot, or solid portion
of a dark red colour, which is called the crassamentum, or cruor,
and consists chiefly of fibrin, and a yellowish liquid called the

176 NUTRITIVE FUNCTIONS.

serum. The proportion between these two parts has been vari-
ously estimated; and does not indeed admit of accurate deter-
mination, from its being variable in itself under different circum-
stances. On an average, it may be stated that the crassamentum
amounts to about one-third of the weight of the serum. Dr.
Scudamore and Mr. Wood found, however, by taking the mean
of twelve experiments, that the crassamentum amounted to
53.307 per cent. The period at which coagulation begins and is
completed, varies not only with the condition of the blood itself,
but also with the circumstances in which it is placed. It com-
mences sooner as the vessel is more shallow ; but on an average
it may be said to begin in about three or four minutes, and to be
completed in seven or eight. But the contraction of the coagulum
continues for a long time after, and sometimes does not cease
till the fourth Hay. It does not appear that the specific gravity
of the blood is sensibly altered during its coagulation.

386. Great difference of opinion has existed as to the occur-
rence of a change of temperature during this process of coagula-
tion. The analogy of other instances in which the conversion of
a fluid into a solid is accompanied with the evolution of heat, has
induced many to think that a similar effect attends the coagula-
tion of the blood. Fourcroy seated, that a rise of temperature
actually takes place ; but Hunter on the contrary, produced facts
leading to an opposite conclusion. The result obtained by Four-
croy has, however, been confirmed by the experiments of Dr.
Gordon, who found that the coagulating portion of a quantity of
blood was warmer than the rest by about six degrees. On re-
peating the experiment on blood drawn from a patient labouring
under inflammatory fever, the .rise of the thermometer was no
less than twelve degrees. Subsequent researches by Dr. John
Davy, have, however, thrown considerable doubt upon the accu-
racy of the above conclusion, by pointing out some sources of
fallacy in the investigation of Dr. Gordon. Dr. Scudamore, on
the other hand, found that heat was produced during coagulation,
but to a less degree.* Vogel and Brande have ascertained that
carbonic acid gas is disengaged ; and this appeared to happen to
an unusual extent in blood drawn soon after a meal.f

387. The coagulation of the blood is a phenomenon not strictly
analogous to any other with which we are acquainted, and has
never been satisfactorily explained. The operation of external

* [The discrepancy of observers on this subject is great. Mr. Thackrah
and Schroder van der Kolli, accord with Mr. Hunter in the belief, that the
increase of temperature from this cause is very slight, or null, whilst Raspail
asserts, that the temperature falls !]

I [A similar discrepancy exists on this point. Neither Dr. John Davy,
nor Dr. Duncan, junr.. nor Dr. Christison, could procure it during the coaiju-
lation of the blood. Yet there is no doubt, that the blood contains carbonic
acid. See, on all this subject, Dunglison's Physiology, ii. 54.]

SANGUIFICATION. 177

agents upqn it is not so well marked as to enable ns to refer it to any-
general operation of the physical properties of matter. Moderate
differences of temperature produce scarcely any perceptible dif-
ference in the tendency which the blood has to coagulate. Within
the range of from 07° to 105°, blood coagulates in the same time
as at tlie usual temperature of 98°, Sir Humphrey Davy found
that no difference in this respect takes place when blood is ex-
posed to nitrogen, nitrous, nitrous oxide, carbonic acid, carbo-
nated hydrogen gases, or atmospheric air, although the contrary-
had been asserted. Blood, indeed, coagulates more quickly when
placed in a receiver from which the air is rapidly exhausted,
when slowly drawn into a shallow vessel, or when exposed to
atmospheric air, at a temperature of 120°. This process is re-
tarded by a very low temperature. Mr. Hewson placed blood in
oil at a temperature of 38°; at the expiration of six hours it con-
tinued fluid ; but being then allowed to attain a warmer tempera-
ture, it became coagulated in twenty-five minutes. The same
physiologist froze a portion of blood confined by ligatures in the
jugular vein of a rabbit ; when thawed, the] blood became liquified,
and coagulated. Admixture with certain neutral salts prevented
altogether coagulation from taking place. This happened when
half an ounce of sulphate of soda was mixed with six ounces of
fresh blood ; but on the addition of a double quantity of water
coagulation took place. Dr. Turner states that the coagulation
of tile blood is prevented by the admixture of saturated solutions
of chloride of sodium, hydrochlorate of ammonia, nitre, and potass ;
while, on the contrary, alum and the sulphates of the oxides of
zinc and copper, promote coagulation. Blood coagulates slowly
when drawn quickly into a deep vessel, or when detained at rest
in the vein of a living animal between two ligatures. In the latter
case, Mr. Hewson found the blood two-thirds fluid after the lapse
of three hours and a quarter. When the experiment was varied
by blowing air into the vein, the blood was found to have coag-
ulated in a quarter of an hour. Blood extravasated through the
rupture of vessels, and retained in the cavities of the body, often
preserves its fluidity for a very considerable time. If the causes
which are capable of postponing coagulation have continued to
operate beyond a certain period, the blood is prevented from co-
agulating ; thus recent blood remains permanently fluid if it be
constantly stirred for some minutes. It has been proved by the
experiments of Hewson, Hunter, Deyeux, and Parmentier, that
the coagulation of blood is not entirely prevented by diluting it
with water; but Dr. Crawford* showed that this process is
retarded for several hours by the admixture of blood with twelve
times its bulk of water.f

* On Animal Heat, p. 248.

f [From recent experiments, made by Magendie on agents that are capable

17^

NUTRITIVE FUNCTIONS.

388. There are many conditions of the living system that have
a prodigious influence on the tendency of the blood to coagulate,
and that operate in a manner which it is impossible to explain.
Many causes of sudden death, as a blow upon the stomach, or
violent injury of the brain; lightning and electricity; several
animal poisons, as that of venomous serpents ; narcotic vegetable
principles, as cyanogen ; also excessive exercise, or even violent
mental emotions, when they produce the sudden extinction of
life, prevent the usual coagulation of the blood from taking place.

389. The doctrine maintained by Hunter, that the blood pos-
sesses life, and that its coagulation is one of the acts of this living
principle, is but little calculated to remove the difficulty ; for the
operation of this principle in producing coagulation would be as
much in need of explanation of the phenomenon itself, which it
professes to account for. We must, in the present imperfect state
of our knowledge, content ourselves with referring this pheno-
menon to an inherent disposition which the fibrin possesses to
assume the solid form, when no counteracting cause is present.
Dr. Bostock* observes, that as it is gradually added to the blood
particle by particle, whilst this fluid is in a state of agitation in
the vessels, it has no opportunity of concreting ; but when it is
suffered to lie at rest, either within or without the vessels, it is
then able to exercise its natural tendency.

390. We have already stated that the crassamentum consists
chiefly of fibrin ; but it owes its dark colour to the presence of
what are called the red particles of the blood, and which are
entangled in it during its coagulation. The serum, which is the

'part of the blood that remains fluid after the coagulation of the
fibrin, is itself coagulated by heat, in consequence of the large
proportion of albumen it contains ; the remaining portion, which
still continues fluid, is termed the serosity. The following is

of rendering the blood liquid, and such as are possessed of the power of pro-
moting its coasulalion, he is led to offer the followins arrangement ; observino-,
at the same time, that he does not put it forward as final, but that, on the con-
trary, it will no doubt be found necessary, from improved experience, to more or
less modify it.

1. Substances ivhich promote the coagulation of the blood. — Water, sugared
water, hydrochlorate of soda ; hydrochlorate of potassa ; hydrochlorate
of ammonia; hydrochlorate of baryta ; serum of ascites ; boric acid ; borax;
nitrate of silver; hydrosulphate of potass and ammonia; Seltzer water;
Vichy water; Seidlitz water; ioduret of potassium; tartrate of antimony
and potassa ; sulphate of magnesia ; alcohol; cyanuret of gold ; cyanuret of
mercury ; acetate andhydrochlorate of morphia, and mannite.

2. Substances which oppose the coagulation of the hhod. — The sulphuric, hy-
drochloric, nitric, tartaric, oxalic, citric, lactic, acetic, tannic, and hydrocy-
anic acids ; soda, potassa, lime, ammonia, and the carbonates of soda, potassa,
and ammonia. Legons sur le Sang, &c. and the translation in Lancet, Jan. 20th,
IS39.]

* Physiology, p. 371.

SANGUIFICATION. 179

therefore the arrangement of the principal proximate parts of
the blood, in the order of analysis.

Coagulated C Crassamentum | ^e^^ particles.

^^'?f A „ (Albumen.

consists of ( Serum | Serosity:

The crassamentum is a mass of soft consistence, which easily
bears cutting with a knife. Its mean specific gravity is about
1-245. By long-continued ablution in water, it may be freed
from the red particles which it contains, and which are soluble
in water. This may be conveniently effected by enclosing the
crassamentum in a linen bag, immersing it repeatedly in water,
and at the same time pressing it gently ; or by allowing a stream
of water to fall upon it, till the water runs off colourless. There
remains a white, solid fibrous, and elastic substance, which has
all the properties of fibrin, and is almost exactly similar to the
basis of muscular flesh obtained b}' long boiling. It may also be
procured directly from recent blood, by stirring it, as it flows
from the vessel, with a bunch of twigs ; or receiving it into a
bottle, and shaking it during its coagulation. When formed under
these circumstances, it exhibits a fibrous appearance, and the
whole is converted into an irregular net-work of dense fibres.
Fibrin was formerly known under the name of coagulable lymphs
or gluten.

392. The red particles or globules, contained in the blood, and en-
veloped in the fibrin during its coagulation, have long attracted the
attention of physiologists, from the irregularity of their appearance,
and the importance which was supposed to attach to them. The
first notice which we find of them occurs in the writings of Mal-
pighi, soon after the introduction of the use of the microscope.
They were soon afterwards examined with great care and mi-
nuteness by the indefatigable Leewenhoek, whose name stands
foremost among those who made observations with this instrument.
They soon became the subject of much speculation, and laid the
foundation of many fanciful hypotheses which were current at
the time, but are now consigned to deserve neglect. Leewen-
hoek him.self was led by his imagination to the belief that these
red globules were each composed of a series of globular bodies
of different orders descending in regular gradations. He supposed
eachtobemadeupof six particles of serum; each particle of serum
of six particles of lymph, and so on in succession. This strange
hypothesis, visionary as it now appears, was so accordant with the
prevailing taste for mathematical disquisitions, that it was very
generally adopted, and held a powerful sway over the opinions and
reasonings of the physicians of that age. It forms a leading feature

180 NUTRITIVE FUNCTIONS.

in the pathological speculations of Boerhaave ; and although its
futihty was sufficiently exposed by Lancisi and Senac, it main-
tained its ground even to the time of Haller.

393. But a better spirit began at length to prevail ; the illusive
dreams of fancy were superseded by the sober and attentive obser-
vation of nature ; and truth was sought by the judicious cultiva-
tion of experimental inquiry, the only legitimate path by which
it can be approached. About the middle of the eighteenth century,
the Abbe de la Torre, employing microscopes of considerable
power, obtained the appearance of flattened annular bodies,
with a perforation in the centre. Hewson, who observed them
with still greater attention to accuracy, states them to be
hollow vesicles of a flattened shape, and containing a smaller,
solid, and spherical particle, which was freely moveable within
them, or, as he compares it, "likea. pea in a bladder." He as-
serted, that by adding water, these particles swell out into a
globular shape, and afterwards burst and disappear, in conse-
quence of their being dissolved in the water ; but if moistened
with an aqueous solution of any neutral salt, they preserve their
natural flat shape, Cavallo describes them as much more irre-
gular in their form than Hewson represented them ; and he was
led from his observations to the conclusion that the appearance
either of a perforation, or of a central particle, is in reality an
optical deception, arising from the refraction of the light by which
the objects are viewed, as it passes through the convex surfaces
of the globules. He also endeavours to explain the appearance
which led Hewson to believe that the central nucleus is moveable
within the external vesicle, by some apparent change in the
position of the luminous image, in consequence of accidental
variations in the direction in which the light is viewed. Very
small artificial globules of solid glass which he constructed for
the purpose, presented under the microscope very nearly the same
appearances, as the globules of the blood ; and hence he con-
cluded, that the latter, notwithstanding these appearances, were
nearly globular and composed of a uniform material.

394. Notwithstanding the ingenuity displayed in this reasoning,
the more profound examination which the subject has received
from Dr. Young, induces us to revert, to a certain extent, to the
opinion of Hewson. He observes that in such examinations it
is only necessary to employ a full and unlimited light, in order to
obtain a very distinct outline of what appears manifestly to be a
very simple substance. But we should remember that where
the substances to be examined are perfectly transparent, it is only
in a confined and diversified light that we can gain a correct
idea of their structure. The eye is best prepared for the inves-
tigation by beginning with the blood of a skate, ,of which the
particles are, from their greater size, so conspicuous, and of so

SANGUIFICATION. 181

unequivocal a form, as at once to set aside the idea of a simple
homogeneous substance. They are oval and depressed, like an
almond, but less pointed, and a little flatter. Each of them
contains a round nucleus which is wholly independent in its
appearance of the figure of the whole disc, being sometimes a
little irregular in its form, seldom deviating from its central situa-
tion, but often remaining distinctly visible, whilst the oval partis
scarcely perceptible. This nucleus is about the size of a particle
of human blood, the whole oval being about twice as wide, and
not quite three times as long. The nucleus is very transparent,
and forms a distinct image of any large object which intercepts
a part of the light by which it is seen, but exhibits no inequalities
of light and shade that could lead to any mistake respecting its
form. But if we place some particles of human blood under
similar circumstances, near the confines of light and shade,
although they are little, if at all less transparent, we immediately
see an annular shade on the disc, which is most marked on the
side of the centre on which the marginal part appears the brightest,
and consequently indicates a depression in the centre, which De
la Torre mistook for a perforation. It is most observable when
the drop is dying away, so that the particles rest on the glass ;
and when a smaller particle is viewed, it has merely a dark cen-
tral spot, without any lighter central space. Dr. Monro had
represented the globules of the blood as being of an exceedingly
flattened shape, or, as he expresses it, " as flat as a guinea."
But Dr. Young never saw them of this shape, although he states
their axis as being sometimes not more than one-third, or one-
fourth of their greatest diameter. He also states that they do
not seem, as Hewson asserted, to have their dimensions much
affected by the fluid in which they are suspended, since they may
easily be spread thin on glass, and dried without much change
in their magnitude, at least in the direction of the surface to
which they adhere ; and they remain distinct as long as the access
of moist air is completely excluded. When they have been kept
for some time in water, and a little solution of salt is added, their
form and structure, as Hewson observed, are more easily ex-
amined, and appear to resemble those of a soft substance, with
a denser nucleus ; but the comparison which he makes of their
being like a pea in a bladder, Dr. Young thinks is quite inappli-
cable.

395. It has commonly been asserted, and especially by Hew-
son, that these particles are readily soluble in water ; but Dr.
Young has shown that this opinion is erroneous, and depends
partly on their passing readily through the filtering paper, a cir-
cumstance observed by BerzeUus, and partly on the extraction of
a great part of their colouring matter, together with which they
lose much of their specific gravity, so that instead of subsiding,

16

182 NUTRITIVE FUNCTIONS.

they are generally suspended in the fluid. Their presence may
still, however, be detected by a careful examination ; and they
seem in this state to have recovered in some measure their origi-
nal form, which they had lost when first immersed in the water.
A curious observation on the influence of circumstances on the
form of the globules, has been made by Mr. Bauer. He remarks
that in the skate they are oval during the life of the animal, but
become flattened after its death. This circumstance may per-
haps tend to reconcile some of the discordant statements which
have been made on this subject.

396. The size of the red globules has also been very differently
estimated by different observers. These discrepancies receive
some explanation by the circumstance which Dr. Milne Edwards
appears to have established, of the globules dilfering considerably
in their size in the same individual.* The most accurate mea-
surements appear to be those of Dr. Young, and of Captain
Kater, who both agree that the particles of human blood are
between the four-thousandth and the six-thousandth of an inch in
their diameter; and they may therefore be taken at a medium
at the five-thousandth of an inch. Mr. Bauer has stated them
to be considerably larger, even as much as the one thousand-
seven-hundredth of an inch in their entire state, and that the cen-
tral part is the two-thousandth of an inch in diameter. But the
observations of Dr. Young are more probably correct, from their
coincidence with those of Captain Kater, which were conducted
in a dififerent manner. <■

397. The diificulty of procuring the red particles in a separate
state, unmixed with serum, is so great as to preclude us from ob-
taining any distinct knowledge of their chemical composition and
properties. The colouring matter of the blood has been termed
hematine, or hematosine. But according to M. Lecanu, the sub-
stance usually termed hematine is in reality a combination of
albumen and the pure colouring matter of the blood, which he
proposes to designate glohuline. Although it appears from Dr.
Young's observations, that the globules themselves do not dis-
solve in water, yet they impart to it the whole of their colouring
matter. The watery solution turns syrup of violets green; and
after some time deposits a flocculent precipitate, probably from
the coagulation of albumen, the presence of which is indicated
also by the effect of boiling the solution. Hence it has been con-
cluded that the colouring matter consists of albumen, dissolved
by an excess of pure soda. When evaporated and calcined in a
crucible, a residuum is obtained, amounting to about one-thou-
sandth of the weight of solid matter, and composed, according to
Pourcroy and Vauquelin, chiefly of subphosphate of iron.

* Cyclopasdia of Anat. art. Blood.

SANGUIFICATION. 183

398. Berzelius,* who has made minute inquiry into this subject,
informs us that the colouring matter of the ijlood, separated from
tile other part, leaves one-eightieth of an incombustible residuum,
of which rather more than one-half is an oxide of iron. The ex-
istence of iron in the blood was first discovered by Menghini ;
but its amount was much over-rated both by himself and many
of the earlier chemists who succeeded him. It is difficult to
determine in what state this iron exists in the blood. It would
appear not to be in the state of any of the known salts of this
metal ; because before the blood has been calcined, the iron
escapes detection by any of the tests which usually indicate its
presence in solutions ; and yet the solubility of the colouring
matter in the serum would, on the other hand, appear to support
the opinion of its possessing saline properties. Berzelius has been
able to deduce from his numerous experiments on this point,
merely the negative conclusion, that no salt of iron which he
tried was capable of being combined with the serum, so as to
produce a compound similar to the colouring matter of the
blood; thus refuting the alleged synthetic proof adduced by
Fourcroy, who had stated that subphosphate of iron dissolves in
albumen, and imparts to it a bright red colour, resen)bling that
of blood.t

399. It has long been the prevailing opinion that the blood
derives its red colour from the iron it contains ; but the truth of
this opinion has been called in question by many writers of high
authority, and in particular by Dr. WellsJ and by Mr. Brande.§
The experiments of Dr. Wells, however, as is remarked by Dr.
Bostock, seem only to prove that the colour of the blood is not
occasioned by any salt of iron, or by iron in such a state as to
be affected by the ordinary tests. Mr. Brande procured the
colouring matter from venous blood in a detached state, by re-
moving the fibrin from it by agitation while it was coagulating,
and suffering the red globules to subside in tlie serum, from which
they could be obtained in a concentrated form. Examining this
portion by means of different reagents, he arrived at the conclu-
sion, that the colouring principle of the blood is an animal sub-
stance of a peculiar nature, susceptible, like the colouring matter
from vegetables, of uniting with bases, or mordants, and there-
fore admitting of being applied in the art of dyeing. The most
effectual mordants for the colouring matter of the blood are the
salts of mercury, especially the nitrate, and the bichloride or
corrosive sublimate. On examining the colouring matter distinct
from the crassamentum, Mr. Brande did not discover a greater
proportion of iron than exists in the other principles of blood.

* Medico-Chirurgical Transactions, vol. iii. p. 215.

f Systeme de Connais, Chymiques, vol. ix. p. 207, 208.

X Phil. Trans, for 1797, p. 410. § Phil. Trans, for 1812, p. 90.

184 NUTRITIVE FUNCTIONS.

These results, in as far as they relate to the quantity of iron, are
at variance with the later and apparently more elaborate experi-
ments of Berzelius, who still maintains that the colouring matter
of the blood contains iron, not indeed discoverable by reagents,
but decisively proved to exist in its ashes. In every respect,
except in containing that metal, the colouring matter agrees with
fibrin and albumen ; and he seems disposed to believe that its
colour, though not depending on the presence merely of an oxide
of iron, may be produced by a compound of which the oxide is
an essential part. ^

Vauquelin's experiments* may in some respects be deemed to
corroborate those of Brande, inasmuch as they show that iron
cannot be detected by liquid tests in solutions of the colouring
matter; but they at the same time show that this metal is readily
detected by these tests in the fluid from which the colouring
matter has subsided.

400. The changes in the colour of the blood produced by its
exposure to different gases, are probably owing to their action on
the red globules. Arterial blood is blackened, and venous blood
rendered darker, by nitrogen, or carbonic acid gases ; but its
bright florid hue is restored by exposure to oxygen gas. We
shall have occasion to revert to this subject in treating of respi-
ration.

401. Besides the ordinary red globules, others of a much
smaller size have been detected by Mr. Bauer floating in the
serum, and even apparently generated while the fluid is under
examination. To these Sir Everard Home gave the name of
lymph globules.i

402. The serum of the blood, or the fluid part which is left
after the separation of the crassamentum, is a transparent and
apparently homogeneous liquid, of a yellowish and sometimes
greenish colour, of a saline taste and adhesive consistence. Its
specific gravity is variable, but may be taken, on an average, at .
about 1-025.J When exposed to a temperature of 160°, the
whole is converted into a firm white mass, perfectly analogous
to the white of an egg which has been hardened by boiling. It
may, in fact, be regarded as identical with coagulated albumen,
the chemical properties of which we have already described.

403. Although the whole of the mass of serum appears to be
rendered solid by the process of coagulation, yet if this coagu-
lum be cut into slices, and subjected to gentle pressure, or if it
be placed on the mouth of a funnel, a small quantity of a slightly

* Annales de Chiniie et de Physique, i. 9.

t Phil. Trans, for 1819, p. 2.

if. [This may be near the average, but the specific gravity differs greatly.
Thackrah, (^Inquiry into the Nature and Properties of the Blood, &c., Lond
1819,) found the extremes to be 1.004 and 1.080.]

SANGUIFICATION. 185

opaque liquor drains from it, whicii is called the serosity. It has
a saline taste, and a peculiar odour, and consists of several ingre-
dients. Its existence as a substance distinct from the albumen
was first pointed out by Dr. Butt in 1760, and its properties were
further examined by Dr. Cullen, who speaks of it as a solution of
fibrin in water. Hewson believed it to be of a mucous nature.
Parmentier and Deyeux published, in 1790, an elaborate set of
experiments which they made upon it, from which they drew the
conclusion, that the animal substance contained in the serosity
was gelatin. This statement seemed so satisfactory, from the
apparent accuracy of the investigation, that it was generally
acquiesced in. Not only was jelly considered as one of the con-
stituents of the blood, but means were pointed out for ascertain-
ing its proportion ; and its supposed agency in the economy was
made the foundation of many physiological speculations. But
Dr. Bostock has since proved that this opinion is not founded in
fact. He was unable to detect the smallest quantity of jelly
either in the serosity of the blood, or in any other of the albumi-
nous fluids. In this conclusion he is fully supported by the testi-
monies of Berzelius, Marcet, and Brande.

404. It may be inferred from the experiments of Mr. Brande,
that serosity consists of a small quantity of albumen, still retained
in solution by a large proportion of alkali. According to Berze-
lius, the serosity contains no sulphuric acid, and only a vestige of
the phosphoric, and consists chiefly of water, with some pure
soda holding albumen in solution, of muriates of soda and potass,
of lactate of soda, and a peculiar animal matter which always
accompanies the lactate. Dr. Bostock found the amount of solid
contents to vary from the forty-sixth to the seventieth part of its
weight, or, on an average, about the fiftieth. It has been a
matter of dispute which of the mineral alkalies exists in serum in
an uncombined form. Dr. Pearson maintained that it was potass;
but Drs. Bostock, Marcet, and Berzelius, with much greater
appearance of correctness, allege that it is soda.

405. The component parts of human serum, according to the
analysis of Dr. Marcet, are —

Water, - - - -

Albumen,

Muriates of potass and soda,
Muco-extractive matter, ...
Subcarbonate of soda,
Sulphate of potass, ...

Earthy phosphates, . . -

1000-

406. This analysis coincides verv nearly with that of Berzelius,

16*

900-

86-8

6-6

4-

1-95

•35

•6

186

NUTRITIVE rUNCTIONS.

who considers the substance ternned by Dr. Marcet muco-exirac-
tive matter to be impure lactate of soda. But Dr. Bostock is led
by his experiments to the conclusion, that a peculiar animal sub-
stance exists in the serosity, not coagulable by heat, or by any
other means ; not affected by corrosive sublimate, or by tannin,
which are the appropriate tests of albumen and of jelly respec-
tively, but copiously precipitated by muriate of tin, and still more
readily by the acetate of lead ; and he thinks this substance is
quite independent of the lactate of soda, which may exist at the
same time in the blood.

407. Wienholt discovered that the serosity contained a small
quantity of the peculiar substance which exists in greatest abun-
dance in the flesh of animals, and was first noticed as a distinct
proximate principle by Rouelle. It was subsequently termed
ozmazome by Thenard, who examined its properties more minute-
ly. This substance is of a yellowish brown colour ; it is soluble
both in water and in alcohol, and is precipitated by infusion of
nutgalls, nitrate of mercury, and by the acetate and nitrate of
lead. It is still a matter of uncertainty what connexion exists
between this substance and the muco-extractive matter above
mentioned. There is also another proximate principle, namely,
urea, of which we shall afterwards have occasion to speak, which
is found in small quantity in the blood, when that fluid is in its
natural state, but which is abundantly found in the blood of ani-
mals from which the kidneys have been removed. Besides these,
Dr. B. Babington discovered the presence in the blood of an oily
substance, separable from the other parts by means of ether.
Lecanu, in addition to this oily matter, found a crystallizable
fatty matter in the blood ; and similar observations have been
made by Chevreul. Manganese is said to have been detected in
the blood by Wurzer. M. Boudet has also lately discovered a
new substance in the serum, which he has termed iiroline. This
is a white, slightly opalescent substance, fusible at 94° Fahren-
heit, not forming an emulsion with water, soluble in alcohol, not
saponifiable, and apparently containing nitrogen.*

* [Dr. B. Babington is of opinion, that the blood, whilst circulating in the
vessels consists of two parts only — a fluid which he calls liquor sanguinis,
and red globules ; and he is induced to believe, from his experiments, that
fibrin and serum do not exist as such in the circulating fluid, but that the
liquor sanguinis, when removed from the vessels, and no longer subjected
to the laws of life, has then, and not before, the property of separating into
fibrin and serum. Med. Chirurg. Transact, vol. xvi. pt. 2. Lond. 1831, and
art. Blood (morbid conditions of the), in Cyclop, of Anat. and Physiol. Lond.
1836.1

CIRCULATION OF THE BLOOD. 187

CHAPTER VIIL

CIRCULATION. *

Sect. I. — Apparatus fm- Circulation.

408. The object of the function of circulation is twofold.
The first is to distribute to all the organs that due share of nutri-
tive fluid which they require for the performance of their respec-
tive offices, for the maintenance of their temperature, and for
nutrition, and to keep up a constant supply of this fluid. The
second, and no less important object, is to expose every portion
in succession of this fluid, which is the blood, to the influence of
atmospheric air in an organ appropriated to this particular pur-
pose ; the continual renewal of the action of the oxygen, contained
in the air upon the blood, being necessary for the maintenance of
its salutary qualities, and indispensable to the preservation of life.
The organs in which this process is carried on are the lungs;
and the function by which it is accomplished is respiration. The
great agent for the distribution of the blood both generally to
the organs of the body, and specially to the lungs, is the heart ;
the pipes through which it is conveyed to those parts are the
arteries ; those through which it is brought back to the heart, the
veins. A set of finer vessels interposed between the minute ex-
tremities of the arteries, and the minute beginnings of the veins,
are called the capillaries. The structure and distribution of all
these parts belongs to Anatomy. The following brief capitulation,
however, of the structure of the heart, will assist us in understand-
ing the physiology of its action.

1. Cardiac Apparatus.

409, The heart is a hollow muscle, of a conical shape, occupy-
ing the central and inferior part of the cavity of the thorax, hav-
ing its basis turned towards the right side, and its point or apex
towards the left, nearly opposite to the space between the sixth
and seventh ribs. Its lower surface is somewhat flattened, where
it lies upon the diaphragm. Its basis, with which the great ves-
sels are connected, is covered with fat. The whole heart, and
the roots of the large blood-vessels at its basis, are protected by
a general investment of membrane, which is a reflected produc-
tion of an extended serous membrane, forming a cavity for its
reception, and for allowing it considerable freedom of motion.
This membrane, which is remarkable for its strength, is called

188 NUTRITIVE FUNCTIONS.

the pericardium, and is situate between the laminae of the medias-
tinum, which are separated in order to contain it.

410. The heart is principally made up of muscular fibres, the
course of which is extremely complex ; some extending longi-
tudinally from the basis to the apex, others taking an oblique or
spiral course ; and a third running in a more transverse direc-
tion. There are two considerable cavities, called ventricles, dis-
tinguished, according to their situation, into the right and left.
The former has also been called, in reference to its functions, the
pulmonic, and the latter the systemic ventricle. They are sepa-
rated by a strong and thick partition, called the septum ventricu-
lorum, which is composed of fleshy and tendinous fibres. At-
tached to these, at the basis of the heart, are two hollow and
fleshy projecting appendages, called the auricles, the cavities of
which are also separated from each other by a partition, distin-
guished by the name of septum auriculorum, and they open into
those of the ventricles. The right auricle, which, together with
the right ventricle, is placed more in front, receives the blood
from the venee cavae, and transmits it to the right ventricle, by
which it is propelled into the trunk of the pulmonary artery.
The left auricle, in like manner, collects the blood from the four
trunks of the pulmonary veins, and transfers it into the left ven-
tricle, by which it is forcibly driven into the aorta, or main trunk
of the arterial system of the body at large. The membrane
which lines the cavities of the heart, and the great vessels just
mentioned, is produced so as to form valves at the two orifices
of both the ventricles; that is, where the auricles open into them,
and also at the origin of the arterial trunks which arise from the
ventricles. The valves placed between the right auricle and ven-
tricle, are usually three in number, and are called, valvulcB tricus-
pides; but in the left ventricle there are only two, and these are
namecl the valvulcB mitrales. The membranes which form these
valves are attached so as to project somewhat forward in each
of these cavities, and are connected with tendinous strings, called
chordcB tendinecB, which arise from detached and projecting por-
tions of the muscular substance of the heart, named from their
cylindrical form, carnea columncB.

411. The valves at the origin both of the pulmonary artery
and of the aorta, are three in number, and are called the vahulce
semilunares, from their semicircular figure ; their convexities are
turned towards the ventricle ; they are concave next to the cavity
of the artery ; and in the middle of their loose edge is found a
small hard triangular substance called corpus Arantii, and some-
times corpusculum Morgagni, or sesamoideum. When these valves
are made to approach each other, by the pressure of the blood
in the artery in the direction of the ventricle, they unite so as
completely to close the passage, and prevent any of the blood

CIRCULATION OF THE BLOOD. 189

from returning. Opposite to tlie semilunar valves, the artery
bulges out and forms three projections, which have correspond-
ing pits or depressions within, and are called, from their dis-
coverer, si7ius VahalvcB.

412. Where the two venai cavae meet, there is a small angular
projection, which has been called the tuberculum Loweri. The
term auricula more properly applies to the jagged portions which
project from the sides of the base of the heart, like the ears of a
dog from its head ; whilst the expanded cavity where the venous
tubes enter is called the sinus venosus. On the side next to the
auricula, there is a remarkable semilunar fold, projecting within
the cavity, between the vein and auricle, so as to be convex next
to the vein, and concave next to the auricle. This doubling has
been called the Eustachian valve. Between the concave part of
this fold, and the opening into the ventricle, is the orifice of the
coronary vein, which returns the blood that has circulated
through the substance of the heart itself, and which is provided,
at this point, with its proper valve. In the septum auriculum is
seen a depression, the fossa avails, which is the remains of a pas-
sage of communication between the right and left auricles that
had existed in the foetal state. The sides of the fossa ovalis are
strong and thick, and have received the name of isthmus Vicus-
senii, or columnce, or annulus fosscE ovalis.

2. Sanguiferous System in general.

413. The blood-vessels, consisting of arteries, veins, and capil-
laries, compose by their assemblage what is termed the sangui-
ferous system ; and the channels which they form for the trans-
mission of the blood constitute a double circuit. The principal
circuit consists of that through which the blood is distributed to
all parts of the body indiscriminately, and which includes there-
fore the whole system. But there is also another circuit of lesser
extent, which is performed by the blood, by its being sent from
the heart to the lungs, and again returned to the heart, after cir-
culating through those organs. This is termed the lesser circu-
lation, by way of contrast with the circulation through all the rest
of the body, which constitutes the greater circulation. For
effecting this lesser circulation, a distinct set of blood-vessels,
namely, the -pulmonary vessels, is provided.

414. Thus, there are two separate systems of blood-vessels,
which have no communication with each other, except through
the medium of the heart, which is the common origin and termi-
nation of both. The aortic system, or, as some modern anatomists
have chosen to designate it, the systemic system, is that which,
taking its rise from the left ventricle of the heart, begins with the
aorta, or main trunk of the arties which transmit the blood to the

190 NUTRITIVE FUNCTIONS.

body at large, and is completed by the veins which are collected
into two trunks, called vencB cavce; which trunks, again, terminate
in the right auricle of the heart. The pulmonary system, on the
other hand, comprises the pulmonary arteries, which arise by a
single trunk from the right ventricle of the heart, and after cir-
culating the blood through the lungs, are continued into the pul-
monary veins, and terminate by four large trunks in the left
auricle of the heart.

415. All these vessels, whether arteries or veins, may be com-
prehended under the following general description. They are
flexible and elastic tubes, for the most part of a cylindrical shape,
and composed principally of a membranous or fibrous structure
formed into distinct layers, and composing what are called the
coats of these vessels. The number of these coats has been
differently estimated by different anatomists ; but it is now
generally agreed that those proper to the vessels themselves are
principally three : the external, the internal, and the middle, or
what has been called the muscular coat. Besides these tunics,
each vessel is surrounded by a loose and flocculent cellular sub-
stance, which connects it with the parts through which it passes,
and accompanies it in its whole course; but this substance, being
merely a continuation of the cellular substance which fills up all
the vacuities of the body, is common to the vessel and to other
parts, ought not properly to be considered as belonging to the
former, but as adventitious ; although some anatomists have
dignified it with the title of the cellular coat.

416. The first proper coat of the vessel is the external coat,
which is thicker than the rest, and formed of a membranous
structure, in which are intermixed a few filaments of fibro-cellular
substance, disposed obliquely with respect to the course of the
vessel, and interwoven with the membranous fibres. The inner-
most membrane is thinner than the former, of a whiter colour,
more or less pellucid, and presenting a more uniform homogene-
ous structure. Its inner surface is perfectly smooth, and much
resembles in appearance the serous membranes. Between these
membranous coats, there exists a layer of fibres, which have
been generally supposed to be muscular, constituting what has
been accordingly called the muscular coat. Compared with the
diameters of the vessels, these coats are proportionably thicker
in the smaller than in the larger vessels.

417. After giving this general description of the structure of
the blood-vessels, we proceed to notice some of the peculiarities
which distinguish each class of blood-vessels.

3. Arterial System.

418. Each of the great arterial trunks, belonging respectively

CIRCULATION OP THE BLOOD. 191

to the aortic, and to the pulmonic systems, are furnished, at their
origin from the ventricles of the heart, with valves of a semilunar
shape, adhering by one of their sides to the margin of the aper-
ture of the ventricle, or mouth of the artery, and having their
loose edges turned towards the axis of the artery. These valves
are formed by a duplicature of the internal coat, which contains
between their folds a thin layer, of ligamentous fibres, giving
them considerable strength. No valves are found in any other
part of the arterial system.

419. The external coat of an artery is formed by a dense
tissue of fibres, which are interwoven together in, different direc-
tions, generally very obliquely with regard to the length of the
vessel. This texture becomes more compact as we trace it
towards the interior, so that the individual fibres can with diffi-
culty be distinguished, unless by a forcible tearing asunder of the
substance they compose. Hence the older anatomists have dis-
tinguished this inner layer of the external coat, as forming a
separate tunic, to which they have given the name of the nervous
coat, implying thereby a participation in the structure of ten-
dons which were not at that time distinguished from nerves.
The division of the external coat into these two layers, is well
marked in the larger arteries ; but in proportion as we examine
the smaller branches, we find a more uniform appearance, the
whole assuming the firm and compact texture of fibrous mem-
branes. This portion of the arterial structure is exceedingly strong
and elastic, both with respect to a force stretching it in the direc-
tion of its length, and also transversely, or in that of its diameter.
Its toughness is such that it is not easily cut asunder by a thread
employed as a ligature upon the vessel.

420. The intermediate, or muscular membrane, is of consider-
able thickness, has a yellow colour, and is composed of fibres,
all of which are arranged circularly ; that is, in the circumfer-
ence of the cylinder. In the large arterial trunks, these fibres
form a distinct layer or tunic ; but the membrane acquires a still
greater proportional thickness in the smaller branches, and then
admits of subdivision, by dissection into several layers. The
exterior layers are less dense than the interior ; and those which
are innermost are the densest of all. The elasticity and firmness
of this coat is chiefly in the direction of the circular fibres of
which it consists ; so that it opposes considerable resistance to
any force which tends to dilate the vessel, but yields readily to
any power applied for its elongation. It may be considered as
partaking of the properties of muscular and ligamentous struc-
tures.

421. The internal membrane of arteries, which has also been
called the nervous, arachnoid, or common coat, is the thinnest of
the three ; |Jthough still, in the larger arteries, it admits of divi-

192 NUTRITIVE FUNCTIONS.

sion into two or more layers. The innermost of these is ex-
tremely thin and transparent, and its surface is smooth and
highly polished, in order that no resistance may be opposed to
the motion of the blood, The outer portions are white and
opaque, and pass gradually into the substance of the muscular
tunic with which it is connected. Its elasticity is very small,
and its power of resistance is limited, so that a ligature applied
on the vessel generally produces a laceration of the internal coat,

422. The general form of the arterial system, if it were iso-
lated from all other parts, would resemble two trees, the trunks
of which would be constituted by the aorta, and by the pulmo-
nary artery, and which divide and subdivide successively into
smaller and smaller branches, till they arrive at an extreme de-
gree of tenuity. Each portion which intervenes between these
divisions preserves the same uniform diameter, and is, therefore
exactly cylindrical. Each branch is of course smaller than the
trunk from which it arises ; but the sum of the areas of all the
branches into which an artery divides itself, is in general greater
than the area of that artery ; and consequently the total capacity
of the arterial system is progressively inci'easing in proportion to
the number of subdivisions which take place. Hence the whole
system may in reality be considered as composing a conical
cavity, of which the aorta is the apex, and the ultimate subdivi-
sions the base.' The number of subdivisions in the whole course
of an artery scarcely ever exceeds twenty, according to the esti-
mate of Haller, who took pains to ascertain this point. The most
usual mode of ramification is that of bifurcation, or division of a
trunk into two branches, which generally form between them an
acute angle. In some instances, especially among the larger
arteries, we meet with a branch sent off at right angles from the
main trunk, or still more rarely at an obtuse angle.

423. Arteries have numerous communications among their
different branches. These communications, or anastomoses, as
they are called, are effected sometimes by the re-union of two
arteries of nearly equal size, which happen to be proceeding in
similar directions, so as to compose one common trunk, which
proceeds in an intermediate direction, sometimes by collateral
branches proceeding obliquely from the one to the other ; while
on other occasions, arteries unite from greater distances, so as to
form a wide arch, in which each appears to be continuous one
with the other; and from the convex side of which, branches are
again sent off, which are distributed in minuter ramifications. In
some parts the anastomoses are so frequent and numerous, as to
resemble a net-work, or plexus of vessels.

424. The principal arteries of the limbs are generally found
running in situations where they are best protected from injury,
and where they are most secure from pressure during the actions

CIRCULATION OF THE BLOOD. 193

of the muscles. Hence they are chiefly met with in the hollow
spaces formed on the inner side of the flexures of the joints.

4. Venous System.

425. The chief peculiarities in the structure of the veins, as
distinguished from that of the arteries, consist in the greater
thinness, and diminished density of their coats, the tenuity or ab-
sence of the muscular tunic, and the numerous valves which
occur in different parts of their course. The outer coat resem-
bles that of the arteries, but does not present so dense or so fine
a texture of fibres; and it possesses less absolute strength. The
middle coat is formed of fibres which are more extensile and
flexible than those of arteries ; and their direction, instead of be-
ing transverse, is principally longitudinal. These fibres are not
constantly met with in all the parts of the venous system, but
vary much in their proportion to the rest of the structure in dif-
ferent veins, as well as in their directions and thickness. It is
only in the large veins, near the heart, that this coat presents
any appearance of muscular fibres. The inner coat is thin and
transparent, like that of the arteries ; but difl^ers from the latter
in being more extensible, less easily torn, and in its containing a
certain proportion of ligamentous fibres in its composition. Some
of the veins, such as those within the cranium, which are called
sinuses, as well as the veins which traverse the bones, being pro-
tected by the surrounding parts, appear to consist altogether of
this inner coat, and are unprovided with either the muscular or
the cellular coats.

426. The large veins follow in general the course of the arte-
ries, but are usually twice as numerous ; so that where we meet
with an artery, we generally find it accompanied by two veins.
Their general disposition is arborescent, like the arterial system ;
but with reference to the function they perform, they may be
more aptly compared to the roots than to the branches of a tree ;
for in following the course of the blood in its circulation, they
may be said to take their rise from the minutest vessels, and suc-
cessively uniting into larger and larger tubes, to terminate by one
or two main trunks in the heart. The total capacity of the
venous system is at least twice as great as that of the arterial
system. The distribution and general mode of ramification of
the veins, correspond very exactly to that of the arteries, pre-
senting the same ramified appearance, and the same frequent
anastomoses. These collateral communications are exceedingly
numerous in the superficial veins, and wherever they are liable
to partial obstruction from external pressure. It is in these situa-
tions also, that we meet with a great number of valves in the
course of the veins. The veins of the deep-seated organs are

17

194 NUTRITIVE FUNCTIONS,

generally unprovided with valves in any part of their course.
The arteries, as we have already seen, have no valves except at
their commencement.

427. Besides the two venous systems appropriated to the
greater and lesser circulations, the former uniting in the venae
cavag, and the latter in the pulmonary veins, and therefore cor-
responding to the two arterial systems, there is also another, and
more partial system of veins, peculiar to the circulation in the
liver, and other viscera of the abdomen. This particular system,
which is that of the vena portce, as it is called, is complete within
itself; that is, it constitutes a tree, having a common stem, with
its proper roots and branches, the whole of which is placed as
an intermediate system between the ultimate branches of the
gastric, intestinal, and splenic arteries, of which the roots of the
vena porta? may be considered as the continuations, and first
radicles of the proper hepatic veins, which are the continuations
of the ultimate ramifications of the vena portas. By this arrange-
ment, the blood which has circulated through the stomach, the
intestines, and the spleen, is distributed by a new set of veins,
throughout the substance of the liver, and is returned to the
general mass of blood in the vense cavee, after circulating through
that organ. ^

To this pecuUar venous system there is no corresponding arte-
rial system.

5. Capillary System.

428. The ultimate ramifications of the arteries, as well as the
beginnings of the veins, are, in almost every part of the body,
vessels of such extreme tenuity, as to be imperceptible wdthout
the assistance of the microscope ; and they cannot even then be
discerned, unless the part be artificially prepared by the injec-
tion of some coloured substance into the vessels, or unless they
have been accidentally enlarged by disease, so as to have
received the colouring matter of the blood. Hence the ancients,
who were ignorant both of the art of injecting, and of the power
of the microscope, were precluded from a knowledge of the
existence of these minute vessels. They believed that a sub-
stance, which they termed parenchyma, and which they con-
ceived to be of a spongy texture, was interposed between the
terminal branches of the arteries, and the beginning of the veins ;
and this opinion was adopted almost universally by anatomists
before the epoch of the discovery of the circulation, and has
been entertained even after this period, by a great number of
eminent anatomists, down to the present day. But the injections
of Ent, and the microscopical observations of Malpighi and of
Leewenhoek, have sufficiently demonstrated the continuity of

CIRCULATION OF THE BLOOD. 195

the canals by wliich the blood is made to pass from the arteries
into the veins. The researches of modern anatomists, indeed,
by showing the amazing extent to which the minute division of
the vascular system is curried, and in which they pervade every
part of the frame, have finally exploded the hypothesis of the
existence of interposed parenchyma, and have given rise -to
another hypothesis of an opposite kind, namely, of all the textures
of the body being ultimately resolvable into vessels.

429. The name of capillary vessels is given to those minute
branches of either arteries or veins, whose diameter is finer than
a hair, and which can therefore scarcely be distinguished by the
unassisted eye. Authors have endeavoured to establish three
gradations of size in this class of vessels ; the largest being those
"which can be but just perceived by the eye without a magnifying
glass ; the next, those which require the aid of the microscope
for their detection ; and the third, those which are capable of
admitting only a single red globule of blood, and of which the
calibre must consequently be only a very little larger than these
globules.

430. The larger capillaries undergo several subdivisions in
their course, before they arrive at this extreme degree of tenuity;
and indeed, their lateral branches of communication are so mul-
tiplied as they proceed, that the whole forms a general and
extensive net-work of vessels. The total capacity of .the capillary
system far surpasses that of the arteries and veins; and they
contain therefore by much the greatest portion of the blood in
the natural and healthy state of the circulation.

431. The vascular branches which form the channels of com-
munication between the arteries and the veins, are, with but very
few vexceptions, referable to the class of capillary vessels. In
this continuous course it is scarcely possible to mark with preci-
sion, at what point the arterial portion may be said to terminate,
and the venous portion to commence. Neither the limit of size,
nor the change of direction, is sufficient to lay the foundations of
such a distinction; for the alteration of diameter is gradual, and
the inflexions are various, and frequently tortuous, so that no de-
terminate criterion can be assumed as characteristic of either
artery or vein. Hence arises the propriety of constituting a
distinct class of capillary vessels.

432. The texture of the capillaries, from the minuteness of
their size, scarcely admits of accurate observation. Their coats
are thin, soft, pellucid, and therefore invisible to the naked eye,
and hardly discernible with the microscope. It is most probable
that they are formed, in every instance, by a prolongation of the
internal coats of the larger arteries and veins with which they
are continuous.*

* [It would not be easy to account for the phenomena of nutrition, unless

196 NUTRITIVE FUNCTIONS.

433. As the capability of admitting coloured substances is ap-
parently an indispensable condition for their being visible, the
existence of vessels of still smaller diameter, containing only
colourless fluids, must more or less be matter of conjecture. A
very great number of anatomists and physiologists, however,
among whom may be enumerated Boerhaave, Vieussens, Farrie-
nus, Haller, Soemmerring, Bichat, Bleuland, Chaussier, have
admitted the existence of another order of capillaries, or serous
vessels, as they have termed them, of which the diameter is too
small to admit even a single red globule, and which therefore
circulate only the serous part of the blood. On the other hand,
the reality of these pi'etended vessels is contested by Prochaska,
Mascagni, Richerand, and others. Beclard, in his Anatomie
Genirale, has given a review of the arguments employed on both
sides in this controversy, which is by no means as yet set at rest,
and which will probably have to be decided, more by considera-
tions of a physiological than of an anatomical nature.

434. In speaking of the communications between the arteries
and the veins, it remains only to be noticed, that in many parts
of the body there appears to be interposed between the extreme
branches of each, a spongy or cellular structure, into which the
arteries occasionally pour out blood, so as to distend these cells,
and from which the veins arise by open orifices, and absorb the
blood, in order to unload the cells, and remove the accumulation
which has taken place. Such a structure has been denominated
the erectile tissue. It is exemplified on a large scale, in the spleen,
and in some of the sexual organs. We shall notice this struc-
ture afterwards.

435. The different parts and textures of the body are supplied
with vessels in very different proportions. The organs which
rank first in respect to its vascularity, is the lungs ; after which
come the integuments, the pia mater, and choroid coat of the
eye; next the glands, the glandular follicles, the lymphatic glands,
the cortical substance of the brain,- the nervous ganglions. To
these will succeed in the order of vascularity, the muscles, the

we were to presume that some part of the capillary or intermediate system
consists of coatless or merabraneless tubes; and that, in the passage of the blood
through them, the different tissues may act on the blood and conversely. The
mode, indeed, in which the blood is distributed through the tissues may not be
inaptly compared to that, by which the water of a river is distributed through
a marsh, conveying to the vegetable bodies that flourish on its surface, the
materials for their nutrition. Wedemeyer, Gruithuisen, Dollinger, Cams, and
others, consider that the blood is contained in the different tissues, or channels,
which it forms in them : even under the microscope, the stream is seen to
work out for itself, easily and rapidly, a new passage in the tissues, which it
penetrates; and it seems certain, that in the figura venosa of the egv, the
blood is not surrounded by vascular parietes. See, on all this subject,
Dunglison's Physiology, 3d edit. ii. 154, and 206.]

PHENOMENA OF THE CIRCULATION. 197

periosteum, the adipose tissue, the medullary nervous substance,
the bones, and the serous membranes. The tehdons and liga-
ments are amongst the least vascular parts. Still less so are the
cartilages, and the arachnoid membrane of the brain; and lastly,
the epidermis, and its appendages, as the nails and hair, together
with the enamel of the teeth, maybe considered as parts entirely
devoid of vessels.

, 436. The actual mass of blood which the organs of the circu-
lation have lo move through the channels we have just pointed
out has been variously estimated by different physiologists. The
lowest computation is that of Moulins and Abeildgaard, who
made it out to be only eight pounds. Borelh estimated it at
twenty pounds ; Planche at twenty-eight ; Haller at thirty; Dr.
Young at forty; Hamberger at eighty; and Keil at one hundred.
Blumenbach states the propoi'tion in an adult healthy man to be
one-fifth of the entire weight of the body ; but Dr. Good, who
has collected these authorities, is disposed to place but Uttle reli-
ance on the latter mode of estimation, on account of the great
diversity in point of weight and bulk of adults, whose aggregate
quantity of blood would appear to be nearly the same. He
thinks the mean of the above numbers,, which is between thirty
and forty pounds, may safely be taken as nearest to the truth.
The proportions of the whole mass of blood which is contained in
different parts of the vascular system, varies according to age.
In early life, there is nearly an equal quantity contained in the
arteries as in the veins. In the adult, one-fourth only is contained
in the arterial, and three-fourths in the venous system ;* and the
disproportion is greater as age advances.

Sect. II. — Phenomena of the Circulation.
1. Course of the Blood in its Circulation.

437. Having premised this general outline of the course which
the blood takes during its circulation, we shall now follow the
several steps more in detail, examining, as we proceed, the
evidence afTorded us that such is its real course ; and we shall lastly
inquire into the several powers concerned in its propulsion.

438. We shall, for this purpose, begin at that part of its circuit
at which the blood is brought back from the lungs, after receiving
the vivifying influence of the air, and being thereby arterialized,
as it has been called. The pulmonary veins, which convey it in
this state to the heart, are collected into four great trunks, which

* [The general approximation is one third in the arteries, and two thirds in
the veins. Haller estimated that the arterial blood is to the venous as four
to nine.]

17*

198 NUTRITIVE FUNCTIONS.

' open into the left auricle of the heart. As soon as the auricle is
distended beyond a certain degree by this flow of blood into it, it
contracts and pours the whole of its contents at once into the left
ventricle. The constant stream of blood which is flowing towards
the auricle from the lungs, prevents any portion of the blood of the
auricle from flowing back into them when the auricle contracts.
No sooner has the ventricle received this blood, which has passed
into it by a sudden influx, than it is stimulated to a vigorous
contraction of its muscular fibres, which, surrounding the cavity
in a spiral direction, contract its cavity, and exerting a powerful
pressure on the contained fluid, propels it with prodigious force
into the aorta. The contraction of the ventricle is attended with
the raising of the mitral valve, interposed between it and the
auricle, and the sides of that valve being closely applied to the

' aperture by which the blood had entered the ventricle, all return
of the blood into the auricle is thereby prevented. The whole of
it rushes, therefore, as an impetuous torrent into the aorta, or
main trunk of the arterial system. The blood which has entered
the artery is again prevented from flowing back into the ventricle^
by a valvular apparatus of the same kind as that which occurs
between the auricle and the ventricle. These valves, placed at

- the entrance of the aorta, are called the sigmoid, or semilunar
valves. They are three in number, each being attached by its
convex edge to the coats of the artery, to which it is closely
applied when the stream of blood is flowing in a direction from
the heart, but which is immediately raised, and the three loose
edges joining together, form a complete barrier to the passage of
the blood when moving in the contrary direction.*

439. The blood, having passed into the aorta, is conveyed
through its branches and ramifications to all the parts where
these ramifications extend, till it reaches the capillaries, where
it moves more slowly, yet still proceeds on its course, supplying
every part with the materials necessary for the maintenance
of their nutrition and vital powers. From the capillaries the
blood is brought back by the minuter branches of the veins,
which, uniting successively to form larger and larger trunks,
are at length collected into the two vense cavee, the one descend-
ing from the head and superior parts of the body, and the other
ascending from the inferior parts, and both joining at the right
auricle of the heart. The same process now takes place in the
right cavities of the heart, which was described as occurring in
the left. The rifjht auricle is filled with blood from the venag

* [The use of the sinuses or dilatations immediately abovp these valves, is to
prevent them from being so closely applied to the sides of the vessel, that the
reflupnt blood, during the diastole of the ventricles, cannot readily strike them
so as to depress them.]

PHENOMENA OF THE CIRCULATION. 199

cavae ; it contracts* and pours its contents into the cavity of the
right ventricle, which, being in its turn stimulated to contract,
propels the blood it had received from the auricle into the trunk
of the pulmonary artery ; which artery likewise distributes it, by
a similar system of ramifications, to the membrane lining the air
vesicles of the lungs. All retrograde motion of the blood is pre-
vented as efiectually in this case as in the former, by the interpo-
sition of the tricuspid valves between the auricle and ventricle,
and by the semilunar valves placed at the entrance of the pulmo-
nary artery.f

440. From the ultimate ramifications of the pulmonary artery
the blood is conducted into the capillary vessels, which are spread
over the membrane of the air-cells of the lungs, where it under-
goes the change of quality from venous to arterial, consequent
upon its exposure to the chemical action of the oxygen which is
contained in the atmospheric air admitted into those cells. From
these capillaries it is collected by the pulmonary veins, and re-
turned, as before stated, to the heart, to be again distributed to
every part of the body.

441. Whilfe one portion of the blood is circulating in the sys-
tem, another portion is circulating in the lungs. Both auricles
are filled at the same moment, and contract together ; each send-
ing its blood into the corresponding ventricle. In Uke manner, the
two ventricles contract simultaneously, and propel their contents
into their respective arterial trunks. The contraction of the
heart is called the systole ; its relaxation the diastole.

G. Proofs of the Circulation.

442. The discovery of the course which the blood takes in
its circulation, a discovery of such vast magnitude, that almost
the whole of the present doctrines of physiology and pathology
are either directly founded on it, or are more or less immediately
related to it, was made in the beginning of the seventeenth century.
It was one of the earliest fruits of that active spirit of inquiry,
and rational process of investigation, which, since the era of

" [There is great reason for the belief, both'from anatomy, and the evidences
afforded by ocular inspection of the living heart whilst in action, that too much
importance has been assigned to the energetic contraction of the auricles. It
appears indeed probable, that the great use of the auricles is to act as tnie
sinuses or gulfs, for the reception of the blood proceeding from every part of
the body, and that little effect is produced on the circulation by their varying
condition. Dunglison, Op. cii. ii. 159.],

f [The action of the tricuspid, in this respect, is not as perfect as that of the
mitral valve. It seems, indeed, to be destined to permit a certain degree of
reflux; and in this M^ay, perhaps, to be a provision against the mischief that
might, under certain circumstances, result from an excessive afflux of blood
to the lungs: the tricuspid thus acting as a safety valve. Mr. King, Guy's
Hospital Reports, No. IV. April, 1837.]

200 NUTRITIVE FUNCTIONS.

Bacon was beginning to diffuse itself in Europe. It was an honour
reserved for our illustrious countryman Harvey, whose fame must
live as long as science is cherished among men. While it is the
fate of other discoveries, that their authors are either soon for-
gotten, or only known to a small class of those who devote their
attention peculiarly to the subject to which they relate, the name
of Harvev is become familiar to all who have any acquaintance
with general literature, or pretensions to a liberal education.
However firmly the truth of his great discovery be established
in the present time, it was, in its first promulgation, keenly con-
tested by many contemporary physiologists. To us who have
no such prejudices to warp our judgment, and who are furnished
with so large a body of evidence on the subject, the controversy
appears exceedingly frivolous and absurd. Yet we must recol-
lect that in every subject of human opinion, it requires a consider-
able time to wean mankind from errors which have been long
and deeply rooted in their minds, however palpable such errors
may appear to the eyes of those who have not been so blinded.
As it may still, however, be satisfactory to know the grounds
upon which the doctrine is founded, we shall briefly enumerate
the leading facts and arguments that establish it.

443. The most striking proofs that the course of the blood
along the arteries is from the heart towards the extremities of
those vessels, and along the veins in the contrary direction, are
obtained from ligatures on those vessels. If any of the larger
arterial branches be tied, that portion of the vessel which is
situate between the ligature and the heart, immediately swells,
becomes distended with blood, and exhibits strong pulsations ;
and if while in this state it be punctured, the blood rushes out
with violence, and in successive jets, corresponding to the pulsa-
tions of the heart. The part beyond the ligature, on the other
hand, or that farthest from the heart, is flaccid and empty, and
affords no blood when divided ; it is also void of pulsation. Phe-
nomena precisely the reverse of these are exhibited when similar
experiments are made on the veins; in them, the part most dis-
tant from the heart becomes turgid, while the nearer part is
empty. This last experiment is one that is made every time a
person undergoes the operation of blood-letting. A ligature is
applied round the arm, from the pressure of which on the sub-
cutaneous veins, they are made to svv^eU every where below the
ligature, that is, farther from the heart ; while all the veins above
the ligature are empty, the blood having been propelled onwards
in its course towards the heart. Those parts which are swelled
pour out their blood profusely on being punctured ; and when the
bandage is removed, the flow is stopped, in consequence of the
blood finding a ready passage to the heart.

444. In the veins, we have additional evidence, from the struc-

PHENOMENA OF THE CIRCULATION. 201

ture of the valves, that the blood can move only in one direction,
namely, towards the heart. The valves at the entrance of the
ventricles and arterial trunks, which allow of motion only in a
particular course, lead to a similar conclusion with respect to the
direction of the current in its passage through the heart. It is
impossible by artificial means to force fluid injections through
the heart, in a course contrary to that in which the blood moves ;
and the same insuperable resistance is experienced in the attempt
to pass injections in other parts of the circulating system, when
in opposition to the natural course taken by the blood, while the
same fluids readily find their way from the arteries into the
veins, when thrown in that direction.

445. Ocular demonstration of the course of the blood while
circulating in the smaller arterial and venous branches, and also
in the capillaries, is afforded by the microscope, when a very
thin and transparent membrane in which such vessels are distri-
buted is placed in the field of a good microscope. The web be-
tween the toes of a frog, the surface of its vesicular lungs, the
mesentery, the membrane in the tail of small fishes, are all of
them capable of exhibiting these phenomena, and present, indeed,
a spectacle of the highest interest.

'446. The successive action' of the cavities of the heart, in the
order above enumerated, may also be seen when the hearts of
living creatures are exposed to view ; and this spectacle may be
afforded without pain to the animal, if, after its head has been
completely separated from the body, respiration be kept- up by
artificial means.

447. The transfusion of the blood of one animal into the ves-
sels of another is a curious illustration of the doctrine of the
circulation. In this operation, the artery of one animal is con-
nected by a tube with the vein of another animal ; the conse-
quence of which is that the first is gradually emptied of its blood,
while the vessels of the other are in a state of repletion. If an
opening be made at the same time in the veins of this second
animal, the blood originally belonging to it will escape, and thus
the whole mass of its circulating fluid will be changed. Experi-
ments of this kind were at one time very common, but they
have long ceased to excite curiosity, and are now rarely prac-
tised.*

That the blood moves with great rapidity and force through
the larger vessels, is proved by the immense quantity that is
quickly lost if any great artery or vein be wounded.

* [Transfusion has been practised by Dr. Blundell, and others, in cases of
extensive uterine hemorrhage, where life has been ahnost despaired of, and
occasionally with good eifeot.]

202 NUTRITIVE FUNCTIONS.

Sect. III. — Powers concerned in the Circulation.

448. We have next to inquire into the nature and, magnitude
of the forces by which the blood is impelled in its course, the re-
sistance opposed to its progress, and the general laws by which
its movements are regulated.

449. The subject will naturally divide itself into four parts ;
namely, as relating to the powers of the heart, of the arteries^ of
the capillaries, and of the veins.

1. Action of the Heart.

450. The intention and purpose of the auricles, which are placed
as ante-chambers to the ventricles, is to receive the blood in a
constant stream from the veins, which fill it gradually and equa-
bly, so that when the distension has reached a certain degree,
the auricle may contract* and discharge the whole of its contents
with a sudden impetus, into the ventricle. The thickness and
muscular force of the auricles are very inferior to those of the
ventricles, which being destined to propel the blood with consi-
derable momentum into the arterial system, are exceedingly
powerful, but seem to require the stimulus of a sudden and forci-
ble distension, in order to excite them to a sulRciently energetic
action.' It appears, indeed, that this mechanical distension and
separation of their sides from the influx of fluid, is the natural
stimulus that excites them to contraction ; for they are not affected
by any of the causes which produce contractions in the voluntary
muscles, such as irritation of the nerves which supply the heart.
On the other hand, the mere introduction of warm water into
these cavities, when previously emptied of blood, is sufficient to
renew the action of the heart.t

451. It is exceedingly difficult to form any probable estimate
of the absolute force exerted by the heart, and more particularly
by the left ventricle, in propelling its contents. No inquiry in
physiology was pursued with more ardour, has been the subject
of more various controversy, or has given rise to so many volu-
'minous and elaborate calculations.

* [See § 457,]

t [The organ will contract and relax after it has been removed from the
body. In the case of a monstrous foetus, its motion continued for some time
after the auricles and ventricles were laid open ; the organ roughly handled
and thrown into a. basin of cold water. In the rattlesnake, Dr. Harlan ob-
served the heart, torn from the body, continue its contractions for ten or twelve
hours; and Dr. J. K. Mitchell saw the heart of a sturgeon beat until the sides
rustled from dryness, after it had been inflated and hung up to dry. Dungli-
son's Physiology, ii. 169.]

POWERS CONCERNED IN THE CIRCULATION. 203

452. It will be quite evident that a very considerable power
is required, in order to enable the heart to propel the blood
through the arteries, when we consider the enormous resis-
tances opposed 10 its progress, and when we also take into
account the great velocity given to it in its motion. The co-
lumn of blood already contained in the arterial system, must
have its velocity accelerated, in order to admit of the pas-
sage of fresh blood into the aorta. The arteries require also to
be distended for the admission of this additional quantity of blood
every time that the ventricle contracts. The angles and flexures
■which the blood is obliged to follow in its course through the
vessels, must be causes of retardation, and must be productive of
a loss of force, which the muscular power of the heart is ulti-
mately called upon to supply. The operation of all these retard-
ing causes is so complicated, that we need not be surprised at
the problem of the force exerted by the heart, having baffled the
skill of the best mathematicians, and their calculations being so
widely different from one another. Thus, while Keil estimated
the power of the left ventricle at only five ounces, Borelli calcu-
lated that its force could not be less than one hundred and eighty
thousand pounds. Dr. Hales computes it to be exactly fifty-one
pounds and a half; while Tabor concludes its amount to be one
hundred and fifty pounds. Such irreconcilable results sufficiently
show the futility of most of the reasonings on which they are
founded, and the impossibility of making any satisfactory approach
towards the solution of the problem. We should, on the whole,
be more disposed to place confidence in the estimate of Hales,
who moreover states, that the velocity with which the blood
passes into the aorta, is about one hundred and fifty feet per
minute, or two feet and a, half per second ; and that the quantity
of blood passing through the heart during each hour, is about
twenty times the whole mass of blood contained in the body ; or,
in other words, that the whole mass completes twenty entire cir-
culations in an hour. The great velocity of the blood in the
vessels is exemplified by the fact, that a fluid introduced into one
of the jugular veins of a horse, has been detected in the opposite
vein, and even in the vena saphena of the leg, in the course of
half a minute.

453. It has been keenly disputed whether the heart is able
completely to empty its cavities at each contraction; and the
question, which is not one of any real importance, is hardly yet
decided.

454. Another subject of controversy which was much agitated
among the French physiologists in the middle of the last cen-
tury, is, whether the heart is shortened or elongated during its
systole ; that is, whether the apex approaches the base during
the contraction of the ventricle, or recedes from it. From the

204 NUTRITIVE FUNCTIONS.

numerous observations of Spallanzani, as well as of other experi-
mentalists, there seems to be no doubt that during the systole all
the parts are brought nearer to the tendinous ring surrounding
the auriculo-ventricular orifices, which may be regarded as the
fixed pivot of its movements, and consequently the length, as well
as the other diameters of the heart, is shortened. During this
action, however, the curvature being suddenly straightened, the
apex is projected forwards, and produces that striking against
the ribs which is felt by the hand applied externally to the chest.*

455. The right ventricle having only to perform the lighter
task of circulating the blood through the lungs, is much inferior
in thickness and strength to the left ventricle, which has to pro-
pel the blood through the whole aortic system, forming a course
of much greater magnitude than that of the pulmonary vessels.
But, on the other hand, the capacities of the two ventricles are
nearly equal, as might be expected, when it is considered that
the same quantity of blood which is forced out from the one,
must, in the course of circulation, pass through the other; and
that both the ventricles contract the same number of times in a
given interval. The quantity of blood expelled by the heart at
each contraction, is estimated by Blumenbach at two ounces.
So that, reckoning the whole mass of blood at thirty-five pounds,
or four hundred and twenty ounces, and the contractions to be
repeated seventy-five times in a minute, the whole of the blood
will have passed through the heart in about three minutes ; thus
agreeing very nearly with the estimate of Hales already stated
(§ 452).

456. It has been supposed that the heart exerts some force in
the diastole as well as systole ; and that the recoil of the mus-
cles when they spring back, after they have performed their
contraction, creates a force of suction, which promotes the flow
of blood in the great veins towards the heart. But the truth of
this proposition is exceedingly dubious.f

457. The movements of the heart are completely involuntary ;
that is, are entirely beyond the control of the will. Nor are its
natural actions accompanied by any sensations. They are,
generally speaking, totally independent of the nervous system ;
for they may be maintained after the destruction of the brain
and spinal cord, and even after all the nerves which supply the

* [This is one view ; but, perhaps, the great agency is the expansive force of
the heart, which tends to project it forward. It must be admitted, however, with
J. Miiller, (Physiology, Baly's Translation, p. 175,) that great uncertainty
still rests, as to whether the impulse is produced during the contraction or the
dilatation of the ventricles.]

f [The existence of the suction power of the heart or derivation, although
doubted by many, appears to us to be fully established. It has been observed
in the living body ; and the observer has been forcibly struck with the activity
with which the diastole was effected. Dunglison, Op, cit, ii. 182.]

POWERS CONCERNED IN THE CIRCULATION. 205

heart have been divided. Yet these movements arc capable of
being influenced, often very suddenly, by an impression made
upon any considerable portion of the nervous system. The regu-
lar contractions of the heart appear to be excited simply by the
stimulus of distension from the periodical influx of blood into its
cavities. This organ is evidently endowed with a very high
degree, and a very peculiar kind of irritability, not subject, like
that of the voluntary muscles, to exhaustion, by the most power-
ful exertions, reiterated for an indefinite time.*

2. Action of the Arteries.

458. Whatever be the velocity with which the blood is pro-
jected from the heart into the aorta, that velocity is soon retarded,
in the course of its progress from the larger to the smaller branches
of that arterial trunk. This is amply illustrated by the observa-
tion of the effects which follow the division or wounds of arte-
ries in difterent parts of their course. A wound of the carotid
artery is almost instantly fatal, from the deluge of blood which
rushes out from the opening. The division of the other large
arterial trunks is no less certainly fatal, if means be not at hand
to stop the torrent that gushes out with resistless impetuosity.
In the smaller arteries, such as those in which the motion of the
blood can be viewed with the microscope, the current is very
languid and feeble. It is, in reality, however, much slower than
it appears to be ; for it should be recollected, that in viewing the
magnified image of an object, its motion is magnified in the same
proportion as its dimensions.

459. The cause of this continual retardation of the blood is to
be traced in the structure of the arterial system itself. The velo-
city of a fluid passing through a tube of unequal diameter in
different parts, must be inversely as the area of the tube at each
respective point of its length ; that is, invei'sely as the square of
the diameter." Accordingly, if we suppose two cyhnders of dif-
ferent diameters joined together, and that a fluid is passing from
one end to the other, it must evidently move with less velocity
in the wider than in the narrower part ; for if it did not, it would
leave behind it a vacant space. But a vacuum of this kind can
never take place in the living body, in which, with whatever
properties they may be endowed, the fluids are still obedient to
the laws of hydraulics. The arterial system consists of an assem-
blage of tubes, which, though they continually diminish in their
diameter as they divide into branches, yet as the united area of
of the branches is always greater than that of the trunk out of
which they arose, they constitute, when taken as a whole, a sys-

* [See section 450, note *]
18

206 NUTRITIVE FUNCTIONS.

tern of channels of continually increasing capacity, as we fol-
low them from the heart to the extremities. The whole cavity
through which the blood moves, may therefore be represented
by a cone, having its apex at the heart, and its base at the ter-
mination of the minutest arterial ramifications. The beginning
of the aorta is, in reality, the narrowest part of the whole channel,
considered with reference to the united areas of the successive
orders of branches as they divide. The sum of all the areas of
the minutest ramifications of the arteries existing in the body,
comprising myriads of myriads of vessels, if they could be col-
lected together, would form an area of immense extent. No
wonder, therefore, that the motion of the blood, when it arrives
at this part of the circulation, should be so prodigiously retarded
as actual observation shows us that it is.

460. Notwithstanding this great difference in the velocity of
the blood in diflJerent parts of its arterial circulation, it would
appear from the experiments of Poiseuille, that the pressure
exerted by the blood, as measured by the column of mercury it
will support at different distances from the heart, is not very
different.

461. The arteries being always full of blood, and their coats
distended by its pres-ence, the elasticity of these coats is always
exerted, and produces a constant pressure on the blood, inde-
pendently of any force that may urge it forwards. The entry of
a fresh quantity of blood forced into them by the action of the
heart, produces a slight additional distention of their coats, and
a consequent reaction of their elasticity. This reaction of the
arteries in each interval of the heart's pulsation, tends much to
equalize the motion of the blood ; and has the effect also of pro-
pagating the impulse originally given to it by the heart very
quickly to the remoter parts of the arterial system. The velocity
with which this impulse is transmitted, is much greater than the
actual motion of the blood, and partakes of the^nature of a wave,
which, as is well known, advances with incomparably greater
rapidity than the progressive motion of the fluid itself. It is the
impulse given to the sides of the artery by this wave, as it may
be called, which constitutes the pulse, and which is more par-
ticularly rendered sensible on compressing the artery with the
finsjer.

462. It has been a much disputed question, both here and on
the continent, whether the arteries assist the circulation by ex-
erting any contractile power of their own. The evidence in
favour of their exerting such an action is very strong, and ap-
parently irresistible. The power of the heart, however enormous
we may suppose it to be, would appear to be quite inadequate to
drive the whole mass of the blood through the infinite number of
narrow and contorted channels through which it actually moves,

POWERS CONCERNED IN THE CIRCULATION. 207

were it not assisted by some additional force, derived from the
contractions of the arteries themselves. Many facts prove that
variations in the impetus of the blood, and in the quantity which
circulates in particular parts, occur at different times, quite inde-
pendently of any general alteration of the circulation, or of any
corresponding change in the action of the heart. The only as-
signable cause for such differences is a variation in the extent of
action of the arteries. Numerous experiments show that stimuli
applied to the smaller arteries occasion in them a temporary
constriction at the points where irritation has been excited ;
which, after a certain time, goes off spontaneously. Various
■other facts also prove that the arteries have a power of spon-
taneous contraction; this power is exhibited in the most unequi-
vocal manner when an artery has been cut across; the consequent
hemorrhage being, after some time, stopped by the action of the
coats of the artery. This contractile force of arteries is probably
deriv^ed from muscularity, although the muscular structure is not
distinctly perceptible. It is considerably greater in the smaller
than in the larger arteries; and it is probably greatest of all in
the capillaries.

463. Notwithstanding the facts above stated, the muscularity
of the arteries is denied by some of the most eminent of the con-
tinental physiologists ; and among others, Magendie, Broussais,
Adelon, Alard, Rolando, and Muller.*

3. Action of the Capillaries.

464. The particular agents by which the circulation is carried
on in the capillary vessels cannot be very precisely determined ;
and the subject has given rise to much controversy among phy-
siologists. The action of these vessels is evidently of the greatest
importance in relation to every other function, and more espe-
cially to the production of every permanent change which may
take place in the form or composition of the organs. The vari-
able state of the circulation in different organs at different times,
must be occasioned principally by diversities in the actions of the
capillaries. It appears from the experiments of Hunter, that
while the larger arteries possess a greater proportion of elastic
power, the saialler arteries have a comparatively greater muscu-
lar contractility; and this reasoning may, with great appearance
of probability, be extended to the capillaries. It would appear,
indeed, from various observations on the inferior animals, and in
particular from those made by Dr. W. Philip, that the circula-
tion in the capillaries may be kept up for some time after the

* See Milligan's Translation of Magendie, and Bostock's Pliysiology,
p. 344r. [Also, Dunglison, Op. cit. ii. 170.]

208 ' NUTRITIVE rUNCTIONS.

pulsation of the heart has entirely ceased, and even when that
organ has been altogether removed from the body. In many
cases, indeed, the capillaries, when viewed with the microscope,
have been seen to contract on the application to them of stimuli,
which, in other cases, excite contractions in the muscular fibre.
The pulsatory motion of the blood given to it in the arteries by
the periodical contractions of the heart, is scarcely sensible in
the smaller arteries, and is totally lost in the capillaries, where
we find the blood moving in a uniform stream. This is a ne-
cessary consequence of the tortuous course of the channels
through which it passes, and of the numerous communications
among these vessels, which equalize the ejEfects of the original-
impulse, and extend them over the whole period of time that
intervenes between one pulsation and the next.*

4. Action of the Veins.

465. The blood which is returned from every part of the sys-
tem by the veins, is gradually accelerated in its progress towards
the heart, for a similar reason that it was retarded in its trans-
mission through the arteries, namely, that the capacity of the
channel through which this fluid is passing is continually diminish-
ing; for the united area of the beginnings of the veins is incom-
parably smaller than the conjoined area of the two vense cavag.
The office of the veins generally appears, on the whole, to par-
take more of a mechanical action than that of the arteries, though
it is probable that the smaller veins may derive from their struc-
ture powers analogous to those of the capillaries. The power
which impels the blood forwards in the veins is chiefly the
impulse it has already received, and the pressure exerted on it
from behind, or what has been technically termed the vis ti tergo.
This force is assisted also in many situations by the pressure
made on the veins by the action of the neighbouring muscles,
which, in consequence of the valves placed in the course of the
veins, preventing all retrogade motion in the blood, must contri-
bute to force it onwards towards the heart. It is probable,
however, that the veins are not altogether destitute of a power
of contraction, though less considerable than that possessed by
the arteries ; and that the exertion of this power has some share
in accelerating the motion of the blood in the venous system.
Whatever power may arise from the force of dilatation exerted
by the auricles of the heart during their diastole, which, hovi^-

* [The capillaries have been supposed, by some, to possess a vital power of
expansibility or turg^escence ; but this is probably owing to the afflux ofblood to
an irritated part. The erectile tissues become turgid, but not until excitation
is induced, directly or indirectly, in the nerves of the parts, and this is probably
the case with the capillary or intermediate vessels.]

POWERS CONCERNED IN THE CIRCULATION. 209

ever, we have reason to believe is very trifling, naust be added to
the account of the forces that tend to promote the motion of the
blood towards tliose cavities. Some have supposed that a similar
power is derived from the expansion of the chest in the act of
inspiration ; but this, if it exist at all, is of very inconsiderable
amount. The vena3 cavae near their termination in the auricles,
are furnished with a distinct layer of muscular fibres, apparently
for the purpose of enabling them to resist the retrograde impulse
communicated to the blood by the contraction of the auricles.*

5. Pulmonary Circulation.

466. There is nothing very different in the circulation through
the pulmonary arteries, capillaries, and veins, from what takes
place in the corresponding vessels of the systemic circulation
excepting that junctions are occasionally formed between the
smaller branches of the bronchial arteries which have their origin
from the aorta and the pulmonary artery. The phenomena
"which occur in asphyxia, or death from suffocation, prove that
the pulmonary capillaries have a distinct action of their own in
carrying on the circulation. The beautiful net-work formed by
the inosculating branches of the pulmonary capillaries was first
observed by Malpighi, and has received the name of Rete mira-
hile Malpighi. The pulmonary veins are wholly destitute of
valves, not being exposed to variations of pressure from the ac-
tions of the surrounding muscles. They are furnished, like the
venae cavae, with a reinforcement of muscular fibres, in the neigh-
bourhood of the left auricle in which they terminate.

467. In one respect, the vessels of the pulmonary circulation
differ from those of the sysremic, namely, that the arteries are
carrying dark-coloured blood, and the veins florid blood ; the
former being termed venous, from having the qualities of that
which is returned by the veins of the system ; the latter being
termed arterial, because it has the qualities of that which circu-
lates in the systemic arteries.

* [The same alternate contraction and dilatation has been observed in the
venae cavse after the heart was removed from the body as in the heart itself,
Dunglison's Physiology, 3d edit. ii. 181, and Dr. J. J. Allison, in Amer.
Journ. of the Med. Sciences, Feb. 1839.

In addition to the powers already mentioned as concerned in the circu-
lation, it has been maintained by many, that the blood possesses a power of
automatic or self motion, either in consequence of its own vital properties, or
of some electroid agency derived from the vessels in which it circulates ; but
granting that such may be the fact, — as in the embryo, in which blood in
motion can be detected before vessels are in esse, — it can exert but little
influence on the circulation.]

18*

210 NUTRITIVE FUNCTIONS.

CHAPTER IX.

RESPIRATION.

468. The object of the function of respiration js the conversion

of venous into arterial blood, by its exposure to the chemical
influence of atmospheric air received into the lungs. This ar-
terialization of the blood is a process more essential to the con-
tinuance of Hfe than even the assimilation of aliment. The
necessity for air is more imperious than the demand for food ;
and the interruption to its supply cannot be continued for a few
minutes without being fatal to life. In comparing the extent to
which this function '' is carried on in the different classes of
animals, we shall find that in general the intensity of all the vital
actions is nearly in proportion to the perfection in which the
objects of this function are accomplished.

469. The consideration of the function of respiration, then,
comprises an inquiry into the three following objects ; first, the
mechanical means by which the air is alternately admitted and
discharged from the lungs ; secondly, the provision made for
bringing the blood to the lungs, and exposing it to the action of
the air ; and, lastly, the chemical changes which are produced
on the blood by the action of the air in that organs The means
of fulfilling the second of these objects has already been suffi-
ciently explained in the account we haye just given of the cir-
culation. It remains, therefore, that we consider the first and
tiiird branches of the inquiry.

Sect. I. — Mechanism of Respiration.

470. The anatomical structure of the organs of respiration,
namely, the lungs with the air pr.ssages, including the trachea,
bronchia, and air cells, together with the general conical cavity
of the thoi'ax, bounded by the sternum in front, the spine behind,'
and the ribs on every other side, while its lower side, or basis of
the cone, is closed by the diaphragm, are subjects of anatomical
inquiry.

471. The mechanical act of respiration is divisible into two
periods, that of inspiration, during which air is drawn into the
lungs, so as to distend their vesicles, and expiration, during which
the air which had been so.received is expelled.

472. Inspiration is accomplished by enlarging the capacity of

MECHANISM OF RESPIRATION. 211

the thorax in all its dimensions. This is eflected by the action of
different sets of muscles. The principal muscle of inspiration is
the diaphragm, which has an arched form, the convexity being
towards the chest. Its attachments, by radiating fibres arising
from a central tendinous portion, and inserted into the ribs
which form the lower margin of the chest, are such, that when
they contract they draw down the middle tendon, and render the
diaphragm more f^at than it was before. Hence the space above
is enlarged. The flattening of the diaphragm takes place chiefly
in the fieshy lateral portions, but the middle tendon is also slightly
depressed.

473. The second set of muscles employed in inspiration are
those which elevate the ribs ; and the principal of these are the
two layers of intercostal muscles. Each rib is capable of a small
degree of motion on the extremity by which it is articulated
with the vertebrae. This motion is chiefly an upward and a
downward motion. But since the ribs, as they advance from the
spine towards the sternum, bend downwards in their course, the
effect of the vertical motion just described will be that of raising
the sternum, and increasing its distance from the spine ; enlarg-
ing, consequently, the capacity of the chest. The intercostal
muscles are disposed in two layers, each passing obliquely, but
with opposite inclinations, from one rib to the adjacent rib.
Hence they act with the advantage of oblique muscles on the
principles formerly explained.

474. Thus there are two ways in which the chest may be
dilated ; first, by the diaphragm, and, secondly, by the muscles
which elevate the ribs. In general, when the respiration is
natural and unconstrained, we chiefly breathe by means of the
diaphragm ; but we also employ the intercostal muscles when
the respiration is quickened or impeded by any cause. If respi-
ration should be rendered difficult several other muscles are
called into play in aid of the intercostals ; namely, the great
muscles situate in the back and sides, which connect the ribs to
the spine and to the scapula ; and several of the muscles of the
neck are also thrown into action as auxiliaries on these occasions,
when the respiration becomes laborious.

475. The glottis is kept open, during inspiration, by the muscles
of the larynx which perform that office ; and when a foixible
inspiration is made, the nostrils are expanded, the lower jaw
depressed, and every action, which can in the remotest degree
concur in the effect of removing all obstruction to the passage
of the air into the trachea, is exerted.

476. Having thus shown how the cavity of the thorax is
dilated, let us next trace the effect of this expansion upon the
lungs. It is obvious, that if when, by the descent of the diaphragm
and elevation of the ribs, the cavity of the chest is enlarged, the

212 NUTRITIVE FUNCTIONS.

lungs were to remain in their original situation, an empty
space would be left between them and the sides of the chest. But
no vacuum can ever take place in the living body ; the air already
present in the air-cells of the lungs must, by its elasticity, expand
these organs ; and the external air, having access to them by
means of the trachea, will rush in through that tube in order to
restore the equilibrium. This, then, is inspiration.

477. The expulsion of the air from the lungs constitutes expi-
ration. This takes place as soon as the air which had been in-
spired has lost a certain portion of its oxygen, and received in
return a certain quantity of carbonic acid gas and of watery vapour,
by having had communication with the blood in the pulmonary
capillaries. When thus contaminated it excites an uneasy sensa-
tion in the chest, and the intercostal muscles relaxing, the ribs
fall into their original situation, and the relaxed diaphragm is
pushed upwards by the action of the abdominal muscles. The
lungs, being compressed, expel the air they had received, and
this air escapes through the trachea. The movements of inspir-
ation are in like manner prompted by an uneasy sensation con-
sequent upon the presence of venous blood in the pulmonary
system.

478. Thus the lungs are merely passive agents in the me-
chanism of respiration ; for it does not appear that they have,
as was at one time supposed, any inherent power of extension or
contraction, if we except only that arising from the elasticity
which they possess in common with all membranous textures.
Hence, if an opening be made in the sides of the chest, the lung
on that side immediately collapses, in consequence of the inter-
nal pressure of the air against its air-cells, which kept the lung
expanded, being balanced by the external pressure of the atmos-
phere which has been admitted on the outer surface of the lung.

479. The alternations of inspiration and expiration, which
together constitute one act of breathing, take place, in ordinary
health, about once for every four pulsations of the heart; and as
both are generally accelerated in the same proportion, the same
rule usually holds good in states of disease.*

480. The quantity of air taken into the lungs at each inspira-
tion has been very variously estimated by different experi-
mentalists. It differs, indeed, considerably in different persons,
and in different states of the system ; but from the concurrent
testimony of the most accurate experimentalists, the average
quantity appears to be about forty cubic inches. By a forcible
expiration there may be expelled, in addition to this quantity,
about a hundred and seventy inches more. But even after this

* [The number of expirations or inspirations, in a given time, varies.
The average may be estimated at about 18 per minute.]

CHEMICAL EFFECTS OF RESPIRATION. 213

effort has been made, there still remain about a hundred and
twenty cubic inches in the lungs ; so that, adding all these quanti-
ties together, it will appear that the lungs are capable of contain-
ing, while in their most expanded state, after ordinary inspiration,
about three hundred and thirty cubic inches of air. One-eighth
of the whole contents of the lungs, therefore, is changed at each
respiration. If we suppose that we respire twenty times each
minute, the quantity of air respired during twenty-four hours
will amount to six hundred and sixty-six cubic feet.*

Sect. II. — Chemical Effects of Respiration.

481. Before we inquire into the changes produced on the blood
by its exposure to the air in the lungs, it will be proper to notice
the changes which the air undergoes by this process. The air
of the atmosphere is found by chemical analysis to consist of
seventy-nine per cent, of nitrogen, twenty of oxygen, and one of
carbonic acid.f When expired, the principal change which has
taken place in it is the substitution of a certain quantity, which,
on an average, is about seven and a half per cent, of carbonic
acid gas for a nearly equal quantity of oxygen gas, and the addi-
tion of a quantity of aqueous vapour. Air which has passed
through the lungs only once is incapable of supporting the com-
bustion of a taper, which is accordingly extinguished the moment
it is immersed in the air. The weight of the oxygen consumed
in the air respired in the course of a day, will be found to
amount to about two pounds and a quarter avoirdupois, or nearly
15,500 grains, occupying in its gaseous state a volume of 45,000
cubic [inches, or a little more than twenty-six cubic feet. The
quantity of carbonic acid expelled from the lungs is somewhat
less ttian this; its total bulk in the twenty-four hours amounting
on an average only to 40,000 cubic inches, or 23-2 cubic feet.
Its total weight is 18,600 grains, or 2-86 pounds avoirdupois.
The weight of the quantity of carbon contained in this amount
of carbonic acid is 5,208 grains, or very nearly three quarters of
a pound ; and that of the quantity of oxygen is 13,392 grains.
Hence the quantity of oxygen which disappears from the air
respired, over and above that which enters into the composition
of the carbonic acid gas, is 2,108 grains, and had occupied, while
in a gaseous state, 5000 cubic inches. The only way in which
we account for the disappearance of this oxygen is, by supposing
it to have been absorbed by the blood.

* See Bostock on Respiration, and also his Physiology, 3d edition, pages
321 and 361.

f The recent experiments of De Saussure tend to show that the propor-
tional quantity of carbonic acid gas in atmospheric air is even less than this.
He estimates it at only four parts by volume in a million volumes of air.

214 NUTRITIVE FUNCTIONS.

482. The numbers given above are, of course, to be taken as
imperfect approximations to the truth, being deduced as the mean
of the best authenticated observations, in which, however, there
exist such great discrepancies as to render any accurate appre-
ciations nearly hopeless. An excellent summary of the results
which have been arrived at by different experimentalists, with
critical remarks on their respective values, will be found in Dr.
Rostock's Elementary System of Physiology.*

483. Much difference of opinion has prevailed with respect to
the absorption or evolution of nitrogen during respiration. From
the accurate experiments on this subject made by Dr. Edwards,
it appears that on some occasions there is a small increase, and
in others a diminution of the nitrogen of the air respired. But
the limits within which we must confine ourselves in this treatise,
forbid our entering into the experimental details from which this
conclusion is deduced.

484. The quantity of water exhaled from the lungs in the
course of a day, has been estimated by Dr. Thomson at nineteen
ounces, and by Dr. Dalton at twenty-four.

485. It should be observed, that the quantity of carbonic acid
thrown off from the lungs, is liable to great variation from several
causes ; it has been found by Dr. Prout to be greatest at noon,
and least at midnight. It has also been ascertained that it is less
in youth than in middle age ; and that it is diminished by causes
which induce fatigue or lessen the vital energies.

486. We have next to inquire what changes have, in the mean-
while, been effected in the blood by the action of the air to which
it has been subjected in the lungs. A visible alteration in the
first place, is produced in its colour, which, from being of a dark
purple, nearly approaching to black, when it arrives at the air
cells by the pulmonary arteries, has acquired the bright intensely
scarlet hue of arterial blood, when brought back to the heart by
the pulmonary veins. In other respects, however, its sensible
qualities do not appear to have undergone any material change.
Judging from the changes produced on the air, which has been
in contact with it, we are warranted in the inference that it has
parted with a certain quantity of carbonic acid and of water,
and that it has in return acquired a certain proportion of oxygen.
Since it has been found that the quantity of oxygen absorbed, is
greater than that which enters into the composition of the car-
bonic acid evolved, it is obvious that at least the excess of oxygen
is directly absorbed by the blood ; and this absorption, constitutes,
no doubt, an essential part of its arterialization.

. 487. It has been much disputed whether the combination

*|We refer particularly to the 3d section of chap. vli. p. 336-362. [See,
Iso, on the whole of this subject, Dunglison's Physiology, 3d edit. ii. 99.]

CHEMICAL EFFECTS OF RESPIRATION. • 215

"which seems to be effected between the oxygen of the air and the
carbon furnished by the blood, occurs during the act of respira-
tion, and takes place in the air cells of the lungs, or whether it
takes place in the course of circulation. On the first hypothesis,
the chemical process would be very analogous to the simple
combustion of charcoal, which may be conceived to be contained
in the venous blood in a free state, exceedingly divided and ready
to combine with the oxygen of the air; and imparting to that
venous blood its characteristic dark colour; while arterial blood,
from which the carbon had been eliminated, would exhibit the
red colour natural to blood. On the second hypothesis, we must
suppose that the whole of the oxygen, which disappears from the
air respired, is absorbed by the blood in the pulmonary capilla-
ries, and passes on with it into the systemic circulation. The
blood becoming venous in the course of the circulation, by the dif-
ferent processes to which it is subjected for supplying the organs
with the materials required in the exercise of their respective
functions, the proportion of carbon which it contains is increased,
both by the abstraction of the other elements, and by the addition
of nutritive materials prepared by the organs of digestion. The
oxygen, which had been absorbed by the blood in the lungs, now
combines with the redundant carbon, and forms with it either
oxide of carbon, or carbonic acid, which is exhaled during a
subsequent exposure to the air in the lungs. Many facts tend
strongly to confirm our belief in the latter of these hypotheses.*
488. It appears from a multitude of experiments, as well as
from observations of the phenomena which take place in asphyxia,
(that is, in the suspension of the vital actions from an interrup-
tion to respiration, as in hanging or drowning, or immersion in
any gas not fitted for respiration,) that if the blood be not arte-
rialized, and if, retaining its venous character, it be circulated in
that state through the arteries of the system, it will act as a
poison to the organs to which it is sent, destroying both the
nervous and sensorial powers, and impairing the irritability of
the muscles ; and that this is the cause of the rapidity with which

* [The knowledge we have attained, of late years, on the transmission of
gases through animal membranes, aids us materially in the solution of this
interesting question. The rate of transmission of carbonic acid is greater than
that of nitrogen. We can hence understand, that more oxygen than azote
may pass through the coats of the pulmonary blood-vessels, and can compre-
hend the facility with which the carbonic acid, formed, as we conceive, in the
course of the circulation, permeates the same vessels, and mixes, by diffusion,
with the air in the lungs. Miiller considers, that the air passes into the blood-
vessels of the lungs, where he thinks it is decomposed, owing to the affinity
of oxygen for the red particles of the blood; carbonic acid being formed,
which is exhaled in the gaseous form, along with the greater part of the
' nitrogen.]

216 NUTRITIVE FUNCTIONS.

death ensues under these circumstances.* It thus appears that
respiration requires to be constantly kept up in order to free the
blood from the continual additions of carbon which are made to
it by the various processes of assimilation and absorption. It is
also a principal agent in perfecting the animahzation of the chyle,
which is added to the blood, and in converting it into fibrin.

Sect. III. — Animal Temperature.

489. Since we find that the human body, as well as those of
all warm-blooded animals, is constantly maintained during life at
a temperature higher than that of the surrounding medium, at
least in temperate cUmates, it becomes interesting to inquire into
the sources whence this heat is evolved. The union of carbon
and oxygen, which takes place in consequence of respiration, is
the most obvious of these sources ; and suggests that the evolu-
tion of animal heat takes place in a manner somewhat analogous
to the ordinary combustion of carbonaceous fuel. The circum-
stance of the equable heat of every part of the body, excepting
the immediate surface where it is cooled by the, contact bf the
air, and by cutaneous perspiration, would be in perfect accord-
ance with the theory of Dr. Crawford already explained ; for if
the combination of oxygen with carbon take place gradually in
the course of the circulation, it will follow that the evolution of
heat will also take place at the same time, and in the vessels
employed in the circulation. Or even if the combination took
place in the lungs, if it could be shown, as Dr. Crawford endea-
voured to prove, that arterial blood has a greater capacity for
caloric than venous blood, all the heat that would have been
.evolved in the pulmonary vessels would be absorbed by the

arterial blood, and given out in the course of its circulation,
during its gradual conversion into venous blood, which has a less
capacity for caloric.

490. It would, appear, however, from some recent experiments
of Dulong and Despretz,f that only three-fourths of the whole

* [This was the view of Bichat, but there are numerous difficulties in the
way of its adoption. The experiments of Williams (Edinburg Med. and
Surgical Journal, Ixxvii. 1823,) and of Kay (Ibid. xxix. and the Physiology
and Pathology, &c. of Asphyxia, Lond. 1834.) have shown, that the inter-
ruption is owing to the nonconversion of venous into arterial blood, and to the
non-adaptation of the radicles of the pulmonary veins for anything but arterial
blood ; owing to which causes, stagnation of blood supervenes in the pulmo-
nary radicles, and the passage of the blood from the right to the left side of
the heart is prevented. Art. Asphyxia, in Amer. Cyclopedia of Practical
Medicine and Surgery, Part X. Philadelphia, 1836 ; and Dr. W. P. Allison, in
Edin. Med. and Surgical Journal, Jan. 1836.]

t See Miiller's Physiology, by Baly, p. 83.

SECRETION.

217

quantity of caloric produced by the living system can be explained
by the combination of oxygen with carbon in respiration. Proba-
bly, therefore, several of the other chemical changes induced on the
blood by the processes of secretion and nutrition, contribute to
the further evolution of caloric, and to the maintenance of the
animal temperature.* This evolution appears, although primarily
dependent on respiration, to be in a great measure controlled by
the action of the nervous powers; and to be regulated by a variety
of circumstances in the condition of the other functions, espe-
cially that of the circulation, which are very imperfectly known;
and the inquiry into which would lead us into a field of discussion
far too extensive for the limits within which we must confine
ourselves in the present treatise. We must content ourselves,
therefore, wilh again referring to the work of Dr. Bostock for
more ample information on these subjects.f

CHAPTE

SECRETION. *J&

491. Secretion is that function by \vhiSlT*^^?*eHS-^ubstances
are cither separated from the blood or formed from it, in order
to be applied to some useful purpose in the economy. We have
noticed, in the course of the preceding inquiries, several instances
of fluids prepared from the blood, and rendered subservient to
different uses in the economy. The saliva, the gastric and pan-
creatic juices, the bile, and the mucus lubricating the surface of
the alimentary canal, are all examples of secretions subservient
to digestion and assimilation.

492. Such being the general purpose answered by this function,
we have first to examine the apparatus provided for its perform-

* [The view of those who regard the evolution of caloric to take place in
the system of nutrition over every part of the body appears to be most con-
sistent with observed phenomena. It would seem, that caloric is disengaged
in every part by a special action under the nervous influence, and the presence
of arterial blood. In this way we can account for the increased heat met
with in certain local affections, and for the different temperatures of different
portions of the body, — the activity of the function varying according to the
organs. It would not be easy to explain this difference without sup-
posing that each part has the power of disengaging its own heat, and that
the conduction of caloric from one part to another is not sufficiently ready to
prevent the difference from being perceptible.]

f [See an elaborate chapter on this subject, in Dunglison's Physiology,
3d edit. ii. 238.]

19

218 NUTRITIVE FUNCTIONS.

ance ; secondly, the nature of the effects obtained ; and, thirdly,
the peculiar powers which are concerned in their production.

Sect. I. — Apparatus for Secretion.

493. The apparatus employed by nature for the performance
of secretion varies considerably in its structure, in different in-
stances, according to the nature of the product which is to result
from the operation ; and according as that product is merely
separated from the blood, in which it may already have existed,
oris formed by the combination of certain elements and proximate
principles furnished by that fluid. In the simplest cases, where
that product is principally aqueous, and apparently consists of
nothing more than the serous portion of the blood separated from
it by mere transudation, we find no other organs requisite than
those smooth membranous surfaces which we have already des-
cribed under the name of the serous membranes. The mucous
secretions proceed, in like manner, from the modified yet still
simple action of a membranous surface, of a rather more refined
structure, namely the mucous membranes. The more elaborate
products of secretion, on the other hand, which are apparently
formed by combinations of pre-existing elements, are obtained
by the agency of organs of a more complicated structure, which
are denominated glands.

Sect. II. — Glandular Apparatus.

494. The essential part of the structure of a gland consists in
a collection of tubes, more or less convoluted, united by cellular
substance into masses of a rounded form, constituting a lobule.
Each lobule has a separate investment of membrane ; and the
whole aggregate of lobules is furnished with a general membra-
nous envelope, or capsule. In every gland we meet with a com-
plex arrangement of numerous arteries, veins, nerves, a'nd lym-
phatics, provided with ramified excretory ducts, which conduct
away the secreted matter that has been prepared in the substance
of the gland.

495. The above description of a gland does not include those
organs, which, although resembling the proper glands in their
general appearance, perform no distinct office of secretion, and
are therefore unprovided with any excretory duct. This is the
case with those bodies belonging to the absorbent system, which
bear improperly the title oi lymphatic or conglobate glands. The
spleen, the renal capsules, the pineal gland, the thyroid gland,
and the thymus, are, in like manner, improperly included in the

GLANDULAR APPARATUS. 219

class of glands ; for we have no evidence of their secreting any
fluid, and indeed know nothing of their real functions.

496. The catalogue of glands, strictly answering to the defini-
tion, will comprise the following organs, nanaely, the liver,
pancreas, and kidneys ; the salivary, lacrymal, and meibomian
glands; the tonsils, the ceruminous glands of the ear, and the
sebaceous glands of the face; the mammie, the prostate, the tes-
ticle, Cowper's glands, the gland ulee odoriferas, and the extensive
system of mucous glands about the head and trunk. These parts,
although differing widely from each other in many respects,
agree in a sufficient number of particulars to allow of being
classed together in one organic system, which Bichat has termed
the glandular system.*

497. Most of the glands are arranged in pairs, as the kidneys,
testicles, salivary and lacrymal glands, while others are single,
as the liver and the pancreas.

498. The organization of the glandular system is exceedingly
complex, and cannot be unravelled without great difficulty. The
tissue of which they are composed presents us with no regular
arrangement of tibres, such as we see in the muscles, ligaments,
nerves, or bones; but the whole structure is made up of a con-
geries of vessels and cells, having no very firm cohesion amongst
themselves, and hence admitting very readily of being separated
by slight mechanical causes. Whilst organs which have a more
extensive fibrous organization possess considerable powers of
resistance, a very moderate degree of violence is sufficient to
tear asunder the texture of a gland. The resistance in the latter
case is owing solely to the cohesion of the cellular tissue which
connects their parts, and which differs in its density and strength
in different glands.

499. There are three different ways in which the glandular
tissue, ov parenchyma of glands, as it has been generally termed,
is disposed. In those glands which have been called conglome-
rate, a term which, as we have seen, has been used in contradis-
tinction to the conglobate, or lymphatic glands, the organ is made
up of distinct portions, connected together by a large quantity
of loose cellular tissue, in the intervals of which the vessels and
nerves are situated. These larger lobes are again made up of
smaller lobes united in the same way. By successive divisions
we obtain smaller and smaller component portions, till we arrive
at last at very small bodies still visible to the naked eye, and

=f [A more common division at the present day of the organs of secretion is
into, 1. The simple exhalanl, as met with in the serous membrane. 2. The
follicle, in which there is a crypt without any distinct duct, as in the tonsils,
mucous crypts of the mucous membranes, sebaceouscrypts of the skin, &c.; and,
3. T\\e gland, an organ of a solid and more complex organization, furnished
with a distinct excretory duct, as in the kidney, liver, &c.]

220 NUTRITIVE FUNCTIONS.

which are called by anatomists glandular acini. These succes-
sive lobules are firmer in proportion as they are smaller, being
surrounded and connected with the adjoining portions, by shorter
and denser cellular substance. The second, third, and even the
fourth subdivisions of these lobes may easily be followed with
the scalpel. _The acini themselves are of a roundish figure and
pale colour, and readily distinguishable from other parts by the
absence of fibres. The microscope shows them, however, to be
still farther divisible into smaller portions, between which are
seen plates of cellular substance, and if we attempt to pursue
these subdivisions with successively greater magnifying powers,
we do not find that -^e can reach their limit. The above descrip-
tion is particularly applicable to the saUvary, lacrymal,and pan-
creatic glands.

500. The second modification of glandular structure occurs in
the liver and the kidneys, in which it is impossible to trace these
successive divisions into lobules, after we have distinguished the
primary lobes which they present. Their structure exhibits an
uniform and even tissue, made up of glandular acini, closely united
together into one substance. The connecting cellular substance,
if any such exist, is short and very small in quantity; and
hence these organs may be torn asunder with great ease, and
their ruptured surfaces present the appearance of granulations.

501. The third description of glands applies to the prostate, to
the tonsils, and in general to all the mucous glands.

502. On examining the course of the blood-vessels, the small
arteries which enter into a gland are found to ramify in various
ways through a mass of cellular texture. But it is a matter of
great uncertainty what specific structure intervenes between the
secreting arteries and the commencement of the excretory ducts.
Two opinions have long divided anatomists on this subject.
Malpighi, who was one of the first who investigated the minute
anatomy of glands, asserted that the acini invariably contain a
central cavity, or follicle, as it was termed, on the inner surface
of which the arteries are distributed, while the secreted fluid is
collected in the follicle, and conveyed away by the branch of
the excretory duct which arises from the follicle. He considered
the mucous glands of the alimentary canal, which undoubtedly
present a structure of this kind, as the most simple forms of
glandular structure ; the larger glands being only aggregations
of these simpler structures.

503. The theory of Ruysch, who also bestowed extraordinary
care in the examination of glandular structures, is founded on
the supposed continuity of the extremities of the arteries with the
commencements of the excretory duct. This theory is so far
opposed to that of Malpighi, that itpre-supposes all the glands to
consist merely of an assemblage of vessels and of cellular sub-

GLANDULAR APPARATUS. 221

stance, without any membranous cavities interposed between the
arteries and excretory ducts. The opportunities of dissection
which Ruysch enjoyed, and his unrivalled skill in the arts of in-
jecting the vessels, and tracing their modes of distribution, gave
great weight to his opinions, which seemed to be immediate
deductions from what he saw, and had established as matters of
fact. Fluids could be made by injection to pass very readily
from the blood-vessels into the excretory ducts, both in the kid-
neys and liver. After these organs have been accurately injected,
they may be resolved, by subsequent maceration, into small
clusters of blood-vessels ; what Malpighi had represented as
hollow acini, seemed to be in reality composed of a congeries of
these minute vessels. This appeal to the evidence of the senses,
and the admirable preparations which supported it, brought over
almost all the anatomists of that time to the opinion of Ruysch ;
and Boerhaave himself, who had been a zealous defender of the
doctrine of Malpighi, and written in support of it, was at length
induced to adopt the views of Ruysch.

504. This controversy was sustained for a great many years
in the schools of medicine ; and the opinions of anatomists con-
tinue even at the present time to be divided upon this subject.
Probably both these opinions may in part be correct, as applied
to different glands, though not universally trtie ; and secretion
may perhaps be in some cases performed by continuous vessels,
and in others by an interposed parenchyma, of a cellular or more
intricate organic apparatus.

505. As the structure of the secreting organs admits of great
variety, it may be useful to advert to some of the terms by which
these minute parts have been designated. The terms acini,
cotulcB, cryptce, folliculi, glandulcB, lacuncB, loculi, utriculi, have
been almost promiscuously used ; being, as Bell humorously ob-
serves, " so many names for bundles, bags, bottles, holes, and
partitions." The term acinus has been already explained (§499).
CotuIcB are merely superficial hollow's, from the surface of which
the secretion is poured forth. A crypta is a soft body, consisting
of vessels not completely surrounded with a membrane, but re-
solvable by boiling or maceration. Follicles are little bags ap-
pended to the extremity of the ducts, into which the secretion is
made, and from which it is carried ofi' by the ducts. LacuncB are
little sacs, opening largely into certain passages, and into which
generall}' mucus is secreted.

506. The excretory ducts, whatever maybe their exact origin,
consist at first of an infinite number of capillary tubes, which,
like the veins, soon unite together into more considerable tubes.
These generally pursue a straight course through the glandular
tissue, unite wilh one another, and form at last one or more large
tubes. The only exception to this general proposition occurs in

19*

222 NUTRITIVE rUNCTIONS.

the excretory ducts of the testicle,/which pursue a singularly-
tortuous course before they unite into the vas deferens on each
side.

507. There are three varieties in the mode of termination,
with regard to the excretory ducts of glands. In the first case,
the ducts unite into several distinct tubes, which open separately,
and without any previous communication. Sometimes these
separate apertures are met with in a more or less distinct pro-
minence, as in the breasts, the prostate, and the sublingual glands.
At other times, the orifices are found in a depression, or kind of
cul-de-sac, as in tjie tonsils, and in the foramen coecum of the
tongue. In the second case, which includes the greater number
of glands, their fluids are poured out by a single tube, having a
simple orifice. In the third case, some glands deposit the pro-
duce of their secretion in a reservoir, where it is retained, in
order to be expelled at particular times : as is exemplified in the
kidneys, liver, and testicles. In this case there must be two ex-
cretory tubes ; one to convey the secretion from the gland to the
reservoir, and the other to transmit it to its final destination.
The size of the excretory ducts will, of course, be regulated very
much by their number : when several are produced from one
gland, they are very small, and sometimes scarcely perceptible.
Those which are single are longer with reference to the size of
the gland, and generally pass for some distance, after quitting
the gland. In the pancreas, however, this is not the case, the
common duct being concealed in the substance of the gland.

508. Whatever the arrangement of the excretory ducts may
be, they aU pour their fluids, either on the surface of the body,
or on the surface of some of the mucous membranes. In no
instance whatever do they terminate on serous or synovial sur-
faces, or in the common cellular membrane. All the excretory
ducts are themselves, indeed, provided with an internal mucous
membrane, which is a continuation of the cutaneous, or mucous
surface on which they terminate. In addition to this they are
furnished with an exterior coat, formed of a dense and compact
membranous and fibrous substance. Every excretory duct may
therefore be considered as made up of these two coats, namely
the external one, which is membranous, and the internal one,
which is mucous.

509. Amongst the latest theories relating to the structure of
the organs of secretion, is that adopted by Muller,* who con-
ceives that the glandular organization consists essentially of a
modification of the excretory duct, the remote extremity of
which, or that most distant from the discharging orifice, is

* De Glandularum Secernentium Structura, &c. Lipsiae, 1830.

PROPERTIES OF THE SECRETIONS. 223

closed ;* and the particles of which exhibit a fine net-work, or
plexus of minute blood-vessels, whence the secretion is in the
first place derived, and afterwards conveyed away by the duct,
into the cavity of which it is poured. The duct itself may be
variously divided and subdivided; and its trunk and ramifica-
tions may be variously contorted and convoluted in different
cases, without, however, constituting any material difference in
its essential structure.

Sect. III. — Arrangement and Properties of the Secretions.

510. The classification of the various secretions which are
met with in the system has been attempted by different physiolo-
gists, but great difficulty has presented itself in fixing on a princi-
ple susceptible of being practically apphed to substances of such
different chemical and mechanical properties, as are those which
are to be the subjects of this arrangement. Haller,t adopting
for his basis their chemical qualities, distributed them under the
four classes of aqueous, mucous, gelatinous, and oily. Fourcroy
arranged them under eight heads ; namely, the hydrogenated,
the oxygenated, the carbonated, the azotated, the acid, the saline,
the phosphated, and the mixed.J Richerand adopts the six
classes of lacteous, aqueous, salivary, mucous, adipose, and
serous ;§ and Dr. Young those of aqueous, urinary, milky, albumi-
nous, mucous, unctuous, and sebaceous. ||

511. Dr. Bostockl distributes the secretions under the eight
heads of the aqueous, the albuminous, the mucous, the gelatinous,
the fibrinous, the oleaginous, the resinous, and the saline ; an ar-
rangement which, in a chemical point of view, is the clearest
and most natural that has yet been devised.** We shall briefly
notice these several classes in the order above stated.

* [This arrangement, sn far as regards the biliary system, was well shown
in a pathological case, which fell under the observation of Dr. Dunglison.» In
consequence of cancerous matter obstructing the common choledoch duct, the
whole excretory apparatus of the liver was enormously distended ; ihe common
duct was dilated to the size of the middle finger; at the point where the
two branches that form the hepatic duct emerge from the gland, they Avere
large enough to receive the tip of the middle finger, and as they were propor-
tionately dilated to their radicles, in the intimate tissue of the liver, their ter-
mination in a blind extremity was clearly exhibited. These blind extremities
were closely clustered together, and the ducts proceeding from them were
seen to converge, and to terminate in the main trunk for the corresponding
lobe.]

f Elementa Physiologiae, v. b. 2.

X Systeme des Connaiss. Chym. ix. 159. § Physiologie, § 8B. p. 235.

II Med. Lit. p. 109. <j[ Physiology, p. 480.

** [Other classifications have been founded on the nature of the secreting
organ, or the functions of the secreted fluid. Bichat, Magendie, Lepelletier,
and others, adopt the division into exhaled, foUicuhr, and glandular secre-
tions (See note to § 496). Boyer, Sabatier, and Adelon, divide them into

»Physiologj-, ii.28!.

224 NUTRITIVE FUNCTIONS.

1. The Aqueous Secretions.

512. The aqueous secretions are those which consist almost
entirely of water, and of which the properties depend principally
on its watery part; any other ingredient it may contain being in
too small a quantity to give it any specific characters. The two
secretions which are referable to this class are the cutaneous
perspiration, and the exhalation from the lungs.

513. With regard to the fluid of perspiration, it seems doubt-
ful whether it contains any ingredients that are constantly pre-
sent in it, or that are essential to its nature. It appears to differ,
indeed, considerably in difierent individuals ; and varies even in
the same individual, according to the state of the system. Its
analysis was attempted by Berthollet, and afterwards by Four-
croy ; but the most complete examination into its properties is
that of Thenard, who considers it to be essentially acid, and that
acid to be the acetic. He found in it, also, an appreciable quan-
tity of the muriates of soda and potass, with traces of the earthy
phosphates and of oxide of iron, together with a very minute
quantity of animal matter. Berzelius, on the other hand, who
has examined this fluid still more recently, finds the free acid to
be the lactic, accompanied with the lactate of soda. An elabo-
rate analysis of the fluid of perspiration in a person labouring
under disease, has also been made by Dr. Bostock.* The aqueous
exhalations from the lungs appears to be so perfectly similar to
that from the skin, as not to require further notice.

2. The Albuminous Secretions.

514. The albuminous class of secretions are numerous, and
comprehend both solid and fluid substances. We have already
seen that all membranous and fibrous textures, but especially the
latter, are composed principally of a material corresponding in
its chemical properties to coagulated albumen (see § 165). But
there are many fluid secretions which contain large proportions
of this ingredient in an uncoagulated, or liquid state ; such as the
secretion M'hich exudes from serous membranes, and also occu-
pies the interstices of the cellular texture, and which has been
termed the liquid of surfaces (see § 135). This fluid also con-

recrementitial secretions, or such as are taken up by internal absorption, and
re-enter the circulation"; and into excremenlifial, or such as are evacuated from
the body, and constitute the excretions. Some have added a third division;
the recreinento-excrementitial, in which a part of the humour is absorbed, and
the remainder ejected.]

* Medico-Chirurgical Transactions, xiv. 424.

PKOPERTIES OP THE SECRETIONS. 226

tains, besides coagulable albumen, an animal matter similar to
that which is tbund in the serosity of the blood, and a small
quantity of the usual saline matters which enter into the compo-
sition of almost all animal products.

3. Mucous Secretions.

515. The mucous secretions are characterised by the presence
of a substance which does not pre-exist in the blood, but which
is prepared by a proper secretory or glandular action. The
properties of this substance, or mucus, have been already noticed
(§ 301). To the head of the mucous secretions. Dr. Bostock is
inclined to refer also the saUva, the gastric and pancreatic juices,
the tears, and the semen.

4. The Gelatinous Secretions.

516. The gelatinous secretions derive their essential character
from the predominance of gelatin in their composition. This
substance is found in great abundance in most of the soUds, and
particularly in the nnembranous structures. It is strictly a pro-
duct of secretion ; for it is not met with in the blood, and must
therefore be formed by some chemical change in the elements of
the blood, from which the materials for its preparation are derived.
There is reason to believe, from the discovery of Mr. Hatchett of
the possibility of converting albumen into gelatin by digestion
in diluted nitric acid, during which the albumen combines with
an additional quantity of oxygen, that some change analogous to
this is effected in the Uving body during the process of its secre-
tion. The characteristic properties of gelatin have already been

' noticed (§279).

5. The Fibrinous Secretions.

517. The fibrinous secretions compose the fifth class, and are
so named from their correspondence in chemical properties to
the fibrin of the blood, which fibrin is probably the source from
whence these secretions derive this ingredient. They constitute
the organic products most completely animalized in their che-
mical constitution ; and they at the same time retain, in their
physical properties, the peculiar cohesive tendency and fibrous
character of the substance from which they are produced. The
muscular fibre is the principal, if not the only substance which
comes under this head.

226 NUTRITIVE FUNCTION?.

6. The Oleaginous Secretions.

518. The oleaginous secretions derive their essential character
from the presence of an oily ingredient. They compose a nu-
merous and varied class, comprehending those in which the oil
forms the greatest part of the substance, and those in which it is
more or less mixed with a large proportion of other animal prin-
ciples. The fat is the principal secretion included in the first
division; a substance which, from its being extensively deposited
ixi various parts of the body, must evidently be formed by some
peculiar action of the capillary system of vessels. As it consists
almost wholly of hydrogen. and carbon, we must conclude that
its formation is effected by the exclusion of nitrogen and oxygen
from the proximate elements of the blood, and the consequent
intimate combinations of their carbon and hydrogen. It is well
known, that the formation of fat, by whatever chemical operation
it may be effected, often proceeds with great rapidity, whenever
circumstances favour its production. The marrow, as was for-
merly observed, belongs also to this class of secretions. Dr.
Bostock is disposed to refer to the same head the substance termed
cholesterine, which forms the basis of biliary calculi.

519. Milk is a secretion owing its principal characters to the
oil which it contains, and which is combined with albumen, so
as to form a kind of natural emulsion. When collected in a
separate mass, it forms the well-known substance termed butter.
The oily particles are, however, in the "original state of milk,
merely diffused by mechanical mixture throughout the watery
fluid, as is evident from the appearance of milk under the micro-
scope, when it exhibits a multitude of extremely minute globules
swimming in a transparent liquor. The size of these globules
has been variously estimated by different observers, and indeed
appears to be by no means uniform, varying in different instances
from the 10,000th to the 5000th of an inch in diameter. These
oily globules have a tendency to adhere together when the milk
is allowed to rest, and in the course of a few hours collect at
the surface in the form of cream, and by further coalescence
they compose butter. The albumen 'may be obtained from the
remaining fluid by the ordinary means of coagulation, and con-
stitutes curd, which, as is well known, is the basis of cheese. The
clarified liquor which remains, yields, by evaporation, a saccha-
rine substance capable of being crystallized, and which is known
under the name of sugar of milk. It differs from common sugar
by being less soluble in water, and by its insolubility in alcohol.
Milk contains, besides these ingredients, several saHne substances,
as the muriate and sulphate of potass, the phosphates of hmeand
of iron, and also a peculiar animal matter, which yields a pre-
cipitate with infusion of galls. Milk is found to differ from the

PROPERTIES OF -THE SECRETIONS. 227

blood, and from most of the animal fluids, by the base of its salts
being potass instead of soda. A, peculiar acid, called the lactic,
is formed by the fermentation of milk, and even alcohol may be
obtained during this process. By the action of nitric acid on the
lactic acid, a new acid is produced, termed the sacc/iolactic or
rnucic acid, which unites readily with alkaline or earthy bases,
and forms a peculiar class of salts.

520. The substance of the brain bears a considerable analogy
to the oleaginous secretions, more especially to that of milk ; for
it consists of albumen intimately combined with a peculiar oily
ingredient. Rather more than one-fourth of its solid substance,
consists, according to Vauquelin,* of a fatty substance, and nearly
one-third of albumen; the remainder being composed of osmazome
phosphorus, acids, salts, and sulphur.

7. The Resinous Secretions.

521. The resinous secretions, which compose the seventh class,
derive their specific characters from an ingredient which is solu-
ble in alcohol, and is analogous to resin. Of these the most
remarkable is the substance which constitutes the basis, or specific
ingredient of bile. (See § 366.) ,

522. In connexion with the process of secretion which takes
place in the liver, we have here to notice the remarkable pecu-
liarity which occurs in the mode in which the blood is circulated
through that organ. The liver is supplied, like the other organs,
with arterial blood, by the hepatic arteries, which are branches
from the aorta. But it likewise receives a still larger quantity
of venous blood, which is distributed through its substance by a
separate set of vessels derived from the venous system. The veins
which collect the blood that has circulated in the usual manner
through the abdominal viscera, unite together into a large trunk,
termed the vena portce; and tiiis vein, on entering the liver, rami-
fies like an artery, and ultimately terminates in the branches of
the hepatic veins, which transmit the blood in the ordinary course
of circulation to the venae cavse.

523. This complex arrangement of the vessels which compose
the hepatic system has lately been unravelled with singular feli-
city by Mr. Kiernan, who, in a paper contained in the Philoso-
phical Transactions, gives an account of his valuable discoveries,
of which we shall present the following abstract. The hepatic
veins, together with the lobules which surround them, resemble
in their arrangement the branches and leaves of a tree, the sub-
stance of the lobules being disposed around the minute branches
of the veins like the parenchyma of a leaf around its fibres. The

* Annales de Chimie, Ixxxi. p. 37.

228 NUTRITIVE FUNCTIONS.

hepatic veins may be divided into two classes, namely, those con-
tained in the lobules, and those contained in canals formed by
the lobules. The first class is composed of interlobular branches,
one of which occupies the centre of each lobule, and receives
the blood from a plexus formed in the lobule by the portal vein ;
and the second class of hepatic veins is composed of all those
vessels contained in canals formed by the lobules, and including
numerous small branches, as well as the large trunks terminating
in the inferior cava. The external surface of every lobule is
covered by an expansion of Glisson's capsule, by which it is con-
nected to, as well as separated from, the contiguous lobules, and
in which branches of the hepatic duct, portal veins, and hepatic
artery, ramify. The ultimate branches of the hepatic artery
terminate in the branches of the portal vein, where the blood
they respectively contain is mixed together, and from which
mixed blood the bile is secreted by the lobules, and conveyed
away by the hepatic ducts which accompany the portal veins in
their principal ramifications. The remaining blood is returned
to the heart by the hepatic veins, the beginnings of which occupy
the centre of each lobule, and when collected into trunks, pour
their contents into the inferior cava. Hence the blood whiclj^
has circulated through the liver, and has thereby lost its arterial
character, is, in common with that which is returning from the
■other abdominal viscera, poured into the vena portas, and con-
tributes its share in furnishing materials for the biliary secretion.*'

524. The general conclusion which Mr. Kiernan draws from
his anatomical researches is, that the hepatic artery is destined
solely for the nutrition of the liver, and has no direct connections,
except with the branches of the vena portee, after its own blood
has become venalized.

525. Urea is another substance of a resinous nature, which
may be ranked among the secretions, and which constitues the
peculiar or specific ingredient in urine. It is remarkable for
containing a very large proportion of nitrogen, which is by this
channel discharged from the system. This substance has been

* [This is one view. Analogy, however, would suggest, that the bile, like^
every other secretion, is secreted from arterial blood ; and sufficient function,
it appears to us, remains for the vena porta, in being the agent for the admix-
ture of the various heterogeneous fluids, which are received into the stomach,
and pass by imbibition into the venous blood. Were there no capillary
system through which the veins of the stomach and duodenum had to pass
in their way towards the heart, these fluids would be but imperfectly mixed
with the blood, and would reach the central organ of the circulation in such a
state of concentration, as to interfere materially, perhaps fatally, with its
functions. The capillary distribution of the vena porta in the liver must
obviate this; and the same circumstances will aid us in accounting for induration
of the liver in the spirit-drinker. Light is thrown on the subject of 'he secre-
tion of the bile, by the pathological case referred to in the note to § 509.]

THEORY OF SECRETION. 229

found in the blood of animals from whom the kidneys had been
removed.

526. The peculiar proximate animal principle, termed by
Th6nard osmazome, is referred by Dr. Bostock to the class of
resinous secretions. It was procured originally from the muscu-
lar fibre, of which it forms one of the component parts ; and it
appears to be the ingredient in which the peculiar flavour and
odour of the flesh of animals principally depends. It is found,
however, in most of the component parts of the body, as well
solids as fluids. The cerumen, or ear-wax, appears also from the
analysis of Vauquelin, to have a relation to the resinous secretions.

8. The Saline Secretions.

527. This class comprehends all those fluids in which saline
ingredients predominate ; they are very numerous, are dispersed
over every part of the system, and are more or less mixed with
its constituents. They consist of acids, alkalies, and neutral and
earthy salts. The following are the acids entering into the com-
position of animal substances, and which are, for the most part,
united with alkahne or earthy bases ; namely, the phosphoric,
muriatic, sulphuric, fluoric, hthic, lactic, benzoic, carbonic, and
oxalic acids ; and perhaps also the rosacic and the amniotic. Soda,
potass, and ammonia, are found in almost all animal fluids ; but
only the first of these is met with in an uncombined state. Of
the earths, lime is by far the most abundant ; magnesia is found
in small quantity, and also silex.

528. With reference to their saline qualities. Dr. Bostock pro-
poses a division of the secretions into four classes. 1. Those
which are nearly without any admixture of salts. 2. Those
which possess a definite quantity of salts, and these salts different
from those which exist in the blood. 3. Those containing salts
similar both in their nature and quantity to those of the blood.
And, 4. Such as contain salts different from those in the blood,
and which are also variable in quantity. The fat, the sahva, the
liquor of surfaces, and the urine, may be given as examples of
each of these divisions.

Sect. IV. — Theory of Secretion.

529. The nature of the powers and processes by which the
products of secretion are prepared, is a subject involved in the
greatest obscurity. There is scarcely any question in physiology,
indeed, the investigation of which presents greater difficulties.
At the very outset of the inquiry we are embarrassed by the very
imperfect state in which the science of organized chemistry still

20

230 NUTRITIVE FUNCTIONS.

remains ; a^nd it follows as a necessary consequence, that the
precise nature of tiie chemical changes effected during secretion
cannot be properly understood. That the operations themselves
are of a chemical nature, must be inferred from their results,
consisting of substances which differ in most instances very con-
siderably from the constituents of the blood, whence their elements
are obtained. The blood is evidently the great reservoir of
nutriment, and the fountain whence all the materials of the
secretions are derived. In a few instances, as we have seen, the
process of secretion appears to consist simply of the separation
of some of the proximate principles of the blood. The operation
is, in that ease, more of a mechanical than of a chemical nature,
and is analogous to mere transudation or filtration, subject, how-
ever, to a certain power of selection exercised by the secreting
organ. In the greater number of instances, however, the product
of secretion appears to be a new formation, differing entirely
from any of the proximate principles contained in the blood, and
resulting therefore from a new combination of its elements.

530. Scarcely any light has been thrown on this mysterious
subject by the'anatomical investigation of the organs of secretion.
Their intimate structure is generally so minute and complicated,
as to elude the severest scrutiny of the anatomist, even when as-
sisted by the best optical instruments. What increases the diffi-
culty of finding any clue to the labyrinth, is, that we often see
parts having apparently very different structures giving rise to
secretions w^hich are nearly identical in their qualities ; and
conversely, we see substances having very different properties
produced by organs very closely resembling each other in their
structure.

531. Sometimes we find no distinct secretory apparatus, the
whole process appearing to be conducted in the capillary vessels,
out of the sides of which the product seems to transude. In
other instances, the secreted fluid exudes from the smooth surface
of a membrane, as is the case with the serous secretions in all
the closed cavitiefe of the body, such as those of the peritoneum,
pleura, pericardium, and pia mater. The matter of perspiration
finds its way through the skin and cuticle without any visible
ducts or even pores, appearing simply to transude through the
bibulous substance of the latter.

532. In other cases we find the secreting membrane furnished
with minute processes, or villi, from the extended surface of
which the secretion is produced. At other times, there are

follicles, or crypts, as they are called, into which the secreted fluid
is poured, and where it is collected previously to its discharge
by its appropriate channels. These minute cavities are occa-
sionally grouped together, and covered with a denser investing
membrane common to the whole assemblage, constituting the

THEORY OF SECRETION. 231

masses which are called glands. But no practical advantage
has arisen from the technical or anatomical classification of
glands, neither has any information of value been gathered from
the examination of the mode in which the blood-vessels are dis-
tributed in those organs ; although this mode of distribution is
apparently very diflerent in different cases, each seeming to be
intended for the application of some definite but unknown princi-
ple of action. Being wholly in the dark with regard to the
specific objects intended to be answered, we can form no ra-
tional conjecture as to the designs of nature in the contrivances
she has adopted. We see, in some instances, the smaller arteries
divide suddenly, as soon as they have reached the gland, into
very numerous minuter branches, like ihe fibres of a hair pencil.
This has been called the fencillated structure. The arrangement
in other cases is somewhat different, though similar in its princi-
ple ; the minuter branches spi'eading out from their origin, like
rays from a centre, and forming a stellated structure. Sometimes
we observe the arteries of the secreting organ much twisted and
contracted in their course, and collected into spiral coils, before
they terminate. All the varieties of secreting organs, as Mr,
Mayo observes, appear to be only contrivances for conveniently
packing a large extent of vascular surface into a small compass.
So intricate, indeed, are those complex arrangements, that it is
impossible to attempt to unravel them with any prospect of suc-
cess. In a word, nothing hitherto known relative to the structure
of glands has explained the mode in which they act, or has
thrown any light upon the nature of the substances they produce.
533. In this, as in other subjects, where facts are wanting for
its- elucidation, we find numberless hypotheses 'proposed in their
stead. Secretion was formerly pronounced to be a species of
fermentation, by those who could attach no definite idea to the
term they emploj^ed. Others sought to explain secretion by vari-
ous mechanical hypotheses, supposing it to be the result of a
mere organic filtration of particles already existing in the blood ;
they racked their imaginations for the invention of forms of
apertures and channels capable of admitting particles having
corresponding figures, and of refusing a passage to the rest.
Leibnitz compared the glands to filters, of which the pores were
originally impregnated with a particular fluid, which fluid would
therefore be allowed to pass, to the exclusion of all other fluids,
in the same manner as a paper impregnated with oil prevents the
passage of water, but allows oil to be transmitted. This unche-
mical theory proceeded on the hypothesis that all the secreted
matters pre-exist ready formed in the blood, and require only to
be separated by the glands ; a supposition of which the latter
improvements in animal chemistry have sufficiently exposed the
falsehood.

232 NUTRITIVE FUNCTIONS.

534. But even admitting the operation of the secretory organs
to be wholly of a chemical nature, we are still completely in the
dark as to the means which nature employ's in the hidden labora-
tories of organization; nor do they appear in any way reconcile-
able to the ordinary laws of chemical affinities to which inorganic
substances are obedient. The means employed are superior to
mere chemical agency, in the same degree as the operations of
chemical affinities transcend those of mechanism. All that we
can conceive to be the office of the different series of vessels,
which, by ramifying into smaller and smaller tubes, have the ef-
fect of subdividing the blood, as by a strainer, to certain degrees
of tenuity, is that merely of preparing it for the changes it is to
undergo in that stage of the process in which the essential con-
version consists. Farther than this we cannot venture to specu-
late, knowing, as we do, so imperfectly either the changes produ-
ced, or the means by which these changes can be effected ; unless,
indeed, we endeavour to call to our assistance the power of gal-
vanism, which has been, in modern times, proved to be so impor-
tant and powerful an agent in effecting changes of chemical com-
position. But the analogy is yet too vague to serve as the basis
of any solid theory.

535. There is no doubt that in many cases the process of secre-
tion is considerably influenced by the condition of the nervous
powers. Thus the section of the par vagum is invariably follow-
ed by the diminution or total suppression of the gastric juice, and
by the increase of the secretion of bronchial mucus. Under these
circumstances, the secretions of the stomach are restored by di-
recting a stream of galvanic electricity through the nerves that
have been divided; a fact which is explicable only in one of two
ways, namely, either by supposing that the galvanic influence is
the same as the influence derived from the nerves, or that galvan-
ism excites a fresh exertion of the nervous influence, in the por-
tion of the nerve on which its action is directed.

536. On the whole, as it appears impossible to refer the pheno-
mena of secretion to any of the other known laws of matter, whe-
ther chemical or mechanical, it becomes us to acknowledge our
ignorance of the real causes that produce them, and to ascribe
them to the agency of those powers to which we have given the
name of the organic affinities; by which term, however, we are
far from wishing to imply that these affinities essentially differ in
their kind from the ordinary chemical affinities which regulate the
coiTibinations of the same elements in unorganized bodies ; but
only that their operation is modified by the peculiarity of the cir-
cumstances in which they are placed. One of the principal causes
of this peculiarity appears to be the influence of the nermus power ;
a power carefully to be distinguished from the sensorial powers
hereafter to be considered, and wholly of a physical character

STRUCTURE OF THE ABSORRENT SYSTEM. 233

exercised by the nervous system, and controlling the actions
of the blood-vessel, and more especially of the capillaries, and
also those chemical changes which produce the evolution of ani-
mal heat, regulating in a particular manner the processes of secre-
tion, and in some instances producing the contractions of the mus-
cles in a v^'ay directed to some beneficial purpose, and in cases
where the interference of the mind does not take place. But of
this latter exercise of the nervous power we shall have to speak
more at large when we come to treat of the involuntary motions.

CHAPTER XL

ABSORPTION.

537. The objects of the function of absorption are, first, the
removal of those materials which have become unserviceable and
noxious from the situations where their presence is injurious ; and,
secondly, their transmission into the general mass of circulating
fluids. The lymphatic vessels are appropriated to this office, and
form, with the lacteals, which perform a similar service with
respect to the chyle, one extensive system of vessels denorni-
nated the ahsorhents.

Sect. I. — Structure of the Absorbent System.

538. The absorbent system, then, is understood to compre-
hend two sets of vessels, distinguished only by a certain dif-
ference in the office which they perform, but agreeing in their
structure and general functions. The first are the lacteals,
which, as we have seen, are appropriated to the conveyance of
the chyle, or nutritious fluid prepared in the intestines, into the
general reservoir of nutriment, the sanguiferous system. The
second are the lymphatics, which perform a similar office with
regard to the materials of the body itself, that have become
either useless or noxious, or with respect to foreign substances
applied to the external surface, or introduced into any part of the
body. The same general description, as to structure, will apply
to both these systems of vessels.

539. Absorbent vessels are met with in almost every part of
the body. They may be regarded as analogous, or even supple-
mentary in their office, to the veins; and, accordingly, their
structure and mode of distribution are very similar to that por-

20*

334

NUTRITIVE PITNCTIONS.

tion of the sanguiferous system. The absorbents arise from the
various surfaces of the body, external as well as internal, by very
minute branches ; but whether these branches commence by open
orifices, or imbibe the fluids they receive through the medium
of their coats, we have hitherto no certain knowledge. The
lesser branches of the lymphatics, like those of the veins, join
together to form larger branches ; while these again successively
unite into larger and larger trunks, till they conduct their con-
tents into the veins, into which they open. They communicate
with one another freely in their course; and these connexions
are frequently so numerous and intricate, as to form an extensive
net-work, or plexus of lymphatic vessels. They are furnished
with numerous valves, which, like those of the veins, are of a
semilunar or parabolic form, disposed in pairs, and placed so
as to prevent any retrograde motion of the contents of the ves-
sels.

540. Like the veins, the absorbents have thin and transparent
coats, which are possessed of considerable strength, so as to
admit of being distended much beyond their natural size, without
being ruptured, by injected fluids urged into them with considera-
ble force. When they are thus enlarged by injection, they
resemble a string of beads ; an appearance arising from the
numerous valves they contain, and which occur at short, but
generally unequal intervals.

541. The absorbent vessels are formed of two coats, which in
the principal trunks are very distinct from each other. The ex-
ternal coat is the one which constitutes the chief bulk of the ves-
sel, and gives it its general form. It is of a membranous struc-
ture, and is connected with the surrounding parts by a loose tissue
of cellular substance. It exhibits, where it joins the inner coat,
more or less of a fibrous structure ; and some anatomists have
pretended even to have perceived traces of muscular fibres at
this part. The interior membrane which lines the former, is more
thin and deUcate; and it is by duplicatures of this membrane that
the valves are formed. These valves are remarkable for their
strength, not being rupiured without the greatest diificulty.

542. The continuity of the course of the absorbents is interrup-
ted in a variety of places, by small rounded bodies, which have
been called lymphatic or conglobate glands, and which are situate
on the track both of the lacteals and lymphatics. They seem to
have a similar relation to the absorbents which the ganglia have
to the nerves ; and they have, on that account, been sometimes
called the lymphatic ganglia. They are of various sizes ; the
smaller being placed near the origin, and the larger on the more
considerable trunks of these vessels. Those of greatest magnitude
are situate at the root of the mesentery, in the course of the lac-
teals, and are denominated the mesenteric glands. These glands

STRUCTURE OF THE ABSORBENT SYSTEM. 235

are sometimes detached, and sometimes in groups or clusters, and
commonly of an oblong rounded shape, and somewhat flattened,
bearing some general resemblance to an almond. Their colour
is a whitish red, of more or less intensity, according as they are
situate more externally. Those of the mesentery are nearly white ;
those of the spleen brown: and those belonging to the lungs are
of a very dark, or almost black hue. Each gland is enveloped
in a thin, fibrous, and very vascular membrane, surrounded with
dense cellular tissue, which sends down processes into the sub-
stance of the gland, dividing it into numerous compartments.

543. It would appear from the extensive researches of Mascag-
ni, that every absorbent vessel, during its course, passes through
one or more of these glands. Previous to their penetrating into
the gland, each absorbent trunk branches out suddenly into nume-
rous subdivisions, distinguished by the name of vasa inferentia.
These vessels are distributed on the surface of the gland in a ra-
diating form, so as to surround it with a kmd of net-work. After
they have entered the gland, their course becomes extremely dif-
ficult to unravel, from their numerous and minute ramifications,
their tortuous course, and their frequent communications. It would
appear, however, that while some acquire and retain an extreme
degree of tenuity, others become dilated, and form cells, somewhat
resembling the erectile tissue formerly described. That portion
of the vessels which is destined again to collect the fluid, and con-
duct it forwards on its course, appears to have a similar structure,
presenting a congeries of minute ramifications, and of dilatations
or cells.

544. By the successive reunion of these branches, they are all
collected into a certain number of trunks which emerge from the
gland, under the name of the liasa efferentia. The total capacity
of the vasa efferentia is, in general, less than that of the vasa in-
ferentia. Large clusters of lymphatic glands exist in the neck,
the groin, the axilla, as well as in the course of the greater trunks,
not far from their termination in the thoracic duct.

545. The great trunks of the lymphatics occupy two principal
. situations ; the one near the surface, and the other more deeply

seated ; and for the most part they follow the course of the
veins. The main branches are finally reduced to three or four
great trunks, which terminate for the most part in the thoracic
duct. This is a vessel of considerable size, passing upwards close
to the spine, in a.somewhat tortuous course, to about half an inch
above the trunk of the left subclavian vein. It then bends down-
wards, and opens into that vein, nearly at its junction with the
jugular vein. Another similar, but shorter trunk, is found on the
opposite side, which pours its contents into the right subclavian
vein.

546. The nature of the lymph, or fluid contained in the lym-

236 NUTRITIVE FUNCTIONS,

phatic vessels, is but imperfectly known, in consequence of the
difficulty of collecting it in sufficient quantity for examination.
When viewed under the microscope it is seen to contain a num-
ber of colourless globules, much smaller and less numerous than
the red particles of the blood.* Mr. Brande separated a small
quantity of albumen from it by the application of voltaic elec-
tricity: he found that it also contained some muriate pf soda.
Berzelius states that the lactates are likewise present in it,
derived, as he supposes, from the decomposed substance of dif-
ferent parts of the body, which is taken up by the absorbents.
Reuss, Emmert, and Lassaigne obtained fibrin from the lymph
of the horse, and Nasse and Miillerf obtained some also from
human lymph. When removed from the body, this fluid fibrin
coagulates in less than ten minutes. Besides the above ingre-
dients, Tiedemann and Gmelin state that the lymph contains
salivary matter, osmazome, carbonates, sulphates, muriates, and
acetates of soda and potass, with phosphate of potass.

Sect. II. — Function of the Absorbents.

547. Whilst the office of the lacteals is confined to the absorp-
tion of a particular kind of fluid, namely, the chyle, the power
of the lymphatics extends to the removal of every species of
matter which enters into the composition of the body, as occa-
sion may require, as also various extraneous substances that may
happen to be placed in contact with their mouths. Whether the
lymphatics have the power of taking up solid materials of the
body without their being previously liquified, is a point which is
yet far from being determined. We are certain that the hardest
and densest structures, such as the bones, are liable to absorption,
in various instances, not only during the natural processes of their
formation ?nd growth, but also on occasions when they are
subjected to extraneous pressure. We find that the bones are
modelled by the pressure even of soft living parts, during their
natural growth, or morbid enlargement. The rapid disap-
pearance of the red tinge, which the use of madder in the food
had communicated to the bones, when that food is discontinued,
has been supposed to warrant the conclusion that the particles of
bones are at all times undergoing a quick periodical renova-
tion. But it appears from more recent inquiries, that this in-
ference has been too hastily drawn : the change of colour being the
result of the disappearance of the colouring particles of the mad-
der only, without its being at all necessary to suppose that the

* Miiller's Elements of Physiology, by Baly, p. 258. f Ibid. p. 259.

VENOUS ABSORPTION. 237

earthy particles of the bone are themselves changed, or succes-
sively absorbed and deposited along with the madder.*

548. The nature of the process by which the particles to be
absorbed are prepared for being taken up by the lymphatics ; the
mode in which they are conveyed to the orifices of these ves-
sels, if indeed they take their rise like the lacteals, by open
orifices ; and the power by which they find their way into these
vessels, and are conveyed onwards to their termination in the
thoracic duct ; are all subjects involved in the greatest obscurity.
Capillary attraction is the only power to which the rise of the
lymph in the lymphatic vessels appears to bear any near resem-
blance ; but the analogy is far too vague and remote to be of
much assistance to us in the solution of the difficulty. How far
the powers recently discovered, and which have been termed
endosmose and exosmose, whereby membranous substances allow
the transmission in a certain direction, of particular fluids only,
to the exclusion of others, are concerned in the phenomena, re-
mains a subject for future investigation. It seems likely, how-
ever, to throw some light on the processes both of secretion and
absorption ; and perhaps may furnish an explanation of the
selection evinced by the lymphatics in absorbing certain mate-
rials in preference to others. Absorption takes place with great
facility from the mucous surfaces, and also from those formed
by ulceration. It also takes place from the surface of serous
membranes, though with less activity. From the external surface
of the skin, absorption takes place with great difficulty, and only
under particular circumstances, as when substances ai-e forcibly
pressed through the cuticle. Considerable absorption often oc-
curs from the interior of the pulmonary air-cells. ■'' Absorption
from the surface of the body is diminished, or even suspended,
by greatly diminishing the pressure of the atmosphere on the
part, as by the apphcation of a cupping-glass.

Sect. III. — Venous Absorption.

I
549. Soon after the discovery of the lymphatic absorbents, a
keen controversy arose as to whether absorption was performed
exclusively by these vessels : for it was contended by many that
the veins assisted in this process, and occasionally acted as ab-
sorbinaj vessels. The arguments and reasonings of Hunter and
Monro, founded on numerous experiments, appeared to nave
completely decided the question, and established the exclusive
agency of the lymphatics in the performance of this function.

* See a paper on this subject by Mr. Gibson, in the Memoirs of the Literary
and Philosophical Society ot' Manchester. Second Series, i. 146.

238

NUTRITIVE FUNCTIONS.

Of late years, however, the ancient opinion has been revived by
Magendie and others, who seem to have satisfactorily proved
that absorption is occasionally carried on by the veins themselves;
and that many of the lesser lymphatic vessels terminate in the
small veins, instead of proceeding to the thoracic duct. It has
been ascertained, for instance, that where the great lymphatic
trunks are tied in animals, substances injected into the stomach
quickly find their way into the general mass of circulating blood,
and may be detected in the urine. Poison, introduced into a
portion of intestine, completely isolated from the rest of the body,
with the exception only of the artery and the vein, produces its
effect upon the system nearly in the same time as if the natural
connexions had been preserved. The same result takes place
when a limb is separated from the body, by dividing every part
excepting the artery and the vein, and the poison is introduced
under the skin. It proves fatal in the usual time, ahhough the
only medium through which its influence can be supposed to be
transmitted is the circulating blood, which must therefore, it is
concluded, have received the poison by venous absorption.

550. The subject of venous absorption, and of the connexion
between the lymphatic and sanguiferous systems, has of late
years much occupied the attention of physiologists. Great labour
has been bestowed on its investigation by Fohmann, Lauth, and
Panizza, on the continent ; and recently in this country by Dr.
Hodgkin, who was appointed, with others, to form a committee
for conducting this inquiry by the British Association for the
advancement of science. A short provisional report by this
gentleman is pubhshed in the report of the sixth meeting of that
association, in vol. v. p. 289, to which we must refer our readers,
as containing the latest information on this important branch of
physiology. Many facts render it exceedingly probable that the
contents, both of the lacteals and of the lymphatics, are inter-
mixed with that of the veins in the lymphatic glands.*

Sect. IV. — Effects of Absorption.

551. The absorbents have a powerful influence in modifying
the fluid secretions, as well as the solid materials of the body.
Their agency in assisting the arteries and capillaries which

* [A careful investigation of the whole of this interesting subject leads us
to infer, that the chj'liferous and lymphatic vessels form only chyle and lymph,
refusing all other substances with the exception of saline matters, which enter
probably by imbibition ; that the veins admit every liquid which possesses the
necessary degree of tenuity ; and that whilst all the absorptions, which require
the substances acted upon to be decomposed and transformed, are effected by
the chyliferous and lymphatic vessels, those that are sufficiently thin, and
demand no alteration, are accomplished directly through the coats of the veins
by imbibition. See Dunglison's Physiology, 3d edit. ii. 81.]

FUNCTION OF THE LYMPHATIC GLANDS. 239

effect the growth and nutrition of the body is beautifully exem-
plified in the processes of ossification and of dentition, where
the changes can more easily be followed than in the progressive
modifications of softer organs. All these facts lead to the con-
clusion that the absorbent vessels possess very extensive powers
in modelling the organization of the body in all its parts. In the
progress of life, various changes are efl^ected in the size and form
of different parts, either in the natural course, or from the effects
of disease. We see various organs diminish in size, sometimes
with great rapidity, from the general absorption of their sub-
stance, or, as it has been termed, from interstitial absorption ;
and in other instances from causes external to the organ affected,
such as pressure or ulceration ; in which cases the process is
denominated progressive absorption. In some structures, espe-
cially those which are but scantily furnished with vessels, the
renewal of particles is much slower than in more vascular parts ;
but even these are in a certain degree subject to a constant ab-
sorption and renewal of their particles.

Sect. V. — Function of the Lymphatic Glands.

552. Of the offices performed by the lymphatic glands, which
are so numerously interspersed in the course of the vessels, we
are still in profound ignorance ; an ignorance which is little to
be wondered at, when it is considered that we are but imperfectly
acquainted with their structure, and the course which the branches
of the absorbents take in the interior of those bodies, and that we
are also very much in the dark with regard to the nature of
glandular action, and of the changes which it induces on the
fluids subjected to its influence. These glands may either be
proper secreting organs, intended to prepare a peculiar substance,
which is to be mixed with the chyle and lymph, in order to assi-
milate them more and more to the nature of the blood with which
they are to be united; or they may, by their tortuous passages,
offer a mechanical obstruction to the progress of these fluids, and
thus occasion in them spontaneous changes in the arrangement
of their constituent parts. This latter view of the uses of the
glands was taken by Mascagni, and he endeavoured to confirm
it by pointing out differences in the nature of the lymph before
and after it had passed through a gland ; but this fact, if esta-
blished, would be equally explicable on either hypothesis. The
greater size and vascularity of these glands in youth, when the
growth of the organs is most rapid, would lead to the belief that
their functions are of importance in the elaboration of nutritive
matter to meet the greater demand for the materials of growth
at that period of life.

240 NUTRITIVE FUNCTIONS.

CHAPTER XII.

EXCRETION.

553. The expulsion from the system of those materials which
are useless or noxious, is the office of excretion ; and the organs
or channels by which it is performed are called the excretory or-
gans. They consist of the lungs, the skin, the kidneys, and pro-
bably also the liver.

Sect. I. — Excretory Function of the Lungs.

554. Of the office of the lungs in purifying the blood from its
redundant carbonaceous matter, we have already fully treated.
Besides carbon, or rather carbonic acid, a large quantity of water
is also exhaled by means of the lungs. As, however, there is
reason to beheve that considerable absorption of water also takes
place from the same surface, the amount of loss sustained by the
united operation of these two functions is only the excess of the
exhalation over the absorption. <

Sect. II. — Excretory Function of the Skin.*

555. We have already given the results of the chemical analysis
of the matter of perspiration, in our account of the aqueous secre-
tions (§ 514). The chief ingredient is unquestionably water ; and
the average amount of water which escapes from the body through
the channel of the skin, has been very variously estimated by dif-
ferent physiologists; for, indeed, it is hardly possible to arrive at
any definite conclusion on this subject, from the great variations
that occur even in the same individual at difiierent times, especially
according to the variable states of atmospheric temperature and
humidity, and also according to differences in the activity of the
circulation. The only satisfactory information we can hope to
attain is, as to the aggregate loss by exhalation from the skin and

* [MM. Breschet and Roussel de Vauzeme have described an apparatus in
the skin for the secretion of the sweat, consisting of a glandular parenchyma,
which secretes, and of ducts, which pour the secreted humour on the surface
of the body. These ducts are said to be arranged spirally, and to open very
obliquely under the scales of the epidermis. To this apparatus they apply
the epithet " diapnogenous," and to the ducts the epithet " sudoriferous" or
"hidrophorous."]

EXCRETORY FUNCTION OF THE KIDNEYS. 241

the lungs. The daily loss of weight from these two sources taken
together is stated by Haller* to vary from thirty ounces in the
colder climates of Europe, to sixty in the warmer, and is estima-
ted by Lavoisier and Seguinf at forty-five ounces in the climate
of Paris. But this quantity is, of course, from the causes already
mentioned, liable to extreme variation. It has been estimated
that, of the whole quantity thus exhaled from the skin and from
the lungs, about two-thirds are derived from the former source,
and one-third from the latter.

Sect. III. — Excretory Function of the Kidneys.

556. A considerable proportion of fluid is also carried off from
the system by the kidneys ; the peculiar office of which, however,
appears to be to eliminate more especially the saline materials,
which are to be thrown oft'; and, in particular, the peculiar sub-
stance termed urea, which, as we have already remarked > par-
takes much of the character of resinous bodies. As urea contains
a very large proportion of nitrogen, it is probable that the kidneys
are the channels provided in the economy for the removal of any
excess of this element which takes place in the system.

557. The chemical analysis of the urine has engaged the at-
tention of a great number of physicians and philosophers, not only
from its supposed connexion with various states of the body in
health and disease, but also from its containing a great multitude
of constituents, some of which have very peculiar properties.
Above twenty different substances have been detected as entering
into its composition ; and almost every year is adding to the list
of newly discovered ingredients. The existence of phosphorus
in this fluid has long been known ; and the urine was, till lately,
the only source whence this elementary substance could be pro-
cured in any quantity. Scheele discovered the uric or lithic
acid, which is one of the most remarkable of the animal products.
The labours of Fourcroy and Vauquehn led to the knowledge of
the exact composition of many of the neutral salts contained in
the urine. This analysis was carried still farther by Cruickshank
in England, and by Proust in Spain, but has been brought to its
present state of perfection chiefly by the labours of BerzeliusJ in
Sweden.

558. The daily quantity voided, as well as the sensible qualities
of this secretion, is greatly modified by circumstances. The
former has been estimated at an average as being about two pounds

* Elementa Physiologise, xii. 2, 11.

f Memoires de 1' Academie des Sciences, pour 1790, p. 601.
X Annals of Physiology, ii. 4-28.
21

242 NUTRITIVE FUNCTIONS.

avoirdupois.* Its mean specific gravity has been fixed at l-03.-|-
In a healthy state it generally exhibits acid properties, arising
from the presence of uncombined phosphoric, lactic, uric, benzoic,
and carbonic acids. These acids, together with the muriatic
and fluoric acids, also exist in combination with several . earthy
and alkaline bases, comprising ammonia, lime, magnesia, potass,
and soda; the principal compounds thus formed being the phos-
phates of lime and magnesia, ammonia and soda, the sulphates
of potass and of soda, the lactate of ammonia, the muriate of soda,
and the fluate of lime. There exist, besides, a large proportion
of urea (composing nearly one-thirteenth of the whole quantity
of urine, and about one-half of its solid ingredients), mucus,
gelatin, albumen, and a small portion of the unacidified sulphur.
The presence of a minute quantity of silica has also been detected
by Berzelius, amounting to about the 220th part of the solid
matter contained in the urine. The weight of the solid ingredients
obtained by evaporation is one-fifteenth of the whole fluid, the
rest being water. The several ingredients above mentioned
may each be rendered evident by the application of appropriate
tests.

559. Urea is a peculiar animal product, which is procured
from urine evaporated to the consistence of a syrup and allowed
to crystallize ; after which alcohol is added, which dissolves the
urea, whence that substance is obtained by evaporation. It then
appears in the form of crystalline plates, and has a light yellow
colour, a smell resembling garlic, and a strong acrid taste. It is
chiefly characterised by the bulky flaky compound which it forms
with nitric acid. By distillation it yields about two-thirds of its
weight of carbonate of ammonia: and by spontaneous decompo-
sition it is resolved into ammonia and acetic acid. It possesses
the very remarkable property of changing the form of ihe crys-
tals of common salt of muriate of soda, which, as is well
known, usually crystallize in cubical crystals ; but which, when
mixed with a small quantity of urea, assume the form of octohe-
drons. What adds to the singularity of this effect is, that its
operation is precisely the reverse on muriate of ammonia, or sal
ammoniac ; the ordinary form of the crystals of this salt are
octohedrons, but when urea is present, they take the form of
cubes. Urea contains a much larger proportion of nitrogen than

* [The estimates of observers vary; Boissier states the average daily
quantity to be tweniy-two ounces; Dr. Thomas Thomson fifty-three; and
Lining- from fifty-six to fifty-nine ounces. Perhaps the average in the text
is rather too small.]

t [This is probably too high. Its specific gravity of course varies according
to circumstances. Chossat estimated it from 1.001 to 1.038; Cruickshank
from 1.005 to 1.033; Prout from 1.010 to 1.015, Gregory .from 1.005
to 1.033 ; Elliotson, from 1.015 to 1.025; and Dr. Thomas Thomson found
%he average, during ten days, to be 1.013. Dunglison's Physiology, ii. 299.]

EXCRETORY FUNCTION OF THE LIVER. 243

any other animal principle. This substance has been found in
the blood, after its separation by the kidneys has been prevented,
by the extirpation of those glands. Berzelius has advanced an
opinion, that urea is furnished by the animal matter of the sero-
sity of the blood, from the similarity of some of its properties,
and also from the circumstance, that after the kidneys have been
removed, the animal matter of the serosity is first increased in
quantity, and afterwards assumes the character of urea. It
appears probable that the principal function of the kidney is the
separation from the blood of the excess of nitrogen which it
may contain, and its excretion in the form of urea ; thus per-
forming an operation with respect to this element analogous to
that of the lungs with regard to the superfluous carbon of the
blood.*

Sect. IV. — Excretory Function of the Liver.

560. Cholesterine, or the peculiar matter found in the bile, and
which composes about eight per cent, of that fluid, contains a
large proportion of nitrogen. Whatever may be its uses in con-
tributing to the formation of chyle, it is ultimately rejected from
the body, and may therefore be classed among the excrementi-
tious substances. We have already noticed the singular circum^
stance regarding the mode of its preparation, in being formed
from venous instead of arterial blood, as is the case with all the
other known secretions.

561. It is doubtful how far these two peculiar substances, urea
and cholesterine, may be considered as pre-existing in the blood,
or as formed by the organs which respectively secrete them. It
has been ascertained by the experiments of Prevost and Dumas,
that in animals in whom the secretion of urine is suppressed by
the removal of the kidneys, urea may, after some time, be
detected in the blood ; and Dr. Bostock ascertained that a simi-
lar substance makes its appearance in the human blood, in cases
where the secretion of urine had been much obstructed by disease
of the kidneys. The secretion from the liver is not liable to so
much variation in its amount, as that from the other excernent
organs; it is, however, diminished during febrile excitement and
inflammatory conditions of the circulation, and increased by
moderate exercise, and by external warmth. Both the liver and
the kidneys, accordingly, may be ranked among the compensa-
ting organs, or those which have their actions occasionally
increased in order to supply deficiencies in the functions of
others. The excretion of watery fluid from the skin and lungs

* See Berard, Annales de Chemie et de Physique, v. 296.

244 NUTRITIVE FUNCTIONS.

is evidently made to alternate with that fron:i the kidneys, each
of these organs being capable of occasionally supplying the
office of the others. The chemical properties of the urine are
very much influenced by the condition of the digestive functions.
But the necessity of the excretion of urea is apparent from the
rapidly fatal consequences which ensue from its accumulation
in the system, when the secretion from the kidneys is suppressed,
and which would lead to the conclusion, that this substance, when
present in sufficient quantity, speedily acts on the nervous sys-
tem as a virulent poison.

CHAPTER XIII.

NUTRITION.

562. Nutrition consists in the ayjpropriation of the materials
furnished by the blood in the course of circulation, and modified
by the processes of secretion, to the purposes of growth, and to
the repair of that waste which is continually experienced by the
solid structures of the body, in consequence of the exercise of
their respective offices. We understand as little what are the
particular processes by which these purposes are accomplished
as we do respecting those of secretion. No mechanical or
chemical hypothesis which can be devised appears at all ade-
quate to the solution of this mysterious problem. The analogy
of crystallization, implied in the celebrated definitions of Linnasus,
in which the three kingdoms of nature are contrasted, is, in a
philosophical point of view, utterly fallacious. According to
this great naturalist, " minerals grow, vegetables grow and live,
animals grow, live, and feel." It requires no lengthened argu-
ment to show that the growth of an animal, or of a plant, is a
phenomenon belonging to a class entirely different from the
increase of a mineral body. The latter is effected \)y the succes-
sive accretion of new layers of materials, which merely augment
the volume of the body, without adding to it any new properly;
so that the separation of its parts destroys only the form of the
aggregate, and not any of its essential qualities. But organized
bodies are nourished from internal resources, and the materials
which are incorporated with their substance have undergone a
slow and gradual elaboration in the organs themselves, and have
been assimilated to the qualities of the body of which they are
to form a component part. We may consider them as the result
of the operation of the organic affinities, to which we have
already referred the phenomena of secretion.

OSSIFICATION. 245

563. The only general fact of importance which has been es-
tablished with regard to the succession of phenomena in this func-
tion, is, that the enlargement of any organ appears to depend es-
sentially on the state of the circulation, in that part, and on the
supply of blood by its arteries. The increased growth of a part
at any period, compared with that of neighbouring parts, is always
preceded and accompanied by a marked enlargement of the
arteries which furnish it with blood ; and this is invariably obser-
ved, whether that growth be natural or morbid. A theory has
been advanced, that nutrition is effected by the direct union of
the red particles of the blood, or of their nuclei, with the tissues.
This theory is successfully combated by Miiller.*

564. Although we are unable to trace the exact nature of the
processes of nutrition, yet much curious information may be col-
lected by observing the succession of phenomena in the case of
the formation of particular structures. Those, which we shall
select for the purpose of illustration, are the bones and the teeth,
in which the several stages of growth admit of being observed.

Sect. I. — Ossification.

565. The process of ossification is particularly interesting, from
its exhibiting the operations of nature in the completion of an ela-
borate structure of such great importance in its mechanical rela-
tions to the system, as the osseous fabric. In the early periods
of the foetal state, we can but just trace the figures of some of the
larger bones, which appear to be modelled in a soft gelatinous
matter contained in a delicate membrane. This substance, as
well as its membrane, acquires greater density, and the form
assumes more the appearance of cartilage. In process of time,
opaque white spots are perceived on different parts of its surface,
which, when examined by the microscope, exhibit a fibrous appear-
ance. These lines increase in number and extent ; and, after a time,
red points are seen dispersed throughout the future bone, in conse-
quence of the enlargement of the vessels which now admit the red
globules of the blood. Soon after this, we find the earthy matter
deposited in great abundance, imparting hardness and rigidity to
the structure. In the long bones of the extremities, the osseous
substance forms at first a short hollow cylinder, as if it were
deposited from the vessels of the investing membrane, or perios-
teum. In the flat bones of the cranium, ossification commences
froni a few central points, and spreads on all sides, the fibres
taking a radiating direction. In proportion as the bony material
extends, the cartilage is removed by the absorbent vessels, in order

• Elements of Physiology, translated by Baly, p. 359.
21*

246 NUTRITIVE FUNCTIONS.

to make room for the extension of the bone. After a certain
time, in the cylindrical bones, a cavity is formed in the middle, in
consequence of the absorption of central portions of cartilages and
of bone which had occupied that situation. These two opposite pro-
cesses of absorption and deposition continue during the whole of
the future growth of the bone, the interior parts being removed in
proportion as fresh bony layers are added at the exterior surface.
Thus, when the outer part of the bone is compact and hard, the
interior is either formed into a complete cavity, or into the can-
cellated structure formerly described.

566. Such are the few well ascertained known facts relative
to ossification ; but numberless have been the speculations to

^ which they have given rise. Most of the opinions of the ancients
on this subject were extremely vague and hypothetical, and have
been fully refuted by modern physiologists. Many of the hypo-
theses of the latter have undergone a similar fate. The one
which has acquired most celebrity is that of Duhamel, who, fol-
lowing the analogy of the growth of trees, conceived that the
bones were formed of concentric rings, or laminae, deposited
from the periosteum. He endeavoured to adduce in support of
his theory the results of experim.ents in which bones acquired a
red tinge, when madder vufes given with the food. He alleged
that when the madder wew occasionally intermitted, and again
resumed, many times in succession, the bones of the animal ex-
hibited alternate rings of a red and white colour, corresponding
to the periods when the animal had taken madder, and had in-
termitted it. It has since been shown, however, that his ima-
gination in this instance must have misled him ; for no such result
takes place under the circumstances he describes,

567. The reparation of fractured bones by the powers of the
constitution is a striking instance of the beautiful provisions of
nature for remedying injuries accidentally occurring to the body.
The fractured ends are quickly united by li bony substance called
callus, formed in a manner very similar to that by which the
bone itself is originally constructed. The arteries near the seat
of the injury pour out a kind of lymph, which coagulates, and is
either gradually converted into cartilage, or replaced by carti-
lage after it has itself been absorbed. The deposition of phosphate
of hme then takes place within this cartilage, which is either re-
moved or adapted to its reception, and thus the ends of the bone
are cemented together, and the limb rendered as firm as before
the accident.

Sect. II. — Dentition.

568. No less curious and interesting is the process employed
in the formation of the teeth. The rudiments of every tooth,
when examined in the foetus, consists of a gelatinous pulp, which

NUTRITION OF THE SQFTER TEXTURES. 247

is extremely vascular, enclosed in a' double investment of mem-
brane. The outer membrane is soft and spongy, and is appa-
rently destitute of vessels ; while the inner one is firmer, and
extremely vascular. The first depositions are those of bony
matter, which take place on the exterior surface of the vascular
pulp, and chiefly on the upper part, but within the membranous
coverings already noticed. The shell of bone thus formed has
the shape of the future tooth, and acquires thickness from suc-
cessive deposits of bone in its inner surface, which are still made
by the outer surface of the vascular pulp. When the ossification
is sufficiently advanced, the pulp which has thus served as a
mould for the tooth, divides itself into two or more parts, cor-
responding to the intended number of fangs, so that the ossific
matter is now deposited in the form of as many tubes round these
portions of the pulp, and growing in a direction towards the jaw,
forces the tooth in the contrary direction ; thus ip the lower jaw
the tooth rises, and in the upper jaw it descends. The enamel is
deposited after the body of the tooth is considerably advanced in
its formation. It is the product of a secretion from the inner
surface of the outermost of the two membranes, which form the
capsule of the tooth, and the materials deposited from it adhere
strongly to the bony crown of the tooth which they surround.
This secreting capsule has been called the chorion by Herissant,
who has given an accurate description of the process of denti-
tion. Layer after layer of enamel is thus deposited, till the
growth of that part of the tooth has been completed ; then the
chorion shrivels and is absorbed, and the tooth still continuing to
grow at the root, pierces the gum, the resistance of which has
been gradually diminishing by the absorption of its substance.

Sect. III. — Nutrition of the Softer Textures.

569. Greater difficulty exists in following the succession of
changes which attend the growth and nutrition of the softer
textures, than of those we have now considered, because the ma-
terials employed in their construction are less distinguishable by
the eye from the other animal substances, and their changes are
less easily traced, than those exhibited by the calcareous deposits
of the osseous fabric.

A question here presents itself, of great importance with rela-
tion to our knowledge of the nature of the vital powers, but of
which the solution is attended with the greatest difficulties. It
is this : how^ far, it may be asked, are the powers of secretion
exerted in merely separating from the blood those organic pro-
ducts which are already contained as ingredients of that fluid,
and how far do they also extend to the actual formation of new

248 NUTRITIVE FUNCTIONS.

1

proximate elements; and next, what reason is there to believe
that the vital powers are capable of producing, from the mate-
rials presented to them, originally derived from the food, or the
atmosphere, any quantity of those chemical substances, which,
never having hitherto been decomposed, must, in the present
state of the science, be regarded as elementary?

The consideration of the chemical analysis of the blood, and
of the substances prepared from it will suffice to show that most,
if not all the secretions, may very possibly be produced solely
by the operation of ordinary chemical affinities. It has been
found, indeed, that we are able, by certain chemical processes,
to form from the blood, out of the body, substances similar to
many of the secretions; and we are therefore warranted in the
supposition that operations of the same kind are carried on by
the secreting organs within the body. It is interestng, however,
to trace the orig,in of many of the products of the secretion, from
the ingredients contained in the blood itself. On this subject
Muller*' remarks, that some of the proximate elements of the
tissues exist in part ready formed in the blood. The albumen
which enters into the composition of the brain and glands, and
of many other structures, in a more or less modified state, is
contained in the blood ; the fibrin of the muscles and muscular
structures is the coagulable matter dissolved in the lymph and
blood ; the fatty matter, which contains no nitrogen, exists in a
free state in the chyle; the azotised and phosphoretted fatty
matter of the brain and nerves exists in the blood combined with
the fibrin, albumen, and cruorin. The iron of the hair, pigmen-
tum nigrum, and crystalline lens, is also contained in the blood;
the silica and manganese of the hair, and the fluor and calcium
of the bones and of the teeth, have not hitherto been detected in
the blood, probably from their existing in it in but very small
proportion. The' matters here enumerated are attracted from
the blood by particles of the organs analogous to themselves,
partly in the state .in which they afterwards exist in the organs ;
in other instances, their ultimate elements are newly combined
in them, so as to form new proximate principles; for the opinion
that all the component elements of the organs exist previously in
the blood in their perfect state, cannot possibly be adopted ; the
components of most tissues in fact present, besides many modifi-
cations of fibrin, albumen, fat, and osmazome, other perfectly
peculiar matters, such as the gelatin of the bones, tendons, and
cartilages, nothing analogous to which is contained in the blood.
The substance of the vascular tissue, and also the different glan-
dular substances, cannot be referred to any of the simple compo-
nents of the blood. Even the fibrin of muscle cannot be consi-

* Physiology, &c. p. 361.

GENERAL PHENOMENA OP NUTRITION.

249

dered as exactly identical with the fibrin of the liquor sanguinis.
Between coagulated fibrin and coagulated albumen, there is
scarcely any chemical difl^erence, except in their action on
peroxide of hydrogen; the only very important distinction be-
tween the fibrin dissolved in the blood and the albumen is, that
the former coagulates as soon as it is withdrawn from the
animal body, while the latter does not coagulate spontaneously,
but requires a heat of from 158° to 167° Fahr., or some chemical
agents, such as acids, concentrated solutions of fixed alkali, or
metallic salts ; and the fibrin of muscle in its chemical characters
has scarcely a greater analoijy with coagulated fibrin, than with
coagulated albumen. In its vital properties the fibrin of muscle
differs from both. The comparison of nervous substance, again,
with the fatty matter containing nitrogen and phosphorus, is only
justified by the present imperfect state of organic chemistry.

The blood, as Dr. Bostock* observes, is a substance, the com-
position of which is peculiarly well adapted to undergo the change
necessary for the processes both of secretion and of nutrition, as
it consists of a number of ingredients, which are held together by
a weak affinity, liable to be disturbed by a variety even of what
might appear the slightest causes. As examples of the facility
with which these changes may be effected, we may cite the
numerous reagents which have the power of coagulating albumen;
the action upon it and upon fibrin of dilute nitric acid, which
converts these substances respectively into adipose matter and
jelly, changes which are probably the result of the addition of
oxygen to the fibrin and to the albumen ; and there is some reason
to believe that by applying the same reagent to the red particles,
we may obtain a substance nearly resembling bile.

With regard to the formation of the saline secretions,! and of
those substances, the elements of which are not to be found in
the blood, or at least not in sufiicient quantity to account for the
great accumulation that takes place in certain parts of the system,
and of which the source is not apparent, we must confess that
the present state of the science aitords no means of explaining
the phenomena. " To suppose," as Dr. Bostock justly remarks,
" that we are affording any real explanation by ascribing it to the
operation of the vital principle, or to any vital affinities, which
is merely a less simple mode of expressing the fact, is one ot
those delusive attempts to substitute words for ideas, which have
so much tended to retard the progress of physiological science."

Sect. IV. — General Phenomena of Nutrition.
570. The instances we have above given of the processes

* Elementary System of Physiology, p. 518. t ^^^^- P- ^32.

250 NUTRITIVE FUNCTIONS.

employed in ossification and dentition, together with the varied
operations concerned in the formation and nutrition of all the
softer textures of the body, forcibly illustrate the beneficent care
displayed in the construction of every part of the frame, and the
admirable adjustment of the long series of means which have
been provided for the attainment of these diversified and fre-
quently remote objects of the animal economy. Every part
undergoes a continued and progressive change of the parti-
cles which compose it, even though it remain to all outward
appearance the same. The materials which had been united
together by the powers of nutrition, and fashioned into the several
organs, are themselves severally and successively removed and
replaced by others, which again are in their turn discarded, and
new ones substituted in their place, until, in process of time,
scarcely any portion of the substance originally constituting the
organs remains as their component part.

571. We see from the examples of the bones, that this con-
tinual renovation of the materials of the body takes place in the
most solid, as well as in the softest textures; and so great is the
total amount of these changes, that doubts may reasonably be
entertained as to the identity of any part of the body at different
epochs of its existence. The ancients assigned a period of seven
years as the time required for the complete renovation of all
the materials of the system, but perhaps this entire change may
take place during a shorter interval.*

572. The two functions we have been considering, namely,
nutrition and absorption, may be regarded as antagonist powers,
each continually counteracting the effects of the other. In the
early periods of life, though both are in full activity, the former
predominates ; all the organs enlarging in their dimensions by the
addition of fresh materials in greater quantity than the losses by
absorption, the whole body is in a state of growth. In the course
of time, the frame having attained its prescribed dimensions,
these opposite processes of reparation and decay approach nearer
to an equality ; and at length are exactly balanced. The parts
then cease to grow, and the system may be said to have reached
its state of maturity. This is the condition of the adult, in which
the equilibi'ium of the functions is maintained for a great num-
ber of years. At length, however, the period arrives when
the balance, hitherto so evenly kept, begins to incline, the reno-
vating powers of the system are less equal to the demands made
upon them, and the waste of the body exceeds the supply. It
contracts in its dimensions ; it has attained its period of declen-
sion, which marks the progress of age, and ultimately leads to

* See the Article Age, in the Cyclopaedia of Practical Medicine, vol. i.
p. 34.

SENSORIAL FUNCTIONS — GENERAL VIEWS. 251

decrepitude. The fabric then betrays unequivocal symptoms
of decay, the functions are imperfectly performed, the vigour of
the circulation flags, the flame flickers in the socket, and is finally
extinguished in death. Thus is the whole duration of life, from
the first development of the germ to the period of its dissolu-
tion, occupied by a series of actions and reactions, perpetually
varying, yet constantly tending to definite and salutary ends.

573. We have now concluded the account we proposed to
give of the long series of functions which maintain the various
organs of the system in that mechanical condition and chemical
composition fitting them for the exercise of their several offices
in the economy. We have next to enter into the consideration
of the higher order of functions connected with the nervous sys-
tem.

CHAPTER XIV.

THE SENSORIAL FUNCTIONS.

Sect. I. — -General Views.

574. The functions we have hitherto considered, however
admirably contrived, and beautifully adjusted, are calculated
only for the maintenance of a simply vital existence. All that
is obtained by their means is a mass of organized materials, which
lives, which is nourished, which grov/s, which declines, and which
perishes in a certain definite period, by its mere internal mecha-
nism. But these can never be the real ends of animal existence.
Sensation, voluntary motion, pleasure and pain, together with all
the intellectual operations to which they lead, these must be the
proper objects of animal life; these the purposes for which the
animal was created. In man we find the extension of these
latter faculties to an extraordinary degree, and the addition of
moral attributes which elevate him so far above the brute crea-
tion, and place him one step nearer to that divine essence after
whose likeness he was made.

575. The functions of sensation, of voluntary motion, and of
thought, are those which establish our mental connexions with
the external world; which enable us to acquire a knowledge of
the existence and properties of the material objects that surround
us ; which awaken in us the operations of our own minds ; which

252 SENSORIAL FUNCTIONS.

bring us in communication with other intellectual and sentient
beings, and which enable us to react on matter, to exercise over
it the dominion of the will, and to influence the condition of those
other beings which like us have received the gift of hfe, of sen-
sation, and of intellect.

576. Throughout the whole of the inquiries in which we are
about to engage it is important to keep steadily in view the
essential and fundamental distinction between mind and matter.
Of the existence of our own sensations, ideas, thoughts, and voli-
tions, we have the highest degree of evidence that human know-
ledge can admit of, — that of our own consciousness. Of the
existence of matter, that is, of causes foreign to our own mind,
but acting on it, and giving rise to sensations, which are strictly
mental affections, we have merely a strong presumption ; still,
however, the belief in the existence of those causes, however
irresistibly it may operate in producing in us convictions, and in-
fluencing our actions, is yet but an inference from the regularity
in the succession of our sensations. We are not justified in
saying that it is impossible we can be deceived in this belief;
whereas in the consciousness of our mental existence we can-
not possibly be mistaken, because that consciousness implies the
very fact of our existence.

577. It is, however, most true, that notwithstanding our ideas
of mind and matter are such as wholly to exclude our conceiving
any property to belong to both of them in common ; yet some
inscrutable link of connexion has, in our present state of exist-
ence, been established between them, so that each may, under
certain circumstances, be affected by the other. External matter
acts on our bodily organs, which are still mere matter; but
our bodily organs act on our minds ; and our minds in turn react
on our bodily organs, and occasion movements which enable us
to act on extraneous objects. Moreover, it is impossible for us
ifi our present state to carry on any intellectual operation, but by
the instrumentality of our material organs ; we can neither feel,
nor think, nor will, without the healthy condition of the brain,
and all the other physical conditions which such a state implies.
Disturbance of the physiological functions of the brain is invari-
ably attended by a disturbance of the mental operations connected
with those functions. Both are excited by certain states of the
circulation in the brain ; both are instantly suspended by pressure
upon that organ ; both are restored by the removal of the pres-
sure, or other disturbing cause.

578. The nervous system is the name given to that assemblage
of organs which perform the important functions of which we
are now speaking. The primary office of the fibres composing
that system appears to be to transmit certain affections, which
we may call impressions, from one part of that system to another ;

SENSORIAL FUNCTIONS — GENERAL VIEWS. 253

and more particularly to convey thenn both to and from that
particular part of the brain, the aflbctions of which give rise to
sensation, and accompany our mental operations. In the one
case, the impression made on one extremity of a nervous fibril,
adapted to receive such impression, in a part called an organ
of sense, is propagated to the part of the brain above described,
and to which the name of sevsorium has been given, and
thereby producing a certain physical effect, the nature ^f
which is wholly unknown ; sensation, which is a mental effect,
ensues. In another case, the fibres of the brain are by their ac-
tion instrumental in retracing, in combining, in modifying these
impressions, and forming them into ideas, which are linked to-
gether by the laws of association. Again, the mental act we
term volition, and of which we are always conscious, affects
some particular fibres or portion of the sensorium, the impres-
sion made upon which is followed by an affection of certain
nervous filaments proceeding from those parts of the brain, and
conveying an influence, (which for want of a more specific term
we may also call irritation) to the muscles in which these nerves
terminate; and this is immediately follow^ed by the contraction
of those muscles. This constitutes voluntary motion.

579. But the office of the nerves extends yet farther. Various
muscles subservient to many of the vital functions, such as tlie
heart, the stomach, and the intestines, act without any interfer-
ence, or even control of the will. They compose the class of
involuntauj muscles ; yet these muscles are supplied with nerves,
and have a certain dependence on the nervous system, which is
of a very peculiar kind, and will be considered afterwards. These
nerves supplying the involuntary muscles, appear to have the
office of establishing connexions between the actions of these
muscles, and of uniting the various organs of the different func-
tions into one connected harmonious whole.

580. Thus the various phenomena which relate to the nervous
system in the performance of the functions we are considering,
will arrange themselves under the following heads, according to
the natural order of their sequence :

First, the impressions made by external objects on the sentient
extremities of the nerves distributed to the organs of sense, through
the medium of those organs. Secondly, the transmission of the
impressions so made to the sensorium, through the medium of the
nerves of sensation. Thirdly, the physical changes made on the
sensorium. Fourthly, the mental change consequent on this phy-
sical change in the sensorium ; which mental change is termed
sensation ; and in experiencing which the mind is wholly passive.
Fifthly, the recurrence, associations, and combinations of the
phvsical changes originally induced in the sensorium, but probably

22

254 SENSORIAL FUNCTIONS.

extended through various parts of the substance of the brain, and
simultaneous with various mental operations, in exercising which
the mind is partly passive and partly active. Sixthly, the mental
act denominated volition, which is accompanied with conscious-
ness, and in which the mind is wholly active. Seventhly, the
corresponding change induced by volition on the sensorium, or
origin of the nerves of voluntary motion. Eighthly, the trans-
mission of the impression so received by the nerves of voluntary
motion, to the muscles on which they are distributed. Ninthly,
the contractions of these muscles, constituting voluntary motion^
Tenthly, the influence of the nerves on the muscles of involuntary
motion, and on various functions apparently depending on invo-
hmtary actions.*

Sect. II. — Organization of the Nervous System.

581. The nervous system comprises organs of a curious and
complicated structure, and which are of the highest importance
in the animal economy. Their study is exceedingly interesting,
whether they be viewed as instruments of sensation, as sources
of action, or as the medium of connexion between the body and
the mind. This system is composed of a considerable mass of
a soft pulpy substance called the brain, which occupies the cavity
of the skull; a prolongation of this substance filling the canal of
the spine, and called the spinal cord, or spinal marrow ; and
of various processes in the form of cords, called nerves, which
extend from the brain and spinal cord, to almost all parts of the
body. There are found also interspersed in various parts along
the course of the nerves, small rounded or flattened bodies, called
ganglia, which also belong to this system of organs. All the
parts of this system are intimately related to each other, and
although they differ considerably in their general appearance,
they possess many characters in common. In point of structure
they present us with three different modifications ; the ^rst com-
prehending the substance of the central masses, which include
the brain and spinal cord ; the second, the nerves ; and the third,
the ganglia. We shall proceed to consider each of these in the
above order.

1. Organization of the Brain and Spinal Cord.

582. The brain, or general mass which fills the' cavity of the
skull, is composed of a number of parts of various shapes, the par-
ticular forms and dispositions of which belong properly to descrip-

* See Bridgewater Treatise on Animal and Vegetable Physiology, vol. ii.
p. 535, note. [Amer. edit. ii. 376.]

ORGANIZATION OF THE NEUVOUS SYSTEM. 255

live anatomy. It will be sufficient for our present purpose to state
that it is divided into three masses distinguished by the names of
cerebrum, which is by far the largest portion, and which occupies
the whole of the upper and fore part of the cavity of the skull ;
cerehelhim, or lesser brain, which is situate at the hinder and
lower part of the cerebrum ; and medulla ohlongata, which lies at
the central part of the base, or inner surface of the cerebrum,
and connects it with the cerebellum, and with the spinal cord.
All these parts, as well as the spinal cord itself, are formed of
two kinds of substance ; the cineritious, or ash-coloured substance,
which has also been called the corizca/ substance; and the white,
or medullary substance. These two substances ai'e variously
intermixed, sometimes forming strata of different thickness, and
sometimes the one enveloping separate portions of the other, in
different parts of the whole mass. There is a layer of cortical
substance placed on the outside of the cerebrum ; it does not
however form a smooth uniform plane, but is moulded into con-
volutions. In the cerebellum there is a similar superficial stratum
formed into concentric lamina). The convolutions are of con-
siderable depth ; and if any of them be cut through, they are
seen to consist of both cortical and niedullary substance. The
cortical forms a layer of considerable thickness ; and on looking
attentively on its divided edge, a very narrow lamina of medullary
substance will be perceived passing through it, and following it
through all its windings. This fact has been particularly noticed
by Dr. Baillie. The concentric laminae on the surface of the
cerebellum, are composed also of cortical and medullary matter.
By this arrangement, the quantity of cortical substance, as well
as the extent of its surface on the outer part of the brain, is very
much increased.

583. In the interior of the brain we find cavities of consider-
able size, termed ventricles, and bodies of regular, but various
shapes, presenting many different mixtures of two species of
matter. Where these bodies appear, from their outside, to be
formed of cortical substance only, on cutting into this, there is
found a considerable mixture of medullary matter ; and where
they seem, from their outside, to be formed of medullary matter
alone, they are discovered, on dividing them, to contain some corti-
cal substance in the interior. Thus there is no particular part of the
brain composed purely of the one kind of substance or the other;
although the proportions of each in the various parts may be very
different. A similar intermixture of cortical and medullary mat-
ter exists in the spinal cord ; but contrary to what takes place in
the large mass of the brain, the cortical part is placed in the
interior, and is enveloped by the medullary.

584. The medullary substance has generally been considei'ed
as constituting the most perfect state of nervous matter, or that

256 SENSORIAL FUNCTIONS.

which more especially exercises the functions of the nervous
system. Some physiologists, on the contraiT, consider the grey
substance as the seat or origin of nervous power; whilst the
fibres of the white substance act merely the part of conductors
of nervous influence from one part to another. This medullary
portion is obviously of a firm.er consistence than the cortical,
and contains fewer blood-vessels interspersed throughout its sub-
stance. Both the one and the other are almost perfectly homoge-
neous in their appearance. Ruysch had fancied that the cortical
substance was entirely composed of blood-vessels, connected by
cellular membrane; and in this opinion he was for a long time
generally followed, although the pulpy consistence it exhibits is
scarcely compatible with such a notion. Malpighi supposed that
he had detected in it a glandular structure; but this must also be
regarded as a mere hypothesis, unsupported by any substantial
evidence. The medullary matter presents traces of a fibrous
structure ; a fact which was first observed by Malpighi, and
which is particularly insisted on by Drs. Gall and Spurzheim ;
and notwithstanding the existence of such a structure is denied
by other eminent anatomists, it appears to have been sufficiently
established by the elaborate researches of Reil, a detailed account
of which has been given by Mr. j\Iayo.*

585. Anatomists are far from being agreed as to the minute
and ultimate structure of nervous matter. De la Torre asserts
that it consists of a mass of innumerable transparent globules
immersed in a transparent fluid : and that these globules are larger
in the brain than in the spinal marrow. Prochaska describes the
same globular structure, which he represents as united by a trans-
parent elastic cellular membrane disposed in fibres. Monro.f
in his first inquiries, thought that these fibres w'ere convoluted,
but afterwards acknowledged that he had been misled by an
optical fallacy, incident to the employment of high magnifying
powers. The WenzelsJ also recognized the globular composi-
tion of the nervous substance, and considered the globules them-
selves to be vesicles filled with a material either of a medullary
or cineritious appearance, according to the portion examined.
Bauer§ states that the globules are of about the same diameter
as the central particles of the globules of the blood, some,
however, being still smaller ; and that they are of a gelatinous
consistence, and soluble in water. The cineritious substance, he
finds, is composed chiefly of the smallest globuhs, surrounded
by a large proportion of a gelatinous and^ serous fluid. The
medullary substance, on the other hand, is formed principally by
the larger and more distinct globules which adhere together in

* In his Anatomical and Physical Commentaries.

t On the Nervous System. f De Structura Cerebri.

§ Philosophical Transactions for 1818, and 1821.

ORGANIZATION OP THE NERVOUS SYSTEM. 257

lines, and have a smaller proportwn of fluid, that fluid being more
viscid than in the r.ineritious substance. Dr. Edwards* has con-
firmed by his observations, these results, as far as the general
globular composition of nervous matter is concerned. He
asserts the diameter of the globules to be one three-hundredth
of a millimetre, which is equivalent to the seven thousand six
hundred part of an inch ; and that these globules are arranged
in hncar series, constituting the primary linear fibres. Beclard
states that he has verified these observations.!

2. The Nerves,

586. The nerves are white cords extending from different parts
of the brain and spinal cord, to different parts of the body, and
more especially to the muscles, the integuments, and other organs
of sense, and to the viscera and blood-vessels. Their general
form is cylindrical ; but they divide, in their course, into a great
number of branches, many of which again reunite, or are joined
with the branches of other nerves, so as to form in many parts a
complicated nervous net-work, or plexus, as it has been termed
by anatomists. The nerves are usually spoken of as originating
in the brain or spinal cord, and as proceeding from thence to their
termination in other, and generally distant parts. As the united
branches would form a cord of much larger diameter than the
trunk from which they arise, it is evident that the total quantity
of nervous matter they contain is augmented as they proceed in
their course. When examined with the microscope, their surface
presents a number of transverse lines or wrinkles, which are
evidently for the purpose of admitting of flexion ; and thus accom-
modating them to the difierent movements of the parts witli*which
they are connected.

587. The nerves appear to consist of filaments of medullary
substance, enclosed in a tough cellular membrane. At their origin
from the central organ, whether it be the brain or the spinal cord,
they consist of detached fibrils, sometimes isolated, but in general
arranged so as to constitute flat bands. There are two such bands,
namely, an anterior and a posterior fasciculus, which unite to
form each of the nerves arising from the spinal cord. Some
nerves are composed of pure medullary matter, as the optic nerve ;
but in the greater number this matter is so enveloped in a tough
cellular membrane, which has been termed by anatomists the
neurilema, that it cannot distinctly be perceived. In the olfactory
nerves there is an evident junction of cortical wdth medullary
matter, but in most others we find nothins; but filaments of medul-
lary matter, each of which is contained in a separate envelope
or neurilema, that forms tubes for their reception.

* Surla Structure Elementaire. j See his Anatomie Generals.

22*

258 SENSORIAL FUNCTIONS.

588. Many anatomists have attempted the investigation of the
minute structure of nervous fibrils by means of the microscope.
De la Torre* perceived in them globules similar to those of which
the matter of the brain is composed. Monrof and Fontana des-
cribe the nervous filaments as being connected by cellular sub-
stance, much in the same way as the muscular fibres, and arranged
like them in fasciculi of various sizes. They represent the ultimate
fibril- as being twelve times greater than the muscular fibre, hav-
ilig a serpentine or tortuous form, and being composed of a cylin-
drical canal, containing a viscid pulpy matter, evidently different
from the substance of the canal itself. Reil has pursued this
investigation with still greater care and minuteness, and states that
the ultimate filaments differ in thickness from that of a hair to the
finest fibre of silk. Their arrangement into larger and larger fas-
ciculi is analogous to what we observe in the structure of muscles,
but with this diflference, tliat the nervous fibres in their course
along the nerve, frequently divide and subdivide, and are again
variously united and conjoined, so as to produce an extensive
connexion among all the parts of the same nerve. The mem-
branous neurilema, besides giving support to each individual fila-
ment of nerve, and uniting them into fasciculi, furnishes also a
general covering to the whole nerve J

589. What has now been stated must be understood as appli-
cable to nerves in general. Many differences have been pointed
out in the structure of different nerves; but it is not necessary to
descend into these minute particulars in the general view we are
now giving.

3. Ganglia.

590. Ganglia are small rounded nodules, which are placed in
different situations in the course of nerves, sometimes in the
trunk of a single nerve, and sometimes where two nerves unite.
They are most numerous on those nerves which are distributed
to the viscera, and to the muscles of involuntary motion. Their
appearance is very different from that of a mere dilatation of a
nerve, being of a reddish-brown colour, having a minute fibrous
texture, a firmer consistence, and a greater number of blood-
vessels than ordinary nerves. The nerves which pass out from

* Philosophical Transactions for 1769. | On the Nervous System.

:|: [Ehrenberg and some other recent writers are of the old opinion, from
their microscopic researches, that the nerves are tubular. See Dunglison's
Physiolog-y, .3d edit. i. 86 ; and Miiller's Physiology, translated by Baly,
part 3, Lond. 1838.

For an excellent epitome of the recent researches of Ehrenberg, Berres,
Remak, Valentin, Emmert, Burdach and others — into the intimate structure
and distribution of the nerves— see the British and Foreign Medical Review,
No. XII. for Oct. 1838, p. 394, and No. XIV. for April, 1839, p. 394.]

THE EXTERNAL SENSES TOUCH. 259

a ganglion are generally of a larger size than those which entered
into it, as if they had received, in their passage through it, an
additional quantity of matter. It would appear, from numerous
observations, that the filaments of the different nerves which join
the ganglion proceed through it individually without interruption,
but are, at the same time, involved and twisted together in a very
complicated manner ; the result being, that filatnents from many
different nerves are united in the formation of a new nerve ; so
that the parts to which the nerve is distributed receive a supply
of filaments from many different sources, and are in very exten-
sive communication with various parts of the brain, spinal cord,
and indeed the whole nervous system.

591. Besides this junction and intertexture of nervous fila
ments, the ganglia contain a soft semi-fluid matter, which appears
to be analogous to the proper substance of the brain, and like
the latter, may be distinguished into cineritious and medullary
portions. It would appear, therefore, that the ganglia have some
peculiar office with regard to the nerves which traverse them,
and that they do not serve the purpose only of a plexus of fila-
ments, establishing mere mechanical connexions between them,
as some anatomists have alleged.

CHAPTER XV.

THE EXTERNAL SENSES.

592. The external senses have usually been reckoned five in
number, namely, touch, taste, smell, hearing, and sight; but this
arrangement has reference more to the organs by w^hich they
are exercised than to the nature of the sensations they excite in
the mind. A variety of sensations have been referred to the
sense of touch, which are wholly different in their kind, and
which are received by means of impressions made on the skin,
and also others which are conveyed by nerves in other parts of
the body, without any connexion with the skin. These we shall
notice after we have considered the sensations more peculiarly
belonging to the sense of touch.

Sect. I. — Touch,
1. Sensation of Pressure.

593. Every part of the surface of the body is exposed to the
contact of foreign bodies ; and in most parts of the skin very

260 SENSORIAL FUNCTIONS.

slight pressure made by those bodies gives occasion to the primary
sensation of touch, which is in fact simply that of resistance to
the part of the skin on which it presses. This sensation is quite
specific, and distinguishable from all other sensations. It may
be conveyed, though less perfectly, by several of the internal
surfaces of the body, as those of the mouth and pharynx. Cer-
tain parts of the skin possess, however, a more peculiar delicacy
of nervous sensibility to the impressions of touch, and are there-
fore to be considered as more especially the oi'gans of this sense.
In man the points of the fingers are particularly employed for
receiving the finer impressions of touch, and for distinguishing
the qualities of external objects, of which this sense is fitted to
convey us information. The greater vascularity of the skin of
the fingers, and greater development of its papillary structure,
have been assigned as the causes of the apparent increase of sen-
sibility with which they have been endowed. There is no doubt,
however, that much depends on the education given to the ends
of the fingers, by their constant employment in this office ; for
we find that the toes and other parts of the body may, by use,
be trained to the acquisition of an equal degree of sensibility ; of
this we see examples in individuals who have been born without
hands. Parts where the epidermis is very thin, such as the lips,
are also endowed with considerable sensibility to the impressions
of touch, and with the power of discriminating differences in
those impressions which cannot be felt or appreciated by means
of the fingers.

594. Professor Weber of Leipsig* has made a series of very
interesting experiments on the relative sensibilities of the skin in
different parts of the body, with reference more particularly to
its power of conveying to the mind accurate perceptions of me-
chanical impressions made upon it. He found this power pos-
sessed in the highest degree by the tip of the tongue and ends of
the fingers, the sensibility of which he estimated at eighty times
greater than that of the skin of other parts of the body. He ob-
served, also, that even the skin in different parts of the face,
when touched with the points of a pair of compasses opened to
a small distance, showed the greatest diversity in the power of
conveying distinct perceptions of touch#as to the object in con-
tact being single or double, and as to the distance between the
points, when they were perceived to be double.:

2. Sensations of Temperature.

595. The same organs which, when pressed by an external
body, convey the impression of resistance, communicate also

* An account of these researches is contained in the Edinburgh Medical
Journal, xl. p. 83.

SENSATION OF PAIN. 261

sensations of heat and cold, and nearly in the same relative pro-
portion. Thus, the fingers are more sensible to variations of
temperature in the bodies they touch than other parts of the skin
less accustomed to discriminate them. The lips are still more
sensible than the fingers to the diflbrences of temperature in the
bodies to which they arc applied. This peculiar sensibility aflbrds
a ready mode of distinguishing genuine diamonds and other
precious stones from such as are counterfeit ; for the former,
being better conductors of heat, produce a more lasting impression
of coldness when applied to the lips or to the tongue.

The sensations of heat and cold are, however, far from being
in exact proportion either to the actual temperatures of the bodies
which are in contact with the skin, or even to the differences
between their temperature and that of the skin. The actual
condition of the sensibility of the skin at the time, which depends
on a multitude of causes hereafter to be noticed, has a very con-
siderable influence on the sensations. The difference which is
observable in the sensibilities of the same part to the impression
of resistance, and to that of heat or cold, suggests a doubt whether
a different set of nerves may not be employed to transmit to the
brain these different kinds of impressions. We find in certain
states of disease, that the general sensibility of the surface of the
body may be much impaired, and yet it may preserve its sen-
sitiveness with regard to heat and cold; and it is also certain,
that differences of temperature produce sensations in parts, the
stomach for instance, which are wholly disqualified from com-
municating the feeling of resistance.

3. Anomalous Sensations.

596. Hunger and thirst are sensations referred to the mouth,
throat, and stomach, which are also quite specific in their nature,
though generally referred to the sense of touch.

597. The same observation applies to a variety of peculiar
sensations, many of which are common to the whole surface of
the body, and may even be felt in some internal parts, but which
it would be difficult to class, or even completely enumerate. The
sense of tingling and of itching are examples of this species of
sensations. The feeling of nausea is an undefinable sensation
referred to the stomach.

4. Sensation of Pain.

598. Every sensation thus referred to the sense of touch, when
it rises beyond a certain degree, is accompanied with the addi-
tional feeling of pain, which, if considerable, engrosses the whole
attention, and eftaces all marks of discrimination as to its origin.

262 SENSORIAL FUNCTIONS.

Pain is generally readily referred to a particular part of the body,
as being the origin, or as it is commonly called, the seat of pain,
especially when the part is external. But in internal parts, this
specific reference is often extremely vague and imperfect ; and
there frequently exists a general feeling of uneasiness, often more
intolerable than any other, and to which it is impossible to assign
any particular locality. It may also be observed, that in general
the actual sensibihty bears no relation to the capacity for feeling
pain.

599. A vast number of experiments were made by Haller,
with a view to ascertain the comparative sensibilities of the dif-
ferent textures and organs of the body. In general, those which
have but a small degree of vascularity, such as the cartilages,
tendons, hgaments, fibrous membranes, and bones, and even the
simple cellular texture, and serous membranes, in a state of
health, have a very obscure degree of sensibihty, when cut
across, pricked with a pointed instrument, or burned by a hot
iron. Yet many of these textures, though deficient in sensibihty
to these stimuli, are yet extremely sensible to injuries of another
kind, namely, forcible stretching, when applied suddenly and in a
'degree which endangers the integrity of their structure. This is
sufficiently illustrated by the acute pain that is attendant on a
sprain. Bones, also, though scarcely communicating any feeling
of pain when sawn through in the living body, yet feel acutely
the concussion produced by violent blows, as any one may be con-
vinced of who has suffered a blow on the knee. It is also re-
markable that all those parts, which are apparently so incapable
of sensation under ordinary circumstances, become highly sensi-
ble when in a state of inflammation.

600. The internal parts of most of the glands and other solid
organs, have but little sensibility ; and the chief source of pain,
when they are attacked with inflammation, arises from the affec-
tion spreading to the membranes which invest them. Inflam-
mation of the mucous membranes does not occasion any propor-
tionate degree of pain. Those parts of the body which receive
no blood-vessels^ as the cuticle and its appendages, the nails and
the hair, are absolutely insensible. The cuticle consequently is
well adapted to protect the highly sensitive organ which it covers,
and to blunt its sensibility.

601. Pain often arises from internal causes; from pressure, or
distension, or other mechanical or chemical irritation applied to
nerves ; or from some changes taking place in the texture of the
nerve itself. It will appear evident, on a general review of the
sensibihty allotted to the different organs of the body, that each
has received from nature that particular kind and degree which
is most needed, and which best accords with the relative import-

TASTE. 263

ance of its functions, and the dangers to whicii, in the ordinary
course of events, it is exposed.

5. The Muscular Sense.

602. A very important class of sensations has been referred
to the sense of touch, which require to be particularly distin-
guished from the rest ; they are those attending the contractions
of the voluntary muscles, which render us sensible of the move-
ments of our limbs, and of other parts which are voluntarily
moved. These are the feelings which give rise to the idea of
extension, and which, combined with the feeling of resistance,
communicate to us a knowledge of the forms, magnitudes, and
relative positions of external objects. Thus, by moving the hand
over the surfaces of bodies, we gain the ideas of their tangible
extension, together with most of their mechanical properties, such
as their roughness, hardness, weight, texture, and dimensions.
In these examinations we avail ourselves of the admirable pro-
perties of the hand, an instrument which, by the number and
variety of its parts, and the motions of which they are capable,
is exquisitely fitted for procuring us this useful kind of knowledge.
By the perceptions we acquire in infancy from the active employ-
ment of the limbs in various kinds of progressive motion, our
sphere of knowledge of the material world is prodigiously ex-
tended ; and these perceptions are an important source of gra-
tification, in consequence of the feelings of pleasure with which,
by the beneficent ordination of nature, the active exercise of the
voluntary muscles is accompanied.

603. The sense of touch, in the comprehensive view which
we have now taken of it, is unquestionably the most important
of all our external senses, bringing us more immediately ac-
quainted with the essential qualities of the material world, and
laying the great foundations of all the knowledge which the other
senses supply, by a reference to the ideas derived from touch.

Sect. II. — Taste.

604. It was the fashion among the French -metaphysicians to
resolve all the senses into that of touch; so that in speaking of
vision, for instance, they would allege that we see by means of
the light which touches the retina. But this is a mere refine-
ment not warranted by facts, and in which the real distinctions
existing among the sensations themselves are overlooked,

605. If any of the senses could be considered as a finer sense
of touch, it would be that of taste, by which we receive impres-
sions of a peculiar kind from the sapid qualities of bodies in

264 SENSORIAL FUNCTIONS.

contact with the upper surface of the tongue. This sense is
manifestly intended to guide us in the choice of our food, and it
is accordingly placed at the entrance of the alimentary canal.

1. Organs of Taste.

606. The principal organ of taste is the tongue, bu^several of
the neighbouring organs are auxiliaries in the exercise of this
sense. The soft parts of the mouth consist of the lips and cheeks,
the gums, the soft palate, the velum, uvula, tongue, the membra-
nous hning of the mouth', and the salivary glands. The osseous
parts are the upper and lower maxillary bon'es, the teeth, and the
palate bones.

607. The lips and cheeks are principally composed of muscles;
they are covered on the outside by the common integuments,
and lined within by the membrane of the mouth, in which are
situate numerous mucous glands. The membrane of the mouth
is covered with fine villi, which are most conspicuous on the
edges of the lips. A small doubling of this membrane is met
with in the middle of both the upper and under lips, which fixes
them more closely to the jaws. These doublings have been
termed ihefrcBua lahiorum. The union of the lips at the corners
of the mouth form what has been called the commissures of the
lips.

608. The gums, which surround, and firmly adhere to the col-
lar of the teeth, are very vascular, and composed of a dense and
compact cellular substance.

609. Thepa/afeis divided into the palatum durum, and palatum
molle. The former is composed of the palate plates of the upper
jaw, covered by periosteum, and by the membrane of the mouth,
which here forms numerous rugse. The soft palate, or velum
pendulum palati is the name of that membranous curtain which
hangs from the posterior edge of the ossa palati, and pterygoid
processes, and forms a flexible partition between the mouth '
and throat. It serves to conduct the fluids of the nose down-
wards, and at the same time acts as a valve in preventing the
passage into the nostrils of what is swallowed. In the middle
of the edge of the velum, a conical papilla, termed the uvula, is
met with, and in the relaxed state hangs pendulous over the root
of the tongue.

610. The tongue is a complex organ, principally consisting of
a mass of muscular fibres, irregularly disposed, and crossing each
other in a great variety of directions, and being also intermixed
with a soft kind of fat. It is invested by a mucous membrane,
being a continuation of that which fines the mouth generally, and
which here presents large and numerous papillcB. These papillae
are distinguished by anatomists into three kinds, according to

ORGANS OF TASTE. 205

their size, form, and situation. Tiic first class of these, called
papillce, maximce, lentlculares, or capitatce, are by much the
largest, have a lenticular form, with round heads and short stems.
They are placed at the base of the tongue, in superficial fossulee.
They have been regarded as auxiliary salivary glands, and have
each a perforation in the middle of their convex surface, for the
excretion of mucus. The second class, or papillcB medicB, or
semi-hrdiculares, are much smaller than the former, and are
scattered over the upper surface of the tongue, at some distance
from each other ; their form is cylindric, while some are termi-
nated by a round, but not dilated extremity. Others are more
or less tuberculated at the summit. The third class, or papillce
minima;, which have also been termed conicce, or villosce, are ex-
ceedingly numerous, but of very minute size. They cover almost
the whole of the upper surface of the tongue, but are most
abundant towards the tip, where the sense of taste is most acute.

611. The membrane covering the root of the tongue abounds
with mucous follicles. At the root of the tongue, and behind the
papilla maximee, there is a hole or deep depression, called the
foramen cacum Morgagni, which penetrates only a small way

into the substance of the tongue, and receives the mouths of se-
veral excretory ducts that open into it. A line is also observable
runninar forwards alons; the middle of the tongue, from the fora-
men ccecum ; this is the linea Ungues mediana. The tongue is
somewhat restrained in its motions by the franum lingiics, which
is formed by a duplicature of membrane at its under part, con-
necting it with the jaw.

612. All sapid substances require, in order to produce an im-
pression of taste, to be applied in a state of solution to the nerves
of that sense. Nature has accordingly provided a fluid secretion
for the purpose of efl'ecting their solution, and difllising them over
a sufficient extent of the surface of the tongue. This secretion,
which is the saliva, is prepared by the salivary glands, which
consist of three large glands on each side of the face, namely,
the parotid, the submaxillary, and the sublingual. The parotid is
the largest of the three, and occupies the whole space between
the ear and the angle of the lower jaw ; its excretory duct, called
Steno's salivary duct, passes off from the upper and fore part of
the gland, and perforates the buccinator muscle, so as to open in
the inside of the cheeks, opposite to the second or third molar
tooth of the upper jaw. The submaxillary, or inferior maxillary
gland, is situate on the inside of the angle of the lower jaw; its
duct is called the ductus Whartonii, and it terminates by a small
orifice on the surface of a papilla on the side of the frsenum
linguae. The sublingual gland is still smaller, and is under the
anterior portion of the tongue above the duct of Wharton, and

23

366

SENSORIAL FUNCTIONS.

its ducts open by several orifices arranged in a line near the
gums, a little to the outside of the fr^nuni.

2. Ftmciions of Taste.

613. Attempts have often been made, but with no great suc-
cess, to establish a classification of tastes. The general characters
of the tastes denominated acid, sweet, bitter, saline, alkaline,
aromatic, astringent, acrid, and spirituous, are sufficiently known,
but their combinations are endless; and there exists besides these,
a greater number of other tastes, which it would be impossible
to reduce to any of the above classes.

614. The principle on which sapid bodies act upon the tongue
is probably resolvable in all cases into chemical action. It is
observed, accordingly, that substances which are in a sohd form
and absolutely insoluble in saliva, are invariably tasteless ; just
as in chemistry it is an established axiom that bodies do not act
chemically unless they are either in a liquid or gaseous state.
Mr. Mayo observes, that the sensations of taste are not perfect
until the mouth is closed, and the tongue pressed against the
palate, by which means the sapid liquid is brought into more
exact contact with the surface of the tongue, and perhaps forced
into the texture of its mucous membrane.

615. The organ of taste appears to be exclusively the upper
and papillated surfaceof the tongue ; for although the impressions
of this sense are often referred to the palate, inside of the cheeks
and gums, accurate discrimination shows that this reference to
the parts against which the sapid body is pressed by the tongue,
is deceptive, that the real seat of the sense is confined to the
tongue itself, and that its immediate organs are the papillae, and
more particularly those denominated conicce or mllosce. which
are highly vascular and erectile, being observed to rise above
the surface of the tongue when any sapid substance is applied to
it. On the other hand, no papillae are discoverable on the palate.

Some substances, such as peppermint, produce a pungent
impression on the back of the fauces; and others, again, such as
mezereon, excite in the same part a peculiar sense of irritation,
which appears to proceed more from a generally acrimonious
property, afi^ecting particularly the nervous surfaces, than from
any real sapidity; indeed, if the impressions made on the organs
of smell be excluded from consideration, it will be found that the
extent of the part of the tongue which really receives impressions
of taste, is very limited. Mr. Mayo* states that salt, aloes, sugar,
or acids, which excite the most acute sensation when applied to
the tip or edge of the tongue, produce none at the fore or upper

*■ Outlines of Human Physiology.

ORGANS OF SMELL. 267

part of the organ, or on the hard palate. But at the back of the
tongue they again excite sensation enough to be distinguishable,
and they are still more perfectly tasted on the middle of the soft
palate and uvula. The participation of the soft palate in the
sense of taste has been recently pointed out by MM. Guyot and
Admyrauld, and has been carefully verified by Mr. Wheatstone
and Mr. Mayo. These latter gentlemen did not find that one taste
was perceived more distinctly than another, at any point of the
tongue or soft palate.

There is no circumstance more remarkable, with relation to
this sense, than its intimate connexion with that of smeil of which
we are next to speak.*

Sect. III. — Smell.

616. The purpose answered by the sense of smell is apparently
to guard against the introduction into the lungs of injurious efflu-
via, as that of taste is to watch over the qualities of the substances
introduced into the stomach. Its seat is the Schneiderian mem-
brane lining the cavity of the nostrils; and more particularly the
turbinated bones, which are placed so as to catch the odorous
effluvia directly as these enter the nostrils, and which, together
with the cavities or sinuses in the contiguous bones, contribute to
extend considerably the surface on which the impression of these
effluvia is made.

1. Organs of Smell.

617. The organ of smell may be divided into the external and
internal farts.

The external part, oi* nose, properly so called, consists princi-
pally of an upper bony portion commonly called \]\e bridge of the
nose, composed of the ossa nasi, supported by a vertical process
from the ethmoid bone, together with the vomer, and an inferior
cartilaginous portion, of which the middle prominence is called

* [Much dissidence has existed as to the precise nerve of taste. The view
generally embraced is that of Sir Charles Bell ; who considers the ninth pair,
which arises from the anterior or motor tract of the spinal marrow, as the
nerve of motion for the tongue ; the Ungual branch of the fifth, a nerve having
a posterior root, as the nerve of taste, and the glonso-pharyngeal, as the nerve
by which the tongue is associated with the pharynx in the function of deglu-
tition. Recent researches, by Messrs. Panizza and Broughton, encourage
the idea that the hypoglossal, or ninth pair, is the nerve of motion for the
tongue ; the lingual branch, or the fifth pair, the nerve of general sensibility,
and the glosso-pkarjpigeal, the nerve of gustation. The matter is undecided,
but the weight of evidence appears to be in favour of the first opinion. Dun»
glison's Physiology, 3d edit. i. 112.]

268 SENSORIAL FUNCTIONS.

the dorsum; the rounded portions below are the alee nasi, or wings ;
and the cartilage forming the partition between the nostrils is
termed the columna nasi. These cartilages have a degree of
elasticity which preserves the form of the organ.

The internal parts are contained in the cavities of the nostrils,
which are divided by the septum, narium into two lateral passages.
In the upper part of each nostril, there is a spongy bone of a
lengthened but irregular shape, the os turhinatum superius, which
belongs to the ethmoid bone. Below this extends the inferior
turbinated bone, so that the general cavity is divided by these
bones into three passages for the air, running from before back-
wards ; they have been respectively nained by Hall the meatus
narium superior, medius, and infei^ior.

618. The extent of the cavities belonging to the nose is much
increased by their communicating with various sinuses, or cavities
in the neighbouring bones, namely, the frontal, splienoidal, and
maxillary sinuses. Posteriorly the nostrils open into the pharynx,
by two orifices, termed the posterior nares. All these cavities,
together with the sinuses with which they communicate, are lined
with a sensible and delicate mucous membrane, termed \\\e pitui-
tary membrane, or sometimes, from the anatomist who first accu-
rately described it, the membrana Sclmeideriana. The lower
part of the lacrymal sac becoming somewhat narrower, but with-
out forming any valve, passes into the nose, under the name of
lacrymal duct, canalis, nasalis, or ductus ad nasum. At the pos-
terior part of the nares is the opening of the Eustachian tube,
leading to the tympanic cavity of the ear.

2. Function of Smell.

619. The impressions made on the two senses of taste and
smell, have not only a great affinity to each other, but also an
intimate connexion; inasmuch as many of those referred to the
organ of taste are in reality made on the organ of smell, and are
not perceived at all if the nostrils be closed, and the odorous effluvia
arising from the substance placed on the tongue be consequently
prevented from ascending, and acting on the sentient membrane
lining their cavity. When the Schneiderian membrane is inflamed,
the taste of all those substances, of which the flavour consists in
their scent alone, is altogether lost ; and as this is the case with
by far the greater number of substances employed as food, the
sense of taste appears, under these circumstances, to be very
imperfect. Both these senses, but particularly that of smell, are
possessed by man in a degree very inferior to that in which they
exist in the lower animals.

620. It is essential to the exercise of this sense, that the mem-
brane of the nostrils should be in a moist state ; for when it hap-

HEARING. — ACOUSTIC PRINCIPLES. 269

pens to be dry from a deficiency of secretion, the extrenaifies of
the olfactory nerves are unfitted for the reception of the impres-
sion of odours. It is also necessary for smelling that the air
charged with the odorous effluvia should impinge with some
degree offeree against the Schncidcrian membrane.

The seat of greatest sensibility to odours is the upper part of
the nostrils ; and the form of the nose and of its apertures are
obviously adapted to direct the stream of air towards those parts.
It is found, accordingly, that when the nose has been destroyed
by disease, the smell is greatly impaired, if not altogether lost.*

621. Odours as well as tastes have been attempted to be classed.
Linnseus distributed them into seven classes: 1, ambrosial, of
which the smell of the rose and musk are examples; 2, fragrant,
as the smell of the lily, of the jasmin, and of saffron ; these are
more evanescent than the former; 3d, arojnatlc, as the smell of
the laurel ; 4, alliaceous, partaking of the odour of garlic ; 5,

fetid, exemplified in valerian and mushrooms ; 6, virous, or
narcotic, as in the smell of opium ; 7, nauseous, as that of the
gourd, melon, and cucumber. But this classification is obviously
incomplete, as it omits several very distinct classes of odours,
such as that of alcohol, of sdther, of camphor, of ammonia, of
chlorine, 6tc.

622. Any very acrid or stimulating vapour admitted to the
nostrils, instead of producing the sensation of smell, gives rise to
mere painful irritation, which excites sneezing, and a copious
secretion of mucus.

Sect. IV. — Hearing.
1. Acoustic Principles.

623. The object of the sense of hearing is to convey to us certain
impressions made on the nerves of the ear by the vibrations of the
air; which vibrations are the result of some mechanical impulse
communicated to it by the motion of a body at a distance. Other
media besides air are also capable of transmitting sonorous vibra-
tions to the organ of hearing; thus water is known to convey sounds
to great distances; and solid bodies possess the same power in a
degree proportioned to their molecular elasticity. If the body
which is the source of sound be insulated from any such medium, its
vibrations cannot be communicated, and no sound is heard. Thus
if a bell be placed in the receiver of an air-pump, in proportion

* [The olfactory or first pair of nerves is distributed to this part of the
nasal fossae; and the fifth pair to the lower portion of the nasal fossae.
The integrity of both seenris to be necessary for olfaction ; althoiisrh the first
pair appears to be the proper nerve of smell ; — the fifth pair being the nerve
«f general sensibility.]

23*

270 SENSORIAL FUNCTIONS.

as the air is exhausted the sound it produces when struck becomes
more and more faint, till at length, when the rarefaction has been
carried a certain length, it is quite inaudible. If the same bell
be placed in a vessel of condensed air, the sound it gives out will
be louder than in air of the ordinary density.

624. The velocity with which sound is transmitted in air of
the same density is uniform at all distances, and for all sounds
whatsoever. As the air of the atmosphere varies in its density,
and also in its degrees of humidity, the velocity of sound is not
constantly the same. It may be taken at an average as being
1100 feet in a second, or nearly thirteen miles in a minute.

2. Organ of Hearing.

625. The organ of hearing is divided into the external and the
internal ear.

626. The external ear, comprehends the auricula, or ear, pro-
perly so called, and the meatus auditorius externus.

627. The auricula is chiefly composed of an elastic cartilage
bent into various folds and hollows, and covered with a thin layer
of common integuments, the lower fold of which, enlarged by
the addition of cellular substance, forms the depending part called
the lohe of the ear. The cartilaginous portion is termed the
pinna, or ala. Its outer circle, or prominent margin, is called,
from its winding direction, the helix. The semicircular ridge
within this is the antihelix ; and the small protuberance, in which
the helix appears to terminate below at its inner edge, is called
the tragus, from its being frequently covered with hair. Another
eminence, nearly opposite to this, below the anterior extremity
of the antihelix, and projecting outwards over the hollow of the
ear, is called the antitragus. Between the helix and antihelix, is
the cavity called the scaphus, or fossa navicularis.

628. The concha is a large depression under the antihelix, and
divided into two parts by the hehx. The lower of these leads to
the meatus auditorius, a passage which at its commencement is
composed of cartilage, and farther on is joined to the orifice of
the same name in the temporal bone. The cartilaginous tube is
lined by a soft membrane, giving rise to hairs, and containing
small glands, the glandulce ceruminosce, which secrete the wax of
the ear. This cartilaginous portion of the ear is attached to the
temporal bone by several ligaments and muscles ; the effects of
which in moving the different parts of the external ear are in
general very little sensible.

629. The membrane lining the meatus is continued along the
osseous portion of the canal, which is closed by the dymm of the
ear, or memhrana tympani. This is a firm, oval, and almost
transparent membrane, fixed in an osseous groove at the bottom

ORGAN OF HEARING. 271

of the meatus, across -which it hes in an oblique position. It is
shghtly concave on the external side ; and is capable of being
stretched or relaxed by the action of particular niuscles.

630. The membrane of the tympanum divides the external
from the internal ear. Behind it we find an irregular cavity,
called the tyjnpanic cavity, or cavity of the tympanum, which is
filled with air ; it is about seven or eight lines wide, and about
half that space in breadth ; and is every where lined by a fine
membrane. It has four openings ; the first is the small orifice
of a passage of communication with the back of the cavity
of the nostrils, which is called the Eustachian tube, and is
shaped like a trumpet, expanding as it approaches the fauces.
The second aperture leads to a number of irregular cells,
formed in 4he mastoid process of the temporal bone, and
called the mastoid cells. At the back part of the tympanum we
find an oval opening, called the fenestra ovalis, and below this a
round perforation, termed the fenestra rotunda. Between these
fenestree, is a bony eminence, called the promontory.

631. Within the cavity of the tympanum are contained four
small bones, the ossicula auditus, placed in a series or chain ex-
tending across from the membrana tym.pani to the fenestra ovalis.
The malleus, or hammer, is the first of these bones ; a long pointed
process from which the handle is fixed to the membrana tympani.
It is articulated by its round head with the next bone, the incus,
or anvil, which much resembles in its shape a molar tooth, having
a body and two unequal crura. With the longest of these pro-
cesses is articulated the os orbicularis, of a rounded figure, and
smaller than a grain of mustard seed. It forms the medium of
connexion between the incus and the stapes, which is the last
bone„in the series, and is so named from its striking resemblance
in form to a stirrup. The base of the stapes is fixed to the margin
of the fenestra ovalis, which it accurately closes. The articula-
tions of these minute bones are furnished with capsular ligaments,
and all the apparatus of the larger joints ; appropriate muscles
being also provided for their movements. Between the malleus
and the incus, there passes a small nervous cord which crosses
the tympanum, and is accordingly named the chorda tympani.

632. The principal cavity of the organ of hearing is situate
still more internally, and from the intricacy of its winding sinuo-
sities it has received the general name of the labyrinth. All its
cavities and passages are lined with a very delicate periosteum,
and filled with a watery fluid, and within them is suspended a
pulpy membrane of a similar shape, on which are distributed
various nervous filaments presently to be described. This saccular-
shaped membrane is termed by Breschet the membranous laby-
rinth, in order to distinguish it from the osseous labyrinth, in
which it is contained. It forms one continuous closed sac extend-

272 SENSORIAL FUNCTIONS.

ing within the vestibule and canals, excepting those of the cochlea;
and contains a fluid, perfectly similar to the perilymph, and
termed by Blainville, vitrine auditive, which intervening between
it and the osseous parietes of the labyrinth, surrounds it on all
sides, and prevents its coming in contact with those bones.

The central cavity, in which all these passages meet, is termed
the vestibule ; it is of an oval figure, and is situate nearly in the
centre of the os petrosum, and at the inner side of the fenestra
ovalis. On the side of the vestibule next to the mastoid process,
there are five orifices leading to the three semicircular canals, as
they are called, or passages formed within the substance of the
bone. The extremities of two of these canals unite, and termi-
nate by a common opening ; hence there appear in the vestibule
only five openings, instead of six. These canals are distinguished
by the names of the superior, or vertical, the posterior, or oblique,
and the exterior, or horizontal. They each form a curvature of
more than three-fourths of a circle, and have an enlargement,
termed ampulla, or cavitas elliptica, at one end, the other ex-
tremity being nearly of the same size as the rest of the canal.

633. The cochlea, which is the third division of the labyrinth,
has a conical shape, and is situate at the anterior part of the os
petrosum, and at the fore-part of the vestibule, with its base to-
wards the meatus auditorius internus, and its apex in the opposite
direction ; that is, facing outwards. It contains a double spiral
passage, winding round like the shell of a snail. This passage
begins by a round hole from the vestibule, and after forming two
turns and a half, becomes suddenly smaller on arriving at the
apex, where it communicates with a similar tube which takes its
rise at the base of the cochlea from the fenestra rotunda, for-
merly noticed as one of the apertures of the cavity of the. tym-
panum ; but which is closed by a membrane. The partition
which divides these two winding passages is called the lamina
spiralis, or septum scalx ; for the passages themselves are known
by the name of the scales cochlece ; that which communicates with
the vestibule being distinguished as the scala vestibuli, and the
other, from its connexion with the tympanum, the scala tympani.
The central bony pillar, around which these turns are made, has
a horizontal direction, and is called the modiolus. It has the
shape of a cone, at the apex of which is situate another hollow
cone in a reverse position, termed the infundibulum, which, how-
ever, is an imperfect funnel, having a common apex with the
modiolus, and its base being covered by the apex of the cochlea,
which is called the cupola.

634. It has been supposed that when the fluid in these cavities
is in too great a quantity, the superfluous portion is carried off
by two minute canals or aqueducts, discovered by Cotunnius.
One of these opens into the bottom of the vestibule, and the other

FUNCTION OF HEARING. 273

into the cochlea, near the fenestra rotunda. They bear the
names respectively of the aqucechictus vestihuU and aqiioiductus
cochlece. They both pass through the os pelrosum, and commu-
nicate with the cavity of the cranium.

The form of that part of the membranous labyrinth which
occupies the cavity of the vestibule, and which has accordingly
received the name of the membranous vestibule, though having a
general resemblance to that of the cavity itself, yet differs from
it in some degree, being composed of two sacs opening into each
other. One of these sacs is termed the utricle ; and the other
the sacculus. Each sac contai;is in its interior a small mass of
white calcareous matter resembling powdered chalk, and which
seems to be suspended in the fluid contents of the sac by means
of a number of nervous filaments, derived from the acoustic
nerves, and of which they appear to be the ultimate ramifica-
tions.*

635. Through an opening at the base of the modiolus, a branch
of the auditory nerve, which has entered by the meatus audito-
rius intern us, passes into the funnel-shaped cavity, and is thence
extended through the spiral canals; while another branch passes
backwards through the vestibule, and dividing into several
branches, enters the orifices of the semicircular canals. The
minute branches perforate a. part of the bone, which has been
termed, from its appearance, the cribriform plate.

3. Function of Hearing.

686. We thus see that the ear is an organ extremely compli-
cated in its structure, evidently intended to convey the sonorous
undulations of the air, after they are collected by the more
external parts of the organ, to the branches of the auditory
nerve, which are spread over the membranes lining the different
cavities of the labyrinth, and the cretaceous bodies suspended
within those membranes. We may therefore distinguish the
several parts of the apparatus employed for this purpose, ac-
cording as they are merely designed to collect the aerial undula-
tions, and increase their intensity by concentrating them into a
smaller space ; or according as they contain the expanded
nerves on which the impression is ultimately made. It appears
that the medium by which this last effect is produced, is the

* The most accurate and complete description of the anatomy of the ear,
is that given by Breschet, Sur les Orp;anes de I'Onie, which first appeared in
the Annales dns Sciences Naturelles, xxix. 129. [See, also, Breschet,
Memoir, de I'Academie de Medecin. torn. v. ; and Recherches Anatomiqnes et
Physiologiqnes sur I'Orcrane de I'Ouie, &c., Paris, 1836.] A compendious
account is contained in Dr. Roget's Bridgewaler Treatise, ii. 420. [Amer.
edit. ii. 305. See, also, Dunglison's Physiology, 3d cit. i. 141.]

274

SENSORIAL FUNCTIONS.

perilymph, or fluid filling the cavities of the labyrinth, and con-
taining the exquisitely delicate membrane and cretaceous bodies
which the extreme fibrils of the auditory nerve are expanded.
This fluid is put in motion by the air in the cavity of the tympa-
num, and thrown into corresponding undulations.

637. The accessory parts of the organ of hearing may there-
fore be divided into three parts. There is, first, the external ear,
which is an elastic cartilaginous appendage 1o the organ, curiously
grooved, so as to form a series of parabolic curves, adapted to
receive the undulations of the air, and convey them into the
passage of the meatus externus, serving apparently an office
similar to that of the expanded part of a trumpet. The sonorous
undulations are thus hiade to strike against the membrane of the
tympanum, or ear drum, which is stretched across, and closes
the passage. The cavity behind this membrane is filled with air,
which is next thrown into undulations by the medium of the ear-
drum, the vibrations of which have been excited by those of the
external air. In order to preserve an equilibrium between the
air in the cavity of the tympanum and the external air, so that
the membrane may not sustain a greater pressure on one side
than on the other, a communication is kept open with the back
part of the throat by means of the Eustachian tube. Hearing is
always much impaired, if from any cause the Eustachian tube is
obstructed, as it sometimes is by a common cold, which then
produces a temporary deafness.

638. The cavity of the tympanum is of a very singular form,
extending into the mastoid process of the temporal bone, which
has a cellular structure. A chain of minute bones, the ossicula
auditus, extends, as we have seen, across the cavity, terminating
at the fenestra ovalis, or aperture leading to the vestibule; while
another aperture, the fenestra rotunda, also closed by membrane,
leads to one of the spiral turns of the cochlea. Thus, the fluid
in the labyrinth receives from the impulse made on these two
membranes, which are situate in two different planes, a double
undulation; and these two undulations, the one circulating along
the semicircular canals, the other through the spiral turns of the
cociilea, probably unite at some focal spot, like the meeting of
two tidal waves, and increase the effect produced. These undu-
lations must of course be variously modified, according to their
frequency, and the order of their succession, and the impressions
made on the nerve must undergo corresponding modifications.
But we are so completely in the dark as to the real office of the
several parts of this elaborately constructed organ, that it is
exceedingly difficult to prosecute the physiology of this sense
with such imperfect data. We are unable even to form a rational
conjecture as to the offices of the delicate muscles provided for
directing the movements of those ossicula, which are articulated

VISION. 275

with such great nicety, and which seem calculated to alter the
tension of the niembrana tympani, and bring it into a state
capable of vibrating in unison with the sonorous undulations that
impinge upon it. What adds in no small degree to our embar-
rassment, is the knowledge we have a.cquired of the power of
hearing being retained, without apparent diminution, when the
greater part of this apparatus of bones, with their joints and
muscles, and even the ear-drum itself, has been destroyed by
accident or disease.* It should be observed, however, as Mr.
Mayot remarks, that the stapes is so strictly applied to the
membrane of the fenestra ovalis, that the loss of this bone
necessarily produces incurable deafness, by the attendant injury
of the labyrinth.

639. Sir Everard Home imagined that the muscular structure
of the membrana tympani, enabling it to contract or relax
according to circumstances, so as to vibrate in unison with the
musical notes which reached the ear, conferred the power of
distinguishing musical tones. But this ingenious hypothesis is
completely overturned by the fact above stated, of the integrity
of the membrane of the tympanum not being necessary for the
perfect accuracy of the sense of hearing, even with relation to
the distinction of musical sounds. Dr. Young thinks it probable
that the semicircular canals which are disposed in a remarkable
manner in three orthogonal planes, corresponding to the three
dimensions of space, enable us to estimate the acuteness or pitch
of a sound ; and that the cochlea serves the office of a micro-
meter of sound. J But the grounds of these opinions are too
vague and conjectural to inspire us with any confidence in their
solidity. When the external passages are totally obstructed, sono-
rous vibrations may still be transmitted to the auditory nerves
by means of the bones of the head. Thus, the sound of a tuning
fork applied to the teeth, or even to other parts of the head, is
perfectly audible under these circumstances. We thus possess a
criterion for determining, in cases of deafness, whether the disease
consists in the insensibility of the nerves to these impressions, or
is seated in the passages leading to the labyrinth.

Sect. V. — Vision.

640. The physiology of the eye is more interesting than that
of any of the other organs of the senses; because, from the
knowledge we possess of the laws of optics, to which it is so admi-

* See two papers by Sir Astley Conper, in the Philosophical Transactions
for 1800, p. 151 ; and for 1801, p. 437.

f Outlines of Human Physiology, 3il edition, p. 221, note.
^ Medical Literature, p. 98 ; and Lectures, vol. i. p. 387.

276 SENSORIAL FUNCTIONS.

rably adapted, we can understand the offices of its several parts,
and the mode in which they concur in the production of the
resulting effect. The study of the eye has been said to be the
best cure for atheism ; and it furnishes, indeed, the most striking
and unequivpcal proofs .of the existence of design and intelli-
gence in the construction of the animal fabric. These proofs
have accordingly been always amongst those most prominently
adduced by philosophers in support of the arguments of natural
theology.

641. The organs subservient to vision are lodged securely in
bony cavities of the orbits, where the surrounding bones protect
them on every side, excepting in front. They may be divided
into the internal and the external parts; the former consisting
of the spherical bodies denominated ihe globes of the eye, or eye-
halls ; and the latter comprising parts which give motion to the
globe, and otherwise assist it in its functions.

1. Internal Parts of the Eye.

642. The eye-ball is composed of segments of two unequal
spheres ; one of which, constituting about four-fifths of the whole,
forms the portion which is in the orbit ; while the other fifth is
that part which is seen in front, and which, being a portion of a
smaller sphere, is more protuberant. The diameter of the eye-
ball, from behind forwards, is accordingly longer than its trans-
verse diameter; the proportion being that of twenty-five to
twenty-three.

643. The eye-ball is made up of coats and humours. The
former consists of the sclerotica, cornea, choroides, and retina,
together with the conjunctiva. Of the latter there are three, viz.
the vitreous, crystalline, and aqueous humours.

644. The sclerotica, which is the exterior coat, is, from its
compact fibrous texture, the densest and strongest, as well as the
thickest of the tunics of the eye, and the one from which the
other parts of the eye-ball derive their principal support. It
covers all that portion of the globe of the eye, which has already
been pointed out as constituting its largest segment. At its ante-
terior edge it is joined to the more convex tunic, which com-
pletes the figure, and is named the cornea, from its being com-
posed of a great number of concenti'ic lamina, of a horny elastic
texture. Some authors have given it the name of the cornea
incida, from its perfect transparency, and by way of contrast to
the sclei'otica, which they had named the cornea opaca.

645. The choroid coat, or tunica choroides, lies immediately
within the sclerotica, and is composed of a congeries of blood-
vessels connected together by membrane. It has been distin-
guished into tvvro layers, the innermost of which has been termed

INTERNAL PARTS OF THE EYE. 277

the tunica Ruyschiana. At the middle of the choroid coat are
observed numerous vessels convoluted into a spiral form. These
have been termed the vencB vorticosce. The interna] surface of the
tunica Ruyschiana, or tapetum, as it has been called, seems, from
its villous or fleecy appearance, to be a secreting surface. It is
everywhere lined with a black or deep-brown mucous substance,
included in a fine cellular tissue. This is \he pigmentum nigrum,
which forms a laver, separating the choroides from the next
coat, or retina. This latter tunic is an expansion of the pulpy
substance of the optic nerve, spread over a fine membrane. The
optic nerve, from which this medullary matter is derived, enters
the eye at its back part, at a point nearer to the nose than the
centre, or axis of the eye, and perforates the sclerotic and
choroid coats.

646. From the inner margin of the junction of the cornea and
sclerotica, there extends across the fore part of the globe of the
eye a membranous partition, called, from the variety of its colour,
the iris; it is perforated in the centre by an aperture, called the
pupil, because, as it is said, it represents objects no larger than
a pupilla, or puppet. The structure of the iris is exceedingly
peculiar: it appears to be made up of a number of fibres, which
pass from the inner to the outer margin in a radiated direction,
together with others W'hich run circularly. These fibres have
been presumed to be of a muscular structure ; but doubts are
still entertained with regard to this point. The posterior surface
of the iris is lined wdth a pigment similar to that which is found
W'ithin the choroid coat. It has been called the uvea, from its
fancied resemblance in colour to the grape.

647. The iris is connected with the choroid coat by an inter-
mediate structure, called the ciliary ligaments, ciliary circle, or
orhiculus ciliaris, which is a circular belt, more than a line in
breadth, made up of a soft and pulpy tissue, and of a whitish
colour. It is at this part that the choroides adheres firmly to
the sclerotica. From this part, also, there extends inwards a
dark coloured ring, which is a continuation of the choroides, and
is termed the c&rpus ciliare. It is about the sixth part of an inch
in breadth towards the temple, but somewhat narrower towards
the nose. It is covered in every part by the pigmentum nigrum.
It is marked by radiated striae at its inner part, but they are
somewhat obscured by the pigmentum nigrum. At the outer part
these striffi become gradually broader and more elevated, and
appear like folds, only the intervals between them being covered
with the pigment. These folds are termed the ciliary processes.
Each of these processes is of an irregular triangular figure, with
the base outwards, or at the ciliary circle, and its apex inwards,
or towards the axis of the eye. Their number is generally about
sixtv, and they are alternately longer and shorter.

24

278 SENSORIAL FUNCTIONS.

648. About three-fourths of the globe of the eye, within these
several tunics, is filled by a very transparent and gelatinous
humor, which, from its supposed resemblance to melted glass, has
been termed the vitreous humor. It is nearly of the consistence
of the white of an egg, and consists of a fluid substance con-
tained in the cells of a very fine and delicate cellular tissue,
called the hyaloid membrane. It is invested by a transparent
ntiembrane, termed the tunica vitrea, or capsule of the vitreous
humors. The anterior surface of the vitreous humor is de-
pressed, for the lodgment of the crystalline lens, or humor, which
is a dense body, perfectly transparent, and has the shape of a
double convex lens, of which the posterior surface has a greater
convexity than the anterior surface. The lens is composed of a
great number of concentric laminse, which become more and more
dense towards the centre, and each lamina is made up of very
distinct parallel fibres. It is enclosed in its own peculiar capsule,
in which it appears to float loosely, a watery fluid, called the
liquor Morgagni, being interposed.

649. The fore part of the eye-ball, between the crystalline lens
and the cornea, is filled by a watery fluid, called the aqueous
humor, in the middle of which the iris is suspended, thus dividing
the space into what are called the anterior and posterior chambers
of the aqueous humor. The aqueous humor, like the other humors,
is contained within a dehcate membrane, which fines the inside
of the cornea, and passes over the crystalline lens and the convex
margin of the vitreous humor.

650. The capsule of the lens adheres closely to the tunica
vitrea. Behind the edge of the former, and between the margin
of the ciliary zone and capsule of the vitreous humor, a triangular
passage is formed, called, from its discoverer, the circle of Petit,
or canalis Petitianus. When air is blown into this passage, it
passes freely round the edge of the lens.

651. At that part of the retina which is situate in the axis of
the eye, there is a small circle, where the retina is transparent,
giving rise to the appearance of a hole, as if the retina were
deficient in that part. It was discovered by S3mmerring, and
bears the name of the foramen centrale of Sommerring. It is
surrounded by a yellow circle, about a line in diameter. The
fibres of the optic nerve, in passing to form the retina, per-
forate a thin plate of membrane which is extended from the
sclerotica, and which is termed the lamina cribrosa. The centre
of the optic nerve is perforated by the arteria centralis reiince,
forming an aperture which has been called the porus opticus.

2. External Parts of the Eye.

652. The orbit is a conical cavity, in the fore part of which
the globe of the eye is situate, the remaining space behind the

EXTERNAL PARTS OF THE EYE. 279

globe being chiefly filled with fat, which surrounds the optic
nerve, and intervenes between it and the straight muscles, that
extend between the margin of the foramen opticum, through
which the optic nerve passes out of the skull, and the fore part
of the sclerotic coat, where they are inserted by broad and flat
tendons. These tendinous expansions have been improperly con-
sidered as composing one of the tunics of the eye, which being
of a white colour, has received the name of tunica alhuginea.

653. The globe of the eye is covered at the fore part by two
eye-lids or palpebrcB, which are composed of muscular fibres,
covered by the common integuments, supported at their edge by
a cartilage called the tarsus, and furnished with a row of hairs,
termed cilia, or eye-lashes. At the roots of the eye-lashes are
sebaceous follicles, named from the anatomist who first observed
them, the glandulcB Meibomii, and which secrete a glutinous lini-
ment. The eye-lids are lined on their interior surface by a very
fine and smooth serous membrane, which is reflected over the
anterior part of the globe of the eye, and even over the surface
of the cornea. This membrane is called the tunica conjunctiva.

654. Between the ball of the eye and the upper vault of the
orbit, on the temporal side, lies the lacrymal gland, which
secretes the tears. It is composed of a number of small, whitish,
granular bodies, which are collected together into two lobes.
There is also a chain of smaller glands lying between the prin-
cipal gland and upper eye-lid, and connecting them together.
The excretory ducts from all these glands are exceedingly mi-
nute, and terminate in the inner surface of the upper eye-lid, near
the outer angle of the eye. After moistening the surface of the
eye, the tears are again collected by tw^o small orifices, called
the puncta lacrymalia, placed on a small eminence in each eye-
lid, near the inner angle of the eye, at the extremity of the tarsus.
They are the beginnings of two small canals that run in the
direction of the edges of the eye-lids, towards the side of the
nose, where they approach each other, and terminate together in
the lacrymal sac, v^hich is a membranous bag situate on the os
unguis, and leading to a passage into the cavity of the nostrils.
The puncta are kept separate by the interposition of a small
reddish body, called the caruncula lacrymalis, situate between
the inner angle of the eye-lids and the ball of the eye. Minute
hairs are found upon the surface of this body, which serve to
entangle small objects which might otherwise get into the eye.
There is also a reduplication of the tunica conjunctiva, shaped
like a crescent, and hence termed the valvula semilunaris, the
points of ,which are directed towards the puncta, and which
assists the caruncle in directing the tears to the puncta.

Having thus described the apparatus for vision, we shall now
proceed to consider the mode in which that function is performed.

280 SENSORIAL FUNCTIONS.

3. Optical Principles.

655. The object of this sense is to convey to us a knowledge
of the existence and visible qualities of distant objects, by means
of the light which they send to the eye. This is accomplished
by altering the natural direct course of these rays, so that they
may form a distinct image of these objects on the retina. That
such images are actually formed on the retina may be easily
shown in the eye of an animal recently killed, by carefully re-
moving the opaque sclerotic and choroid coats, together with the
black pigment from the back of the eye, so as to expose the
retina. The objects on the other side, in front of the cornea, will
then be seen beautifully depicted on the retina, their images being
inverted ; precisely in the same way, and on the same principles
as they are seen in a simple camera obscura.

656. In order to understand and trace the operation of the prin-
ciples concerned in these phenomena, it will be necessary to
refer to- the laws of optics.

The rays of light in traversing any medium of uniform density,
move always in straight lines; but when the density changes they
deviate somewhat irom this rectilinear course, according to the
direction of the ray with respect to the planes in which the change
of density occurs. Thus a ray from the sun, or other celestial
body, traversing obHquely through our atmosphere, the different
strata of which are of increasing density as they come nearer
to the earth, is gradually bent in its course, and arrives at the
surface of the earth in a direction somewhat nearer to a perpen-
dicular line than if there had been no atmosphere. This deflexion
from a straight line is termed refraction. Refraction takes place
suddenly, if the ray passes abruptly from one medium to another,
which sensibly differs from it in its density ; the direction of
the deflexion being always towards the denser medium ; or, to
speak more accurately, towards a line drawn perpendicular to
the surface common to the two media, and situate in the denser
medium.

657. In the case of the passage of a ray through the surface
of a new medium of very different density from the first, another
phenomenon takes place ; the ray is decomposed, part being trans-
mitted and refracted, while another portion is turned completely
back into the medium it was already traversing. This is termed
reflexion. Objects which are not luminous in their own nature
are rendered visible only by the reflexion from their surfaces of
the light which ihey receive from other bodies. The law in this
case is, that the angle of reflexion, by which is meant the angle
which the course of the reflected ray makes with a line perpen-
dicular to the surface, is equal to the angle of incidence, or the
angle which the incident ray makes with that same perpendicular;

FORMATION OF IMAGES IN THE EYE. 281

and also, that it is in the same plane with the incident ray, and
the perpendicular hne.*

658. The law of refraction is, that the course of the refracted
ray is deflected towards that part of the perpendicular which is
situate in the denser medium, and tiiat the sine of the angle of
refraction, (or the angle it makes with the perpendicular) has to
the sine of the angle of incidence the same constant ratio. This
ratio increases in proportion to the difference there is between
the two media in respect of density.

4. Formation of Images in the Eye.

659. It follows as a consequence of the above laws, that a
pencil of rays proceeding through the air, and falling on the
convex spherical surface of a medium of greater density than the
air, (as is the case with the cornea of the eye,) is so refracted
as to be collected, after proceeding a certain distance, into one
and the same point. This will readily appear when we consider
that those rays fall with more obliquity on the cornea, according
as they are more distant from the central ray of the pencil, or
that which may be conceived to fall perpendicularly on its sur-
face. These more oblique rays are consequently more refracted ;
that is, more bent from their original course ; and this law being
observed throughout the whole pencil, all the rays will tend
after refraction to the same point, which point is called ihejocus
of that pencil of rays.

660. The same process taking place with regard to all the
other pencils of rays proceeding respectively from the several
points of the objects viewed, and each being collected into sepa-
rate points in different parts of the retina which receives them,
images of those objects will be delineated on that membrane ;
for it is evident that all the focal points will have, with respect
to one another, the same relative positions as the points of the
external objects from which each pencil of rays proceeds, when
referred to the sphere of vision. The impression thus made on

* [Some interesting points of diagnosis are connected with the reflection
which takes place from the humors of the eye. If a lighted candle be held
before an eye, the pupil of which has been dilated, and in which there is no
obscurity in the humors or their capsules, three distinct images of the flame
are perceptible — two upright and one inverted ,- one of the former being re-
flected from the cornea, and the other from the anterior part of the crystalline
lens ; the last inverted image being caused by the reflection from the posterior
concave surface of the crystalline. Mr. Sanson has proposed this "catoptric
method" of examining the eye as a means of diagnosis between cataract and
amaurosis ; and Dr. Hays, who has employed it to some extent, regards it as
a most valuable mode of investigating various conditions of the eye, which
might not be readily understood without its agency. See Mr. Sanson, cited in
Amer. Journal of the Med. Sciences, August, 18,38, p. 4,94* aod Dr. Hays, Ibid,.
May, 1839, p. 255,1

54*

282 SENSORIAL FUNCTIONS.

each respective point of the retina, is transmited to the sensorium,
where it makes a distinct impression, and gives rise to the sen-
sation ofUght and colour; and in conjunction with the experience
gradually gathered from the sense of touch, imparts to us a
knowledge of the existence, relative situation, form, magnitude,
distance, and colour of the objects before as. This, then, is
vision.

661. Such is the general outline of the mode in which vision
is accomplished; but there are a thousand beautiful contrivances
and adjustments provided for ensuring the accuracy with which
this picture of the surrounding scene is portrayed on the retina.
The perfection of vision is entirely dependent on the distinctness,
the vividness, and the fidelity of this picture; and the whole
apparatus of the eye is calculated to obtain these qualities.

662. The purposes, served by the. apparatus external to the
globe of the eye, are sufficiently obvious. The effectual pro-
tection given to the eye by the arched form of the bones which
compose the orbit, — the provision of a soft cushion in the fat
which occupies the bottom of the cavity, — the beautiful con-
trivance of the eye-lids, which, on the least appearance of danger,
are ever ready to close upon the organs they are appointed to
guard, — and even the direction of the eye-brows, intended to
divert the course of the perspiration from the forehead, are all
calculated to call forth our admiration, because the end to be
answered being obvious, we can judge of the fitness of the means
for the accomplishment of those ends. A still further proof of
exquisite design offers itself in the lacrymal apparatus, which
provides the means of preserving the surface of the cornea
always clean and transparent, and fitted for its office of regu-
larly refracting the rays of light.

663. The humors of the eye, through which the light passes
before arriving at the retina, have different degrees of density,
and consequently have different degrees of refractive power.
The first and greatest refraction of the rays takes place at the
outer surface of the cornea ; the next is at the inner surface,
where the rays meet with the aqueous humor. Now this humor
is rather less dense than the cornea, and consequently the rays
already refracted, and rendered convergent by the cornea, have
their convergence slightly diminished, when they traverse the
aqueous humor. These, in fact, are converging towards points
at some distance beyond the retina. The iris is interposed in the
course of the rays while they are passing through the aqueous
humor ; the circular aperture of this membrane, the pupil, admit-
ting only the more central portion of each pencil of rays. By
intercepting the extreme rays, which, in consequence of a pecu-
liarity in the law of spherical refraction, hereafter to be explained,
would, if allowed to reach the retina, somewhat confuse the

CORRECTION OF ABERRATION. 283

image, greater clearness of that image is obtained, at the sacri-
fice, indeed, of a portion of brightness. It serves, accordingly,
the same purpose with regard to the eye, which the circular
ring, placed in the interior of a telescope, effects in contracting
the aperture of the instrument; rendering the image more dis-
tinct, though less illuminated than it would otherwise be. But
the iris has this great superiority over the circle in the telescope,
inasmuch as it is capable by its contractile power of enlarging
or diminishing the aperture of the pupil, as occasion requires.
Thus, when the object viewed is but faintly illuminated, the pupil
is enlarged, and admits more light, thus giving greater bright-
ness to the picture; an advantage which more than compensates
for the slight indistinctness of the fainter images composing
that picture. When, on the contrary, an object is too bright, so
that its image would produce too vivid an impression on the
retina, the pupil immediately contracts, so as to reduce the
quantity of light admitted into the interior of the eye, and to
prevent any injurious effect upon the retina.

5. Adjustments for the Correction of Aberration.

664. That part of the converging pencil of rays, which is admit-
ted through the pupil, falls upon the anterior convex surface of
the crystalline lens, which being denser than the aqueous humor,
occasions a new refraction of the rays, and gives them an increased
degree of convergence, so that they now tend to foci nearer to the
retina than before, though still somewhat beyond it.

665. An exquisite provision is found in the peculiar structure
of the lens for correcting what is termed the spherical aberration.
It is a necessary consequence of the mathematical law of refrac-
tion, that in a pencil of rays falling on the convex spherical surface
of a denser medium, those rays which are farthest from the cen-
tral ray, will be bent somewhat more than is requisite to bring
them to the same focal point as the rays which are nearer to the
centre of the pencil ; hence all the rays can never be collected
accurately into the same point ; although in ordinary optical instru-
ments, such as com.mon telescopes, and camera obscura, the aber-
ration thus resulting is confined within such narrow limits as not
to produce any very great inconvenience. But in the eye even
this minute defect of ordinary optical instruments is remedied.
The lens is composed of successive lamina;, increasing in their
density and refractive power, in proportion as they approach the
centre ; that central part being the hardest and densest of the
whole. The central rays of each pencil, therefore, are subjected
to a greater refractive action than the more exterior rays, and the
whole are brought accurately to convergence at the same focal
point.

284 SENSORIAL FUNCTIONS.

666. After passing through the crystalline lens, the rays enter
the vitreous humor, where, again, there is a change of density in
the nnedium. The density of the vitreous humor is less than that
of the lens ; and were its surface convex, the convergence of the
rays would be diminished by the refraction they would then expe-
rience ; but the surface being concave, the refraction contributes
still farther to increase the convergence of the rays, which now
traverse the aqueous humor, and are collected accurately into
their respective foci on the retina itself

667. Rays proceeding from objects at different distances from
the eye, will arrive at the cornea with different degrees of diver-
gence, and the same refractive powers of the humors would cause
them to converge at different distances ; in order, therefore, to
obtain distinct images of these objects on the i^etina, either the
distance of that membrane from the cornea must be altered, or
the refractive power of the humors must be changed. Thus, if
the power of the eye at any one time be suited to distinct vision
of distant objects, near objects will appear confused, from the
indistinctness of their images on the retina ; because the focus of
convergence of the rays proceeding from those objects is farther
back than the situation of the retina. If, either by elongating the
axis of the eye, the retina could be removed to this new focal
distance, or else by increasing the refractive power of the humors,
the rays could be made more convergent than before, we should
again obtain distinct images of those near objects on the retina ;
but then the images of distant objects would, at the same time,
and from the contrary cause, be indistinct ; and in order to give
distinctness to these, the contrary changes are required to be made
in the eye to, those already mentioned. Now, it is found that
the eye really possesses the power of accommodation here des-
cribed, adapting itself, by some internal changes, to the vision of
both near and remote objects, according as the attention is directed
respectively either to the one or to the other.

668. The effort by which the eye changes its internal state, so
as to accommodate its powers to the vision of near objects, after
having viewed those more distant, is always attended with a
contraction of the pupil; and the exclusion of the remoter rays,
consequent upon this diminution of aperture, must partly contri-
bute to the greater distinctness of the images, by excluding the
rays near the circumference of each pencil. But it is certain
that the refractive powers of the eye are also increased ; and it
is a question of considerable difficulty to determine the manner
in which this increase is effected. Sir Everard Home* supposed
that it was accomplished by the joint actions of the straight mus-

* See Philosophical Transactiohs for 1794, p. ^l; 1795, p. I; 1796, p. };
1797, p. 1.

CORRECTION OF ABERRATION.

285

cles which surround the ball of the eye, and which, by compress-
ing it all round its sides, might elongate its axis and increase the
distance of the retina from the cornea, while they at the same
time would make the cornea more convex, by drawing back
its circumference, and thus rendering its central part more
protuberant. This plausible theory is overturned by the fact
discovered by Dr. Young,* that when the efiect of any change
in the curvature of the cornea is removed by placing the eye
under water, the eye still retains its power of accommodation to
the vision of objects at different distances, by changes which take
place in its refractive powers.

669. The most probable supposition relative to this operation
is, that the ciliary ligament has the power of contracting at the
same time with the sphincter of the iris ; a change which will
be attended with the effect of bringing the lens somewhat for-
wards, and of increasing the convexity of its surfaces, while the
convexity of the cornea will also be increased. Any cause which
produces the contraction of the pupil, such as a bright light,
enables the eye to adjust itself more rapidly to vision at a shorter
distance ; and, on the contrary, the suspension of this power of
contraction of the circular fibres of the iris, occasioned by bella-
donna, is accompanied by the total but temporary loss of this
power of adjustment. Those who, by frequent practice in expe-
rimenting on their own eyes, have acquired a considerable volun-
tary power of changing the refracting condition of the eye, even
although there be no object before the field of vision requiring
such change, when they exert this power, also contract the pupil,
which by this means indirectly acquire the character of a volun-
tary muscle ; although in other respects, and with other persons,
it is strictly to be ranked in the class of the involuntary muscles.
The writer of this treatise possesses this power, and has given an
account of the circumstances attending its exertion in a letter to
Mr. Travers.f

670. The same gradation of density in the successive lamina?
of the crystalline lens, and the consequent successive refractions
of the rays effected by the several humors of the eye, have also
the effect of correcting the dispersion of light, arising from the

* Ibid, for 1793, p. 169 ; and for 1801, p. 53.

I Contained in the sketch of the Physiology of the Eye, prefixed to Mr.
Travers' Synopsis of the Diseases of the Eye and their Treatment, p. 72.

[It is very doubtful whether such power of adaptation really exists. Magen-
die's opinion (Precis Elementaire, i. 72, 2de ^dit.) is decidedly in the negative ;
and the late Dr. Fletcher (Rudiments of Physiology, Part 3, p. 48, Edinb.
1837), after alluding to the various hypotheses on the subject, adds : "It
appears absurd to atlempt to explain a fact which has no real existence,
since it has never been proved that the eye-ball has any capability of adapt-
ing itself to different distances, or that any such adaptation is required."
See, on all this subject, Dunglison's Physiology, 3d edit. i. 219.]

286 SENSORIAL FUNCTIONS.

difference in refrangibility of the differently coloured rays.* The
eye, in addition to its other perfections, has the properties of an
achromatic optical instrument, correcting the confusion of colour
in the images it forms on the retina.

671. All extraneous Hght, which might be reflected from one
part of the eye to another, and might be mixed with the rays
which should exclusively form the image on the retina, is ab-
sorbed by means of the pigmentum nigrum, which is placed
immediately behind the retina, which lines' every part of the in-
terior of the eye, and which extends over the cihary circle, and
over the posterior surface of the iris.

672. Different parts of the retina possess different degrees of
sensibility ; the centre, or that situate in the axis of the eye as it
is called, immediately opposite to the pupil, being by far the most
sensible part. We accordingly see most distinctly those objects,
the images of which are formed on that spot. Hence, whenever
we pay attention to an object, we immediately direct both eyes
towards it in such a manner as that the centre of both retinae
may receive its image. It is very remarkable that there is a mi-
nute circular space situate exactly in the axis of the eye, where
the retina seems to be deficient, so as to produce the appearance
of a perforation at the very point where vision is most distinct.
No satisfactory explanation of this curious circumstance has yet
been given.

673. When the eye is at rest, the field of distinct vision is very
limited ; it extends, however, according to Dr. Young, to a space
formed by a radius of about 60 or 70 degrees ; it extends to a
greater distance outwards than inwards, being 90 degrees in the
former direction, and only 60 degrees in the latter. It extends
downwards 70 degrees, and only 50 degrees upwards.

674. Mariotte,-)- of the French Academy of Sciences, made the
curious discovery that there is a part of the retina situate at the
termination of the optic nerve which is insensible to light ; so
that when the image of any object falls upon that precise spot, it
is no longer seen. The conclusion which he drew from this fact
was, that the seat of vision is not the retina, but the choroid coat ;
for at this spot the choroid coat is wanting, being perforated to
admit of the passage of the optic nerve. But the phenomena is
better accounted for by the consideration, that there is present at
that spot the central artery of the retina, which here divides itself

* [The iris has also a great agency in correcting this aberration of refrangi-
bility, by preventing the rays of light from falling near the margins of the
crystalline, and causing them to innpinge upon the centre, where the opposite
surfaces are nearly parallel, and consequently the dispersion of the rays is
least.]

t Phil. Trans, for 1668, vol. iii. No. 35, p. 668 ; and also Memoires de
I'Acad. i. 68, and 102.

PHENOMENA OP SENSATION. 287

into a number of radiating branches, and excludes the presence
of nervous matter, in which, judging from the analogy of all the
Other senses, the power of communicating sensation exclusively
resides. This defect in vision, if we may so term it, is seldom
perceived when both ej^es are used, because the optic nerve
enters each eye obliquely, and on different sides of the centre of
the retina ; so that they can never both receive the image of the
same object at the same time.

675. The defects of the eyes of some persons with respect to
their refractive powers produce what is called long-sightedness,
when these powers are deficient ; and short-sightedness, when too
great. The source of former imperfection, which constitutes the
presbyopic eye, may often be traced to the effects of age, which
produces a flattening of the cornea ; and probably also impairs
that voluntary power by which the refractions may be increased
when near objects are viewed. The short-sighted or myopic eye,
has generally an excessive convexity of the cornea, which may
be diminished, but is very seldom materially so, by the progres's
of age. The remedies for these defects are obvious ; namely, the
use of convex spectacles for the presbyopic, and of concave spec-
tacles for the myopic eye ; the former supplying the deficiency
in the power of refraction ; the latter correcting its excess.

676. Such then are the means employed for producing certain
impressions on each retina, which it is the office of the optic
nerves to transmit to the sensorium, where these give rise to cor-
responding sensations. The inquiry into the perceptions arising
in the mind in consequence of these sensations belongs to another
branch of the subject hereafter to be considered. It will be suffi-
cient in this place to point out the general fact relating to the
physiology of the eye, that the impression made upon each point
of the retina, produces in the sensorium a distinct impression,
suggesting to the mind a distinct sensation.

CHAPTER XVI.

PHYSIOLOGICAL LAWS OF SENSATION".

Sect. I. — Phenomena of Sensation.

677. Having examined the different modes in which impres-
sions are made upon the extremities of the nerves situate in the
respective organs of sense, we have next to direct our attention
to the physiological phenomena, which ensue on those impres-
sions being received.

288 SENSORIAL FUNCTIONS.

1. Specific Endowments of the Nerves of Sensation.

678. The extremities of the nerves intended to receive these
impressions appear in general to be expanded over a certain
extent of surface, and to be of a softer texture than the nerves
themselves. This difference appears to arise from their being
divested of the membranous covering which closely binds to-
gether the filaments composing the nerves, while they are pursu-
ing their course from one part to another. Such expansions are
noticed in the optic, auditory, and olfactory nerves, and probably
also in those distributed to the papillse of the tongue, and the
cutis. The nerve of each particular sense appears to have dif-
ferent specific endowments. Thus the optic nerve and retina
are peculiarly adapted to be afllected by the impressions of light ;
and are not fitted to convey^any other impressions. There are
experiments recorded which tend to show, that irritation of these
nerves does not communicate pain, as is the case with that of
nerves sent to other parts of the body. On the other hand, no
other nerve in the body is capable of exciting, by any change
that can be induced upon it, the sensation of light, as was pre-
tended in the case of the celebrated imposture of Miss M'Avoy
of Liverpool, who endeavoured to persuade people that she could
see with the tips of her fingers : or in the more elaborate delu-
sions of animal magnetism, in which persons are stated to be
able to read a piece of writing applied to the pit of the stomach,
or nape of the neck, by optical impressions made on different
parts of the skin.

679. That the optic nerves are incapable of exciting by their
action any other sensations than those of light, is farther rendered
probable by the circumstance that these sensations may be pro-
duced by other causes than those which usually give rise to
them ; such as impressions of a mechanical nature. A blow in
the eye, producing sudden pressure on the retina, excites the
sensation of a flash of light. The appearance of brilliant spangles
in the field of vision is often the result of too active a state of
circulation in the vessels of the retina, which excites in the fibres
of the nerves actions similar to those produced by the presence
of fight. The galvanic influence affecting the same, or even
neighbouring nerves, produces, in like manner, the sensation of a
flash of light. Analogous facts have been noticed with regard
to other senses. The v^'ell-known sensations of singing in the
ears is the consequence of an action of the auditory nerves,
excited by the state of the circulation in the organ of hearing,
and is probably totally unconnected with any real sonorous vi-
brations communicated to that organ.

MODIFICATIONS OP IMPRESSIONS. 289

2. Modifications of Impressions.

680. In order that an in:ipression made upon the sentient
extremity of a nerve may excite sensation, it must be applied for
a certain time; for if it be of too transient a duration, no effect,
as far as regards sensation, is produced. This is well exempli-
fied in the case of vision ; we lose sight of an object in very
rapid motion, because the impression made by its image on the
different points of the retina on which it is successively formed,
is of too transient a nature to excite those actions which produce
sensation.

681. On the other hand, when a distinct impression has been
made on the nerve, that impression has a certain duration, inde-
pendently of the continuance of the cause which excited it ; for
the sensation produced is, to a certain extent, permanent. This
is also shown, in the case of vision, by several experiments
familiar to all, such as whirling rapidly, with a circular motion,
an object brightly illuminated, which gives rise, as is well known,
to the appearance of a continuous circle of light. Many optical
deceptions are founded on the same principle, such as that of the
Tliaumatrope, of the Phantascope, or Phenikisticope, and the
curved appearance of the spokes of a revolving wheel when
viewed through parallel bars, of which last phenomena the theory
has been elsewhere given by the writer of this treatise ;* and also
the appearance of a similar kind noticed by Mr. Faraday .f

682. One of the consequences of the law of the permanence
of sensations is, that impressions, which rapidly succeed one
another in the same nerve, are not distinguishable as separate
impressions, but produce a blending together, or coalescence into
one sensation. Thus, if a circle painted in different parts of the
circumference with different colours, be rapidly whirled round
its centre, the colours are blended together into one tint ; and if
the different prismatic colours of the spectrum be properly adjusted
as to their relative proportions, the effect of this coalescence of
the sensations excited by the whole is that of a white colour.
The thaumatrope may also be made to illustrate this principle ;
for the pictures on the two sides of the card appear, by the rapid
revolution of the card, to coalesce into one.

683. The most remarkable and complete illustration of the
same principle is afforded by musical sounds, which though they
appear continuous, are, in fact, composed of separate impulses,
repeated at very short, but regular intervals of time.

684. Another law of sensation, is, that when a nerve has re-
ceived a strong impression, that nerve is proportionally weakened

* Philosophical Transactions for 1815.

f Journal of the Royal Institution, vol. i. p. 205. See also Dr. Roget's
Bridgewater Treatise, vol. ii. p. 524. [Amer. edit. ii. 368.]

25

290 SENSORIAL FUNCTIONS.

for a certain time after, and is less susceptible of a similar impres-
sion from the application of the same cause. The eye, after
being dazzled by a strong light, has its sensibility diminished to
the impressions of a weaker light. Different parts of the retina
thus acquire different degrees of susceptibility of being affected
by the same quantities of light. Thus, if the eyes be directed
steadily to a bright object for a certain length of time, and be
then transferred to a white sheet of paper, a dark spot, having
the figure of that object, will be seen on the paper, in consequence
of that portion of the retina, on which the luminous image had
been impressed, being fatigued, and rendered less excitable than
those parts of the retina which did not receive that image. The
light from the paper which arrives at that part of the retina,
which had received the impressions of the bright object, will
produce less effect on that part, than the light of equal intensity
from other parts of the paper does on the other parts of the
retina. Those parts^of the paper, which are situate so as to
have their image on the exhausted part of the retina, appear
darker, therefore, than the rest; and hence arises the appearance
of a dark image. The experiment may be reversed by fixing
the eyes attentively for some time on a dark object on a white
ground, and then transferring it to some other part of the white
ground ; when imrnqdiately a brighter spot, corresponding in size
and figure to the dark object, will be seen.

685. These appearances, which imitate those of real objects,
have been called ocular spectra. The susceptibility of the retina
to receive impressions of particular colours is also found to be
affected in the same manner, when any one of them has been
strongly impressed. Thus the spectrum of a coloured object,
while it has the same dimensions and figures as the object, will
at the same time have an opposite colour, when the eye is trans-
ferred to a white ground. It will have what is called the com-
•plernentary colour to that of the object itself; that is, it will have
that tint which results from the admixture of all the colours
composing white light, \yhen the latter colour is left out. Thus
red and green, yellow and purple, blue and orange, being com-
plementary colours respectively to each other, the ocular spec-
trum of a red object will be green, that of a green object red,
and so with all the others.* ■'

686. We may here observe, that the appearances of spectra,
above described, are merely temporary ; for the several parts of
the retina soon regain their natural state of equable sensibility.

687. Illustrations of this law readily present themselves when
we search for its application with regard to all the other senses.

* For more ample details on this subject, the reader may be referred to an
Essay on Ocular Spectra, By Dr. Charles Darwin, published in the 76th^
volume of the Philosophical Transactions, and reprinted in Dr. Darwin's
Zoonomia.

' CONDITIONS NECESSARY FOR SENSATION. 291

Sounds which are too loud produce temporary deafness, or at
least impair for a time the scnsibihty of the ear to weaker sounds.
Similar phenomena are observed as to odours and tastes, with
reference to their appropriate senses. The sensibiHty of the skin
to different temperatures varies considerably according to the
previous impressions which have been made upon it. Thus the
same body may appear either hot or cold, according to the pre-
vious temperature of the hand which is applied to it.

Sect. II. — Conditions necessary for Sensation.

688. The sensibility of the sentient extremities of nerves or
their capabilit}/ of receiving such impressions as lead to their appro-
priate sensations, is dependent on certain conditions of the organ.
These conditions are principally the folUowing. First, it is
necessary that the organ receive a proper supply of arterial
blood by the vessels circulating through it, and particularly through
that part on which the nerves are distributed. Secondly, it is
required that the expansion of the nerve belonging to the organ
should be exempt from excessive pressure. Compression of a
nerve in any part of its course immediately puts a stop to all its
functions; and consequently its power of receiving and convey-
ing impressions is suspended as long as the pressure is continued.
On the removal of the pressure, provided it has not been too violent,
or too long continued, the nerve after a certain time, generall)^
recovers its powers. Thirdly, a certain temperature is requisite
for the maintenance of sensibility in the nerves. The benumbing
effect of cold is well known, and extends generally to all the func-
tions of the nervous system. It is very probable, that this operation
of cold is referable to its retarding or arresting the circulation in
the capillary vessels ; and it might, therefore, perhaps, be included
in the causes which influence the first of the conditions here
enumerated. Lastly, the office of every nerve being to transmit
impressions from one of their extremities to the other, it is neces-
sary for the due performance of this function, that an uninterrupted
continuity of their filaments should be preserved throughout their
whole course. The complete division of a nerve in any part,
necessarily prevents this transmission, and destroys the function
of the nerve.

689. Irritations applied to the nerve in any part of its course^
produce sensation, provided the communication of that part with
the brain be uninterrupted by any of the causes above specified.
Thus, if a nerve be tied or divided at any point, irritations applied
below the ligature or division will produce no effect as to sensa-
tion ; but when applied above that point, sensation immediately
follows. What is here said applies more particularly to the nerves

292 SENSORIAL FUNCTIONS.

distrbuted to various parts of the body, and especially to the
integuments ; the irritation of which nerves gives rise to a sense
of pain. The nerves of the senses of' sight, of hearing, of smell,
and of taste, are so situate as hardly to admit of being the subjects
of experiments which might decide the question as to what kinds
of sensation would be excited by irritations directly applied to
them : and whether these sensations would be similar to those
they usually convey from impressions made upon their extremities.
Analogy would undoubtedly be in favour of such similarity.
Persons who have lost a limb by amputation, experience sensations
not only of pain, but also of touch, and of muscular motion, exactly
similar to those which they formerly derived from the parts of the
limb which they have lost. These sensations arise from imitations
taking place, either in the lower extremities of the nerves which
have been divided, and which remain in the stump, or in the brain
itself.

690. The most remarkable circumstance attending the commu-
nication of irritations along the nerves of sensation, is the celerity
of the transmission. It appears, indeed, to be instantaneous, and
can be compared only to the rapidity of the electric fluid passing
along a conducting body.

Sect. III. — Theories of Sensation.

691. We are completely ignorant of the nature of that powder
by which the nerves effect this rapid communication along the
lines of their fibres, and even of the changes which take place in
the nerve while it is performing this function. Several hypotheses
have been proposed with a view to supply this chasm in our
knowledge. The oldest of these, and that^which maintained its
ground for many centuries, is, that the brain and nerves are
furnished with a certain fluid, which was called the animal spirits,
and was the medium of communication between the different
parts of the nervous system. Traces of this theory may be found
in the writings of Hippocrates ; but it derived its principal support
from Descartes, who reduced it to a regular form, and powerfully
recommended it by the force of his authority. According to the
views of those who espouse this theory, the brain is considered
as an organ whose principal office it is to secrete the animal
spirits, which are of a very subtile and ethereal nature, and to
supply them to the nerves, which were considered to be the natural
excretory ducts of the brain. The existence of this fluid was, for
a very long period, universally admitted by physiologists, and the
doctrines founded upon it were more or less mixed up with all the
reasonings of physicians respecting the causes and phenomena of
diseases, and the effects of remedies. Traces of the influence of

THEORIES OP SENSATION. 293

this doctrine may be found in the popular language of medicine
even in the present day, when the hypothesis from which it is
derived is deservedly exploded as perfectly gratuitous, and devoid
of any just foundation.

692. Another hypothesis invented to account for the propaga-
tion of impressions along the fibres of nerves, was that of their
depending on vibrations or periodical oscillations of their parti-
cles, analogous to those of the strings of a harpsichord when
producing musical notes. The great champion of this doctrine
was Hartley,* who embellished it by his beautiful applications to
a great variety of phenomena relating to sensations, and even to
the intellectual operations. It afforded a happy explanation of
many of the phenomena of ocular spectra, and of those depend-
ing on the permanence of sensations. It is needless to remark,
that this hypothesis is equally visionary and destitute of any solid
basis as the former.

693. All these mechanical theories are overturned by the fact
that no tubular structure can be discovered, on the minutest ana-
tomical scrutiny, to exist in the filaments which compose the
nerves ;f nor can the slightest motion be detected in any of their
parts, while they are actively transmitting the impressions of
sensation.

694. The latest hypothesis as to the nature of nervous power
is, that it is identical with electricity. It is supported principally
by the experiments we have already mentioned, in which, after
the par vagum was divided, so as entirely to intercept its action
in promoting the secretion of the gastric fluid, secretion was re-
stored by transmitting the galvanic fluid along the lower portion
of the nerve. The experiment, indeed, applies only to a parti-
cular office of the nervous power, namely, that of promoting
secretion ; but the hypethesis it suggested has been extended to
all the other functions of the nerves, and of course to their power
of transmitting thbse impressions which give rise to sensation.

* On Man. A full account of Hartley's theory is given by Dr. Priestley,
in a separate work bearing that title.

f [We have already shown, (note to §588,) that some distinguished ob-
servers of the present day still maintain, that the neryes are tubular.]

25»

294 SENSORIAL FUNCTIONS.

CHAPTER XVII.

FUNCTIONS OF THE SENSORIUM. ^

Sect. L — Locality of the Sensorium.

695. If we except the nerves appropriated to the organs of the
specia] senses of sight, hearing, smell, and taste, and those dis-
tributed on the face, and other neighbouring parts, all the nerves
subservient to sensation appear to terminate in the spinal cord.
We are then, in the first place, to determine whether the impres-
sions which these nerves convey to that organ, are transmitted
to any other part of the nervous system, previously to sensation
being produced.

696. Experiments in all the animals whose structure, as far as
regards this part of the nervous system, is analogous to the human,
have established the general fact, that sensation does not take
place, unless the part of the spinal cord to which the nerve is
connected, communicates by an uninterrupted continuity of sub-
stance with the brain. The division of the spinal cord near the
foramen magnum, instantly renders the whole body insensible ;
but it does not appear so immediately to deprive the parts about
the face of sensibilitj^ for some degree of it appears to be retained
as long as the circulation continues. The injury, indeed, soon
becomes fatal, by the circulation ceasing in consequence of the
interruption to the function of respiration. The effects of injuries
to the spinal cord occurring to men from accidents of various
kinds, afford ample confirmation of the fact that the brain is the
general centre to which all impressions -made upon the nerves
must ultimately be brought before they can excite sensation.

697. Admitting the brain to be the immediate organ of sensa-
tion, it next becomes a question, whether any particular part of
the brain is more especially appropriated to the exercise of this
function. It is to such a part, supposing it to exist, that the name
of sensorium has been applied. There are two modes of con-
ducting this inquiry ; the first is by tracing, very carefully, the
filaments of all the nerves which are immediately connected with
the brain, and endeavouring to discover if they unite in any
central part of that organ, which may accordingly be supposed
to be the seat of sensation ; or, in other words, the sensorium.
The second mode of investigating the subject, is to ascertain if
any one part of the brain can be discovered, on which impressions
directly made, are invariably productive of sensation.

' REQUISITE CONDITIONS OF THE SENSORIUM. 295

698. The fibrous substance of the spinal cord, being directly
continuous with the medulla oblongata, nfiay be supposed to ter-
minate in that part of the brain ; so that, viewing the spinal cord
as a collection of all the fibres of the nerves of sensation continued
along its whole length, these nerves themselves may be considered
as following this course, and having this termination. These
fibres are found more particularly to converge towards the cor-
pora quadrigemina, and crura cerebri. Now, it happens that
this is also the very spot with which the nerves of the senses,
whose organs are in the head, namely, the fifth, seventh, and
eighth pairs, are more particularly connected. It appears, also,
from the late investigations of the French physiologists, that no
part of the brain higher than the corpora quadrigemina, and no
part whatever of the cerebellum, is essentially concerned in sen-
sation ; for it is found that in animals the power of sensation
remains, even after the removal of all the parts of the brain, or
of the cerebellum, higher than this spot. The conclusion which
has been deduced from these experiments is, that the medulla
oblongata, and more particularly that segment of it to which the
nerves of the head are united, is the organ most essentially con-
nected with the mental change constituting sensation. But it is
not probable that these corporeal changes immediately connected
with sensation, are confined to a single point in the brain, which
might emphatically be termed the seat of the soul, as Descartes
expressed it, when he boldly pronounced the pineal gland to be
that spot.*

Sem:!T. II. — Requisite Conditions of the Sensorium.

699. A multitude of facts tend to confirm the view of the sub-
ject which has here been taken. The same conditions as those
which are required for the exercise of the functions of the nerves
in every part of their course, are equally necessary for the per-
formance of those of the brain. It is indispensable that the
circulation in the brain should be in a healthy state, and that
arterial blood be supplied by its vessels. It is indispensable that
a proper temperature be preserved ; and it is likewise indispen-
sable that the brain be not compressed by any considerable force.
A failure in any one of these conditions, produces total depriva-
tion of the power of sensation, as well as of all the other
functions of the brain. This effect is found to result more
particularly when pressure is made in the direction of the
medulla oblongata ; for in that case complete insensibility takes
place; and on the removal of the pressure, the faculty of sensa-

* [Dunglison's Physiology, 3d edit. i. 308.]

296 SENSORIAL FUNCTIONS.

tion slowly returns; but if any considerable injury has been
inflicted on that part, the power of sensation is irrecoverably
lost.

700. It is probable that most of the laws which regulate the
functions of the nerves with respect to sensation, apply with
equal truth to the sensoriurn itself; but with regard to several of
the phenomena, it is difficult to determine whether they depend
on affections of the sensoriurn, or of the extremities of the nerves,
situate in the organ of sense. We must despair of being able
to resolve this question, because the change which takes place in
both these parts, appear to be simultaneous. The impaired power,
for example, which is the result of a strong impression from an
object of sense, may arise equally from the exhaustion of that
part of the sensoriurn to which the impression is communicated,
as of that of the sentient extremity of the nerve ; and we hkve no
means of discriminating between them.

701. Another point of resemblance is, that irritations applied
to the sensorium, from other sources than the nerves themselves,
give rise to the same train of sensations as impressions commu-
nicated through the nerves. These irritations may be given by the
pressure of blood circulating in the arteries of the sensorium ;
and this is probably the source of many of those sensations gene-
rally ascribed to affections of the nerves, or of the organs of
sense. Pains, and other sensations in various parts of the body,
arise from affections of the brain. The same origin may often
be assigned to sensations which arise in dreams, and likewise to
various spectral illusions which affect persons who are awake,
and aware of their being deceptions of the sense. In delirium
and insanity, the sensations from this cause assume a fearful de-
gree of intensity, and are accompanied by a fixed belief in their
reality.

Sect. III. — Laws of Recurrence, and of the Association of
Impressions.

702. With regard to all the subsequent changes and operations
which take place when sensation has been excited, it is extremely
difficult to pronounce how much of the phenomena are purely
mental, and how much are strictly the result of corporeal changes
connected and associated together by physical laws. In other
words, it is difficult to determine what are the operations in
which the mind is purely passive, and dependent on the actions
of its bodily organs, and what are those in which it exerts a
spontaneous power of action, and thereby reacts upon those
organs, and produces in them a series of changes which lead to
the most important results. The distinction we are attempting

ASSOCIATION OF IMPRESSIONS. 297

to draw, is founded upon this essential difference in the order of
sequence of the phenomena, that in the one the organic change
precedes the mental change, and in the other succeeds to it.

703. The two principal physiological laws relating to the former
of these physical changes, namely, those which precede the mental
affections, are, first, the law of spontaneous recurrence. When-
ever an impression of a certain intensity has been made upon the
organs of sense, the sensation which is produced by it, after dis-
appearing for a certain time, recurs without the presence of the
cause which originally excited it ; and this happens repeatedly,
and without any corresponding effort of the mind, and often in
opposition to any effort which can be made to counteract the
tendency. This spontaneous recurrence of sensations is proba-
bly the result of the repetition of those changes in the sensorium
which originally gave rise to them. In the language of meta-
physics, the corresponding mental nffections are termed ideas,
in order to distinguish them from the similar and more vivid
affection excited by the primitive impression, and to which the
term sensation is more particularly appropriated.

704. The second law which regulates the unknown affections
of the brain connected with the passive phenomena of mind, is
that oi association, or the law by which impressions, and conse-
quently the corresponding ideas, recur in the same order of
sequence as that in which they were originally excited. The
phenomena of disease, and the operation of different agents wdiich
modify the state of circulation in the brain, and the conditions of
the nervous powers, afford ample evidence that the modes of as-
sociation, and of the sequence of impressions and ideas, are de-
pendent on the physical condition of the brain, and result from
certain changes taking place in that organ.

705. The views here presented, far from being favourable to
the doctrine of materialism, are directly opposed to it ; since they
necessarily imply the existence of an essential distinction be-
tween mind and matter, and aim only at tracing the connexions
which have been estabhshed between them by the divine Author
of our existence.

706. Such, then, being the physiological connexions which
exist betv^'een the physical changes taking place in the brain, and
the passive phenomena of the mind, it is not an unreasonable
supposition, that the voluminous mass of cerebral substance
which, in the human brain especially, has been superadded to
the medulla oblongata, or to the immediate physical seat of sen-
sation, is in some way subservient to that astonishing range of
intellect and combination of mental faculties which are found in
man. We may conjecture also, with much appearance of pro-
bability, that in the lower animals, the intellectual endowments
which mark several of the more intelligent races are connected
with similar, though inferior, expansions of cerebral substance.

298 SENSORIAL FUNCTIONS.

707. All the mental phenomena in which the mind is passive
have been referred by metaphysicians to the principle of associ-
ation, and consequently may, in as far as this principle is con-
cerned, be connected with the physical changes above noticed.
Hence we find the memory, which is the direct result of that
law, is more especially liable to be impaired by certain physical
states of the brain, such as those induced by severe concussion,
by fevers, and by the progress of age.

708. As scarcely any thing is known with regard to the phy-
sical changes which take place in the brain in the relations which
they bear to mental phenomena, the further consideration of
these phenomena belongs properly to psychology rather than to
the subject of this treatise. The inquiry must here be taken up
by the metaphysician, whose province it becomes not the physio-
logist to invade.

Sect. IV. — Volition and Voluntary Motion.

709. Leaving, therefore, to the metaphysician the analysis of
those mental phenomena, which, however dependent they may
be for their existence on the healthy actions of the brain, require
modes of investigation different from those of physiology, and
lead to results very remote from any conceivable laws of mate-
rial agency ; we may resume the subject at the point when, in
consequence of the mental acts of volition, by which term we
here mean to express the endeavour to produce certain specific
movements of the body, new changes are again produced in the
cerebral organs, and new trains of physical phenomena succeed.
That this mental effort of volition constitutes a distinct step in
the series of phenomena, is proved by the instances of paralysis,
in which the patient is conscious of making the effort to move
the palsied limb, yet no motion, or even sensation of motion,
ensues. Another illustration of the same distinction is derivable
from a different disease affecting the limbs, namely, anesthesia,
which consists of the loss of sensation only, while the power of
voluntary motion remains ; and in which the voluntary act so
exerted produces the intended muscular contractions, unattended,
however, with the feelings which usually accompany them. The
same complete ignorance in which we are with regard to the
changes which take place in sensation, pervades our notions of
those which attend vohtion, in as far as they occur in the brain.
A few facts, indeed, have been collected with regard to those
parts of the brain which are impressed, if such a term may be
used, antecedently to the voluntary motions of the limbs. They
appear to be chiefly the crura of the cerebellum, and the adjacent
parts of the medulla oblongata.

VOLITION AND VOLUNTARY MOTION. 299

710. All the physical conditions which are necessary in order
that sensations may be felt, are equally necessary for rendering
the cerebral organs capable of receiving from the mind those
impressions which lead to voluntary motion. The mental stimulus
of volition produces a certain effect on the origin of the nerves,
leading to the muscles employed in these motions, which impres-
sion, being propagated along the course of those nerves, excites
these muscles to contraction. The transmission of those impres-
sions is made with the same celerity, and probably by the same
agency, as those which produce sensation ; but they are made in
the contrary direction, namely, from the brain, instead oitoicards
it. The same condition of perfect continuity of fibres, of freedom
from pressure, and of healthy circulation, are essential requisites
in both cases; and every thing that has been said with regard to
the former, is also appHcable to the latter. Mechanical irrita-
tions, applied either at those parts of the brain v/hich adjoin the
origin of the nerves, or to the nerves themselves, either at their
origin, or in any part of their course, whether that portion of the
nerve situate between the point to which the irritation is applied
be entire or divided, or compressed by a ligature, are found to
produce the same muscular contractions as those which are the
result of volition.

711. Mr. Mayo* ascertained, that after any nerve which sup-
pHes a voluntary muscle is cut through, either in a living animal,
or immediately after death, mechanical irritation of the part of
the nerve disconnected with the brain, as for instance the pinch-
ing it with a forceps, causes a single sudden action of the muscle
or muscles it supplies. On the other hand, a like effect cannot
be produced by irritating mechanically the nerves distributed to
those muscles over v^'hich the will has indisputably no influence.
"It must be admitted, however," he remarks, "that this phenome-
non is not exclusively confined to those muscles which are allowed
on all hands to be voluntary ; nor, indeed, is it shown in all the
muscles which seem at first sight to be directly under the control
of the will." But it is not easy, in various instances, to determine
whether muscular actions are voluntary or not; while the point
of distinction proposed by Mr. Mayo has the recommendation of
being easily verifiable. Setting aside, therefore, in the first instance,
the question of the influence of the will, let us be satisfied with
observing what muscles act when a divided nerve that enters their
substance is mechanically irritated," and what do not. We may
afterwards trace the collateral differences of the two classes of
muscles which are thus distinguished.

712. The parts which are susceptible of this mode of excitement,
are the muscles of the trunk, head, and limbs, of the tongue, of
the soft palate, of the larynx, of the pharynx, and oesophagus, and

* Outlines of Human Physiology, 3d edit. p. 39 to 42.

300 SENSORIAL FUNCTIONS.

of the lower outlet of the pelvis. The opposite class comprehends
the heart, the stomach, the small and great intestines, and the
bladder.

713. The collateral differences which characterize either class
are, with exceptions afterwards to be adverted to, the following : —

Of the muscles which act when a nerve distributed through
them is mechanically irritated, it may be remarked ; 1. That
they admit of being thrown into action by an effort of the will.
2. That with sufficient attention and resolution, their action may
be refrained from. 3. That their action is attended with a con-
scious effort, and is guided by sensation. 4. That if divided,
the separate parts retract instantaneously to a certain distance,
and subsequently undergo no farther permanent shortening.
5. That when mechanically irritated, a single and momentary
action of their fibres alone ensues. 6. That they remain relaxed,
unless excited by special impressions, both in the living body, and
before the loss of irritability after death. 7. That their action in
the living body habitually results from an influence transmitted
from the brain or spinal cord through the nerves.

714. The exceptions to be made against this statement, if ap-
plied generally, are, that the three first affections are not easily
brought home to the muscular fibres of the oesophagus, or of the
lower part of the pharynx ; but it deserves at the same time to
be considered, that the lower part of the pharynx and the cbso-
phagus are in the peculiar situation of parts employed on one
object alone, instinctively and habitually, on the recurrence of
one impression ; a condition which would soon reduce a strictly
voluntary muscle to a state apparently removed from the control
of the will.

715. Muscles of the preceding class, if we except the fasciculi
belonging to the pharynx, and oesophagus, and urethra, are so
disposed as to extend from one piece to another of the solid
frame-work of the body ; they enlarge or straighten the cavities
of the trunk ; they produce the phenomena of the voice ; they
close the excretory passages ; the greater number are employed
to move the limbs on the trunk and the frame on the ground.
Muscles of the second class are used, like the exceptions in the
preceding, as tunics to the hollow viscera, the cavities of which
they diminish in their action, and thus serve to give motion to
their contents. The oesophagus, indeed, appears to partake of
the nature of both classes oi" muscles; when the nervi vagi are
pinched, one sudden action ensues in its fibres, and presently
after a second of a slower character may be observed to take
place.

716. Of the muscles which do not act on the mechanical irri-
tation of any nerve distributed through them, it may be remarked,
1. That the will cannot instantaneously or directly produce action

VOLITION AND VOLUNTARY MOTION. 301

in them. 2. That the resolution to abstain from their action is
insufficient to repress it. 3. That their action is not attended
with a conscious eflbrt, and seldom has reference to sensation.
4. That if divided, the retraction which follows is in most in-
stances slow and gradual. 5. That if they are mechanically
irritated, not one, but a series of actions ensues. C. That their
natural state, in the absence of external impressions, is not con-
tinued relaxation. When the heart and bowels are removed
from the body of an animal immediately after death, they con-
tinue for a time alternately to contract and to dilate. 7. That
an impression transmitted through the nerves does not appear
the usual stimulus to their action.

717. From the experiments of the French physiologists it
would appear, that in an animal deprived of all the upper portions
of the brain, but in which the medulla oblongata is preserved, all
indications of the more complex operations of thought disappear,
but the animal still remains capable of executing such voluntary
motions as are of an instinctive character, as, for example, swal-
lowing. Animals deprived of the cerebellum, provided the me-

, dulla oblongata remains, and is free from compression, not only
appear to be capable of sensation, but give all the usual indica-
tions of intelligence, and evidently exert volitions, which occasion
the action of many voluntary muscles. But they have lost the
power of regulating the contractions of those muscles so as to
execute any definite voluntary action, excepting those which are
instinctive. All the other voluntary movements of the body and
limbs are performed in so irregular a manner, that they are, ge-
nerally ineffective for the purposes for which they are intended ;
and most of the usual complex movements required for progres-
sive motion cannot be performed at all. This has been explained
by the supposition that the animal has lost all I'ecollection or
association of those trains of muscular sensations which used to
accompany and to guide these movements, inconsequence of the
loss of the cerebral organs which are instrumental in furnishing
those associations. One of the inferences drawn from these facts
(which themselves require more ample confirmation before they
can be regarded as established) is, that the recollection of those
associations connected with voluntary motion depends on the
cerebellum, in the same way in which the associations of sensa-
tions and ideas depend on the hemispheres of the brain.

718. It is a remarkable circumstance that injuries or diseases
occurring in the hemispheres either of the cerebrum or cerebellum
produce paralysis, that is, destroy the power of voluntary motion,
of the muscles situate on the opposite side of the body. This has
been endeavoured to be explained by the alleged decussation or
crossing of the nervous fibres of the lower part of the corpora
pyramidalia on each side. But in order to account for all the

26

302

SENSORIAL FUNCTIONS.

phenomena of this kind, we must suppose the decussation to take
place between the fibres which compose the posterior and the
anterior columns of the spinal cord.

719. Although the function of the nerves in transmitting impres-
sions from the organs of sense to the brain, which give rise to
sensation, and in transmitting impressions of volition from the
brain to the muscles of voluntary motion, which give rise to the
contraction of those muscles, appear to be of the same kind, and
to difler only in the direction in which the impression is trans-
mitted, the question has often been asked, whether the same
nervous filaments which transmit the one class of impressions are
employed to transmit the other likewise ; or whether difi^erent
portions of the nerve are appropriate to these different offices.
The truth of the last of these propositions may now be considered
as being firmly established.

720. The observations which first suggested the idea of there
being two sets of nervous filaments, the one subservient to sensa-
tion, and the other to volition, were those in which a limb was
only partially paralysed, the power of motion being retained,
while that of feeling was lost. Experiments had also been made
in which nerves that had been divided, and had afterwards spon-
taneously united, were found to have recovered the power of
placing the muscles to which they were distributed under the
command of the will, but yet had no power of conveying sen-
sitive impressions. Erasistratus and Herophilus had long ago
taught the doctrine of there being two species of nerves respec-
tively appropriated to these opposite functions ; and Galen was
inclined to the same opinion, from observing that both the tongue
and the eye are supplied with two separate sets of nerves, the one
apparently subservient to sensation, the other to motion. But it
is to Sir Charles Bell and Magendie that the merit belongs of
bringing forward decisive proofs of the reality of this distinction
between nerves for sensation and nerves for motion, the idea
having before been only loosely thrown out by speculative physi-
ologists as a plausible conjecture.

721. It results from this discovery that the transmission of
impressions in opposite directions, that is in the one case from
the extremities to the brain, and in the other from the brain to
the muscles, is effected by different nerves, or at least by different
sets of nervous filaments, and that no filament is capable of
transmitting impressions both ways indiscriminately, but always
in one particular direction. These two kinds of filaments
are, it is true, conjoined together into one nerve ; but the ob-
ject of this union is not community of function, but conve-
nience of distribution, the two kinds of filaments still remain-
ing distinct in their functions as they are likewise distinct in
their origins. We know that all the nerves connected with
the spinal cord have a double origin ; that is, are composed of

VOLITION AND VOLUNTARY MOTION. 303

two nerves, the one proceeding from the anterior, and the other
from the posterior columns of the spinal cord. It is found that
an injury done to the anterior roots of those nerves excites con-
vulsions in the muscles which they supply, but does not appear to
excite any sensation of pain in the animal on which the experi-
ment is made; and the division of those nerves is followed by the
immediate paralysis of those muscles, that is, by their incapability
of being excited to contract by any voluntary efforts. On the
contrary, the irritation of the posterior roots of the same nerve is
attended with no contractions of muscles, but calls forth expres-
sions of violent pain. The section of these nerves is followed by
insensibility of the parts which those nerves supply, while the
power of voluntary muscular contraction remains.

722. From the symmetrical situation of these nerves with
reference to the spinal cord, Sir Charles Bell has given them the
name of the original, or symmetrical nerves. They comprehend,
of course, all the spinal nerves which arise by double roots, the ,
posterior of which has invariably a ganglion near its origin, while
the anterior branch has no such appendage. These spinal nerves
are distributed laterally to the two halves of the body ; those of
the one side having' no connexion with those of the other. Sir
Charles Bell ranks the fifth pair of the cranial nerves in the same
class as the spinal nerves ; considering its two roots as composed
of filaments, appropriated the one to sensation, the other to motion ;
the former being provided with a ganglion near its origin, and
the latter having no ganglion. He regards the third, probably
the fourth, the anterior branch of the fifth, the sixth, the portio
dura of the seventh, and the ninth, as being exclusively motor
nerves, distributed to the muscles of the eye-ball, lower jaw, face,
and tongue, and placing these muscles under the control of the
will. The ganglionic portion of the fifth pair, on the other hand,
he regards as the great sentient nerve of the head ; which gives
exclusively sensibility to the face, eye-ball, mucous membrane of
the nose, mouth, and tongue. This nerve is in communication
with the posterior column of the spinal cord ; whilst the motor
nerves, above enumerated, appear to communicate with the ante-
rior column. An exception to this rule, however, occui's in the
CE^se of the fourth pair, which has never been proved to commu-
nicate with the anterior column of the spinal cord. It would
appear also that the larger portions of the eighth pair, which seem
to be more connected with the posterior than with the anterior
columns, are nerves both of sensation and of motion : so that the
exclusive appropriation of the nervous filaments, originating from
the different surfaces of the spinal cord, to motion or to sensation,
is perhaps not yet rigidly demonstrated.

72.3. It is remarkable that the peculiar sensations conveyed by
tha optic, the olfactory, and the auditory nerves, have been found

S04

SENSORIAL FUNCTIONS.

by Magendie to be much impaired, or even entirely lost, by injur-
ing the branches of the fifth pair of nerves, w^hich also supplies
the respective organs to which the above nerves appear to be
• particularly appropriated. The cause of this anomaly has not
yet been satisfactorily explained.

724. Sir Charles Bell has distinguished another class of nerves,
which he conceives to be altogether subservient to the function
of respiration, and to be distributed to the muscles concerned in
that function. These he terms the irregidar, or the superadded,
or the respiratory nerves. They arise by single roots ; they pass
from one organ to another in various directions, and pursue a
very irregular and intricate course, passing across the nerves
belonging to the symmetric system, occasionally uniting with
them, and connecting together the two halves of the body.
These nerves, according to Sir Charles Bell, are not under the
control of the will, and are not capable of exciting sensations;
their only office being that of transmitting impressions from one
part to the other. The nerves which strictly belong to this class'
are the eighth pair, the spinal accessory nerves, the phrenic, the
external respiratory nerve of Sir Charles Bell, and the great
sympathetics.

725. The first pair, or the olfatory nerves, the second, or the
optic, and the portio mollis of the seventh pair, are wholly nerves
of sensation ; and from the special nature of the impression they
convey, may be considered as forming a separate class of nerves.

726. Most nerves pass through ganglia,, or are interwoven .
with others in plexuses before they reach their destination. The
purposes answered by this intermixture of filaments, which, in
either case, appears to take place, is to provide extensive con-
nexions between the parts supplied with nerves and different
portions of the spinal cord, or medulla oblongata, from which the
several fibres originate. Thus the sensitive and the motory fila-
ments are intimately united in the same nervous cord, which is
thus rendered capajjle of performing all the functions of nerves.
Many hypothetical uses have been assigned to the ganglia, which
appear to be unsupported by facts. Drs. Gall and Spurzheim
suppose that they contribute to increase the nervous power in
those nerves on which they are placed ; but there does not seem
to be any solid foundation for this opinion.

727. Muscular contractions, then, may be distinguished, with
reference to the nervous power which excites them into four
classes; namely, 1. The purely voluntary motions ; 2. The auto-
matic motions; 3. The instinctive motions; 4. The involuntary
motions. We have now fully considered the first of these classes,
the purely voluntary motions, which may be defined to be those
consequent on an effort of volition of which the mind is conscious,
and which is accompanied by a distinct idea of the end interi^ed

AUTOMATIC MOTIONS. ^ 305

to be accomplished. No examples or illustrations are necessary
of motions belonging to this class, as they are those with which
■we are most familiar. We pass on then to the other classes in
the order in which we have enumerated them.

Sect. V. — Automatic Motions.

728. Automatic motions are those which consist of a series of
actions, each of which was originally the object of a distinct
volition ; but which by habit, that is, by repeated association,
have become linked together in such a manner, that a simple act
of volition is sufficient, apparently, to renew the whole series,
without requiring any separate effort of attention to each. Most
of the actions which we daily perform, such as walking, speak-
ing, writing, or playing upon a musical instrument, afford exam-
ples of automatic motions, being linked together by associations
which, far from requiring any conscious acts of volition, follow
one another in a regular order of sequence that cannot be broken
unless by the exertion of a separate effort of attention. All these
movements, however, are still voluntary, inasmuch as they re-
main under the control of the will, which commands their com-
mencement, can regulate their course, and can stop them at
pleasure.

729. The muscular actions required for respiration may pro-
bably be classed under this head. The immediate exciting cause
of the act of inspiration is a sensation felt in the chest from the
presence of venous blood in the capillary vessels of the lungs ;
and this sensation, if not speedily relieved, increases rapidly to
one of extreme distress, and even agony. The influence of this
sensation in exciting the very complicated actions which are ne-
cessary to relieve it by drawing air into the lungs, and which,
indeed, are continued during sleep, and even when sensibility to
all other impressions appear suspended, as in the state of apo-
plexy, is rendered manifest by the increased frequency and energy
with which these actions are performed whenever any cause
exists obstructing the free access of air into the lungs, and thus
augmenting the intensity of the sensation.

730. Since the actions of respiration are caused, in the first
instance, by sensations, they must be dependent on the sentient
nerves of the lungs, and especially on those that establish the
most direct communication between them and the medulla oblon-
gata, namely, the eighth pair of nerves. We find, accordingly,
that after the sections of those nerves the actions of respiration are
performed more slowly and less perfectly than when entire.
They, nevertheless, continue, probably by means of the other
communications which the lungs have with the brain, through

26*

306 (jB. SENSORIAL FUNCTIONS.

the branches of the great sympathetic proceeding from the spinal
cord. When the part of the medulla oblongata from which these
nerves originate is injured, all attempts at inspiration are arrested,
because a final stop is put to the sensation which prompts them.
The section of the phrenic nerves, or an injury to the spinal cord
at any part above the origin of those nerves, paralyses all the
respiratory movements of the chest, and thus occasions asphyxia
and sudden death.

731. When the sensation which prompts inspiration, is intense
and long continued, all the muscles performing movements auxi-
liary to this act, such as those which assist the intercostals in
elevating the ribs, which hold the glottis open, which raise the
velum pendulum, which open the mouth, and which expand the
nostrils, are called into simultaneous action, and the movements
themselves are performed in concert, and with perfect precision.
These actions are under the control of the will, as respects their
force, their rapidity, and their frequency, and they may even be
performed at pleasure, either separately or in conjunction ; unless,
indeed, the sensation which prompts them be unusually intense;
in which case they cease to be voluntary and automatic, and
pass into the class of instinctive motions we are next to describe.
Sir Charles Bell supposes that the nerves of all the muscles em-
ployed in these auxiliary actions have peculiar connexions among
themselves at their origin from the lateral columns of the spinal
cord, from which the eighth pair, which is the great sentient
nerve of the lungs, also arise ; and that these connexions are the
principal cause of their conjunction of action, whenever the sen-
sation imperiously demands that they should act in concert. Yet,
on other occasions, we find that all the muscles concerned in
these actions, are strictly voluntary muscles, and are perfectly
obedient to the will.

Sect. VI. — Instinctive Motions.

732. It is the essential character of motions which are strictly
voluntary, that they are accompanied not only.by a consciousness
of their being performed, but also by a corjviction that we may,
or may not perform them, as we please ; or, to speak more philo-
sophically, according as there exists or not, a sufficient mo/itJe for
their performance. But there are also, in the healthy state, many
muscles, of the actions of which we are always conscious, and
which, under ordinary circumstances, are perfectly obedient to
the will, but whose actions we have, on other occasions, no direct
power of controlling by any effort of the wilL They occasionally
seem even to be rebellious to its authority, and as if they were
transferred to the agency of some other power. They are always

INSTINCTIVE MOTIONS. 370

preceded by some sensation, as in the case of coughing, sneezing,
and vomiting; or some internal affection of the mind, whicii has
been termed emotion, as in the case of laughing and weeping ;
and they take place without any previous conception of the object
they are calculated to attain, and therefore without the previous
existence or operation of a motive. A very large proportion of
the actions of brute animals appear to belong to this class ; being
characterized hy the absence of that train of nrental operations,
which imply the agency of motives, and the previous knowledge
of the consequences resulting from such actions ; operations which
are comprehended under the term reason, as contradistinguished
from instinct, or blind and inexplicable impulse derived from other
sources.

733. Instinctive motions are distinguished by Dr. Alison into
two kinds, the one comprising such as are not only prompted by
an act of which we are conscious, but are also directed without
our being aware of it at the time, to an end which we desire; the
other, those in which our actions are consequent indeed on a sensa-
tion, but are prompted by a blind impulse, the consequences which
are to flow from the action being either unknown or disregarded;
as, for instance, in gratifying the appetites, guarding the eye from
danger by closing the eyelids, or the body from falling by throw-
ing out the hands. Dr. Alison, in his Outlines of Physiology, to
which we are indebted for several of the preceding remarks and
illustrations, has very clearly treated of the whole subject of the
functions relating to muscular motion. He farther remarks that
the instinctive actions are closely connected with the motions
which proceed directly from sensations on the one hand, and with
the strictly voluntary motions on the other. In the adult human
being, it is hardly possible to distinguish them from movements
which have been prompted by reason, and become habitual ; but
in the infant, and in the lower animals, they are easily recognised,
being distinguishable by two marks ; first, that they are always
performed in the very same way ; whereas actions which are
strictly voluntary, and prompted by reason, although directed to
the same end^, vary considerably in different individuals; and,
secondlv, that, however complicated the movements may be, the
truly instinctive actions are performed equally well the first time
as the last; whereas even the simplest of the strictly voluntary
movements require education. The complex acts of sucking and
deglutition performed by a newborn infant may be given as exam-
ples of strictly instinctive motions.

734. It is important, however, in the consideration of this sub-
ject, that we bear in mind, that these actions, although in them-
selves instinctive, are yet performed by muscles which are at
other times voluntary, and whose nervous connexions with the
sensorium, render it necessary for the performance of these ac-

308 SENSORIAL FUNCTIONS.

tions, that the muscles themselves should communicate by their
respective nerves with the sensorium. We may fairly presume,
therefore, that such actions are immediately dependent on a
change taking place in the sensorium, through the medium of
which alone the impression, which is the occasion of the actions,
becomes effective in their production.

735. The same remark applies also to those sensations which
arise from sympathy, as it is termed ; that is, which are referred
to a part of the body very different to that to which the actual
irritation is applied. Of this kind is the pain of the shoulder ac-
companying inflammation of the liver; pain of the knee from
disease of the hip-joint ; and itching of the nose from irritation in
the bowels. These sympathetic sensations may perhaps be
explained by the nerves of those corresponding parts having
their origins from the same parts of the brain ; but much yet
remains to be done towards establishing the truth of this
hypothesis.

Sect. VII. — Involuntary Motions.

736. Under the head of the involuntary motions, we mean to
comprehend all those muscular contractions which are performed
Vi^ithout the intervention of any change in the sensorium, and
consequently without being attended with either sensation, con-
sciousness, or any other mental change. The most unequivocal
examples of this class of motions are those in which muscular
actions are excited by irritations applied directly to the motor
nerves which are sent to the muscles themselves ; for although,
in the living body, such irritations are usually accompanied with
the sensation of pain, that sensation must be regarded as an ac-
cidental concomitant, and not a necessary part of the pheno-
menon ; as is proved by the absence of all sensation, when the
nerve has been divided between the brain and the part to which
the irritation is applied, and yet the muscles in which the nerve
terminates, exhibit the same involuntary contractions as before.
The same phenomenon, indeed, may be reproduced after the
death of the animal, or when the brain or head has been removed.

737. Other cases are met with of a more complex and dubious
.character; namely, those in which muscles usually under the

influence of the will, exhibit contractions in consequence of irri-
tations applied, not to their own nerves, but to some more dis-
tant part, which receives other nerves. It is manifest that in
these instances, the irritation of these latter nerves produces an
impression which is propagated along their course towards the
central parts of the nervous system, and is from thence again
transmitted along the course of the nerves supplying the muscles,

INVOLUNTARY MOTIONS. 309

in which they excite contractions of the same kind as those ori-^
ginating in voUtion. Yet these motions may tai<e place wholly
independently of the sensorium, and are found to occur, indeed,
when all communication with the brain is intercepted. For if,
a few seconds after an animal has been deprived of life, the
spinal cord be divided in the middle of the neck, and also in the
middle of the back, upon irritating either by a mechanical or
chemical stimulus, or by the application of heat, any sensitiv^e
portion of the body connected by nerves with either of these
isolated segments, the muscles of that portion of the limb, so con-
nected with the spine, are thrown into action. If, for instance,
the sole of the foot be pricked, the foot is suddenly retracted,
with the same gesture as it would have been during life, and of
course with the same apparent indication of suffering.* It is
evident that here an irritation applied to a nerve, the usual office
of which during life was to transmit impressions to the sensorium
productive of sensations of pain, has now produced an impression ''
which is conveyed to the spinal cord only ; but which yet is
followed by the contractions of those very same muscles, which,
during life, obeyed the determinations of the will, and produced
a motion of the limb directed to its removal from the cause of
injury.

738. Phenomena of this description may be observed more
readily, and are exhibited in a manner still more marked, accord-
ing as the animal on which the experiment is made, occupies a
lower place in the scale. Among vertebrated animals, the mo-
tions just described, and others of a similar character, indicative
of sensation and volition, are most easily produced in reptiles, as
in the turtle, the serpent, and the frog ; in which we find that
isolated portions of the spinal cord perform functions analogous
to those of the brain, as far as relates to the receiving of impres-
sions from a certain set of nervous filaments, and the transmitting
of impressions to other nervous filaments, which proceed from
the same part of the spinal cord, and are distributed to the mus-
cles. These two sets of nerves correspond in their functions to
the sensory and motor nerves by which sensorial phenomena are
produced (see § 721). In articulated animals, whose spinal cord
consists of a series of nodules of nervous matter, resembling
ganglia, connected by two longitudinal cords, and severally
giving origin to their respective bundles of nerves, which radiate
on each side from these ganglia, as from so many centres, the
capability of each ganglion to perform this double function is
still more susceptible of demonstration ; and each segment of a
worm or an insect, for example, appears, in consequence, to
enjoy a separate life, and exhibits the semblance of possessing

* See Mayo's Outlines of Human Physiology, p. 231.

310 ' SENSORIAL FUNCTIONS.

powers of sensation and voluntary motion independently of tfie
rest.

739. The question now arises whether these indications of sen-
sorial powers actually proceed from the exercise of those facul-
ties ; that is, whether they are accompanied by actual feeling
and actual volition, of both of which consciousness is the essence ;
or whether they exist in appearance only, and without any real
consciousness on the part of the individual percipient being. This
question, taken in all its generality, it is extremely difficuU, per-
haps impossible, to decide ; and its solution involves that of
another problem, equally obscure, which is presently to come
under our notice : namely, as to the locality and extent of the
sensorium in all the classes of the animal kingdom. The plan of
structure, and the vital constitution of articulated animals, are so
different from what occurs in the system of animals of the ver-
tebrate type, that whatever may be the conclusions we may form
with regard to the sensorial powers and the organs which exer-
cise them in the former class, we are not M^arranted in extending
the same conclusions to the latter class of beings, in all of which
we cannot fail to recognise the most decided character of indi-
viduality. It is hardly possible to conceive the co-existence of
two separate centres of sensation and volition in any vertebrate
animal, because we find it impossible to understand how con-
sciousness can be subdivided into portions corresponding to the
different segments into which the spinal cord may be divided.
If, therefore, we regard the sensorium as occupying any portion
of the brain, or rather of the encephalon, such as the medulla
oblongata, we cannot admit the existence of a separate or acces-
sary sensorium, situate in any part of the spinal cord, and capable
of exercising the sensorial functions independently, when all
nervous communication with the principal sensorium is cut off.
If the power of sensation could ever be retained, even for a se-
cond, after the head has been severed from the body, we must
suppose that the seat of that faculty is still in the head, and not
in the trunk, the movements of which, when excited by galvan-
ism, however they may resemble those which were performed
during life in obedience to volition, in conformity to the design,
and prompted by motives arising from bodily sensations, must
be regarded as purely mechanical, or rather as the result of
mere nervous irritation, and without the existence of either sen-
sation or volition of any kind. We have decisive proofs that in
the human system phenomena of this kind occur without any
participation of the mind, that is, without either sensation, per-
ception, or volition, in cases where, from accident, the spinal
cord has been divided or compressed in the neck, or back, and
where the muscles of the trunk that receive their nerves from
that part of the spinal cord, which is situate below the injury,

INVOLUNTARY MOTIONS. 311

are affected with involuntary movements. We are therefore
fairly entitled to extend the analogy to other animals whose con-
struction does not materially differ from that of man, however
appearances may seem to countenance the hypothesis of the sen-
sibility of the trunk, after its communication with the brain has
been intercepted.

740. Great confusion has been introduced into this subject by
the inaccurate language employed by physiologists in theorizing
•on these phenomena ; and in using which language they have lost
sight of the essential distinction which should ever be kept in
view between psychological and physical phenomena. The term
sensibility should be strictly confined to such properties as are
immediately connected with the mental changes which are deno-
minated sensations, and which are characterized by attendant
consciousness. All other corporeal properties or phenomena
which do not produce these mental changes, are simply of a
physical nature, and belong to another class to which the same
appellation' ought never to be applied. Bichat has committed this
great error in employing the term organic sensibility to denote
phenomena of this latter kind ; and the introduction of this term
has led to an interminable confusion of ideas among those who
have adopted his system, and who have^ been thereby led, from
this misapplication of terms, to some vague notion of a pecuhar
but obscure kind of actual sensation, which they attributed to
portions of the nervous system unconnected with the sensorium,
independent of all percipience, and partaking of the mystical
doctrines of Stahl and Von Helmont as to the operations of their
supposed anima and archceus. (See § 10 J.)

For the dissipation of these clouds which have too long ob-
scured the ideas and perplexed the reasonings of the physiolo-
gists, we need only direct on the subject the searching light of
philosophical analysis, which will render its outlines clear and
distinct, and enable us to follow their various flexures and.
crossings, and obtain more correct views of the landscape in all
its details.

741. The power exercised in the instances we have described
by the central parts of the nervous system, independently of all
sensorial phenomena, is that power which we have already dis-
tinguished by the term nervous power, in contradistinction to the
sensorial power exercised by the same system. (See § 96, 536,
537.) To Dr. Wilson Philip belongs the merit of having first
clearly pointed out the distinction between these two orders of
functions, and of having given them specific appellations. Dr.
Marshall Hall has lately introduced a new term, that of /•Cy^e.c
function, to designate the series of phenomena consisting of the
transmission of impressions by certain nerves to the central parts
of the nervous system, (which he limits to the spinal cordj and

312 SENSORIAL FUNCTIONS.

the consequent transmission of an action by the muscular nerves,
^ which is followed by the contractions of muscles. To the whole
system concerned in this function he gives the name of the excito-
motory system; the nerves receiving the impressions he calls the
incident nerves ; and those conveying it to the muscles, the rejiex
nerves.^

742. It would appear from what has been already noticed
(§ 711), that every muscle the action of which is capable of be-
ing brought under the dominion of the will, and which is there-
fore entitled to be classed among the voluntary muscles, may
occasionally be made to act by other causes, applied either directly
to their own fibres, to the nerves distributed to them, or to other
parts connected with them only by the medium of portions of the
brain,spinalcord,orthegangliaof the sympathetic: and ithasbeen
conjectured that the sets of nervous fibrils which are instrumental
in the performance of these latter functions, are different from those
which are employed to transmit the impressions of sensation and
volition. This latter view is the one adopted by Dr. W. Philip,
who observes that, " however blended the organs of the sensorial
and nervous powers may appear to be, we are assured that they
are distinct organs by the fact, that while the organs of the ner-
vous power evidently reside equally in the brain and spinal mar-
row, those of the sensorial power appear to be almost wholly in
man, and chiefly in all the more perfect animals, confined to the
former. "f It does not, however, appear that we as yet possess
any direct means of either establishing or disproving the truth of
this supposition.

743. There yet exists another class of muscles, comprehending
those which never, under any circumstances, become voluntary.
To this class belong the heart and blood-vessels; the muscular
fibres of the excretory ducts, and other parts of the organs of

* [Dr. Hall, whose views have given rise to much discussion lately, pro-
poses to divide the nerves into 1, the cerebral, or the sentient and voluntary:
2, the true spinal or excito-motory, and 3, the ganglionic, or the nutrient and
secretory. If the sentient and voluntary functions be destroyed by a blow
upon the head, thesphinctermuscles will still contract when irritated, because
the irritation is conveyed to the spine, and the reflex action takes place in the
muscle, so as to throw it into contraction. But if the spinal marrow be now
destroyed, the sphincters remain entirely motionless, because the centre of
the system is destroyed. Dr. Hall is of opinion, that a peculiar set of nerves
constitute, with the true spinal marrow as their axis, the second subdivision
of the nervous system, and as those of the first subdivision are distinguished
into sentient and voluntary, these may be distinguished into the excitor and
motory. To the cerebral system he assigns all diseases of sensation, percep-
tion, judgment, and volition ; and therefore all painful, mental, and comatose,
and some paralytic diseases. To the true spinal or excito-motory system be-
long all spasmodic and paralytic diseases. Lectures on the Nervous System
by M. Hall, M.D., Amer. edit. Philad. 1836: see, also, Dunglison's Ph)'-
siology, i. 73.]

t Quarterly Journal of Science, xiv. 93.

INVOLUNTARY MOTIONS. 313

secretion ; and the coats of the stomach and of the intestines.
As the influence of the nervous system on those muscles is of a
very peculiar kind, and as their motions are governed by different
laws from those which regulate the voluntary muscles, it will be
necessary to bestow on them a separate consideration.

744. M. Le Gallois, in a work entitled Experiences sur le
Principe cle la Vie, notamment sur celui des Mouvemens du Cceur,
et sur le Siege de ce Principe, thought he had proved that the
muscular power of the heart is derived altogether from the spinal
cord, and not from the brain. He found that on injuring the
spinal cord, the heart is so enfeebled as no longer to be capable
of propelling the blood ; but that the contractility of the heart may
continue unimpaired when the brain, and even the whole head, is
removed, provided respiration be kept up by artificial inflation of
the lungs. He conceived, therefore, that the use of the cardiac
nerves is to establish the connexion between the spinal cord and
the heart; and that whenever the heart is affected by passions
and emotions of the mind, which produce their first changes on
the brain, it is influenced through the medium of the spinal cord,
which is itself affected by the brain. Dr. Wilson Philip has
shown the fallacy of this conclusion ; and has completely esta-
blished, by direct experiment, that under similar circumstances,
the brain has just as much influence on the motions of the heart
as the spinal cord. The motion of the heart is no more affected
by the removal of the spinal cord than by that of the brain, if the
same precautions be taken in either case, of effecting the removal
slowly, and with as little disturbance to the remaining parts of
the system as possible. If, on the other hand, either the brain or
the spinal cord be suddenly crushed by a blow, which at once
destroys its texture, the heart is instantly paralysed, and its motions
cease. iVlthough the muscular fibres of these organs are not
excited to contraction by irritations of any kind applied to their
nerves, nor their contractions arrested by the section of those
nerves, yet these actions are immediately accelerated by the
application of chemical stimulants, such as alcohol, either to the
brain or to the spinal cord ; and retarded by the application of
opium, tobacco, or other narcotic agents, to the same parts.

745. It would appear, therefore, that although there is no essen-
tial difference between the real nature of the irritability of the
involuntary, and that of the voluntary muscles, yet that each is
influenced by different kinds of stimuli, and by stimuli applied
through a different medium. Mechanical stimuli, such as punc-
tures or partial divisions of the fibres of the muscles of voluntary-
motion, act on them only through the medium of their nerves; and
if applied to the parts of the brain whence these nerves originate,
will throw those muscles into the most violent spasmodic contrac-
tions. The heart, on the contrary, is but slightly disturbed in its

27

' 314 SENSORIAL FUNCTIONS.

movements by the same kind of injury done to the brain or spinal
cord, provided the injury be confined to a small portion of those
organs. That important organ appears to be affected only in
proportion to the extent of the parts that have suffered injury, and
to the suddenness vv^ith which that injury has been inflicted; as is
exemphfied by wounding the brain rapidly in many directions.
Chemical stimuli, on the contrary, applied to any part of the brain
or spinal cord, produce considerable and immediate increase of
the action of the heart i while the voluntary muscles continue all
the while unaffected ; and the animal betrays no sense of pain.
Accordingly the heart, having no direct dependence on any part
of the nervous system, may continue its action when the brain
and spinal cord are destroyed, and even when it is itself removed
from the body.* The nerves with which it is supplied, however,
render it capable of being influenced through those causes, as, for
example, by the passions, and by various poisons, which effect a
considerable portion of the nervous system.

746. The contractile powers of the other parts of the vascular
system, and most of the secreting organs,'as well as the irritability
of the stomach and intestines, are, like those of the heart, indepen-
dent of the nervous system, yet capable of receiving an influence
through the medium of the nerves; and the same law appears to
extend generally to all the involuntary muscles. The extensive
nervous communications which are naturally established between
the whole system of involuntary muscles, and the organs in which
they enter, seem to be necessary in order that any one set of these
organs should be subjected to the influence of all the others. This
purpose is effected by that complex arrangement of nerves, which
has been termed the ganglionic system, from the great number of
ganglia annexed to them. The great sympathetic nerve forms
the principal connecting nerve in this system between all the
muscles of involuntary motion; which, through the medium of
filaments from the extensive chain of ganglia belonging to this
nerve, are placed in connexion with every part of the brain and
spinal cord. Each ganglion belonging to the sympathetic system
has been considered as a secondary centre of nervous influence,
receiving supplies from all the latter parts, and conveying to the
former organs the united influence of the nervous system in
general. The muscles of voluntary motion, on the other hand,
are subjected to the influence of only small portions of these cen-
tral parts of the nervous system, and receive their nerves directly
from those parts; and usually without the intervention of ganglia,
and with comparatively few intermixtures of nervous filaments ;
such intermixtures being designed for the purpose of effecting
combinations with the nerves of sensation, and especially with
those which convey impressions relative to muscular motion.

* [See § 450, note.]

PSYCHOLOGICAL RELATIONS, 315

747. The ganglia of the sympathetic system have, accordingly,
been considered by many physiologists as performing functions
similar to those of the portions of the spinal cord exercising mere
nervous power ; that is, in the language of Dr. Marshall Hall,
performing reflex functions, and belonging, together with the
branches of the sympathetic nerve, to the excito-motory system.*

Sect. VIII. — Psychological Relations of the Sensorium.

748. In treating of the functions of the nervous system which
involve operations both of the body and of the mind, it is very
diflicult to draw the strict line of distinction between them, and
avoid treating of subjects which properly belong to metaphysics.
We have endeavoured, in the preceding account of the physio-
logy of man, to confine ourselves strictly to the consideration of
the corporeal changes which accompany the different mental
affections, and to avoid, as much as possible, encroaching upon
the province of the metaphysician. That certain physical
changes take place in some portion or other of the cerebral mass
in connexion with various mental changes, we have the clearest
evidence : but of the nature of these physical changes we are
wholly ignorant ; nor does the present state of our information
afford a shadow of hope that we shall ever gain any more pre-
cise knowledge of them. The mental changes, on the other hand,
constitute a distinct and separate branch of science ; to the know-
ledge of which we arrive by channels totally different from those
which instruct us relatively to the former ; namely, by conscious-
ness, and by reflexion on the series of phenomena furnished to us
by consciousness. These two subjects of study, the material and
the immaterial, however numerous may be the subtle and inscru-
table links that connect them, constitute two worlds, which in
our conception must for ever remain totally distinct ; nor is it
even possible for us to conceive how any knowledge which we
can obtain with relation to any physical changes in our corporeal
frame, or any physiological laws that may regulate the succes-
sion of those changes, can in the smallest degree assist us in
understanding the phenomena of intellect, and the affections of
the soul.

749. The brain has been very justly regarded as the organ of
the mind ; that is the corporeal instrument invariably employed
in the operations of the mind. This is a necessary corollary from
the proposition that no mental operation can take place without
the co-existence of some physical change in the brain. But a

* See Grainger's Observations on the Structure and Functions of the
Spinal Chord,

316 SENSORIAL FUNCTIONS.

s6cond proposition, the converse of the former, has been advanced ;
namely, that the mental operations are the " functions of the brain."
But this latter proposition would be true only on the supposition
that the physical change in the brain, and the corresponding
mental change of which we are conscious, are one and the same
thing. Until this fundamental doctrine of materialism, namely,
the identity of matter and mind, be proved, we cannot include
under the functions of the brain, both the mental changes and
the corporeal changes. The physiological office, or function of
the brain is the production of certain corporeal changes, connected
in some inexplicable manner with certain mental changes ; which
two classes of changes are in their nature, as far as we are capable
of forming any conceptions of them; radically and essentially dif-
ferent from each other.

•750. The ambiguity of ordinary language is, indeed, a frequent
source of confusion of ideas on this subject. We speak correctly
when we say that the eye is the organ of vision, because it is an
instrument without which vision could not be exercised ; but were
we to regard vision as the function of the eye alone, we should
evidently be guilty of inaccuracy in extending too far the purpose
of that instrument. The function of the eye is to produce certain
impressions upon the retina, which impressions are but links in the
series of changes, of which only the last constitutes vision. These
impressions made on the retina are followed by changes in the
course of the optic nerves, and these again by changes in the
sensorium. The function of the optic nerves, and of that part of
the sensorium in which they terminate, is the production of these
physical changes. Vision, an affection of the mind, is undoubt-
edly the effect of these physical changes ; but is not properly the
function of any of these organs, except the term function be used
in that loose and popular sense, in which it is made to embrace
all the remote consequences of the phenomena, in the production
of which the organ in question is concerned. In this sense, indeed,
vision, and all the mental affections consequent upon vision, might
certainly be said to be functions of the eye ; but in the strict phi-
losophical sense, the function of the eye is limited to the formation
of images on the retina, and the impressions thereby received by
the retina ; and, in like manner, the proper function of the brain
is the production of certain physical changes in the fabric of the
brain, consequent upon certain impressions made on the nerves
by external causes, and consequent also upon certain internal
affections of the mind, which are capable of exerting on it this
influence.

751. The affections of the mind are very various and compli-
cated ; a great multitude of ideas and associations are treasured
up in it, and constitute a variety of powers, of faculties, of pro-
■ pensities, of instincts, and of passions. The conformation of the

SLEEP.

317

brain, which is the organ of the mind, is also very complex, and
appears to consist of an assemblage of different parts, constructed
evidently with extreme refinement, and arranged with great care,
and with very elaborate design. The idea naturally suggests
itself, that these different portions recognised by the anatomist,
may perhaps have some correspondence with the several facul-
ties into which the phenomena of the mind have been analyzed
by the metaphysician. This question has indeed been_ often
started, and is quite distinct from that of the materiality or imma-
teriality of the soul ; for it is perfectly conceivable that if the
immaterial soul acts by means of material organs, and receives
impressions from those organs, its different operations may
require different organs. But this subject, together with the
theories to which it has given rise, are amply discussed in the
Appendix on Phrenology.

Sect. IX. — Sleep.

752. Whilst the functions, which have for their object the re-
paration of the state of the body, and which include assimilation,
absorption, circulation, respiration, secretion, and nutrition, con-
tinue in constant activity, all those connected with sensation and
volition require intervals of repose, and cannot be maintained
beyond a certain time without great exhaustion of the nervous
power. These periodical intermissions in the activity of the
animal functions, so necessary for the renovation of the power
on which they are dependent, constitute sleep. The eye-lids
close to protect the eye from injury, and the eye-ball is turned
upwards ; the external senses and all the active intellectual oper-
ations are suspended; the voluntary muscles are relaxed; and
we become insensible to all external impressions. The movement
of the involuntary muscles continues, though with somewhat less
energy than during our waking hours. The heart beats with
diminished force and frequency, and the muscles of respiration
act more slowly ; but the inspirations are more full and deep, and
the secretions are in general less abundant ; but digestion and
absorption are carried on with great activity. The power of
sensation, though blunted, is not altogether lost during sleep, as
is proved by the continuance of that part of the movements of
the muscles of respiration, which depend on sensation. Instinc-
tive movements of the hmbs, producing a change of posture,
frequently take place from an obscure sensation of constraint at
their continuing long in the same position. Any unusual impres-
sions made on the organs of the senses are felt during sleep, and
even remembered ; and, if the impression be sufficiently vivid.
will interrupt sleep.

27*

318 SENSORIAL FUNCTIONS.

753. Neither is the mind wholly inactive during sleep ; it is
still occupied with a succession of ideas, which is often more
rapid than when we are awake ; the imagination is even more
vividly exerted, and the images that pass before the mind are
considered as realities. This constitutes dreaming, a state which
is characterized also by the pecuhar circumstance of the want of
all voluntary power of directing the succession of ideas. Trains
of ideas and images commence and follow one another, being
indissolubly linked together by those laws of association which
are independent of volition.

754. An extraordinary modijfication of dreaming occurs in
what is called somnambulism, or sleep-walking; where the will
recovers a certain degree of power over the mental operations,
and over the voluntary muscles both of speech and motion, whilst
the body is still less capable of receiving external impressions
than in ordinary sleep. In this peculiar kind of sleep, the insen-
sibility to most external impressions is so profound, that it is
scarcely possible to awaken the person without employing a con-
siderable degree of violence. When at length he does awake,
which often happens as suddenly as from natural sleep, he usually
retains little or no recollection of what happened to him, or of
what he did whilst in this singular state.

755. A state very similar to that of natural somnambulism, is
induced in some nervous constitutions, especially those of young
females, by certain manipulations which produce a long-continued
reiteration of impressions made on the senses, and which proba-
bly act through the medium of the mind. These have been
ascribed to a special agency, termed Animal Magnetism, or
Mesmerism.*-

CHAPTER XVIII.

THE VOICE.

756. The function of the voice, and its modulation into articu-
lated sounds, by which it is rendered subservient to speech, has
been already pointed out as an important part of the animal

* [The whole history of animal magnetism exhibits that impressible per-
sons may have hysterical or hysteroid irregularities of nervous distribution
induced through the medium of the senses, especially through those of vision
and touch ; but there is no adequate evidence to shovi% that the effects can be in-
duced without impressions being made on some organ of sense; or that there
is any special agency of the Idnd that has been imagined. The clairvoyance
or lucidity of vision of the magnetized is a delusion, — perhaps in all cases a
deception.]

THE VOICE. 319

economy of a being designed, as man evidently is, to hold exten-
sive communion with his fellow-creatures, and effect the rapid
interchange of ideas and feelings, through the medium of the
sense of hearing (§ 24).

757. In order to understand the mode in which articulate
sounds are produced, it will be necessary again to advert to the
principles of acoustics, of which a brief account was given in
introducing the subject of the physiology of hearing, (§ 623.)
The object to be accomplished in the function of the voice is
the production, not so much of single sounds, (such as those
which result from single impulses given to the air,) but of con-
tinued sounds, composed of reiterated vibrations, repeated at
short and equal intervals, and constituting a musical note. There
are two principal modes in which such sounds are produced ; the
one, that which is practised in stringed musical instruments, in
which the impulses are given to the air by the vibrations of solid
bodies, which are generally chords having different degrees of
tension ; and the other, such as is adopted in wind instruments,
where the air is thrown into undulations at regular intervals, by
alternations of expansion and condensation, generally taking
place during the passage of a stream of air through a cavity in
which it suffers certain reflexions and reverberations, alternately
impeding and promoting its progress. In many cases the effect
is obtained by a combination of both these means, as in a haut-
boy, where an elastic plate, or reed, is placed in the course of
the air which is passing along a tube, capable by its form of
producing a musical note, independently of such addition.

758. In the construction of the vocal organs of man, nature
has resorted to combinations of this kind. Advantage is taken
of the function of respiration to convert the passages through
which the air is admitted to, and expelled from the lungs, into a
sounding instrument; by adapting to the upper part of the
trachea, a curious mechanism, consisting of a frame-work of
elastic cartilages, with an apparatus of ligaments, muscles, mem-
branes, and mucous glands, the assemblage of which is termed
the lai'ynx. The aperture through which the air passes is deno-
minated the glottis. Here it is that the breath is vocalised ; that
is, rendered not only sonorous, but also modulated in its pitch, so
as to give rise to a musical sound. Modifications are subse-
quently impressed on these sounds, by the changes which the
undulations are made to undergo in the cavities of the pharynx,
of the nostrils, and of the mouth, according to the various forms
and dimensions given to those cavities by the motions of the
muscles of the pharynx, the velum pendulum, the uvula, the
tongue, the cheeks, and the lips ; and according to the obstacles
placed in the way of the passage of the air by the movements of

320

SENSORIAL FUNCTIONS.

these parts, and the application, in particular, of the tongue and
of the lips to the palate and to the teeth.

759. The cartilages of the larynx are five in number, namely,
the thyroid, the cricoid, the two arytenoid, and the epiglottis.
The thyroid., which is also called the scutiform, or shield-like
cartilage, is placed at the upper and fore-part of the larynx, and
is the largest of the whole. It consists of two lateral wings of a
quadrangular form, uniting in front in a longitudinal angle, which
is felt projecting in the fore-part of the throat, and has obtained
the name of the pomum adami. From the posterior corners, four
pi'ocesses project, called its cornua, distinguished into two superior,
and two inferior. The cricoid, annular, or ring-like cartilage, is
placed below and behind the former ; and it has four articular
surfaces, two below, for its connexion with the inferior cornua of
the thyroid cartilage, and two above, for the articulation of the
arytenoid cartilages, which are bodies of a pyramidal shape,
much smaller than the rest, and placed one on each side, upon
the upper posterior and lateral parts of the cricoid cartilages, .
They give attachment to ligaments, and compose a part of the
sides of the opening called the glottis. The whole passage is
lined internally by a delicate mucous membrane.
\ 760. The epiglottis is a cartilaginous lid, which has a pointed
shape, resembling the leaf of an artichoke. It is fixed at its base
to the OS hyoides, to the thyroid cartilage, and to the root of the
tongue ; and hangs obliquely backwards over the opening of the
glottis, which extends in a line from behind forwards, and is
formed by the approximation of the vocal ligaments, or chordce
vocales. These ligaments, which consist of fibres endowed with
a high degree of elasticity, are covered with the fine membrane
which invests the whole of this delicate apparatus, and extends
down the trachea into the lungs, and above to the posterior
fauces. These are attached together in front to the thyroid
cartilage, and behind to the arytenoid cartilages, where, in the
relaxed condition of the organ, they are at some distance from
each other, so as to leave a triangular opening for the passage
of the air. The effort to speak, or to utter a vocal sound, com-
mences with the action of certain muscles, more particularly the
crico-thyroidcei, which stretch the vocal ligaments, and the crico-
arytcBUoidei laterales, and the arytcBUoidci transversi and obliqui,
which conspire to make the arytenoid cartilages approximate.
By these combined actions, the vocal ligaments are brought near
to each other, in parallel directions, so that the interval between
them or rima glottidis, as it is called, is reduced to a mere nar-
row linear fissure.

761. When, therefore, the air is forcibly propelled from the
lungs through the glottis, whilst the vocal chords are in this ap-
proximated position, different vocal sounds will be produced, ac-

THE VOICE.

321

cording to the degree of tension which is given to the chordae
vocales. The greater the tension of these ligaments, the more
frequent will be their vibrations, and the higher the pitch of the
note they produce. The loudness of the sound ennitted is pro-
portioned, not to the frtiquency of the vibrations, but to their
extent, or the naagnitude of the excursions made by the vocal
chords in vibrating. The varied degrees of tension which can
be imparted at will, and instantaneously, to the vibrating liga-
ment of the larynx, by the finely regulated actions of their differ-
ent niuscles, constitute the chief source of superiority in the vocal
organ to any instrument of human invention.

762. The muscles above enumerated as giving tension to the
vocal ligaments, and closing the glottis by the approximation of
the arytenoid cartilages, are opposed by their antagonists the
tiiyreo-arytcenoidei, which relax the vocal ligaments, and place
them in the vocalizing position, and by the crico-arytcenoidei
postici, which separate the arytsenoid cartilages, and thereby
open the glottis. Thus the instrument we are considering is
capable of an infinite number of changes of form, and susceptible
of the finest modulation.

763, It should be stated, however, that many physiologists
have maintained that the musical tones of the voice depend, not
merely on the tension of the vocal ligaments, but also on the size
and form of the aperture through which the stream of air is^
propelled, and that the larynx partakes as much of the properties
of a wind as of a stringed instrument. The principal advocate
of this opinion was Dodart, whose first paper* contains a histori-
cal account of the views on this subject taken by the earlier
physiologists. His chief antagonist in this controversy was
Ferrein,-|- who compares the larynx to a violin, or harpsichord,
and conceives that the voice is produced by the vibrations of the
edges of the ligaments of the glottis ; and compares the action of
the air to that of a bow setting these parts into vibration. The
hypothesis of Dodart has been adopted by Blumenbach, who
conceives the action of the larynx to be analogous to that of the
flute. But the generality of physiologists consider the action of
the ligaments of the glottis to be vibration, and similar to that of
strings resounding by their tension alone. Such is the view taken
of the subject by Dr. Young4 Sommerring,§ Magendie,|| WilUs,1[
and Mayo,** who all maintain that the voice depends on the
vibration of the chords ; the frequency of which must, according

* Memoires de I'Academie, pour 1700, p. 244; 1707, p. 66.

t Ibid, pour 1741, pp. 409, 416, 422.

X Lectures, p. 400, and Philosophical Transactions for 1800, 141.

§ De Corporis Humani Fabrica, vi. 93. H Physiologie, i. 196.

•[ Cambridore Philosophical Transactions, iii. 231.

** Human Physiology, 3d edit. p. 350.

323

SENSORIAL FUNCTIONS.

to all acoustic principles, be regulated solely by the tension of
the chords.

764. Dr. Willis observes that, for the production of laryngeal
sounds, something more is requisite than a definite tension of the
vocal ligaments. He has shown, by experiment, that in order
that the edges of two membranes, such as those made of leather
or of Indian rubber, opposed to each other with a narrow interval,
may vibrate, the parts of the membrane near their edges must be
brought paralled to each other. Comparing this disposition of
membrane in his experiment with the parts of the larynx, he
supposes that the latter will not vocalize, unless some change,
independent of, and superadded to, the tension of the ligaments,
be produced in their relative position.

765. The experimental proof on which Mr. WiUis founds his
conclusion that some change in the relative position of the vocal
chords is necessary to produce an audible vocal sound, is the
following. If the finger be placed upon the membrane which
intervenes between the thyroid and cricoid cartilages, their approx-
imation or increased remoteness may readily be felt. Now their
approximation being produced by the action of the crico-thyroid
muscles, involves an increased tension of the ligaments. But it
is possible by an effort to keep these cartilages approximated,
whilst something is still wanting in the internal arrangement of
the larynx, to fit it for the production of sound. When the thyroid
and cricoid cartilages are thus approximated, and the ligaments
thus shown to be in a state of tension, if air be impelled through
the larynx, sound does not necessarily follow ; the ligaments have
still, Mr. Willis concludes, to be placed in the vocalizing position.*

766. There are still other parts of the vocal apparatus con-
nected with the sounds produced at the larynx, which require to
be adverted to. Amongst these the varying conditions of the
trachea appear to have the greatest influence on those sounds,
and of this influence Mr. Wheatstone proposes the following
theory :f

" Such a vibrating apparatus as we have described the ligaments
of the glottis to compose, is by itself capable, from the varying
tension of those ligaments, of producing all those sounds of which
we find the voice to be susceptible. But the intervention of a tube
between the lungs and the larynx, must necessarily exercise an
important influence on the voice, though it has never yet been
taken into consideration. For, if we unite such an apparatus, or
a free reed, which may serve as a substitute for it, with a tube
(supposing it for the moment fixed to a determinate degree of
pitch), it is found, that, unless the column of air in the tube is of

* See Mayo's Outlines of Human Physiology, 3d edition, p. 350, 351,
from which the above account of Willis's theory is extracted.
t Ibid. p. 252.

THE VOICE. 323

such a length as to be. separately capable of producing the same
number of vibrations, the sound cannot be obtained in its greatest
force and purity, and that when the tube is half this length, the
discordance between the tube and the reed is so great, as to prevent
the production of the sound : between these limits the sound is
intermediate in intensity and quality. This influence of the tube
is by experiment found to be the same, whether the tube be placed
after the reed, as in several wind instruments, or before it, as in
the vocal organ. We will now suppose the tube to be unaherable
in its length, and the reed necessarily to undergo all its varying
modifications of pitch; the sounds, instead of being of even quality,
will be irregular in intensity, and require different degrees of
effort to produce them, whilst in some parts of the scale, they
will be totally extinguished. All this may be prevented, and the
utmost regularity obtained, by shortening the tube, in proportion
as the vibrations of the reed increase in frequency. The trachea
is obviously incapable of changing its length within limits suffi-
ciently considerable to serve this purpose ; but Savart's experi-
ments have shown, that a tJibe of constant length may be made to
produce a great range of sounds, by making it of elastic sides
susceptible of variable tension. The analogy between such a
tube and the trachea is perfect."

767. One mode of giving increased tension to the windpipe is
the action of the transverse muscular fibres which bind the ends
of its cartilages together. Another is the elevation of the larynx,
which follows in so remarkable a degree the elevation of the
pitch of the voice. Practice in singing improves the voice, partly
by giving us a more ready command over the tension of the
trachea, and partly by enabling us to regulate and vary the
opening of the glottis whilst we preserve the tension of the vocal
chords.

768. Such being the mode in which vocal sounds are produced
in the larynx, the next step in the inquiry will relate to modifica-
tions they receive from the shape of the cavities of the pharynx
and mouth, through which the expired air has yet to pass. When
thus modified they become not merely vocal, but articulate
sounds, and constitute the elements of speech.

769. This branch of the subject has been ably investigated by
Sir Charles Bell,* who has traced the influence which the changes
produced by the muscular actions of the tongue and fauces, on
the shape of the cavities of the mouth and pharynx, have on the
resulting articulate sounds. He has examined the succession of
actions which must be performed before a word can be uttered,
and which he finds to consist in the compression of the thorax,

* Philosophical Transactions for 1832, p. 299.

324 ' SENSORIAL FUNCTIONS.

as well as the adjustment of the glottis, the elevation and depres-
sion of the larynx, and the contraction of the pharynx.

770. The elementary articulate sounds of a langua'ge consist
of vowels and consonants. Vowels are continued sounds, pro-
duced when the passage of the air through the fauces is uninter-
rupted, the fauces being only more or less narrowed. Each
vowel requires a different elevation of the tongue or contraction
of the lips. Thus the sound of the broadest pronunciation of the
letter a, which occurs in the word awe, results from the lowest
position of the tongue, giving its greatest depth to the cavity of
the mouth. The ordinary sound of a, as in the word age, is pro-
duced by a certain elevation of the tongue, reducing considerably
the capacity of the mouth. The vowel e, pronounced as in eve,
is sounded by raising the tongue still more, so as to leave a more
contracted channel for the exit of the air. The positions for o
and 00, are obtained by placing the fauces in the position first
described, namely, that for au, and then approximating the lips.

771. The pronunciation of consonants is effected by interrup-
tions to the passage of the air in some part of the cavity of the
mouth, by various motions of the tongue and lips, which, when
applied to the palate of the teeth, narrow or close the channel for
its exit.

772. The following experiment is mentioned by Mr. Mayo*
as having been made by M. Deleau, demonstrating that the
articulation of vocal sounds takes place in the fauces. He intro-
duced through the nostrils into the pharynx a flexible tube, and,
by means of a gum bottle, impelled air through it into the fauces ;
then closing the larynx he threw the fauces into the different
positions requisite for producing articulate sounds, when the air
impelled from the gum bottle became an audible whisper. Dr.
Bennati repeated this experiment, allowing at the same time
laryngeal sounds to pass into the fauces, when each articulated
letter was heard double, in a voice at once, and in a whisper.

773. Consonantal sounds may be divided, first, into aspirates
and sonants, or, secondly, into continuous and explosive.

114:. The aspirates are those which may be rendered audible
without a vocal sound, as in the case with p, t, k, h,f, th, s, and
sh. The sonants are those which, without any appreciable dif-
ference in the shape of the fauces from the form required for the
pronunciation of the preceding to which they are allied, are not
heard without a vowel sound, either previously uttered, as in b,
d, g, V, z, and /, or subsequently, as in g, or in conjunction with
it, as in r.

775. Continuous consonants are pronounced when the vocal-
ized air passes through some part of the organ, previously ren-

* Outlines of Human Physiology, p. 354.

THE VOICE. 325

dered very narrow. Explosive consonants are those which are
produced by the interruption to the current of air occasioned by
the entire closing of the passage, and its being allowed to burst
out with some force by the sudden opening of the same passage.

776. The nasal consonants, w, n, and^, are distinguished from
the rest by the peculiur character of their articulation arising
from the breath being allowed to pass through the nostrils ; whilst
in the pronunciation of the others, the soft palate being raised
closes the posterior nostrils, and prevents the sound from diffusing
itself in that direction.

777. We refrain from entering into any further details with
regard to the position of the fauces, tongue, and lips, in the pronun-
ciation of the different consonants, having already treated of this
Subject at some length.*

778. The low pitch of the voices of men compared with those
of wom.en and boys, arises both from the greater general size of
the larynx, and also the greater length of the chordse vocales,
which has been found to measure nearly double that of the latter.
In attempting to utter high notes, voices naturally grave, assume
the character of the falsetto. This, Mr. Willis supposes, may
result from the shortening of the vocal chords ; but Mr. Wheat-
stone is disposed to ascribe it to the tension given to the windpipe
being such as to reinforce the laryngeal sounds by subdivisions.

779. Some curious observations on the mechanism of the voice
during singing have lately been given by Dr. Bennati,t who states,
that the compass of his own voice extends to three octaves. He
concludes from his inquiries, that it is not merely the muscles of
the larynx which modulate the sounds, but those also of the os
hyoides, and the other neighbouring parts. He mentions that, on
removing part of the tonsils, the operation was followed by the
raising of the voice half an octave, without ahering its compass.
Mr. Mayo supposes this effect to result from the cicatrix stretch-
ing the mucous membrane of the larynx, and thus giving increased
tension to its inner surface.^

* Art, Deaf and Dumb — Encyclopeedia Britannica, 7th edit. See also
Haller's Elementa de Physiologiae, ix. 4 ; Dr. Young's Lectures, ii. 276 ;
and the work of Mr. Mayo, already quoted.

f Annales des Sciences Naturelles, xxiii. 32. «

X [See an elaborate article on the voice in its various manifestations, in
Dunglison's Physiology, i. 395.]

28

326 REPRODUCTIVE FUNCTIONS.

CHAPTER XIX.

GENERATION.

Sect. L — General Views.

•780. As far as we are permitted to scan the designs of the
Almighty Creator in the formation of organized beings, they ap-
pear destined to a mode of existence characterized by perpetual
mutation. Their Hving state is made to consist of a perpetual
series of actions and reactions, in which nothing is intended to
be permanent, not even the materials of which the combinations
constitute the substance and organs of the body. All is subject
to displacement, alteration, renewal, and renovation, during a
certain definite period, which varies in each species, according
to the primordial law of its constitution ; and all must bend, when
that period is exceeded, to the imperative law of mortality, to
which every individual endowed with life is subjected.

781. But the same counsels which prescribed these limits, and
decreed the extinction of life, and the dissolution of the frame in
which it had resided, have providently ordained most ample
means for the continuance of the race, and the indefinite multi-
plication of its numbers. Individuals perish, but the species is
preserved in endless perpetuity by means of Generation ; a
function of paramount importance in the economy of nature, and
for which the most ample provision has been made, and the
greatest solicitude manifested to secure the accomplishment of
its pui'poses. Nutrition and generation, indeed, constitute the
only functions which can be said to be universally exercised by
all organized beings, whether belonging to the vegetable or the
animal kingdom, or whatever rank, from the lowest to the highest,
they may occupy in the scale of nature.

782. But although the purpose is thus manifest, and the provi-
sions for its execution thus eflfective and even exuberant, the
immediate agency by which one living being is rendered capable
of giving rise to another sim.ilar to itself, is enveloped in the most
profound and most hopeless obscurity. No means within the
compass of our understanding, no combination of the powers of
matter which we can possibly conceive, no process of which the
utmost stretch of human imagination can give us the most remote
idea, has ever made the least approach towards the solution of
this most inexplicable of all enigmas, — the production, nay, the
apparent creation, of a living plant or animal by powers inherent

GENERATION. 327

in the organization of a similar being. We must content our-
selves, in studying this inscrutable mystery, to observe and
generalize the phenomena, in silent astonishment at the marvel-
lous manifestation of design and of povi^er exhibited in this depart-
ment of the vv^onderful works of the Almighty.

783. Various plans of reproduction are exhibited in the differ-
ent classes of animals, but they are all reducible to three general
heads, which may be designated by the titles o( fissiparous, gem-
mijyarous, and sexual reproduction. Many physiologists, however,
have been disposed to admit the existence of a fourth mode of
reproduction, which they have termed spontaneous, or equivocfd
generation. It is contended by the advocates of this hypothesis,
that in many of the lower tribes, instances occur of the formation
of animals without the intervention of any parents, and produced
by the spontaneous union of certain elements, which might for-
tuitously be found in juxtaposition, in collections of the decom-
posing materials of other organized structures, after the extinction
of their life. Although this opinion was at one period the gene-
rally prevailing doctrine, it is now, in consequence of the more
extensive knowledge, which has been obtained of the procedure
of nature in the multiplication of animals, very generally exploded.
The principal arguments in its favour were, in the first place,
those drawn from the existence of intestinal worms, and other
parasitic entozoa, in the bodies of animals, the germs of which
appear neither to be introduced into the system from without, nor
to have any assignable origin from within ; secondly, those
derived from the rapid appearance of infusory animalcules in all
infusions of decaying animal or vegetable matter that are exposed
for a short time to the air. But the analogy of every other de-
partment of the animal and vegetable kingdom is directly opposed
to the supposition that any living being can arise, unless it has
originally sprung from an individual of the same species as itself,
and of which it once formed a part. The difficulty which the
hypothesis of the spontaneous production of infusory animalcules
professes to remove, consists in our inability to trace the pre-
existence of the germs in the fluid where these animalcules are
found to arise, and to follow the operations of nature in these
regions of infinite minuteness. But the recent discoveries of
Ehrenberg relative to the complete organization of these beings,
in which he in many instances detected the presence of genera-
tive organs, has very much diminished the difficulty of conceiving
the possibility of their ova, so minute as to be wholly impercep-
tible, existing in great numbers in the fluid, or even in the
atmosphere, and giving rise to all the observed phenomena.*

* See Bridgewater Treatise, on Animal and Vegetable Physiology, vol. ii,
p. 591, note. [Amer. edit. ii. 415.]

328 REPRODUCTIVE TUNCTIONS.

784. Fissiparous generation, the simplest of all possible modes
in which the species can be multiplied, consists in the spontane-
ous and gradual division of the body of an individual animal into
two or more parts, which, when the division is completed, sepa-
rate, and each soon assumes the form, and grows to the size of
the parent, and becomes capable of performing all the functions
which originally belonged to the undivided animkl. The most
common form of this mode of generation is met with in some of
the simpler of the infusoria, as the monas, the gonium, the cycli-
dium, the vorticellse, and the volvox. In the instance of the
volvox, however, we find an approach to the next order ; for the
young are seen forming within the body of the parent, which is,
in course of time, reduced to a mere membranous vesicle, and
then bursts, and is torn into shreds, setting free the enclosed
young, each of which immediately begins to execute its indepen-
dent movements in the fluid.

785. Gemmiparous generation occurs when a new individual
grows from the parent as a bud or sprout; at first exhibiting but
little resemblance in shape or structure to the parent animal, but
gradually assuming that form whilst still adhering to it, and
being afterwards detached to commence an independent exist-
ence. Numerous examples occur of this mode of reproduction
amongst the lower orders of zoophytes, such as animals belong-
ing to the tribe of polypi, of which the hydra viridis, rendered cele-
brated by the researches of Ti'embley, may be taken as the type.
Sometimes, as happens in the sponge, the actinia, and some of
the lower orders of mollusca, the young are formed from small
detached masses after they are separated from the body of the
parent. These bodies, which are called spores, or gemm.uhs, are
generally of a rounded form and homogeneous structure ; and
the whole substance of which they are composed is converted
during their development into the new animal. Hence they may
be regarded as buds formed in the parent body, but detached
from it before the evolution of the new animal begins. In some
species these gemmules^ are formed in all parts of the body indis-
criminately ; but in most others there is a particular generative
organ provided for their formation.

786. In by far the greater number of organized beings no
reproduction takes place except by the co-operation of two kinds
of generative organs ; laying the foundation of the distinctions
of sex, and constituting sexual generation. As characterising
the female, there is, in the first place, an organ, termed the ovary,
of which the olRce is to form the ova, or eggs. These are
organized bodies of a determinate shape, within which we first
find the earHest rudiments, or germ, of the future animal contained
in a fluid, which is itself enclosed in a vesicle. But the ovum,
or, more properly speaking, the ovulum, thus formed exclusively

GENERATION. 329

by the female organs, never advances in its development beyond
this stage, and can never ffive rise to a new animal, unless it

• • • L L

receive a certain vivifying impression given to it by the contact
of a peculiar fluid, denominated the semen, which has been pre-
pared by a totally distinct apparatus, constituting the male
organs.

787. The nature of the impression thus made by the seminal
fluid on the ovulum, or immature ovum, and which constitutes its
fecundation, and awakening in it a power of reproduction, which
*had before remained dormant, is wholly unknown ; nor is it
accompanied with any immediate alteration in its appearance or
structure. None of the parts of the new animal can yet be
discerned in the fluid contents of the ovulum, the great mass of
which consists of a fluid holding in suspension granules of albumi-
nous or oily matter; and a certain time must elapse, even in the
most favourable circumstances, before the formative process exhi-
bits its effects. The form of the egg is given by the external
coverings, and there is in every egg a determinate part, at which
the minute rudimental germ of the embryo is first visible. It is
to this germ that the power of independent life and development
appears more immediately to belong, the granular fluid serving
only as nutriment laid up in store for the supply of materials for
growth.

788. Thus the processes essential to sexual reproduction consist,
first, in the formation of an ovulum by the female organs ; second,
in the secretion of the seminal fluid by the male apparatus; third,
in the application of the seminal fluid to the ovulum so as to confer
on it fecundity.

789. The mode in which this application is made differs accor-
ding as the male and female organs are both contained in the system
of the same individual, (as occurs in monacious plants and herma-
phrodite animals,) or exist separately in different individuals (as
in dioecious plants, and all the higher classes of animals). In the
former case, self-impregnation may take place, either by the
required seminal access being effected internally in each individual
independently of any other; or, in other cases, by the concurrence
of two individuals in sexual union which reciprocally impregnate
one another (as is exempHfied in the leech, the earth-worm, and
the snail). In the second division, where the male, or fertilizing
organs, are possessed exclusively by one individual, and the female
organs, or those producing the germ, by another, impregnation of
the ova may take place either after their exclusion from the body
of the female parent, by their contact with the male semen ejected
on them when thus excluded (as happens in the case of fishes and.
batrachian reptiles), or within the body of the female ; for which
latter purpose, a new function, that of copulation, becomes neces-
sary. This last mode of procedure is had recourse to by nature

28*

330 , feEPRODUCTIYE FUNCTIONS.

in by far the largest portion of the animal kingdom, including all
the tribes of insects, nearly all the mollusca, and all warm-blooded
vertebrated animals.

■ 790. All the subsequent phenomena relate to the development
of the embryo thus brought into existence; to the supply of nourish-
ment for its growth; and to the advantages of situation, of warmth,
and of -protection, which are necessary for the favourable proce-
dure of the vital powers in the progress of this development.

791. Various plans are resorted to for conducting these pro-
cesses of development of the fecundated ovum. In that which is
termed oviparous generation, the ovum, during its passage through
the oviduct, receives the addition of a considerable quantity of
nutritious matter, sufficient for the supply of all the materials

. requisite for its growth, until the 'period when it is capable of
procuring food for itself; and it also acquires a capsule, or sub-
stantial covering, frequently of a calcareous nature, fitted for its
protection under the circumstances in which it is to be placed.
When thus formed it constitutes an egg, or-eonrplete ovum ; and
in this form it is either excluded from the body of the female parent,
and hatched, if already fecundated, by the influence of external
warmth; or if not previously fecundated, this change is accom-
plished by the seminal fluid of the male being shed upon it. The
former case, which implies sexual congress, is exemplified in all
insects and birds : the latter, which requires no such congress,
obtains in fishes, and many of the reptilia. Both are compre-
hended under the term oviparous animals.

792. In a few instances the eggs, previously fecundated within
the body of the female, instead of being expelled, remain in the
oviducts until they are spontaneously hatched, and the young are
then brought forth alive. This phenomenon, which is exhibited
by many cartilaginous, and a few osseous fishes, by several rep-
tiles, and by some gasteropodous mollusca, insects, annehda, and
entozoa, has been called ova-viviparous generation.

793. In mammiferous generation, on the other hand, the ovum,
which is not perfected in the same degree as in the two former
cases, remains within the female, and is attached, by the medium
of a substance called the placenta, to the inner surface of an
organ termed the uterus, where it receives nourishment from the
maternal system, and where it remains until it is capable of inde-
pendent life, and it is then brought forth. This retention during
growth in the uterus is termed utero-gestation, and its subsequent
exclusion is termed parturition. The young of mammaha after
birth, although they cease to be organically connected with the
mother, continue to derive from her a certain quantity of suste-
nance in the form of milk, which is a secretion from certain
glands termed mammce, the possession of which is the character-
istic feature of this class of animals. An exception occurs in the

GENERATION.

331

case of marsupiate animals, in whom the young leaves the uterus
at a very early period of its formation, while it is yet of a very
small size, and its organs are comparatively imperfectly formed.
On being born it is introduced by the mother into a pouch,
termed the marsupium, formed by a folding of the integuments of
the lower part of the belly ; and a shor^ time after it has been
deposited there, it is found attached by its mouth to one of the
nipples of the mammas, which are concealed within the marsu-
pium, and there receives its nourishment until it has acquired
sufficient size and strength to quit its habitation. Monotrematous
generation, which is peculiar to the ornithorynchus and echidna,
is not yet perfectly understood. The generative organs, and the
ova within the ovaries, in these animals, partake in a great de-
' gree of the oviparous type ; but they are also combined with the
presence of mammary glands, which perform the office of lacta-
tion, as in the strictly viviparous class of animals.

794. The following table, w^hich is nearly that given by Dr.
Allen Thomson,* exhibits a synoptical view of the various forms
of the reproductive process occurring in different classes of
animals : —

OS ^

fFissiparous,

Gemmiparous, ^

Monoecious,
or

C A. The parent splits into two or more parts,
I each part becoming a new animal.
I 1. By transverse fissure.

-<[ 2. By longitudinal fissure.

13. Irregularly.
B. The parent bursts, and the included young
l^are discharged.

f A. Buds sprouting from the parent stock.
B. Gemmse, or Sporules, formed —
1. In all the 'parts of the body.
(_ 2. In one part only.

r Both sexual organs contained in the same in-
) dividual.

<

,S Hermaphrodite,

^M

1. By self-impregnation.
i_ 2. By mutual impregnation.
f A. Oviparous ,- eggs laid, and afterwards hatched.

II. Eggs fecundated externally.
2. Eggs fecundated internally.
1^ Bicecious, . <( B. Ovo-viviparous ,- eggs hatched within the

I maternal body.
Mammiferous ; the parent suckling the young
Lby mammae.

1. Monotrematous.

2. Marsupial.

3. Placental, or strictly viviparous.

795. A wide range of inquiry is here opened to us, compre-
hending, if we were to include in its field the whole of the animal

* Cyclopaedia of Anatomy and Physiology, by Dr. Todd, article Genera-
tion, p. 438, to which article we are largely indebted in the compilation of
this chapter.

332 REPRODUCTIVE FUNCTIONS.

kingdom, an immense multitude of facts, to the complete study
of which the labours of a whole life would be inadequate. We
are, however, to confine ourselves, at present, to the view of
human physiology; but even here the great extent of the subject
obliges us to reduce within a narrow compass the account we
have to give of this important and interesting department of the
science. For this purpose, after a short description of the cir-
cumstances relating to the unimpregnated ovum, we shall proceed
to the physiology of the male and female systems respectively,
bringing its history to the period of the fecundation of the ovum.
This latter subject will lead us to consider some of the most
celebrated theories of generation ; after which we shall briefly
consider the phenomena of utero-gestation and parturition, which
are functions belonging exclusively to the female parent, but
which accompany and are accommodated to the successive
changes attending the development of the foetus. Of these latter
changes, relating to the system of the new individual, it will be
more convenient to give the history separately.

Sect. II. — Unimpregnated Ovum.

796. Much difficulty is necessarily experienced in obtaining
direct evidence of the early changes occurring in the iprocess of
human generation, from the scanty opportunities allowed us of
direct observation of those changes, and from our being precluded
from resorting to the most instructive fountain of knowledge,
namely, experimental research. Whilst, therefore, we obtain
occasional views of the actual phenomena which occur in man,
we must content ourselves with filling up the chasms in the con-
tinuous history of his generation, by the observation of those
which are presented in ^the lower animals that most resemble
him in the mode in which this function is conducted, and by
remoter analogies derived from other classes.

797. It is well estabhshed, from these combined sources of
information, that the essential part of the, female system con-
cerned in generation is the ovary, or ovarium, of which there is
one, situate on each side, in the cavity of the pelvis. The ovaries
are small capsular bodies, of an oblong, or oval, and somewhat
flattened shape, which are enveloped in the fold of the peritoneum,
forming the broad ligaments of the uterus. They are composed
of a white and loose cellular texture, in which we discover
several minute vesicles, or cysts, filled with a transparent fluid,
and termed, from the name of De Graaf, who first observed them,
the Graafian vesicles. Their number is generally from fifteen
to twenty in each ovarium, and they vary in size, the largest
being about one-third of an inch in its longest diameter. The

UNIMPREGNATED OVUM. 333

flui^ which is contained in these vesicles is slightly viscid and
albuminous, inclining to a yellow colour in the most turgid vesi-
cles, containing numerous granules of an irregular shape, and a
few globules of oil, but being otherwise pellucid,

790. Besides the peritoneal covering already described, the
ovarium has a cellular coat proper to itself Each of the Graafian
vesicles has a double investment ; the outer coat consisting of a
close filamentous texture ; and the internal layer being thicker,
softer, and more opaque than the outer, from which it is readily
separable after maceration, and having a slightly villous inner
surface. The membrane immediately containing the granular
fluid above described, also exhibits the appearance of being
studded with granules, and is on that account styled the mem-
brana granulosa. Within the granular fluid is -found a body,
composed of closely coherent granules, which has been deno-
minated by its discoverer, Baer, the discus proUgerus, and which
he represented as having a flattened or discoid form, and as
forming the bed in which is placed the minute vesicle of the
ovulum, or germ of the unimpregnated ovum. The later re-
searches of Dr. Martin Barry, of which he has given an account
in a paper communicated to the Royal Society of London, have
thrown further light on this branch of Zoology. The following
is a summary of the principal conclusions at which he has arrived
on this subject.

800. The ovulum of all vertebrated animals, and of many of
the invertebrata also, is contained in a vesicle, called by some
authors the chorion, but which Dr. Barry thinks it desirable,
wherever found, to call an ovisac. He considers the Graafian
vesicle of the mammalia, and aleo the capsule, or calyx of ovi-
parous vertebrata, as an ovisac which has acquired a covering ;
which covering is the " couche externe^^ of the " capsule cle la
vesicule de Graaf" of Baer. The perfect Graafian vesicle of the
mammalia has been shown by preceding physiologists to be ana-
logous to the perfect capsula, or calyx of the bird ; but the ana-
logy is found by Dr. Barry to be much more remarkable between
the ovisacs of these two classes of animals, before these additional
coverings have been acquired ; and this analogy may also be
extended to those of amphibia and fishes, so that, in fact, the
surfaces of all the vertebrata are in their original structure
essentially the same ; a conclusion which Dr. Barry is disposed
to extend also to the ovisacs of many of the invertebrata.

801. The ovisac, being originally an independent structure,
can be better studied in this state, than at a later period, when
it has become the lining membrane of the Graafian vesicle or
calyx. Thus, while the perfect Graafian vesicle of the mammal,
and the perfect capsule of the bird, are obviously corresponding
structures, there yet exists this difference, that there is a space,

334 REPRODUCTIVE FUNCTIONS.

filled with a large quantity of fluid in the former, not present in
the latter; a difference which does not exist in the early stages
of formation, when ovisacs in general appear in this respect to
be essentially the same. The structure of the ovisac may be
examined, in some mammalia, when it does not exceed in length
the 600th, or even 1200th part of an inch ; so that in the latter
case,*^a cubic inch would contain 1,728,000,000.

802, The ovisac of the vertebrata, and perhaps of other ani-
mals, is at first of an elliptical form. In the mammaha and birds,
myriads of ovisacs and ovula are formed, which never reach
maturity. Many of these are formed in the substance of the
proper membrane of larger ovisacs, and are therefore termed by
Dr. Barry parasitic ovisacs.

'■■ 803. The ovisac is formed in a cavity proper to itself, with
which .it does not appear to have any organic connexion. The
granules found in the fluid of the ovisac are very characteristic
in their appearance, and imply the presence of albumen in a con-
centrated form. A stratum of these granules, found on the in-
ternal surface of the proper membrane of the ovisac, constitutes,
as Baer remarks, a distinct membrane. But the mass of granules
described by that anatomist as being discoid, is believed by Dr.
Barry to be of a spherical form. This latter observer finds that
the ovulum of vertebrated animals is, when first formed, situated
in the centre of the fluid of the ovisac, and more or less obviously
held there by a flake of granules ; and has at first no proper
envelope of granules. In the mammalia, there forms around the
ovulum a granulous covering of a spherical form, which Dr.
Barry terms the tunica granulosa ; but it has no discoid mass of
granules proper to it. At a certain period, the ovulum of the
mammalia passes from the centre of the ovum to the periphery ;
and there, while invested by its granulous tunic, it penetrates the
membrana granulosa, leaving behind it a flake of granules. Here
it lies quite in contact with the proper membrane of the ovisac,
is more or less imbedded in the membrana granulosa, and is
supported behind by a mass of granules, sometimes presenting
the appearance denominated by Baer the cumulus. But this
cumulus does not belong to the proper granulous covering, or
tnnica granulosa, of the ovulum ; for it may in some animals be
separated from this covering, in the form of what Dr. Barry calls
the petasiolus granulosus.

804. After the ovulum has reached the periphery, its tunica
granulosa may, at least in some animals, by contact with the
membrane of the ovisac, become attenuated, or may even disap-
pear at one side ; which circumstance, together with the great
transparency of this tunic, may have been the cause of Baer's
assigning to it a discoid form. This approximation of the ovulum
to the exterior surface of the ovisac, is doubtless for th6 purpose

THE MALE SYSTEM. 33&

of exposing it to the action of the fecundating seminal fluid, which
reaches it while it is in this situation, and still in the ovary. The
next step being now the application of this fluid, we are brought
to the next stage of our inquiry, namely, into the series of appa-
ratus and of functions provided for the preparation of the semen,,
its introduction into the female organs, and its transmission to-
the surface of the ovulum.

Sect. III. — IVie Male System,

805. The preparation of the seminal fluid is the office of the
two glandular bodies called the testicles or testes. They are sus-
pended in a portion of common integument having the form of
sac, termed the scrotum^ by a round band, called the spermatic
cord, which pursues a very serpentine course ; a plexus of veins,
the assemblage of which has received the name ot corpus pampi-
neforme, consisting of the spermatic artery, a plexus of absorb-
ents, a plexus of nerves ; and lastly, the vas deferens, or excre-
tory duct ; and they are further supported by a sub-cutaneous
layer of muscular fibres, termed the dartos. The scrotum is
divided into two chambers, one testis being lodged in each, by a
membranous partition, or septum. Each testicle is loosely con-
tained in a sac, formed by an external serous membrane, the
tunica vaginalis, derived from the peritoneum, which forms a
cavity for its reception similar to that of other serous membranes.
This tunic is reflected, hke those of other cavities, over the body
of the organ ; and the reflected portion, which is called, from its
white colour, the tunica albuginea, forms the proper capsule of
the testis. When this latter tunic is divided, the testis is found to
consist of a flattened oval substance, to the upper, outer, and
back part of which a narrow and flat slip of substance, called the
epididymis, is found adherent.

806. The substance of the testicle is extremely vascular, and
the ultimate branches of its spermatic arteries are collected into
small bundles of fine convoluted vessels, separated from one
another by septulce, or membranous partitions. From these the
v>asa seminifera, or beginnings of the excretory ducts, take their
rise, and gradually unite to form a smaller number of canals of
larger diameter, but exceedingly tortuous in their course. On
arriving at the surface and back part of the testicle, they suddenly
become straight, assuming the name of the vasa recta ; they,
however, agatn subdivide, and their branches have very numerous
communications with one another, composing the net-work of tubes
called the corpus highmoriammi, or the rete testis. From the rete
testis arise the ducts denominated the vasa efferentia, which, after
being again contorted into numerous convolutions, form the conical

336 REPRODUCTIVE FUNCTIONS.

bodies called co7ii vasculosi; these again, alternately join to form
the epididymis, already mentioned, which consists of one slender
tube, of enormous length, coiled upon itself into a small compass.*
The epididymis at length emerges, in the form of a tube of larger
diameter, which is the vas deferens, and which ascends along the
spermatic cord towards the abdomen. On tracing these ducts
into the pelvis, we find them passing up by a circuitous route
through the spermatic passage, and on reaching the pelvis, again
descending by the lower side of the bladder, to the under part of
its cervix. Each duct is here connected with an oblong mem-
branous bag, called the vesicula seminalis, which is a long blind
sac, folded many times upon itself; its open extremity entering
the vas deferens at an acute angle. These sacs are supposed to
be receptacles for the retention ^and accumulation of semen, until
the time when it is required to be expelled. But Hunter remarked
that the fluid contained in them is somewhat different from that
obtained from the seminal ducts of the testicle itself; and he
therefore supposed that these vesicles secrete a peculiar fluid
which may perhaps dilute and add to the bulk of the semen. He
even contended that the proper office of these cavities is not that
of reservoirs of semen ; supporting his opinion by arguments
derived from comparative anatomy, which furnishes many exam-
ples where no direct communication exists between them and the
vas deferens, and others where these vesicles are entirely absent.
Notwithstanding these analogies, the prevaiUng opinion is in favour
of the vesiculffi seminales in man being reservoirs of the seminal
secretion.

807. From the vesiculse seminales and the vas deferens, the
semen is occasionally discharged through a duct common to
both, and about half an inch in length, which perforates a body
called the prostate gland, and then opens on each side into a canal,
termed the urethra, which is continued from the urinary bladder,
close to a small eminence in that canal, termed the verumontanum,
or caput gallinaginis. The prostate gland is of the size of a small
chestnut ; in shape it resembles a heart, with the apex directed
forwards. Its texture is firm and tough ; it is divided into two
lateral lobes, and one anterior lobe, and contains a great number
of follicles, into which a white opaque viscid fluid is secreted.
This secretion is discharged by ten or twelve excretory ducts
opening obliquely into the urethra, in a furrow at the side of the
verumontanum.

808. The urethra is a canal, lined by a mucous membrane,
serving the double purpose of discharging the urine and the

* The whole length-of the excretory vessels of the testes is very extraordi-
nary. Their diameter has been stated to be no greater than the 200th part of
an inch ; and it has been estimated that the total length of the vessels which
compose one of the testes amounts to more than 500 feet.

THE MALE SYSTEM.

337

semen. As it proceeds forwards from the neck of the bladder,
it passes through the prostate gland, on emerging from which it
becomes more contracted in its diameter, and passes under the
symphysis pubis. At this part, for the length of about an inch,
it is supported only by firm cellular and ligamentous membranes;
this part of the canal is termed the membranous portion of the
urethra. It is then dilated into what is called the bulh, or sinus
of the urethra ; and it afterwards receives the ducts of several
mucous glands, which have been denominated the glands of
Coivper, and which are generally very minute, but sometimes
have the size of peas. One of these is placed on each side of the
membranous portion of the urethra, below which they are united
by an isthmus ; and the duct of each^ about three inches in
length, opens by perforating the mucous membrane lining the
spongy body of the penis. Mucus is also furnished to various
parts of the canal by lacunce provided for that purpose. AX its
bulbous part, the urethra takes a considerable curve forwards,
and is surrounded in the rest of its course by a peculiar erectile
texture, denominated the corpus spongiosum urethrtB. This sub-
stance is expanded, at the extremity of the penis, into what is
termed the glans, which is covered by a fold of the skin called
the prepuce. The corpora cavernosa are the cylindrical bodies
which compose the chief bulk of the penis. They arise by two
crura, one from each ascending ramus of the os ischii, and are
chiefly composed of the peculiar structure, termed the erectile
tissue (see § 434). At its extremity, the urethra is considerably
narrower than where it passes along the corpus spongiosum.

809. These parts, namely, the glans and corpora cavernosa
penis, and the corpus spongiosum urethras, consist principally of
large convoluted veins, which in the last named part are particu-
larly dilated and branched, and are bound together and crossed
in various directions by ligamentous bands and fibres. This
arrangement, by obscuring the connexions which the veins have
with one another, as well as their tortuous course, has led to the
mistake that has so long prevailed among anatomists, of ascrib-
ing to these bodies a cellular structure. These bands appear to
have been provided for the purpose of limiting the distention of
the vessels, and adding to the rigidity occasioned by the accumu-
lation of blood in the venous convolutions during erection. The
means by which the blood is made to pass from the small arteries
into these convoluted veins, is not clearly understood. Professor
Milller* has lately discovered a remarkable set of minute dilated
and ramified branches, which he terms arlerice helicince, and
which are appended to the terminal twigs of the arteries distri-
buted on the sides and interspaces of the venous cavities in the

* Archiv. fiir Physiol. &c. 1835. pp. 27 and 220.
29

338 REPRODUCTIVE FUNCTIONS.

penis of man and several animals, and which he represents as
projecting into the interior of the veins, and pouring their blood
into them ; a mechanism which must doubtless have some direct
relation with the process of erection.* Dr. Houston-f has de-
scribed some muscles, under the name of compressores vence
dorsalis penis, to the contraction of which, and the consequent
impediment to the return of the blood from the penis, he attri-
butes the erection of that organ. It is more probable, however,
that this effect is produced principally by an altered action of the
blood-vessels themselves, and is analogous to the turgid state of
the vessels which occurs in blushing, than is owing to any me-
chanical cause. The purpose served by the dilatation, elonga-
tion, and rigidity of the male organ, effected by this vascular-
action, is obviously that of enabling it to penetrate to a sufficient
distance into the female organ during coition, for the conveyance
of the semen to those parts of the latter whose office it is to
carry it on to the ovulum which it is intended to fecundate.
With this view, the secretions from the testes, vesiculse semJnales,
prostate gland, and the glands of Cowper, are poured together
into the bulb of the urethra, and thence expelled with force by
the action of the muscles called the ejaculatores seminis.

810. The seminal fluid, which acts so important a part in the
process of generation, has at all times attracted much atten-
tion. It is found to be considerably heavier than water, and to
have a peculiar odour, which increases on keeping; to exhibit
alkaline properties, and to give off ammonia when heated. From
the analysis of Vauquelin, it appears that human semen contains
six per cent, of animal mucus, three of phosphate of lime, and
one of uncombined soda ; the rest being water. The phosphate
«f lime is deposited in crystals when the fluid is at rest. But the
most remarkable circumstance in its composition is, the constant
presence of immense number of microscopic animalcules, the
form, apjiearances, and size of which are different in almost every
different animal ; but in each species of the more perfect animals,
the kind of animalcules, like that of the entozoa, is constant and
determinate. Leewenhoek claims the merit of having first dis-
covered them ; but the priority of this discovery is assigned by
Haller to Ludwig Hamm, who, when a student at Leyden,is said
to have observed them in the year 1677. Another claimant of

* [The researches of Valentin (Mailer's Archiv., and Lond. Med. Gaz.
June 23, 1838, p. 543,) are not in accordance with those of Miiller.
The result of numerous examinations has convinced him, that the helicine
arteries are not peculiar vessels, but merely minute arteries that have been
divided or torn, and that the real distribution of the vessels of the corpora
cavernosa follows, in every respect, the most simple laws.]

f Dublin Hospital Reports, vol. v.

THE MALE SYSTEM.

339

the discovery is Hartsoeker,* but apparently on no good grounds.
An account of the controversy that arose on this subject, is given
by Dr. Bostock.f Doubts were at one time entertained of the
fideUty of the representations of these singular beings given by
Leewenhoek ; but they have been wholly removed by the later
researches of Spallanzani, and the still more recent inquiries of
Prevost and Dumas. These animalcules have a definite figure,
consisting of a flattish rounded head, from which proceeds a long
tail, exhibiting constant undulatory movements. They are ac-
cordingly classed by naturalists under the title of spermatozoa, as
a species of the genus cercaria, among the infusoi'ia.J

811. It would appear from the elaborate researches of Prevost
and Dumas, that these spermatic animalcules are found, at one
time or other, in the semen of almost all the animals in which
they have been sought for ; but at that period of their life, and in
that season of the year only, when the animals in which they
exist are fit for procreation. They are almost always present in
the fluid secreted by the testicles, and very often in that of the
vesiculffi seminales, into which they have doubtless been intro-
duced along wath the fluid derived from the testicles. Hence it
has been concluded, that their presence is intimately connected
with the power of propagation ; and may be essential to that
process. Wagner infers from his observations, that these ani-
malcules are subject to remarkable changes of form at difl'erent
periods, and that they even go through a regular gradation of
development; and phenomena leading to the same conclusion
have been observed by Dr. Allen Thomson. §

812.ylt is not until the period of puberty that the generative
organs are fully developed, and become capable in either sex, of,
exercisiing their proper functions. Prior to this period, the phy-
sical character of the two sexes is nearly the same : there is the
same dehcacy of complexion, the same high pitch of the voice,
and the same slightness of (figure. But the development of the
sexual organs appears to exercise a peculiar and specific influ-
ence over the system at large, aflfecting the growth of the rest of
the frame, and modifying both its physical and mental powers.
The attainment of this condition is more tardy, by two or three
years, in the male than in the female ; and the age at which it
takes place, differs in different climates, and in persons of different
temperaments, modes of life, and circumstances of physical and
moral education. It occurs at an earlier age in southern than in
northern climates; in this country generally appearing in the
male between the ages of fifteen and eighteen years ; and in the

* Essai de Dioptrique, art. 88, p. 227.

•j- Elementary System of Physiology, p. 642, note. /

^ [See, on this subject, Dunglison's Physiology, 3tl edit. ii. 330,]
§ Cyclopaedia of Anatomy and Physiology, art. Generation, p. 4t)0.

340 ' REPRODUCTIVE FUNCTIONS.

female from that of thirteen to sixteen ; but in the hottest regions
of the great continents, girls are said to arrive at puberty at
ten, or even at nine years of age ; and in the northernmost parts
of Europe, not till that of from fifteen to eighteen. The arrival
of this period is retarded by habits of active bodily exertion.

813. The characteristic changes induced by puberty in the
male besides the development of the genitals, and the secretion of
the seminal fluid, are the enlargement of the larynx, which
changes the quality of the voice ; the growth of the beard on the
chin, upper lip, and cheek, and of an increased quantity of hair
on the rest of the body, and especially on the pubes ; the enlarge-
ment of the chest and shoulders; an increase of physical activity
and power; a greater capability of enduring fatigue; an exalta-
tion of the active powers ,of the mind, and of the qualities of
courage and resolution.

814. The act of sexual union is prompted by instinctive feel-
ings, experienced by both sexes, and which generally depend on
the condition of the body, and of the genital organs in particular,
which are then in a state of high excitement. This mental feel-
ing, and the local aflection appear to be intimately associated
together, and mutually produce one another. According to the
doctrines of phrenology, the cerebellum is supposed to be that
particular part of the encephalon which presides over the sexual
function; and to be, in a word, the sensorium commune of the
feelings relating to it ; that is, the part to which impressions of a
sexual kind proceed, and from which all sexual desire emanates;
and to be the source of that power by which the generative or-
gans execute their appropriate functions. Dr. Allen Thomson,
after enumerating the proofs alleged in favour of this hypothesis,*
observes, that he is not inclined to adopt it as established on suffi-
ciently accurate and extensive data; and remarks, that the com-
parative anatomy of the brain, (in which, rather than in experi-
ments on animals, he would be disposed to place much reliance,
from the acknowledged difficulty of making correct deductions
as to function, from the effects of morbid alteration or artificial
injury of the encephalon,) affords very few arguments in favour
of the phrenological doctrine, and furnishes several facts which
militate strongly against it. (See the article Phrenology in the
Appendix.)

Sect. IV. — The Female System,

815. The female generative system of organs, having to perform
the offices of receiving, conducting, and applying to the ovulum

* Cyclopsedia, &c. p. 444.

THE FEMALE SYSTEM. 341

the seminal fluid, of conveying tiie ovum into a situation where it
can be evolved and properly nourished, and of bringing it forth at
the appointed period into the world, is necessarily much more
complicated and elaborate than the male system. The part per-
formed by the male is quickly accomplished, while the female has
to execute a long series of processes, which require a considerable
time, and are connected with important changes in the economy.

816. The ovaria, of which we have already described the
structure and offices, are connected with a hollow muscular organ,
termed the uterus, matrix, or icomb, by two ducts, called, from the
name of the anatomist who first described them correctly, the
Fallopian tubes. They commence by a trumpet-shaped mouth,
opening from the abdominal cavity, and of which the edges are
fringed or jagged with irregular filaments, or Jimbrice, as they are
termed.* The mouth of the Fallopian tubes are endowed with
the power, on certain occasions of venereal excitement, of attach-
ing itself to the adjacent ovarium, and of firmly grasping it. The
tubes, each of which is about five inches long, in their progress
towards the uterus, soon contract in their diameter, and become
exceedingly narrow at their termination in the upper and lateral
corner of the triangular cavity of that organ. They are enclosed
in the folds of the peritoneum which form the broad ligaments of
the uterus.

817. The uterus itself is a compact, dense, membranous, and
fleshy organ, provided with a copious supply of blood-vessels,
lymphatics, and nerves. It has the shape of a flattened pear, and
is situated in the pelvis, between the rectum and the urinary
bladder. The outer surface of the uterus is covered with a
reflected portion of the peritoneum, which, in passing from the
sides of the uterus to the sides of the pelvis, forms the broad liga-
ments already mentioned, or the Alee Vespertilionis, as they have
been called. It is also provided with round ligaments, connecting it
with the external parts of the pubes. The inner surface of the
uterus is lined with a mucous membrane. The existence of
muscular fibres in its substance has been called in question by
many anatomists, and it is certainly difficult to demonstrate their
presence ; yet the extraordinary mechanical force which this
organ exerts during parturition can scarcely be ascribed to anv
power but a muscular one.t The parts of the uterus are distin-
guished into the fundus, which is the broad end turned towards
the abdomen, the body and the cervix, or narrow end. The
channel of the cervix uteri, which proceeds from the lower angle
of its triangular cavity, leads into the vagina, which is an elastic

* This part has also been termed the morsus diaboli.

f Dr. Bostock has given in his Physiology an enumeration of the authors
who have written on both sides in this controversy, p. 648, note. [See, also,
Dunglison, Op. cit. ii. 403.]

29*

342 REPRODUCTIVE FUNCTIONS.

membranous canal, opening externally, and surrounding at its
upper part the cervix uteri, which forms a protuberance in its
cavity, called the os uteri, or os tinccB, from its supposed resem-
blance to the mouth of a tench.

The membrane which, lines the vaginal cavity is continued
from the mucous membrane of the uterus, but is thrown into
numerous folds and wrinkles, admitting of occasional dilatation
of the canah This is surrounded by a tissue of an erectile struc-
ture, termed plexus restiformis, or corpus cavern'osum vagince.

818. The external parts are the mons veneris, which is formed
by an accumulation of adipose substance on the upper part of
the symphysis pubis. Below this are the labia pudendi, forming
in their progress towards the anus, from which they are divided
by the perineum, what was called by the French anatomists
fourcliette. Between the labia is the fossa magna, in the upper
part of which is lodged the clitoris, a small, -round, and spongy
organ, which is analogous to the penis in its erectile structure,
being composed of two corpora cavernosa, arising from the tube-
rosities of the OS ischii, and terminating in an impervious glans,
furnished with a prepuce. The meatus urinarius, or orifice of the
urethra, which in the female is very short, opens immediately
below the clitoris. From this part, on each side of the fossa,
extends the nyni'phcB, or labia minora, which are membranous
and spongy folds. The vulva, or orifice of the os externum, is in
part closed by a transverse membrane, of a crescentic form, called
the hymen, the remains of which, after it has been lacerated,
compose the folds' called carunculce myrtiformes.

819. The changes which the female system undergoes at the
period of puberty are on the whole as considerable as those of
the male, although many of the external characteristics of the
state of childhood are still retained, such as the deUcate texture
and inferior development of the general frame, the large propor-
tion of subcutaneous fat, smooth skin, and want of prominence
in the muscles of the trunk and limbs. But the genital system
undergoes a considerable and rapid development at this period,
the breasts enlarge, the pelvis becomes more capacious, and a
peculiar periodical secretion, from the inner surface of the uterus,
consisting of a certain quantity of sanguineous fluid, is established.
This process, which is termed menstruation, recurs at periods
nearly equal to a lunar month, and continues, with certain inter-
missions, determined by the occurrence of pregnancy, and the
performance of the function of lactation, as long as the organs
are capable of bearing progeny, which is, on an average, a terra
of thirty years. The fluid thus discharged is generally believed
to contain less fibrin than blood, and to be less prone to putre-
faction ; it evidently contains a large proportion of the colouring
particles of the blood, and is very seldom found to coagulate.

THEORIES OF GENERATION. 343

The secretion amounts, on an average, to six or eight ounces,
and usually continues for about four or five days, beginning and
leaving oft' gradually, and being most abundant towards the mid-
dle of the period. The discharge in general takes place slowly,
or drop by drop.

820. The eflectual fecundation of the ovulum, which is by this
change converted into an ovum, and its removal to a situation
where the embryo, then first brought into existence, can be per-
fectly developed, constitute the process of concejption ; but the
exact nature of this process, as well as the precise circumstances
which must concur for its successful accomplishment, have been
but very imperfectly ascertained. The investigation of these
phenomena in the lower animals, however, has rendered it ex-
tremely probable that Graafian vesicles are continually being
produced in the ovarium, and come forwards at intervals, during
the whole period of female fertility, and that they burst in suc-
cession, and shed the contained ovula, whether sexual intercourse
take place or not, although there is reason to believe that their
maturity is hastened by this act. The consequence of the burst-
ing of one of these vesicles is the escape of the ovulum or ovum,
as the case may be, and its passage down the Fallopian tube
into the cavity of the uterus. The lacerated membrane of the
vesicle closes, leaving a scar ; the internal coat becomes thick-
ened, and a yellow substance is deposited in its cavity, giving
rise to the appearance which has been termed a corpus luteum.
The presence of this substance is a certain indication of the pre-
vious bursting of a Graafian vesicle.

821. Much discussion has arisen on the question as to the pre-
cise time when, and place where, the ovulum is impregnated.
There seems now, however, little reason to doubt that the semen,
immediately on its reception into the uterus, is conveyed by the
Fallopian tubes to the ovarium itself, and then comes in contact
with the exposed ovulum, which is ready for fecundation. On
the bursting of the vesicle, the ovum is conveyed down the
Fallopian tube, and arrives at the uterus, where the changes it
next undergoes will be the subject of future inquiry.

Sect. V. — Theories of Generation.

822. Having thus stated the provisions which have been made
by nature for the fecundation of the ovulum, by the concurrent
offices of the two sexes, we may here examine various specula-
tions and opinions which, from time to time, have been enter-
tained relative to the nature of this marvellous and mysterious
process ; speculations which, although for the most part exceed-
ingly hypothetical, and often completely visionary, have been

344 REPRODUCTIVE FUNCTIONS.

dignified with the appellation of theories of generation. This it
is our intention to do very briefly, and to notice only the more
important of these theories ; for the total number of hypotheses
which have been advanced on this subject is so great, that their
mere enumeration might occupy many pages. Drelincourt, who
lived in the latter part of the seventeenth century, collected from
the writings of his predecessors as many as two hundred and
sixty-two " groundless hypotheses" concerning generation : and
" nothing is more certain," observes Blumenbach, " that Drelin-
court's own theory formed the two hundred and sixty-third."

823. These theories may be arranged according as they relate
to the action of the parent organs, or to the changes in the egg
occurring during the formation of the new animal; and Haller
divided the first of these classes into three divisions, according
as the oflspring is supposed to proceed ; first, exclusively from
the organs of the male parent, which is the theory of the Sper-
matist ; or, secondly, entirely from those of the female, which is
that of the Ovists; or, thirdly, from the union of the male and
female products, which is the theory of Syngenesis. The second
class, again, may be arranged under two heads, according as the
new animal is supposed, first, to have its parts rendered visible,
by their being expanded, unfolded, or evolved from a previously
existing though imperceptible condition of the germ, which is the
theory of evolution ; or, secondly, to be newly formed from
amorphous materials at the time when it makes its appearance
in the ovum, which constitutes the theory o{ Epigenesis.

824. The theory of the Spermatists regarded the male semen
as furnishing all the vital parts of the new animal, the female
organs merely affording the offspring a fit receptacle and suitable
materials for its nourishment, until it could exist by the indepen-
dent exercise of its own functions. One of the earliest supporters
of this hypothesis was Galen; but its modern revival dates from
the period of the discovery of the seminal animalcules, which
were regarded by Leewenhoek as the proper rudiments of the
foetus. They were even considered by some to be miniature
representations of men, and were styled homunculi; one author
going so far as to delineate in each, the body, limbs, features, and
all the parts of the grown human body. Even Leewenhoek
describes minutely the manner in which they gain the interior of
the ovum, and are retained after their entrance by a valvular
apparatus.

825. The Ovists, comprising some of the older philosophers,
such as Pythagoras and Aristotle, maintained that the female
parent affords all the materials necessary for the formation of the
offspring, the office of the male being merely to awaken the dor-
mant formative powers residing in the female products. Malpighi
and Harvey asserted that the rudiments of the fcEtus are derived

THEORIES OF GENERATION. 345

principally from the female ovum ; an opinion which was also
elaborately defended by Yallisneri.*

820. The theory of Syngenesis, or of the simultaneous combi-
nation of products derived irom both sexes, which after sexual
intercourse, are supposed to unite together to form the germ, is
also of very ancient date. In connexion with this theory may be
mentioned that modification of it which may be termed the theory
of metamorphosis, according to which a formative substance is
held to exist, but is allowed to change its form, in order to be
converted into the new being ; as also the hypothesis of Buffon,
which was eagerly adopted by Needham, who conceived that
certain molecules which they termed organic, and which they
believed universally to pervade plants and animals, were all
endowed with productive powers, which enabled them, when
placed in suitable situations, to attract one another, and to compose
by their union living organized bodies. They imagined, that in
the process of generation the superabundant portion of these
organic molecules were accumulated in the generative organs,
and there constituted the rudiments of the offspring.

827. The hypothesis of evolution, or of pre-existing germs,
coincides vvith that of the Ovists, in considering the foetus as solely
the production of the female ; but it farther assumes that it already
exists, with all its organs, in some part of the female system
previous to the sexual intercourse; and that it receives no proper
addition from the male semen, the action of which is merely that
of exciting the powers of the foetus, and of endowing it with
vitality. The observations of Haller with respect to the gradual
enlargement or evolution of the chick during'the process of incu-
bation, were conceived to lend great support to the advocates of
this theory, of whom the most strenuous and enthusiastic was
Bonnet. This naturalist, so celebrated for the boldness of his
speculations, contended, not only that the whole of the parts of
the foetus pre-exist in the ovum, before they actually make their
appearance, but that the germs of all the animals which are in
future to be born, also pre-exist in the female parent; so that the
ovaries of the first parents of any species of animal, contained
the gertris of all their posterity, included the one within the other,
like a nest of boxes ; from which comparison he termed his theory
that of " e7nboitement." This extravagant notion was adopted by
many physiologists, principally from its affording some kind of
explanation of what no other theory seemed in the least adequate
to solve. Spallanzani, in particular, was a zealous defender of
the hypothesis of pre-existing germs. It appears, however, to be
totally irreconcileable with the phenomena of hybrid productions,
and of the resemblance which, in so many instances, the oflspring
bears to its male parent.

* Delia Generazione, part 2.

346 REPRODUCTIVE FUNCTIONS.

828. We have already mentioned that Harvey and Malpighi
ascribed the formation of the foetus principally to the powers of
the female. This opinion gave origin to the modern theory of
Epigenesis, first clearly promulgated by Caspar Frederick Wolff,*
who not only described a successive production of organs, of the
previous formation of which there existed no trace ; but showed
also, that after parts are first formed, they undergo many impor- .
tant changes in their shape and structure, before arriving at their
finished state. The more recent researches, aided by delicate
microscopical observation, of Meckel, Pander, Baer, Rathke,
Oken, Purkinje, and Valentin ; Serres, Rolando, Dutrochet, Pre-
vost and Dumas, Coste, and others, have demonstrated that the
theory of Epigenesis, or superformation of parts, is much more con-
sistent with the observed phenomena than that of evolution. The
facts which have thus been brought to light are of peculiar interest
with reference to the plans of nature, into which they give us a
more extended insight, by exhibiting new and unexpected affini-
ties between remote families and classes of animals ; by showing
that at one period the type of their formation is nearly the same,
and by explaining the seeming caprice of nature in instances of
monstrous and defective formation. But to attempt adducing the
proofs and illustrations of these positions, would engage us into
details requiring an extensive survey of the whole animal crea-
tion, to enter into which would occupy more space than is com-
patible with the limits of the present treatise. We must, there-
fore, content ourselves with referring, for more ample elucidation
of this subject, to the Bridgewater Treatise on Animal and Vege-
table Physiology.]

Sect. VI. — Utero- Gestation.

829. On the arrival of the ovum in the cavity of the uterus, to
which we have traced it in a preceding chapter, the first object
of nature is to effect its attachment to a portion of the inner sur-
face of that organ. A provision for this purpose has already
been made, even whilst the ovum was contained in the ovarium.
A vesicle, first noticed and described by Dr. Barry, is formed
around the ovum ; the granules of the tunica granulosa become
less densely aggregated together, and gradually pass into the
state of fluid albumen ; oil globules appearing for the first time
to take their place on the surface of the ovum. This fluid he
supposes to correspond to the yolk of the eggs of birds ; and the

* In his inaugural dissertation, entitled Theoria Generationis, published at
Berlin in 1759.

I Pan iv. chap. ii. on Organic Development ; and chap. iv. on Unity of
Design. Vol. ii. pp. 599, 625. [A.mer, edit. ii. 437.]

UTERO-GESTATION. 347.

membranous vesicle above mentioned, in which it is enclosed,
and which thus forms after impregnation, he considers as the
rudimental chorion, by which the ovum is afterwards attached
to the uterus.

830. It results from these views, that mammalia differ from
oviparous animals in the circumstance, that those parts of their
ovum which are last formed, have a more internal origin ; thus,
the first portion of the albumen and the chorion of the ovum in
mammalia, originate, not in the oviduct, but in the ovary; for
which purpose, chiefly, there is provided the very large quantity
of albuminous fluid in the Graafian vesicle ; a provision which
may be presumed to have especial reference to the development
of the embryo within the body of the mother. The chorion, being
formed in the ovary, it is an ovum, and not an ovuhmi, that is
■expelled from that organ in mammalia. On the other hand, in
birds it is an ovulum, and not an ovum, that leaves their ovary;
and it becomes an ovum, and receives an addition of the albumen,
or yolk, and the shell membrane in their oviduct, and then be-
comes analagous in all its parts to the ovum of the mammal when
the latter leaves the ovarium. The albumen, in the form of
granules, lines the ovisac, constituting the membrana granulosa;
and in the form of the fiake it supports the ovulum in the centre
of the fluid of the ovisac, and afterwards supports it at the peri-
phery of the latter, sometimes in the form of the petasiolus
granulosus, or cumulus of Baer. It closely invests the ovulum in
the form of the tunica granulosa ; it forms, in the rabbit at least,
and probably in other mammalia, two bands or ligaments, termed
the chalazce, which are conspicuous in birds ; and finally, it also
provides the granulous bands by which, in some instances, too
sudden a discharge of the ovum of the Graafian vesicle is pre-
vented.

831. Dr. Barry finds that the ova of the rabbit of five or six
days, when in the uterus, are in bulk about eight thousand times
that of the ovulum in the ovary, and have three concentric mem-
branes ; namely, first, an outer vesicle, (the villous chorion,)
originating in the ovary ; secondly, the primitive membrane of
the yolk, distended so as to fill the chorion ; and, thirdly, an inner
vesicle, or membrane, which has been called the hlastoderyna, or
germinal membrane, presenting in its substance a central spot,
which is the germinal spot, or embryo. Dr. Allen Thomson has
seen this spot very evident in the ova of a rabbit, on the sixth
day after impregnation. It corresponds exactly with that part
called the cicatricula in the egg of a bird, which there lies imme-
diately on the surface of the yolk, imbedded in a disc of granules.
In the centre of the cicatricula, a dark round spot is seen, termed
the colliquamentum, which contains a minute vesicle, discovered
by Purkinje, and which bears his name. This vesicle, which is

348 REPRODUCTIVE FUNCTIONS.

seen in ihe ovulum, afterwards bursts, and leaves in its place a
thin and tender transparent membrane. In the centre of this
transpai'ent spot, may be perceived, seven or- eight hours after
the commencement of incubation, with the aid of a magnifying
glass, a small dark line. This line, or primitive trace, as it has
been termed, is swollen at one extremity, and is placed in the
direction of the transverse axis of the egg. The rounded end is
towards the left, when the small end of the egg is turned
from us.

832. Having traced thus far the changes occurring in the ovum
before it becomes attached to the uterus, we shall defer the consi-
deration of the subsequent stages of its evolution to a future
section, and here attend to the changes which have in the mean
time taken place in the uterus, with a view to prepare it for
the, office it has now to perform.

833. A change has already taken place in the uterus, prepara-
tory to the reception of the ovum, and before its arrival in that
cavity. An increased flow of blood is directed towards that
organ. A substance, consisting of lymph, or organizable fibrin,
exudes from its interior surface, furnishing it with a soft flaky
lining, which, when the ovum is received, is reflected over that
body, so as to give it a double covering. These two folds, the
one being 'in contact with the uterus, and the other with the
ovum, constitute the two layers of the memhrana decidua; the
former portion being termed the decidua vera, and the latter, the
decidua refiexa."* This- membrane soon becomes organized, and
highly vascular.! The vessels in the progress of growth, are in
some parts much dilated, so as to form sinuses, which are ulti-
mately intermingled, though by no means continuous, with the
blood-vessels of the fostus. These latter blood-vessels, consisting
of the umbilical arteries and veins, of which the trunks are col-
lected in the umbilical cord, have passed to the chorion, which
by the end of the first, and during the second month of pregnancy,
has acquired a villous external surface. At the end of this period,
the branches of these vessels penetrate and ramify in these villi,
which become thoroughly vascular ; and this thickening and
vascularity is concentrated on one side of the chorion, generally
on that which is adjacent to the fundus of the uterus, forming the
body called the placenta. This body is of a flattened oval shape,

* [The very existence of a decidua reflexa iias been a matter of dispute ;
and by those who admit it, the mode of formation and arrang^ement has been a
topic for discussion. In the different views of obstetrical Physiologists, the
reader is referred to Velpeau's Embryologie, Paris, 1833, or to Dunglison's
Physiology, 3d edit. ii. 308, in which they are all detailed.]

I [It is denied by many, that the decidua is supplied with vessels. Vel-
peau regards it as vv'holly inorganic ; and denominates it, in consequence,
"anhistoiis" membrane, from a.]/, primitive, and ivto;, texture, that is, mem-
brane devoid of texture or organization.]

PARTURITION. 349

from six to eight inches in breadth, and from an inch to an
inch and a quarter in thicl<ness at the middle part, becoming
thinner towards the edges. It occupies about a fourth part
of the chorion, and at birth is a pound in weight. In rumi-
nant quadrupeds, the substance corresponding to the human
placenta, is confined to a number of circular and spongy eleva-
tions, varying in number from thirty to one hundred, which are
termed cotyledons. The human placenta is evidently formed of a
structure essentially the same, composed of many lobes consoli-
dated by contact into one organ. It has very generally been
supposed that the placenta is of a cellular structure, and that the
arteries and veins of the uterus communicate with its cells; but
the recent researches of Dr. Robert Lee,* renders it very doubtful
if these inter-placental cells really exist.

834. In proportion as the foetus grows, the uterus enlarges, and
about the fifth month it rises out of the pelvis, and rests against
the front of the abdomen. As it enlarges, the distinction between
the body and the cervix is lost ; the os tineas is flatteffed, and
forms only a small rugous hole, not easily discernible ; and it is
closed by a tough glutinous matter, which is fixed in the in'egu-
larities of the surface.

Sect. VII. — Parturition.

835. The ordinary period of utero-gestation is forty weeks ;
on the expiration of which the uterus takes on itself a new kind
of action; its contractility, which had lain dormant for so long
a time, is now suddenly and powerfully excited. A mucous
discharge takes place from the vagina, the external passage is
relaxed, and slight pains are felt in the back and loins, which
usher in the real pains of labour. These are occasioned by
powerful contraction of the uterus, accompanied by a strong
action of the diaphragm and abdominal muscles; and they are
repeated at short intervals. Impelled by this pressure, the mem-
branes of the foetus project into the vagina, and dilate the os
tineas ; on their bursting, the liquor amnii escapes, and at the
next pain the pressure of the uterus falls directly on the foetus.
The head of the foetus gradually descends, urged on by succeeding
spasms, the occiput foremost, the long axis of the head being
disposed obliquely across the lesser basin of the pelvis. The
occiput, as the external parts yield, glides off the inclined surface
of the ischium, presenting at the orifice of the vulva, and bringing
at the same time the long diameter of the shoulders to corres-
pond with the greatest breadth of the pelvis, and the head being

* Philosophical Transactions for 1832.
30

350 KEPRODUCTIVE FUNCTIONS.

thus disengaged, the trunk follows. After a short time, fresh
pains return, and the placenta and membranes being detached
from the uterus, come away. In the majority of natural births,
labour is completed in from four to six hours. The uterus then
very slowly and insensibly contracts, so as to diminish the ample
cavity which has been rendered vacant, and at the same time its
volume is reduced by absorption. During the return of the
uterus to its former state, a discharge, at first tinged with blood,
and afterwards of a whitish colour, termed the lochia, ensues,
which lasts for several days.*

Sect. VIII. — Lactation.

836. The function by which nourishment is prepared, of a nature
suited to the early periods of infant life, belongs to the reproductive
class. The fluid provided for this purpose is the Milk, of which
we have already examined the chemical properties, and noticed
the qualities which peculiarly fit it for the purpose it is intended
to serve. The organs which prepare it are the mammoe,, which
are glands consisting of the union of a great number of lobes,
intermixed with adipose substance, and remarkable for the white-
ness and fineness of their texture. The numerous excretory tubes
from these lobules unite in forming ducts, which open separately
in the folds of the integuments of the nipple. A remarkable sym-
pathy is observed between this gland and the uterus; for it often
enlarges and becomes tender for a few days before each monthly
period. It enlarges during the latter months of pregnancy, and
the brown circle surrounding the nipple, or areola, as it is called,
assumes a dark colour. The secretion of milk would naturally
continue until the middle of the second year, if the child were
retained at the breast as long as it was supplied. During the
period of suckling, the menstrual discharge is not renewed, but
pregnanacy may, however, again take place, before its recurrence.

Sect. IX. — Fadal Evolution.

837. In judging of the changes which take place in the human
embryo from the period when its evolution commences, we must
be guided principally by those which, occurring in the develop-
ment of that of the chick, furnish the best means of following the
whole succession of phenomena. Commencing the inquiry, then,
from the appearance of the primitive trace in the blastoderma, or
cicatricula, already described (§ 831), we find this part gradually

* The above account of parturition is for the most part extracted from
Mr. Mayo's Outlines of ituman Physiology, as presenting a very clear and
compendious account of the phenomena.

FffiTAL EVOLUTION. 351

dilating in bulk, and occupying a situation between the two
layers, namely, the outer and the inner, into which, towards the
twelfih or fourteenth hour of incubation, this cicatricuia has
divided itself The outer of these layers is called by Pander the
serous layer ; and it subsequently gives rise to the nervous, the
musculai-, the osseous, cartilaginous, and tegumentary systems of
the body. The innermost, which is situate in contact with the
yolk, is the 7nucous layer, whence are derived the alimentary canal,
and the glandular and pulmonary systems. A third layer (the
vasczilar layei-), is afterwards formed in the interval between the
two former, and is the origin of the sanguiferous system of the
foetus, including the heart and all the blood-vessels. The respi-
ratory system is the product of the combined changes which this,
together with the last mentioned layer, undergoes.

838. The series of phenomena which present themselves in
following the succession of changes occurring during the forma-
tion of the vital organs, are highly curious, and afford the most
splendid instances of that refined intelligence and that provident
adjustment of a long series of means for the effectual accompHsh-
ment of future and far distant ends, which strike us with pro-
found astonishment when we penetrate into the remoter regions
of physiology, removed from ordinary observation. It would
far exceed the limits within which we must confine ourselves in
the present treatise, to give the detailed history of these organic
changes. We must content ourselves, therefore, with a brief
outline of the principal phenomena, and with referring to works
professedly treating on this subject, for more copious information
on this highly curious department of physiology.*

839. On the outer surface of the serous layer, or that most
distant from the yolk, there are raised two parallel ridges, which,
joining along their upper margins, form a canal; in this canal,
according to Baer and Serres, a semi-fluid matter is deposited ;
this matter, acquiring consistence, becomes the spinal chord,
with a pyriform extremity, which last is the rudiment of the
the future head. Roland, Prevost, and Dumas, on the other hand,
suppose that the primitive trace is itself the spinal cord and brain,
in their rudimental state.

840. When the layei's of the germinal membrane have so far
expanded as to cover nearly one-third of the yolk, they no longer

* The reader will meet with mucii instruction on these subjects, in Dr.
Allijn Thomson's papers on Embryology in the Edinburgh New Philosophical
Journal ; in the Cyclopaedia of Anatomy and Physiology, by Dr. Todd ; and
also in Mr. Mayo's Outlines of Human Physiology, chap. xv. sect. ii. We
would also beg to refer to the summary contained in the Bridgewater
Treatise on Animal and Vegetable Physiology, vol. ii. p. 599. [Amer, edit.
ii. 408.] The greater part of the summary given in the present article is
abridged from Mr. Mayo's work. [See, also, Velpeau's Embryologie ou
Ovologie Humaine, Paris, 1833, and Dunglison's Physiology, ii, 421.]

352 REPRODUCTIVE FUNCTIONS.

retain their flat and uniform appearance, but begin to exhibit
various folds, which afterwards become the different cavities of
the body. Those of the mucous layer turn downwards, and
whilst its remote expansion includes within it the yolk, as in a sac,
the inner folds close inwards, and by the union of their margins
form two tubular cavities, one at each endof the embryo, commu-
nicating in the middle with each other, and also, by a common
opening, with the cavity of the yolk. This tube is the nascent
alimentary canal.

841. The first rudiment of the heart is perceptible at the
anterior part of the vascular layer, which, as we- have already
stated, is developed between the serous and mucous layers. In
the mean time, the surrounding disc of the cicatricula, which
continues to expand, exhibits, in the circumference of the trans-
parent area, which now becomes thicker and more spongy, numer-
ous irregular points 'and lines of a dark yellow colour. These
lines gradually extend, unite together, first into small groups, and
then into one net-work, which composes the vascular area. The
space they occupy is terminated, on each side, by a circular
vessel, of larger size than the rest, the sinus or vena terminalis,
into which the smaller ramifications of the vessels open at the
circumference, whilst towards the central part they unite into a
vessel on each side, the two o7Jiphalo-meseraic arteries, which
penetrate into the vascular layer of the embryo.

842. Simultaneously with these changes, all the important
organs of the body are formed in rapid succession. The spinal
cbrd and brain, of which we have noticed the first traces, are
quickly developed ; the former, appearing first as a membranous
tube, the latter, as three vesicular bodies ; and both being gra-
dually filled with opaque nervous substances of two , kinds, the
one being uniform, the other filamentous. The nerves next ap-
pear, but w^iether they are generally formed in their entire
length at once, or are growths from the brain or spinal cord, or
are first produced at their farthest extremity, and afterwards ex-
tended towards the central organ, are points not yet determined.
Some, however, as the optic, auditory, and olfactory nerves, are
certainly productions from the cerebrum. The muscles become
visible in the human embryo at the third month ; they are then
soft and gelatinous, transparent, of a light yellow tint, and not
distinguishable from their tendons. Each muscle is formed at
once in its whole length, with its attachments perfect. The eyes
are formed at a very early period, and their growth is rapid;
they are situate at first at the sides of the head, as in quadrupeds,
and subsequently move forwards. The iris has no central aper-
ture, the place of the pupil being occupied by the membrana
pupillaris, which disappears completely before birth. The organ
of hearing is formed soon after the eye. The substance of the

FCETAL EVOLUTION. ' 353

bones is at first an homogeneous jelly, enclosed in a menhbrane,
and exhibiting no divisions into joints. This jelly gradually be-
comes cartilaginous, the conversion taking place irom the surface
inwards. It is gradually replaced by ossific matter, which grows
from the interior, resembling a process of crystallization. Ossi-
ficaiion begins in the human embryo in the seventh week.

843. The integument is the outermost fcetal pi'oduct of the
serous layer, which gradually spreads like a mantle over all the
other structures, and dpes not acquire proper strength till the
middle of the fcetal period. At the end of the fifth month the
body is covered with short, whitish, and silky down, which,
however, disappears in the seventh month. The hair of the
head and of the eye-brows, and the nails, are formed in the sixth
month. About the fifth month there appears on the body a yel-
lowish-white greasy substance, at first thinly, and afterwards
more thickly spread, and termed the vernix caseosa. The limbs
are formed originally below the skin, which they reach, pushing
out like little globular shoots, in the sixth week. They originally
grow straight out from the trunk. The upper arm is next laid against
the breast, the fore-arm drawn upwards ; the thigh is bent up to
the belly, the leg drawn ^backwards towards the thigh, and the
feet turned in, and crossed, with the soles turned inwards. When
the fingers are first formed, they are contained in a common
mitten of skin, which, gradually becoming thinner between them,
forms a web, which is finally absorbed.

844. Another product of the serous layer is one still more ex-
ternal than the integument of the foetus, and consisting of a sac
formed 'by a membrane reflected from the sides and from either
extremity of the embryo, so as to enclose a space behind its body.
This is the amnios, which forms a loose bag filled with a liquid
(the liqiLor amnii) in which the fostus floats, suspended by the
umbilical cord. As the walls of the trunk close in front, the
circular edge by which the amnois is attached to the body of the
embryo becomes proportionably contracted ; and it is finally
limited to the umbilical opening, hereafter to be noticed.

The communication which we described as being left between
the intestinal tube and the cavity of the yolk bag, or vitelline sac,
and which in birds continues open, soon becomes closed in mam-
malia, the sac assuming the form of the intestinal vesicle, disco-
vered as such by Bojanus in the ovum of the sheep ; though it
had been before seen and known by the name of vesicula alba ;
it disappears by the third month.

845. The glandular organs which communicate with the ali-
mentary canal are formed by the extension of its mucous mem-
brane in the form of tubular productions, shooting into small
masses of matter lodged in its neighbourhood ; the blind ends of
the tubes being often dilated into spherical pouches. The gall

30*

354 REPRODUCTIVE FUNCTIONS.

bladder is, in like manner, formed by the extension of a tube,
which not being received into a mass of elementary matter, en-
larges into a simple sac.

846. The lungs are regarded as another expansion of the
mucous layer of the germinal membrane, growing from the back
part of the oesophagus, and gradually advancing on either side of
the aorta, so as at length to surround it.

847. The kidneys are preceded in the embryo by a substance
first noticed by Wolff, and called after him the Wolffian bodies,
or false kidneys, which originally extend the whole length of the
spine, from the heart to the end of the intestines ; but they become
afterwards shorter, and, after a time, diminishing by absorption,
wholly disappear. They appear to be subservient to the deve-
lopment both of the true kidneys and of the testes and ovaria.
The bladder and urethra, on the other hand, together with the
external genitals, are formed partly out of a development of the
extremity of the intestine, and partly by fissure and folding of the
integument, in the following manner.

848. There is first the production of a bag of considerable
length, called the aUantois, from the intestine, or that part of it
which may be considered as the cloaca; subsequent contractions
of the sides of the sac, at different parts, next divide it into two
cavities, the proper allantois and the urinary bladder ; and the
lower contraction is elongated into the canal of the urethra. The
separation between the two former afterwards closes, and the
coalesced membrane forms the ligament termed the urachus.
The urethral tube never closes.

849. The testes and ovaries appear in mammalia about the
sa me time at the inner and fore part of the Wolflian bodies, attached
to them by a fold of the peritoneum. From each testis or ovary
there descends to the internal ring a membranous process, which
in the male is called the gubernaculum, and in the female consti-
tutes the round ligament. It passes, in either sex, along the
spermatic passage to the filaQientous tissue of the scrotum or
labium. The ovaries descend to the brim of the pelvis; the testes
pass through the ring into the scr-otum. ,.

850. Every organ begins to be formed without either blood, or
blood-vessels ; the circulation in them being established solely for
the purpose of subsequent growth and perfection. Even the heart
is formed and shaped, and its texture has acquired some degree
of consistency, and it displays an undulatory motion, before the
blood has reached it. We have already described the formation
of vessels and of blood in the vascular area ; but the blood is at
first motionless. It afterwards finds its way from thence by the
omphalo-mesenteric veins to the heart, whence it is expelled
along the aorta, and thence again carried into the vascular area ;
thus establishing a simple circulation. In a few days arterial

rCETAL EVOLUTION. 355

branches extend froin the aorta, and venic cava) are formed,
establishing the systematic circuhition. Five pair of branchial
vessels are formed from the aorta in the neck, the oesophagus
being between the branches on each side, and there are also four
openings in the neck of the embryo on each side. This single
heart, branchial arches, and openings, are permanent parts of the
structure in fishes. In the mammalia, these branchial clefts soon
close ; the heart becomes separated by the growth of partitions
in each ventricle and auricle, into two separate cavities, and the
artery is divided, in like manner, into an aorta and pulmonary
artery. Some of the arches then disappear ; others become
permanent aortic, and others permanent pulmonary branches ;
and the foetus is becoming prepared for pulmonary respiration.

851. The amnios, closing upon the shrunk urachus, forms
with the umbilical artery and veins, and a connecting gelatinous
tissue, the umbilical cord, or navel-string ; connecting the foetus
with the placenta, which, as M'C have before seen, is formed by
a thickened portion of the chorion. The umbilical vein distri-
butes part of its blood to the liver, and then, under the name of
the ductus venosus, joins the inferior cava, through which the
mixed blood of the placenta and of the inferior part of the body
is carried into the right auricle of the heart. Part of this blood
passes directly from the right to the left auricle through the
foramen ovale, which is an aperture in the yet imperfect septum
of the auricles ; the remainder, with the exception of the small
quantity transmitted to the yet imperfectly developed lungs,
passes from the pulmonary artery, through the ductus arteriosus
directly into the aorta. The offices of the placenta are supposed
to be those, first, of introducing nourishment, transmitted by im-
bibition from the maternal to the foetal blood, through the mem-
branes of the interjacent vessels of the mother and the foetus;
and, secondly, of oxygenating the blood of the foetus by impart-
ing to it oxygen from the same source. It has been supposed by
many that the foetus derives sustenance from the liquor amnii
which surrounds it, and which might be introduced through the
mouth into the stomach ; but this opinion is now very generally
abandoned. It is true, however, that the stomach of the foetus
usually contains a considerable quantity of ropy mucus, but with-
out albumen. This last substance is found in the contents of the
duodenum,* and the great intestines contain a green matter
termed meconium, which has the appearance of being the refuse
of a kind of digestion. It has been conjectured that the thymus
.gland has some relation to the function of foetal assimilation.

* See a paper by Dr. Robert Lee, in the Philosophical Transactions for
1829.

356 KEPRODUCTIVE FUNCTIONS.

CHAPTER XX.

PROG-RESSIVE CHANGES IN THE ANIMAL ECONOMY.

852. We have now traced the history of the changes which
the human system undergoes, from the earliest rudimental state in
which it exists in the embryo, tlirough the period of its foetal life,
to the epoch of its birth ; when it is ushered into the world, with
organs fitted for maintaining a comparatively independent exist-
ence, yet still requiring the most tender offices and most fostering
care of that parent, of whose system it had so long formed a part,
and from which it has been so recently dissevered. To follow
the narrative of the successive alterations which take place during
the growth of the system, the proportional development of its
several organs, and the acquisition of its various powers, both
corporeal and mental, during all the subsequent epochs, filling up
the interval between the cradle and the grave, composes a long
chapter in human physiology, and would occupy too large a space
for the present treatise. All that we can pretend to attempt must
be a faint sketch of the outlines of this " strange eventful history."

853. The greatest of all the changes which occur in the animal
existence of every human being, is its emergence from the state
in which it was dependent for its immediate supply of nourishment
and of oxygen on the blood which is circulating in the vessels of
its parent. On its birth, which cuts oft' the placental circulation,
all these ties are at once dissevered. A new element surrounds ,
it, from which it is in future to derive the principle that maintains?
its vital energies. The placental supply is superseded by respi-
ration ; and the first gasp of air received by an instinctive effort
into its lungs alters at once the whole character of its organic
constitution. It is now a breathing animal ; and all the channels
and passages, which had till then been adapted to a difi^erent mode
of being, have now become useless, or rather worse than useless,
and thev must give way to a new order of processes, and a new
mechanism of the hydraulic functions. The ductus venosus, the
foramen ovale, and the ductus arteriosus are superseded in their
functions, and must be speedily closed and obliterated, in order
to give place to new courses of circulation and a new order of
functions.

854. Besides these changes, which, being consequent on the
sudden exercise of the new function of respiration, are immediate,
the whole organization rapidly conforms itself to the great altera-
tion of the circumstances in which it is now placed. As the growth

CHANGES IN THE ANIMAL ECONOMY. 357

of the fcetus had been progressively becoming more and more
rapid in proportion as the term approached when it was to be
ushered into the world; so, on the other hand, the growth of the
body is greatest in the earliest periods of its extra-uterine life, and
becomes more and more slow in proportion as it advances to the
full dimensions it is destined to attain. The principal anatomical
changes which follow birth, besides those already stated, are the
gradual obliteration of the thymus gland, and of the renal capsules.

855. The natural term of lactation is succeeded by that of
teething ; the first set of teeth, or the milk teeth, being furnished
by nature as temporary structures, until instruments of greater
dimensions can be constructed in the enlarged jaws. The appear-
ance of the teeth is an intimation that the organs of assimilation
are prepared for the digestion of soUd food ; and that the proper
period for weaning is arrived.

856. From this period an accurate observer may perceive that
the intellectual education keeps pace with the physical ; whilst
the active exercise of the limbs consolidates the bones, and gives
firmness to the muscles, that of the senses is continually adding
to the store of ideas, and calling forth the latent powers of the
understanding. The moral faculties are developed much earlier
than is generally imagined; and the future character of the indi- ■
vidual often receives a permanent impress from the events of
infancy. No one can have watched its varying aspect at this
tender age, without recognising how early affections are called
forth towards its protector and fosterer ; how quick is the distinc-
tion it makes between kind and unkind treatment, and how keen
is its sense of the least injustice which it may have either to bear
or to witness.

857. To the periods of infancy and childhood succeeds that of
puberty, which we have seen is attended in either sex with re-
markable changes, both physical and moral. During the period
of increase the power of assimilation are in full activity in fur-
nishing a sufficiency of materials for growth; the circulation is
vigorously employed in applying them to that purpose ; and the
supply is even more abundant than the consumption. When,
however, the fabric has attained its prescribed dimensions, the
total quantity of nourishment furnished and expended being nearly
balanced, the vital powei's are chiefly exerted in consolidating
and perfecting the organization of every part, and qualifying them
for the continued exercise, during a long succession of years, of
those functions of which we have given the history in the pre-
ceding part of this treatise.

858. But, in the mean time, the process of consolidation begun
from the earliest period of development, is still advancing, and is
producing in the fluids both greater thickness, and a diminution
of their total quantity. By the gradual conversion of their

358 CHANGES IN THE ANIMAL ECONOMY.

\

gelatin into albumen, all the textures acquire increasing solidity;
the cellular substance becomes firmer and more condensed, and
the solid structures more rigid and inelastic. The contractile power
of the muscles is also impaired ; and the limbs no longer retain
the elastic spring of youth. All these progressive modifications
of structure tend slowly, but inevitably, to disqualify the organs
for the due performance of their functions. Their vascularity
gradually diminishes ; for a large proportion of the arteries which
had been actively employed in building the fabric, being now
thrown out of employment, contract, and, becoming impervious,
disappear. The parts of the body, having acquired greater rigi-
dity, oppose a gradually increasing resistance to the propelling
force of the heart, which is itself, in common with all the other
vital powers, slowly diminishing. The absorbents are now active
in removing the parts which have become useless or superfluous.
Old age steals on by slow and imperceptible degrees, which, even
when obvious to others, are unknown to ourselves. But nature
kindly smooths the path along which we descend the vale of
years, and conducts us by easy stages to our destined place of
repose. When death is the simple consequence of old age, we
may perceive that the extinction of the powers of life observe
an order the reverse of that which was followed in their evolu-
tion. The sensorial functions, which were the last perfected, are
the first which decay; and their decline is found to commence
with those mental faculties more immediately dependent on the
physical conditions of the sensorium, and more especially with
the memory, which is often much impaired whilst the judgment
remains in vigour. The heart, the pulsations of which gave the
first indications of life in the embryo, generally retains its vitality
longer than any other organ; but its powers being dependent on
the constant oxidation of the blood in the lungs, cannot survive
the interruption of this function, and on the heart ceasing to
throb, the death of every part of th6 system may then be consi-
dered as complete.*

"* For more ample details on the subject of the changes which take place
in the progress of age, see the article Age in the Cyclopaedia of Practical
Medicine, and also the chapter on the Decline of the System in the Bridge-
water Treatise on Animal and Vegetable Physiology, vol. ii. p. 619. [Amer.
edit. ii. 433.]

TEMPERAMENTS. 359

CHAPTER XXI.

TEMPERAMENTS.

859. In the natural and healthy condition of the system, all its
functions are nicely adjusted and proportioned to each other, so
as to produce the most perfect harmony. Yet within the limits
of health variations are admissible in this balance of functions,
according as some predominate over others in regard to energy
and activity ; or rather, according as there prevails a tendency
to such predominance, which, though it does not actually overset,
may yet endanger the preservation of that balance which consti-
tutes health, and may thus give at least a proneness to disease.
This peculiar state of the system, depending on the relation be-
tween its different capacities and functions, by whit;h it acquires
a tendency to certain modes of action, is called Temperament.

860. Much attention was paid by the ancients to the subject of
temperaments ; and the nomenclature they established to express
the various combinations of peculiarities in the constitution, cor-
responding with the definition above given, has continued in
general use even to the present day. They described four tem-
peraments, corresponding to the four qualities of hot, cold, moist,
and dry, ascribed to the human frame by Hippocrates, and which
were supposed to confer the specific characters to the four ingre-
dients of which the blood was thought to be composed ; namely,
the red part, the phlegm, the yellow, and the black bile respect-
ively; and hence were derived the names of the sanguine, the
phlegmatic, the choleric, and the melancholic temperaments, as
indicating an excess of each of these principles.

861. In modern times the ancient doctrine of temperaments
was adapted to the humoral pathology, by which all the devia-
tions from the standard of health were attempted to be explained.
Boerhaave, reasoning on these principles, and considering the
several temperaments as being formed by diflerent, combinations
of the four cardinal qualities, increased their number to the eight
following : namely, the warm, cold, moist, dry, bilious, sanguine,
phlegmatic, and atrabilious. Darwin, endeavouring to found his
doctrine of temperaments on varieties in the vital actions of the
system, which he had classified as referring to the four heads of
irritation, sensation,- volition, and association, formed four tem-
peraments in conformity with this arrangement, in which these
functions were conceived respectively to predominate.

862. Most of the modern physiologists, however, following the

360 TEMPERAMENTS.

example of Cullen, havp adopted the four temperaments of Hip-
pocrates, which are characterized by the following peculiarities:

863. The Sanguine temperament is distinguished by a full
habit and relaxed frame of body ; by a greater vascularity, soft-
ness and delicacy of skin, in which the veins are of considerable
size, and are particularly conspicuous by their blue colour, as
seen through the thin layers of the skin. The surface of the body
generally, and more especially the face, exhibits a florid and
ruddy colour. The hair is generally of a light brovi^n ; but has
often a yellow, and sometimes a reddish hue. Persons endowed
with a sanguine temperament are acutely sensitive, and highly
irritable : their pulse is frequent, indicating the general rapidity
and energy of the circulation. Both the secretions and excre-
tions are abundant, and little liable to obstruction. The disposi-
tion is free and open ; the temper cheerful, and rather disposed
to levity.

864. A. remarkable contrast to the temperament just described
is presented by the melancholic temperament, which is marked
by a firm and robust frame, and a spare habit of body ; by an
integument of sr-eater thickness, and of a brown and swarthy
hue ; and by an abundance of dark or black hair, which being
particularly conspicuous in the eye-brows and beard, and being
conjoined with a black colour of the iris, imparts to the counten-
ance a stern and sombre aspect. In persons endowed with tkis
temperament the pulse is habitually slower than the average
condition ; the blood is thicker and more sluggish ; the secretions
and the excretions are less copious, and more apt to be morbidly
deficient tjian with the generality of men. The nervoiis system
is, on the whole, less sensitive and excitable ; but the mind, al-
though not readily moved, when once set in motion, is remark-
ably retentive of its impressions, and tenacious of its purposes ;
persevering and indefatigable in action, ardent and constant in
its affections ; possessing great capacity of understanding, with
a fondness for contemplation, and for speculative inquiries de-
manding profound thought. The temper is naturally grave, and
often gloomy ; the fancy imaginative, and of a poetic turn, but
tinctured with melancholy, and betraying a proclivity to mad-
ness ; when happily tempered, it exhibits that fortunate combina-
tion of genius and industry from which have resulted the noblest
achievements of the human intellect.

865. The Choleric temperament would seem to occupy a place
intermediate between the two former, as partaking of some of
the qualities of both. The frame is more relaxed, the senses
more excitable, and the mind more irascible than in the melan-
cholic temperament. The complexion is less ruddy than in the
sanguine temperament, and the pulse stronger and more frequent;
the secretions are more copious, and the skin fairer and less
hairy than in the melanchohc temperament.

PHLEGMATIC TEMPERAMENT. 361

866. The Phlegmatic temperament is denoted by a relaxed
and feeble frame, prone to obesity ; a pallid complexion, a smooth
integument, with but few hairs, that on the head being of a light
colour. The circulation generally is languid, the pulse slow and
weak, the blood-vessels less capacious, the fluids more bland and
watery. The functions of digestion, secretion, and excretion, are
performed slowly, and are liable to frequent impediments. The
mind is dull, sluggish, disposed to indulge in sleep; not easily
moved, timid, inclined to fear, and prone to avarice.

867. Dr. Gregory has added to these four temperaments a fifth,
which he denominates the nervous temperament, and which owes
its peculiarities to the sensibility of the nervous system existing
in an undue proportion to the conti actllity of the muscles ; con-
joining the qualities of excitability and of debility. Such an union
of qualities, however, is compatible with the characteristics of
other temperaments, but occurs more commonly in the sanguine,
whether existing in its purest form, or blended with the phleg-
matic ; and it is found exemplified chiefly among those whose
occupations are sedentary, and who lead a life of ease and
hjxury.

868. These several temperaments are found variously modified
by occasional intermixture in dilTerent degrees with one another.
Thus, the phlegmatic is often conjoined with the sanguine, and
sometimes with the melancholic temperaments ; and observation
will readily suggest examples of other similar combinations.
The predominance of each of these temperaments varies at dif-
ferent periods of life. At an early age the system inclines more
to the sanguine; in middle life, to the choleric ; and at a more
advanced age, to the melancholic temperament. They admit
also of being variously influenced and modified by climate,
habits, and education; and accordingly each is found to prevail
amongst particular tribes and nations, and in particular regions
of the globe.*

* [The whole doctrine of the temperaments is more specious perhaps than real.
The very foundation, Indeed, of the predominance of particular humors,
systems, or apparatuses is wholly supposititious. It is obvious, too, that the
physical characteristics described, can in no wise apply to the coloured races.
There is doubtless a difference in the organization or constitution of diiferent
individuals, but this is but imperfectly explained by the doctrine in question.
M. Georget, indeed (Physiologie de Systeme nerveux, Paris, 1821), regards it
as a superstition connected with the humoral pathology, and he believes that
the brain, alone amongst the organs, has the power, by reason of its pre-
dominance or superiority, to modify the whole economy.]

31

VARIETIES OF THE HUMAN SPECIES.

CHAPTER XXII.

VARIETIES OF THE HUMAN SPECIES.

869. It has been a question much agitated amongst naturahsts,
"whether the differences observable in the complexion, features,
and the intellectual and moral endowments of different tribes and
nations which are found scattered over the surface of the globe
are sufficiently great to mark an original diversity of species, or
whether they correspond merely to the character of varieties
taking place in a single original race, analogous to those we be-
behold in many domesticated animals, such as the dog, the horse,
and the sheep, and therefore affording no objection to the hypo-
thesis that every individual composing the human race belongs
really to one and the same species. To Blumenbach belongs the
merit of being the first who entered w-ith a philosophical spirit
into the investigation of this great problem. The generally pre-
vaihng opinion at present is, that all mankind are the descendants
of the same original stock; and are therefore to be considered as
members of the same family.

870. It is a matter of considerable difficulty to establish an
accurate classification of the different varieties into which the
human race should be divided. Blumenbach, who, from having
devoted to it much labour and attention, is justly considered as
the highest authority on this subject, has fixed the number of
these varieties at five ; though, as Mr. Lawrence observes, these
five races ought perhaps rather be considered as principal divisions,
each of them including several subordinate varieties. M. Bory de
St. Vincent, in his Treatise on Man, extends the number of primitive
varieties to fifteen. Cuvier, on the other hand, is inclined to refer
all the varieties in the race to three principal heads, considering
the others as merely modifications of these.

871. The five varieties which Blumenbach has pointed out
are designated by the terms Caucasian, Mongolian, Ethiopian,
American, and Malay. He regards the Caucasian race as the
primitive stock, or as the standard and type of the rest. It
appears, indeed, to occupy an intermediate place between the
Mongolian race, on the one side, and the Ethiopian on the other
which latter races are the most wddely different from each other.
The American variety has been considered as intermediate
between the Caucasian and the Mongolian ; and the Malay
race as intermediate between the Caucasian and the Ethiopian.
The various intermixtures which have taken place between these

ETHIOPIAN RACE. 363

several races, in different parts of the world, render it very
difficult, at the present day, to draw those precise Hnes of dis-
tinction which have probaljly, in remoter times, characterized the
primitive races now enumerated. Thus, in Asia, we find con-
siderable mixtures of the Caucasian with the Mongolian races;
whilst in Africa, the Caucasian race has in various instances been
blended with the Ethiopian. The following are the circumstances
by which these several varieties are characterized : —

872. L The Caucasian races are distinguished by the general
whiteness of the skin ; the fairer complexions exhibiting a roseate
tint, particularly conspicuous in the cheeks, and derived from the
abundance of blood circulating in the vessels, and the darker
races inclining to a brown, and by the abundance and softness
of the hair, which is either black, or of a lighter chestnut colour,
occasionally inclining to red. The cranium is large and oval,
and developed especially about the forehead ; the face compara-
tively small, and falling perpendicularly underneath the forehead
The features are distinct from each other ; the nose narrow, and
frequently aquiline ; the mouth small ; the front teeth in both jaws
have a perpendicular direction ; the lips, particularly the lower
one, are gently turned outwards ; the chin is full and rounded,
and the general contour of the face has an oval form, and is
broader in the upper than in the lower portion. This is the race
in which the moral and intellectual energies of man have risen
to a higher degree of excellence than in any other; and it is the
race which has at all times been the most susceptible of cultiva-
tion and improvement. The hope may indeed be entertained
that it is yet far from having arrived at the highest point in these
respects which it is destined to attain.

873. 2. The Mongolian races are characterized by a com-
plexion approaching to an olive colour ; the eyes being black ; the
hair also black, strong, and straight; the beard thin and scanty;
and the head of a form somewhat square ; the cheek bones large
and prominent; the forehead low; the face broad; the features
flattened, and running together; the nose small and flat; the
aperture of the eyelids narrow, and the orbits situate obliquely;
the lips thick; the chin slightly projecting; the ears large. The
stature of most of the nations belonging to this race is, in general,
inferior to that of Europeans.

874. 3. The Ethiopian or negro race is marked by the lateral
compression of the skull, which is elongated forwards ; by the
prominence of the cheek bones, the narrowness and projection
of the jaws, and the recession of the chin. The forehead is low,
and very slanting; the eyes prominent; the nose broad, thick,
and flat ; the lips, the upper one especially, thick ; the upper
front teeth are obhque ; the hair black and woolly ; the legs are

364 VARIETIES OF THE HUMAN SPECIES.

long and slender ; the calf especially is small, and the knees are
bent inwards ; the arms are longer than in the other races.

875. 4. The Aboriginal American race is remarkable for the
red colour of the skin, the strong and straight black hair, the
scanty beard, and low forehead, the deeply sunk eyes, and the
round and prominent cheek bones. The mouth is large, the lips
thick, and the face in general broad and square; characters
which assimilate this race with the Mongolian, from which, how-
ever, it is sufficiently distinguished by the colour of the skin, and
the projection of the features, especially of the nose.

876. 5. The Malay variety of the human species varies consi-
derably in the colour of the skin, from a light tawny brown, to
one approaching to black. The head is narrow ; the bones of
the face are large and prominent ; the m.outh large ; the nose
full and broad at the point. The hair is black, and more or less
curling.

The following account of the filiation of the different races,
and of their distribution over the globe, is given by Cuvier.

877. The Caucasian race has been so named from its presumed
origin in the western part of Asia, in the neighbourhood of the
Caucasian chain of mountains, which are situate between the
Caspian and the Black Seas ; whence it has spread as from a
centre to the adjacent parts .of the Asiatic, European, and African
continents. The present inhabitants of these regions, namely, the
Circassians and the Georgians, are reputed to be still the hand-
somest race on earth. The principal ramifications from the
primitive stock, may be most satisfactorily traced by following
the analogies of the languages of the nations which have pro-
ceeded from it. Thus, the Armenian, or Syrian branch, pro-
ceeded southwards, and gave rise to the Assyrian and Chaldean
nations ; and also to the Arabians, who, after the era of Mahomet,
aspired to the empire of the world. The Phoenicians, Jews, and
Abyssinians may be regarded as Arab colonies, to which class
also the Egyptians may probably be referred.

878. The branch giving origin to the Indian, Germanic, and
Pelasgic tribes was far more widely spread, and became subdi-
vided at a much remoter period of antiquity. Amongst the four
principal languages which prevailed among the nations com-
posing these races, namely, the Sanscrit, tlie ancient Pelasgic,
the Gothic or Teutonic, and the Sclavonic, we may trace the
most multiplied affinities. The primitive Sanscrit is still pre-
served as the sacred language of the Hindus, and is the model on
which all the existing languages of Hindustan have been formed.
The Pelasgic is the primitive source of the Greek, of the Latin,
and of many other tongues now extinct, but from which most of
the present languages of the south of Europe have been derived.
The Teutonic has given rise to the languages of the northern and

MONGOLIAN RACE. 365

the western nations of Europe, such as the German, the Dutch, the

English, the Danish, the Swedish, together with their various
dialects. From the Sclavonic tongue are derived those of the
north-east of Europe, namely, the Russ, Polish, the Bohemian,
and the Vandean.

879. It is amongst this latter extensive race that philosophy,
sciences, and the arts, have been most assiduously cherished, and
have been carried to the highest states of perfection. This race
had, in Europe, been preceded by the Celtic tribes, which origi-
nally came from the north, and were formerly widely spread,
but which are now confined to very narrow spaces in the west
of Europe and Africa, and are nearly effaced by continued in-
termixture with the numerous races which have supplanted
them.

880. The ancient Persians have a similar origin with the
Indians; and their descendants at the present time, bear the
strongest marks of affinity to the modern European nations.

881. The Scythian or Tartaric branch first directed itself
towards the north and north-east, and composed the wandering
tribes which traversed the immense plains of Tartary. In later
times, become more numerous, they returned to spread devasta-
tion amongst the flourishing establishments of their more civilized
brethren. The irruptions of the Scythians in Upper Asia, of the
Parthians, who overthrew the domination of the Greeks and Ro-
mans in those regions; of the Turks, who destroyed that of the
Arabs, and reduced to subjection the miserable remnant of the
Greek nations in Europe ; all proceeded from the overflowings of
the northern swarms from this common race. The Finlanders
and the Hungarians, which belong to this race, may be regarded
as stragglers from these swarms, amidst Sclavonic and Teutonic
tribes. On the northern and eastern coasts of the Caspian Sea,
the original cradle of these races, there are still found tribes which
liave the same common origin with the former, and which speak
a similar language ; but they are variously intermixed with a
great number of other smaller tribes, differing from them both in
language and in origin.

882. The Tartarian tribes have remained more free from
mixture, along the whole of that extensive tract whence they long
defied the power of Russia, but to which they have at length been
forced to submit ; namely, from the mouths of the Danube, to the
countries beyond those of the Irtish. But the conquests of the
Mongols have led to considerable blending of the two races
amongst the Tartarian nations.

883. The Mongolian race inhabits the remoter regions of Asia,
extending from the eastern parts of the continent, where the
Tartar branch of the Caucasian race terminates, to the Eastern
Ocean. The different branches of this MongoUan race, such as

31*

366 VARIETIES OF THE liUMAN SPECIES.

the Calmuc Tartars, and the Kalkas, have no settled residence,
but are -wandering tribes over the extensive deserts of Eastern Asia.
Thrice have their ancestors carried far and wide the terror of
their arms ; first, under Attila ; next under Genghis Khan ; and,
lastly, under Tamerlane. The Chinese are an ancient branch of
this family, which was very early trained to a high degree of
civilization ; at a period, indeed, apparently more remote than
that to which our most ancient histories extend. The Manchew
Tartars, who have recently achieved the conquest of China, are
a third branch of the same Mongolian race. The Japanese, the
Coreans, and almost all the hordes which extend to the north-east
of Siberia, under the dominion of Russia, belong also to the same
division of the human species.

The original seat of this widely-spread race appears to be the
chain of the Altai mountains, the central ridge of Asia ; in the
same way that the race to which we belong was derived from
the inhabitants of mount Caucasus ; but it is quite impossible to
unravel the complicated filiation of these various tribes. The
history of these wandering people is as evanescent as their estab-
lishments ; and even that of the Chinese, confined as it is to the
limits of their empire, supplies only brief and unconnected notices
of the surrounding nations. The afiinities of their languages are
too imperfectly known to afford any clue for our guidance in this
mighty labyrinth.

884. The languages of the north of the Indian peninsula, beyond
the Ganges, as well as that of Thibet, have som.e relations Vk'ith
the Chinese language ; at least they resemble it in their monosyl-
labic structure. There is also a general resemblance of features
amongst all these Mongolian tribes. But the southern division of
the same peninsula is inhabited by a diflerent race, namely,
Malays, distinguished from the former by their greater symmetry
of form, and by a peculiar language. This race is spread over
the coasts and islands of the Indian Archipelago, as well as those
of the Southern Pacific. In the largest of the Indian Islands,
however, we meet with a much more barbarous race of men with
dark Avoolly hair, with black skins, and with the negro features,
and savage and ferocious in their dispositions. They are known
by the name of Papuans, and are principally met with in the
Islands of New Guinea, and the New Hebrides. It has been
conjectured that this singular tribe was descended from negroes
accidentally cast on the shores of these remote islands.

885. The inhabitants of the northernmost regions both of the
old and new continent, comprising the Samoiedes, the Laplanders,
and the Esquimaux, possess many peculiar features, and have been
classed by some naturalists under the Mongolian races, but are
considered by others as degenerated scions from the Scythian
and Tartaric branches of the Caucasian race.

UNITY OF SPECIES. 367

886. The aboriginal American Indians have never been satis-
factorily assimilated to any one of the races of the ancient con-
tinent ; yet they scarcely possess any precise or well marked
distinctive characters, which may entitle them to be regarded as
one of the primitive races of mankind. The copper hue of their
skin is certainly not of itself sufficient to establish such a distinc-
tion. Their dark hair and scanty beard would incline us to refer
them to the Mongolian race, were it not that their well-defined
features, and prominent nose, are opposed to such a classification.
Their languages are as diversified as their tribes are numerous;
and no analogy has yet been traced either amongst o«e another,
or with any of those of the old world.

887. The analogy of what we observe in the inferior animals,
affords the strongest grounds for believing that natural causes
are perfectly adequate to explain the diversities which occur in
the several varieties of the hun)an race, on the supposition of their
having originated from a common stock. The variations in size,
colour, and even forms, which take place amongst difierent kinds
of dogs, characters which are transmitted from the parent to the
otfspring with as much constancy as those of the human race,
are no less considerable than the difl^erences observable between
the European and the negro, and yet are admitted by naturalists
to be perfectly compatible with the unity of the species, and with
a community of source. Of the causes which originally produced
the peculiarities in the several varieties of the race, and which
have become permanent, we can have no certain knowledge;
nor can we even supply the want of precise information by any
rational conjecture. The common hypothesis which ascribes the
black colour of the negro to the more powerful influence of the
solar rays in tropical climates, will not bear the test of close
examination ; no permanent effect of that kind having ever been
produced by the same cause operating for any length of time on
the complexion of Europeans. Difierent opinions have been
entertained with regard to the natural and original complexion
of the human race. Dr. Prichard contends that it was black,
and that the Ethiopian form was the primitive type of the race;
the successive changes produced being that from the imperfect
to the more perfect form, and from barbarism to refinement ;
terminating at length in the Caucasian race, in which it has at-
tained the greatest state of improvement compatible with its nature^
accompanied by the highest degree of capability of civilization,
and of intellectual and moral excellence.*

888. In opposition to the doctrine of the unity of species in all
human races, it has been contended by Rudolphi, Virey, Des-

* See his Researches on the Physical History of Mankind, Third edition.
London, 1806.

3*68 COMPARATIVE PHYSIOLOGY.

moulins, Bory St. Vincent, and others, in the most positive man-
ner, that these races were originally different. The arguments
on each side of the question are fully discussed in the work of
Dr. Prichard referred to.

CHAPTER XXIIl.

COMPARATIVE PHYSIOLOGY.

889. We purpose, in giving an account of the most important
facts relating to the physiology of the animal creation, to take as
the standard of comparison the mode in which the functions of
the human body are conducted. The history we have given of
the animal economy in man will easily enable us to refer all the
facts relating to comparative physiology to this standard type ;
and this view of the subject, besides the interest which naturally
attaches to it, will have the further advantage of reflecting light
on various subjects of human physiology, which, as we formerly
remarked, must ever receive important elucidation from a com-
parison with that of the lower animals.

890. Conformably with this design we shall take a review of
the different divisions of the animal kingdom ; first pointing out
the general characters of organization and of function which are
common to each class and order ; and noticing, in the next place,
the peculiarities that are most worthy of remark in the several
species included in those divisions. By thus following the logical
order of descending from generals to particulars, we shall avoid
the numerous repetitions that would otherwise be requisite, and
comprise in the smallest space the greater number of particular
facts relating to the science. \

Sect. I. — Comparative Physiology of Mammalia.

1. Peculiarities in the Human Conformation.

891. Since man, in his zoological relations, must be compre-
hended in the class mammaUa, it is evident that the general
characters of this class must consist of those possessed by the
human species in common with quadrupeds, and even with the
other families of mammalia still farther removed from man in
their external conformation. Whilst the points of resemblancs
are so numerous, the easiest mode of instituting a comparison

PECULIARITIES OF HUMAN CONFORMATION. 369

between them will evidently be by pointing out, not the features
which they possess in common, but those in which they differ.
We shall begin then with an account of the peculiarities which
distinguish the human structure from that of the lower animals,
and more especially from that of the quadrumanous tribes, which
approach the nearest to him in their conformation.

892. The great distinctive features which characterize the
human conformation, as compared with that of all other mam-
malia, have reference to the superiority of his intellectual powers,
and to his maintenance of the erect position. In the number
and excellence of his mental faculties, and in his capabilities of
improvement, he leaves all other animals behind by^ an immea-
surable distance. The faculty of speech is a consequence of this
development of intellectual power, which is favoured, indeed, by
the conformation of the larynx ; but the organization requisite
for the uttering of articulate sounds would have been in vain
conferred unless it had been placed under the guidance of the
mental faculties ; thus to the parrot the gift of the organs of
articulation, without the mind which is to use them as expressions
of thought, becomes a comparatively unprofitable boon.

893. The superiority of the human intellect is accompanied by
a much greater development of the cerebral hemispheres than is
found in any other animal. Hence also the great magnitude of
the cavity in which it is contained, together with that part of the
skull which protects it, when compared with the face, which is
composed of the organs of the principal senses, and of the appa-
ratus for mastication. The mass of the brain bears also a large
proportion to the size of the cerebral nerves. The cerebellum is
entirely covered by the hemispheres of the brain. The forehead
in man is particularly distinguished by its elevation, and the beauty
of its convex arch. The shortness of the lower jaw, and the
prominence of its mental portion, are particularly remarkable.
The elephant is the only quadruped in which the lower jaw is
equally short jn proportion to the size of the head ; but this
animal is still deficient in the projection of its lowest point, so
that the possession of a chin seems to be peculiar to the human
race.

894. In every particular connected v;ith the mechanism of the
fabric, man enjoys the most decided advantage over those mam-
malia which are most nearly allied to him in their physical con-
formation, Man is the only species amongst the mammalia
whose body can maintain itself for any length of time in an erect
position, and in whom the office of supporting the trunk is en-
trusted solely to the lower extremities. We find that every part
of the osseous fabric, as well as the disposition of the principal
organs of sense, are in obvious conformity with this design. The
lower limbs,' being the great instruments of support and progres-

370 COMPARATIVE PHYSIOLOGY.

sion, are larger, and of greater strength, compared with the body,
than in most quadrupeds, the only exceptions being met with
among those which are formed expressly for leaping, as the hare,
the jerboa, and the kangaroo. In the monkey tribes the lower
limbs are comparatively much weaker than in man; and in other
quadrupeds the disproportion is still greater, the thigh bone being
short, and almost concealed by the muscles which connect it with
the trunk of the body, whilst the rest of the limb is very slender,
and not covered by any considerable mass of muscle. In man
the articular surfaces of the knee-joint are very broad, and admit
of greater extent of motion than in quadrupeds, and the two
portions of ^he limb can be brought into the same straight line,
thus constituting firm perpendicular columns of support for the
body. The long neck of the thigh bone allows of more complete
rotation of the limb at the hip-joint ; and this, together with the
greater breadth of the pelvis, which affords an ample basis for
sustaining the trunk, are circumstances peculiar to the human
frame. The heel in man forms a greater projection than in other
animals ; and by its being extended so as to touch the ground, it
forms, as we have seen, one of the points of support, by which, in
conjunction wdth the toes, a much larger base is comprehended.
The muscles which raise the heel, and which compose the calf
of the leg, are of greater size and strength than in monkeys, be-
sides acting with the mechanical advantage arising from the long
lever which the heel affords for the insertion of their united ten-
dons ; and by the direction of the foot, which forms a right angle
with the leg.

895. The form of the chest exhibits similar differences. In
quadrupeds the thorax is compressed laterally, and is deepest
from the spine to the sternum ; a structure which allows the
front legs to come nearer together, and to support with more
effect the front part of the trunk. But in man the thorax is
flattened anteriorly and extends more in width, that is, from- side
to side, thus throwing out the shoulders, and giving a more ex-
tensive range to the motions of the arms.

896. That the erect posture is natural to man is strongly indi-
cated by the position of the head with respect to its articulation
with the spine, which takes place at the middle of its basis ; and
thus, by the great extension of the occiput, its weight is more
nearly balanced than it is in the monkey. The cervical vertebras
of the monkey have very long and prominent spinous processes,
evidently adapted to give greater purchase to the muscles sus-
taining the head of which the front part considerably preponde-
rates, in consequence of the elongation of the jaws, and the back-
ward position of the centre of motion.

897. The same design may be traced in the position of the
eyes, the mouth, and the face in general ; and is so obvious as to

PECULIARITIES OF HUMAN CONFORMATIOiV. 371

have ebeen noticed by Ovid, while describing the formation of
man, in the following celebrated lines :

"Pronaque cum spectani animalia caetera terram,
Os homini sublime dedit: ccelumque videre
Jussit, et erectos ad sidera tollere vultus."

898. All the internal organs have been regulated by the same
intention. The human heart is placed obliquely in the chest, and
rests by a flat surface on the diaphragm, to which its investing
membrane, the pericardium, is firmly attached. In quadrupeds,
no such attachment exists ; but the heart is situate more perpen-
dicularly with the apex directly downwards, and cannot be felt,
as in man, striking on the left side of the ribs at each contraction
of the ventricles.

899. The fore legs of quadrupeds are in general appropriated
solely to the support and progressive motion of the body. In
some instances, indeed, they are employed, besides, in other actionsj
such as seizing and securing their prey, raking and digging up
the earth, or climbing and laying hold of the branches of trees ;
but it is only in a few species, and chiefly amongst the monkey
tribes, which resemble man in their form, that they are instrumental
in carrying food to the mouth, or even in grasping weapons of
oftence. But in man the superior extremity being entirely
released from the ofiice of maintaining any portion of the weight
of the trunk, is at liberty to be employed for a great variety of
purposes; and the exquisite structure of the human hand, which
has already been noticed, renders this exemption of still greater
value, and constitutes unquestionably one of the great perfections
which mark the human structure, as compared with that of the
brute creation. The arm and head are thus rendered an organ
at once of prehension and of touch, for both of which purposes
it is admirably adapted by the great latitude and variety of move-
ments it is capable of executing. One of the chief sources of
perfection in the hands is the structure of the thumb, which is
furnished with muscles of so great a power, compared with those
of the fingers, as to enable it to oppose and balance their united
strength. Hence it is enabled to grasp a spherical body, and to
retain firm hold of many objects, which otherwise could not have
been held without the united efforts of both hands. This con-
formation is pecuhar to man ; for the paw of a monkey cannot
exercise the same force and readiness of prehension, in conse-
quence of the thumb being inferior in strength to the other fingers.

900. The great perfection of the organs which modulate the
voice and produce so great a variety of articulate sounds, is
another striking instance of the high destination to which the
human structure has been adapted. In those tribes of monkeys
which come nearest to the human conformation, the power of

372 COMPARATIVE PHYSIOLOGY.

Uttering articulate sounds is prevented by the interposition of two
sacks connected with the larynx, which receive part of the air
when the animal uses any effort to expel it from the lungs.

901. The structure of the digestive organs in the human
species is similar to that of many quadrupeds, and has generally
been regarded as intermediate between that of the carnivorous
tribes, and of those that live altogether on vegetable food. Man
may very justly, and almost exclusively be entitled to the appel-
lation of an omnivorous animal ; being equally capable of sub-
sisting on difierent kinds of aliment; and also of using at the
same time a great mixture of different sorts of food. No other
animal is capable of so great a versatility of powers in this re-
spect. It has also been remarked, amongst the characteristic
circumstances of the human race, that whilst other animals are
contented with food in the state in which nature offers it, man
alone employs artificial processes for improving its flavour, and
rendering it more fit for digestion. Man is the only animal that
is known to practise the art of cookery ; an art which indeed
appears necessary to enable the stomach to extract from his
usual food all the nutriment it is capable of yielding.

902. The teeth of man are distinguished from those of all the
other mammalia by their being arranged in either jaw, in a uniform
unbroken series ; and also by the circumstance of their being all
of the same length. The cuspidati, or eye-teeth, as they are
called, which correspond to the canine teeth in quadrupeds, are,
perhaps, at first a little longer than the others, but their sharp
points are soon worn down to a level with the rest. In all the
monkey tribes, these teeth are long and prominent, and are
separated by an interval from the neighbouring teeth. The
cutting teeth in the lower jaws slant backwards in the monkey,
and the jaw itself has the same diredtion ; but in man these teeth
are perpendicular, and in a line with the front of the jaw, which
descends to form the prominence of the chin, a part of the face
which does not exist even in the orang utan. The tubercles on
the surface of the grinders are different in their shape, both from
the ridges of enamel on the crowns of the teeth of herbivorous
anitnals, and from the sharp-pointed eminences on the grinders of
carnivorous animals.

903. Thehumanbrainis not only larger in its relative proportion
to the body than in any other of the mammalia, but its absolute
size is greater, if we except only that of the elephant, and of the
whale. With these few exceptions, all the larger animals with
which we are more commonly acquainted, have brains absolutely,
and even considerably smaller than that of man. Besides the
prodigious expansion of the hemispheres, we may remark in the
human brain a more elaborate structure, and a more complete
development of all its minuter parts. There is no part of the

PECULIARITIES OF HUMAN CONFORMATION. 373

brain found in any animal, which does not exist also in man ;
whilst several of those which are found in man are cither ex-
tremely small, or altogether absent in the brains of the lower
animals. Sommerring has enumerated no less than fifteen visible
and material anatomical differences between the human brain
and that of the ape. The proportion of medullary to cortical
substance is greater in the human brain than in that of other
animals.

904. Although the negro race is a branch of the great family
of man, and although the peculiarities which distinguish the con-
formation of that race rank only as varieties in the species, it yet
cannot be denied, that in almost every one of the circumstances
in which it differs from the type of the Caucasian race, it exhibits
an approach to the structure of the monkey or quadrumanous
tribe of animals. In nothing is this approximation more remark-
able, than in the proportion between the size of the face as com-
pared with that of the brain. One of the most convenient
methods of roughly estimating this proportion is that invented by
Professor Camper. Drawing a line from the most prominent
part of the frontal bone, to the anterior point of the upper jaw
bone, just at the roots of the incisor teeth, which is called the
facial line, it is to be intersected by another hne, drawn from the
external orifice of the ear to the inferior edge of the aperture of
the nostrils. The angle formed by these tw^o lines is the facial
angle of Camper, which determines by its magnitude the degree
of preponderance of the bones of the cranium, in which the brain
is contained, over those of the face, which contain the organs of
sense.

905. In man the facial angle is greater than in other animals ;
it differs, however, in different varieties of the human race, and
appears to indicate with tolerable exactness the comparative
degree of intellectual excellence appertaining to each variety.
In the Caucasian variety the facial angle is between 80° and 90°;
in the MongoUan, 75°; in the American Indian, 73^°; in the
Negro it is only 70°. Pursuing the application of this test to the
lower mammalia, we find it in the orang utan reduced to 65° ;
in the baboon, 45° ; in the mandrill, one of the most ferocious of
that tribe, only 30°. The mastiff has a facial angle of 41°, the
bull-doo; of 35°. In the feline tribe it is still farther diminished ;
being only 28° in the leopard. In the sheep and hare it is 30, in
the horse it is only 23°.

906. The varieties in the magnitude of the facial angle have
thus been traced through a number of gradations amongst differ-
ent tribes of mammalia and also of birds, till we arrive at its
almost total obhteration in the snipe and the wood-cock, animals
which are reputed to be extremely deficient in intelligence.

907. The projection of the bones of the face, which tends to

32

374 COMPARATIVE PHYSIOLOGY.

diminish the facial angle, is universally considered as expressive
of stupidity or ferocity. An ample and projecting forehead, on
the contrary, is associated in our minds with the idea of superior
intelhgence. It was probably for that reason that the owl was
selected by the Athenians as the emblem of wisdom. In the sta-
tutes of their divinities, the Greek sculptors have exaggerated the
facial angle, making it as much as 100°, which is considerably
greater than it is ever found in the human form. The Itahan
painters, also, in their representation of saints, have often given
them a facial angle of 95°.

908. But in applying this method to some of the most saga-
cious species of animals, such as the horse, which, as we have
seen, has a very small facial angle, we meet with great and
striking exceptions. We arrive at more correct determination
of the proportional development of the face and brain, by com-
paring, as proposed by Cuvier, the areas respectively occupied
by each in a longitudinal vertical section of the head. But in the
elephant all these criteria, but especially the admeasurement by
the facial angle, fail, in consequence of the great projection of
the frontal bones, which are raised to a considerable distance
from the brain by the interposition of large cells, or frontal
sinuses, and which give an undue proportion to the size of the
forehead.*

909. Daubenton proposed, for the comparison of different skulls
with one another, what he called his occipital lines; the one

'passing from the posterior margin of the great occipital foramen
through the lower edge of the orbit; the other, taking the direction
of the opening itself, beginning at its posterior edge, and touching
the articular surface of the condyles. The angle formed by the
intersection of these Unes is his occipital angle. But the variations
of this angle are too inconsiderable to furnish sufficient criteria of
the character of the head.f

2. Peculiarities in the Conformation of other Mammalia.'^

910. The bones of quadrupeds appear, as Blumenbach observes,
to possess a less fine and delicate texture than those of man.

'*' [A striking proof, that the facial angle cannot be regarded as a measure of
the intellect is the fact, that in children it reaches as high as 90° ; several
degrees higher than in the adult.]

f [Blumenbach's method, by what he called the norma verticalis, consisted
in selecting two bones, the frontal from those of the cranium, and the superior
maxillary from those of the face, and comparing them with each other, by re-
garding them vertically, placing the great convexity of the cranium di-
rectly before him, and marking the relative projections of the maxillary bone
beyond the arch of the forehead. But this method does not indicate the depth
of the maxillary bone, or of the os frontis, or their comparative areas. The
view thus obtained is, therefore, partial.]

MAMMALIA. 375

Their fibres are more easily loosened by maceration, and are of a
coarser grain ; this is more particularly observable in the jaw-
bones and the ribs.

911. The spine is formed of the same classes of vertebra3 as in
man, namely the cervical, dorsal, lumbar, and sacral. In all
quadrupeds "belonging to the class of mammalia, the number of
cervical vertebras is constantly seven, as in man. The length or
shortness of the neck has no influence on their number, though it
has a material one, of course, on the comparative length of each
individual vertebras. The camelopard, whose neck is extended
to so great a length; and the mole, in which it is so short, have
each of them seven cervical vertebras. An apparent exception to
this general rule occurs in the three-toed sloth, in which Cuvier
found nine vertebrae of the neck instead of seven ; but it has since
been found that the two last of the cervical vertebrae, which
appeared to be supernumerary, ought properly to be classed
amongst the dorsal vertebrse, of which they possess the distinctive
characters.*

912. The number of dorsal vertebrae depends principally upon
that of the ribs, which differ in different quadrupeds, and are
usually more numerous than in man. Their transverse and spinous
processes are generally longer than in man, for the purpose of
affording a broader surface of attachment to the powerful muscles
which support the head and neck.

The number of the lumbar vertebrae is various in different
quadrupeds. There are only three in the elephant; five in the
ass ; six in the horse ; and seven in the camel. Still greater
differences are met with in the number of component parts of the
sacrum.

913. Most quadrupeds have a prolongation of that part of the
skeleton which corresponds to the os coccygis of man, and which
in them composes the tail, and consists of a great number of
imperfectly formed vertebrae.

914. The thorax of quadrupeds is, as we have already noticed,
more compressed laterally, but deeper from the spine to the
sternum, than it is in the human skeleton. The scapula is constantly
found ; but in most tribes there is no clavicle whatever, and in
others only a short rudiment of that bone, connected merely with
the muscles. In other respects, the number and connexions of
the bones of the extremities are generally very similar to the
human conformation; we may observe, however, that the os
femoris is usually much shorter than the tibia, and being covered
by the large muscles which attach it to the trunk, appears to
belong to that division of the body. The bones of the carpus and

* See a paper by Mr. Thomas Bell, Philosophical Magazine, third series,
iii. 376.

376 COMPARATIVE PHYSIOLOGY.

tarsus, together with those of the fingers, are in many cases
exceedingly conripressed, and some of them are so consohdated
together, as not to be distinguishable as separate bones.

915. In all the mammalia we find a peculiar bone, called the
intermaxillary hone, interposed between the two upper jaw-
bones, and locked in between them ; its office appears ..to be to
contain the upper incisor teeth, when these teeth exist ; but it is
also met with when there are no incisor teeth.

916. The number, form, and internal structure of the teeth is
exceedingly diversified in the different tribes ; and afford excel-
lent characters for the distinction of orders and genera of the
class mammalia. As these characters have a strict relation to
zoological classification, we shall abstain from entering here into
the details of this subject.

917. In proceeding to notice the peculiarities of structure in
the mammalia, we shall next examine the organs of the func-
tions of assimilation, to which that part of the skeleton we have
just adverted to, namely, the jaws and teeth, are subservient.

918. The tongue of quadrupeds is, for the most part, more
narrow, long, and slender than that of man. Except in the
genus simia, we do not meet with any structure corresponding
to the uvula. The oesophagus has two layers of muscular fibres,
which have a spiral course, and cross one another. This struc-
ture gives it greater power of propelling its contents into the
stomach ; a power which is the more required, inasmuch as the
food has often to ascend considerably in passing along this
canal.

919. The conformation of the stomach presents very consi-
derable diversities, apparently determined by the habit of the
animal and the nature of its food. From the simple structure it
exhibits in the purely carnivorous tribes, we may observe a gra-
dually increasing compHcation as we pass to those that feed on
fish, and on vegetable aliment. In the latter orders of mammalia,
and especially in the ruminants, we meet with a very complicated
apparatus for digestion. But these diversities will come more
properly to be noticed in the examination of the orders and fami-
lies to which they relate. It will be sufficient here to remark, that
the stomach is often divided into several distinct portions, such
as the cardiac and pyloric ; and often presents several inter-
mediate subdivisions, and expansions into separate pouches, so
as to exhibit the appearance of a multiplicity of cavities or
stomachs. They differ also considerably as to the degree in
which the glandular structures attached to their coats are deve-
loped in different parts.

920. Similar varieties are met with in the structure of the
intestines of different mammalia. As a general rule, to which,
however, there are several exceptions, it may be remarked, that

MAMMALIA. 377

the intestinal canal is much shorter, and more contracted in its
diameter, in carnivorous animals than in those which feed on
vegetables. This probably depends on the more rapid assimila-
tion of animal than of vegetable materials; the latter requiring a
more complicated apparatus, more capacious cavities, and a
more extensive surface both for secretion and absorption. It has
been observed that the canal of the intestines is longer in the
domesticated breed than in the wild animal of the same species.
Thus, in the wild boar, the length of the intestines is to that of
the body in the proportion of nine to one ; but in the tame animal
the proportion is as thirteen to one. In the domestic cat it is as
five to one ; in the wild cat as three to one. It may also be
remarked that in the class mammalia, the comparative length of
the intestinal canal is greater than in any of the other vertebrated
classes ; and diminishes successively as we compare it in birds,
reptiles, and fishes.

921. The liver in the mammalia generally, is divided into a
greater number of lobes, and the divisions penetrate deeper into
its substance, than in man. In a great many instances, as in the
horse and the goat, there is no gall-bladder, the bile being car-
ried at once by the hepatic ducts into the intestine. Occasionally
when the gall-bladder is present, there exist also hepato-cystic
ducts which convey the bile directly from the liver into the gall-
bladder, and not by a retrograde course, as in man.

The mammaha is the only class of animals provided with
omentum, which, in some, as in the racoon, is particularly large
and stored with fat.

The kidney generally presents a lobulated appearance ; some-
times to such a remarkable degree, as to bear a resemblance to
a bunch of grapes, being composed of numerous small and dis-
tinct portions, connected together by their blood-vessels and ex-
cretory ducts. The urinary bladder is more capacious in herbi-
vorous than in carnivorous quadrupeds.

The heart of the mammalia corresponds in every essential
particular of its structure with the human conformation ; but it
differs in its position with regard to the other organs, being
situate more longitudinally, and resting on the sternum, which is
below it, and not on the diaphragm, as in man. Hence, also,
the direction of its axis is not so oblique, and it is placed more in
the centre of the chest ; and the pericardium is scarcely at all
connected with the diaphragm.

922. In many quadrupeds the thoracic duct is double, and
forms more distinctly than in man the enlai'gement which has
been termed the receptaculum chyli. The mesenteric glands are
frequently collected into a considerable mass, called the pancreas
of Jlsellius.

32*

378 COMPARATIVE PHYSIOLOGY.

923. From the consideration of the organs of nutrition we
pass on to those of the sensorial functions, and shall for this pur-
pose revert to the osteology, in as far as relates to the bones
which protect the brain and principal organs of the senses.

924. The divisions of the cranium of quadrupeds into separate
bones, differs but little from that of the human skull. The os
frontis is frequently found divided into two lateral portions by
the prolongation of the sagittal suture forwards to the root of the
nose. Sometimes, again, the sagittal suture is obliterated by the
consolidation of the two parietals into a single bone ; in other
cases, these bones are united with the occipital. We often find,
also, a bone, distinct from the temporal, termed the tympanic
bone, provided for containing the tympanum of the ear. But it
may be observed, in general, that the sutures present fewer in-
dentations, and less irregularity in their course in the skulls of
quadrupeds than in man, a circumstance which is naturally
explicable by the smaller development of the brain, and conse-
quent diminution of the general size of the cranium. From the
position of the head in the quadruped the occipital foramen is
situate less anteriorly in the basis of the skull than in man, and
is for the most part nearly vertical in its position. The tentorium
sometimes contains within the laminae of the dura mater, which
compose it, several strong plates of bone, and the same thing has
also been observed in the falx.

925. The brain of quadrupeds is considerably smaller, when
compared with the size either of the spinal cord or the cranial
nerves, than in man. The cerebral hemispheres are also much
smaller compared with the cerebellum. This arises in a great
measure from the absence of the posterior lobes of the brain,
which in man, when viewed from above, conceals the cerebellum:
whereas in quadrupeds the cerebellum is brought immediate!}'
into view in removing the upper bones of the skull. In the proper
quadrupeds the anterior lobes of the brain extend forwards into
two large processes, called the processus mamillares, which give
origin to the olfactory nerves, and which contains a cavity on
each side, communicating with the lateral ventricle, being in fact
its anterior prolongation. On the other hand, this ventricle has
no posterior prolongation, there being no posterior lobe.

926. Every part of the organ of smell is developed in quadru-
peds in a degree corresponding to the greater extent and acute-
ness in which they enjoy this sense, compared with man. The
ethmoid bone is much more complicated in its structure, as well
as larger in its dimensions ; the turbinated bones are considerably
larger, more intricate in their formation, and present a much
more extensive surface, being composed either of a great multi-
tude of arborescent laminse, or of numerous spiral convolutions.

MAMMALIA. 379

The internal nasal cavities are also generally enlarged, and par-
ticularly the frontal sinuses. ^

927. The organ of hearing also frequently presents a greater
complication of structure than in man. A cavity, called by
Sommerring, the bulla ossea, communicates with that of the tym-
panum, and corresponds with the mastoid cells in the human
subject. In the aquatic mammalia the external meatus is fur-
nished with a valve for the purpose of excluding water from the
passage. In these animals, also, as well as in those that live
under ground, the external ear is altogether wanting. The struc-
ture of the internal parts of the organ agree in all essential points
with those of the human ear. The cochlea sometimes makes an
additional turn in its spiral convolution.

928. The eyes of mammalia exhibit considerable variety as
to the position of their axes with respect to the general direction
of the head. They are generally separated to a greater distance,
and directed laterally. The figure of the globe is nearly spherical,
as in man ; but in several quadrupeds the sclerotic coat is much
thicker and firmer at its posterior than at its anterior part. The
choroid coat is distinctly divisible into two layers, of which the
internal bears the name of the tunica Ruyschiana, and which
often exhibits at the back of the eye the most brilliant colours.
This coloured portion of the choroid is known by the name of
the tapeium.

929. Several quadrupeds have an additional lacrymal gland,
besides that which corresponds to the one in man ; and also
another gland, situate near the nose, and termed the glandula
Harden. The globe of the eye in quadrupeds is also provided
with an additional muscle, the suspensoiius oculi, for the purpose
of supporting its weight. Many quadrupeds also possess a third,
or internal eye-lid, called the nictitating membrane, which is very
large and moveable in the cat, and all the animals belonging to
the same genus.

930. The panniculus carnosus is a muscular expansion, situate
immediately under the skin, and subservient to the movements of
the integuments, which it suddenly corrugates and throws into
wrinkles, thereby driving off insects or shaking away any other
offensive matter, is pecuhar to quadrupeds, not being found in
man ; unless the platysma myoides of the neck be considered as
a muscle having an analogous function with relation to the skin
of the neck.

931. In many quadrupeds some of the sebaceous glands of the
integuments are very much developed. In some predacious ani-
mals, a gland exists in the orbit, described by Nuck, and of which
the excretory duct opens near the last tooth of the upper jaw. It
appears referable to the class of salivary glands. Another gland,

380 COMPARATIVE PHYSIOLOGY.

particularly noticed by Professor Jacobson, and of which the use
is wholly unknown, is generally met with in the anterior and
lower part of the cavity of the nostrils: this he has called the
nasal gland of Steno. i

3. Quadrumana.

932. We have already had occasion, when describing the
distinctive marks by which the human structure is characterized,
when compared with that of the monkey, to point out several
circumstances which are deserving of notice in the anatomy of
this tribe of mammalia. Of all the animals of the family of the
quadrumana, the orang-utan {simia satyrus, Geoff.) is that species
which makes the nearest approach to the human conformation.
This approximation is observable in the position of the great
occipital foramen of the skull, which is placed further forwards
than in other kinds of apes ; in the distinctness and serrated form
of the sutures of the cranial bones ; in the absence of the inter-
maxillary bone ; in the eyes . being directed forwards ; in the
smallness of the os coccygis, cornposed, as in man, of five im-
perforated bones; in the possession both of a coecum- and an
appendix vermiformis; and in the oblique position of the heart
with respect to the cavity of the thorax.

933. A. still more remarkable peculiarity of structure in the
orang-utan is that discovered and described by Camper ; namely,
two membranous sacs, which communicate with the glottis, and
deprive the animal of the power of giving utterance to sounds.

934. In other species of this order we trace still further devia-
tions from the human structure. The laryngeal sacs are found
in many species of baboons ; these are either single or double,
and communicate with the larynx by openings between the os
hyoides and the thyroid cartilage. The simia seniculus, and the
simia beelzebub, have a large dilatation of the middle of the body
of the OS hyoides, which is expanded into a spherical bony cavity.
This cavity, instead of interfering with the sonorous vibrations,
adds to their strength, and gives the power of producing those
loud intonations which are peculiar to this tribe, and from which
they have obtained the name oi howling apes.

935. The mandrill baboon has seven instead of five lumbar
vertebrae. The appendix vermiformis of the coecum is not met
with in many species of apes. The crest of the occipital bone,
though very large in the baboon of Borneo, is scarcely percepti-
ble in most monkeys. The central foramen of the retina disco-
vered in the human eye by Sommerring, has been seen in the
eyes of many animals of this order.

936. In the lemur tardigradus, and in the sloth, a singular
structure has been observed by Sir Anthony Carlisle, with regard

MAMMALIA. 381

to the distribution of the arteries of the limbs. The trunks of these
arteries suddenly subdivide as they enter the limb into a great
number of parallel branches, which are again re-united when they
arrive at the remote end of the first division of the limb; that is,
about the joints corresponding to the elbow and the knee in man.
After tiieir re-union into single trunks, these arteries proceed to
ramifv in the usual manner.

4. Chiroptera.

937. In the bat tribe we have to notice the strictly hinge-like
nature of the articulation of the lower jaw with the skull, which
limits its motion to mere opening and shutting, and excludes all
lateral movements. The zygomatic arches are expanded and
raised, so as to allow room for the large and powerful muscles
which close the jaw. The parietal bones are united into a single
bone. The sacrum is composed of four bones consolidated
together. Four clavicles are met with, and they are of extra-
ordinary length. The ulna is deficient in the fore-arm, or exists
only in a rudimental state, as a slender sharp-pointed process of
the radius. The phalanges of the anterior extremities are enor-
mously lengthened for the purpose of supporting the thin mem-
brane which is stretched between them, and which serves the
office of wings. The tongue of the bat is covered with sharp-
pointed horny papillae.

938. The vespertilio noctula is remarkable for the shortness
of the intestinal canal, which is only twice the length of the
animal's body. In the vampire bat, on the contrary, and in the
vespertilio caninus it is seven times as long. In all bats, not only
is the appendix coeci vermiformis wanting, but also the coecum
itself The epiglottis is also wanting in most of the animals of
this tribe. In many the tongue is slender, and prolonged into an
organ of suction. The pectoral muscles are of enormous size;
and the sternum has a prominent crest for the purpose of affording
an extensive surface for their attachment. The eye is remarkably
small ; but the imperfections which probably exist in the sense
of sight are amply compensated by the singular acuteness of that
of hearing, the organ of which is exceedingly developed ; and
also by the extreme sensibility of the expanded membranes of the
vikings, which is such as to enable the bat to direct its fl[?ght
through the most intricate passages without the aid of the sight,
and without striking against the obstacles purposely placed in its
way.

5. Insectivora.

939. Among the animals arranged by Cuvier in this family,
the mole presents the most remarkable peculiarities of conforma-

382 COMPARATIVE PHYSIOLOGY.

tion, both as regards the skeleton and the internal organs. The
sternum has the same crested process as in the bat, and apparently
with the same design of enlarging the surface of attachment to
the powerful muscles employed in digging. But the anterior
extremity of this crest is still farther prolonged into a sharp
process, having the figure of a plough-share, which is situate
under the cervical vertebras, and resembles the keel-like projection
we shall have occasion to notice in the sternum in birds. The
cervical vertebrae are remarkable for having no spinous processes.
The ligamentum nuchse is particularly strong, and is almost
wholly ossified. The clavicle is of a singular shape, being nearly
cubical. The humerus is very slender in the middle, and re-
markably expanded at both its extremities. The fore-paw is
provided with a bone of a pecuhar shape, called the falciform
bone, placed at the end of the radius. The phalanges have nu-
merous processes, and are furnished with sesamoid bones ; struc-
tures which, by giving considerable mechanical advantage to the
muscles that move them, contribute greatly to increase their
power. The great muscles of the trunk, the pectoraUs major,
the latissimus dorsi, and the teres major, are of great size, and
give the animal great facility in digging the ground, and throwing
up the earth as it proceeds.

940. The ethmoid bone is of very complicated formation in the
mole, especially in the numerous convolutions of its turbinated
processes, by which a very large surface is given to the Schnei-
derian membrane which lines every portion. This structure
indicates the possession of a very acute sense of smell. The
remarkable development of the internal parts of the ears, is also
conclusive evidence of the delicacy of the sense of hearing in this
animal, although it has no external ear whatever. The eye is so
minute, that even the existence of that organ has been denied by
some naturalists ; it is, in fact, not larger than the head of a pin.
The cavities in which they are placed are so very superficial, as
scarcely to deserve the name of orbits. The zygoma is not
arched, but straight, and as slender as a thread.

6. Plantigrada.

941. Animals of the plantigrade family have ~a long but narrow
intestinal canal, unprovided with any coecum or appendix, and
consequently not presenting any marked distinction between the
small and the large intestines.

942. To this family belongs the bear, remarkable for possessing
supernumerary canine teeth, which are small, and situate behind
the principal ones. The stomach is divided into two portions by
a slight contraction in the middle ; the intestines are furnished
with remarkably long and numerous viUi ; the kidneys are con-

MAMMALIA. 383

glomerated ; the tentorium is bony; the nasal cartilages are
extremely mobile.

943. In the racoon, another animal of this tribe, the valve of
the colon is wanting, and the omentum is very large, consisting
of innumerable lines of fat, disposed in a reticular form, and
connected by an extremely delicate membrane having the appear-
ance of a spider's web. The skin of the neck is very loosely
connected bv cellular substance with the subjacent muscles.

7. Digitigrada.

944. The coecum is wanting in the greater number of the
animals of this tribe. It is met with, however, in the ichneumon.
Many have anal glands and follicles, which prepare a strongly
odoriferous secretion. This is the case with the skunk, pole-cat,
and several others. When these animals are pursued, they pour
out this fetid matter, the odour of which is so offensive as to deter
their pursuers from approaching them. The civet has also similar
glands that secrete the peculiar perfume which derives its name
from that animal.

945. The stomach, in the weasel tribe, is a simple cylindrical
canal, having no expanded extremity to the left of the cardia ;
but the oesophagus enters at one end, and the intestine proceeds
from the other, so that the food may pass quickly through it. In
the stomach of the sea otter, Sir Edward Home describes a
remarkable glandular structure near the pylorus. The receptacu-
lum chyli, in this animal, sends two trunks to form the thoracic
duct, which have frequent communications, so that there are
sometimes three, frequently fom', and never fewer than two
branches of this duct, running parallel to one another. In two
instances the foramen ovale of the heart was found open, but the
ductus arteriosus was closed.

946. In the dog a row of mucous glands, corresponding to the
labiales and buccales in man, is found opposite to the molar
teeth, having several small openings into the mouth. A large
salivary gland also exists under the arch of the zygoma, covered
by the masseter muscle. Its duct is nearly equal in size to that
of the parotid, and opens at the posterior extremity of the alveo-
lar margin of the upper jaw. What is called the icorm in the
dog's tongue, is merely a packet of tendinous fibres, passing
longitudinally the whole length of its tongue, and lying loose in
a membranous sheath, unconnected with any of the muscles. It
has been supposed to assist in lapping up fluids in the peculiar
way in which dogs are observed to clrink. There is a popular,
but wholly unfounded idea, that the extirpation of this pretended
worm, is a preservation against hydrophobia. The anal glands
are of considerable size.

384 COMPARATIVE PHYSIOLOGY.

947. The thoracic duct is double in the dog, and forms a large
receptaculum chyli. The crista occipitahs varies considerably
in its degree of prominence in the different breeds of dogs. In
all, the tympanic bone is distinct from the temporal bone, being
separated from it by a suture. The urethra passes along a groove
in a cylindrical bone. In the hysena, however, which in other
respects is very similar to the dog, this bone is not found. The
extremities of the rings of the trachea, in the hyssna, overlap one
another, and admit of being much compressed ; a circumstance

I which has been considered as connected with the shrill and
piercing cry which this animal is capable of uttering.

948. The genus fehs, of which the lion affords the most re-
markable example, resembles the dog in many circumstances of
conformation. We find the same set of mucous glands about
the mouth, and at the extremity of the rectum. The tongue is
beset with sharp prickles, the points of which are directed back-
wards ; they are of such strength as to tear off the skin from any
part which the lion may lick. The stomach is divided by a slight
middle contraction, into a cardiac and a pyloric portion. The
ductus choledochus forms a pouch between the coats of the in-
testine for receiving the pancreatic duct. In all animals of this
genus the tentorium is bony. The zygoma is arched, and very
large and prominent. The long bristly hairs which constitute
the whiskers, receive very considerable nervous filaments, and
appear subservient to the sense of touch in a very remarkable
degree. Two delicate membranes are met with lying under the
ligaments of the glottis, and are probably the cause of the
piercing sound peculiar to animals of this tribe. The retraction
of the claws into a sheath is matter of familiar observation in the
cat. The pupil of the lion is circular, but that of the cat has the
form of a vertical sUt when closed ; and the motions of the iris
appear to be partly voluntary.

8. Amphibia.

949. Whiskers having the same properties are likewise found
in the seal, an animal of aquatic habits, and whose conformation
is modified with reference to the element it is intended to inhabit.
The feet act as fins, adapted for swimming ; the radius and ulna
are flattened ; the spine is very flexible ; the pelvis very narrow.
The bones have no medullary cavities. Neither the parotid nor
the sublingual glands are met with in this or any other animal of
the order of amphibia, belonging to the class mammaha ; and
the teeth are adapted chiefly to the seizing and detention of
objects, and are scarcely capable of serving the purpose of masti-
cation. The stomach is a straight cyhnder, having no cardiac
expansion. The intestinal canal is of great length, thus forming

MAMMALIA. 385

an exception to the general rule of its being comparatively short
in carnivorous animals. The renal veins form a kind of net-
work, the reticulations of which intersect the furrows between
the mammary processes on the outer surface of the kidneys.
The proportional size of the brain of the seal is greater than in
most mammaha.

950. The eye of the Greenland seal is peculiarly formed,
having, according to Blumenbach, the anterior segment of the
sclerotica, or that immediately behind its junction with the cornea,
thick and firm ; its middle circle thin and flexible ; and its pos-
terior part very thick and almost cartilaginous, while the cornea
itself is thin and yielding. The whole eye-ball is surrounded by
very strong muscles capable of shortening the axis of the eye,
and of adapting it, according to circumstances, to distinct vision
in air ; while in their ordinary state of relaxation, the axis of the
eye being lengthened, the animal when under water is still
enabled to see objects distinctly.

951. The walrus, another animal of this order, is remarkable
for the form of its teeth and tusks, part being external ; but these
fall more within the province of the naturalist. The zootomist
may notice in this animal the smallness of the intermaxillary
bone, and the total absence of the gall bladder.

9. Marsupialia.

952. The marsupial family of mammalia compose an interest-
ing group of animals, which present many remarkable singularities
in their internal conformation and economy. The principal of
these is the apparently premature birth of their young, which
come into the world at a period of their development correspond-
ing to that to which the foetuses of mammalia have arrived only
a few days after conception. Nearly the whole extent of the
integument of th^ fore part of the abdomen forms a kind of sac
or pouch for the reception of the foetuses in their early state, and
whilst they present only a shapeless mass, destitute of external
members, and totally incapable of locomotion. They become
attached to the nipples of the mammary glands, situate under the
integument of the pouch next to the abdomen of the mother ; and
they remain in this situation for a long time, imbibing nourish-
ment from these glands, until they acquire a growth equal to that
which the young of other animals attain in the uterus before
birth. Two bones, peculiar to these animals, and therefore called
the marsupial bones, are expressly provided for the protection of
the abdominal viscera, lying in the horizontal position of the
trunk above this extraordinary pouch, which performs the func-
tion of a supplementary uterus. It is farther remarkable, that
the same bones occur in the skeleton of the males, where, of

33

886 COMPARATIVE PHYSIOLOGY.

course, there are no pouches ; and also in those species where
the fold forming the pouch is scarcely perceptible. The uterus
communicates with the vagina, not by a single opening, but by
two curved lateral tubes. This has been called the uterus anfrac-
tuosus, to distinguish it from the ordinary form, which is the
uterus simplex ; the uterus hicornis, which has two horns, either
straight or convoluted ; and the double uterus, or uterus duplex,
which has the appearance of two horns opening laterally into
the vagina, as in the mole, the hai'e, and the rabbit. The Fallo-
pian tubes, in marsupial animals, are much enlarged at their
extremities.

953. In the opossum, the cardiac and the pyloric openings of
the stomach are placed very near one another. The anal glands
are large. The tongue is covered with pointed processes.

954. The kangaroo has a stomach composed of three pouches,
but in consequence of the power which different portions of it
possess of contracting separately, it is occasionally divided into
a much greater number of portions.

955. The phascolome, a species of rat from Australia, which
possesses an abdominal pouch, is remarkable for possessing, in
common only with man, and the orang-utan, both a ccecum and
an appendix vermiformis.

10, Rodentia.

956. In this order of mammalia, we find the incisor teeth fur-
nished with enamel only in front; the frontal sinuses are absent;
the OS frontis is divided into two bones by a middle longitudinal
suture, and the tympanic bone is distinct from the temporal.
The brain presents no appearance of convolutions on its surface,
the eyes are placed on the side of the head, so that the direction
of their axes is completely lateral ; and the orbits are not sepa-
rated from the temporal fossse ; the coecum, in particular, is ex-
ceedingly voluminous, so«s often to exceed the stomach in size.
The dormouse, indeed, presents an exception to this rule, being
■destitute of any coecum.

957. The beaver has a remarkably strong and prominent
zygoma. A peculiar glandular body is found near the upper
orifice of the stomach, full of cavities, apparently for the purpose
of secreting mucus. The urethra terminates in the rectum, thus
constituting a kind of cloaca ; a structure which, as we shall find,
prevails universally in birds. The direction of the axes of the
•orbits is upwards.

958. The common rat has no coscum ; its zygoma has its con-
vexity turned downwards; the testes are capable of being
retracted within the abdomen. A similar circumstance occurs
in the hamster, the squirrel, and the guinea-pig.

MAMMALIA. 387

959. The mus typhlus is remarkable for having its eye covered
over with the common integument of the face, which, together
with the hair growing on it, completely intercept light, and must
destroy the use of the eye as an organ of vision.

900. Cheek pouches are met vi^ith in many species of this
genus ; as in the case of the hamster and marmot. In the ear of
the latter of these animals, a portion of bone is described by Cuvier
as passing between the crura of the stapes, from one side of the
fenestra ovalis to the other, the use of which conformation is
entirely unknown.

901. In the hare, the following peculiarities are met with.
The coronoid process of the lower jaw is almost entirely wanting.
The transverse processes of the lumbar vertebrae are remarkably
large. The stomach may be distinguished into two portions,
differing in the structure of their coats; the cardiac portion being
lined with cuticle, and the pyloric division having the usual villous
and secreting surface. The former may be regarded as a reser-
voir for the food, while the latter is the part which performs the
function of digestion. The undigested state in which the contents
of the stomach is found in the former, and its altered appearance
in the latter, corroborate this view of the different offices of these
two portions of the stomach. The rabbit agrees with the hare
in this conformation. The coecum is of enormous size ; it extends
to a length which is greater than that of the whole animal ; it is
curiously convoluted, and is lined internally with a peculiar spiral
fold or valve. The urinary bladder is peculiarly large in the
hare.

962. The retina exhibits very distinct and beautiful medullary
strias, which pass, for the most part, in a transverse direction.
The glandula Harderi is found in these animals, and unites itself
with the proper lacrymal gland, but is distinguishable by its whiter
colour. Both the hare and the rabbit have a slit, opening into
the lacrymal canal, which serves as a substitute for the puncta
lacrymalia. Sebaceous sinuses exist on the outer side of the
upper jaw, near the nasal bones ; whence a large quantity of a
viscid adipose substance is secreted. Cavities are also formed
in the groins, called by Pallas, antra inguinalia, which contain a
strongly odorus substance prepared by the neighbouring subcuta-
neous glands.

11. Tardigrada.

963. The tardigrade mammalia are distinguished by having
the same peculiar distribution of the arteries of the limbs which
we have already noticed in the lemur tardigradus. They possess
neither coecum nor gall-bladder. The stomach of the sloth is
complicated in its structure, being divided into several pouches ;

388 COMPARATIVE PHYSIOLOGY.

the intestinal canal is very short ; there is also at its extremity
an approach to the structure of the cloaca of birds, inasmuch as
the rectum and urethra have a common termination. The
zygoma is furnished with a large descending process, which
comes from the os mate.

964. The two-toed sloth (bradypus didactylus) has twenty-
three ribs on each side. We have already noticed the apparent
anomaly presented by the three-toed sloth (the bradypus tridac-
tylus), in its seeming to possess nine instead of seven cervical
vertebrae ; this appearance being given to the two last of these
vertebrae, which are, in fact, dorsal, by the ribs which are
attached to them being very short, and rudimental in their con-
formation (see § 911). In the ant-eater and manis, which belong
to Cuyier's family of the edentata, the six last vertebrae of the
neck are anchylosed or united so as to form only one bone.

12. Monotremata.

965. The singular animals which compose this family of mam-
malia, instituted by M. Geoffrey, are all inhabitants of the con-
tinent of Australia, so fertile in extraordinary productions in every
department of natural history. They are included in the genus
ornithorhyncus, and are distinguished into the three species of
paradoxus, histrix, and setosus.

966. Although they are not furnished with abdominal pouches
like the kangaroo and other marsupial animals, yet they are
provided with two bones corresponding in their position to the
marsupial bones, already described (§ 952,) as attached to the
bones of the pubis, and supporting the abdominal viscera. The
number of ribs in the ornithorhyncus is seventeen. Pouches
exist in the cheek of the animal. The bill, shaped like that of the
duck, is abundantly furnished with nerves, chiefly from the second
branch of the fifth pair. Its teeth have no fangs which sink into
the jaw, as in most quadrupeds, but are merely imbedded in the
gum, and are very peculiar in their shape. In the ornithorhyncus
paradoxus, there is one on each side of either jaw ; it consists of
a horney substance of an oblong shape, flattened at the surface,
and adhering to the gum. There are likewise two horney pro-
cesses at the back of the tongue, which are directed forwards,
and prevent the food from passing into the throat before it has
been sufficiently masticated. The tongue is very short, not an
inch long, and the moveable portion not half an inch ; its surface
is beset with long conical papilla. The ornithorhyncus hystrix
has six transverse rows of pointed horny processes at the back
of the palate, and about twenty similar teeth on the corresponding
part of the tongue. The intermaxillary bones are of a very

MAMMALIA. 389

singular shape, consisting of two hooked pieces joined together
at their bases.

The stomach of the ornithorhyncus hystrix is lined with cuticle,
furnished at the pyloric extremity with sharp horny papillge.
There is no valve of the colon, nor is there any coecum, although
we find an appendix vermiformis. They possess a cloaca at the
termination of the rectum, as in birds.

967. Sir Everard Home denied the existence of mammae in
the female ornithorhyncus ; but these glands have been distinctly
delineated by Meckel, and described by him as being largely
developed. In a paper since read to the Royal Society, Sir
Everard Home again asserted that further inquiry had convinced
him of the non-existence of these glands ; but in a paper subse-
quently read to that learned body,* Mr. Griffin describes the
mammae of the ornithorhyncus paradoxus as considerable glands,
which occupy the greater part of the under surface of the animal,
and have numerous excretory ducts perforating the skin in two
circumscribed places, but not forming any elevations analogous
to nipples. This subject has, since that period, been investigated
with great care by Mr. Owen,f who found the structure to cor-
respond very exactly with the account given by Meckel, and he
is accordingly led to regard them as real mammee. The falx,
as well as the tentorium, contains a plate of bone. The external
auditory passage is very long and tortuous, and there are only
two ossicula in the internal ear. A singular kind of clavicle is
found in the skeleton of these animals, common to both the fore
extremities, and situate in front of the ordinary clavicles, bearing
some analogy to the furcular bone of birds. The conformation
of the ribs also exhibits an approach to that of birds. Each rib
consists of two pieces of bone ; a longer one joined to the spine,
and a shorter connected with the sternum ; the two being united
by an intermediate cartilage.

13. Pachydermata.

968. In this natural family of animals, which was established
hy Storr, in his Prodromus Methodi Animalium, the elephant first
claims our notice. In addition to the thick integument common
to all the animals of this tribe, we find that remarkable organ,
the proboscis, which is a prolongation of the nose, formed of a
double cylindrical tube, extremely flexible in all directions, en-
dowed with exquisite sensibility, and terminating in an appendix
very much resembling a finger, all the functions of which it is
capable of performing. The motions of this admirable organ

* December 15, 1831.

f Philosophical Transactions for 1832, p. 517. See also his paper in the
Transactions for 1834, p. 333.

33*

390 COMPARATIVE PHYSIOLOGY.

are executed by an infinite number of muscular fibres, collected
into small bundles, which pass in a great variety of directions,
and are continually interlaced with one another, so as to be
adapted to the performance of every kind of movement. The
enormous tusks which are given to the animal as formidable
weapons of offence, are merely developments of incisor teeth,
])roceeding from the inter-maxillary bones in the upper jaw, and
which on issuing from the mouth are incurvated upwards.

969. That part of the cranium which corresponds to the
frontal sinuses is enormously enlarged ; the two tables of the
skull being separated to a considerable distance from one another,
the intermediate space being occupied by a vast number of cells,
which are full of air, and communicating with .the throat by
means of the Eustachian tube. Camper has very ably pointed
out the advantages resulting from this structure, by the increase
of surface it affords for the attachment of the great muscles of
the lower jaw, neck, and proboscis, and for the augmentation of
their mechanical power. The frontal and parietal bones become
united at a very early period with all the other parts of the
cranium, so as to form a bony cavity in which no trtice of su-
tures can be discerned. The tympanic bone, however, is distinct
from the temporal. The optic foramina commence from a single
canal, which receives the two optic nerves- A rudiment only of
the nasal bones is observable ; and the same remark is also
applicable to the ossa unguis, or lacrymal bones ; neither can we
trace the existence of any lacrymal gland, or lacrymal sac, or
any passage for the tears into the nose. The foramen ovale in
the base of the cranium is very large. Between the arched sides
of the upper part of the cranium, a broad and deep depression is
met with, having a small longitudinal crest in the bottom.

970. Between the eye and the orifice of the external ear, a
gland of large size is situate, occasionally secreting a brown
liuid, which oozes out through an opening in the skin. There
are twenty ribs on each side ; and there appear to be only three
lumbar vertebrae. The ligamentum nuchge is of great size and
strength, for it has to support the enormous weight of the head
with its ponderous tusks and proboscis. The articulation of the
thigh bone with the pelvis, is destitute of the ligamentum teres,
which is found in almost all other quadrupeds. The toes are five
in number, but they are almost concealed by the thickness of the
skin of the foot in which they are encased. The condyles of the
lower jaw are simply rounded eminences. The form and structure
of the teeth are very peculiar, and afford distinctive characters
of the different species of the elephants, which belong more pro-
perly to natural history. In addition to the usual component
parts of bones and of enamel, a third is superadded, called the
crusta petrosa^ which fills up the interstices, left by the duplications

MAMMALIA. 391

of the enamel. The ivory which composes the tusks is exceed-
ingly dense, and diflers considerably in its structure from the
ordinary bone of other teeth. It is distinguished by the curved
lines which pass in different directions from the centre of the
tusk, forming by their decussation, a regular arrangement of
curvilinear lozenges. The tusk is constructed by the successive
depositions of osseous matter from within, being secreted from
the outer surface of the vascular ]5ulp, which occupies the central
part of the growing tusk. Hence, iron balls, fired at the animal,
have been known to penetrate the latter soft portion, and to re-
main fixed in the interior of the tusk, till they were completely
covered over, and imbedded in the successive depositions of
ivory.

971. The stomach is simple in its structure; the intestines are
voluminous, the coecum of great size, and the colon large, long,
and divided into cellular compartments. There is no gall-bladden
The ductus choledochus forms a pouch between the coats of
the intestines, as it does in the cat, for the reception of the pan-
creatic duct.

972. The snout of the tapir bears a slight resemblance to the
proboscis of the elephant; being, although much shorter, ex-
tremely mobile, and provided with a very complex arrangement
of muscles.

973. The rhinoceros is furnished with a rough and slightly
elevated surface of the large nasal bones, consolidated into one
bone, for the attachment of the horn which is supported upon it.
Such, at least, is the structure in the one-horned rhinoceros ; in the
two-horned species it is the front horn to which this description
applies ; for the posterior horn rests on a similar process of the
OS frontis. Like the elephant, the rhinoceros has no gall-bladder.

974. In the hog we also meet with a considerable development
of the frontal sinuses. The molar glands are large, and their
openings very conspicuous. There are two considerable mem-
branous bags in the throat, situate above and in front of the
ligaments of the glottis. Two small flat bones are found at the
base of the heart, at the origin of the aorta from the left ventricle.
Their use has been supposed to be that of giving support to the
valves of the aorta.

975. The peccari, or Mexican musk-hog, has a remarkable
gland situate in the back, near the sacrum; it is composed of
several lobules, the ducts of which unite into one canal, which
passes through the skin, and pours out a secretion having a scent
similar to musk. A singular dilatation is often met with in the
aorta of this animal, as if it were affected with aneurism.

392

COMPARATIVE PHYSIOLOGY.

14. Solipeda.

976. This family comprehends the horse, ass, zebra, and quagga.
The great interest attached to all that relates to the horse, from
its utility to man, has occasioned its anatomy, the study of which
is the foundation of the veterinary art, to be cultivated with
peculiar zeal. The principal circumstances worthy of notice in
the osteology of this animal art the following. As is the case
with most quadrupeds whose necks are very long, the cervical
vertebrae have very short spinous processes. The dorsal vertebrae,
the number of which of course corresponds with that of the ribs,
being eighteen, and sometimes nineteen, have, on the contrary,
very large and broad spinous processes. The space from the
first to the eighth vertebrae, is called the loithers, against which
the upper part of the shoulder rests. There are six lumbar vertebras,
having strong spinous, and also broad and long transverse processes.
Large lateral processes also extend from the sacrum, which is
composed of five consolidated portions ; and the united spinous
processes of these are likewise exceedingly prominent. The tail
is formed of eighteen cylindrical pieces, which, towards the
extremity, have nearly the softness of cartilage.

977. The true ribs are, on each side, eight in number, the
remaining ten or eleven being joined to the sternum by cartilage.
The sternum is composed originally of seven pieces of bone united
into one. Its anterior extremity is sharp-pointed, like the prow or
keel of a ship. In the pelvis of the horse, denominated the haunch,
we find the ilium, or hip-bone, extended in three directions, above,
below, and behind, forming three large processes, for the attach-
ment of the strong muscles which surround the hip joint. The
ischium is much extended, formiing a strong process posteriorly
for a similar purpose. This elongation of the ischium has been
termed, from its figure, the processus triquetrus ischii. By remov-
ing the point of attachment of the muscles to a greater distance
from the axis of motion, it gives them the mechanical advantage
of acting by a long lever. The symphysis of the pubis (or the
junction of the bones of that name) is remarkable for its depth,
thus aflfording an extensive surface for the attachment of muscles.

978. The bones of the extremities of the horse are constructed
on the same general model as the human, though varying much
in the details of their form and relative proportions ; and some
parts only appearing in an imperfect or rudimental state. The
scapula is of an oblong triangular shape, considerably narrower
and longer than the same bone in the human skeleton, and exhi-
biting only faint traces of the acromion and coracoid processes.
Its axis is nearly in the same line with the os humeri, which latter
bone is very short, and scarcely descends below the line of the
chest, and possesses scarcely any rotatory motion on the scapula.

MAMMALIA.

393

The radius and ulna are consolidated together ; the olecranon is
much elongated. The carpus, or as it is vulgarly called, the
knee, of the horse, is composed of seven, or sometimes eight,
small bones, disposed as in the human carpus, in two rows;
though with respect to their individual form, they have but little
resemblance to the latter.

979. That part of the skeleton which corresponds to the meta-
carpus is, in the horse, consolidated into a single bone termed the
shank, or canon hone, to which are united behind, and on the
side, two much shorter and very slender bones, called the styloid,
or splint hones, frequently found consolidated with the canon
bone by ossific union. It is only the latter, or principal bone,
that is articulated with the next, or pastern hone, which corres-
ponds with the first phalanges of the fingers, and may be regarded
as the consolidation of these five bones into one. In like manner,
the second phalanges are consolidated in the horse into the next
bone of the foot, which is termed the coronet hone, and which is
articulated by a divided condyle with the coffin hone, of which
we shall presently speak. Before proceeding, however, we must
notice two or three small rounded bones placed at the back of
the pastern joint, (between that and the shank bone) which cor-
respond in their office to sesamoid bones, and which have
accordingly received that appellation.

980. The coffin bone corresponds in situation to the third
phalanx of the fingers. It supports the single hoof; from which
this family of mammaHa derive their characteristic name. Con-
nected with this is a small bone, called the shuttle hone.

981. In the posterior extremity we find a very similar arrange-
ment of bones. The thigh bone is unusually short, scarcely extend-
ing beyond the trunk of the body, when surrounded by its muscles.
The glutsei muscles, and especially the glutseus medius, are parti-
cularly powerful in their action "for extending the thigh back-
wards, and performing the motion necessary for kicking. There
is a process in this bone of the horse which is not observed at all
in the human os femoris ; it is a strong curved spine, situate on
the outside, opposite to the lesser trochanter. It has been termed
the processus recurvatus femoris.

982. The patella of the horse Is large, thick, and very promi-
nent. From the tihia there arises a small spinous process, w^hich
may be considered as the rudiment of a fibula. The tarsus, or
hock, is composed of six or seven bones, and forms a very obtuse
angle with the tibia, when the horse has his foot to the ground.
The astragalus differs from the human bone of that name, by
having two very large and prominent condyles. The metatarsal
bones correspond in every respect with those of the carpus already
described.

983. In the skull of the horse we mav observe that the tern-

394

COMPARATIVE PHYSIOLOGV.

poral bone is divided by a suture into the squamous and tympanic
portions. The occipital bone has a deep depression in the middle,
where the cervical ligament is attached. The antrum maxillare
and turbinated bones are of great size. The lower jaw-bone is
also very large, and presents a very extended surface for the
attachment of muscles.

The horse is provided with a large salivary apparatus of glands.
Its stomach is divided into two portions ; the first of which, next
to the ossophagus, is lined with a cuticular membrane which ter-
minates in a loose expansion, supposed to have the office of a
valve, and to prevent the possibility of the animal's vomiting.
There are generally found adhering to its coats a great number
of the larvae of the oestrus equi, and the oestrus hsemorrhoidahs,
called in common language, hotts. The intestinal canal is of
great length, the large intestine alone being twenty-four feet in
length. The colon is very capacious, and divided into cellular
compartments. The liver is large, divided by deep indentations
into lobes, and unprovided with a gall-bladder.

984. The peculiar sound produced in neighing is ascribed to
the presence in the trachea of a delicate membrane, attached by
its middle to the thyroid cartilage, and of which the two extremi-
ties pass along the external margins of the rim a glottidis. The
Eustachian tube opens, not immediately over the larynx, but into
a sac peculiar to this tribe of animals, situate on the lateral parts
of the lower jaw ; and these cavities then open by a long
fissure, furnished with a cartilaginous valve, into the pharynx.

985. The eye of the horse presents a remarkably beautiful and
delicate structure in the folds of the internal membrane of the
corpus ciliare. The pupil is oblong, the superior margin of the
iris having a fringed appearance.

15. Ruminantia.

986. The anatomy of the ruminant family of quadrupeds, which
comprises so many of those animals that man has domesticated
and rendered subservient to his most urgent wants, has also very
strong claims on our attention.

987. In their skeleton they correspond very closely with the
horse, of which we have already given so detailed a description.
The principal differences are observable in the terminal bones of
the extremities, each limb presenting us with two hoofs, instead
of one, and a corresponding division of the metatarsal bones and
phalanges into two. On the other hand, the slender traces of a
fibula met with in the horse, disappear in the ox and other animals
of this tribe.

988. The whole track of the alimentary canal in these animals
presents us with objects of interest. The tongue is covered with

MAMMALIA. 395

a thick cuticle, provided with pointed papillas, which being directed
backwards, are fitted for laying firm hold of the grass, and tear-
ing it up from the roots. The salivary glands are extremely
large ; the coats of the oesophagus particularly strong and mus-
cular, in subservience to the function of rumination peculiar to
this tribe. The organs provided for digestion are more compli-
cated than in any of the animals we^have yet considered. There
are no less than four cavities which have been regarded as per-
forming the otfice of stomachs. The first is the paunch, which
is a capacious reservoir, abundantly supplied with secretion from
its coats, which are beset with numerous flattened papillce. The
second is the lioney-comh stomach, so named from the reticulated
appeax'ance of its inner membrane, the folds of which are dis-
posed in polygonal lines, somewhat resembling the hexagonal
margins of the cells of the honey-comb. The third stomach,
which is the smallest, is termed the manyplies, and contains a
greatnumber of broad folds, or duplicatures of its inner membrane,
which have been compared to the leaves of a book. The fourth,
or the reed, has a pyriform shape, an internal villous coat, and a
structure altogether analogous to that of the simple stomachs of
carnivorous animals. It terminates in the beginning of the intes-
tinal canal. A groove extends from the termination of the ceso-
phagus along the edge of the three first stomachs, at the part
where they communicate together ; the edges of this groove are
thick, so as to admit, when brought in close contact, of forming a
canal for the direct communication of the oesophagus with any
one of these four stomachs.

989. The grass which the animal takes into the mouth under-
goes but a small degree of mastication, and passes, on being
swallowed, into the paunch, where it undergoes maceration, and
is transferred, by small portions at a time, into the honey-comb,
or second stomach, which serves to perform an auxiliary office
to the first. Thence it is sent up again directly through the
oesophagus into the mouth, for the purpose of undergoing a second
and more deliberate mastication, which the animal perform.s
when reposing, and from which it appears to enjoy considerable
pleasure. After being thus ruminated it is again swallowed, and
the sides of the groove being brought into contact, so as to con-
stitute a canal, and exclude all passage into the first or second
stomachs, it passes directly into the third stomach ; whence, after
having been subjected to the further action of the secretions of
that organ, it is transferred to the fourth or last stomach, where
the process of digestion is completed. Liquids drunk by the
animal pass at once into the second stomach, and assist in the
maceration of its contents. But the milk taken by the calf,
requiring to be neither macerated nor ruminated, is conveyed
directly from the ojsophagus into the fourth stomach.

396 COMPARATIVE PHYSIOLOGY

990. The biliary organs present us, in horned cattle, with
numerous hepato-cystic ducts, conveying the bile immediately
from the liver to the gall-bladder, which cyst is found in all the
animals of this order, though it is absent in the horse. The
urinary bladder is particularly large. In Hke manner, as we found
in the pig, two small bones are met with also in ruminants, at the
origin of the aorta ; and the same purpose has been assigned to
them as in the former instance. In the stag, these have been
called the hones of the heart.

991. The internal carotid artery, at its entrance into the
cranium, is suddenly subdivided into numerous branches, which
are variously contorted, and afterwards re-united at the basis of
the brain. The intention of this curious structure, which has
been termed the rete mirabile, appears to be to diminish the
impetus with which the blood would otherwise be forced into
the arteries distributed to the brain ; a force which would be
increased by the effect of gravity when the animal stooped in
grazing. The frontal sinus, and other parts connected with the
sense of smell, are much developed. The lacrymal bones and
ossa nasi are of considerable size. The tapetum is particularly
conspicuous in the eyes of ruminants. One or two additional
small bones are found among the ossicula auditus. The mastoid
cells are numerous, and in the arrangement of their compartments
somewhat resemble a ripe poppy head. In the ox and the sheep,
the superior ligam.ent of the glottis, as well as the ventricles of
the larynx, are absent.

992. Ruminant animals are distinguished into two tribes, the
first consisting of those which are without horns ; the second, of
those provided with horns. Of the former, the camel is remark-
able for the great expansion of the hoof, which adapts it for
treading upon sand. It has seven lumbar vertebrae. A pecuhar
moveable bag, glandular in its structure, exists behind the palate,
probably designed for the lubrication of the throat ; it has re-
ceived the name of bursa faucium. Connected with the paunch
is a large receptacle divided into numerous cells, for the purpose
of holding water, as in a natural reservoir. Hence, when a camel
dies in the desert, the Arabs open the stomach, and quench their
thirst with the water it contains, which is found to be pure and
wholesome. Like the horse, it has no gall-bladder. It has no
fibula ; but this latter bone is met with in the musk, which is also
a hornless ruminant.

993. The horned ruminants have an eminence on the os frontis
for supporting the horn. This process is in the stag a real bone,
remarkable for the rapidity of its growth, which is annual, and
for its death and separation from the skull at certain periodic
intervals. The osseous bases of the horns of the ox, the sheep,
the goat, and the antelope, on the contrary, are permanent, and

MAMMALIA. 397

are invested with a horny covering, which has a structure very
different from bone. The camelopard, or giraffe, on the other
hand, has two osseous prominences, which remain permanently
covered with the integuments, and are even surmounted by a
tuft of hair. But the details relating to organs so external as the
horns fall more properly within the province of natural history.

994. The rein deer has, like several of the baboon tribe, large
laryngealsacs on the front of the neck, communicating with the
larynx.

995. In the ox and sheep the spleen is remarkable for being of
a distinctly cellular structure. In these animals we find a great
development of the salivary glands, and more particularly of the
submaxillary gland, which extends along the side of the larynx -
quite to the back of the pharynx.

16. Cetacea.

996. From the consideration of the quadrupeds of the class
mammalia, we pass now to that of a tribe of animals which, al-
though warm-blooded and mammiferous, are formed on a model
adapting them for inhabiting the water ; nature having bereft
them even of the rudiments of hinder extremities. The bones of
the spine are continued, without being interrupted by an inter-
posed pelvis, into the vertebrse of the tail, which terminates in a
horizontal fin. The head and trunk are united by a neck, so
short as to exhibit scarcely any diminution of diameter, and con-
taining cervical vertebrse, which are extremely compressed, and
the greater number of which are consolidated together by a bony
union. The superior extremities are supported by bones, which
have no medullary cavities, and which, compared with the ana-
logous bones of quadrupeds, are much shortened and compressed.
They do not admit of motion amongst themselves, and being
enveloped by a tendinous membrane, are reduced to the office of
fins. The internal organs correspond, however, with that of
other mammaUa. Cetacea breathe by means of lungs, their
circulation is double, and they are warm-blooded. The females
are viviparous, and are provided with mammee for the nourish-
ment of their young.

997. The necessity of occasionally receiving air into the lungs,
whilst the animal is generally immersed in water, renders it re-
quisite that a provision should be made for their readily rising to
the surface in order to breathe. Hence the movements of the
tail are from above downwards ; hence in the cachalot and other
kinds of whale, a large quantity of oil is accumulated round the
head, which gives greater buoyancy to this part of the body.
Hence, also, when the animal, in seizing its prey, takes into the
mouth a large quantity of water, there is a necessity of getting

34

398 COMPARATIVE PHYSIOLOGY.

rid of it, which is effected by its transmission into a sac placed
at the external orifice of the nasal cavity, whence it is expelled
with great force, by the contraction of powerful muscles, through
a passage which conducts it to the top of the head. In this way
are produced the enormous spouts of water that mark the track
of the whale on the surface of the sea.

998. The olfactory organs are not adapted to the possession
of any accurate sense of smell, being furnished neither with
turbinated bones nor with any considerable nerves. The larynx
rises in a pyramidal form into the posterior part of the nostrils,
in order to receive the air from those passages, and convey it to
the lungs, without its being necessary for the animal to extend
more than the end of the snout above the surface of 'the water.
The glottis is simple, and is not interrupted by any projecting
membranes.

999. The stomach is composed of as many as five, or some-
times even of seven distinct pouches. There is no coecum or
appendix vermiformis ; and the gall-bladder is absent in the
greater number. The spleen is divided into a number of small
globular lobes. The kidneys are conglomerate. The brain is
large, and its hemispheres much developed. The tympanic bone
is separated from the rest of the cranium, adhering to it only by
ligamentous connexions. There is no external air ; the stapes is
nearly solid ; in the walrus it exhibits no perforation. The ossi-
cula, semicircular canals, and other parts of the labyrinth of the
internal ear are remarkably small. The external meatus is carti-
laginous, and so small, that its external orifice in the dolphin will
only just admit a pin. It pursues a winding course through the
the fat, which is of great thickness, until it reaches the tympanum.
The Eustachian tube opens at the blowing hole, and is furnished
with a valve preventing the admission of the water which the
animal expels through that passage. The lacrymal organs are
entirely wanting ; the sclerotic coat of the eye is very thick at
its posterior part, so that although the eye-ball has exteriorly a
spherical form, the figure of the vitreous humor is very different;
its structure at the back of the eye has the hardness of cartilage.

1000. In many parts of the arterial system of the cetacea, we
find reticular plexuses, or convolutions of the vessels, the pur-
pose of which is probably to serve as reservoirs of arterial
blood, for the use of the system, when the animal is long under
water.

1001. In the trichecus manatus borealis, or manati, a gland of
the size of the human head is found between the coats of the
stomach, near the oesophagus, discharging, on pressure, a fluid
resembling the pancreatic juice.

1002. The whale is remarkable for having, in place of teeth,
an apparatus apparently intended for filtration, and consisting of

BIRDS. 399

plates of the substance called whalehone, descending vertically
into the mouth from the lower surface of the upper jaw, into
which they are fixed by a ligamentous substance. On each side
their number amounts to three or four hundred. The inner edge
of each plate has its fibres detached so as to form a kind of
fringe, which retains the small fishes and mollusca on which the
animal feeds. The lower jaw is unprovided with any similar
appendages. Although there are no teeth in the upper jaw, yet
an intermaxillary bone is still present. Rudiments of teeth exist in
the interior of the lower jaw before birth, lodged in deep sockets,
and forming a row on each side. The development of these im-
perfect teeth, however, proceeds no further, and they disappear
at an early period. The tongue, which is supported by an os
hyoides of singular shape, is very thick and fleshy. The oesopha-
gus is exceedingly narrow. The stomach is complicated in its
structure. The intestinal canal is of considerable length, and
contains a great number of longitudinal folds. There is a short
coecum. The mesenteric glands contain large spherical cavities,
into which the trunks of the lacteals open, and where the chyle
is probably blended with secretions proper to those cavities. The
eye is extremely small in comparison with the size of the animal;
and it occupies but a small portion of the orbit.

Sect. II. — Comiparative Physiology of Birds.
1. General Description.

1002. The whole of this class of animals exhibits great unifor-
mity in its comparative anatomy ; insomuch that the whole may
easily be comprised in one general description. The structure
of every part of the frame of birds is adapted to facilitate rapid
progression through the air ; for which purpose the anterior
extremities are converted into wings, and are not employed in
any other action. The support of the body when the animal is
not flying, is entrusted solely to the posterior extremities ; so that
birds are, strictly speaking, bipeds. Hence we may trace some
degree of approximation to the human structure in the conforma-
tion of the skeleton.

1003. The bones are dense in their texture, but are at the same
time rendered light by having large cavities, occupied, not with
marrow, as in the mammalia, but with air. There is a smaller
proportion of cartilaginous to osseous structure in the skeleton of
birds than in that of quadrupeds.

1004. The neck of birds being required to be very flexible, we
find the cervical vertebrae very numerous, and freely moveable
upon one another. The swan has twenty-three cervical vertebrae.

400 COMPARATIVE PHYSIOLOGY.

Those of the back, on the other hand, are perfectly fixed and
immoveable, then' spmous processes being large and often united
by osseous substance, so as to preclude the possibility of any
relative motion. As the ribs occupy the whole of the sides of
the trunk, there are properly no lumbar vertebrae. The os
coccygis is short and compressed ; and can scarcely be regarded
as a proper tail, although it affords support to the long feathers
which constitute what is usually called the tail of birds. The pelvis
consists almost entirely of a broad os innominatum, the lateral
portions of which are widely separated, in order to admit of space
for the development of the eggs ; and for the same reason the
two ossa pubis do not join to form a symphysis, biit are at a
considerable distance from one another. The exceptions to this
general rule will be noticed afterwards.

1005. The number of true ribs never exceeds ten pair; the
false ribs are numerous, and directed forwards. Those which
occupy the middle of the body are distinguished by a flat process,
directed upwards and backwards. The sternum is composed of
five pieces, and is of great size and strength. From the middle
of its lower surface there rises a sharp process, or spine, resem-
bling the keel of a ship, and evidently adapted to accommodate
the large and powerful pectoral muscles, which take their rise
from this part of the chest, and which act in depressing the wings.
The bones which connect the wings to the trunk are apparently
three in number; the coracoid process of each scapula being
distinct and largely developed bones, having the semblance of
ordinary clavicles, whilst the real clavicles are consolidated into
a single bone, denominated the filrcular bone, from its resemblance
to a fork, and which in the fowl is better known by the name of
the merry-thought. Its extremities rest on two strong processes
of the scapula. Many anatomists, considering the coracoid as the
true clavicles, have regarded the furcular bone as an additional,
or supplementary clavicle, corresponding to the coracoid apophysis.

1006. The bones of the wing are analogous in their divisions
and distribution to those of the upper extremity in man : there
being a humerus, radius, and ulna ;< tvv^o carpal bones ; and two
metacarpal bones, generally consolidated into one ; one bone cor-
responding to that of the thumb and two fingers ; that next to
the thumb consisting of two phalanges, and the outer one, of a
single bone.

1007. In the legs we find a femur and a tibia, to which there
adheres a very slender fibula, (which is, indeed, often wanting ;)
one metatarsal bone, and the phalanges of the toes. The patella
is often supplied by a process from the tibia.

1008. The muscles possess a high degree of irritability, and
contract with great quickness and force. Many of the tendons
become ossified in the progress of age. A remarkable arrange-

BIRDS. 401

ment exists in the tendons of the flexor muscles of the toes, by
which the flexion of the knee and heel puts them on the stretch,
and thus mechanically bending the toes, enables the bird to lay
firm hold ol" the branch of a tree or perch whilst roosting. This
is effected by the flexor tendons passmg round over the outer
side of the angle formed by each of these joints. Thus a bird,
while roosting, supports itself on one leg only, by the mere eftect
of the weight of the body producing the necessary flexion of the
toes, to enable it to preserve its hold. This remarkable provision
of nature was long ago observed, and well explained by Borelli ;
and though the fact has been controverted by Vicq. D'Azyr, it
appears to be well established. In order to give great latitude
of motion to the head, the articulation of the os occipitis with
the atlas is performed by a single condyle only, which procures
it the advantages of a ball and socket jonit. This condyle is
situated at the anterior margin of the great occipital foramen.
The proper bones of the cranium are not joined by sutures, but
are consolidated into a single piece. The orbits for the eyes are
very large, and are frequently found to communicate laterally in
the skeleton, being separated, in the living animal, only by a thin
membranous partition. The ossa unguis are generally very large.
The upper jaw is almost always moveable upon the other bones
of the head. To this bone is joined the bill, the structure of which
is horney, and thus supplies the place of teeth, occupying
the situation of the palate. The functions of the teeth, indeed,
are not wanted, for the animal swallows its food without any
mastication. The lower jaw is connected with the skull by the
intermedium of a peculiar bone of irregular form, called the os
quadratum. Another small bone resting against the palate is
connected with it.

J 009. The energy of the digestive functions in birds corres-
ponds with that of respiration, and muscular irritability. The
stomach may be considered as consisting of three cavities ; the
first of which, termed the crop, is rather a dilatation of the
oesophagus, furnished with numerous glands disposed in a regular
arrangement of rows ; the second is the ventriculus succenturia-
tus, or pro-ventricuhs, situated lower down, and just at the en-
trance of the proper stomach. It is furnished with a still more
complex glandular apparatus ; and hence has been termed the
hulhus glandulosus. Its form and structure vary much in differ-
ent genera of birds. The third is the proper stomach, which
resembles in the structure of its coats the simple stomachs of the
mammalia, being thin and membranous in those birds which feed
on insects and flesh. But in all granivorous birds the coats of
this stomach are farther armed with a thick cuticular lining, of
nearly the density of horn, which is surrounded by four immensely
thick and powerful muscles, capable of exerting a strong com-

34*

402 COMPARATIVE PHYSIOLOGY.

pression on the contents of the stomach, and a slight degree of
lateral motion, and thus performing the office of trituration.
Such is the structure of what is called a gizzard. Between these
opposite structures there exists, in different species of birds, a
great number of intermediate gradations, corresponding to the
peculiar nature of the food to which nature has adapted their
organization. The trituration of the grain is assisted by small
stones voluntarily swallowed by the animal, and in the selection
of which the animal is directed by a principle of instinct.

1010. The intestinal canal of birds is much shorter than in
most of the mammalia ; but a similar disparity is also noticed in
the former, with regard to the greater length of the canal in birds
consuming vegetable food, when compared with that of the
carnivorous tribes. There is scarcely any distinction in point of
size between the small and large intestines ; though the division
between them is generally marked by the presence of two coeca.
The rectum terminates in an expansion, termed the cloaca, in
which the ureter terminates, and which therefore performs the
function of the urinary bladder. Connected with the cloaca,
there is an oval glandular bag termed the bursa Fahricii, and
opening into it by a narrow longitudinal aperture. The oviduct
in the female also opens into the same cavity. Two bhnd pouches,
opening into the rectum, are found near to its termination.

1011. The liver of birds is usually divided into two lobes; but
in some birds there is in addition a third smaller lobe. Two
ducts proceed from the liver; the one is the hepato-cystic duct,
the other the hepatic duct. The former conveys the bile into
the gall bladder, the latter into the duodenum. 'Thus the bile is
conducted into the duodenum by one hepatic duct distinct from
the cystic duct, and these two alternately with two or three
ducts from the pancreas, which is large, and generally consists
of two distinct glands ; the spleen, on the other hand, is usually
round, and of small size. The gall-bladder is situate under the
right lobe of the liver ; but some birds have no gall-bladder.
There is no omentum. The chyle is transparent; there are no
glands in the mesentery ; the thoracic duct is double. Magendie
has denied the existence of lymphatic vessels in birds ; but they
have been distinctly seen by others. The kidneys form a double
row of conglobate glands, connected together, and situate on the
sides of the lumbar vertebrae, in the hollows of the ossa innominata.
There is no cavity corresponding to the pelvis of the kidneys of
the mammalia ; but renal capsules, similar to those of mammalia,
are found also in birds.

1012. The heart of birds is furnished, as in the mammalia, with
a double set of cavities ; the one subservient to the general or
systemic, and the other to the pulmonary circulation. The valves
of the right ventricle are supplied by a strong triangular muscle.

BIRDS. 403

which gives additional impetus to the blood propelled into the
pulmonary artery. Jacobson has discovered a singular distribu-
tion in the abdominal veins ; those returning the blood from the
hinder extremities being ramified through the kidneys and Uver,
previously to their termination in the vena cava.

1013. The lungs are not divided into lobes, and are fixed in
their situation, being tightly braced in the cavity formed by the
ribs, on-each side, by a membrane, which is perforated by a
number of holes. These apertures are the terminations of col-
lateral branches of the bronchia, through which the air received
into the chest passes out, and circulates through a multitude of
cells interspersed through various parts of the body, and com-
municating ultimately with the central cavities of the bones. An
immense surface is thus exposed to the influence of the air, which,
having access to every part of the body, acts very extensively
on the blood circulating in the vessels lining these air-cells and
cavities. Hence the energy of the function of respiration is
greater, and the temperature higher, than in any of the mam-
malia. There is properly no diaphragm in birds ; a few muscular
fibres only surround the larger air-cells, and assist in expelling
the air from them back again into the lungs. The trachea is
supported by a series of cartilages, which form entire rings, and
overlap each other at their upper and lower margins, so as to
preserve the tube open amidst the violent bendings and twistings
of the neck. It is provided, at its bifurcation, with a peculiar
set of muscles, which, aided by a second rima glottidis, enable
this part to perform the functions of a second larynx, and to give
rise to sounds; and, indeed, to be apparently the principal organ
of the voice. In many aquatic birds, as in the male swan, the
trachea makes a large circumvolution, which is contained in
the hollow of the sternum. In other birds it is not enclosed in
this bone ; but there is a bony structure surrounding the inferior
larynx, which tends to strengthen the voice. These convolutions
and bony cells of the trachea, have been compared in their ofUce
to the turns of the French-horn, or the divisions of a basoon.
This great development of the vocal organs is peculiar to the
male bird.

1014. The brain of birds is characterized by the smallness of
the hemispheres, which are not united by any corpus callosum.
There is no appearance of convolutions on its surface. The
optic thalami are voluminous, and are situate behind and below
the hemispheres ; a cavity is found in each. The crura of the
cerebellum do not form any eminence at their junction with the
medulla oblongata, corresponding to the pons varolii. The
cerebellum is comparatively large, but has no lateral lobes, being
almost wholly constituted by the processus vermiformis. The

404 COMPARATIVE PHYSIOLOGY.

total bulk of the brain, compared with the size or weight of the
body, is generally greater than in the mammalia.

1015. The eyes of birds are very large, in proportion to the size
of the head, and appear to be adapted to a great range of vision.
The adjustment of the position of the lens appears to be effected
by means of a vascular and plicated membrane, called the mar-
swpium, extending obliquely from the bottom of the retina, through
the vitreous humor, to the edge of the crystalline. Its figure is
trapezoidal ; its surface is covered with the pigmentum nigrum,
which of course absorbs all the rays of fight that fall upon it.
The anterior part of the eye-ball is, in many carnivorous birds,
strengthened by a circle of bony plates, lying close upon the
sclerotica, and overlapping each other. Besides the two external
eye-lids, birds are always provided with a strong nictitating
membrane, proceeding from the internal corner of the eye, and
drawn over the cornea by a special muscular apparatus. In
some birds the lower eye-lid is the most moveable, and in others
it is the upper.

1016. There is no cartilaginous external air; what has this
appearance in the owl is formed only by the feathers ; the cavity
of the tympanum contains only one ossiculum auditus. and com-
municates with the air-cells of the skull. The Eustachian tubes
have a common opening over the arch of the palate. The part
corresponding to the cochlea has the figure of a cone, with
scarcely any curvature, but with two scalse. The semicircular
canals are large, and project from the bone.

1017. The nasal organs are unprovided with an aithmoid
bone ; the olfactory nerves, passing to them through the orbits,
and being distributed upon the hullcB turbinatcB, which are oftener
cartilaginous than osseous in their structure.

1018. The tongue is thick and fleshy, covered with a thick
cuticle, and therefore not adapted to be an organ of taste. It is
supported by an os hyoides of a singular shape, having besides
the anterior and posterior processes, and the cornua, with their
appendices, another bone jointed to it anteriorly, and moveable
on it. This last bone, which supports the tongue, is called the
lingual bone.

1019. The evolution of the chick from the egg being a subject
of great interest, has long engaged the attention of physiologists.
The following is an outline of the history of these changes in the
common fowl. The ovulum, or first rudiment of the Qg,g, is
formed in the ovary, and consists simply of a bag containing the
yolk; this afterwards becomes covered in its progress along the
oviduct, by successive layers of albuminous substance, which
composes the white of the egg, so called from the colour it as-
sumes when coagulated. The white of the egg is invested with
a firm membrane, which is easily divisible into two layers; and

BIRDS. 405

there are also other membranes dividing the mass of albumen
into concentric layers. The membrane of the yolk, the mem-
hrana vitelli, or yolk-hag, is connected with that of the white, or
the memhrana alhuminis, by a kind of ligament, which extends
from the two ends or sides of the yolk, to those of the white ;
these, when partially stretched and torn by the motion of the
yolk, have a flocculent appearance, and form what are called the
chalazcB. They appear to act as ligaments to the yolk, keeping
that surface uppermost in which the chick is situated, so that it
may receive warmth from the hen during incubation. In the
lower part of the oviduct the egg acquires a calcareous covering
or shell, which is secreted by the inner membrane of that canal,
and which is composed of nine-tenths carbonate of lime, the
remaining portion being phosphate of lime and animal matter.
Between the two membranes which line the shell, a small quan-
tity of air is contained at the larger end of the egg.

1020. A small, round, milk-white spot, called the cicatricula,
is formed on the surface of the yolk-bag during incubation. It is
surrounded by two or three concentric circles, called the halones.
Previously to the appearance of the embryo, a small shining spot
of an elongated form, with rounded ends, but contracted in the
middle, is seen within the cicatricula. This is called the areola
pellucida. In the centre of this may be discerned, on the second
day, a gelatinous filament, bent into a curve. This is the primitive
trace, or earliest perceptible rudiment of the chick, in which the
first organs that can be discovered are the two lobes of the brain,
and the primitive filaments of the spinal cord, with caudal
dilatation. Vessels begin to appear on the surface of the yolk-bag,
being spread on a separate membrane, and presenting what has
been called the figura venosa, or area vasculosa, the marginal
vessel at the remotest part being termed the vena terminalis.
These veins correspond to the mesenteric veins ; they are collected
together, and form the vena portse, whilst the arteries are derived
from the mesenteric artery of the chick. The heart may next
be perceived, as three red pulsating points, constituting the punctum
saliens. These points are the rudiments of the auricle, ventricle,
and aorta. Next, the separate vertebras may be distinguished,
then the eyes, and afterwards the stomach, fiver, and intestines.
Then a vascular membrane, the allontois, is rapidly formed, having
the form of a bladder communicating with the cloaca. It soon
extends over nearly the whole of the internal membrane of the
shell, and is covered with num.erous ramifications of arterial and
venous vessels, derived from the internal iliacs of the chick ; the
former contain carbonized blood, and are therefore dark coloured;
the latter, which conduct back the same blood after it has received
the influence of the air at the surface, have a bright scarlet hue,
and unite in forming the umbilical vein of the chick. Hence it is

406 COMPARATIVE PHYSIOLOGY.

evident that this membrane performs a function analogous to that
of the placenta in mammalia, and to that of the future air-cells of
the lungs, or, in other words, that it is the organ of embryonic
respiration. The chick is nourished by the matter of the yolk,
which is partly absorbed by yellow vessels {vasa vitelli lutea)
having a fringed appearance, and flocculent extremities, floating
in the yolk, and partly by the direct passage of this matter into
the intestine by means of a canal of communication, called the
ductus vitello-intestinalis. The white of the egg also gradually
disappears, being absorbed into, and mixed with the yolk. Towards
the latter periods of incubation, the whole of the yolk-bag is taken
into the abdomen, and soon disappears. On the twenty-first
day of incubation, the chick, being fully formed, breaks the shell
which confines it, and enters into the world ; for which temporary
purpose it is provided with a hard beak, which is afterwards lost.

2. Peculiarities in particular Families and Genera of Birds.

1021. The shades of difference in the anatomy of each organ
in individual genera and species of birds, are exceedingly numerous,
and to enter into their detail would far exceed the limits within
which we are obliged to confine ourselves in this treatise. We
must not, however, pass over some of the most remarkable
differences which offer themselves to our notice in a few families
of birds. Amongst these none are more singular than those
presented by the tribe of the brevipennes of Cuvier, comprehending
the ostrich and the cassowary. These birds not being intended
for flight, have very imperfectly formed wings ; the sternum
exhibits no carinated figure, but presents a plane and uniform
surface, being destitute of an inferior spine ; the pectoral muscles
of the hinder extremity, on the contrary, are very large and
powerful. The furcular bone exists only in a rudimental state.
The pelvis of the ostrich differs from that of all other birds in
being closed below by the complete junction of the ossa pubis.
The coeca in this bird are furnished with a remarkable spiral
valve. The feathers are also exceedingly peculiar ; but as this
subject belongs rather to the external characters, we cannot dwell
upon it here.

1022. The same consideration prevents us from dilating on
the varieties in the structure of the bill, and of the toes, which
offer to the naturalist abundant topics of interesting inquiry. We
shall only remark that the cellular bills, which are of such enor-
mous size in the levirostres, have free communications with the
air cells subservient to respiration, and may therefore be auxiliary
to that function.

1023. The tongue of the woodpecker is provided with a sin-
gular apparatus for darting it forwards with great rapidity ; this

REPTILES. 407

is effected by a long cartilaginous band, which passes completely
over the top of the craniunn, and is fixed to a groove on the right
side of the upper jaw.

Sect. III. — Comparative Physiology of Reptiles.

1. Reptiles in General.

1024. The class of reptiles comprehends all those vertebrated
animals which breathe atmospheric air by means of lungs, but
which are cold-blooded. This latter quality is a consequence of
the partial extent of their respiration, the heart being so con-
structed as to transmit to the lungs only a portion of the circu-
lating blood, and the remaining part being again sent into the
arterial system of the body without having been exposed to the
,.action of the air. Reptiles are distinguished by the negative
characters of being destitute of either hair or feathers, and having'
no mammffi, organs for which there appears to be no occasion,
in consequence of these animals being oviparous. The limited
degree in w^hich their blood is oxygenated appears to have a
considerable influence on the whole condition of their vital func-
tions. Not only is the temperature of the blood scarcely different
from that of the surrounding medium,* the actions of life seem
to be more sluggish and torpid, and the muscular powers less
energetic ; their sensations are more obtuse, and in cold climates
they pass the winter in a state of torpor. The comparative
smallness of the pulmonary system of vessels, and the less extent
of the surfaces of the air-cells of the lungs, render them less
dependent on respiration than warm-blooded animals; hence
they bear submersion under water for a considerable time with
impunity, although, if the interruption to respiration be too long
continued, they ultimately perish, with as much certainty as any
of the mammalia would do under similar circumstances.

There is ground for believing, according to Geofiroi St. Hilaire,
that crocodiles and turtles possess, in addition to the ordinary
pulmonary respiration, a partial aquatic abdominal respiration,
effected by means of two channels of communication which have
been found to exist between the cavity of the abdomen and the
external surface of the body, and also that some analogy may be
traced between this aquatic respiration in reptiles, by these ^jen-
toneal canals, and the supposed function of the swimming bladder
of fishes, hereafter to be described, in subserviency to a species
of aerial respiration.

* The temperature of animals of this class has been shown by the experi-
ments of Dr. Davy, Tiedemann, Czermack, and Wilford, to be in general
two or three degrees higher than that of the surrounding medium. It par-
takes, however, of the vicissitudes of temperature in that medium.

408 COMPARATIVE PHYSIOLOGY.

1025. As their vital functions do not require for their perform-
ance any elevated temperature, so we find reptiles destitute of
those appendages to the integuments,, such as hair, wool, or
feathers, which in the other classes retain the warmth of the body.
Their brain is very small, compared with the rest of the nervous
system, being less necessary for the exercise of the vital actions.
The parts immediately instrumental in sensation are less con-
centrated in a particular spot, but would appear to be more
diffused over the spinal cord and ganglia. Thus they not only
continue to live, but even exhibit motions which have the sem-
blance of being voluntary, though probably not so in reality, long
after the loss of the brain, or even of the entire head. In like
manner the irritability of their muscles is retained for a much
longer time, after they have been separated from the body, than
in the case of warm-blooded animals. The heart, when removed
from the body, still continues to beat for several hours ; and the
body, thus deprived of its heart, may still possess the power of
voluntary motion, in consequence of the continuance of a species
of obscure circulation, which is carried on in the capillary system
of vessels.

1026. Reptiles present a much greater variety of forms and of
structures than is met with in any other class of vertebrata. The
characters of the orders are derived principally from the form
of their organs of progressive motion. These orders are four in
number, namely, chelonia, sauria, ophidia, and batrachia.

2. Chelonia.

1027. This order comprehends turtles and tortoises, animals
whose skeleton presents a trunk composed of two large plates of
bone, the one derived from an expansion of the dorsal vertebra
and ribs, the other from a corresponding expansion of the sternum ;
these are united at the edges, and form a complete case for the
thoracic and abdominal viscera, leaving apertures in front for
the head and neck, together with the fore legs, and behind for
the hind legs and tail. This arrangement produces a singular
reversal of the positions of the scapula, the pelvis, and the muscles
attached to these bones, all of which, instead of being placed
externally, are situated in the interior of the ribs. The humerus
is remarkably curved, especially in the tortoise, where it has
nearly the form of a semicircle. The radius and ulna are distinct
from each other ; the carpus and phalanges are short and stunted,
forming a compressed sort of hand. The vertebrse of the neck
and tail are the only parts of the spinal column which are move-
able upon one another.

1028. The cavity in which the brain is contained is very
small compared with the size of the skull, the greater part of

REPTILES. 409

which consists of the bones surrounding the orbit, and giving
attachment to the large muscles that move the jaw. There are
no teeth, and the horny coverings of the jaws has some resem-
blance to a horse's hoof in the mode of its connexions with the
bones. The tongue is short, and covered with villi, which extend
also down the ossophagus ; their points are all directed towards
the stomach, so as to prevent the return of the food when it is
once swallowed. The stomach is simple in its structure ; the
intestinal canal of moderate length ; its inner membrane presenting
only longitudinal folds, together with innumerable villi, which
are more thickly set in the upper part of the canal than in the
lower; there is no coecum, but occasionally small processes, or
appendices epiploicas, are attached to the outer membrane. The
urinary bladder is exceedingly capacious. The lungs are volu-
minous, and are contained in the same cavity as the abdominal
viscera. The air-cells are very large, and the general texture of
the lungs is loose. Respiration is performed entirely by the
muscles of deglutition ; the animal in fact closes its mouth, and
swallows the air received from the nostrils, which is thus poured
down into the trachea, the os hyoides being alternately raised
and depressed. The liver is divided into two round irregularly-
shaped masses.

1029. The heart has two auricles, separated by a complete
septum, the one receiving the blood from the venas cavEe, the
other from the pulmonary veins. The ventricle into which these
veins pour their contents is single, but has two chambers of
unequal size, which communicate together, so that the blood
received from the lungs is more or less mixed Math that returning
from the body in the systemic circulation ; and it is this mixed
blood which is sent through the aorta. The pulmonary artery
is merely a branch of the aortic system.

1030. In the internal ear, we find a tympanum, Eustachian
tube, and semicircular canals, together with ossicular, and also
stony concretions in the vestibule. The eye has a bony ring at
the anterior part of the sclerotica, as in birds. There are large
lacrymal glands, and a very moveable membrana nictitans.

3. Sauria.

1031. The various animals included in this order, or the tribe
of lizards, have a heart with two auricles, with generally four
feet, and a scaly integument. They are always provided with
teeth, and with nails; there is invariably a tail. The ribs are
very moveable, and their motions are subservient to respiration.
The lungs are long and vesicular, extending far into the abdominal
cavity.

35

410 COMPARATIVE PHYSIOLOGY.

1032. The crocodile may be taken as an example of this order-
Its jaws are of immense size. The upper jaw consists of a large
intermaxillary bone, which is immoveably joined with the skull,
although the animal, in opening the mouth, appears to raise it
independently, a circumstance which misled the older naturalists
into the belief, that it was really moveable. There is an os quad-
ratum as in birds. The sternum extends to the abdomen, and
consists of seven pair of cartilaginous arches, to which ten ribs,
not however reaching to the spine, are attached. There are no
clavicles. The tongue is thick and flat, and attached very near
its edges to the jaws, so as not to be easily perceived.

The teeth are of the simple conical kind, chiefly adapted to the
prehension and retention of the food ; and each tooth when worn
is replaced by a fresh one, which grows underneath it ; a suc-
cession which takes place several tir|ies during the hfe of the
animal.

The oesophagus has the shape of a funnel, and leads to a stomach
which resembles that of granivorous birds, in the thickness of its
coats, and the approximation of its two apertures. The liver has
two distinct lobes. There is no urinary bladder. The single
ventricle of the heart is divided into three compartments, which
communicate together ; there is one cavity belonging to each
auricle, and an intermediate cavity, into which the blood from the
two others is poured, and where the intermixture of the carbonized
and oxygenated portions is made. There is an external meatus
of the ear, which may be voluntarily closed by a species of lips.
Ossicula auditus are found, as well as stony concretions in the
vestibule. In the other kinds of lizards, the tympanum is on a
level with the integuments, and there is no external meatus. A
membrana nictitans is found in the eye. The area of the section
- of the cavity containing the brain does not occupy the one-
twentieth part of that of the whole head.

1033. The chameleon has comparatively a large head ; but
its brain is only of the size of a pea. Its lungs have numerous
projecting processes. The tongue is constructed in a manner
which bears some analogy to that of the woodpecker in the
mechanism by which it is darted forwards to a considerable
distance from the head, and suddenly retracted. It terminates
in a sort of club, which is moistened with a glutinous secretion,
for seizing flies and other insects, and its upper surface is hol-
lowed. The eyes project considerably from the head, and admit
of being turned very freely in their orbits. The most singular
circumstance in the constitution of this animal, is the change of
colour of its skin under various circumstances of temperature or
excitement. These changes appear to be connected with the
variable activity of respiration, which quickly influences the

REPTILES. 411

colour of the blood circulating under the very transparent skin ;
and which is visible to a greater depth, in consequence of the
ample extension of the lungs along the sides of the abdomen :
when the lungs are inflated, indeed, the whole body appears as
if it were semi-transparent.

1034. The draco volans is a remarkable instance, in this tribe,
of the subserviency of the ribs, which are expanded on each side
so as to support a thin membrane resembling a wing, to the pur-
poses of progressive motion.

4. Ophidia.

1035. Serpents, being wholly without feet, are constrained to
crawl upon the surface of the earth, and are, therefore, more
especially entitled to the appellation of reptiles.

1036. 'Their skeleton presents us with the simplest possible
condition of the vertebral type ; for it consists merely of a simple
spinal column descending from the head, and furnished only with
ribs. There appears, at first sight, to be no vestige either of
sternum, of scapula, or of pelvis; the body of each vertebra is
articulated by a convex surface, which is received into a concave
surface of the next. The number of vertebras is often exceed-
ingly great ; being sometimes as many as three hundred. The
number of the ribs coi responds with that of the vertebrse, and
when acted upon by their muscles, they assist in the progressive
motion of the animal, by pressing on the gi'ound, in succession,
like imperfect feet. In the rattle-snake, the last vertebrae of the
tail are broad and covered with the hollow pieces which com-
pose the rattle. Obscure rudiments of pelvic bones were found
by Mayer to exist in the anguis fragilis, the anguis ventralis, and
the typhlops crocotatus ; and it is probable that they may be
discovered in most reptiles of this order. Some serpents have
external claws, which may be considered as rudiments of feet.
In others they exist concealed under the skin ; and in others,
again, there are cartilaginous filaraents'which Mayer regards as
rudimental claws, connected with a series of small bones, which
appear to be the rudiments of the hones of the lower extremities.

1037. The upper jaw-bone is detached from the rest of the
skull, and admits of great latitude of motion. In most species
of serpents, the jaws are so constructed as to render the mouth
capable of great dilatation, and to enable it to receive objects
even larger than the animal itself, and a corresponding power of
dilatation exists also in the oesophagus.

1038. Serpents that are not venomous have usually four max-
illary bones in the upper jaw, beset with small teeth, placed in
two rows, widely separated from one another. The external
row is not found in venomous serpents, but in their place large

412 COMPARATIVE PHYSIOLOGY.

tubular fangs are met with, which are the terminations of the
ducts from the poison bags, and which convey the venom into
the wound inflicted by the tooth. This poison is secreted by
glands, situated below the eyes, and surrounded by very strong
muscles.

1039. The stomach of serpents can scarcely be distinguished
from the lower extremity of the oesophagus, and is very short,
compared with the great length of that canal. There is no uri-
nary bladder, the ureters opening at once into the cloaca.

1040. The heart has generally two auricles, though in some
genera only one is met with; the ventricle is always single. The
lungs consist of a membranous cavity, on the sides of which there
are cells ; their form is exceedingly elongated. The lungs on
one side is often much smaller than the other. The tongue is
long and slender, and forked at the extremity ; its root is con-
tained in a kind of sheath, whence it can be protruded and re-
tracted at pleasure. There is .properly no tympanum belonging
to the ear; but the long process of an ossiculum is found under
the skin, and is connected with a tympanic bone.

5. Batrachia.

1041. The batrachia, (so termed from the Greek name of the
frog, which may be assumed as a type of this order,) have a
heart consisting of only a single auricle and ventricle; when
arrived at maturity, they are possessed of two lungs ; but in the
earlier stages of their growth, they are wholly aquatic animals,
and breathe like fishes by means of gills, which are affixed to
the sides of the neck, by cartilaginous arches connected with the
OS hyoides. Such is the condition of the tadpole, which is the
young of the frog. The aorta, on its exit from the heart, sends
branches to each of the gills ; whence the blood is collected by
corresponding veins, that unite near the back to form a single
arterial trunk, which again ramifies and distributes the blood to
every part of the body, including the rudimental lungs, which
are not yet developed. In the process of the transformation of
the tadpole into the frog, though these branchial arteries become
obHterated, yet the vessels which supply the lungs remain, and
are afterwards the channels of pulmonary respiration.

1042. In the skeleton of the frog, in place of ribs, small slender
cartilages affixed to the extremities of the transverse processes
of some of the vertebras, which in the dorsal vertebrce are very
broad. The spine is short, and terminates behind in a straight
sacrum, which is impacted into the fork-shaped or innominatum.
The scapula is thin and flat ; and, together with the clavicles, are
united to the sternum; but as there are no ribs, these, with the
bones of the anterior extremities, are detached from the rest of

REPTILES. 413

the skeleton. There are properly no teeth ; but the margin of
the jaw is serrated. The urinary bladder exists, and is even
sometimes double.

1042. Tlie lungs do not collapse on opening the chest ; this
arises from the power which the frog possesses of distending
them by the muscles of the mouth ; the respiration being con-
ducted on a plan similar to the one which has been already
described in the tortoise (§ 1027). Many species, as the pipa,
have the vocal organs much developed. The tongue is of great
length, and doubled back in the mouth ; it is thrust forwards to a
considerable distance in seizing its prey, and retracted with
great rapidity. There is no external nieatus to the ear ; but the
membrana tympani is external, and appears as part of the integu-
ment."^ The Eustachian tube opens at the fauces by an expanded
mouth. There are two ossicula auditus ; and the vestibulum
contains rudiments of the calcareous bodies met with in other
reptiles, and still more remarkably in fishes. The eye has two
fleshy eye-lids, and also an internal nictitating membrane, which
is transparent and horizontal in its direction.

1043. The salamander is constructed on the same model as
the frog, with regard to all its internal organs ; but it is provided
with a tail. Its ear has no tympanum ; but there is merely a
cartilaginous plate laid over the fenestra ovale ; there is no third
eye-lid. The skeleton presents small rudimental ribs, but no
sternum. This animal is remarkable for the power it possesses
of reproducing the parts which have been mutilated, such as
entire limbs ; and even the eyes. In the newt, or aquatic sala-
mander, the lungs have numerous processes, as in the chameleon,
which terminate behind in an elongated bladder.

Muller has lately discovered that the frog, and several other
animals of the same family, are provided with large receptacles
for the lymph, situated immediately under the skin, and exhibit-
ing distinct and regular pulsations, like the heart. The use of
these lymphatic hearts is evidently to propel the lymph in its
proper course along the lymphatic vessels. Their pulsations do
not correspond in time with those of the sanguiferous heart; nor
do those of the right and left sides take place at the same mo-
ment ; but they often alternate in an irregular manner.*

1044. The proteus anguinus, the siren, and the amphiuma, are
remarkable for possessing both gills, Hke the tadpole, and lungs
like the frog. They are, accordingly, adapted for living both in
water and in air; and are the only animals that can strictly be
said to be amphibious. The eye of the proteus is completely
covered by the integuments, as it is in the mus typhlus.

* [Dr. J. J. Allison, of Philadelphia, has also observed these pulsating
organs in the tadpole, the frog, in the sauria, ophidia, and chelonia. Amer.
Journ. of the Med. Sciences, for Aug. .1838.] ^

35*

414 COMPARATIVE PHYSIOLOGY.

Sect. IV. — Comparative Physiology of Fishes.

1045. Fishes are vertebrated animals with red blood, breathing
by naeans of water applied to the gills, or hranchice, which in
them supply the office of respiratory organs. Their powers of
motion are adapted to progression through the medium they in-
habit. This design is conspicuous in the form of their bodies,
the great muscularity of the tail, the shortness of their members,
which are expanded into fins, and the coverings of the body,
which are smooth and scaly. The oxygenation of the blood,
being effected solely by means of the atmospheric air contained
in the water they respire, takes place only to a small extent;
hence the temperature of the body in fishes is not sensibly raised
above that of the surrounding medium, and these animals display
little energy either in their vital or their sensitive powers. The
brain, accordingly, is of small size, and the organs of the external
senses but little developed ; they scarcely possess any organs
calculated to convey accurate impressions of touch. Nature has
denied them any vocal organs. The circumstances in which
they are placed would appear to give little exercise to the sense
of hearing ; and the deep recesses of the ocean, where darkness
eternally reigns, aflx)rd as little to that of sight. No lacrymal
organs are wanted by animals immersed in a liquid medium.
The voracity with which fishes devour their prey, leaves them
scarcely any opportunity of discriminating its taste ; and their
tongue is not adapted by its structure for receiving the impres-
sions of this sense. Neither can the sense of smell be exercised
in the same degree as in animals respiring atmospheric air,
through which odorous emanations are so extensively and so
rapidly diffiised. Exclusively occupied in the two great objects
of animal desire, that of food and of progeny, all their movements
appear exclusively directed to these ends ; they appear insuscep-
tible of attachment, and incapable of any but the lowest degree
of intellectual development.

1046. The osteology of fishes presents a very complicated
subject of study, not only from the great number of pieces of
which their skeleton is composed ; but also from the great
variety of forms exhibited in the different genera and species of
this class. Fishes, with regard to their skeleton, admit of a great
primary division into the cartilaginous and osseous. The former,
or the chondrojjterygii, possess no real bones, but merely carti-
lages, having the form of bones, of a homogeneous and semitrans-
parent substance, sometimes, however, as in the rays and sharks,
presenting on its surface small calcareous granules, very closely
compacted together. In a few fishes arranged under this division,
as the sturgeon, and the chimera, we meet with several true

FISHES. 415

bones in the head and shoulder, while the rest of the skeleton

is cartilaginous. Even among the strictly osseous fishes, the
density of the bones of some species is inferior to that of others,
the calcareous substance, or phosphate of lime, being deposited
in fibres, or layers, in the cartilage which serves as the basis of
the bone. The truly osseous fishes have bones as hard and as
dense as other vertebrated animals ; they are even more homo-
geneous in their texture, and present no appearance of pores or
of fibres, as are seen in the bones of the mammalia. We never
find in them any medullary cavities.

1047. The spinal column consists of dorsal and caudal verte-
brae only, those of the neck and sacrum being absent. The bodies
of vertebras have always a conical depression on both their sur-
faces; the double cone thus left by the junction of their margins
being filled with a gelatinous iiuid. These cavities generally, in-
deed, communicate together throughout the whole spinal column
by apertures in the centre of each vertebra, at the apices of the
cones. In the lamprey this opening is so wide, as to reduce the
vertebral column to a mere series of rings, traversed from one
end to the other by a hgament. The spinous processes are
usually very long, and their roots form a canal for the passage
of the spinal cord. Spinous processes are also frequently found
on the opposite or abdominal side of the vertebrae ; and these
also form a canal for the protection of the aorta, which is admitted
through it. The ribs are attached each to a single vertebra, and
are frequently furnished with appendices adhering to them at
one end, whilst the other end is embedded in the muscles.

1048. The fins of fishes do not present much analogy with the
bones of the extremities of quadrupeds, although such analogies
have been sought with much eagerness. The fins are composed
of parallel bones called rays, which are connected with others,
called by Cuvier interspinal hones, and by Meckel accessory
spinal apophyses. The sternum, where it exists, is composed of
a series of bones, of various figures in different fishes ; but which
unite the lower extremities'of the ribs. In the pectoral fin, or
anterior extremity, are found bones somewhat analogous to the
two bones which compose the scapula of reptiles ; a styloid bone
composed of two pieces, analogous perhaps to the clavicle and
coracoid bone. The two bones corresponding to the radius and
ulna are connected with a row of ossicula representing the carpus,
and which support the rays of the fin itself

1049. The posterior extremity, or base of the ventral fin, is
composed of four bones, which may be considered as a pelvis;
but these support the rays, without the interposition of any bones
comparable to the femur, tibia, or tarsus.

1050. The bones of the head are exceedingly complex, and
the mere enumeration of them would require a more lengthened
discussion than can here be afforded. The bones composing the

416 COMPARATIVE PHYSIOLOGY.

jaws, namely, the maxillary and intermaxillary, are not only
moveable on the skull, but also on each other. The palatine, the
pterygoid, and the tympanic bones, have also independent motions.
A row of suborbitar bones also exists, different from what is met
with in any other class. To the bones of the skull are joined also
the opercular system of bones, which protect the gills, and are
subservient to the motions which open and close them during
respiration. The proper bones of the skull are placed in the midst
of these four systems, and are very similar to those of reptiles,
containing a receptacle for the brain, another for the labyrinth of
the ear, and others for the eyes, and for the nasal cavities. The
OS frontis is composed of six f)ieces ; the parietal of three ; the
occipital of five; each temxporal of two; and the sphenoidal of
five. Much ingenuity has been lavished in the attempt to discover
analogies between these bones and the parts which compose the
skeleton in the other classes of animals. Thus the opercular bones
have been supposed to correspond to the ossicula auditus of
mammalia ; a notion which, although ably supported by Geoffroy
St. Hilaire, may perhaps at first sight appear extremely fanciful
and hypothetical, and which Cuvier represents as utterly un-
founded.

1051. The teeth of fishes exhibit almost every possible variety
in form, number, and situation. They may be distinguished,
according to their position, into intermaxillary, maxillary, man-
dibular, vomerian, palatine, pterygoid, lingual, branchial, and
superior and inferior pharyngean. Some fish have almost all
these denominations of teeth ; others a smaller number, and a few
genera of fishes are entirely destitute of teeth. The teeth are
generally of a conical and incurvated form, like so may hooks ;
sometimes the points are so small and united as to resemble a
brush or file ; others are round, or club-shaped ; others present
more flat surfaces, like a mosaic pavement. Their structure is
always simple, being formed by a single pulpy membrane, which
afterwards ossifies ; and is, in process of time, replaced by a new
tooth. This successive renewal of the teeth of fishes is continued
during the whole period of their lives. The degree of mastication
given to the food depends, of course, on the form and situation of
the teeth.

1052. Deglutition is assisted by means of a membranous velum
placed behind the anterior teeth. There is no appearance of
salivary organs ; unless we regard as such a soft and highly
vascular organ found in the palate of the carp. This organ is
highly irritable, and swells in a remai'kable manner on the ap-
plication of any stimulus; it perhaps performs the function of an
organ of taste.

1053. The oesophagus is generally very short and capacious ;
it is continued into the stomach without anv marked line of se-

FISHES. 417

paration; and part of the food is often retained in the oesophagus
undigested, until room can be made for it in the stomach. In a
few fishes, the parietes of the stomach are muscular, so as to
entitle it to be considered as a gizzard. The intestinal canal
is generally very short; its internal coat is more or less villous;
there is never any coecum ; the only distinction between the dif-
ferent portions of the canal is formed by a valve near its extre-
mity ; but this is not succeeded by any dilatation.

1054. A remarkable structure is met with in the intestines of
rays, sharks, and sturgeons ; which present a spiral valve, or
duplicature of the inner coat, running nearly the whole length of
the canal. A great number of blind pouches, or appendices
pyloricce, as they are called, from their being more numerous in
the beginning of the intestine, are generally found ; their office
appears to be to secrete a quantity of mucous fluid, probably
analogous to saliva, or to the pancreatic secretion. In the stur-
geon, these are short and united by vessels and cellular substance
into one mass, which union becomes more close and compact in
the rays and the sharks, constituting a real conglomerate gland,
having a single excretory duct.

1055. In many fishes, namely, in the ray, shark, sturgeon,
lamprey, and salmon, there are two passages opening outwards
from the general cavity of the abdomen, at the sides of the
termination of the intestine. The use of these passages is un-
known.

1056. The liver is of considerable size, and placed more on
the left side ; great variety exists with regard to its shape and
the number of its lobes in different fishes : its texture is softer
than in quadrupeds and birds, and it contains a large quantity of
oil. There is almost always a gall-bladder of greater or smaller
size. The hepatic ducts are sometimes very numerous, and are
successively joined to the cystic ducts. The mesentery is incom-
plete ; and is often prolonged into folds containing fat, which
folds may perhaps be considered as corresponding to an omentun).
Although the lacteals are numerous, there are no lymphatic glands
in the mesentery.

1057. The lymphatic vessels are very distinct in other parts
of the body. Fohman has succeeded in injecting them in the
gills. Several fishes have a urinary bladder, which is situated
behind the rectum ; in other instances there is merely a common
cloaca, into which the ureters terminate. The kidneys are
more voluminous than in any of the preceding classes, and are
often joined together posteriorly ; there are no suprarenal glands.
The spleen is constantly present, and occupies various situations
in the abdomen.

1058. The circulation in fishes is conducted upon a very
different plan from what it is in reptiles. There is, as in warm-

418 COMPARATIVE PHYSIOLOGY.

blooded animals, one complete circulation for the body in general,
or a systemic circulation; and another for the organs of respi-
ration ; and besides this, a partial circulation for the hepatic
system of organs ; but what more particularly characterizes this
mode of accomplishing that function is, that branchial circulation
is the only one which is effected by a muscular apparatus, that is,
by a heart. The systemic circulation has no such organ for
communicating to it a mechanical impulse.

1059. The muscular apparatus for carrying on the circulation
in fishes consists of four cavities, namely, the sinus venosus, the
auricle, the ventricle, and the bulbus arteriosus; the three latter
are inclosed in the pericardium, and may be said to constitute
the heart, which is situated underneath the pharyngeal bones,
and between the bronchial arches. The blood returning from
the veins of the body and head, is collected in the sinus venosus,
which transmits it by a single opening into the auricle, valves
being interposed at the entrance. The auricle discharges its
contents into the ventricle, which again propels it into the bulbus
arteriosus, whence it proceeds along the bronchial arteries to be
•distributed on the gills. Thence it is returned by the bronchial
veins, which unite near the spine to form a single arterial trunk
corresponding in its oifice to the aorta, and distributing the blood,
by a succession of ramifications, to every part of the body. The
veins from the digestive organs are collected into the vena portaj*,
which as usual ramifies through the liver ; and there appears
also, from the observations of Mr. Jacobson, to be in addition a
lesser venal circulation, independent of either of the former, and
analogous to what has already been observed in birds.

1060. The vivifying influence of the air contained in the water
which is applied to the gills of fishes, is quite as necessary for
the continuance of their vital functions, as that of atmospheric
air is to animals of the preceding classes; and fishes perish with
equal rapidity as mammalia, when their natural element is with-
drawn. This happens whether the water has been deprived of
its air by boiling, or whether the absorption of air from the
atmosphere is prevented by a body capable of intercepting it,
placed on the surface of the water. It appears from the re-
searches of jMr. Ehrmann, that some fishes, as the cobitis, swal-
low air, which passes along the intestinal tube, where it loses
oxygen and acquires carbonic acid. Fishes taken out of the
vs^ater are killed not so much from the want of oxygen, as in con-
sequence of the drying of the branchias, which impedes the circu-
lation of the blood through them. The water is taken in at the
mouth, and, after acting on the gills, which are filamentous organs,
aflixed in rows to the branchial arches, and protected by the
operculum, is discharged through the branchial openings below.
In the cartilaginous fishes there are several openings provided
for the outlet of water, at the side of the head.

FISHES. 419

1061. Most fishes possess a large bladder full of air, called the
swimming bladder, placed immediately underneath ihe spinal
column; it communicates witii the oesophagus, and sometimes
with the stomach, by a canal, called the ductus jmeimaticus. In
the carp, there are valves in this canal which only allow of the
passage of air out of the bladder. In many fishes, especially in
flat fish, no such air-bladder exists. Its figure is very various ;
its cavity is generally simple; but it is sometimes divided by a
number of partitions. A glandular body is met with in the coats
of this bladder, which probably secretes the air. The obvious
intention of this instrument is to give greater buoj^ancy to the
fish when the air is present, and to allow of a sudden increase of
specific gravity by its escape. In by far the greater number of
fishes, however, the air-bladder has no outlet whatever. In
many fishes it is called the sound, and furnishes the best kind of
jelly. Isinglass is the product of the air-bladder of the sturgeon.
The air it contains is usually nitrogen gas, whh a small propor-
tion of oxygen and carbonic acid gases. The swimming bladder
of fishes is regarded by many of the German physiologists as
having some relations with the function of respiration ; and as
being the rudiment of the pulmonary cavity of land animals; the
passage 'of communication with the oesophagus being conceived
to represent the trachea. (See § 1022.)

1062. The brain of fishes is remarkable for the smallness of
its size, not only as compared with the total bulk of the animal,
or with that of the nerves connected with it, but also with the
cavity of the cranium, which it does not by any means fill, the space
left being occupied by an oily secretion, and by loose cellular
texture. The disparity is less observable in young fish ; for it
would appear that the growth of the brain does not keep pace
with that of the rest of the body.

1063. The several parts which compose the brain of fishes are
more detached from one another than in the higher classes, and
are placed in a consecutive series. The foremost lobules give
rise to the olfactory nerves, or rather appear as the bulbous
enlargements of the origin of these nerves. The next in succes-
sion are solid lobes, which give origin to the optic nerves ; be-
hind these we find larger lobes containing a ventricle, wnth a
striated eminence, at the back part of which are four smaller
tubercles corresponding to the corpora quadrigemina. Behind

.. these is the single lobule of the cerebellum, and below are two
inferior lobes. The optic nerves pass before these lobes, and
always decussate in their course to the orbits. Between these
nerves, and in front of the inferior lobes, is the pineal gland.
Behind the cerebellum are also two lobes, which may be termed
the posterior lobes. There is, however, much difterence of
opinion as to the parts in the human brain to which these several
portions of the brain of fishes are analogous.

420 COMPARATIVE PHYSIOLOGY.

1064. Great variety is met with in the size, position, and direc-
tion of the eyes of fishes. In general, however, they are large.
There are neither eye-lids nor lacrymal organs, and the globe of
the eye has but little mobility. In the ray and shark tribes, it is
supported oa the end of a moveable cartilaginous pedicle, articu-
lated with the bottom of the orbit. The anabliss has the cornea
divided into two by an opaque Hne, and two perforations exist in
the iris, but there is only one crystalline lens, vitreous humor,
and retina. The crystalline lens is completely spherical, and of
great size^ so as to leave but little space for the vitreous humor,
it is composed of concentric laminee, which are of greater density
■as they approach the centre. A falciform ligament, commencing
■at the entrance of the optic nerve, following its curvature down-
wards, and containing vessels and nervous filaments, is observa-
ble; its extremity is attached to the capsule of the crystalline
lens. In some fish this ligament has a black colour, like the
marsupium of birds. The sclerotica is often supported by osseous
■or cartilaginous plates, as in birds. The pupil is incapable of
altering its dimensions ; in the rays and flat fish, its border is
fringed with palmated processes. The cornea is nearly flat^ and
there is but httle aqueous humor.

1065. There is found in the eyes of fishes a peculiar body, the
memhrano vasculosa Halleri, having the shape of a horse-shoev
situated between the internal layer of the choroid coat, or tunica
Ruyschiana, and the middle layer ; it gives origin to a vascular
membrane, called the campanula, which proceeds towards the
lens, and has some analogy with the marsupium.

1066. The gastrobranchus appears to be wholly destitute of
any organ of vision. In the blind murena, no trace of an eye
can be perceived externally, but a rudimental organ exists beneath
the skin.

1067. The ear of fishes consists only of the parts belonging to
the labyrinth ; and these organs are generally suspended in a
cavity of the cranium, which is a part of that in which the ence-
phalon is contained. The two vertical semi-circular canals are
suspended to the top of the skull by a vertical ligament. The
oily or mucilaginous fluid which surrounds the brain has free
access to the cavities which surround the membranous labyrinth.
The three semicircular canals are dilated into ampuUee, which
receive the filaments of the auditory nerve. There is an appen-
dix to the sinus medianus, or principal vestibular sac, termed
the utricle, and a smaller one termed the cyticule. The hard
calcareous bodies consist of one in each of these cavities, being
three in number. There is no part corresponding to the cochlea,

1068. In the ray there is a spiral tube, wholly within the skin,
which terminates in a kind of finestra ovale, and appears to be
the rudiment of an external meatus.

FISHES. 421

1069. Many fishes present the extraordinary phenomena of the
development and accumulation of electricity in large quantities,
which they have the power of discharging at pleasure, so as to
give strong shocks to animals coming in electric contact with
them, or forming part of the circuit of the discharge. This effect
is often so powerful as to benumb and paralyse their assailants.
The electric fishes which are known to possess this power in a
high degree are the electric ray {raia torpedo), the electric eel
[gymnotus electricus), and the silurus electricus, or malapterurus
electricus. The first of these are met with principally in the
Mediterranean Sea ; the second in several rivers in South Ame-
rica ; and the last in the Nile and Senegal rivers. Other fishes,
however, are known to be electrical, although they have been
less studied than those already mentioned, such as the rhinobatus
electricus, trichinus electricus, and teirodon electricus.

1070. The electrical organs of the torpedo consist of a great
number of five or six-sided prisms, placed on each side of the
head perpendicularly to the surface, and occupying the whole
thickness of the animal. Each prism consists of a tube, with
membranous sides, surrounded with nerves and blood-vessels, and
containing a vast number of extremely thin plates, parallel to one
another, but in a transverse position; the intervals are filled with
a gelatinous fluid. Three large branches of the par vagum, and
one branch of the fifth pair of nerves, are distributed to these
organs on each side. The electrical apparatus of the gyinnotus
and silurus are disposed somewhat differently ; they are two in
number on each side, and extend the whole length of the fish
from the head to the tail. One of these is situated deeply, and
the other superficially ; the two being separated by a membranous
partition, and each being formed of horizontal plates distant one-
third of a line from one another, with septa passing perpendicu-
larly between them, and directed fi'om within outwards, and a
fluid occupies the intervening spaces. Their nerves are derived
from the intercostals, and are 224 in number.

1071. The identity of the agent called into playby these organs
with electricity is beyond all doubt. The same bodies which
conduct or intercept the transmission of the latter, have the same
property with regard to the former ; and shocks are propagated
through a chain of several persons, when those at the extremities
of the chain touch the fish. Electric sparks have been obtained
by Walsh from the discharge of the gymnotus when passed
through a strip of tin foil gummed to a piece of glass and cut
through in the middle. Dr. John Davy* has obtained electro-
magnetic effects from the torpedo, by the test of the galvanometer;

* Phil. Trans, for 1833 and 1834.
36

422 COMPARATIVE PHYSIOLOGY.

and has also rendered needles naagnetic by the electrical discharge
from the fish.* '

1072. It appears that the power of producing these electrical
discharges is quite voluntary, and dependent on the nervous
influence; for it does not take place every time that the fish is
touched, and it wholly ceases on the destruction of the brain, or
the division of the nerves. The animal appears to have the power
also of determining the direction of the discharges ; and often,
when irritated, it refrains from giving shocks. The destruction
of the electric organ on one side does not interrupt the action of
the opposite organ. Dr. Davy states, that the dorsal surface is
charged with positive, and the ventral surface with negative
electricity, and that unless both surfaces be simultaneously touched,
no shock is felt ; and Matteuci and Colladonf arrived at the same
conclusion by experiments made with the galvanometer, as to the
direction of the electric currents. Electric fishes, when vigorous,
exert this power as strongly in the air as in the water. We are
quite in the dark with regard to the theory of these phenomena.
Matteuci imagines that the source of electric power in these fishes
is in the brain ; and that the purpose served by the complex
arrangement of parallel plates, with intervening fluid, which
composes the structure of the electric organs, is that of mere
accumulation, analogous to the property of the Leyden phial.

1073. What may be called the nasal cavities or nostrils of fishes,
are placed generally in front of the head, and their openings are
a valvular membrane or partition; behind this is found an elegantly
plaited membrane, disposed in semicircular folds, on which the
ramifications of the olfactory nerves terminate.

Sect. V. — Comparative Physiology of Mollusc a.

1074. The class mollusca comprehends all the variety of what
are commonly called shell-fish, together with the animals, such
as the slug, which resemble them in their anatomical character,
but which are not furnished with shells. Their comparative
anatomy has been studied M'ith great care and diligence by Cuvier,
whom chiefly we shall follow in our general description of this
class.

1075. The mollusca have neither articulated skeleton nor
vertebral canal. Their nervous system does not present a central
spinal cord, but merely a certain number of medullary masses,
dispersed in diflferent situations in the body, and of which the

* [See some observations by Dr Faraday on the electric conditions of the
Raia torpedo and Gymnotus electricus, in Lend. Med. Gazette, Jan. 26, 1839,
p. 647.]

f Seances de I'Acad. des Sciences, Oct. 1836.

MOLLUSCA. 423

largest, which may be designated the brain, is placed near the
oesophagus, where it is connected with a collar of nerves that
embraces that tube. The circulation is always double, like that
of fishes, that is to say, the pulmonary circulation is always
complete in itself, as well as the systemic. But the muscular
vt'ntricle, or heart, is not, as in fishes, placed at the commencement
of the former, but of the latter ; it impels the blood not into the
branchial arteries, but into the aorta. The blood is either white
or of a bluish colour ; and it contains less fibrin than that of
vertebrated animals. The veins probably perform the office of
absorbents.

1076. The muscles are endowed with great irritability, and
retain this property long after they are divided. They are
attached to different points of the skin, which is smooth and
moistened with a viscid liquor. The muscular actions produce
contractions and inflexions of the different parts, and elongations
of others, by means of which the animal is enabled to accomplish
different kinds of progressive motion, whether in water or on
land, without the aid of articulated members, or the advantage
of solid unyielding structures, Hke the bones of the vertebrated
classes. These movements, however, are necessarily less rapid
and energetic, and less perfectly executed.

1077. A leading characteristic of the structure of the mollusca,
consists in a muscular expansion, connected with the integument,
which envelopes all the viscera, and is hence denominated the
cloak or mantle. It assumes various forms in the different genera,
being sometimes contracted into a flat disc, at other times being
folded into a tube, or doubled into a sac, or expanded into the
form of fins or oars. Most frequently we find a calcareous secre-
tion formed on difl^erent parts of one or both of the surfaces of
the mantle, which hardens and forms a layer of shell. Succes-
sive depositions take place, occasioning the enlargement of the
shell in different directions; when the shell is wholly external to
the animal, it serves for its habitation and protection; this is the
case with the testaceous mollusca ; in others which have no such
covering, (or the naked mollusca,) there frequently takes place
an internal deposition of the same material, forming an internal
shell. The calcareous matter is always intermixed, when
deposited, with animal matter, which is sometimes in the form of
a distinct membrane, and which has frequently a shining or irri-
descent appearance, constituting the substance known by the
name of mother-of-pearl.

1078. Great variety exists in the organs of the digestive func-
tions, as will be seen by the examples we shall give in speaking
of the diflferent orders established in this class by Cuvier.

424 COMPARATIVE PHYSIOLOGY.

1. Cephalopoda.

1079. The various genera of sepise or cuttle-fish, are compre-
hended in this order.

In these animals, the mantle is folded so as to form a sac
enveloping all the viscera ; its sides being more or less extended
into fins. The head alone protrudes from the sac ; its form is
round, furnished with large eyes, and with long processes or
tentacula, flexible in every direction, endowed with great muscular
power, and having on the surface a great number of suckers, by
which they are capable of adhering with great force to the objects
to which they may apply them. These tentacula, or feet, are
employed by the animal in walking, which it does with the head
downwards; in swimmiing, which it executes with the head
turned backwards ; and also in seizing hold of bodies, for which
action they are well adapted. Between the basis of the feet is
placed the mouth containing strong horny mandibles, resembling
in their form the beak of a parrot. The excretions pass out
by a funnel-shaped aperture, situate at the mouth of the sac, and
near the head.

1080. The pulmonary organs consist of two branchise situate
within the sac, one on each side, and having the figure of a fern
leaf. The great vena cava, on arriving near them, divides into
two trunks, terminating in two muscular ventricles placed at the
base of the branchiae, for the evident purpose of propelling the
blood with more force into the branchial arteries. The branchial
veins corresponding to these arteries, unite in a third ventricle
situate near the bottom of the sac, and which sends the blood
forwards through the aortic system as usual. Thus there may
be said to be three separate hearts in the cuttle-fish, one aortic
and two branchial. The water respired enters at the open margin
of the mouth and passes out by the funnel-shaped aperture already
described.

1081. There is found a tongue, of which the surface is bristled
with sharp horny points ; the ossophagus is dilated into a crop,
and terminates afterwards in a gizzard, equally muscular with
that of a granivorous bird. To this succeeds a third stomach,
which is membranous, coiled into a spiral form, and receives the
bile by two ducts from the liver.

1082. A singular secretion is prepared by a gland in this
animal, of a deep black colour, resembling ink, which, when ef-
fused, darkens the surrounding water to a considerable distance,
and gives the animal an opportunity of escaping from its pursuers.
The brain is large ; a nervous ganglion surrounds the oesophagus.
The optic ganglions are very large ; and the nerves form plexuses
in the abdomen and in other parts. The eye is similar in its
conformation to that of the higher classes of animals ; but the

MOLLUSCA. 425

ear is constructed in a still simpler manner than that of fishes,
having neither simicircular canals nor external meatus, but con-
sisting merely of a membranous sac lodged in a cavity near the
brain, in which a small cretaceous body is contained.

2. Gasteropoda.

1083. The mollusca which have a shell consisting of a single
valve, compose a numerous order, a familiar example of which
occurs in the snail. The slug, on the other hand, belongs likewise
to this order, although it has no external shell. Mollusca of this
description are termed gasteropodous, because they crawl on a
flat disc placed under the belly; the back is covered with the
mantle, which is of greater or less extent, and secretes the shell.
The head comes out more or less from the mantle, under which
it is occasionally retracted, so as to be both concealed from view,
and protected from injury. A small number of tentacula, from
two to six, appear above the mouth, but do not surround it. The
eyes are exceedingly small, and sometimes adhere to the head,
sometimes to the base, or the side, or the extremity of the tenta-
cula ; but occasionally none are found. The position and struc-
ture of their respiratory organs varies in the different families of
this order; and they are always situated under the last turn of
the shell when this latter has, as is generally the case, a spiral
form ; and they receive the water either by a broad opening
under the mantle, or by a narrower aperture, and often through
a tube formed by the prolongation of the mantle, which is fre-
quently protected by an indentation or tubular process of the
shell. A further protection is often afforded by a flat, horny, or
calcareous plate, which closes the shell when the animal has
retired within it, and which is termed an operculum.

^084. Instead of branchrse, the pulmonary gasteropoda are
provided with cavities for the admission of atmospheric air, which
they respire in its gaseous /orm. These cavities are opened and
closed at the pleasure of the animal, the mechanism of their
respiration consisting in these movements.

The stomach and intestinal canal are of very various structure
in the different genera. In some, as the scyllsea, we find cutting
teeth implanted in the coats of the stomach itself; in the pleuro-
branchus there are four stomachs, like those of ruminant quadru-
peds. The aplysia is provided with a very capacious crop,
which leads to a muscular gizzard, armed, moreover, with a
number of cartilages of a pyramidal shape ; a third stomach suc-
ceeds to this, having its inner coat lined with sharp hooks ; and
a fourth, shaped like a coecum ; and the intestines are, besides,
exceedingly voluminous.

Many of the gasteropodus mollusca present the curious phe-

36*

426 COMPARATIVE PHYSIOLOGY.

nomena of the double hermaphrodite generation formerly adverted
to (§ 781.) Impregnation of the ova requires the union of two
individuals, the female organs of each receiving the male organs
of the other, and the fecundation being mutual. This is the case
with the helix and the lymneus.

3. Acephala.

1085. The acephalous mollusca, so named from their having
no head, have all the vital organs enclosed in the two folds of the
mantle, which shuts like a portfolio, leaving apparent only the
orifice of the mouth ; but in some cases the mouth is here pro-
longed in the form of a tube. In almost every case each of the
two sides of the mantle is covered by a valve of shell, so as to
constitute a bivalve molluscous animal ; in another tribe the shell
is multivalve. The brain is situated immediately over the mouth,
and consists of a certain number of small ganglions. The
branchise have almost always a laminated form, the plates, gene-
rally four in number, being covered with a net work of blood-
vessels. The mollusca of ihis order are unprovided with teeth,
the food brought by the water being received into the mouth,
and swallowed in its original state, whence it passes into the
stomach; sometimes there are two successive cavities perform-
ing the functions of the stomach; the intestine is of various
length. The liver surrounds the stomach,* and pours its secretion
directly into the cavity by several apertures.

1086. A large fleshy process, resembling in appearance a
tongue, and which has been compared to a foot, projects from
the body, and by the varied movements of which it is capable,
enables the animal to perform a slow progressive motion. Mus-
cles are also provided foreclosing the shell, and they generally
pass directly from one valve to the other ; sometimes there are
two muscles, but commonly only one. The valves are separated
by the force of an elastic ligament placed at the extremity of the
hinge, which is called into action when the muscles that close
the shell are relaxed.

1087. The threads, or byssus, spun by many acephalous mol-
lusca in order to attach themselves to rocks, as a ship is moored
by her cables, is another peculiarity in these animals, and parti-
cularly of the genera mytilus and pinna.

1088. In many mollusca of this order the rectum passes
through the cavity of the heart, and this latter organ receives
the blood from the veins by means of two auricles.

Some acephala are hermaphrodite ; but the union of the sexual
organs necessary for fecundation takes place in a single individual.
This occurs in the holothinia.

1089. One of the most singularly constructed of the animals

ARTICULATA. 427

referred to this division of mollusca is the ascidia. The mantle
and its envelope, which is a thick and cartilaginous tunic, form
together a sac, everywhere closed, excepting at two orifices, the
one corresponding to the termination of the intestine, the other
leading into a cavity, of which the sides are the branchias, and
at the bottom of which is placed the mouth, the principal viscera
subservient to nutrition occupying a second cavity, and the heart
being lodged in a third. The principal nervous ganglion is
situated between the two external orifices of the sac.

Sect. VI. — Comparative Physiology of Articulata.

1090. This great division of the animal kingdom comprises all
those tribes possessing what may properly be called an external
skeleton ; that is, a series of rings or hollow cases, of a hard
texture, which enclose all the important organs of the body, and
which, by their muscular connexions, allow of various kinds of
movements, at the same time that they afford protection to all the
softer tissues of which those organs are composed. The best
idea that can be formed of this mechanical construction may be
obtained by examining the body and the limbs of a lobster, in
which it will be seen, that contrary to what obtains in vertebrated
animals, the harder parts are external, and the muscles are within
them, a construction allowing of very free movements of the
limbs.

1091. A remarkable degree of uniformity prevails with regard
to the distribution of the nervous system in all these animals.
The brain, which is situated above the oesophagus, but is still in
the head, as in the higher classes of animals, is exceedingly
small ; and after sending out filaments of nerves to the different
parts about the head, is connected with a double nervous cord,
which encuxles the oesophagus, and runs along the under side of
the animal, being joined at intervals by nodules or ganglia, from
which, as from new centres, other nervous threads radiate, and
are variously distributed to the different vital organs, and to the
limbs. Each of these nervous ganglia appears to perform the
office of a subordinate brain in relation to the system of nerves
which proceeds from it, and to the parts of the body supplied by
those nerves, so that when the animal is divided into several por-
tions, each portion seems to possess its own independent vitality.
The form and structure of the digestive organs is very various;
but jaws are always found, and their motion is lateral instead of
vertical, as in vertebrated animals.

1. Annelida.
1092. The first class of articulated animals are the annelida.

428 COMPARATIVE ' PHYSIOLOGY.

or worm-shaped animals. They are remarkable for possessing
red blood, which circulates in a double S3'stem of complicated
vessels, without any heart, or niuscular ventricles. The body is
soft, more or less elongated, and composed of a great number of
segments. The foremost of these, which may be regarded as
the head, contains the lai'gest of the ganglia, or brain, the mouth,
and the principal organs of the senses. The branchiae are gene-
rally external, and sometimes uniformly spread on the surface of
the body ; and at other times are confined to the anterior' divi-
sions. Tufts of hair or bristles supply the place of feet. The
mouth is either furnished with hard jaws, or else extended in the
form of a tube.

1093. The leech, which is referable to this class, has a very
capacious stomach, nearly of the size of the whole body, or rather
a series of pouches, or dilatations proceeding from each side of
the central cavity.* Tentacula, situate on the head, are their
principal organs of touch; and the small black points, observable,
in some tribes, have been regarded as organs of an imperfect kind
of vision. The earth-worm has a remarkably complicated appa-
ratus for circulation, consisting of a great number of dilatations of
the dorsal vessel, forming a series of hearts.f

2. Crustacea.

1 094. The articulated form is more perfectly developed in the
Crustacea than in the annelida. Their blood is white, and is
circulated by the aid of a muscular ventricle, or heart, situated
■in the back, propelling it through an arterial system; whence it
returns by a system of veins, which collect in a trunk passing
along the lower part of the abdomen. In some species the heart
assumes a very elongated shape. There are always organs
termed antennce, or feelers, situated in front of the head ; and these
are generally four in number. The jaws are of complicated
structure. It is only in a few species that an internal ear is met
with, and it then consists of a sac full of fluid, in which a calca-
reous concretion is contained. The eyes are generally two in
number, often placed at the end of pedicles, and consisting of a
great number of facets, each provided with a separate cornea,
retina, and branch of the optic nerve; and the whole constituting
what is termed a composite eye. The branchiae are of a pyramidal
form, composed of plates, or filaments, or feathery tufts, generally
situated at the base of the legs.

1095. The larger genera of this class, as the lobster, have a
horny stomach, with strong teeth implanted in its coats, for the

♦ See a description and delineation of this structure in the Bridgewater
Treatise on Animal and Vegetable Physiology, ii. 103. [Amer. edit. ii. 77.]
t Ibid. ii. 255. [Amer. edit. ii. 184.]

ARTICULATA. 420

evident purpose of breaking and bruising the shells that are
swallowed. All these animals cast off their shells several times
in the progress of their growth, a new shell being successively
formed of larger dimensions than the preceding, and adapted to
the increased size of the animial.

3. Arachnida.

1096. The third class of articulated animals, or the arachnida'
have been separated from that of insects with which they had
been before associated ; being distinguished by the following
peculiarities in their conformation and economy. They have a
distinct circulation of the blood by means of an elongated dorsal
vessel performing the office of a heart, propelling its blood into a
system of arteries, and receiving it back again from a system of
veins. They are without antennae, but are provided with palpi.
They have pulmonary cavities subservient to the respiration of
atmospheric air. The head is united W'ilh the trunk without the
intervention of any neck. The mouth is armed with jaws ; and
there are several simple eyes situated on the upper part of the
head.

4. Insects.

1097. Nothing can exceed the endless variety of forms dis-
played by this class of the animal creation. Their internal ana-
tomy and economy, however, present many points which are
common to the whole class. There is no other trace of a heart,
than a long cylindrical tube extending along the back, and termed
the dorsal vessel ; but which seems to be closed on all sides, and
neither to give out, nor to receive communicating branches of
any sort. This vessel appears to contain a fluid, which is irre-
gularly undulated backwards and forwards, by a kind of pulsation,
or occasional contraction of one part of the canal, and dilatation
of another. It had been supposed, in the absence of any visible
blood-vessels, that nutrition in insects is performed by a kind of
gradual transudation, or imbibition, as it has been termed. Pro-
fessor Carus, however, has lately made the discovery of a distinct
circulation in the vessels of the larvas of several insects, and other
observers have found a system of partial circulation in even later
periods of insect life. But, in general, in the last stage of trans-
formation, all these vessels, excepting the dorsal vessel, become
obliterated.* There being neither branchiae nor pulmonary
organs where the nutritious fluids could receive the vivifying

* The dorsal vessel of the sphinx lio;ustri is delineated in the Bridgewater
Treatise on Animal and Vegetable Physiology, ii. 245. [Amer. edit. ii. 177.]

430

COMPARATIVE PHYSIOLOGY.

influence of the air, a complex mode of respiration is resorted to.
Apertures are found in different parts, generally along the sides
of the body, and which are called spiracles or stigmata. These
are the commencements of elastic tubes, which remain continually
open, and which are subdivided and ramified like the blood-vessels
of other animals, for the purpose of conveying air to every part
of the system. These tubes are' termed trachecs.

1098. Insects are unprovided with glands for effecting secre-
tions ; that purpose being answered by means of long spongy
vessels, which appear capable of absorbing the materials they
require from the general cavity in which they float.

1099. The temperature of insects, like that of other animals
said to be cold-blooded, varies with that of the surrounding me-
dium ; but is generally one or two degrees higher. In bee-hives
and ant-hills, a much higher temperature prevails. This is proved
by an elaborate series of experiments made on the temperature
oi insects, and its connexion with the functions of respiration and
circulation, by Mr. Newport.*

1100. Their nervous system is formed upon the general model
already described (§ 1091). The digestive organs admit of the
greatest possible variety, according to the habits and particular
kinds of food consumed. To specify all these diversities would
far exceed the limits assigned to us in this work. The external
organs connected with the limbs, the antennae, the mouth, and
the different functions of sense, fall more properly under the
consideration of the naturalist, inasmuch as they furnish the best
characters for the distinction of genera and species, and for per-
fecting their systematic classification. The subject is rendei^ed
infinitely more complex in consequence of the metamorphoses
which the same insect undergoes in passing through the different
stages of its existence, from the egg to the larva, the nympha and
the imago, or the perfect insect. But for the history of these
changes, we must again refer to the naturalist, to whose province
it more strictly belongs to record them. We must content our-
selves with mentioning in this place a few of the more striking
peculiarities of internal conformation which are observable in
some of the insect tribes.

1101. The first that we shall point out is, the remarkable
structure of the digestive organs of the orthoptera, an order of
insects which comprehend the blatta, or cockroach, and the
mantis or leaf insect, the ear-wig, the locust, the grasshopper, and
the cricket. Their stomachs bear some analogy to those of ru-
minant quadrupeds, in complication at least, if not in oifice. The
first stomach, or crop, is membranous ; to this succeeds a mus-
cular stomach, or gizzard, the internal surface of which is armed

* Philosophical Transactions for 1837, p. 25.

ZOOPHYTES. 431

either with scales, or with horny teeth. Around the pylorus
there extend two or more blind pouches, furnished at their extre-
mities with numerous vessels conveying bile. Many similar
biliary ducts are inserted in the course of the intestinal canal. It
has been strongly suspected that the insects in which these com-
plex stomachs are found, actually possess the power of ruminating
their food.

1102. The abdominal cavity of the working bee presents us
with two stomachs, together with the intestine and the poison
bladder. The anterior stomach in which the oesophagus opens,
is the receptacle for the honey, which is occasionally returned
into the mouth in order to be stored in the honey-cells, as a ma-
gazine of food for the winter. The next stomach is destined to con-
tain the pollen, or material gathered from the antennae of flowers.
Its inner coat has a great number of circular folds. Wax is a
secretion of a peculiar kind from the bee.

1103. The alimentary canal of the caterpillar, before transfor-
mation, consists of a straight and capacious tube, of which the
anterior portion is somewhat dilated into what may be considered
as the stomach ; and of which the posterior portions form a
cloaca; the biliary vessels, which are four in number, and very
long, are inserted very far behind. When the caterpillar is
transformed into a butterfly, this alimentary canal is much dimi*
nished, both in its diameter and length ; the first stomach, or
crop, is situated on the side of the tube ; there is next a second
stomach full of irregular dilatations, a slepder but long intestine,
and a coecum near the cloaca.*

J 104. The nervous system undergoes corresponding changes
during the transformation of insects, the ganglia uniting in several
places,, so that their number is much diminished.f The external
senses of insects have for the most part a considerable range of
action. Organs of vision are almost constantly present, but those
of the other senses are but imperfectly known. The principal
organs of touch are the antennce, which probably also perform
other offices relating to sensation, of which we have no certain
knowledge.

Sect. VII. — Comparative Physiology of Zoophytes.

1105. The animals which occupy the lowest division in the
scale of life, and constitute an approach to vegetable, namely,
the class of zoophytes, present us with much simpler forms of

* These successive conformations of the digestive organs, in the sphynx

/is:ustri, or privet hawkmoth, are delineated in the Bridgevvater Treatise on

Animal and Vegetable Physiology, ii. 217. [Amer. edit. ii. 157.]

t Ibid. ii. 547.

432 COMPARATIVE PHYSIOLOGY.

organization than any of those which have passed under our
review^. Yet amongst these we may trace gradations in the
mode in which the more refined organs of the animal economy
successively disappear, and their functions are supplied by other
parts, and also in the gradual simpUfication of those functions,
till we appear to arrive at an approximation to mere vegetative
existence. The great characteristic of the more perfect animals,
the circulation of the fluids in vessels which distribute them to
every part for the purposes of nutrition and secretion, is wanting
in zoophytes ; or if any traces of a circulation can be discovered,
it is exceedingly partial and limited in degree. There is a well
marked disposition in all the organs to assume a symmetrical
arrangement about a common centre ; being either disposed in
radii proceeding from the centre, or arranged in a uniform man-
mer round the circumference of a circle. In those instances in
which a nervous system can be traced, which is the case oi^ily
among the higher order of echinodermata, the disposition to as-
sume this radiating form is particularly observable.

1106. Many amongst the lowest orders present us with the
singular spectacle of compound animals, associated in great
numbers for the purposes of a common defence and habitation,
and having even nutrition in common. These more particularly
constitute an approach to the vegetable kingdom.

I. Echinodermata.

1107. The zoophytes arranged in this division, which are
chiefly the asterias, or star-fish, the echinus, and the holothuria,
present us with some appearance of an external skeleton, or hard
encasement, consisting of parts which are often articulated
together, an imperfect vascular system, and the appearance of
a system of nerves.

1108. The rays of the asterias are composed of numerous
pieces, which have been compared to vertebras, are slightly move-
able upon one another, and allow of a slow flexion of the entire
ray. It is hollowed below into a longitudinal groove, abounding^
in perforations for the passage of numerous rows of short tenta-
cula, which perform the office of feet, for the progressive motion
of the animal, and which also absorb water, and convey it into
the general internal cavity for the purpose of respfration. The
centre of the star is occupied by a large stomach, the entrance
to which, or the mouth, is below, and which sends out two pro-
longations, or coeca, to each ray; these are ultimately ramified
into minute vesicles, suspended by a membrane which performs
the office of a mesentery.

1109. The structure of the echinus is still more complicated.
The calcareous covering of the body has a globular shape, but

ZOOPHYTES. 433

is composed of several angular pieces joined together, and
perforated by rows of lobes, through which the short feet, or
tentacula, protrude. Besides these, there are a multitude of spines
articulated to the surface of the shell, and subservient to voluntary
motion. The mouth is armed with five teeth, inserted in a com-
plicated apparatus of jaws, resembling a pentagonal lantern, pro-
vided with numerous muscles, and suspended over the great open-
ing in the centre of the lower surface of the shell. The intesti-
nal canal is of great length, and forms a spiral tube attached to
the interior of the shell by a mesentery. A double vascular sys-
tems extends the whole length of this canal, and is partly spread
over the mesentery.

1110. The holothuria resembles in its structure the echinus,
but it has a cylindrical instead of a globular form. The respira-
tory organ is ramified like the branches of a tree, and fills and
empties itself at the pleasure of the animal. The mouth has no
teeth, and is only protected by a circle of calcareous plates.
The intestine is very long, and makes many folds, being also
attached to the sides by a mesentery. A partial circulation
takes place in a double system of a very complicated arrange-
ment of vessels, which has relation exclusively to the intestinal
canal, and of which some of the branches are interlaced with
the arborescent respiratory tubes already described.

2. Entozoa.

1112. Very little is known concerning the physiology of in-
testinal worms ; the information that has been collected being
chiefly of a negative kind. They have no visible respiratory
organs, and no apparent nervous system or organs of sensation :
and still less can we discover any traces of a circulation. The
only very distinct organs are those belonging to the functions of
nutrition and of reproduction. Some naturalists, indeed, allege ,
that they have detected some filaments of nerves; but the real
nature of these filaments is still very doubtful.

1113. The alimentary canal may in most intestinal worms be
recognised without much difficulty ; it is sometimes enclosed in
an abdominal cavity, but at other times apparently passes through
the solid parenchyma of the body. In some, as in the taenia, or
tape-worm,, we may discern ramified vessels for the distribution
of the nourishment; but these are not seen in others. The
simplest animal of this tribe is the globular hydatid, which con-
sists altogether of a vesicular sac filled with a transparent fluid,
and with an indistinct mouth ; but without any other apparent
external organ. This tribe of entozoa exhibit the simplest example
of the gemmiparous mode of reproduction ; the young appearing
as gemmae, or buds, which at certain periods spout from the

a?

434 COMPARATIVE PHYSIOLOGY.

homogeneous parenchyma composing the body of the parent, and
by a sort of vegetative growth, gradually assume the form of the
original animal, and are detached when capable of exercising an
independent hfe.

Some of the entozoa, as the taenia, or tape-worm, are capable
of being multiplied like plants, by division ; each segment re-
sulting from the division being converted into an independent
animal, acquiring whatever parts may have been deficient, and
after a time admitting of further subdivision, with a repetition of
the same phenomena.

3. Acalepha.

1114. These are either fixed on rocks, or float in the sea;
they exhibit more or less of a fibrous texture, and contain vessels
which are excavated out of the substance of the body itself, and
are not contained in any distinct cavity.

1115. The actinia, or sea anemone, is provided with numerous
hollow tentacula surrounding the mouth and stomach. The
space between the stomach and the outer skin is divided into
compartments by vertical partitions, and the fluid contained in
these compartments may be projected into the tentacula so as to
render them turgid.

1116. The medusa has a hemispherical form, and a gelatinous *
consistence. The mouth, which is situated in the centre of the
flat disc below, is surrounded by fringed tentacula. It leads into
a singularly-shaped cavity, which is the stomach, formed of four
arches proceeding like radii from the centre', and terminating in
tubes which are variously divided, and the branches derived from
them freely communicating with one another by anastomoses.
These are apparently for distributing the nourishment which has
been prepared by the stomach, but not for any real circulation.
There are four large cavities in the body which appear to be
subservient to respiration.

1117. In some species, forming the genus rhizostoma of Cuvier,
there is no central mouth, but a canal commences by an open
orifice from the extremity of each of the fringe-like processes of
the tentacula, and these, uniting with others in their course up-
wards, form at length a single tube or oesophagus, w^hich termi-
nates in the central stomach already described.

Most of the animals of this order, which are found fixed on
rocks, are propagated by means of spores or gemmules, consti-
tuting one of the modes by which the gemmiparous form of re-
production is efiected. These gemmules are minute bodies,
formed either on the surface or in some special internal organ of
the parent, and which are immediately detached and swim with
a spontaneous and independent motion in the circumambient fluid.

ZOOPHYTES. 435

by means of cilia or short filaments, which are in rapid and
incessant vibration. They ])ursue these motions for a certain
time till they find a convenient place for their future habitation,
where, when they are once fixed, they generally remain ever
after, growing to the dimensions and exercising all the functions
of the parent animal. In the acalepha, which are not stationary,
the gemmules retain their liberty of moving during the whole
period of their existence.

4. Polypi.

1118. The organization of this numerous order of zoophytes
presents, in every essential particular, great uniformity, and bears
a great analogy to that of the actinia. The gelatinous sac or
tube, constituting the digestive cavity, is closed at one end, the
opening at the other end being the mouth, which is surrounded
by a circle of tentacula ; and the nutritive fluid passing by im-
bibition through the coats of the general sac or stomach for the
purpose of nourishment. The hydra may be taken as the type
of this tribe of animals. It consists of a mere stomach provided
with flexible tentacula for catching food and for progression.
This sac may be inverted or turned inside out, without detriment
to the animal, digestion being then performed by the new cavity,
which is the result of the operation. These animals present the
simplest examples of gemmiparous generation (§ 777).

No further discovery can be made respecting the organization
of these animals, even by applying the microscope, which shows
only a semitransparent substance interspersed with opaque grains.
The greater number secrete on their outer surface a calcareous
or a horny substance, which serves for their mechanical support,
but at the same time fixes them on the spot to which they
adhere.

1119. The most remarkable feature in their history is their
disposition to congregate together in vast numbers, so as to
compose by their united architecture whole rocks and even
submarine mountains, rising from the bottom of the ocean. Some
of these animal republics exhibit amongst the individuals thus
associated together communications of nutritious vessels, so that
the materials for the sustenance of each passes into the bodies
of the neighbouring polypi, and is applied to the purposes of their
economy. All. these fixed polypi are propagated by spores or
gemmules in the manner already described in our account of the
stationary acalepha.

5. Infusoria.
11.20. These being all microscopic animalcules of extreme

436 HISTORY OF PHYSIOLOOr.

minuteness, it is scarcely possible to arrive at any exact know-
ledge of their internal organization or economy. Many, and pro-
bably all, are possessed of distinct organs for the reception of
food, for reproduction, and for voluntary motion ; but conjecture
alone can fill up the imperfect outline, or suggest any plausible
hypothesis as to their powers of sensation, which, however, we
are unwilling to refuse to any being which appears to possess
the properties and attributes of animality, especially since the
splendid discoveries of Ehrenberg have made us acquainted with
the complex organization observable in some of the minutest of
this prodigiously diversified tribe of beings. It is remarkable,
indeed, that those very animalcules, as the monads, Mdiich had
been ranked by naturalists among the agastrica, or beings totally
without alimentary cavities, are now found to have a very consi-
derable number of stomachs, and to be entitled accordingly to
the title oi polygastrica.

It is chiefly amongst the various tribes of infusoria that the
simpler modes of generation, such as that termed fssijparous, are
exemplified. In the monas, for instance, a groove is seen to form
around the equator of their globular bodies, which groove, gra-
dually deepening, changes their form to that of an hour-glass, and
the connecting ligament of the two portions being soon broken,
the segments move away from one another, each commencing
its independent existence, and being capable of performing all
the functions of the undivided monad. In the bell-shaped vorti-
cella, the division commences at the mouth or wide extremity of
the bell, and gradually extends in a longitudinal direction towards
the insertion of the stem, dividing the body into two equal por-
tions, each being now a distinct and individual animal. The
gonium divides itself into four instead of two portions, each por-
tion being again subdivided into four others, the new animalcules
assuming rapidly the dimensions and appearance of the one of
which they originally formed a part. Other species are propa-
gated by means of gemmules ; and some of the infusoria are
apparently oviparous-

1^' '■^■' QmL^^R XXIV.

\ trx ^^L '"^ * * "^ ihs^Jr^^f physiology.

V,&\_ - -^ "*

Nl^t^he study of the history of any science furnishes to the
mind aFody of knowledge not merely ornamental or superfluous,
but one that is fraught with instruction and utility, and is condu-
cive to the just comprehension of the subject to which it relates.

HISTORY OF PHYSIOLOGY. 437

It is scarcely ever necessary, indeed, for the understanding of
any proposition, that the student should follow the same laborious
course and travel through the same tortuous mazes by which the
discovery had originally been achieved ; for the acquisition of
any body of knowledge already systematized by the labours of
our predecessors, is in general most readily attained by the
synthetic method. But as soon as this point has been reached
we can conceive no course of study more calculated to improve
that knowledge, and to invigorate the faculties by which it may
be extended and perfected, than reverting to the analytic process,
and following the series of discoveries in the order in which they
have actually occurred. From an historical survey of the succes-
sive steps by which science has proceeded from a rude origin to
its present state of advancement, and which mark its varied
progress and even occasional retrogressions at different periods,
according to the prevailing disposition of the age, either to a
servile submission to authority or to the hasty adoption of crude
and visionary theories, we are enabled to derive most important
rules for the conduct of the understanding in the search after
truth.

The history of each particular branch of science may, indeed,
be regarded as a separate chapter in the history of the human
mind. It indicates the sources of its activity and of its strength,
and also of its weakness and fallibility ; it holds out the most
powerful incentives to exertion ; it exhibits much to admire and
to emulate, and, at the same time, discloses enough to check pride
and teach humility.

1122. The history of physiology must necessarily comprise a
large portion of the history of anatomy, which consists in the
mere knowledge of the organs and minute structure of the body,
such knowledge being, in fact, the foundation on which the higher
science of the philosophy of life is built. It is scarcely possible,
indeed, to study mere organization, without extending our views
to the functions that we see performed, and to the energies that
are exerted by the living organs. Our object will therefore be in
the present place, to inquire how far these higher qualities of mind
have been displayed by the cultivators of this department of
knowledge at different periods, so as to mark the progress of the
philosophy of life, as contradistinguished from the more mechan-
ical, though equally useful labours of the mere anatomist.

1123. The phenomena which constitute the subjects of physio-
logical inquiry must, indeed, have attracted the attention of
mankind long before any accurate knowledge had been acquired
of the structure of the organs whose actions give rise to these
phenomena. Life in its different forms must have been familiar
to all ; and every savage and warlike people must have been
conversant with the diversified aspects of death, which they

37*

438 HISTORY or physiology.

inflicted in such various modes. Speculations on the nature of the
vital principle, and the physiological conditions on which it is
dependent for its origin, maintenance, and decay, must have
been formed and pursued in every state of society, removed but
one degree from barbarism; and such speculations must have
stimulated inquiry into the internal mechanism with which that
principle is associated, and the hidden springs which regulate its
course-

1124. Opportunities mhst frequently have occurred in the
rudest ages, of observing the different parts of the structure of
the bodies both of men and animals. The curiosity even of the
savage could not fail to be attracted by the remarkable appear-
ance of the internal organs, in the animals which he slaughtered for
food, or prepared for sacrifice. Although deterred from the actual
examination of the human body, by an instinctive repugnance,
or superstitious terror, various casualties occurring in battle, or
arising from accidents, would occasionally afford an insight into
the human frame. Human bones, and sometimes entire skeletons^
would often present themselves to those who revisited the fields
of carnage. Thus would the principal bones, and the most con-
spicuous viscera of the human body, soon become known, and
they would be designated by particular names. Evidence to
this effect may be collected from the rudest and most ancient
languages ; from which we may infer that a certain progress
must have been made in this kind of knowledge, long before it
had been so arranged and methodized as to deserve the name of
a science.

1125. The prevailing custom amongst most of the ancient
nations, of consigning all dead bodies to destruction by fire, was
one of the greatest obstacles to the advancement of anatomical
and physiological knowledge. But opportunities were on the
other hand afforded of learning the structure of certain animals,
by the religious rites, during the celebration of which these
animals were sacrificed, and especially by the examinations which
were made by the priests of the yet palpitating entrails of their
victims, for the purpose of prognosticating future events. Infe-
rences were thus drawn by analogy as to the organization and
functions of the human body. The Egyptians, indeed, who
composed the most ancient nation of whose manners and customs
we possess any authentic records, were supposed to have acquired
considerable knowledge of the human structure from the practice
of embalming the dead. This operation was performed by a
particular class of men, and consisted in taking out a portion of
the viscera, washing them with antiseptic fluids, and filling the
cavities with aromatic substances. But as this process appears
to have been conducted in the rudest manner, it required no skill
in anatomy, and was but little calculated to improve the science.

HISTORY OF PHYSIOLOGV. 439

It was in the hands of a few persons only ; and such was the
contempt and abhorrence in which these persons were held by
their countrymen, that whatever knowledge they might have
acquired by the practice of their art, was not likely to be com-
municated to others.

1126. Whatever splendour may have attended the pride of
power or extent of empire in these rude and unenlightened ages,
the dawn of science was coeval only with that of liberty. The
same energies by which man had thrown off the yoke of tyrann)^
animated them likewise with the desire of knowledge ; and na-
tions had no sooner emancipated themselves from despotism, than
they began to emerge from barbarism and ignorance. The
Greeks, who were the most free, were also the most polished of
all the nations of antiquity, and far excelled them in every species
of science and of art. So great was the ardour of their philo-
sophers in the pursuit of knowledge, that they frequently travelled
into distant countries to collect useful information, and impart it
to their pupils. Even in the time of Homer, the Greeks seem to
have possessed much general knowledge both of anatomy and
physiology, as may be collected from the writings of that poet.
He relates that the stone which was hurled at vEneas by Diomed,
not only crushed the thigh-bone, but also tore the ligament of the
acetabulum. Morion is represented as being wounded in one of
the large veins which return the blood to the heart, or venag
cavee ; and Ulysses aimed a blow at the Cyclops at the part
where the liver adheres to the diaphragm. It has even been
supposed that Homer has purposely often wounded his heroes
that he might have opportunities of displaying by the minuteness
of his descriptions, his accurate acquaintance with anatomy.

1127. But though curiosity was roused, and a multitude of
detached facts had been observed and collected, it was long be-
fore the proper methods of investigation were known, and the
true principles of inquiry established. Although it appears that
the studies of anatomy and physiology were prosecuted with
considerable ardour in the school of Pythagoras, yet as they
were regarded merely as a part of natural history, the informa-
tion relating to these subjects was not sutSciently connected or
concentrated to be embodied in one science. Alcmeon and
Empedocles, who cultivated anatomy, belonged to this school ;
but the most remarkable of the pupils of Pythagoras, belonging
to the Eleatic sect, was Democritus of Abdera, a man whose
eccentric manners, as well as penetrating genius, and undisguised
contempt for the follies of mankind, have procured him so much
celebrity. He is said to have devoted considerable time to the
dissection of animals, especially with a view to discover the
origin and course of the bile. His fondness for seclusion, and
his perseverance in a pursuit which appeared to his countrymen

440 HISTORY OF PHYSIOLOGY.

to be without any rational object, led them to suspect the sound-
ness of his intellects ; and Hippocrates was sent to visit him in .
his solitary abode. He found the philosopher seated on a stone,
under the ample shade of a plane tree, with a number of books
arranged on each side, one on his knee, a pencil in his hand, and
several animals which he had been dissecting lying before him.
His complexion was pale, his countenance thoughtful ; at times
he laughed, at times shook his head, mused for a while, and then
wrote, then rose up and walked, inspected the animals, sat
down, and wrote again. Hippocrates, who perceived the nature
of his inquiries, observed him for some time in silent admiration,
proclaimed to the bystanders the importance of his researches,
and declared to them his regret that want of leisure from his
own professional employments did not allow him to engage in
similar pursuits.

1128. But it was only from men whose minds are capable of
enlarged views, and can perceive the bearings and connexions
of the several parts of the subjects they embrace, that a powerful
impulse is given to science, such as to make it almost the crea-
tion of their hands, that it is raised to its proper rank among the
departments of human knowledge. Such was the vigorous mind
of Hippocrates ; and so great was the improvement which medi-
cine derived from his genius, that the foundation was thus laid
for the more rapid progress of all the sciences connected with it
in succeeding times. Hippocrates was born in the island of Cos,
in the first year of the 80th olympiad, or 460 years before Christ;
an era which is therefore remarkable in the history of medical
science. It appears that at that period a knowledge of medicine
had been in a great measure hereditary in certain families,
amongst whom the information which had descended from the
successive generations was thus retained and augmented. This
was the case in the family of Hippocrates, who is said to have
been the fourteenth descendant from Esculapius, on his father's
side ; while his maternal ancestry could be traced to Hercules.
He had been instructed in all the learning of those times ; but
particularly dedicated himself to the cultivation of medicine,
which he formed into a distinct science, collecting and arranging
all the information on the subject that was then known. Not
satisfied with the knowledge which he could acquire in his native
place, he travelled for several years through difl^erent parts of
Greece and Asia Minor. He visited the temple of Diana at
Ephesus, and was at the pains of transcribing and arranging the
records of cases and of successful methods of pure, which it was
the custom to deposit on tablets in these temples. On retiring to
his native island, after the laborious proofs he had given of his
diligence and ardour, he continued to exercise his profession, and
enjoyed the highest and most extensive reputation. Such was

HISTORY OF PHYSIOLOGY. 441

the estimation in which his talents were held, that even princes
were soHcit'ous to allure him to their courts ; but he was so
strongly attached to his native country, that he resisted every
temptation which the splendour or the favour of monarchs could
hold out.

1129. Excepting one or two particular treatises, which bear
his name, but the authenticity of which is dubious, the writings
of Hippocrates are to be regarded rather as medical than phy-
siological ; but he seems to have been the first who formed a
clear conception of the value of anatomy and physiology as the
basis of medical reasoning. #- Originality of thought, combined
with accuracy of observation, forms the characteristic feature of
his writings ; which contain, however, many traces of the Pytha-
gorean philosophy, with which he seems to have been early
imbued. He formed the bold conception of the existence of a
principle, which he calls ?i/3-«, or nature, exercising a general
direction and superintendence overall the actions and mov^ements
of the body, and endowed for that purpose with a species of
intelligence directed to beneficial ends. As subservient to this
great and prime agent, he imagined that the functions were car-
ried on by means of other subordinate powers or faculties; and
also that they were subjected to the influence of the stars. He
regarded the body as being composed of three kinds of substances,
namely, solids, fluids, and spirits, and ultimately resolvable into
the four primary elements of earth, water, air, and fire, the pre-
dominance of each of which in particular individuals gave rise
to the prevaihng temperaments, characterised by the peculiar
combinations of the four qualities of dry, moist, cold, and hot.
Hence arose his doctrine of temperaments, already noticed
(§ 862). The anatomical details which are interspersed through-
out his works are numerous, but do not exhibit any profound
knowledge of the subject, besides being in many instances incor-
rect. The confession which he made on his visit to Democritus
shows that he had not devoted any considerable portion of his
time either to physiology or to practical anatomy. It is very
apparent, indeed, that he never dissected a human body ; and
much could not be learned from the occasional dissection of
brutes. So far was he from having any idea of the real nature
of the circulation of the blood, which some have done him the
honour to suppose he had discovered, that he seems to have iixi-
agined that the arteries contained air, and he was at a loss to
determine whether the veins took their origin in the liver, the
heart, or the brain. He includes under the same name the liga-
ments, the tendons, and the nerves, and makes no distinction
between their respective offices in the economy. But these
imperfections were more to be imputed to the unavoidable dis-
advantages of the times, than to his own deficiency either of

442 HISTORY OF PHYSIOLOGY.

industry or of talent ; for wherever he had opportunities of dis-
playing these qualities, and of exerting the whole force of his
original mind, he far surpassed all his cotemporaries. Hippo-
crates must indeed be regarded as the father of physiology, as
well as of medicine ; and his name will ever be cherished by
posterity, as one of the most illustrious in the annals of science.

1130. Amongst the Athenian philosophers who paid attention
to physiology, Socrates must not be passed over in silence ; since
he cultivated the science with a view to establish upon it, as
upon the most solid foundation, the principles of natural theology.
Plato, the friend and pupil of Socrates, hkewise devoted a por-
tion of his time to the study of animal structures, and indulged
in a variety of fanciful speculations concerning the uses and func-
tions of the vital organs.

1131. Aristotle, the tutor of Alexander the Great, whose trans-
cendant genius embraced the whole domain of human science,
prosecuted this, as well as every other branch of the history of
nature, with an ardour and perseverance that have rarely been
equalled, and never surpassed. Gifted with a mind of extraor-
dinary acuteness and comprehension, he appears to have con-
centrated within it all the learning of his age, which, moulded and
transformed by the power of his genius, assumed new forms of
arrangement, yielded new products of generalization, and spread
its luminous irradiation over every department of human know-
ledge. At the request of his pupil he undertook an extensive
treatise on the natural history of animals ; he was liberally fur-
nished with specimens of all kinds, and empowered to command
the services of numerous assistants, from every part of the vast
empire of Alexander. He spared no labour in the prosecution
of this undertaking, and in making the most profitable use of the
resources thus placed at his disposal ; and contributed in no small
degree to the advancement of our knowledge of the animal
economy in the diversified forms of life presented by nature.
Yet with all the advantages he possessed, it would appear that
his knowledge of human anatomy was exceedingly imperfect.
He even acknowledges that the internal parts of the human body
are but little known ; and points out the probable advantages that
might result from the examination of animals which have the
nearest resemblance to the human species, for supplying these defi-
ciencies. But his work on the history of animals, tt^i ^rea,)/ urTopiac,
is unrivalled by the magnitude of the field which it embraces, and
by the vast information it contains. To him belongs the merit
of arranging the facts in the order, not of their zoological, but
their physiological relations ; referring every organ to the func-
tions it performs in the animal economy, and thus anticipating
the very principle on which, in recent times, Hunter, Blumen-

HISTORY OF PHYSIOLOGY. 443

bach, and Cuvier have founded their more rational and philoso-
phical views of comparative physiology.

1132. The encouragement given by the Ptolemies, the succes-
sors of Alexander in Egypt, to every kind of learning, tended
greatly to the advancement of anatomy and physiology. Permis-
sion was granted by these monarchs to dissect the human body,
which none would otherwise have dared to attempt, in opposition
to the prejudices of the Egyptians, which were no less violent
against dissection than those of the Greeks.

1 133. One of the earliest of the physiologists of this period was
Erasistratus, the grandson of Aristotle, and the pupil of Chrysip-
pus. Under the patronage of Nicanor, king of Sicily, he enjoyed
frequent permission to dissect the bodies of those who were exe-
cuted, and is even reported by Celsus to have had criminals
delivered to him for the purpose of their being opened while
alive, in order that the natural living state of the internal organs
might be examined. This account, however, deserves to be re-
garded rather as a popular tale, which has no other foundation
than irrational prejudices against dissection, and was propagated
by idle credulity, and a passion for exaggerated scenes of horror.
The works of Erasistratus are now lost ; but from the quotations
of later authors, he appears to have greatly advanced the know-
ledge of the structure of the human body, more especially by
pointing out the circumstances in which it differs from that of
other animals, whose anatomy had been previously studied as
making the nearest approach to the organization of man.

1134. Another no less distinguished anatomist of the same
period was Herophilus of Chalcedon, who also flourished at
Alexandria. He was the disciple of Praxagoras, and was con-
sidered as the founder of the medical school at Alexandria. He
was much occupied in the dissection of human bodies, and directed
his attention particularly to the nervous system. One of the
sinuses of the brain, which he is said to have more particularly
described, bears to this day the name of the torcular of Hero-
philus. He is stated to have been the first anatomist who taught
osteology from the human skeleton. He distinguished the nerves
from tendons and ligaments, with which they had, before his
time, been confounded. He also paid minute attention to the
varieties of the pulse, and thus laid a foundation for a knowledge
of the important function of the circulation.

1135. Few physiologists of any note are recorded as having
flourished from the time of Herophilus to that of Galen. The
nam.es of Lycus of Macedonia; of Marinus, who lived in the
reign of Nero, have been transmitted to us as the author of some
elaborate treatises on the muscles ; and also of Rufus Ephesius,
who wrote a work entitled Onomasia, which was considered as
the best system of anatomical knowledge extant at that period.

444 HISTORY OF PHYSIOLOGT.

1136. Galen, the most celebrated and indeed the last of the
physiologists of Greece, was born at Pergarpos, in Asia Minor,
about 131 years before the Christian era. His father was imbued
with the love of letters, and was anxious that his son should
receive the benefit of a learned education, which the early pro-
mise he gave of superior talents showed that he was well quali-
fied to turn to advantage. He was placed under the tuition of the
best philosophers of the time, and studied in all the schools with
extraordinary diligence. His father died long before he could
form any probable anticipation of the future fame of his son. It
was two years after this event, that young Galen, who was now
in his nineteenth year, first turned his attention to medical pur-
suits, of which he soon became passionately fond. As Alexandria
was still the most celebrated school of medicine in the world, he
travelled thither with a view of prosecuting his studies ; in order
to reap every advantage which foreign countries could afford, he
visited in succession different parts of Asia Minor and the islands
in the JEgean Sea. Anatomy was ever his favourite pursuit ;
but being debarred from the advantage of examining human
bodies, the dissection of which had then been prohibited, even at
Alexandria, he had recourse to that of such animals as were
supposed to have the greatest resemblance in their structure to
man. He has written very fully on every part of anatomy ; so
that his works may be considered as a system, exhibiting every
thing which was known on the subject in his time. He was
much impressed with the importance of anatomy as the basis of
medicine and surgery, and enforces his opinion with singular
acuteness and energy. This is evinced by the following passage
in his second book of Academical Administrations :

" What can be more useful in wounds which are received in
battle, in the extraction of darts, excision of bones, the reduction
of luxations, the opening of fistulse, than to be well acquainted
with the anatomy of the limbs ? It is of more use to be acquainted
with the exterior than the interior parts of the body, as the
shoulders, back, breast, the ribs, the belly, and the outward
covering of the neck and head ; for we are often required to cut
into abscesses and sinuses. In the excision of bones it is necessary
to cut and dissect ; and if we do not know where the artery, vein^
or nerve may be, we are more likely to be the cause of death
than of health to the patient."

1137. Galen is entitled to great praise for having applied
himself to the investigation of physiology in connexion with
anatomy; so little had hitherto been known on this subject, that
we cannot be surprised at the mixture of error which his works
exhibit; but although he may often have proceeded on false
principles and fallacious hypotheses, yet the reasonings themselves
which he employs are always clear and conclusive. His account

HISTORY OF PHYSIOLOGY. 445

of the uses of the hand, for example, is remarkably perspicuous
and correct. He succeeded in estabUshing by experiment the
fact that arteries contain blood, and thus refuted the doctrines of
the Alexandrian school that they are merely filled with air, which
they serve to distribute throughout the body. It is interesting
also to trace the eifect whicTi these subjects of contemplation
produced on Galen's mind. After reviewing the structure of the
hand and foot, and their adaptation to their respective functions,
he breaks out into the following apostrophe, admirably charac-
teristic of a mind imbued with the genuine spirit of piety :

" I esteem myself as composing a solemn hymn to the author
of our bodily frame, and in this I think there is more true piety
than in sacrificing to him hecatombs of oxen, or burnt-oflTerings
of the most costly perfumes ; for I first endeavour to knov/ him
myself, and afterwards to show him to others, to inform them
how great is his wisdom, his virtue, his goodness."

1138. The great reputation which Galen had acquired, instead
of promoting, tended rather to impede the progress of anatomy
and physiology during several succeeding centuries. Where no
hope was entertained of emulating the fame of one who was re-
garded as an infallible oracle, all motive to exertion was repressed.
But other causes of a political nature also contributed to the
decline of anatomy, as well as of other branches of learning, from
the time of Galen to the downfall of the Roman empire, and
during the ages of intellectual darkness which followed. Learning,
however, still continued to be cultivated at Alexandria, until the
capture of that city by the Saracens, in the year 640, when its
magnificent library was burnt.

1139. Anatomy and physiology began slowly to revive among
the Arabians ; but no addition seems to have been made by them
to the knowledge which the Greeks had possessed on these sub-
jects. The Arabian physicians were satisfied with what Galen
had taught them ; and as the rites of the Mahometan religion
prohibited all contact with a dead body, an effectual bar was
opposed to all improvement in anatomical or physiological know-
ledge. The work of Avicenna on anatomy is merely a compi-
lation from Galen and other Greek authors ; and whenever he
ventures to differ from his authorities he is generally wrong.
For more than a thousand years after the time of Galen, anato-
mical and physiological science may be considered as nearly
stationary; for scarcely any discovery of the least importance
was made during the whole of that period.

1140. The expeditions of the crusaders were the means of
introducing into Europe some knowledge of the literature of the
Arabians ; and the light of science, after a. long period of dark-
ness and ignorance, began at length to dawn. In the fourteenth
century, anatomy was revived by Mundinus, a Milanese, who

38

446

HISTORY OF PHYSIOLOGY.

had become acquainted with the writings of Galen through an
Arabian translation, and who published a system of anatomy in
1315.

1141. The destruction of the Greek empire by the Turks, in
the succeeding century, tended to diffuse throughout the west of
Europe, whatever portion had remained of the literature of the
east. The learned of every profession fled from Constantinople,
which had fallen into the hands of barbarians, and sought an
asylum in Italy, where they disseminated the seeds of knowledge.
The writings' of Galen and of the ancients, could now be read in
the original ; their superiority to the Arabian authors was soon
discovered ; and such implicit deference was paid to their opi-
nions, that for many ages no one would venture upon the shghtest
innovation. The improvement of anatomy was therefore exceed-
ingly slo4% It was promoted, however, by the exertions of
eminent painters, such as Raphael, Albert Durer, Titian, and
above all, Leonardo da Vinci, whose drawings evince consider-
able knowledge in that study.

1 142. The sixteenth century was more auspicious to the pro-
gress of anatomy, which was beginning to be cultivated with
ardour in Germany and France, ^as well as in Italy. Berengarius
of Carpi, professor at Bononia, acquired such reputation by his
skill in dissection, that he was regarded as the restorer of this
science. The structure of the ligaments and bones was success-
fully studied by Charles Stephens ; that of the blood-vessels by
Fernelius ; and that of the muscles by Andernach. Sylvius was
also at this time celebrated as a teacher of anatomy.

1143. But the extravagant veneration of antiquity, that spell
which has for so many ages held the medical world in thraldom,
was at length broken by Vesaiius, who boldly ventured to call
in question the authority of Galen. This extraordinary man was
born at Brussels in 1514, of a family which has for a long time
cultivated medicine. He united to remarkable talents, a degree
of ardour and perseverance which enabled him to overcome
every difRculty ; and his progress in the study of anatomy, for
which he had very early shown a partiality, was commensurate
with these great qualities. He commenced his studies at Lou-
vain, and prosecuted them in Italy. In a short time he made
himself master of the Hebrew^ Greek, and Arabic languages ; so
that before he had attained his twentieth year, he had already
read the works of Galen and Avicenna in the original. Such
was his zeal for anatomy, that it is reported he used to rob the
gibbets, and dissect the bodies in his bed-chamber. In a few
years he excelled his teachers, Fernelius and Sylvius, who were
esteemed the first anatomists of their time. He soon detected
many errors in Galen, some of whose descriptions of parts had
been taken from quadrupeds, and applied to man. These errors

HISTORY OF PHYSIOLOGV. 447

he ventured to disclose and to correct in his publications ; but
his boldness in appealing to nature from the authority of Galen,
drew upon him the enmity of all the admirers of that great
master. He was assailed from all quarters with the bitterest in-
vectives ; and Sylvius himself has not scrupled, in the heat of con-
troversy, to brand him with the epithet of Vesanus, or madman,
in allusion to his real name. The criticism which Vesalius had
passed on Galen, was retorted by his enemies upon himself; and
it must be confessed that in the plates which Vesalius published,
some errors of the same kind were detected. But still their
general accuracy was undeniable. The work of VesaUus was
soon acknowledged to be unrivalled, and its author eventually
enjoyed a complete triumph over all his opponents.

His fame reached the eyes of Charles V., who appointed him
his physician; but after being raised to that distinguished station,
he was soon doomed to experience the inconstancy of fortune.
Having obtained permission/ to examine the body of a Spanish
gentleman, whom he had attended in his last illness, he began to
lay open the chest, when the bystanders imagined they perceived
a tremulous motion of the heart. This circumstance soon got
wind, and probably with much exaggeration, reached the ears
of the relations of the deceased, who, seized with horror, denounced
Vesalius as a murderer ; and coupling this charge with that of
impiety, arraigned him at the tribunal of the Inquisition. Where
superiority of knowledge was esteemed a crime, Vesalius, how-
ever unjustly he might be accused, was certain of condemnation.
By the influence, however, of Philip H., who had then succeeded
to his father Charles V., Vesalius was permitted to commute his
punishment to a pilgrimage to the Holy Land, the merit of which,
it was thought, might sufficiently atone for the heinousness of
any crime. This journey he was accordingly obliged to perform ;
and on his return he was invited by the senate of Venice to teach
anatomy, but he perished by shipwreck before he reached that
city, when he was about fifty years of age.

1144. The impulse which had been given by Vesalius to the
progress of anatomy, continued to operate; and many were the
inquirers who pressed forward in the path in which he had so
nobly led the way. The barriers to investigation had been
removed ; nature was open to inquiry ; and men had only to
observe and to think for themselves. Every year was now
adding some new discovery ; and it becomes no longer easy to
trace the order of their succession, or to ascribe each to their
proper authors. We shall endeavour, however, briefly to enume-
rate those which are most worthy of being noted.

1145. In the year 1561, Fallopius published, in Italy, his
Observationes AnatomiccB, a work of much merit, and the fruit of
great industry, xlbout the same period also, Eustachius arrived

448 HISTORY OF PHYSIOLOGY.

at great eminence as an anatomist, and published a set of plates
which he himself engraved ; their beauty and accuracy excite
astonishment even in the present day.

1146. Fabricius ab Aquapendente, a professor of anatomy at
Padua, was also one of the most distinguished anatomists and
physiologists of that period. He published a splendid volume on
the formation of the foetus, and bestowed much pains in investi-
gating the mechanism of the motions of animals. He was the
first who delineated and drew the attention of the public to the
valves of the veins, which, had indeed, been imperfectly seen by
Stephens, Sylvius, and Vesalius, and the existence of which had
been denied by Fallopius and Eustachius. It was this discovery,
perhapS; more than any other, which paved the way for that of
the real course of the blood in its circulation; a discovery which
was reserved for the illustrious Harvey; and which has justly
rendered his name immortal. As it may be interesting to review
the steps which led to this important physiological discovery,
we shall retrace its history to a period somewhat more remote.

1147. It is perfectly well ascertained, from an examination of
the works of Galen, and of others who have copied from him,
that the ancients had not the most distant notion of the real nature
of the circulation. The blood was believed by them to have its
origin in the liver, and to be undulated alternately in opposite
directions in the veins ; they imagined that the finer part of it
transuded through the septum, or partition separating the cavi-
ties of the heart, from the right to the left side, where it mingled
with the air received into the lungs, and forming a vital spirit,
was moved by a sort of flux and reflux along the arteries.

1 148. On the revival of anatomy in Europe some vague notions
of the pulmonary circulation appear to have suggested themselves
to many eminent men. Vesalius demonstrated that the blood
could not possibly pass from the right to the left ventricle through
the septum of the heart. Realdus Columbus, who was professor
of anatomy at Padua, and had been a pupil of Vesalius, distinctly
traced the passage of the blood through the vessels of the lungs.
The same fact had, however, been already discovered by Michael
Servetus, who was born in Aragon in 1509, a,nd who is more
celebrated as a theologian than as a physiologist. Further pro-
gress was made by Andrew C^salpinus, an Italian physician,
who speaks of a communication existing between the veins and
arteries at their remote extremities, and notices the effect of the
valves of the arteries and of the auricles as calculated to prevent
a reflux of the blood ; but he is quite at a loss to reconcile this
observation with the common notions, which he had imbibed, and
to which he still adhered, of the functions of these vessels. But
notwithstanding these apparent approximations to the truth, it is
probable that many ages would have elapsed before the complete

HISTORY OF PHYSIOLOGY. 449

discovery of the circulation, if some bold and penetrating genius,
such as that of Harvey, had not arisen.

1149. This illustrious man was born in the year 1578; and
the circumstances of his family gavp him the advantage of a
liberal education. After six years spent at Cambridge, where
he was instructed in all the philosophy of the times; finding that
the university furnished but very imperfect means of studying
either anatomy or medicine, he repaired, at the age of twenty-
one, to Padua. Here he became the pupil of Fabricius, who
was at the time demonstrating to his students, with all the
enthusiasm of a discoverer, the newly observed valvular structure
of the veins. The attention of Harv^ey being thus directed to
this remarkable conformation, he became anxious, on his return
to England, to prosecute the inquiry into the purposes which were
accomplished by it. He was obliged, for this purpose, to make
many experiments on living animals; and these revealed to him
the real course of the blood in its circulation; a discovery which
ranks unquestionably as the noblest and most important ever
made in Physiology. Harvey taught this new doctrine in his
lectures about the year 1616 ; but did not publish any account of
it till the year 1628. On its being made known to the world, it
met with the most violent opposition ; and so inveterate were the
prejudices of the public, that the practice of Plarvey was con-
siderably diminished in consequence of his discovery. It was
remarked that no physician who had passed the age of forty
would admit the truth of a doctrine so much at variance with all
the systems in which he had been educated. Envious of his
growing reputation, many of his cotemporaries had recourse to
all kinds of sophistry with the view of detracting from his merit.
They at first vehemently contested the truth of the doctrine ; but
afterwards, when forced to admit it by the decisive evidence
adduced in its support, they changed their ground of attack, and
alleged that the merit of the discovery did not belong to Harvey,
the circulation having been known even to the ancients. But
vain were all the efforts of envy and detraction to lessen that
fame, which will command the admiration of all future ages.
The physiological researches of Harvey were not confined to the
function of circulation ; but extended also to that of generation,
and to the evolution of the ovum, on which he made a series of
very valuable observations.

11.50. The beginning of the seventeenth century was an import-
ant era in anatomy, for it was also marked by another brilliant
discovery, namely, that of the lacteals by Aselli in 1622. It
appears, from the testimony of Galen, that Erasistratus had
noticed white vessels on the mesentery of kids; but the observation
was not followed up, and these vessels were supposed to have
been merely veins. Aselli was born at Cremona, and was professor

38*

450 HISTORY OF PHYSIOLOGY.

of medicine at Pavia. He observed on the mesentery of a dog
numerous vessels, filled with a white fluid ; he was immediately
convinced that he had made an important discovery, and uttered
in the fulness of his feelings, the exclamation " Et//i«za." Perceiv-
ing similar vessels upon the surface of the liver, and entertaining
spme theoretical views concerning the functions of that organ,
he too hastily concluded that the lacleals terminated in the liver.
Aselli. published an account of his discovery With coloured prints
in 16--^7.

1151. It was not till about thirty years after this discovery of
Aselli, that the lacteals were traced by Pecquet, a Ji'rench
anatomist, into the receptaculum chyli, and thence into the thoracic
duct, which he also followed to its termination in the great veins
near the heart. These observations were published in the year
1651. All these discoveries were made in brutes ; and it remained
to be shown, that similar structures existed in man. This was
accomplished by Veslingius, w^ho had already demonstrated the
human lacteal vessels, in the year 1634; and the human thoracic
duct in 1649. These parts were afterwards more fully investigated
by Peirish and Vanhorne. Shortly afterwards, the general absor-
bents of the body were discovered by Olaus Rudbeck, a Swede,
who was born at Avosa, in the year 1630. This discovery was
also claimed by Thomas Bartholin, who was born at Copenhagen
in the year 1616: but by his own account he had not seen these
lymphatic vessels till December 1651, whilst Rudbeck had not
only observed them, but had distinguished their peculiarities the
year before; Rudbeck had also traced them to the thoracic duct,
which Bartholin had failed to do. Dr. Joliffe, an English physician,
has also contended for the honour of this discovery ; but from a
comparison of dates, the priority is clearly in favour of the
Swedish anatomist. When we consider the minuteness of these
vessels and the transparency of their coats, we are able to
appreciate the difficulty of detecting their existence, and our
surprise must cease at their having remained unknown for so
many ages.

1J52. No discovery of equal importance to those we have
mentioned has been made in anatomy since that period. Many
parts of the body, which were unknown in Harvey's time, have
indeed been brought to light; but the principal improvement has
consisted in a more accurate knowledge of the composition and
minute structure of the several organs. For this we are chiefly
indebted to the invention of new anatomical processes, both of
investigation and of demonstration. Two principal means were
employed in these researches ; the one was the microscope, the
other the practice of injections.

1153. The microscope was first applied to the purposes of
anatomical inquiry about the year 1661, by Malpighi, who was

HISTORY OF PHYSIOLOGY. 451

born near Bologna, in the year 1638. He examined, by the aid
of this instrument, the minute organization of all the vital parts ;
and more particularly the glands. These researches into the
intimate texture of various parts of animals were prosecuted with
great ardour by Leewenhoek, a Dutch anatomist, about the
year 1680. In explonng this new field of inquiry, which opened
views so remote from common apprehension, his enthusiasm has
often carried him beyond what was real, both in the power of
the instrument, and in the results it afforded. But still much has
been effected, and the boundaries of the science have been greatly
enlarged by the skilful employment of the microscope.

1154. The arts of preserving the parts of animals when dis-
sected, by drying and varnishing them, and by other modes of
preparation, had long been practised ; and in these Vanhorne is
said to have attained superior excellence. But the most valuable
invention of this kind was that of injecting into the vessels cer-
tain fluids which would, after a time, become solid, and admit of
the course of these vessels being easily traced. The injecting
syringe used for this purpose was invented by De Graaf, a Dutch
anatomist, about the middle of the seventeenth century ; and soon
after, the proper materials for injection were discovered by
Swammerdam. The art of injection was carried to a very high
degree of perfection by Ruysch ; but with a degree of selfish
illiberality which cannot be too strongly condemned, he kept secret
the methods he employed.

1155. The advancement of Physiology was greatly promoted
both by the practice of this art, and by the dexterous employment
of the microscope ; and discoveries in this science have succeeded
one another so rapidlj^ from the period of their invention, that in
giving an account of them, it is scarcely possible to preserve an
unbroken narration ; and it would be impossible, in this sketch,
to I'ecount the numerous minor improvements which have been
made in our knowledge of this department of science from the
epoch down to which we have now brought its history. Much
error was still mingled with the acquisition of real knowledge on
these subjects ; and it has required the exertion of the more severe
and scrutinizing spirit of inquiry which characterizes the philoso-
phers of a later period, to winnow the grain from the chafl', and
refine the pure metal from the superfluous ore which had been dug
up along with it from the mine. Physiologists were slow in
recognising the peculiarities which appertain to the vital powers,
and those of the beginning of the eighteenth century long persisted
in ascribing the phenomena of life to the operation of the same
laws which regulate those of inanimate nature. Hence the
history of physiology is occupied at that period, chiefly by the
contentions which arose between the rival sects of chemists, and
mathematicians ; each striving to apply to physiology the princi-

452 HISTORY OF PHYSIOLOGY.

pies and methods of investigation which prevailed in their respec-
tive sciences. Much ingenuity was wasted in these unprofitable
researches ; for although some important fact was occasionally
brought to light by the prosecution of elaborate inquiries, prompted
by endeavours to support each favourite speculation, yet not one
of these hypotheses could long maintain its ground, nor could it
be said that a single general principle had been established.

1 1 56. A new light was now thrown on the subject of physiology,
which tended to dissipate the clouds of error in which it had
been obscured by the dogmatical tenets of both the chemical and
the mechanical sects ; and to effect a complete renovation in the
science. The new doctrine which thus superseded the former,
originated in Stahl ; who, although educated in the school of the
chemists, soon shook off the trammels of his instructors, and with
the vigour of native genius began to reflect for himself. He per-
ceived the futility of their doctrines, and strongly impressed with
the wide differences observable between the phenomena presented
by organized beings, and those which the same bodies exhibit
when devoid of vitality, conceived that they were governed by
some agency opposed to the ordinary physical powers of matter;
and to this agent he gave the name of anima (see § 101), ascrib-
ing to it endowments allied to intelligence, which controlled all
the changes in the system, and of which the operations were
alwa3^s directed to salutary ends. This hypothesis, gratuitous
and unphilosophical as it was, had the beneficial effect of direct-
ing the attention of physiologists to the phenomena which pecu-
liarly characterise the living state, and prepared them for the
study of the laws of these vital phenomena. Much praise is also
due to Hoffmann, who, although too hasly in his conclusions to
inspire confidence in their correctness, appears to have been
amongst the earliest of the followers of Stahl, who entertained
proper views of the principles and objects of physiology. Boer-
haave was celebrated at this time for the extent of his information,
the soundness of his judgment, and his talent in the art of instruc-
tion. His doctrines had extensive influence in the schools of
medicine ; but being destitute of the solid support of facts, they
did not long survive their propounder.

1157. But the great founder of modern physiology is unques-
tionably Haller, whose labours in this field of inquiry are so pro-
digious in extent, and so fruitful in results, that the publication of
his Elements, to which it may be perceived we have had occa-
sion in the course of this treatise perpetually to refer, must be
considered as forming an important era in the history of the
science.

1158. The attention of physiologists was beginning to be more
particularly directed to the functions of the nervous system; and
the labours of Whytt at this period had tended much to give it

HISTORY OF PHYSIOLOGY. 453

this impulse. Amongst the host of names which claim our notice
as having contributed their share in the rapid progress of disco-
very, since this time, we can point out only a few of the most
illustrious. William Hunter, the Monros, and CuUen, are amongst
those most eminent for the services which they have rendered to
physiology ; but perhaps the largest contributor to the mass of
facts collected in modern times was John Hunter. The merits
of Bichat v/ere also of the first order ; and considering how early
his career was cut short by the hand of death, the additions
which he has made to the stock of facts, and the influence which
his opinions have had on the progress of the science, must excite
astonishment. Germany and Italy, as well as France, have been
prolific in ardent devotees and successful cultivators of physiology ;
and although it might be invidious to point out particular names, we
should be sorry to omit those of Spallanzani, Blumenbach, Som-
merring, Meckel, Gmelin, and Miiller ; nor should the justly
earned fame of Cuvier be passed over in silence, even in this
brief and imperfect retrospect of the benefactors of our race, for
such we must esteem all those who enlarge the sphere of human
knowledge, and thereby confer the most solid accession to the
power and happiness of man.

APPENDIX.

ON PH'RENOLOGY.

Phrenology, derived from p/i«v, the mind, and Koyog, discourse, is a
term which has been recently applied to denote a new doctrine of
mental philosophy, founded on a presumed knowledge of the functions
of different portions of the brain, obtained by comparing their relative
forms and magnitudes in different individuals, with the propensities
and intellectual powers which these individuals are found respectively
to possess. This term has of late years totally superseded ihe more
unpretending titles of Craniology and Cranioscopy, by which this
doctrine, in its earlier periods, and before it had aspired at effecting a
revolution in psychology, was designated, and which simply implied
the study of the external forms of the skull, both in men and animals,
with a view to determine the size of the subjacent parts of the brain,
and thence to derive indications as to the mental and moral qualities of
each individual.

' The original propounder of the doctrine which is the basis of
phrenology was Dr. Gall, a physician of Vienna, whose system, ma-
tured in conjunction with Dr. Spurzheim, has attracted so much at-
tention, and been so keenly discussed, both here and on the continent,
that we think it our duty to present our readers with a general outline
of this pretended science.

Of the several parts which compose the human body, the mechanism
of which has been so thoroughly unfolded by the diligence of modern
anatomists, there are few wiiose use in the economy is wholly un-
known. The intention and operation of every part of our frame sub-
servient to the mechanical purposes of connexion, of locomotion, and
of strength, such as the bones, muscles, and ligaments, are, in general.
Sufficiently apparent; the functions performed by the abdominal and
thoracic viscera are, for the most part, well ascertained ; and we are
able, in like manner, to discern the adaptation of the organs of sense
to receive appropriate impressions from surrounding objects. One
organ alone, and an organ of vast importance in the system, connected
"with every other, and essentially interwoven with our sensitive exist-
ence, has baffled all investigation, and still presents a wide blank in
this rich and cultivated field of knowledge. The brain, that large mass
of pulpy substance, which fills the cavity of the cranium, is, even at

456 ' APPENDIX. PHRENOLOGY.

the present day, as incomprehensible in its functions, as it is subtle
and complex in its anatomy. It appears, indeed, to be sufficiently
established, that the brain is, in some unknown way, subservient to
sensation and voluntary motion, and is thereby the immediate agent
by which the soul and body mutually exert an influence over each
other: and it has also been very generally supposed, that this organ
is immediately concerned in all our mental operations, besides being
the instrument by which we feel and act. But the phenomena com-
prehended under the operations of the mind are exceedingly various
and complicated, and are also of very different kinds ; so that before
we can reason concerning them, it is necessary that they should be
properly distinguished and arranged. Metaphysicians have, accord-
ingly, classed them as referable to our sentient, our intellectual, our
active, and our moral powers. Further subdivision again is required ;
and the intellectual phenomena, for instance, are arranged according as
they relate to the faculties of conception, association, memory, abstrac-
tion, judgment, imagination, invention, &c. Other phenomena are distri-
buted under the heads of the different active principles, such as the propen-
sities, the instincts, the afiections, and the passions, which belong to our
nature. Whilst we thus discover a great diversity in the functions of
the mind, we observe also as great a complexity of structure in the organs
by which they are performed. Shall we rest satisfied with an acqui-
escence in the general proposition, that the brain is the organ of thought?
May we not rather regard it as a congeries of distinct organs, corre-
sponding to the different faculties into which the mind may be analysed ;
each organ having its appropriate office, and being immediately subser-
vient to some particular function of the mind ? The question has,
indeed, presented itself to many physiologists ; but few have ventured
farther in attempting its solution, than to thi-ow out some vague and
general conjectures as to the uses of certain parts, or as to the supposed
habitation of the sentient principle. Thus, for a long period, it was
held, that the cerebrum was the organ of perception, and the cerebellum
the organ of memory. The cavities which are met with in the interior
of the brain have often been considered as the scene of the intellectual
operations. Nemesius, the flrst bishop of Emesa, under the reign of
Theodosius, taught that the sensations had their seat in the anterior
ventricles, memory in the middle, and understanding in the posterior ■
ventricles. Albertus Magnus, in the thirteenth century, went so far
as actually to delineate upon a head the supposed seat of the different
faculties of the mind. He placed common sense in the forehead, or in
the first ventricle of the brain, cogitation and judgment in the second,
memory and moving power in the third. Peter de Montagnana, in
1491, published the figure of a head, on which were indicated the seat
of the sensus communis, the cellula imaginaiiva, cellula sestimativa
sell cogitativa, cellula memorativa, and cellula rationalis. Ludovico
Dolci, Servito, and a great number of other writers, have hazarded
similar hypotheses as to the locality of the different faculties. Both
Haller and Van Swieten fancied that the internal senses occupy differ-
ent places in the brain ; but they considered its whole organization as
too complicated, too intricate, and too difficult, to allow of any hope

DR. gall's speculations. 457

that the seat of memory, of judgment, or of imagination, could ever be
detected."

In the pursuit of this speculation, no one has engaged with more
ardour and perseverance than Dr. Gall, who, after many years of patient
labour, and much fruitless wandering in searcli of the truth, conceived
that he had at last discovered the clue which was to conduct us through
the mazes of this labyrinth, and enable us to arrive at a more accurate
knowledge of human nature, and of the means which may conduce to
its perfection. The account which he gave of the circumstances that
gradually drew his attention to the subject, and of his progress in this
new path of discovery, is as follows : Brought up in the midst of a
numerous family, and naturally gifted with the talent for observation,
he was struck, even when a boy, with the diversities of disposition and
of character amongst his brothers and sisters, and the companions with
whom he was educated. He remarked, that each excelled in a particular
study, or was distinguished by a peculiar turn of mind. One was noted
for the beauty of his handwriting; another for his quickness at arith-
metic ; a third for his aptitude in learning languages ; a fourth for
remembering everything that he read in history. ' This diversity was
apparent in all that they did ; thus the style of composition of the one
was remarkable for its flowing and elegant periods ; of another for its
baldness and dryness ; of a third for its condensation and vigour. Many
displayed talents for arts which had never been taught them ; they
excelled, perhaps, in drawing, or in the execution of works of mechan-
ism ; some, sought for amusement in noisy sports, others preferred
cultivating their gardens ; a few placed their chief delight in rambling
through fields and forests, and in collecting birds, insects, and flowers.
One was of a social and afl^ectionate disposition, another was selfish
and reserved ; a third was fickle, and not to be depended upon. The
great facility with which some of his school-fellows could commit their
tasks to memory, which to him was a work of immense labour, although
in matters of reasoning and judgment he felt "himself their superior,
often proved a grievous source of mortification, and excited in him a
strong desire to know the cause of this difference. He at length
remarked, that all the boys gifted with this kind of memory had large
and prominent eyes. He afterwards went to the university ; and
directing his attention to all those among his fellow-students, who
presented the same peculiarity of feature, he learned that they were all
distinguished by the tenacity of their memories; as, indeed, he soon
found to his cost, for ihey were sure to leave him far behind in every
competition, where the exercise of this faculty was essential to success.
This observation gave rise to others ; it suggested the notion, that other
intellectual endowments might also be indicated by the features ; and
Gall, by degrees, came to imagine that he had discovered a number of
external signs, which respectively indicated a decided turn for painting,
for music, for mechanical arts, or other objects. He had by this time
commenced the study of medicine ; and, in the course of his academical
instructions, he heard much about the functions of the muscles and
viscera ; but nothing was taught about those of the brain and its different
parts. It then occurred to him, that the differences he had already

39

458 APPENDIX. PHRENOLOGY.

noticed in the external configuration of the head, as connected with
certain dispositions of mind, were occasioned by differences in the form
of the brain. Delighted with the prospect which this idea opened to
him of discovering the functions of particular parts of this organ, and
of obtaining an insight into the connexion between the mind and the
body, he formed the resolution of prosecuting the research, till he had
either accomplished his object, or satisfied himself that it was not to be
attained by that method. Natural history, which had long been his
favourite study, furnished ample scope for the extension of these
inquiries. He had been in the practice of collecting plants and animals-
of various kinds, and of arranging them, not according to the artificial
methods of classification detailed in books of science, but according
to their more obvious resemblances. He now studied the relations
between their external forms, and their natural habits and dispositions.
Dogs, showed him the greatest diversities in their capabilities of being
educated. He remarked that some were naturally expert at the chace,
while others, of the same breed, could not be trained without the utmost
difficulty ; that some perpetually lost themselves, while others found
their way home from great distances. In birds, he observed that one
would listen with attention to a tune which it heard, and immediately
learn it ; while another of the very same brood would sing nothing but
the note that was natural to it. Whence, he would ask himself, can
arise this wide diversity among individuals ?

The solution of this difficult question was not to be hoped for, unless
by means of observations conducted on the largest possible scale. He
therefore set about examining all the skulls he could lay hold of, that
had belonged to individuals whose history was known. He looked
out for all persons in any way distinguished for a particular talent or
moral quality. He examined their heads with great attention, and
noted the peculiarities in their shape. He also collected observations
on other individuals, who were remarkable for the weakness of any
faculty, and then compared together the positive and negative indica-
tions. On the other hand, when he chanced to meet with a head that
presented some singularity in shape, he was at much pains to obtain
information as to the moral and intellectual character of the person to
whom it belonged. When he had no other resource, he did not scruple,
as Dr. Spurzheim informs us, to address his questions directly to the
person in whose head he observed any distinct protuberance. We are
also told, that he was in the habit of collecting around him the boys he
met with in the streets of Vienna, and of inducing them, by petty bribes,
to confess their own faults, and betray those of their companions. He
excited them, for instance to fight together, in order to discover which
possessed most courage, and thence drew inferences as to the organ
which prompted that sentiment. In order to obtain more precise data
for his conclusions, he endeavoured to procure models of the more
remarkable heads that he met with, and generally got permission from
the individuals themselves to take a cast of their heads in plaster of
Paris. The Count of 8auran, then minister of police at Vienna, gave
him material assistance in effecting these objects ; and he was thus
in no long time in possession of a very large collection of casts, all
bearing more or less upon the several points of his theory. If he hap-

DR. GALL S RESEARCHES. 459

pened to hear of the death of any one whose head he had already-
moulded, he was at great pahis to procure his skull, that he might
compare the form of its different parts with the shape of the head
during life. As it was soon known that the doctor aimed chiefly at
those who possessed some remarkable talent, a very general alarm
spread itself amongst the inhabitants of Vienna; and not a few were
pursued with the terror of being selected as the subjects of craniosco-
pical investigation, and of their skulls being destined to make a figure
in his anatomical cabinet. The aged Mr. Denis, librarian to the em-
peror, is said to have inserted an express clause in his will, to protect
his head from the keen scalpel of Dr. Gall. Notwithstanding these
fears and precautions, he contrived to amass an extensive collection of
skulls, as well as of heads, in illustration of his doctrines. He next
availed himself of the aid of comparative anatomy ; and having no family
to provide for, spared no expense in procuring skulls of all sorts of
animals, with a view of tracing the form and size of corresponding
organs throughout the whole series. Being physician to the establish-
ment for the deaf and dumb at Vienna, he had opportunities of observ-
ing the natural features of uncultivated minds, and the various degrees
in which they were susceptible of education. With the same view,
he used to call together into his house persons of the lowest class, such
as coachmen, and beggars in the street, and excite them to display their
characters before him. His professional practice made him acquainted
with a great number of families, and afforded him many opportunities
of making valuable observations. He neglected no means of instruction
that could be derived from the inspection of the heads of patients
labouring under different forms of insanity. He was physician to the
director of establishments for education, and was allowed to examine
every child who excelled, or showed any remarkable disposition. He
visited the prisons and houses of correction, as well as the hospitals
for idiots and lunatics. He took casts of the heads of criminals, in-
quired into the offences for which they were confined, and collected
the history of their lives ; and thus derived from every quarter materials
for bringing his theory to perfection.

As his observations multiplied, he became sensible that he had
fallen into many errors in the earlier periods of his inquiries, and was
forced to give up many of his favourite opinions, which he found had
been too hastily adopted, with regard to the general form of the head,
as connected with the character of the individual. He felt the neces-
sity of being in future more on his guard, and resolved to institute a
separate examination of the different regions of the skull ; and although
he was here, also, frequently obliged to shift his ground in assigning
the function of each part, his researches were, on the whole, attended
with more uniform success. By degrees he acquired greater confidence
in the stability of his conclusions, and at length ventured to announce
them to the public, by the delivery of lectures on his new science.
His doctrines were eagerly received, and much canvassed at Vienna;
but their fame had no sooner reached the Austrian court, than a violent
outcry was raised against them by the bigoted priests, who controlled
all the operations of that weak and misguided government, and who

460 APPEN^DIX. PHRENOLOGY.

represented these doctrines as tending to materialism and atheism. The
consequence of this senseless clamour was, that Gall was interdicted
from lecturing. But the number of those to whom he had communi-
cated the principles of his art, and in whom he had infused a strong
desire to continue to profit by his instructions, was by this time very
considerable, especially among the strangers who happened to be at
Vienna. They formed a strong party in his favour, and made such
interest at court, principally through the medium of the foreign ambas-
sadors, that the doctor was again permitted to resume his prelections,
on condition that he delivered them to foreigners only ; as it was
wisely considered that their being exposed to the dangers of know-
ledge, would not be of any material consequence to the state, as long
as care was taken that the infection did not spread farther ; the em-
peror kindly preserving the bliss of ignorance for the exclusive enjoy-
ment of his Austrian subjects.

It was long before Gall committed himself by writing on the subject
that had procured him so much celebrity. He merely announced, in
1798, in a letter addressed to Baron Retzer, which appeared in the
Deutsche Merkur of Wieland, his design of publishing a large work
on the new theory, of which he affords his readers only an imperfect
glimpse. A detailed account was afterwards given by M. Froreiss, one
of his pupils, in the second volume of Voight's Magazin Physique;
and an amusing outline appeared from the pen of M. Charles ViUers, in
a letter addressed to Cuvier. * Various surreptitious copies of his lec-
tures were also circulated throughout the protestant states of Germany,
where they excited so much curiosity, that Dr. Gall was at length
induced to make a tour for the purpose of delivering them himself at
the principal universities in the north of Germany. "With this view
he visited Dresden, Berlin, Halle, Jena, Weimar, Gottingen, Ham-
burgh, &c. and every where met with the most flattering reception,
being invited to the several courts of the states through which he
passed, and treated with the honours due to a distinguished literary
character. By frequenting the first societies, and conversing with the
best informed persons, he had ample opportunities of extending his
observations, and he was attentive to improve these opportunities to
the utmost of his power. Dr. Spurzheim, who had at an early period
been associated with him in these inquiries, and who had devoted
himself particularly to the anatomical researches they comprised, ac-
companied him in this tour, and participated in all his labours. Dr.
Gall at length settled in Paris, where he continued his pursuits and
lectures, and united with them the practice of his profession.

In 1810 Drs. Gall and Spurzheim published, in conjunction, the
first volume, in quarto, of the work they had announced, and which
was to contain a full account of their doctrines, under the title of
Anatomie ct Physiologie du systeme nerveux en general, et dii
cerve.au en pariiculier, avec des observations sur la possihiliie de
reconnoitre plusieurs dispositions intellectu'elles et morales Vhomme
et des animaux, par la configuration de leurs tetes. The first part of
the second volume appeared in 1812. This work, together with the
one published in 1815, by Dr. Spurzheim, entitled The Physiogno-

MENTAL FACULTIES INNATE. 461

mical System of Drs. Gall and Spur zheim, founded on an anatomical
and physiological examination of the nervous system in general, and
of the brain in particular, arid indicating the dispositions and mani-
festations of the mind, contain the most authentic account of their
system. Information on the subject may, however, be derived from
the following books, besides those of Froreiss and Villers, already
mentioned. The best of the foreign works is that of Professor Bischoff,
entitled Darstellung der GaW schen Gehirnund Schddellehre, nebst
Bemerkungen uber diese Lehre, von D. W. Hufeland, Berlin, 1805.
At Dresden, in 1806, Bloede published a similar work, viz. Galls
Lehre Uber die Verrichtungen des Gehirns, nach dessen zu Dresden
gehaltenen Vorlesungen ; and at Paris, in the same year, we have,
from the pen of Demangeon, Physiologic intellectuelle, ou develope-
ment de la doctrine du Professeur Gall. A small tract in English,
entitled Some Account of Dr. GalVs new Theory of Physiognomy,
founded upon the Anatomy and Physiology of the Brain, and the
Form of the Skull, appeared in London in 1807, and is chiefly taken
from Dr. Bischoff''s work, including the critical strictures of Dr. Hufe-
land. Soon after the publication of Dr. Spurzheim's book, a small
volume, principally reprinted from a short tract in the Pamphleteer,
was given to the public by Mr. Thomas Forster, under the title of
Sketch of the New Anatomy and Physiology of the Brain and Ner-
vous System of Drs. Gall and Spurzheim, considered as comprehend-
ing a complete system of Zoonomy, with observations on its tendency
to the improvement of education, of punishment, and of the treatment
of insanity. Two pamphlets in opposition to these doctrines were
published by Professor Walton of Berlin, in 1805, of which, as well
as of BischofF's work, a short account is given in the Edinburgh Medi-
cal and Surgical Journal for July 1806. Dr. Spurzheim having
conceived that he was unfairly attacked by some of the Reviews, thought
proper to publish a reply, in a pamphlet which made its appearance at
Edinburgh, in 1817, entitled Examination of the Objections made in
Britain against the Doctrines of Gall and Spurzheim. These,
together with the lectures delivered in London by Dr. Spurzheim, are
the sources which have supplied the materials for the following sum-
mary.

It is laid down both by Gall and Spurzheim as the foundation of their
doctrines, that the nature of man, like that of all other created beings,
is determinate, and that the faculties with which he is endowed are
innate ; that is, that they are implanted in him at his first formation,
and are not the result merely of the external circumstances in which
he may afterwards happen to be placed, nor of the wants and necessi-
ties to which these circumstances may have given rise. They warn
us that this opinion is by no means at variance with that of Locke,
who argues against the innateness of ideas, and not of the faculties or
capacities of receiving ideas. Education, doubtless, has a powerful
influence in modifying and giving certain directions to these faculties ;
but the faculties themselves, that is, the capacities of feeling, of intel-
lect, and of action, must have already pre-existed before they could be
called into play, and thus produce the various phenomena which diversify

39*

462 APPENDIX. PHRENOLOGY.

the scene of human life. Savages have at different times been found in
woods destitute of all the ordinary faculties of rational beings. Their
resemblance to brutes has been supposed to be the consequence of
of their total want of education; but, when we eome to examine into
their real condition, we shall find that they are wretched beings, with
great bodily defects ; for the most part deeply tainted with scrofula,
and almost always complete idiots. In general, they appear to have
been abandoned in their childhood by their parents, to whom they were
burdensome. The pretended savave of Aveyron, who was kept in
the Institution for the Deaf and Dumb at Paris, was almost completely
idiotical. He was quite deaf, and his head atid body were incessantly
in motion from side to side, even when he was sitting.

In estimating the causes of that diversity which we see prevailing
in the characters and faculties of individuals, much has been ascribed
to the influence of diet, mode of living, and the impressions received
in early infancy, while the organs are yet tender, and highly suscepti-
ble of every kind of external influence. But the operation of these
causes, as well as the power of education in general, is much t^
limited to explain the immense differences we observe among different
men, and even among different children of the same family. Helvetius
and other bold metaphysicians have maintained the paradox, that all
men are born originally the same, and are moulded into what they
afterwards become solely by the force of external circumstances.
Genius, according to this doctrine, is a mere creature of the fancy, and
originally belongs no more to one man than to another. Train all
men alike, and their powers, their attainments, and their actions, will
all be similar. Accident, more than design or premeditation, has fixed
the destinies of great men, as well as disposed of those who are unknown
to fame. " Demosthenes," say these philosophers, " became eloquent,
because he heard an oration of Callistratus, whose eloquence made so
deep an impression on his mind, that he aspired only to acquire this
talent. Vaucanson excelled in mathematics, because, being obliged,
when a child, to stay alone in the waiting room of his mothers con-
fessor, he found there a clock, examined its wheels, and endeavoured,
with the help of a bad knife, to make a similar machine of wood.
He succeeded : and one step leading on to another, he arrived at the
construction of his wonderful automatons. Milton would not have
composed his Paradise Lost, had he noi been deprived of his place
of secretary to Cromwell. Shakspeare composed his tragedies because
he was an actor, and he became an actor because he was forced to
leave his native place on account of some juvenile errors. Corneille
fell in love, made verses for the object of his passion, and thence
became a great poet. An apple fell from a tree at the feet of Newton,
while he was in a contemplative mood : this event, so trivial in itself,
led him to the theory of gravitation," Reflections of a similar kind
are often met with in the writings of poets and moralists. Those con-
tained in Gray's J^hgy must be familiar to all our readers. Dr. John-
son considered talents or genius as a tiling that, wiien once existing,
might be directed any way. Newton, he thought, might have become
a Shakspeare, for, said he, a man who can run fifty miles to the south,
can run fifty miles to the north.

FACULTIES DEPENDENT ON THE BRAIN. 463

Yet these are but the ingenious speculations of the theorist, more
calculated to dazzle than to convince, and obviously in contradiction
with the daily experience of mankind. Original dilierences in the
constitution of the mind exist as certainly as in that of the body ; and
doubtless are dependent upon differences in -organization. Children
often show, from their earliest infancy, the germs of those peculiarities
of character which adhere to them through life, which hardly any
education can alter, and which no condition of life or variation of
circumstances can afterwards affect. It is needless to expatiate on the
subject of the diversities of intellectual powers exhibited by different
individuals under the very same circumstances of birth and education ;
diversities which, as we have already seen, first directed the mind of
Dr. Gall to his physiognomical researches. Many of these peculiarities
are unquestionably derived from the parent, and are observed to prevail
in certain families, and to descend througii several successive generations.

That no sensation, or other affection of the mind, and that no
operation of intellect can take place without a certain condition of the
nervous system, is a position established by so many direct proofs, that
its truth must be generally admitted. The question becomes more
difficult when we come to inquire what pait of the system it is that
exercises these functions. It is quite clear that the sentient principle
does not reside in the nerves, or in the part which receives the first
impression from the external cause of sensation. The opinion which
has been embraced by many physiologists, and particularly Bichat,
that while the brain is the organ of the intellectual faculties, the nerves
of the great viscera of the abdomen and thorax are the seat of the moral
sentiments, is at variance with a multitude of facts in comparative
anatomy. There are animals endowed with the faculties ascribed to
these nervous plexuses, or ganglions of the great sympathetic nerves,
distributed to certain viscera, which have not the viscera in question.
On the other hand, most quadrupeds have viscera analogous in their
whole structure to those in man, without having the faculties of which
in man it is pretended they are the seat. We have a complete series
of proofs that the nerves, of then>«elves, and without an uninterrupted
-continuity with the brain, can produce neither sensation nor voluntary
motion. Compression of the brain, by any cause, produces an entire
suspension of all sensation and consciousness, and puts a complete stop
to every operation of ihtellect. All the other parts of the body, on the
other handi may be wounded or destroyed, and even the nervous mass
of the spinal marrow may be compressed or injured, at a certain distance
from the brain, without the immediate destruction of the feelings and
intellectual faculties. In tetanus, produced by a cause remote from the
brain, the other nervous systems are affected in the most violent manner,
while the functions of the mind continue unimpaired.

In children. Dr. Spurzheim observes, the brain is yet pulpy, and
the faculties imperfect ; its growth accompanies their improvement ;
its maturity marks their greatest degree of vigour. If its development
has been considerable, the manifestations of these powers are energetic ;
if small, they are comparatively weak. In proportion as the organiza-
tion of the brain decreases, the strength of the moral sentiments and

464 APPENDIX. PHRENOLOGY.

intellectual faculties decreases also. If the development of the brain
take place too early or too late, the faculties exhibit corresponding
variations. Certain faculties are more active in men, and others in
women, according to the difference of their cerebral organization ; and
peculiarities of character are hereditary, according as the corresponding
organization of the brain, on which they depend, is propagated from
parents to their children.

Although many facts show that considerable injuries may be sustained
by the brain without detriment to the mental faculties, yet as a general
principle, it is contended by Dr. Spurzheim, that these faculties are
weakened or destroyed in proportion as the brain is mechanically
altered. It is, however, certain, that physiologists are by no means
agreed as to this point; and that innumerable cases might be quoted
in direct contradiction to this principle. These are attempted to be
explained away by the general supposition, that most of them are the
result of very inaccurate observations, in which the statement of the
facts has been distorted and vitiated by ignorance, prejudice, or cre-
dulity ; and that the rest are inconclusive as to the general question,
from the observers not being aware of the real functions of the injured
parts, and being inattentive to the circumstance, that almost all the parts
of the brain being double, the loss of those on one side would scarcely
be felt, as long as the corresponding organs on the other side remained
entire. On the other hand, it should be recollected, that a derange-
ment in an organ may occur of such a nature as that our senses cannot
enable us to discover it. How often is this exemplified in fatal dis-
eases of the nervous system, such as hydrophobia, tetanus, and atonic
gout. Analogy shows us other parts where apparently no proportion
is preserved between the injury and the derangement of function.
Sometimes large abscesses are -met with in the lungs without much
disturbance of the function of respiration ; and ossification of the heart,
without any sensible affection of the circulation. In persons possessed
of great irritability, very slight wounds of the brain may produce
serious effects, while considerable wounds in others, who are less
irritable, shall be attended with no bad consequences. This consider-
ation will go a great way towards explaining the fact, that in many
cases of insanity, instead of our discovering any change in the brain, a
diseased state has been observed in the liver, the bowels, and other
viscera ; and may serve as an answer to the assertions and objections
of Pinel, who states that the most accurate dissections have not taught
us any thing with regard, to the seat of mental alienation, and that we
have no sufficient data to conclude, from diseases of the brain, that it
is exclusively the organ of the intellectual faculties.

Those who have opposed the theory of the subserviency of the brain
to the operations of mind, have laid great stress upon an argument
derived from the phenomena of hydrocephalus. In patients afflicted
with this disease, the brain appears to be destroyed and replaced by
water ; and yet the intellectual and moral faculties have remained
perfect to the last. Drs. Gall and Spurzheim conceive, that the facts
have been very erroneously represented ; and that the only alteration
which the brain sustains in these cases, is a displacement of its parts,

OPINIONS OF PHYSIOLOGISTS.

405

and not an absorption of its substance. The effused fluid, by accu-
mulating in the ventricles, gradually unfolds the convolutions of the
hemispheres of the brain, and expands them to such a degree, that
they are reduced to a thin stratum of substance, constituting a sort
of bag, within which the fluid is still contained. This stratum of
brain is sometimes not more than a line in thickness, and is generally
lacerated in attempting the dissection ; in which case the water rushes
out, the real structure escapes notice, and the fluid is erroneously
supposed to have been accumulated between the brain and its mem-
branes.

It has been advanced, as another objection to the same theory, that
monsters are sometimes born without any brain, who yet suck and
perform various movements. Actions of this kind, however, are purely
automatic, and appear to be unattended with consciousness ; with such
actions the brain has no concern whatever. Some have founded their
opposition to the theory, on the result of some experiments of Duverney
on pigeons, which, it is alleged, continued to perform all their animal
functions after the whole of the brain had been removed from the skull.
But Dr. Spurzheim, on repeating these experiments on birds and
rabbits, found, indeed, that the destruction of the superior parts of the
brain does not destroy the functions of the five senses and of voluntary
motion, but that it is impossible to take out all the cerebral mass with-
out killing the animal. As soon as the corpora striata and optic
thalami are wounded, convulsions and death ensue ; consequently he
does not hesitate to pronounce the account given by Duverney to be
entirely false. He, in like manner, wholly discredits the stories related
by Morgagni, Zacutus Lusitanus, Bartholine, Haller, Vallisneri,
Moreschi, Giro, Dr. Simson, Sommerring, and others, concerning
petrified or ossified brains being found in individuals, without prejudice
to the exercise of their intellectual faculties. He admits it to be
doubtful, how far, in perfect animals, the brain may be necessary to
the passive consciousness of the external senses ; but deems it certain,
that the exertions of the will, including voluntary motion and reflection,
depend entirely upon the brain ; no phenomenon of this kind ever
taking place without that organ.

Concluding, therefore, that the brain is the organ of the sensitive,
the intellectual, and the moral faculties, we have next to inquire,
whether these faculties are exercised in common by the whole, or any
particular portion of the brain, or whether, on the other hand, they are
more especially the offices of different parts of that organ. Dr. Gall
adopts the latter of these opinions, ami upon this view of the subject is
the whole of his system founded. The following is the reasoning on
which he builds it.

Physiologists, influenced by the metaphysical tenets of the schools,
have often maintained, that the soul, being simple, its material resi-
dence must be simple also, and that all the nerves must end at one
point ; or, which amounts to the same, that they can have but one
common origin, because each individual has but one soul. Bonnet,
Haller, and others, who had extended its seat to the whole substance
of the brain, were opposed by these metaphysicians, who did not re-
flect that a little more or less room could not enable them to explain

466 APPENDIX. PHRENOLOGY.

any better the nature of the soul ; nor that, as Van Swieten and Tiede-
mann, remark a material point, in which all ideas and sensations should
centre, is inconceivable, in consequence of the confusion and disorder
that would result from such an arrangement. It appears ridiculous,
indeed, that the physiologist, to whom all nature is open, should direct
his researches and inductions by the guidance of such frivolous specu-
lations. Great pains wers, however, taken to determine this central
point, or sensorium commune; but it is enough to enumerate the vari-
ous and contradictory opinions that have been held with regard to it, in
order to be satisfied of the utter futility of this research. Descartes, in
his treatise on the Passions, labours to prove that the soul is concen-
trated in the pineal gland. This hypothesis continued in fashion for
some time, till it found an enemy in a follower of Descartes, the Dutch
physician Boutekoe, who dislodged the soul from its narrow watch-
tower in the pineal gland, and confined it in the more spacious prison
of the corpus callosum. Lancisi, Maria, and La Peyronie, successively
declared themselves in favour of this new opinion ; and the latter of
these anatomists wrote a memoir in support of it, which was printed
by the Academy of Sciences in 1741, and which has since been repub-
lished separately. Digby next transferred the soul to the septum lucidum
in place of the corpus callosum. Vieussens allowed it greater latitude,
assigning for its boundaries those of the centrum ovale of the medullary
substance. Willis, again, restricted it to the corpora striata; Serveto,
to the- aqueduct of Sylvius. Wharton and Schellhammer placed it in
the commencement of the spinal marrow ; Molinetti and Wrisberg in
the pons Varolii ; Crusius and Meig in the origin of the medulla oblon-
gata ; whilst Drelincourt and others lodged it altogether in the cere-
bellum. Lastly, Sommerring imagined the soul to reside in the serosity
which moistens the inner surface of the ventricles, to which he had
traced the extremities of many nerves from the organs of sense ; and
conceived that the different motions or oscillations of this fluid are the
immediate material cause of our sensation.

Discarding the notion that the functions of sense and intellect are
concentrated in any particular point or portion of the brain, let us
next examine the opinion that all the faculties are exercised by the
whole mass of brain considered as one organ. We may, in the first
place, remark, that the analogy of other parts of the system is adverse
to this hypothesis. Every different secretion has its appropriate gland,
the offices of which are never interchanged. The liver never secretes
urine, nor the kidneys bile. The five external senses are distinct and
independent of one another. Every where do we observe that nature,
in order to produce various effects, has varied the material organs.
The structure of the brain in its different parts, is far from being simple
and uniform ; it is composed of two substances ; the one soft, pulpy,
and ash-coloured ; the other white, opaque, and fibrous in its texture.
The fibres of the latter run parallel to each other, having, at the same
time, various collateral connexions, but by no means uniting in any
one central part which can be considered as their common origin or
termination. The parts of the brain are numerous, and distinct from one
another, bearing evidence of a very complex and artificial construction.

PLURALITY OP ORGANS. 467

They are constant in their general arrangement in different subjects,
showing in this respect a striking contrast with the distribution of
blood-vessels, or even the disposition of the muscles and viscera, in
which it is so common to meet with variations. Comparative, as well
as human anatomy, furnishes strong analogical arguments in favour of
a plurality of the cerebral organs, corresponding to the plurality of
faculties. However defective may be our knowledge of the structure
of these organs in the lower animals, still a general comparison of their
faculties, as we ascend in the scale of being, shows us that the number
of these faculties increases in proportion as the cerebral parts are mul-
tiplied. The immense augmentation of the powers of intellect which
we behold in man, when compared with the limited instincts of ani-
mals, is neither in proportion to the increased size of the five external
senses, nor of any other part of the body, but to the increase of the
cerebral organs only. It is the great size of the hemispheres of the
brain, more especially, that characterizes this organ in man, and esta-
blishes superiority, as an instrument of intellect, over that of all other
animals. Man unites in himself all the organs which are variously
scattered and distributed among the brute creation ; but he has also
organs in his brain, which no other animal besides himself possesses ;
and these are the seats of faculties of a higher order, peculiar to him
alone.

Considerations arising from the differences in the proportional energy
with which the faculties manifest themselves in different individuals,
are also in favour of the plurality and independence of the organs. If
the brain were one simple organ of mind, and alike instrumental in all
its faculties and operations, wherever we meet with any one faculty in
a state of high energy, we must suppose the whole organ adapted to
produce this degree of energy, and ought to expect its other operations
to be equally energetic. Yet we may find the same individual remark-
ably deficient in other faculties, which are equally dependent on this
organ. One person shall excel in verbal memory, while he cannot
combine two ideas philosophically ; another is a great painter, but a
bad musician, or a wretched poet ; another is a good poet, but a bad
general. If the brain be a single instrument, it cannot be at once both
weak and strong; it cannot exhibit one faculty in its perfection, and
another in a very limited extent. But all difficulty vanishes if we
admit it to be an assemblage of many organs ; for the combinations of
these organs may be as infinitely diversified as the actions and powers
of man. The argument derives additional force from the readiness
with which this theory may be applied to explain the diversity of cha-
racter we meet with in the brute creation, and especially to the varieties
of disposition observable among some of our domestic animals, which,
under the same circumstances of education, exhibit such different
qualities. In like manner, the diversity of character in the same indi-
vidual, at different periods of his life, are most readily explicable on
the supposition of distinct organs, which have their respective periods
of growth, maturity, and decline. The analogy of the external senses
is also strongly in favour of the same doctrine. Thus the taste and
smell appear earlier than the senses of seeing and hearing, because

468 APPENDIX. PHRENOLOGY.

their respective organs are earlier developed. This reasoning will be'
confirmed when it is found, as will afterwards be shown, that the pro-
portional size of the different parts of the brain is very different in dif-
ferent individuals. Is it not, therefore, reasonable to suppose, that the
different energies of the several functions of the mind are connected
with these differences in the structure of the organs which respectively
produce them ?

The faculties of animal life are incapable of long continued exertion ;
rest is necessary for the renovation of their powers. Fatigue is the
consequence of the prolonged action of the muscles of voluntary mo-
tion ; but when one set of muscles are fatigued, the power of others is
still unimpaired, and they are ready to be employed in a different ac-
tion, without any additional fatigue. When we have been long sitting,
we are relieved by standing ; and even the bed-ridden find ease from a
change of posture. Our eyes, in like manner, may be fatigued by
looking at pictures ; but we can then listen to music, because there is
one organ for seeing, and another for hearing. It is well known that
study, long protracted, produces fatigue ; but we can continue to study,
provided we change the object of attention. If the brain were a single
organ, the whole of which is employed in performing all the functions
of mind, a new foTm of study should increase instead of relieving the
sense of fatigue. Thus the analogy is complete between the pheno-
mena of mental and bodily exertion. Are we not, then, justified in
extending it to the instruments by which these operations of mind and
body are effected ?

The phenomena of sleep are also readily accounted for on this
hypothesis. During this state all the organs do not remain inactive ;
but sometimes a particular organ enters into action, and this constitutes
dreaming. The state of vigilance is that in which the will can put in
action the organs of intellectual faculties, of the five senses, and of
voluntary motion ; but it is incorrect to define it as the state in which
all these organs are active, for it is impossible that all the faculties
should be active at the same moment. Somnambulism may be re-
garded as a state of still more incomplete sleep, or one in which
several organs are watching. If, during sleep, the action of the brain
is partial and is propagated to the muscles, locomotion takes place ; if
to the vocal organs, the sleeping person speaks. All this may take
place in different degrees. Some persons dream and speak in their
sleep ; others dream, speak, hear, and answer; others, besides dream-
ing, rise, walk, and do various things. This latter state is called
somnambulism ; that is, the state of walking during sleep. Now as
the ear can hear, so the eyes may see, while the other organs sleep ;
and thei-e are undoubted facts which prove that several persons in the
state of somnambulism have seen ; but it has always been with the
eyes open. There are also convulsive fits in which the patients see
without hearing, or vice versa. Some somnambulists do things of
which they are not capable in a state of watching ; and dreaming per-
sons reason sometimes better than they do when awake. This phe-
nomenon is not astonishing. If we wish to reflect upon any subject,
we avoid noise, and all external impressions ; we cover the eyes with

PLURALITY OF ORGANS. 469

onr hands, and we put to rest a great number of organs, in order to
concentrate all vital power in one, or in a few. In the state of dream-
ing and somnambulism this naturally happens ; consequently the
manifestations of the active organs are then more perfect and more
energetic ; the sensations are more lively, and the reflections deeper
than in a state of watching.

States of disease are also adduced as proving tlie plurality of the
cerebral organs. In many cases of insanity we find only one faculty
deranged, whilst all the rest are in a perfectly sound state. Lunatics, on
the other hand, are met with, who are reasonable only while pursuing
some particular train of thought. There was a chemist, for instance,
who was insane on every subject except chemistry. An embroiderer,
during her paroxysms of insanity, while uttering the greatest absurdities,
calculated correctly how much stuff was necessary to such or such a piece
of work. The effects of blows, or other injuries on the head, supply
facts of a similar kind, which afford still more convincing proofs that
the brain is susceptible of being very partially affected. Some per-
sons lose from this cause the memory of proper names, while they
preserve the memory of words which indicate the qualities of objects.
One Lereard of Marseilles, after having received a blow from a foil in
the orbit, lost entirely the memory of names ; sometimes did not recol-
lect those of his intimate friends, or even of his father. Cuvier, in his
historical eulogium on Broussonet, states that this celebrated botanist,
after having recovered from an apoplectic fit, never could recollect
proper names nor substantives, though he had recovered his prodi-
gious memory with respect to other objects. He knew plants, their
figure, leaves, and colovirs ; he recollected the adjectives, but could
never recover the generic substantives by which they were designated.
These, and similar instances of partial affections of the faculties, support
the supposition of their being owing to different conditions of various
parts of the brain subservient to these faculties.

Lastly, the doctrine that different portions of the brain exercise
different mental functions, is countenanced by numerous authorities in
former as well as in modern times. It is expressly stated in the writings '
of Boerhaave, Van Swieten, Haller, Prochaska, Sommerring, &c. ;
and the Academy of Dijon long ago proposed it as a prize-question,
to determine the situation of these different cerebral organs. Charles
Bonnet, indeed, went the length of maintaining that each fibre of the
brain is a particular organ of the soul.

It seems hardly necessary to expose the absurdity of the accusation
that these doctrines tend particularly to materialism, although the
dread of such a consequence has been sanctioned by royal edicts.
There are two opinions only, which, in respect to this question, stand
opposed to each other ; namely, that which asserts perception to take
place by the intervention of a material organ, and that which asserts it
to take place immediately by the energies of the mind itself, or at
least without the intervention of the body. The doctrines of Gall are
unquestionably incompatible with this last opinion, that is, with pure
immaterialism, which may in fact be regarded as denying the existence
of matter altogether. This sceptical spiritualism can be avoided only

40

470 APPENDIX. PHRENOLOGY.

by the admission of the necessity of a material organ ; and if this be
admitted, any modification of such opinion, that does not exclude mind
as the ultimate percipient, must be equally remote from absolute
materialism. The immalerialist believes that it is the soul which sees
and the soul which hears, as much as that it is the soul which judges
and the soul which imagines; and since he does not condemn, as im-
pious, the allotment of different organs of sight and hearing, what
greater heresy is there in the allotment of different parts of the
sensorium, as the organs of judgment and imagination? If, indeed,
one were to say, that the affections of these parts are themselves judg-
ment and imagination, he would be a materialist, but he would be as
much a materialist, if he should say, that the affections of the organs
of sight and hearing are themselves the ideas of colour and sound.

Supposing it, then, established that each function of the mind is
exercised by a separate portion of the brain, let us next inquire whether
observation can furnish us with any means, of determining the precise
nature of the function, to which each particular organ is subservient.
Although it is clear that the adaptation of each organ to the performance
of its office, must be wholly dependent on its particular organization,
yet it is equally evident that no consideration of its general structure,
as shown to us by anatomy, can teach us a priori what such function
really is, and still less what may be its degree of energy, or its peculiar
quality and modifications. The energy of the function must in all
cases depend on certain conditions of the organ, such as the perfection
of its original constitution, its elaborate texture, its relative size, and
the degree of exercise it has received ; and will also be regulated by
the influence which other faculties may exert on its operations. The
only one among these conditions, which is open to observation, is the
relative size of the organ. In general, we find that the properties of
bodies act with an energy proportionate to their size. A large load-
stone attracts a greater mass of iron than a small loadstone. A large
muscle, in like manner, is stronger than a small one. If the nerves
of the external senses be larger on one side of the bod)', the functions
on that side are also stronger. Comparative physiology shows us that
the olfactory, optic, and auditory nerves of those animals which are
distinguished for the excellence of their smell, sight, or hearing, are
marked by being numerous and large, evincing a more elaborate deve-
lopment. The coincidence is so uniform as to justify the general
inference, that wherever any organ is met with in a higher state of
development, we may there expect to find the power dependent on it
increased in energy in the same proportion. May not this analogy be
fairly extended to the organs which compose the brain? Our present
object, it must be recollected, is not to determine every degree of
activity existing in a cerebral part, but merely the nature of its func-
tion ; and for this purpose the indication afforded by its comparative
size, in different cases, will suffice.

We may observe in different individuals a considerable variation in
the proportional development of different parts of the brain. It is
reasonable to suppose, that the organs which are more developed in
one person than in others, will be more active, and manifest them-
-selves with more energy, than those which are less developed.

CORRESPONDENCE BETWEEN THE SKULL AND BRAIN. 471

Those which are comparatively small we may expect to be less
active, and the;r powers more feebly exerted. Let us tlien select
as the subjects of observation such persons as ar^ marked by
strong peculiarities of mind or character, and especially such as are
endowed with a partial genius, as it is called ; that is, who manifest
in a very high degree any particular faculty of mind: let us note the
peculiarities in the form of their heads, and observe what organs in
them are of-an unusually large size. By repeated comparisons we sjiall
arrive at the knowledge of the particular organ in which that faculty
resides. The converse method, on the other hand, must be pursued
with those who betray a singular deficiency of power in any faculty.
With such persons we must endeavour to discover what particular part
of the brain exhibits an imperfect development. The results of both
these modes of determining the functions of each organ, when com-
pared together, will correct, and, if just, will ultimately corroborate
each other. Experience, multiplied and extended, will finally confirm
and establish our conclusions, and complete the system in all its parts.

But the living brain can never be exposed to observation, and, from
the nature of its substance, loses much of its form and texture soon
after death. It may appear impossible to discover the form or size of
particular parts of the brain during life, since the whole mass is inclosed
in the bony case of the skull, of which the thickness varies in different
parts ; and since the skull itself cannot be immediately inspected, being
covered by muscles and integuments, which, by contributing to smooth
all the inequalities of its surface, must preclude us from forming an
exact estimate of its real shape. This obvious objection to the proposed
inquiry, Drs. Gall and Spurzheim labour to remove by the following
considerations. If we attend to the succeseive stages of the growth of
the skull, we find that its ossification begins at different points ; and
the bony processes extend in divergent lines, adapting themselves
exactly to the form and size of the cerebral parts they are destined to
inclose and protect. Whatever violence may be done to the bones of
the skull during birth, they soon return to their natural state, partly
from their elasticity, and partly from the inherent powers of the brain,
which tend constandy to restore its original shape. The compression
of the brain is besides of too transient a nature to produce any perma-
nent change in the primitive forms either of the skull or of the brain.
If it ever amounted to what could irrecoverably derange the organiza-
tion, and hinder its future development, the necessary consequence of
such a degree of violence would be death or idiocy.

In the progress of its growth, the increasing dimensions of the skull
keep pace with those of the brain. All the cerebral parts do not increase
simultaneously; and this partial development is equally observable in
the skull. The forehead, for instance, which at birth is narrow and
flat, grows wider and more prominent from the age of three months to
that of eight or ten years. After this period, the middle part of the
forehead is less developed in proportion to the other parts. The neck
of the child is very small, because the cerebellum, which is situate at
the inferior occipital /ossa?, is not yet developed ; but in proportion as
this organ increases in size, the skull grows prominent at that part.

472 APPENDIX. PHRENOLOGY.

The same happens with all the other cerebral parts which increase
progressively. The shape of the skull cannot be in any degree influenced
by external causes, such as occasional pressure in one direction, as
happens in carrying burdens on the head, or artificial modelling of the
heads of infants, as is asserted to be practised among the Caribs and
other savage nations. In other parts of the body we may remaik, that
whatever soft parts are inclosed in bones, the shape of the latter is
adapted to the dimensions of the former, and is regulated by the changes
they undergo ; the ribs, and even the spine, yield to the pressure of an
abscess, or the enlargement of an aneurism ; and the bones of the face,
in like manner, make way for the increase of tumours, and adapt
themselves to the new form these render necessary. By experience in
feeling the living head, we may readily learn to distinguish the form of
the bones which lie beneath the integuments. The observation of the
shape of the skull, or of the head, is therefore capable of giving us
exact information as to the relative size and shape of the different parts
of the brain, and on the knowledge thus obtained is founded the art of
Cranioscopy.

In practising this method, however, it is necessary to guard against
several sources of error. We must take into account several protu-
berances, which belong to the natural state of the skull, and which had
some particular destinations foreign to the immediate functions of the
brain ; such as the mastoid processes behind the ears, the crucial spine
of the occiput, the zygomatic processes, and the frontal sinuses. The
cerebral parts, situate behind the orbits, indeed, require some exercise
on the part of the organoscope, in order to be exactly determined. The
development may be perceived by the configuration and position of the
eyes, and by the circumference of the orbits. It is therefore necessary
to examine whether the eyeball is prominent or hidden in the orbit,
whether it is depressed or pushed sideward, inwai-d, or outward. Ac-
cording to this position of the eyeball, we may judge that such or such
part of the brain, which is situate against such or such part of the orbit,
is more or less developed. The functions of those organs, which lie
wholly at the basis of the brain, can be ascertained only by examina-
tion after death.

It may be objected, that the organs are not confined to the surface,
or convolutions of the brain ; but although this be the case, and al-
though they really extend from the surface to the basis of the brain^ or
medulla oblongata, yet the degree in which they are expanded at the
surface, where they form the convolutions, will indicate, in general,
the relative magnitude of the whole organ. The analogy of the five
senses, of which the peripheric expansions indicate the development
of their respective nerves, shows the reasonableness of this supposition.
From a large eye, implying a large retina, or peripheric expansion of
the optic nerve, we naturally infer that the nerve itself is of considera-
ble magnitude : may we not draw the same conclusion with regard to
the organs of the moral sentiments and intellectual faculties, whenever
we find that the convolutions, which are their peripheric expansions,
are much developed ?

In feeling for the organ. Dr. Gall recommends the use, not of the

THE PROPENSITIES. 473

fingers, but of the middle of the pahii of the hand; and declares that
habit, as well as a certain natural delicacy of tact, is necessary to
qualify a person to make these observations with certainly and success.
We are warned, also, to confine our observations to young and
grown-up persons in the flower of their age ; for at an advanced period
of life the brain diminishing by degrees, and retiring from the skull,
leads to the recession of its inner table, and conseijuent inequality in
its thickness, which renders it impossible to judge exactly of the size
or shape of brain from that of the head. Analogous changes occur in
the skulls of some lunatics, and occasion similar difiicullies in applying
the rules of cranioscopy. It is also to be considered, that our aim is
to distinguish the size, and not the mere prominence of each organ.
If one organ be much developed and the neighbouring organ very little,
the developed organ presents an elevation or protuberance, but if the
neighbouring organs be developed in proportion, no protuberance can
be perceived, and the surface is smooth.

We have already stated the mode in which Dr. Gall proceeded to
apply and to verify these principles ; it is now time that we should
present our readers with the result of his labours.

He arranges the faculties of ihe mind, with their corresponding
organs, according as they relate to the feelings and to the intellect :
the first class comprehending ihe propensities, a\\ which are common
to man and animals, and the sentiments, which constitute what the
French denominate fame, and the Germans gemiith ; and the second
class comprising the faculties by which we acquire knowledge, or the
knowing faculties, as he terms them ; and also the reflecting faculties,
which last compose what the French call Vesprit, the Germans glidst,
and what we should generally understand by the term intellect. He
finds that the organs of those faculties, which men possess in common
with animals, are situate towards the basis and back part of the brain ;
while those of the superior faculties, which are peculiar to man, are
placed somewhat higher; and tlie organs subservient to the intellectual
faculties occupy exclusively the forehead. The total number of special
faculties is thirty-three, as may be seen by the following enumeration.

1. Of the faculties common to man and animals, the first is that
physical propensity which has for its final purpose the continuance of
the species. The cerebellum, a part which occupies the lowest situa-
tion in the encephalon, is affirmed to be the organ, the actions of which
give rise to this propensity. Accident led Dr. 'Gall to this discovery,
by his noticing the size of iho back of the neck in a lady whose cha-
racter, in respect to this passion, was not equivocal : and subsequent
observation on an extensive scale, both in the human subject and in the
lower animals, have abundantly confirmed him in his opinion. The
following are the leading arguments on which he has rested it. First,
the great size of the organ indicates the importance of the function to
which it is subservient, and there is no cause, except the existence of
such an organ in the brain, that is adequate to account for this propen-
sity. The function of copulation takes place only in those animals
which have a nervous mass or cerebellum. Throughout the whole
class of quadrupeds, the neck of the male is thicker than that of the

40*

474 APPENDIX. PHRENOLOGY.

female, as may be observed particularly in the bull, the ram, and the
stallion. It is also remarked that vigorous pigeons are distinguished
by the size of their necks. The development of the cerebellum is
simultaneous vi^ith that of the genital organs at the period of puberty,
and early castration prevents its development, as well as that of the
beard, and the organs of the voice. Wounds of the neck have been
observed by Hippocrates to be sometimes followed by impotency. In
other cases, however, they produce erotic excitement. Apollonius
^ Rhodius, in speaking of the love of Medea, represents her as suffering
a violent pain in the back of her neck. A case occurred to Professor
Reinhold, at Leipsig, in which an excitement of the genital organs
succeeded the introduction of a seton in the neck, in a boy who
laboured under ophthalmia. Spirituous frictions on the neck in hyste-
rical fits are very useful. J^astly, the position of the cerebellum is
supposed to prove its destination. After hunger and thirst, no function
is more necessary than that of propagating the species. This function
is the most common in animals, after nutrition, and the cerebellum is
in the inferior part of the head. Hence it is probable, that it is destined
to the propensity of propagating, or that it is, as Dr. Spurzheim ex-
presses it, the organ of amativeness.

2. Philoprogenitiveness, or the love of progeny, the a-Tofyn of the
Greeks, has its seat in those convolutions of the brain situate imme-
diately above the hind part of the tentorium, and corresponding, there-
fore, on the outside of the skull with the crucial spine of the occiput.
Dr. Gall had observed a distinct protuberance on this part of the head
in women, and comparing the skulls in his collection, found a similar
elevation on the skulls of children, and on those of monkeys. During
five years he was in search of a faculty that was common to all the
subjects of those observations, and was in the habit of suggesting this
difficulty to his auditors. At length a clergyman who attended, ob-
served that monkeys have much attachment to their progeny. The
Doctor pursued this idea, and found that it applied perfectly to the
observed appearances, as the development of this part coincided always
with the energy of this propensity. In animals it is generally larger
in the females than in the males of the same species. This rule holds
good in the human subject, although it is liable to occasional excep-
tions ; for there are men who manifest the strongest propensity to
associate with children, and in whom we accordingly find this organ
larger than in the generality of women. In negroes we find this organ
more prominent than in Europeans. In the cuckoo, the crocodile, and
other animals to whom nature has not appointed the office of rearing
their progeny, this organ is extremely defective. The crime of infan-
ticide is more likely to be perpetrated by mothers in whom this organ
is deficient in size ; and accordingly out of 29 women who were guilty
of this crime, Dr. Gall found 25 who had this organ extremely small.
On the other hand, a female, who, being seized with delirium during
child-birth, imagined that she was pregnant with five children, was
found to have this organ unusually large. It must, no doubt, have
been of gigantic dimensions in the lady, who, stricken by the curse of
the gipsey whom she had refused to relieve, was impressed with the

THE PROPENSITIES.

47h

belief that she was about to give birth to as many children as there are
days in the year.

3. The organ of Inhabitiveness, or the propensity which some ani-
mals, such as the chamois and the wild-goat, have to inhabit high situa-
tions, is placed still higher in the occiput than the former, in a line
proceeding towards the top of the head. In animals of the same
species which live in low countries, we do not meet with an equal
degree of protuberance in this part of the brain, as is observable in
those which prefer living in elevated and mountainous districts. This
is seen even in the rat, some varieties of which choose for their dwelling
corn-lofts or the higher parts of a house, while others prefer living in
the cellars. This faculty is not very active in man ; but Dr. Gall
conceived that it was in him allied to pride and haughtiness. Dr.
Spurzheim, however, disclaims this doctrine ; as he thinks it impossi-
ble to confound the " instinct of physical height'' with the moral senti-
ment of self-love and pride. Mr. Combe, conceiving that this organ
has a more extensive sphere of action, and that it confers the power of
being conscious of every thing going on in the mind, and of concen-
trating the attention, terms this power Concentrativeness.

4. The organ oi Jldhesiveness, or the propensity to attach ourselves
to persons, animals, or other objects, is situate on each side of the
former, immediately under the lambdoidal suture, and gives a fulness
to the lateral and posterior part of the head. This organ is the source
of friendship, moral love, society, marriage, and attachment of all
kinds. Dogs have it in an eminent degree, especially those races
whose fidelity and constancy are characteristic, as the terrier, spaniel,
and lap-dog. It is less prominent in the butcher's dog, greyhound,
and mastiff. It was very large in a notorious highwayman at Vienna,
distinguished equally as a robber and a friend, and who chose rather to
die than to betray his confederates.

5. Comhaliveness, or the propensity to fight, results from the
operation of an organ, situate immediately behind the ears on each side,
at a part corresponding to the posterior inferior angle of the parietal
bone, and behind the mastoid process. It is the seat of anger, as well
as of pugnacity ; and its locality is fully established, in Dr. Gall's
estimation, by an extensive series of facts. His first discovery of the
seat of this faculty, was from his observation of the head of the Austrian
General Wurraser; and it was subsequently confirmed by the experi-
ments we have already mentioned which he made on boys he had
collected from the street. The breadth of the occiput is a criterion of
the spirit and courage of horses, dogs, &c. The bull-dog and pug-dog
are in this respect superior to the mastiff. The hysena is strongly
contrasted with the hare, and the guinea-hen with the robin red-breast.

6. Destrucfiveness, or the propensity to destroy in general, but
more especially to destroy life, has its seat just above the ears ; the
prominence of which part will account for the strange pleasure which
some people take in killing or tormenting animals, in seeing executions,
and for their inclination to commit murder. Among animals, this
instinct for blood is strongly marked in the carnivorous tribes, especially
iji the lion, tiger, and others of the feline tribe ; and the breadth of their

476 APPENDIX. PHRENOLOGY.

skulls in this part shows us the great size of this organ, compared with
that of their victims, the sheep, the goat, or the hare. The heads of
murderers have in general been found to possess a visible prominence at
this place. When the band of ferocious robbers and assassins, who so
long infested the left banks of the Rhine, under Schinderhanns, had
been caught, and a number of them executed. Dr. Gall found this organ
strikingly developed in the heads of these banditti. This propensity
is frequently strong in children, in idiots, and in madmen. Its object,
in the lower animals, is evidently to procure the food on which nature
destined they should live; yet some animals kill more than is necessary
for their nourishment. In man this propensity presents different degrees
of activity, from a mere indifference to the pain of animals, to the plea-
sure of seeing them killed or tortured, or even the most imperious
desire to kill. Dr. Gall called this faculty murder ; but Dr. Spurzheim
thinks it produces the propensity to destroy in general, without deter-
mining the object to be destroyed, or the manner of destroying it. " It
gives,"' says he, " the propensity to pinch, scratch, bite, cut, break,
pierce, devastate, demolish, ravage, burn, massacre, strangle, butcher,
suffocate, drown, kdl, poison, murder, and assassinate." It would
seem, therefore, that this organ has a great deal to answer for.

7. Constructive/less, the propensity to build, or the disposition to-
the mechanical arts, is indicated by the development of the brain at the
temples. Dr. Gall found this to be the case in great mechanicians,
architects, sculptors, and designers ; and also in the skulls of the beaver,
maririot, held- mouse, and rabbit, which construct habitations. Hares,
on the contrary, which lie in the fields, have this organ defective,
although in general they resemble rabbits. He possesses the skull of
a milliner of Vienna, who had a good taste, and understood perfectly
the art of changing the forms of her merchandise ; in this skull the
organ in question is prominent. It is by means of this faculty that birds
build nests, savages huts, and kings palaces. It produces also fortifi-
cations, ships, engines of war, manufactures of all kinds, furniture,
clothes, toys, &c. There was a lady at Paris, who, every time she
was pregnant, felt the greatest propensity to build. The excessive
size of this organ may lead a man to ruin liis family by building, or to
coin false money.

8. Covetiveness, or the propensity to covet, gather, and acquire
without determining the object to be acquired, or the manner of jtc-
quiring it, has its organ situate at the temples, on the anterior inferior
angle of the parietal bone. This faculty gives a desire for ail that
pleases ; money, property, animals, servants, land, cattle, or any thing
upon earth. It produces egotism and selfishness, and may, when
abused, lead to usury, plagiarism, fraud, or theft. The instinct of
stealing, it is asserted, is not always the effect of bad educalio'n, of
poverty, idleness, or the want of religion and moral sentiment. This
truth, says Dr. Spurzheim, is so generally felt, that every one winks
at a little theft committed by rich persons, who in other respects con-
duct tliemselves well. Mr. Combe terms this faculty Jicquisiliveness.

9. The organ of Secretiveness, or the propensity to conceal, or to
be clandestine in general, is situate in the middle of the side of the

THE SENTIMENTS. 477

head, above the organ of the propensity to destroy. Dr. Gall first
observed this organ in a person who had many debts, but who had the
address to conceal his real situation, so that the creditors could have
no knowledge of each other. He ascribes to this faculty cunning,
prudence, the s avoir /aire., the capacity of finding means necessary to
succeed, hypocrisy, lies, intrigues, dissimulation, duplicity, falsehood;
in poets, the talent of finding out interesting plots for romances and
dramatic pieces ; and finally, the quality of slyness in animals, as in
the fox and the cat, who conceal their intentions, and are clever in
hiding themselves.

To the second genus of the order of feelings, namely, Sentiments,
belong the following faculties: —

10. Self-love, or self-esteem. Dr. Gall first noticed this organ,
which lies in the middle of the upper posterior point of the head, in a
beggar, who stated that he was reduced to his present condition by his
pride, which made him neglect his business. The animals endowed
with this organ are the turkey-cock, peacock, horse, &c. Dr. Gall
thought this organ is the same as that of the faculty which makes cer-
tain animals dwell upon mountains ; but Dr. Spurzheim, as we have
already observed, draws a line of distinction between them. The too
great activity of this faculty is the cause of various abuses, as pride,
haughtiness, disdain, contempt, presumption, arrogance, and insolence.
The want of it disposes to humility. It is said to be more active in
women than in men, and that its excess ' is sometimes the cause of
madness.

11. Love of Approbation. Persons fond of the good opinions of
others, have the upper posterior and lateral part of the head much
developed. This may be called the organ of ambition or vanity,
according to the object, which may be of various kinds. A coachman
endowed with this faculty is pleased if his manner of conducting horses
be approved ; and a general is elated if he be applauded by his nation
for leading his army to victory. This faculty is more active in women
than in men, and even in certain nations more than in others. More
women become mad from this cause than men.

12. Organ of Cautiousness. Two persons at Vienna were known
to be remarkable for their extreme irresolution. One day, in a public
place, Dr. Gall stood behind them, and observed their heads. He
found them extremely large on the upper posterior part of both sides
of the head. Hence he derived the first idea of this organ. Circum-
spect animals also, as the stag, roe, pole-cat, otter, and mole, and those
which place sentinels to warn them of approaching danger, as the
chamois, cranes, starlings, and bustards, have this cerebral part much
developed. This faculty produces precaution, doubts, demurs ; and, in
general, exclaims continually " take care.''' It considers consequences,
and produces all the hesitations expressed by the word but. When
excessive, it produces uncertainty, irresolution, unquietness, anxiety,
fear, melancholy, hypochondriasis, and suicide. Dr. Gall finds this
organ more strongly marked in children than in grown persons.

13. The organ of Benevolence in man, or of meekness in animals,
is situate on the superior middle part of the forehead. In most ani-

478 APPENDIX.- — PHRENOLOGY.

mals it is restrained to a passive goodness ; but in man its sphere of
activity is very considerable, producing all the social virtues, or in one
word, Christian charity.

14. The organ of Veneration, or of Theosophy, occupies the centre
of the uppermost part of the os frontis. Dr. Gall has observed in
churches, that those who prayed with the greatest fervour were bald ;
and that their heads were much elevated. The pictures of saints show
the very configuration which he had thus noticed in pious men ; and
the head of our Saviour, also, is generally represented of this shape.
It is by this faculty that man adores God, or venerates saints, and per-
sons and things deemed sacred.

15. The organ of Hope is situate on the side of that of veneration.
Dr. Spurzheim considers the sentiment of hope as proper to man, and
as a sentiment necessary in almost every situation ; it gives hope in
the present, as well as of a future life. In religion it is called faith.
Its excessive development produces credulity.

16. Ideality, or the poetical disposition. The heads of great poets
are enlarged above the temples, in an arched direction. The sentiment
inspired by this organ is the opposite of circumspection ; it renders
us enthusiasts, while circumspection stops our career by saying
" take care." If the part of the head above this organ, and a little
backward from it, be very much developed, the person is disposed to
have visions, to see ghosts, and to believe in astrology, magic, and
sorcery.

17. The faculty of Fighteousness, or Conscientiousness, which
produces the sentiment of just and unjust, right and wrong, has its
organ situate a little more forward than the organ of approbation. It
produces the sentiment of duty, and constitutes what is called con-
science or remorse. Dr. Spurzheim admits farther an organ o^ jus-
tice, which he seeks for on the side of the following organ.

18. Determinateness, or Firmness. Dr. Gall observed that persons
of a firm and constant character have the top of the brain much deve-
loped. Lavater had made the same observation. This faculty contri-
butes to maintain the activity of the other faculties by giving constancy
and perseverance. Its too great activity produces infatuation, stub-
bornness, obstinacy, and disobedience. Its deficiency engenders fickle-
ness and inconstancy.

To the order called Intellect, and the first genus of that order, viz.
the knowing faculties, belong the following species :
. 19. Individuality, or the faculty which procures us the knowledge
of external beings, after we have received impressions from them by
the external senses, occupies the middle of the lower part of the fore-
head. Dr. Gall found this part very prominent, indicating a great
development of the anterior and inferior part of the brain, in all per-
sons, who, from their extensive, but superficial knowledge in the arts
and sciences, were capable of shining and taking a lead in conversa-
tion. It has been not unaptly, though satirically characterized as the
blue-stocking faculty. Tame animals have the forehead more developed
than wild ones, and are more or less tameable in proportion as the
forehead is more or less developed ; Dr. Gall, therefore, calls this organ

THE INTELLECTUAL FACULTIES. 479

that of educability. Dr. Spurzheim, however, objects to this term,
and has substituted that of individuality; he also remarks that the
organ is early developed in children, because they are obliged to ac-
quire a knowledge of the external world.

20. The organ of Form leads us to take cognizance of the forms of
objects, with the existence of which the preceding faculty had made
us acquainted. Persons endowed with it in a high degree, have a
great facility of distinguishing and recollecting persons ; they are fond
of seeing pictures, and if they make collections, they collect portraits.
Crystallography is the result of this faculty. The conception of
smoothness and roughness also belongs to it. This organ is placed
in the internal angle of the orbit, and, if much developed, it pushes
the eyeball toward the external angle, that is a little outward and down-
ward. The Chinese appear to have it in perfecton.

21. Size. After the existence and figure of any body, the mind
considers its dimensions or size, for there is an essential difference be-
tween the idea of size and that of form. The organ must therefore be
different ; it is probably however in the neighbourhood of the former.

22. Weight. The ideas of weight and resistance, density, softness
and hardness, cannot be attributed to the sense of feeling, and require,
therefore, a particular faculty for their conception. Its organ must be
situate in the vicinity of the two last.

23. Colour. The faculty of conceiving colour is, in like manner,
totally distinct from the sense of vision, or the faculty of perceiving
light. Its organ is placed in the midst of the arch of the eye-brows, giv-
ing them, when expanded, a vaulted and rounded arch. This configura-
tion is characteristic of painters, and is strikingly displayed in the
Chinese, who are well known to be very fond of colours. This faculty
is generally more active in womeai than in men.

24. Space, or Locality. The faculty of local memory, by which
we recollect localities, and find our way to places where we have been
before, is much stronger in some persons than in others. Animals are
also endowed with it, and it enables them to return to their dwellings
and their progeny, when obliged to leave them in search of food. It is
conspicuous in some dogs ; while others are very deficient in this
respect. The migration of birds is the result of this faculty. The
pictures and busts of great astronomers, navigators, and geographers,
as of Newton, Cook, Columbus, &c. present a great development of
this organ, which is situate under, but extends a little beyond, the
frontal sinuses. The swallow, the stork, and the carrier-pigeon, have
all this organ. This faculty conceives the places occupied by the ex-
ternal bodies, and makes space not only known to us, but inspires a
fondness for this kind of knowledge. It makes the traveller, geogra-
pher, and landscape painter ; it recollects localities, judges of symmetry,
measures space and distance, and gives notions of perspective.

25. Order. This faculty enables us to conceive order. It gives
method and order in arranging objects as they are physically related.
Its organ is probably situate outward, but not far from the organs of
size and space.

26. Time. Ideas of time are the result of a distinct faculty ; for they

480 APPENDIX. PHRENOLOGY.

may exist without those of order and number. They seem to be
higher in the scale, and their organ, accordingly, occupies a higher
place in the brain.

27. Number. All the ideas that are concerned about unity or
plurality, that is, about number, belong to a faculty whose organ is
situate in a part of the brain near the external angle of the orbit. The
object of this faculty is calculation in general. When much developed,
the arch of the eye-brows is considerably depressed, or is elevated at
the outer extremity. This conformation is apparent in the portraits
and busts of great calculators, as Newton, Euler, Kastner, Jedediah
Buxton, and Pitt. The heads of negroes are very narrow at this part ;
and, in general, they do not excel in this faculty.

28. Tune. The perception of musical tone is distinct from that of
sound, and implies a different faculty from that of hearing. Its organ
is placed on the lateral parts of the forehead. Its form varies accord-
ing to the direction and form of its convolutions. In Gluck and Haydn,
it has a pyramidal form ; in Mozart, Viotti, Zumsteg, Dusseck, and
Crescentini, the external corners of the forehead are enlarged but
rounded.

The heads and skulls of singing birds, especially the males, exhibit
this organ fully developed. Monkeys are absolutely destitute of it,

29. Language. The organ of the faculty of learning the artificial
signs for the operations of the mind, of perceiving their connection
with the thing signified, and of remembering them, and judging of
their relations, occupies a transverse situation in the midst of the
knowing faculties, and presses upon the basis of the orbit of the eye,
so as to project the eye forwards when much developed. This pro-
duces what is commonly called a goggle-eye, denoting strong verbal
memory. Sometimes the eyes are not only prominent, but also de-
pressed downward, so that the under eye-lid presents a sort of roll, or
appears swollen. Such persons are fond of philology, that is, they
like to study the spirit of different languages.

The second genus of the order Intellect, viz. the reflecting faculties,
contains the following species : —

30. Comparison. This faculty compares the sensations and ideas
of all the other faculties ; and points out their difference, analogy,
similitude, or identity. Dr. Gall observed various persons, who, in
every conversation, had recourse to examples, similitudes, and ana-
logies, in order to convince others ; and seldom to reasoning and phi-
losophical arguments. In them he found, in the midst of the superior
part of the forehead, an elevation which presented the form of a re-
versed pyramid, and he named this organ, according to its functions,
the organ of analogy. Nations who have this faculty in a high degree
are fond of figurative language.

31. Causality. This faculty examines causes, considers the rela-
tions between cause and effect, and always prompts men to ask, Why ?
Persons fond of metaphysics have the superior part of the forehead
much developed and prominent in a hemispherical form, as Mendel-
sohn, Kant, Fichte, and others. The ancient artists have given to

APPLICATIONS OF PHRENOLOGY. 481

Jupiter Capitolinus a forehead more prominent than to any other an-
tique head.

32. Wit. Persons who have this faculty, who write like Sterne,
Voltaire, Piron, &c. have the superior external parts of the forehead
elevated. The essence of tiiis faculty consists in its peculiar manner
of comparing, which always excites gaiety and laughter. Jest, raillery,
mockery, ridicule, irony, &c. are its offsprings.

33. Imitation. Persons who have a considerable elevation of a
semi-globular form at the sv*perior part of the forehead, have the faculty
of imitating, with great precision, the gestures, voice, manners, and,
in general, all the natural manifestations of men and animals. They
have a disposition to be actors, and are prone to gesticulation. This
organ is, in general, more developed in children than in adult persons.

To the above catalogue of the organs enumerated by Dr. Spurzheim,
Mr. Combe has since added the two following, namely,

34. The organ of Wonder (situate immediately above Ideality, in
the lateral parts of the anterior regions of the vertex), which occasions
the belief in the reality of ghosts, and other mysterious af)paritions and
visitations, and inspires a love for all that is marvellous and super-
natural, and also a taste for novelty and fashion. When largely
developed, it excites young men, born and bred in inland situations, to
choose the sea as a profession.*

35. The organ oi Eventuality, which, when large, gives prominence
or a rounded fulness to the middle of the forehead. " The function of
this faculty is to take cognizance of changes, events, or active pheno-
mena, indicated by active verbs. In such expressions as the rock
falls, the HORSE gallops, the battle \s fought, the substantive springs

from Individuality, and the verb from Eventuality. It prompts to
investigation by experiment, while Individuality leads to observation
of existing things. Individuality gives the tendency to personify
abstract ideas, such as Ignorance and Wisdom ; and Eventuality to
represent them as acting. An author in whom Individuality is large,
and Eventuality small, will treat his subject by description chiefly,
and one in whom Eventuality is large and Individuality small, will
narrate actions, but deal little in physical description. "t

Two other primary faculties are mentioned by Mr. Combe ; one,
which he terms Alimentiveness, or the desire of eating and drinking ;
and another, which had been called by Spurzheim VitativenesS, or the
Love of Life; but the seat of these powers has not been exactly
determined.

Excepting in the case of idiots, all the thirty-five organs above des-
cribed are possessed by every persbn, but they exist in greater or less
perfection in different individuals. Peculiarity of character is the result
of irregularity in the original structure, or inequality in the relative
development of the several organs ; circumstances which, according as
they are diversified, lay the foundation of every excellence, as well as
constitute the fatal sources of vice and depravity. These doctrines
should, however, by no means be understood as lending their sanction

* System of Phrenology, fourth edition, p. 381. -j- lb. 518.

41

482 APPENDIX. PHRENOLOGY.

to the latter ; for crimes are considered as flowing from the abuse ,of
certain faculties, and as still requiring for their prevention the coun-
teracting influence of morality, and the salutary coercion of law. It
must be of importance to every individual to know, if such knowledge
be attainable, what is the degree of energy of the propensities and
other faculties with which he may have been naturally and originally
endowed ; because every organ and corresponding faculty may be
invigorated by proper exercise. The business of education will ac-
cordingly consist in exciting or restraining the development, according
to their natural deficiency or exuberance. Phrenology, by pointing
out what are the strongest faculties in a child, will enable us to adopt
the best plan of intellectual, as well as moral discipline ; will assist us
in regulating his passions, and maintaining a due balance between all
his moral sentiments ; and guide us in the choice of a profession for
our pupil, conformable to the particular bent of his genius. " What
benefit would arise to society," says Mr. Forster, the zealous advocate
of these doctrines, ^'should we be enabled to make a just election of
objects in youth, to be placed in situations capable of ripening their
naturally energetic faculties. Phrenology will lead to important con-
siderations regarding criminal punishment, particularly in houses of
correction. It will enable us to distinguish, not only between those
who have naturally strong evil propensities, from those whom distress
or other contingencies may have hurried on to crime, but will point
out the particular nature of the evil propensities to be corrected." It
will also tend, he conceives, to establish important distinctions between
different kinds of insanity, and enable us to discover the treatment ap-
propriate for the cure of each. Lastly, it may prepare the way to a
radical improvement of the human race, by pointing out those confor-
mations of the head which it is desirable to eradicate or to perpetuate,
and which should therefore be avoided or preferred in the choice of
marriages. " It is certainly a pity," says Dr. Spurzheim, " that, in
this respect, we take more care of the races of our sheep, pigs, dogs,
and horses, than of our own qff'spring."

Such is the body of doctrines, and such the reasonings in their sup-
port, which have emanated from the school of Gall and Spurzheim,
and which they have dignified with the appellation of a new science.
A host of opponents, as might be expected, have arisen against a sys-
tem so much at variance with common notions, leading to conclusions
so remote from vulgar apprehension, and admitting so easily of being
held up to ridicule by partial or exaggerated statements. We have
already noticed the objection founded upon its supposed tendency to
favour materialism, and shall pass over others of a similar nature,
which proceed upon the presumption of a greater knowledge of the
laws of the creation than we really possess, or which are derived from
imperfect or mistaken views of the theory itself. We shall also refrain
from employing the weapons of ridicule against a system so vulnerable
to its attacks, and which would have been so capable of affording
Swift a new incident for the history of the philosophers of Laputa.
The simple exposition of the sandy foundation on which it has been

OBJECTIONS TO PHRENOLOGY. 483

built, of the flimsy materials of which it has been composed, and the
loose mode in which they have been put together, will snfrice to enable
our readers to form their own conclusions as to the soundness and
solicUty of the edifice.

It is, in the first place, obvious, that nothing like direct proof has
been given that the presence of any particular part of the brain is essen-
tially necessary to the carrying on of the operations of the mind. The
truth is, that there is not a single part of the encephalon, which has
not, in one case or other, been impaired, destroyed, or found defective,
without any apparent change in the sensitive, intellectual, or moral
faculties. Haller has given us a copious collection of cases, which
bear upon this point ; and a similar catalogue has been made by Dr.
Ferriar, who, in a paper in the fourth volume of the ManchestPr
Transactions, has selected many of Haller's cases, with considerable
additions from other authors. The evidence afforded from tiiis mass
of facts, taken conjointly, appears to us to be sufficient to overturn
their fundamental proposition. This evidence is not impeached by the
feeble attempts of Dr. Spurzheim to evade its force, by a general and
vague imputation of inaccuracy against the observers, or by having
recourse to the principle of the duplicity of each of the cerebral organs ;
a principle of very dubious application, on a subject of so much uncer'
tainty as the physiology of the brain. Poor, indeed, must be his
resources, when we find him resorting to the following argument, in
proof that the brain is the organ of thought, namely, that " every one
feels that he thinks by means of his brain." We doubt much if any
one has naturally that feeling.

It requires, also, but a slight attention to perceive, that the very
ground-work on which the whole of the subsequent reasoning proceeds,
namely, that the different faculties of the mind are exercised respec-
tively by different portions of the brain, is in no resj^ect whatever
established. The only arguments in its favour which bear the least
plausibility, are derived from analogy. Now, analogy, in reasoning
concerning the unknown operations of nature, is, at best, but slippery
ground ; and when unsupported by any other kind of evidence, cannot
lead to certain knowledge, far less constitute the basis of an extensive
system. The utility of analogical deductions as to what takes place in
one department of nature, from our knowledge of what occurs in
another, consists chiefly in their afl^ording indications of what may pos-
sibly happen, and thus directing and stirnulating our inquiries to the
discovery of truth by the legitimate road of observation and experiment.
But to assume the existence of any such analogy as equivalent to a
positive proof, resulting from the evidence of direct observation, is a
gross violation of logic. Yet it is upon assumptions of this kind that
Drs. Gall and Spurzheim have ventured to found all the leading propO'
sitions of their doctrine. In the secretions of the body, they observe,
the preparation of different fluids is consigned to different glands, having
different appropriate structures"; and they consider this analogy as a
demonstrative proof of what happens in the operation of thought, and
the phenomena of the passions, which, because they differ as much in
their nature as milk does from gall, must, accordingly, be th.e result of

484 APPENDIX. PHRENOLOGY.

actions in different portions of the brain ; which portions are, there-
fore, to be regarded as so many different organs, rather than as parts
of one organ. Even in a case where all the analogies are favourable
to one side of a question, such a loose mode of reasoning would be
entitled to little confidence ; but how fallacious must it not prove, when
analogies can be pointed out whjch apply in the opposite direction ? It
requires no extensive knowledge of the animal economy to perceive,
that modifications of functions equally diversified with those of the
'intellect, are, in many cases, the result ef actions taking place in the
same organ. Does not the same stomach digest very different and
even opposite kinds of aliment ? Yet we do not find that one portion
of that organ is destined for the digestion of meat, and another for the
digestion of vegetable matter ; although the operations required for the
conversion of such different ingredients into the same chyle, cannot-
possibly be the same. Nerves perform the double office of volition
and sensation ; but the different bundles of fibres which convey each
impression, the one to the muscles, the other to the sensorium, are
wrapped up in the same sheath, and are so intimately intermixed during
their course as to constitute a single cord. The same organ serves for
the hearing of acute and of grave sounds. The whole retina, and not
merely different portions of its surface, receives the impression of dif-
ferent kinds of colour ; there is not one organ for the perception of
blue and'another for the perception of red rays. Guided by such ana-
logies as these, might we not be equally justified in concluding, that
the same part of the brain may serve for the memory of words, as for
the memory of things ; and the same portion of that organ which ena-
bles us to conceive the idea of figure, may also suggest to us that of
size ?

The same doctrine of the plurality of cerebral organs, is endeavoured
to be supported by another analogy, equally vague and loose with the
former, namely, that the sense of fatigue from long continued muscular
exertion, resembles, in its circumstances, the effects of long continued
study on the mind, and is equally relieved, in both cases, by a change
of action. To us, however, it appears, that this analogy might, with
equal justice, have been adduced, as favouring the opposite view of the
subject; for we can just as readily conceive the sense of fatigue to take
place from the exercise of the whole organ in a particular mode, as
from that of any part of the organ ; and relief must equally, in both
cases, be experienced from the ceasing of that action, or from the
substitution of one of a different kind. The muscles admit only of one
kind of action ; and the energy which each derives from the nerves,
when once exhausted, is not so readily replaced from the general stock
belonging to the system. In the finer textures of the body, which
approach more to that of the brain, the analogy not only fails of giving
support to the doctrine, but has an opposite tendency. The same
retina, when fatigued by the continued impression of a particular colour,
is still as ready as before to receive the impression of another colour.
The circumstance of partial fatigue with regard to one set of actions,
may, therefore, exist, without implying the necessity of a separate
organ for the performance of these actions. Indeed, if the brain have
any laws similar to those of muscular motion, it must have a much

I

PRACTICAL DIFFICULTIES. 485

greater number peculiar to itself, and all such distant analogies as those
we have been considering, must be perfectly inconclusive. Similar
observations will apply to the explanation of the phenomena of sleep,
of dreams, of somnambulism, of partial losses of memory, and of
^insanity. It is equally conceivable, that they should result from the
imperfect or differently modified actions of one organ, as from the
separate activity of different parts of that organ, whilst the other parts
are inactive. Analogies may be equally adduced in support of both
sides of the question, and can certainly prove nothing on either.

Dr. Gall and Spurzheim appeal with great confidence to anatomy,
and particularly to their own anatomical discoveries, as affording a solid
support to their doctrines. " We never," say they, " separate anatomy
from physiology, for physiology without anatomy is unfounded; while
anatomy without physiology is useless. A physiological system of
the brain would necessarily be false, were it in contradiction with its
anatomical structure." This conclusion, which at best is but a negative
one, is totally inapplicable to the theories in question. The anatomy
of the brain is so complex, and so void of apparent adaptation to any
purpose we can understand, that it will suit any physiological system
nearly equally well ; at least it can never be adduced in contradiction
of any hypothesis, however wild, that can be framed as to the mutual
operation of soul and body. All that these anatomists have done, in
this respect, is to show that there is no appearance of a common centre
of departure or of a collection of nervous filaments. The separation of
the parts of the brain and their diversity of shape, can no more be
evidence of a diversity in their functions, than the multitude of distinct
and separate lobules which compose th,e kidneys of birds, and of a
great number of quadrupeds, are indications that each part performs a
different office. Comparative anatomy, indeed, upon which so much is
made to hinge, is of all guides the most fallible in questions of this
nature ; since we behold, in numberless instances, a great variety of
ways in which nature accomplishes the same function and the same
purpose, in different departments of the animal creation. But on a
comparison of animals with each other, it may even be doubted, whether
there is any connexion or proportion observable between their intellect
or inclinations and the number of parts in their brains.

The possibility of discovering the size and the shape of the different
parts of the brain from the external examination of the head, is also
discountenanced by anatomy. There are often considerable impres-
sions on the interior of the skull, where the corresponding exterior
surface does not exhibit the slightest appearance of projection, and is
sometimes even depressed ; and there are frequently large prominences
without, where there are no corresponding concavities within ; so tliat
when the outer surface of the bony case is compared with a mould in
plaster or wax of the cavity itself, they exhibit considerable differences,
and, from the great variation which may take place in the thickness of
the bones, this difference is not the same in degree in any two skulls.

Hollow as are the foundations of this theory, the materials which
compose the superstructure will prove, on examination, to be still
more frail and unsound. The whole fabric rests upon the validity of

41*

486 APPENDIX. PHRENOLOGV.

a single proposition, which in itself is extremely questionable, namely,
that the size of an organ is in general a criterion of the energy with
which its function is performed. If any doubt should remain as to its
truth, the whole of the pretended discoveries relative to the functions
of the several parts of the brain are shaken, and the fantastical edifice
has no auxiliary prop to arrest its fall. So essentially, indeed, does
the whole of this system depend upon the truth of a number of inde-
pendent propositions, that if any one of them should turn out to be
incorrect, the whole fabric must give way. The evidence in its favour,
instead of being cumulative, is disjunctive. Where each proposition
must be sustained by a separate series of proofs, as is the case here, it
is evident that the chances of error must be multiplied in proportion to
the number of steps we must ascend before we can arrive at the last
conclusions. Let us, for example, examine the logic by which the
above fundamental principle is deduced. " A large muscle," say they,
" is stronger than a small one ; and a large loadstone is more powerful
in its attraction than a smaller one. Why should it not be the same
with regard to the brain ?" Thus again do they confide in a loose
analogy, derived from another and a totally different part of the econo-
my ; and as if the organization and functions of the animal body were
not sufficiently remote from the nature and operations of the human
mind, the inanimate world, is ransacked for the shadows of an analogy,
which, when viewed through such a distance of intervening mist, may
wear the semblance of reality. But the phantom must immediately
vanish upon a near inspection. For the perfection of a refined and
delicate instrument, such as must be that which is subservient to the
operations of the intellect, innumerable conditions must concur;
amongst which that of size, it is reasonable to suppose, is the least
important. Delicacy of texture, fineness of organization, and harmony
of adjustment between the several parts of its complex structure, must
contribute infinitely more towards rendering it capable of perfoi;ming
its office, than superior magnitude ; a circumstance which in itself is
quite as likely to prove a source of imperfection, as to impart additional
facility. Increase of size in the viscera of the body is often the indi-
cation of a diseased, instead of a healthy state. Small eyes. Professor
Hufeland observes, see with more strength, and last longer than large
eyes. Why may not this be also the case with the organs of the
brain ? But really, in our present state of ignorance as to the mode of
operation by which they are subservient to the processes of intellect
and sensation, all such reasonings « priori on their functions, as con-
nected with their size, must be completely illusory.

Even were we to admit so questionable a doctrine as that the ener?-
gies of the parts of the brain are proportional to their magnitude,
insuperable difficulties would still be opposed to the determination of
their relative size, in the living head ; crowded as all these organs are
in a narrow compass and completely hid from our view by an irregular
bony case which protects them from injury, and which is itself
covered by a thick and variable layer of muscle and integument. Let
us, however, for the sake of argument, suppose that the form of each
organ within the skull can really be ascertained by external examina-

PRACTICAL DIFFICULTIES. 487

tion of the head ; shall we allow it to be an easy task to determine the
real character of the individual who is the subject of observation?
Are we always able to discriminate between real and affected senti-
ment ; or to mark with certainty the operation of all the various motives
which constitute the springs of action ? Is the transient glance of a
passing observer sufficient for unravelling the complex web of our
affections, or unveiling the secret and tortuous recesses of the human
heart, so as to assign to each principle its precise sphere of agency ?
Can the most profound moralist, or acute metaphysician pronounce
with confidence what are the natural dispositions of any human beiil^,
knowing, as we do, that these dispositions must have been changed
or modified, exalted or subdued, perverted or refined, by the force of
habit, education, example, and a multitude of other powerful causes,
which, in his progress through life, have moulded his intellectual and
moral constitution ? Can he trace them through the guise of falsehood,
artifice, and dissimulation, which so commonly hide his real character
from the world, and which occasionally deceive the eye of the closest
and most vigilant observer ? Is it to the behaviour of a person who
knows that he is watched ; is it to the partial report of his friends ; is
it to the testimony of the individual himself, the most fallible of all,
that the phrenologist is to trust for his knowledge of human character ?
Such, however, is the kind of experience, from which it appears that all
the doctrines relative to the functions of the difTerent parts of the brain
have been derived ; and it is in this experience, as in an impregnable
fortress, that the adherents of the system make their last and most
resolute stand. Quitting the airy region of theory, they fancy them-
selves posted upon a rock, secure against the insiduous minings of
scepticism, and bidding defiance to the rude assaults of argument. The
appeal to the evidence of induction, as to the supreme authority in the
court of philosophy, is made with confidence ; and all the wild effusions
of a bewildered fancy are presumed to be sanctioned by a supposed
conformity with experience. You may speculate or reason, they ex-
(?laim, as you please ; observation shows that such and such forms of
the head, are the invariable concomitants of such and such predominant
dispositions and faculties. Who will dare to set up his opinion in
opposition to ascertained facts ? We venture only to express strong
doubts as to the reality of these facts, on which so much is made to
depend, possessing the character of general facts., that is, of being the
results of legitimate induction ; and to suggest the expediency, pre-
viously to any admission of their truth, of inquiring not only into the
manner in which the knowledge of these pretended facts has been
obtained, and in Avhich induction from them have been made, but also
into the talents and qualifications of the observer upon whose testimony
we receive them for the exercise of this philosophical process. We
should know in what spirit he conducted the inquiry ; with what pre-
vious dispositions he examined the objects of his contemplation ; what
motives led him to these researches ; and what interest he i^ay have
in the event. Experience, we should recollect, leads to very dififerent
results, according to the sagacity and good faith of the person who
acquires it. Minds already prejudiced collect from it only a confirma-

488 , APPENDIX. PHRENOLOGY.

tion of their errors, and become, by its means, only the more obsti-
nately wedded to their opinions. The sailor, steadfast in his belief that
his whistling to the sea will raise a wind, or conjure up a storm, instead
of being undeceived by experience is only the more strengthened in his
faith by the observations which it furnishes to him. In what a multi-
tude of instances do we not find men deceiving themselves as grossly,
when they draw inferences from what they see, if prepossessed with
the expectation of meeting with a certain coincidence, or succession of
events. How disposed are we all to disregard the exceptions to a
prtconceived rule, and to allow undue weight to every example that
conforms to it. How willingly we repel the evidence that opposes,
and how eagerly we catch at whatever corroborates our previous notions,
especially when those notions have originated with ourselves, and are
viewed as the darling offsprings of our own lucubrations.

The discerning reader may already have perceived strong indications
of this bias in the framers of the phrenological system, from the
account we have already given of its origin and history, and of the
kind of evidence on which they pretend to establish its doctrines. In
order, however, to enable him to form a correct idea of the species of
logic which they have been in the habit of employing, and which they
deem conclusive, and of the tone of mind with which they prosecute
the investigation of subjects where nothing but the exercise of consum-
mate prudence can secure from error, we shall conclude by offering
one or two specimens of their mode of reasoning. We shall pass over
the numerous stories, each more ridiculous than the preceding, of irre-
sistible natural inclinations to wander from place to place, to commit
murder, theft, infanticide, and other crimes, without any assignable
object. We shall refrain from criticising the wonderful accounts of
people who were insane on one side of the head only, and observed
their insanity with the other side, and of others who heard angels sing,
and devils roar, only on one side; nor shall we stop to investigate the
curious case of the woman who declared in a court of justice, when
accused of having destroyed her infant, that her sole motive for becom-
ing pregnant was that she might enjoy the exquisite pleasure of killing
her own child. . Neither shall we venture to involve ourselves in that
metaphysical labyrinth of the thirty-Jive special faculties into which
they pretend to have analyzed the hurgan soul ; but content ourselves
with examining, what in fact alone deserves examination, the sort of
evidence brought forward to establish the relation between each faculty
and a particular defined portion of the brain. .We shall take, for this
purpose, the following passage, which may be esteemed a fair specimen
of the whole.

" Dr. Gall examined the head of a woman at Vienna who was known
as a model of friendship. She suffered different changes of fortune ;
she became alternately rich and poor ; but was attached to her former
friends. Gall found the part of her head situated upward and outward
from the organ of philoprogenitiveness, very prominent, and called it
the organ of friendship. Our observations are not multiplied enough
to enable us to decide positively on this organ ; yet its seat appears to
be more than probable. It must be inferiorly, because this faculty

REASONING EMPLOYFJD BY PHRENOLOGY. 489

exists in the lower animals, and is a propensity. For this reason it
belongs to their region of the head ; and according to its mimical signs,
and the motions of the head when it is aetive, it lies laterally and
backward." Dr. Spurzheim, it is obvious, here reasons in a circle;
for he assumes as true the thing to be proved, namely, that faculties of
a certain class reside in a certain department of the head, and then
applies it to establish the very proof on which the proposition itself
ouglit to have rested. In order to render intelligible the latter part of
his argument, the reader should be informed that Drs. Gall and Spurz-
heim believe, that, when any faculty of the mind is strongly excited, the
action of the corresponding organ in the brain tends to raise that part .
of the head in which it is situated ; so that the person has a propensity
to lay his finger upon the nearest external part of the head, or some-
times to apply his hand to it, either to cool it when too hot, or to
warm it when too cold, and that he is occasionally prompted to rub it
in order to excite it when too sluggish. Thus, when we endeavour to
recollect a name or a word, we unconsciously slap our foreheads, or
rub the skin a little above the eyes, or perhaps higher still, just where
the appropriate organ of memory is situated, that it may awake and
exercise its peculiar faculty. When embarrassed by any difficulty, we
gently stimulate in like manner, the organ of contrivance, by scratching
the head at the part under which is the seat of constriictiveness. The
timid man scratches his head on the organ of courage behind his ear,
as if he tried to rouse the feeble organ into activity. A proud man
holds his head erect upon his shoulders, and raises himself upon his
toes, for no other reason than because the organ of the sentiment lies at
the very top of the head, and is therefore elevated by the action. A
sense of danger, or the necessity of circurnspection, leads all animals,
man not excepted, to stretch their necks forwards horizontally, thus
presenting the broad extent of that organ, as it were, in front. Devo-
tion raises the head gently ; and our adorations are all directed up-
wards, not because we regard ihe Deity as above, but because the
organ of adoration is situated in the centre of the upper part of the
head. When busied in deep contemplation, we cover the whole fore-
head with our hands, as.it is 'there that the reflecting faculties are
lodged ; and, accordingly, when we reproach any one for his want of
reflection, we put our hand to this part of the head ; and exclaim,
" he wants it here." If we try to recollect a date, we put into action
the organ of time, which being situated over the eyebrows, and a little
to one side, occasions an involuntary movement of the eyes upwards
and towards the temples. In beating time to a musical air, we make
the head oscillate from side to side, because the organs of tone as well
as of time, being situated on each side, and being alternately in action,
occasion these gesticulations. Sterne excelled in wit : and we find
him represented in all his portraits with his head leaning on his hand,
the fore-fing;er of which is placed on a particular part of the forehead.
Dr. Spurzheim considers this as one of the proofs that the organ of wit
occupies that very spot.

With minds capable of allowing any weight to such observations,
and imbued with such notions of the nature of philosophical inductions,

490

APPENDIX. PHRENOLOGY.

as are implied by the grave admission of such frivolous arguments as
these, the investigation of the laws of nature must be an easy and a
delightful task. With the abundant and all-povs^erful resources, which
their indulgent method of reasoning is ever ready to supply, all diffi-
culties may be smoothed away, all chasms immediately filled up, and
all obstacles made to vanish the moment they arise. We need not be
under any embarrassment at meeting with "a skull exhibiting a particu-
lar prominence, although the faculty which should correspond to it be
deficient. Doubtless the individual must have been strongly gifted by
nature with this faculty, but education has long ago taught him to dis-
guise or suppress its manifestations. It exists, perhaps, unknown to
the person himself, and wants only a proper occasion for its being ex-
hibited ; or more probably the other faculties, having received a greater
proportional development, have overpowered and prevented it from
appearing. If we find, on the contrary, a strongly marked faculty,
without the corresponding shape of the head, we may still conclude
that the organ exists notwithstanding ; for the neighbouring organs,
having received a greater extension, may have pushed it from its true
place, or have grown up around it, and have concealed it from vulgar
observation. Its not having been recognised is only a proof of want
of skill in the observer ; no doubt, it would easily have been discovered
by the eye or hand of a true believer, and experienced cranioscopist ;
for it should be recollected that the differences are often very minute,
and require the tactus eruditus for their detection. Besides, how can
we be certain that the excellence of the faculty in question is not of an
artificial or relative kind, and that it results from education, or the
weakness of opposite faculties, rather than from nature ? If all these
expedients should fail us, we have nothing to do but to plunge into the
depths of metaphysics, to refine and make subtle distinctions, or loosen
the signification of a few words, till we have entangled ourselves in a
wood, and lost sight of the real difficulty that had perplexed us. Thus
will the theory be freed from all exceptions, and the induction be ren-
dered complete. With such a convenient logic, and accommodating
principles of philosophizing, it would be easy to prove any thing.
We suspect, however, that on that very account, they will be rejected
as having proved nothing.

We have here re-printed the Essa.y on this subject which originally
appeared under the head of Cranioscopy, in the Supplement to the
Sixth Edition of the Encyclopaedia Britannica. We have done so be-
cause we have not seen any reason to alter our views. Since the year
1818, when that essay was written, replies have been attempted to
some of our strictures ; particularly by Mr. George Combe, in his
'■^Essays on Phrenology, and on the objections made against it,''^
Edinburgh, 1819; and by Dr. Andrew Combe, in \\\e Phrenological
Journal. Although the conductors of this Journal have admitted that
our Article was " regarded in the South as the most formidable attack

REPLY TO CRITICISMS. 491

Phrenology ever had*to sustain,"* and have in so far paid lis a com-
pliment, we deem it unnecessary to answer, otherwise than very
generally, their comments on the reasonings contained in it ; because
most of those comments are founded on a misconception of the scope
of our arguments. When, for instance, we attempted to show, that,
in establishing a philosophical principle, mere analogies ought not to
be esteemed as equivalent to proofs, and when we maintained that they
are still less to be relied on, when other analogies, of a contrary ten-
dency, can be adduced on the other side of the question, we are re-
presented by Dr. Combe as building our arguments on analogy, the
very principle of which we were pointing out the fallacy, and repu-
diating the authority ; and we are even charged with being guilty of
the strange inconsistency of endeavouring to " refute direct inductive
evidence, by that drawn from analogy."t Any reader who had paid
the least attention to the train of reasoning we employed, must have
perceived that our reasoning was diametrically the reverse of that
which is imputed to us ; and that we had even guarded against the
possibility of mistake by the sentence concluding with the words,

" all such reasonings a priori must be completely illusory."

By the help of a mis-quotation, in which the qualifying adverb
" nearly" is omitted, we are represented as having asserted that the
anatomy of the brain " will suit any physiological system equally
well. "J All the notions we can form of the nature of mental opera-
tions are so completely and essentially different from any of the affec-
tions of which we can conceive matter to be capable, that it is utterly
impossible for us to understand the mode in which a connexion has been
established between them ; or to imagine any physical structure what-
soever, which shall, in the remotest manner, correspond with the meta-
physical constitution of the soul. This, however, we may confidently
assert, that amongst all the hypotheses which have been propounded
respecting the correspondence between the corporeal instruments of the
mind, and the mental faculties themselves, the one which is the least in
accordance with the actual structure of the brain, is that devised by the
phrenologists. Let a person, unacquainted with the anatomy of that
organ, be shown the phrenological map of the cerebral regions, and
let him be told, that to each corresponding subjacent portion of the brain
is ascribed, as to a separate organ, a certain special mental function ;
one set of these organs being appropriated to the establishment of
certain definite propensities, whilst another set gives rise respectively
to various sentiments, and a third confers on each its peculiar intellectual
power; with what immeasurable surprise, on lifting up the bony
covering which had concealed this expected assemblage of well defined
organs, would he behold a uniform mass of pulpy substance, divided
by furrows only, into serpentine but continuous convolutions, bearing
no conformity or even similitude to the notions which his previous
instructions had led him to form of distinct masses, divided from each
other in accordance with their phrenological functions.' Each of these
pretended organs, far from being isolated in its structure, as its alleged

* PhrenoIogicalJoumal, i. 166. f lb. i, 168, 169. i: lb. 366.

492 APPENDIX. PHRENOLOGY.

isolated functions would imply, from the neighb(#iiring parts, is seen to
pass on, without visible boundary, to the next, by a continuity of
cerebral substance. Turning round upon his instructor, would he not
complain of being misled by him ; and would he not require him to
explain what intermediate function he can ascribe to those portions of
the same convolution which occijpy an intermediate place between two
organs, to which he has already assigned functions utterly heterogeneous
with one another? What lucid ideas can he convey of a function
intermediate between benevolence and imitation, between ideality and
acquisitiveness, between cautiousness and adhesiveness, or between
self-esteem and concentrativeness or inhabitiveness, of which the
respective organs are not merely contiguous, but pass insensibly into
one another ; and what is the curious and hitherto nondescript office
that he will assign to those portions of the brain which occupy the
central space at the junction of quintuple groups of organs, such as
those of ideality, acquisitiveness, constructiveness, tune, and wit, all
of which, though separated by the fancy of the phrenologist, have been
by nature amalgamated into one continuous mass, undistinguishable by
any visible lines of demarcation ?

Not content with expressing his dissatisfaction at our failing to
perceive the accordance between the structure Of the human brain and
the doctrines of phrenology, Dr. Combe extends his censure to our
objection as to the evidence which observations on lower animals are
supposed to afford in their favour ; and to our assertion, that in the
construction of their system " much was made to hinge" on facts derived
from compjtfalive anatomy. That the founders of the system placed
great reliance on this kind of evidence, is a proposition sufficiently borne
out by the testimony of Sir George Mackenzie, who, when speaking
of inhabitiveness, remarks, "it is chiefly from observation on the lower
animals that Dr. Spurzheim seems to consider it as certain, that there
is such a faculty in man."* The fallacy of the reasoning by which
comparative anatomy has been pressed into the service of phrenology,
has been so ably exposed by Dr. Prichard, in his Treatise on Insanity,
that we shall beg leave to borrow from that work the following judicious
■ remarks. "The chief peculiarity," observes Dr. Prichard, "of Dr.
Gall's psychological theory, was the attempt to draw a parallel between
the animal qualities displayed by the lower animals and the individual
varieties discovered among men." He proceeded " on the principle,
that the innate or original faculties are common to man and the lower
tribes of animals, to those at least which bear to man a general analogy
in their organization, and especially in the structure of their nervous
system ; and sought for analogies in physical phenomena between the
brute tribes, tracing in them the rudiments of those properties which,
taken collectively, and in their highest degree of development, form
the human character, and which, in lower degrees and various relations,
constitute the distinctive nature of each of the inferior kinds. The
attempt was ingenious, and seemed to hold out the prospect of dis-
covering curious and interesting relations ; but it is necessary, before

* Illustrations of Phrenology, p. 92.

REPLY TO CRITICISMS. 493

embarking in the inquiry, to determine whether the analogies are real
or apparent ; for it has been tacitly assumed that the supposed distinc-
tion between instinct and reason is unreal, and that the active principles
are of the same kind in the higher and lower beings of the creation."
" Perhaps metaphysical writers have been mistaken in laying down
so broad a line of difference as they have established. We must, then,
either elevate the brutes, or lower the superiority of mankind. Shall
we say, after tracing the operations of a constructive instinct so
wonderfully displayed by the beaver, or in the cells in which the bee
lays up his honey, that an impulse to action precisely similar gave
origin to the pyramids of Egypt, or to the building of Constantinople?
Shall we venture to affirm that the tunnel under the Thames owes its
existence to a burrowing propensity resembling that of the rabbit or
the mole ? Shall we conclude that Parry and Franklin sought the
regions of the north, impelled by the instinct of the migratory rat ; and
that Magellan and De Gama traversed the Southern Oceans directed
by an influence analogous to that which moves the flight of swallows?
Or may we, with greater probability, determine that the lower tribes
act under the guidance, not of blind instinct, but of enlightened reason ;
that metaphysicians were mistaken when they laid down the principle,
' Deus est anima brutorum,' that the birds of passage have some ac-
quaintance with physical geography, and know the quarter where
tropical warmth exists and 'genial breezes blow ; that the bee has
studied the exact sciences, and knows by calculation the form most
advisable for its cells ? In short, that there is a real analogy and cor-
respondence between the mental faculties of man and the physical
endowments of those creatures whom he conceitedly regards as his
inferiors ? If either of these positions can be maintained, there will
be a sound foundation for the comparative psychology of Dr. Gall and
his followers ; but if they should be rejected as improbable, we must
admit that the analogies pointed out are remote, the things compared
are diff"erent in kind, they agree only in external appearances; and we
shall be brought to the conclusion that it has pleased the Author of
nature to bring about corresponding results in the rational and irrational
departments of the creation, by very different means."

" If the evidence," continues Dr. Prichard, " brought in support of
the organological system depends so entirely on universal coincidence
between psychical properties and corresponding varieties in the struc-
ture of the nervous fabric, it must be important to determine whether
there are any departments of the animal kingdom in which instincts
and motive habitudes, and an entire psychical nature are displayed
analogous to those of vertebrated animals, while yet in these depart-
ments there is no structure which can be said to bear resemblance to
the complicated cerebral system of the so termed higher animals. In
all the vertebrated kinds, the organization of the nervous fabric is in
one principle, and the same fundamental type, with diff'erent degrees
of development, is traced in man and all other mammifers, in birds,
reptiles, and fishes ; but here the resemblance terminates, and the
nervous system of molluscous animals and insects presented but few

42

494 APPENDIX. PHRENOLOGY.

and remote analogies to that which belongs to the first great branch of
the animal creation. It is, indeed, to be presumed that the nervous
system, taken as a whole, fulfils, in the tribes last mentioned, the same
offices as in those animals who have it enclosed in a bony case. Still,
nothing exists at all resembling the complicated formation of a brain,
with its lobes and convolutions. It is so much the more surprising
to find the higher instincts, which had almost disappeared in fishes,
display themselves with new splendour and variety in the brainless
insects ; creatures which, in the wonderful imitations of intelligence
that govern their motive habits, rival, if they do not even exceed, the
sagacity of the animals wfeich most approximate to man."

" Now, if it should be established, that all those properties of animal
life, approximating to intelligence, or bearing analogies so striking to
the manifestations of mind, which, in one great division of the animal
kingdom are assumed to be essentially connected with, and depending
on, a particular system of organization, exist in another department,
and display themselves in all the same various profusion, while the
creatures belonging to this latter department are yet destitute of that
sytem of organization, and of any thing that bears the resemblance to
■ it, the advocates of Phrenology will be obliged to abandon that broad
ground on which they have attempted to fortify their position. Within
the more confined field which the vertebrated tribes alone present, it
will be more easy to maintain such an assumed connexion of physical
properties with a peculiar structure ; or, rather, it is more difficult to
disprove it when assumed. The general analogy which prevails
throughout these tribes in the organization of their cerebral and nervous
system, affords no room for so decisive a contradiction to the relation
which the phrenologists would establish. Yet even within this field
great and striking facts display themselves which are adverse to the
hypothesis. Birds and reptiles, as Jacobi has observed, are nearly, if
not wholly destitute of many cerebral parts, which in mammifers are
held as of high importance for the manifestation of psychical proper-
ties, and yet they display psychical phenomena similar to those of
mammifers. Whenever an undoubted and tangible fact be laid hold
of in the diff'erent proportional development of cerebral parts, which
can be brought into comparison with the relative diff"erences of animal
instinct, or of psychical properties in general, there is, if I am not
mistaken, a manifest failure of correspondence between the two series
of observations. This has been shown by Rudolphi in a striking
manner, with respect to the cerebellum. The cerebellum, as this writer
has observed, is found to lessen in its proportional development as we
descend in the scale of organized beings, without any corresponding
diminution, and even with an increase of the. propensity which Gall
connects with it. How remarkably powerful is this instinct in birds ;
and yet how small is the cerebellum in the feathered tribes compared
with its size in mammifers, and even in the latter, when we consider
the magnitude which it attains in the human species ? We observe
those tribes in which the cerebellum nearly or entirely ceases to exist,
obeying, nevertheless, the impulsion of instinct as blindly or devotedly

TESTIMONY ADVERSE TO PHRENOLOGY. 495

as other kinds which have the organ in question remarkably developed.
When we consider the great amplitude which the cerebellum attains
in man, in comparison with its size in lower animals, we are obliged,
if we really attach any importance to such a system of correspondence,
to acknowledge some relation between this circumstance and the
transcendant superiority of the human intellect, compared with the
psychical powers of brutes."

"• The facts which suggest themselves as we follow these trains of
reflection, are scarcely to be reconciled with the phrenological theory:
they seem, in the first place, to show, that the relations which in it
are assumed to prevail through all nature are subject to vast exceptions ;
and as one great proof of the doctrine is the assumed universality of
such relations, or the endowment of psychial properties in co-extension
with certain peculiarities of structure in cerebral parts, the exceptions
endanger at least the outworks of the whole doctrine. When, in a
mpre limited survey, we confine our observation to the sphere of verte-
brated animals, and discover that variations in psychical phenomena take
place without any evidence of corresponding changes in the structure
of cerebral parts^ and that these changes, on the other hand, occur
without such alterations as we are led to anticipate in psychical pro-
perties, the system of organology seems to be shaken to its very
cejitre."*

Whilst the defenders of phrenology have, on the one hand, misre-
presented the minor points of our argument, they have, on the other,
disguised from their readers that it is on the insufficiency of the evi-
dence adduced in support of their doctrine, that we rest our main objec-
tion to its credibility. We maintain, that they have taken only a
one-sided view of what nature presents to our observation ; that they
have paid attention to those facts alone, which are confirmatory of
phrenology, and shut their eyes to tliose which oppose it. In order
to establish what they consider as the rule, they have collected to-
gether all the instances in its -favour, and have passed over or sup-
pressed all the exceptions. What we assert is, that more enlarged
inquiry, conducted with a more entire devotion to the cause of truth,
and a scrupulous rejection of error, would have shown the latter to be
at least equal, if not superior in number to the former. Our own^ ob-
servations, as far as we have pursued them, have led us to this conclu-
sion ; and it was on the result of these observations that our scepticism
was principally founded. So frequent, indeed, are the exceptions, that
even the founders of the system, Drs. Gall and Spurzheim themselves,
on applying it practically, cominitted, as is well known, very glaring
mistakes ; giving frequently the most false judgments of the characters
of various individuals. Have these mistakes, we may ask, been any
where recorded by the phrenologists, and candidly set off" against the
instances in confirmation of their sagacity ? What avails their collec-
tions of thousands of examples of coincidences, when the perhaps
equally numerous instances of discordance are excluded from the cata-

* Treatise on Insanity, p. 465 to 474.

496 APPENDIX. PHRENOLOGY.

logue ? The fact, that the brain of Cuvier was of unusual magnitude,
has been triumphantly proclaimed in all the publications on phreno-
logy ; but we are not aware that any phrenologist has brought forward
the equally well-certified fact, that the brain of Sir Walter Scott was
found on exan;iination to be " not large."*

In like manner, a long catalogue of persons avowing their belief in
phrenology, including many men of eminent talents and extensive
knowledo-e, has been paraded before the public ; but we have not yet
seen any counter list of unbelievers prepared with the view of ascer-
taining, in a science professedly of pure observation, on which side'
the weight of authorities preponderates. The class of men who, from
the nature of theii* pursuits, are perhaps best qualified to form a correct
judgment in matters of this nature, are the members of the medical
profession ; yet how inconsiderable, compared with the total number,
is the proportion of those belonging to that profession who, according
to Mr. Combe's catalogue, have given in their adhesion. Sculptors,
again, compose another class of men whose studies lead them more
especially to the most minute and accurate knowledge of the external
form of the human head ; yet amongst the many who are at present
engaged in the active exercise of their noble art, Mr. Combe has been
able to bring forward the name of one solitary individual as lending a
countenance to phrenology.

" It is not enough," as Dr. Prichard very justly observes, "to have
a few chosen coincidences brought forward by zealous partizans, who
go about in search of facts to support their doctrine, and pass by, or
really cannot perceive, the evidence that ought to be placed in the oppo-
site scale. The principles of the system ought to be applicable in
every instance. The phrenologists, however, aware of numerous and
striking exceptions, elude their evidence by asserting, that when ^
certain portion of the cranium and of the brain is greatly developed,
while the faculty there lodged has never been remarkably distinguished,
it nevertheless existed naturally, though the innate talent, for want of
proper cultivation, has never been displayed; the predominant organic
power was never discovered by the owner, though according to the
principles of the doctrine, with this organic power a proportional
impulse to exertion, or an instinctive energy is combined, which com-
municates of itself a strong and irresistible tendency to particular pur-
suits. When, again, a strongly marked propensity, or a decided talent
has been manifested without any corresponding amplitude of structure,
it is in like manner pleaded, that by sedulous exercise and culture, a
natural deficiency has been overcome. Thus the phrenologist avails
himself of a double method of elusion ; his position, like the cave of
Philoctetes, affords him an escape on either side ; and in one direction
or another he contrives to baffle all the address of his opponents.

" If, however, the testimony of facts in a great scale should be
found adverse to the alleged coincidences, or to the correspondence
of given mental equalities with certain conditions of the brain, phre-
nology will not continue to make proselytes, and ,it will be ultimately

• Life of Sir Walter Scott, by Lockhart, vol, vii. p. 395, note.

TESTIMONY EVAJ)ED BY PHRENOLOGISTS. 497

discarded as an hypothesis without foundation. At present, most
inquisitive persons seems to b^ in doubt on this subject, and to be
looidng out for evidence. 1 have taken every opportunity that has
occurred to me for many years of making inquiries of persons who
had a great field of observation within their reach, what had been the
result of their experience on this subject. Many of the persons have
been physicians, who were superintendants of extensive lunatic
establishments. Some of them had been men who had addicted
themselves to the study of phrenology, and were predisposed to imbibe
the opinions of its authors : some have been persons distinguished by
their researches in the anatomy and physiology of the brain and
nervous system. Among these I do not remember to have found one
who could say that his own observation had aflorded any evidence
favourable to the doctrine. Yet we should imagine, that a man who
lives amongst hundieds of monomaniacs must have constantly before
his eyes facts so obvious that he could not be mistaken in their bear-
ing. Some hundreds, and even thousands of such persons have passed
a part of their lives under the inspection of M. Esquirol, who possesses
most extensive resources for elucidating almost every subject con-
nected with the history of mental diseases, and has neglected no
i'nquiry which could further the attainment of that object. The result
of his observations will be allowed to be of some weight on the decision
of this question, in which the appeal is principally to facts of the precise
description of those with which he has been chiefly conversant. At
his establishment at Ivry he has a large assemblage of crania and casts
from the heads of lunatics, collected by him during the long course of
his attendance at the Salpetriere, and at the Royal Hospital at Charenton,
which is under his superintendance. While inspecting this collection,
I was assured by M. Esquirol, that the testimony of his experience is
entirely adverse to the doctrine of the phrenologists ; it has convinced
him that there is no foundation whatever in facts for the system of
correspondences which they lay down between given measurements of
the head and the existence of particular mental endowments. This
observation of M. Esquirol was made in the presence of M. Mitivie,
physician to the Salpetriere, and received his assent and confirmation.
M. Foville, physician to the extensive lunatic asylum at St. Yon, gave
me a similar assurance. There are few individuals in Europe whose
sphere of observation has been so extensive as that of M. Esquirol and
M. Foville, and certainly there are none wliose science and habits of
observation better qualify them to be witnesses in such a subject of
inquiry; but testimonies to the same result may be collected from
unbiassed witnesses, whose evidence taken collectively may have nearly
equal weight. Among these there are men unscientitic, though capable
of correct and unprejudiced observation, as well as anatomists and
physiologists. In the number of the latter is Rudolphi, who declares
that he has examined many hunderds of brains without finding any
thing that appeared to him favourable to the phrenological theory."*

* Treatise on Insanity, pp. 476, 477,
« 43*

498 APPENDIX. PHRENOLOGY.

The mode in which Dr. Combe. evades the force of the strong testi-
mony here adduced, is quite characteri^stic of the disposition to be found
amongst confirmed phrenologists, of resolutely rejecting all evidence
that militates against the system they have adopted. Thus, he says,
in reference to the passage vi^e have just quoted, "If Dr. Prichard
believes that the intelligent and benevolent Esquirol, is that person,"
(namely, one " competent to form a judgment on the subject,") and if
his collection of crania and casts be the hostile evidence vi^hich is relied
on, this only proves, in a forcible manner, that Dr. Prichard is himself
not competent to judge, or that he has not taken time either to examine
the collection of crania, or to ascertain the competency of Esquirol and
Metivie, to decide on the merits of the question on which they volun-
teered an opinion."* We cannot help remarking here, that, on another
occasion, when criticising the suggestion Ave threw out, in the Essay
on Cranioscopy, of the propriety of inquiring into the talents and
qualifications of observers before admitting the truth of the facts received
on their testimony, a very different language was held. " When they"
(the advocates of phrenology) "affirm that the subjects of observation
are patent to the whole world, who have eyes to see, and understandings
to comprehend ; and when they say, compare manifestations with
cerebral development, and you are at the bottom of the problem yourself;
what need for inquiry into their talents and qualifications to observe?"
" When Gay Lussac hears that Sir Humphry Davy has made a
discovery in chemistry, and reads Sir Humphry's statement of the way
in which it was made, does he begin by inquiring first, whether it be
possible to make the discovery at all, seeing natural substances are 'so
changed and modified, exalted and subdued' by a multitude of powerful
causes ? And, after settling this point, does he, in the secoml place,
proceed to inquire into Sir Humphry Davy's talents and qualifications
as a chemist, and into his capacity to make the discovery, and then
believe it, or not, according to the result of this investigation ? No
man who knows the first rudiments of philosophy would follow so
absurd and preposterous a course. What should we think of Gay
Lussac's refutation of Sir Humphry's discovery, founded on a meta-
physical inquiry into the possibility of making it, and into the ' talents
and qualifications' of the discoverer ? We should pity him for his
ignorance of the rudiments of philosophy. "f

This happy talent, possessed by the champions of phrenology, of
shaping their course either one way or the opposite, according as it
may suit the convenience of the occasion, enables them, at one time,
to proclaim, that the evidences of their science are palpably and de-
monstrative, that the field of nature is open to all inquirers, that
" every one who has eyes may see" and judge for himself; and at
another, when such judgment is against them, they can turn round,
and allege that in order to arrive at the truth a peculiar discretion and
tact, acquired by long experience and careful appreciation of minute

* Phrenological Journal, viii. p. 654.
-j- Essays on Phrenology, p. 71. '

PROCESS OF VEKIFICATION. 499

and hair-breadth differences of size is necessary. They can then
declare that the observer who has not arrived at the same conchisions
as themselves, is doubtless incompetent to the task he has attempted ;
and that his testimony, being of no value, ought to be wholly set
aside.

Let it be borne in mind, then, by the practical inquirer into the truth
of phrenology, that he will not be esteemed qualified to verify its
doctrines, unless he be previously deeply versed in the new system
of psychology, can assign to each of the thirty-five special and
primary faculties of the soul its sphere of operation, and has acquired
a readiness in unravelling their multifarious combinations, so as to
analyze, by this subtile metaphysical chemistry, all human qualities
into their proximate and ultimate elements, refer all actions to their
proper innate impulses, and assign the proportions of the various
ingredients which are mixed up in the formation of the character of
each individual. No one is competent to excel in this new branch of
philosophy who doubts the possibility of appreciating the intensities of
moral or intellectual qualities by geometrical measurements, on scales
divided into tenths and hundredths of inches. The young and ardent
phrenologist, who after having applied his callipers to the skull sub-
jected to his examination, and taken a note of the dimensions of each
of the thirty-five organs, proceeds to verify his observations by com-
paring them with the character of the possessor of those organs, will
never fail to meet with ivonderful coincidences, sufficient to give him
the greatest satisfaction, and confirm him in the persuasion that he pos-
sesses the real key to the secrets of nature in the hitherto recondite
science of mental philosophy. A moderate share of dexterity in re-
conciling apparent discrepancies will suffice to ensure a preponderance
of favourable evidence ; since, fortunately, there have been provided in
the brain different organs, sometimes of similar and sometimes of opposite
properties, capable, by a litde adjustment o{ plus or minus on either
side of the equation, of furnishing the requisite degrees of the mental
quality sought for, and of thus solving every psychological problem.
We shall suppose, for instance, that he is inspecting the head of a
person known to have given credit to the prophecies of a weather
almanac ; he finds, on reference to the " system of phrenology," that
a belief in astrology is the oflTspring of No. 16, that is, ideality ; so
that if this organ happen to be sufficiently large, the phenomenon is at
once accounted for. But if it be not, our phrenologist will have an-
other chance ; for he will probably discover it to arise from the dimen-
sions of No. 15, which inspires hope, the source of \he propensity to
credulity. Habitual irresolution may result either from the magnitude
of No. 12, or thediminutiveness of 18 ; thus affording very great con-
venience for making our observations of the character square with those
of the dimensions of the organs, and vice versa. If, again, the magni-
tude of the organ of combativeness accord with the manifestations of
pugnacity given by the individual, it is well, and we need inquire no
farther, but set it down at once as an irrefragable proof of the accuracy
of phrenological determinations. Should the correspondence, how-

500 APPENDIX. PHRENOLOGY.

ever, not prove satisfactory, the organ being large for instance, and the
manifestation small, we have then further to examine the dimensions
of the organ of caution, the influence of which is to moderate and
check the operation of the fornier ; and we shall perhaps find this
organ sufficiently large to account for the phenomenon. -Both these
organs may be large, or both small, or the first may be small and the
second large, or the converse ; and other modifications of action may
result if either one or both be only of moderate size, allowing great
latitude of choice in the a.ssignment of motives. Should we be so
unfortunate as to exhaust all the combinations without meeting with
the success we desire, there is still an abundance of auxiliary faculties
of which we may avail ourselves with advantage. If we were to ex-
plain the fact of the individual in question having accepted a challenge,
he might have been inspired by combativeness, whose voice was
" still for war," or goaded on by destrudiveness, to fight that he
might destroy ; firmness may have urged him to persevere by the con-
sideration that he had previously resolved it, and concenirativeness, by
rivetling his attention to the subject, may have screwed his courage to
the sticking place , or he may have been prompted by imitation to
follow the example, or by approbation to gain the applause of his
friends. We have also to take into the account the countervailing
influence of faculties which are pulling in the opposite direction, and
qualifying the combined powers of the former incentives: And should
cautiousness not be in sufficient force, we are to consider the power of
conscientiousness, which preaches forbearance, meekness, and forgive-
ness ; of veneration which appeals to the high authority of religion
and of law ; of benevolence restraining the hand from inflicting pain
and death ; of approbation, who qualifies her sanction by raising other
voices condemnatory of the deed ; and last, though not least, the love
of life which recoils with instinctive dread from the possible catas-
trophe. Drawing, then, a diagrjim of all these component moral
forces, in their proper directions, and suitable proportions, it will not
be very difficult to obtain by this artificial dynamieo-phvenological
process, the exact resultant which corresponds with the actual fact to
be explained.

Lest it should be imagined that the above description is a caricature
of the new method of philosophizing, so admirably calculated to esta-
blish the truths of phrenology, we shall beg to quote the following
passage from Sir George Mackenzie's Illustrations, as an example of
this satisfactory process of ratiocination.

" In discussing the conjectured faculty of inhabitiveness with Mr.
Combe, he had the goodness to make us acquainted with a case, in which
locality and inhabitiveness were both very moderate in development,
but the propensity to wander, as he informed us, very powerful. Dr.
Spurzheim mentions this propensity as belonging to locality, and he
states several remarkable cases in which the organ was much deve-
loped, and the propensity strong. The case referred to by Mr. Combe
was, on this account, interesting ; and we will state the result of our
inquiries into the particulars, for the purpose of giving an example of

INFLUE^CE OF EDUCATION". 501

the caution with which we ought to receive the description of any case
brought in opposition, since it sometimes appears to be necessary even
among friends.

" The young man to whose case we refer, had a very strong desire
to adopt a seafaring life, contrary to the wishes of his friends. It oc-
curred to them, that a voyage up the Baltic, during the stormy months
of October and November, might have the effect of giving him a dis-
gust to the profession for which he showed so ardent a desire. He
suffered so many privations and hardships, that he yielded to the
wishes of his friends, although the desire to go to sea continued as
strong as ever. On proposing a few questions, we found that the pro-
pensity was confined to being at sea; that this propensity did not
originate in a desire to wander ; for neither travelling on land, nor
mere change of place, would have gratified the propensity. At the
same time, the person referred to declared, that regular voyages to the
same place would not have satisfied him. The propensity had haunted
him as long as he could remember any thing. Being anxious himself
to contribute to the unravelling of what appeared mysterious and irre-
concilable to the system, he stated that he used to go once or twice
a-day to examine the mechanism and rigging of ships in Leith har-
bour, an employment of which he was passionately fond ; and long
before he commenced his trial voyage, he had become familiar with
the names and uses of every part of a ship, and of the rigging. He was
fond of machinery, and has often amused himself by making models of
ships ; and his mechanical turn was so strong, that he had constructed
a model of machinery, by which a ship's motion may be applied to
work the pumps. This mechanical propensity, and his early attach-
ment to naval machines, together with firmness, appear to us to have
given rise to his desire for a sea-faring life. Courage might also have
prompted his wish to enter the navy. Thus the supposed propensity
to wander appeared not to exist ; and it was found that a mechanical
genius, an early attachment* to the mechanism of a ship, perseverance,
courage, and probably also love of approbation, or ambition, and
ideality, all of which were well developed in the individual referred to,
combined to inspire the desire to enter the navy." (Illustratioris of
Phrenology, p. 170.)

It is to be lamented that, at the period when this elaborate investi-
gation was undertaken, the organ of wonder had not yet been made ;
for as one of the functions of this organ, according to Mr. Combe, is to
" incite young men to choose the sea as a profession," much light
would have been thrown upon the object of the inquiry by a critical
examination of its dimensions compared with those of all the other
organs which were taken info consideration as combining their influ-
ence in producing the result.

There is this very remarkable peculiarity in the pursuit of phre-
nology, that the student is perplexed, not with the difficulties, but

* " Dr. Spurzheim has shown, that the faculty of attachment extends its influ-
ence to inanimate things, as well as to animate beings."

502 APPENDIX. PHRENOLOGY.

with the facilities it affords for explaining every phenomenon. The
pliability of its doctrines is exemplified, not merely in the analysis of
motives, but likewise in the influence vi^hich we are allowed to ascribe
to the habitual exercise, or education of the faculties. The observed
magnitudes of the respective organs indicate, not the acquired, but the
natural powers, sentiments, and propensities. Now, the character of
the individual is the joint result of the force of natural endowments,
and of the amount of moral and intellectual cultivation which has been
bestowed upon them. But can we ever know enough of the minute
history of the progress of the mind of any individual to enable us to
form a correct estimate of the relative power of these two elements,
which have, in the formation of each respective faculty, combined
their operations ? If it be true that an organ may be the seat of a faculty
varying in its activity according to the occasions which call it forth,
by what physical criterion can we distinguish the active from the
dormant conditions of that organ ? Unless we can draw, with pre-
cision, these distinctions, it is evident that the ground of all craniosco-
pical observation is cut from under us.

It may be indeed alleged, that at all periods of life, and even after
the bones of the skull are consolidated, the organs increase or diminish
in size according to the exercise or disuse of the faculty associated
with it, whether such change may have been brought about by voluntary
training, or by the discipline of circumstances ; and certainly, if such
were the fact, our experience would repose on a much surer basis,
than if the form of the organs merely retained the stamp originally
impressed upon them by nature. But the hypothesis that the cerebral
organs acquire additional size by the exercise of their powers was posi-
tively rejected as untenable by Dr. Spurzheim, as we have heard him
publicly declare ; and it is, we believe, repudiated by the generality of
phrenologists.

We do not think it difficult to account for the progress which phre-
nology has made amongst the very numerous class of persons who
find in it a source of agreeable occupation, giving exercise to their inge-
nuity in discovering striking coincidences, and gratifying their self-
complacency by inspiring them with the fancy that they are penetra-
ting far into the mystic regions of psychology. For the last twenty
or thirty years, various popular writers, and lecturers without number,
have been displaying their powers of elocution, exercising their skill
in the critical examination of developments, and expounding the doc-
trines of the new philosophy to wondering and admiring audiences.
With all these advantages and appliances to boot, the wonder seems
to be not that phrenology has met with the success of which so much
boast is made, but that it has not speedily gained the universal assent ;
for had it been a real science, like that of Chemistry and other branches
of Natural Philosophy, founded on uniform and unquestionable evidence,
it could not have failed, by this time, of being generally recognised as
true.

When we consider that the present age is not one in which there is
any lack of credulity, or in which a doctrine is likely to be repudiated

PROGRESS OF PHRENOLOGY. 503

on the score of its novelty or its extravagance, we cannot but smile at the
complaints of persecution uttered by the votaries of the system of Dr.
Gall, and at the attempts they make to set up a parallel between its
reception in this country, in these times, and that which, two centuries
ago, attended the speculations of Galileo, and subjected him to the
tyrannous cognisance of the Inquisition ; or to establish an analogy
between the dogmas of phrenology and the discoveries of the circula-
tion of the blood, and of the analysis of light, which have immortalized
the names of Harvey and of Newton.

INDEX.

THE NUMBERS REFER TO THE PARAGRAPHS.

Those references to which the word (note) is attached have been added in the American

edition.

Abeildgaard, 436.
Aberration, chromatic, 670.

parallactic, 667.

of retrangibility, 670 (note).

spherical, 665.

Absorbent system, 539.
Absorption, interstitial, 551.

lacteal, 38, 40, 538.

lymphatic, 45.

venous, 45 (note).

Abstinence, effects of, 324.
Acalepha, 1114.
Acephala, 1085.
Acid, lactic, 519.

in stomach, 347.

Acini, 499, 505.

Acoustics, 623, 757.

Actinia, 1115.

Adelon, 84 (and note), 50 (note).

Adipose texture, 122.

Admyrauld, 615.

iEthmoid bone, 617, 940.

Agastrica, 1120.

Age, 570, 858.

Air bladder, 1061.

Alar ligaments, 170.

Albinus, 113, 178.

Albugineous ^bre, 114, 165.

Albumen, 285, 517.

Albuminous secretions, 514.

Alison, 86.

AUantois, 848, 1020.

American race, 875.

Ammonia, formation of, 270.

Amnios, 844, 851.

Amphiuma, 1044.

Amphibia, 949.

Ampulla, 632.

Anaesthesia, 709.

Analysis, ultimate, 272.

Anastomoses, 423.

Anatomy, .56.

Animal kingdoin, 2.

Animal food, 313. ,

Animalcules, spermatic, 810.
Annelida, 1092.
Annulus ovalis, 412.
Antagonist powers, 570.
AntennsB, 1094, 1104.
Antiquity of man, 72. (
Antiseptic power, 342.
Antitragus, 627.
Antra inguinalia, 962.
Aponeuroses, 156, 161.
Apparatus neurothelic, 178 (note).

blennogenous, 183 (note).

chromatogenous, 179 (note).

diapnogenous, 555 (note).

Appendices pyloricse, 1054.
Applications of Physiology, 57.
Aqueous secretions, 512, 513.

exhalations, 484.

humor of the eye, 649.

Arabians, 1139.
Arachnoid, 133.
Arachnida, 1096.
Archseus, 7, 101.
Area vasculosa, 1020.
Areola, 828.
Areola pellucida, 1020.
Aristotle, 1131.
Arrangement of functions, 77.

ancient, 81.

Adelon, Beclard, &c. 84.

Bichat, 83.

Bostock, 85.

Cuvier, 84.

Dumas, 83.

Dunglison, 84 (note).

Haller, 82.

Magendie, 84 (note).

/Mayo, 87.

Richerand, 82.

Roget, 88.

D Azyr, 82.

Arteries, 42.

43

506

INDEX.

Arterise helicinae, 809.
Arterial system, 418.
Arterial action, 458.
Articulate sounds, 768.
Articulata, 68, 1U90.
Articulations, 167, 244.
Aryteenoid, 759.
Ascidia, 1089.
AsELLi, 377, 1150.
Asterias, 1108.
Assimilation, 39, 307.
Association, 702, 704.
Attraction, 107.

of life, 223.

Automatic motions, 728.
Auricle, 412.

AVICENNA, 1139.

Babington, Dr. B. 407 (and note).
Baer, 803, 804.
Baillie, 582.
Balance of afRnities, 265.
Barry, Dr. M. 799, 800.
Bartholin, 1151.
Base of support, 250.
Bat, 937.
Batrachia, 1041.
Bauer, 199, 395, 401, 585.
Bear, 942.

Beaumont, 323 (note), 347 (note),
349 (note).

Beaver, 957.

Beclard, 84, 117, 199, 585.
Bee, 1102.

Bell, Sir Charles, 615 (note), 720,
724, 731, 769.

Bennati, 772.

Benson, 143.

Berres, 588 (note).

Berzehus, passim.

Bichat, passim.

Bile, 40, 864.

Biology, 1.

Birds, 1003. /

Bivalves, 1085.

Blainville, 73.

Blane, 208.

Blastoderma, 831.

Blennogenous apparatus, 183 (note).

Blood, 42, 383.

Blumenbach, passim.

Blundell, 447 (note).

Boerhaave, 113, 392, 504, 1156.

BoissiER, 558 (note).

Bones, 30, 35, 137, 565.

Bonnet, 69.

BoRELLi, 198, 436, 1008.J

BosTocK, passim.
Botany, 2.
Botts, 983.

BOUDET, 407.

Bourdon, 84.

BoGER, 511 (note).

Brain, 14, 173, 521, 581, 749, 1014.

Branchiffi, 1045, 1060.

Brande, 287, 303, 386, 399, 404.

Breschet, 178, (note), 179 (note),

183, (note), 555 (note).
Broughton, 615 (note).
Brevipennes, 1021.
Brown, 100.
BuFFON, 154 (note), 818.
Bulbus arteriosus, 1059.
Bulbus glandulosus, 1009-
Bulla ossea, 829.
Bullffi turbinatae, 1017.
BuRDACH, 588 (note).
Bursa faucium, 992.
Bursa Fabricii, 1010.
Bursse mucosae, 170.
Butt, 403.
Butter, 522.
Byssus, 1087.

Cadet, 368 (note), ,

CjESAlpinus, 1148.

Callus, 567.

Camel, 992.

Camel opard, 993.

Campanula, 1065.

Camper, 904. \

Canals, 131.

Canalis Petitianus, 650.

Cancelli, 139.

Canon bone, 879.

Capillaries, 428, 429, 464.

Capsules, 1-56, 1.59.

Capsule of the lens, 650.

joints, 170.

vitreous humor, 648.

Capsular ligament, 171.
Caput Gallinaginis, 807.
Carbon, 49, 271.
Carbonic acid, 481.
Carlisle, 198, 936.
Carnese columnss, 410.
Carpenter, 103, note.
Cartilages, 147.

Cartilages, articular, or diarthrodial-.
151, 169.

interarticular, 1-52.

interosseal, 150.

raembraniform, 14t7.

INDEX.

507

Cartilages, temporary, 148.

semilunar, 171.

of larynx, 761.

Caruncula lacrymalis, 654.

Carunculae myrtiformes, 818.

Cassowary, 1021.

Carus, 432 (note).

Carus, 1097.

Cat, 948.

Caterpillar, 110.3.

Catoptric examination of the eye, 657

(note).
Caucausian race, 872.
Cavallo, 393.
Cellular texture, 32, 118.
Centre of gravity, 252.
Cephalopoda, 1079.
Cerebellum, 582, 925.
Cerebral substance, 520.
Cerebrum, 582.
Ceruminous glands, 628.
Cetacea, 996.
Chalazee, 821, 1019.
Chameleon, 1033.
Chaussier, 114, 165, 179, 181.
Cheeks, 607.
Cheek pouches, 960.
Cheese, 519.
Chiroptera, 937.
Chelonia, 1027.
Chemical functions, 38, 307.
Chemical conditions of organized

matter, 263.
Cheselden, 178.
Chevalier, 183.
Chevreul, 407.
Choleric temperament, 865.
Cholesterine, 518.
Chondropterygii, 1046.
Chordae tendineae, 410.
Chorda tympani, 631.
Chordae vocales, 761.
Choroid coat, 645.
Chorion of teeth, 568.
Chorion, 792, 830.
Christison, 386 (note).
Chromatic aberration, 670.
Chromatogenous apparatus, 179 (note).
Chossat, 558 (note).
Chyle, 40, 356.
Chylification, 40, 354.
Chyme, 39.
Chymificatioii, 338.
Cicatricula, 823, 1020.
Cilia, 653.
Ciliary circle, 647.

ligament, 647, 669.

processes, 647.

Cineritious substance, 582,
Circle of Petit, 650.
Circulation, 38, 42, 102, 408.

proofs of, 443.

Classification, zoological, 60, 64.

of tastes, 613.

of odours, 621.

of Cuvier, 67.

Claviculi of bone, 143.
Clitoris, 818.
Cloaca, 848.
Cloak, 1077.
Coagulable lymph, 391.
Coagulation of albumen, 286.

of blood, 387.

by gastric juice, 342.

Coalescence of impressions, 682.

Coats of blood-vessels, 415.

Cochlea, 633.

Coffin bone, 979, 980.

Colliquamentum, 831.

Columna nasi, 617.

Colon, 40.

Complementary colours, 685.

Complexity of organize d matter, 263.

Conception, 820.

Concha, 628.

Concoction, .350.

Condiments, 320.

Conglobate glands, 495.

Conglomerate glands, 499.

Coni vasculosi, 798.

Connexions, mechanical, 167.

Consonants, 771.

Contractility, 93, 201.

Constituents, animal, 268.

Continuous gradation, theory of, 69.

Convolutions, 582.

Cow PER, 198.

Corion, 177.

Cornea, 644.

Coronet bone, 979.

Corpus aurantianum, 411.

cavernosum, 818.

ciliare, 647.

luteum, 820.

papillare, 178.

— — spongiosum, 808,
Corpusculum Morgagni, 411.
Corrugation, cellular, 121, 226.
Cortical substance, 582.
Cotulae, 506.

COTUNNIUS, 634.

Cotyledons, 833.
Cowper's glands, 800.
Cranium, 229.
Crassamentum, 385, 391.
Crawford, 387, 489.

508

INDEX.

Cribriform plate of ear, 635.
Cricoid, 762.
Crocodile, 1032.
Crop, 1009, 1081.
Crucial ligaments, 172.
Cruickshank, 179, 181, 556, 558

(note).
Cruor, 385.

Crura corporis spongiosi urethras, 80i
Crusta'petrosa, 970.
Crustacea, 1094.
Crypts, 188.
Crystalline lens, 648.
CuLLBN, 101, 317, 1158.
Cumulus, 803.
Cupola, 633.
Cuticle, 180.
Cuttle-fish, 1079.
CuviER, 67, 71, 73, 84, &c.
Cyanogen, 270.
Cysticule, 1067.

Dalton, 484.

Davtos, 805.

Darwin, Charles, 861.

Davy, John, 142, 386 (and note).

Death, 37, 858.

Decidua, 833.

Decline, 570.

Decussation of nerves, 718.

Deer genus, 68.

Defoecation, 40.

Deglutition, 39, 336.

De Graae, 797, 1154. -

De la Torre, 393, 585, 588.

Deleau, 764.

Delirium, 701.

Dkmocritus, 1127.

Dentition, 568.

Derham, 75.

Descartes, 691, 698.

Design, 79.

Development, 51.

Deyeux, 387, 403.

Diaphragm, 472.

Diaprogenous apparatus, 555 (note).

Diastole, 441.

Digestion, 39, 102, 338.

Digitigrada, 944.

Discus proligerus, 799.

Diploe, 139.

DODART, 763.

Dog, 946.

Dorsal vessel, 1097.
DoLLiNGER, 432 (note).
Draco volans, 1034.
Dreaming, 753.
Drelincourt, 822.

Duct, 131.

Ductus arteriosus, 851, 853.

pneumaticus, 1061.

venosus, 851, 853.

vitello-intestinalis, 1020.

Duhamel, 143, 560.
Dumas, 199, 222, 336.

DUMERIL, 66.

Duncan, 386, (note).

DuNGLisoN, 84 (note), 323 (note), 347

(note), 509 (note).
Duodenum, 40, 364, 851.
Dura mater, 133, 158.
Duration of impressions, 680.

DUTROCHET, 199.

Ear, 626, 1016.

Ear-drum, 629.

Eberle, 340 (note).

Echinus, 1109.

Echinodermata, 1107.

Education^ 856.

Edwards, 116, 199, 585.

Edwards, Milne, 396.

Egyptians, 1125.

Ehrenberg, 588 (note), 785.

Ejaculatores seminis, 809.

Elasticity, 120,

Elasticity of arteries, 461.

Electrical fishes, 1069.

Elemental material, 112.

Elements, animal, 268, 275.

Elephant, 968.

Elongation, 210. /

Elliotson, 588 (note).

Emmert, 588 (note).

Emmet, 347 (note).

Emboitement, theory of, 827.

Emphysema, 119.

Emotions, 732.

Emunctories, 48.

Endosmose, 548.

Ent, 428.

Entozoa, 1112.

Epididymis, 805.

Epidermis, 180.

Epidermoid substance, 114.

Epigenesis, 828.

Epiglottis, 760.

Erasistratus, 1133.

Erect position, 894. ,

Erectile tissue, 434, 800, 801.

Ethiopian race, 874.

Eustachian tube, 630.

Eustachian valve, 412.

EUSTACHIUS, 1145.

Evolution, 50.
theory of, 827.

INDEX.

509

Evolution, fetal, 837.
Excito-motory system, 741.
Excretion, 48, 553.
Excretory duct, 43, 506.
Exhaustion, 209.
Expiration, 477.
Eye-ball, 641, 642.
Eye-lids, 653.

Fabricius, 1146.

Face, bones of the, 234.

Facial angle, 904, 905.

Falciform bones, 941.

Fallopian tubes, 821.

Fallopius, 1145.

Falsetto voice, 770.

Faraday, 681.

Farina, 315.

Fasciae, 34, 156.

Fascicular ligaments, 172.

Fasciculi of muscular fibres, 194.

Fat, 47, 122, 5 J 9.

Fecundation, 50, 789.

Fermentation, 351, 533.

Ferrien, 755.

Fibrin, 294.

Fibrinous secretions, 517.

Fibro-cartilaginous textures, 153.

Fibrous tissues, 34, 155, 164.

Fibrous membranes, 158.

Fibrous capsules, 159.

Figura vasculosa, 1020.

Filtration, 534.

Fimbria, 816.

Final causes, 8, 78.

Fingers, 258.

Fishes, 1045.

Fletcher, 669 (note).

Fluids and solids, proportion of, 111.

Focal adjustment, 659.

Fohman, 1057.

Follicles, 188, 502, 5^33.

FONTANA, 198, 588.

Food, 311.

, animal, 313.

, vegetable, 314.

Foot, 250, 1086.
Foot of moUusca, 1086.
Foramen coecum Morgagni, 611.
Foramen centrale of Sommerring,

651.
Foramen ovale et rotundum, 85L

FORDYCE, 317.

Fossa ovalis, 412.
Fossil remains, 71-
FoujiCROY, 386, 398, 511, &c.
Fractured bones,
Fraenum labiorum, 607.

43^

Fraenum linguae, 611.

Frog, 1041.

Fuel necessary for vitality, 261.

Functions, gradation of, 11.

animal, 81.

chemical, 38.

mechanical, 30.

natural, 81.

sensorial, 13. {

vital, 81.

Furcular bone, 1005.
Gagliardi, 143.
Galen, 722, 1136.
Gall, 584, 725.
Gallendobff, 368.
Ganglia, 581, 590, 726, 747.
Ganglia, lymphatic, 543.
Gas, 346, 374.
Gasteropoda, 1083-
Gastric juice, 39, 323, 340.
Gelatin, 279.

Gelatinous secretions, 516.
Gemmules, 784, 1113, 1117.
Generation, 50, 780.
Geology, 71.
Georget, 868 (note).
Germ, 786.
Gestation, 50.
Gibson, 547.
Gills, 1045, 1060-
GirafFe, 993.
Gizzard, 1009.
Glands, 43, 494, 845.

, lymphatic, 543, 552.

Gland ulae ceruminosse, 653.

Hardsri, 929.

Meibomii, 653.

Glandular system, 496.
Glans, 800,
Glisson, 93, 203.
Globules of milk, 520.

of blood, 392.

Globular tissue, 115.

Globuline, 397.

Glottis. 760.

Glue, 279.

Gluten, 314, 391.

Gmelin, 348, 370, 372 (note), 380,

Good, 436.

Gordon, 179, 386.

Graafian vesicle, 797, 820, 829.

Gradation of functions, 11.

of po Vipers, 98.

Granular tissue, 115.
Greeks, 1126.
Gregory. 558 (note).
Growth, 46, 262, 570.
Grtjithuisen, 432 (note).

510

INDEX.

Gubernaculum, 849.

GUENEAU DE MoNTBEILLARD, 154

(note).
Gums, 6U8.
GuRLT, 183 (note).
GuYOT, 615.
Gymnotus, 1070.

Hair, 184.

Hales, 452.

Halitus, 135, 384.

Hall, 741, 747.

Haller, 112, 436 (note), 1157,

passim.
Hamberger, 436.
Hamster, 960.
Hand, 256, 260, 899.
Hare, 961.
Harlan, 450 (note").
Hartley, 692.
Hartsoeker, 810.
Harvey, 442, 820, 1149.
Hatchett, 289.
Havers, canals of, 140.
Hays, 657 (note).
Hearing, 18, 623, 636, 927.
Heart, 41, 409, 459, 744, 841, 920.
Heat, animal, 489.

sense of, 595.

Helix of ear, 627.
Hematine, 397.
Hematosine, 397.
Henry, 290.
Herissant, 141.
Herophilus, 720, 1134.
Hewson, 387, 393.
Hidrophorous ducts, 555 (note).
Hippocrates, 691, 1128.
History of Physiology, 1121.
Hock bone, 982.
HooKE, 198.

HODGKIN, 116, 200.

Hoffmann, 101, 1156.

Hog, 974.

Holothuria, 1110.

Home, 371, 639, 668.

Honey-comb stomach, 939.

Horns, 993.

Horse, 978.

Houston, 809.

HowsHip, 140.

Human peculiarities, 891.

Hunger, 321, 596.

Hunter, Wm. 113, 118, 169, 181.

Hunter, John, 1158, et passim.

Hybernation, 47.

Hydrogen, 271.

Hygrometric property, 129.

Hymen, 818.

Ideas, 703.
Ileum, 40.

Illusions, visual, 681.
Images in the eye, 659.
Imbibition, 1097.
Impressions,. 94, 578.
Incident nerves, 741.
Incubation, 1019.
Incus, 631.
Induction, 78.
Infundibulum, 633.
Infusoria, 1120.
et Ink of Sepia, 1082.
Insanity, 701.
Insalivation, 331.
Insects, 1097.
Insectivora, 939, 940.
Inspiration, 471, 472.
Instinct, 732.
Instinctive motions, 733.
Integument, 176, 930.
Intention in organization, 9.
Intercostal muscles, 473.
intermaxillary bone, 915.
Interspinal bones, 1048.
Interstitial absorption, .551.
Intervertebral ligament, 238.

substance, 154.

Intestines, 40, 370.
Intestines large, 373.
Involuntary motions, 736.

muscles, 579.

Iris, 646, 663, 669.
Iron in the blood, 398.
Irritability, 93.

of heart, 456.

Irritation, 94, 578.
Isthmus Vicussenii, 412.
Itching, 597.

Jacobson's gland, 931.
Jejunum, 40.
Jelly, 280.
Joints, 168, 244.

Kangaroo, 954.
Kater, 396.
Kay, 488 (note),
Keill, 436.
Kidney, .556, 847, 926.
Kiernan, 524.

Labyrinth of the ear, 632.
Lacerti, 194.
Lacrymal duct, 618.

gland and sac, 654.

I Lactation, 50, 836.
Lacteals, 40, 538.
Lacteal absorption, 376.

IXDEX.

511

Lactic acid, 520.
Laws of nature, 89.
Lacunee, 506, 800.
Lamina cribrosa, 651.

spiralis, 633.

Lancisi, 392.

Larva, 1100.

Larynx, 764.

Lassaigne, 372.

Lavoisier, 555.

Laws of vitality, 86, 103.

Lecanu, 397, 407.

Lee, Robert, 825.

Leewenhoek, 182, 183, 195, 392,

428, 824, 1153.
Lemur tardigradus, 936.
Lens, 648.

Lepelletier, 511 (note).
Leuret, 372.
Levirostres, 1022.
Ligaments, 30, 84, 155.

alar, 170.

articular, 245.

capsular, 172.

crucial, 172.

fascicular, 172.

lateral, 172.

round, 849.

vocal, 762.

Ligatures on vessels, 443.

Light, 655.

Limbs in general, 241, 843.

Lingual bone, 1018.

Lining, ^58 (note).

LiNN^Tjs, 62, 562.

Lion, 948.

Lips, 607.

Liquid of surfaces, 135.

Liquor aranii, 844.

Liquor Morgagni, 648.

Lister, 116, 200.

Liver, 40, 522, 524, 560.

Lizard, 1032.

Lochia, 835.

Locomotion, 28.

Loculi, 505.

Lobster, 1095.

Lower extremities, 246.

Lungs, 49, 408, 554, 846, 1013.

LUZURIAGA, 387.

Lymph, 546.
Lymph globules, 400.
Lymphatics, 539, 547.
Lymphatic absorption, 45.
Lymphatic glands, 495, 542, 552.
Lymphatic hearts, 1043.

Macaibe, 362 (note).

Macavoy, Miss, 678.

Macleay, 70.

Magendie, 84 (note), 319, 320 (note),
374, 387 (note), 511 (note), 549,
669 (note), 720, 722, 755.

Magnetism, animal, 755.

Malay race, 876.

Male system, 805.

Malleus, 631.

Malpighi, 141, 178, 179, 392, 428,
502, 584, 1153.

Mammalia, 891, 910.

Mammaj, 793, 826.

Manati, 1001.

Mandril, 935.

Manganese in the blood, 407.

Mantle of moUusca, 1077.

Manyplies stomach, 988.

Marcet, 359, 362 (note), 405.

Mariotte, 674.

Marmot, 960.

Marrow, 125, 145.

Marsupial ia, 952,

Marsupium, 1015.

Mascagni, 113, 165, 543.

Mastication, 39, 327.

Mastoid cells, 630.

Materialism, 576, 705.

Mascagni, 378 (note).

Mayo, 87, 615, 638, 711, 737, 755.

Meatus auditorius, 628.

Mechanical functions, 30, 36.

Mechanism of respiration, 470.

Meckel, 116, -378 (note).

Meconium, 851.

Medicine, 58.

Medulla oblongata, 582, 730.

Medullary substance, 14.

Medusa, 1116.

Melancholic temperament, 864.

Membrana granulosa, 790.

nictitans, 930.

papillaris, 841.

tympani, 629.

vascularis Halleri, 106.5.

vitelli, 1019.

Membrane, 33, 127.

Menghini, 398.

Menstruation, 819.

Merry-thought, 1005.

Mesenteric glands, 543.

Mesmerism, 755.

Metaphysics, 4.

Microscopical observation, 116,449.

Miescher, 142 (note).

Mitchell, J. K., 450 (note).

Milk, 318, 520, 828.

Milk teeth, 855.

512

INDEX.

Mind distinct from matter, 576, 577,

705.
MojoN, 378 (note).
Mole, 939.
Mollusca, 68, 1074.
Mongolian race, 873.
Monotremata, 965.
Monro, 143, 242, 394, 585, 588.
MORGAGNI, 611, 648.
Motion, voluntary, 23.
Motor nerves, 719.
Movements, animal, 27.
Mucous follicles, 611.

layer, 837.

membranes, 185, 493.

secretions, 187, 51.

Mucus, 302.

MiiLLER, 340 (note), 436,454 (note),

487 (note), 509, 563, 569, 801.
Multivalves, 1085.
Mundinus, 1140.
MuRATORi, 366 (note).
Mas typhi us, 959.
Muscles, 26.
Muscular action, 201, 202.

power, 26, 93, 219.

structure, 193.

sense, 602.

Muscularity of arteries, 462.
Musical note, 757. •
MuYS, 196.
Myopia, 675.

Nails, 184.

Natural methods of classification, 64.

Natural Philosophy, 1, 2.

Natural history, 72.

Nausea, 621.

Needham, 826.

Negro race, 874.

Neighing, 984.

Nerves, 14, 581, 586.

motor, 25.

sensiferous, 25.

influence on digestion, 352.

influence on temperature, 490.

influence on secretion, 535.

Nervous substance, 14.
Nervous system, 14, 578, 581, 1062,
1091.

, types of, 68.

Nervous temperament, 867.

Neurilema, 587.

Neurolhelic apparatus, 178 (note).

Newport, 1099.

Nictitating membrane, 929.

Nitrogen, 270.

Nitrogen, absorption of, 483.
Nutrition, 37, 38, 46, 562.
Nutritious principle, 317.
Nutritive matter required, 261.
Nymphee, 818, 1100.

Obliquity of muscular fibres, 217.

Occipital angle, 909.

Ocular spectra, 684, 685.

CEsophagus, 715, 1061 .

Oil, 319.

Oily matter in blood, 407.

Oleaginous secretions, 518.

Omphalo-mesenteric vessels, 841.

Operculum, 1083.

Ophidia, 1035.

Opossum, 953.

Optical laws, 655.

Orang Utan, 905, 932, 933.

Orbicular bone, 631.

Orbiculus ciliaris, 647.

Organic aflinities, 86, 92, 103, 536.

molecules, 826.

phenomena, 6.

Organization, 110.
Ornithorhyncus, 966.
Orthoptera, 1101.
Os quadratum, 1008.
Os tincse, 817.
Osseous fabric, 35, 137.
Ossicula auditus, 631.
Ossification, 565.
Osmazome. 407, 526.
Ostrich, 1021.
Ovary, 797.
Ovisac, 801, 802, 803.
Ovists, 823, 825.
Ovulum et ovum, 800.
Ox, 995.
Oxygen in respiration, 481.

Pachydermata, 968.
Package of organs, 173.
Palate, 609.
Paley, 75.
Palpebrae, 653.
Pain, 598.
Pancreas, 40.
Pancreas Asellii, 922.
Pancreatic secretion, 40, 365.
Panizza, 615 (note).
Panniculus carnosus, 930.
Papillae, cutaneous, 178.

of tongue, 610.

Pappenheim, 352 (note).
Parallactic aberration.
Parenchyma, animal, 667.
Parmentier, 385, 428.

INDEX.

513

Parturition, 50, 735.

Pastern bone, 979.

Pathology, 55.

Paunch, 988.

Peccari, 975.

Pecora, 64.

Pecquet, 377, 1151.

Pelvis, 240.

Pencillated structure, 532.

Penis, 808.

Penniform muscle, 315.

Pepsine, 340 (note).

Perception, 13.

Pericardium, 133, 409.

Perichondrium, 147.

Perilymph, 632.

Periosteum, 144, 146.

Peristaltic action, 338.

Peritoneum, 133.

Perspiration, 515, 555.

Petasiolus granulosus, 803, 830.

Petit, circle of, 650.

Phantascope, 681.

Phascolame, 955.

Phenikisticope, 681.

Philip, 96, 352, 464, 741, 742, 744.

Philosophy of mind and matter, 21.

Phlegmatic temperament, 866.

Phosphorus, 268.

Phrenology, 814 (Appendix).

Physical and vital laws, 89.

Physical sciences, 1, 2, 21.

Physiology, general views, 1.

object of, 10.

applications of, 57.

to medicine, 58.

to zoology, 60.

to geology, 71.

to natural theology, 74.

Phy tology, 4.
Pia mater, 133.
Picromel, .367.
Pineal gland, 495, 698.
Pigmentum nigrum, 671.
Pituitary membrane, 618.
Placenta, 833.
Plan of animal creation, 73.
Planch, 436.
Plantigrada. 941.
Plato, 1130.
Pleurae, 133.
Plexus, 586.
Poison-teeth, 1038.

POISEUILLE, 460.

Polygastrica, 1120.
Polypi, 1118.
Pomum Adami, 759.
Pores in cuticle, 183.

Portal system, 427, 523, 524.

PORTKRFIELD, 242.

Porus opticus, 651.

Powers, vital, 98.

Prehension, 29.

Presbyopia, 675.

Pressure, 593.

Prevost, 199, 222.

Prichard, 887.

Priestley, 692, note.

Primitive trace, 831, 1020.

Proboscis of elephant, 968.

Processus mam_millares, 925.

Prochaska, 197, 585.

Promontory of ear, 630.

Proteus anguinus, 1044.

Proust, 557.

Prout, 318, 352 (note), 362, 485,

558 (note).
Proximate animal principles, 272,

277.
Prussic acid, 270.
Psychology, 21.
Psychological relations of sensorium?

748.
Ptolemies, 1132.
Puberty in the male, 812.

female, 812, 819.

Pulmonary circulation, 439, 466.

exhalation, 484.

Pulse, 461.

Puncta lachrymalia, 654.
Punctum saliens, 1020.
PuRKiNJE, 352 (note).
Pylorus, 353.
Pythagoras, 1127.

Quadrumana, 932.

Racoon, 943.

Racornissement, 226.

Radiata, 68.

Raspail, 368, 386 (note).

Rat, 958.

Reason, 732.

Reaumur, 343.

Receptaculum chyli, 377.

Recipient organs, 131.

Recurrence of impressions, 702.

Red globules, 392.

Reed of ruminants, 988.

Rees, 142.

Reflex function, 741.

Reflexion of light, 657.

Refraction of light, 656.

Reil, 584, 588.

Rein-deer, 994.

Relaxation, muscular, 207.

514

INDEX.

Remak, 588 (note).
Renal capsules, 495.
Renewal of materials, 44, 570.
Reparation, 46, 262.
Reparatory functions, 307. •
Reproduction, 50, 783.
Reptiles, 1024.
Resinous secretions, 521.
Respiration, 38, 49, 468, 1060,
Respiratory muscles, 728.

nerves, 723.

Rete Malpighianum, 179.

mirabile, 991.

mirabile Malpighii, 466.

mucosum, 179.

testis, 806.

Retina, 645.
Rhinoceros, 973.
Rhizostoma, 1117.

RiCHERAND, 82.

Rodentia, 956.

RoGET, 88, 222, 349, 668, 681.

Roosting, 1008.

ROUELLE, 407.

RoussEL DE Vauzeme, 183 (note),
555 (note).

RUDBECK, 1151.

RuDOLPHi, 135 (note), 378 (note),

888.
Rugse palati, 609.
Ruminants, 986, 1101.
Rumination, 989.

RuYscH, 113, 178, 503, 584, 1154.
Ruyschian tunic, 645, 928.

Sabatier, 511 (note).

Saccharine principle, 316.

Saccho] actio acid, 519.

Sacculus, 634.

St. Hilaire, Geoffroy, 73, 1050.

Salamander, 1043.

Saline secretions, 527.

Saliva, 39, 332.

Salivary glands, 612.

Sanguification, 41, 382.

Sanguiferous system, 413.

Sanguine temperament, 863.

Sanson, 657 (note).

Sauria, 1031.

Savigny, 72.

Scalag cochlear, 633.

Scaphus, 627.

SCHEELE, 556.

Schneiderian membrane, 618.

Schwann, 340 (note).

Schroder van der Eole, 386 (note).

Sclerotica, 644.

Scrotum, 805.

Scudamore, 386.

Seal, 949.

Seat of the soul, 698.

Sebaceous glands and follicles, 189,

931.
Secretion, 38, 43, 491.
Secretion, theory of, 529.
Secretions, 513.

albuminous, 514.

aqueous, 512.

gelatinous, 516.

fibrinous, 517.

oleaginous, 518.

resinous, 521.

saline, -527.

Seguin, 555.

Semen, 810.

Semicircular canals, 632.

Senac, 390.

Sensation, 13, 21, 95, 578.

laws of, 677.

theories of, 691.

Sefises, external, 16, 592.
Sensibility, organic, 740.
Sensiferous nerves, 25, 719.
Sensorial functions, 13, 574, 923.
Sensorial power, 96.
Sensorium, 578, 695, 697, 699.
Sepia, 1079.
Septum narium, 617.

vetriculorum, 407.

Serosity, 403.

cellular, 120.

of the blood, 390.

Serous capillaries, 433.

layer, 829.

membranes, 133, 493.

Serpents, 1035.
Sleep, 995.
Shoulder-joint, 255.
Sight, 17.

Silurus electricus, 1070.
Simple bodies, 275.
Sinus medianus, 1067.

terminalis, 842.

valsalvae, 410.

venosus, 410.

Sinuses, 425.

nasal, 616.

Siren, 1044.
Skeleton, 30, 137,227.
Skey, 200.
Skin, 176, 843.

excretion by, 555.

Skull, 229.
Sleep, 752.
Sloth, 964,
Smell, 19, 616, 619, 926.

INDEX.

515

Socrates, 1130.

SoMMERING, 651.

foramen of, 651.

Solids and fluids, 111.

Solipeda, 976.

Solvent power of gastric juice, 343.

Somatology, 21.

Somnambulism, 754.

Sound, 623.

Sound of fishes, 1061.

Spallanzani, 343, 454, 819.

Specific gravity of muscles, 208.

Spectra, ocular, 684.

Speech, 24.

Spermatic animalcules, 810.

cord, 797.

Spermatists, theory of, 82.

Spermatozoa, 810.

Spherical aberration, 664, 666.

Sphincters, 212.

Spinal cord, 581,' 842.

Spine, 236, 911.

Spiracles, 1097.

Spirit of animation, 7.

Spirits, animal, 691.

Spleen, 371, 495.

Splint bone, 979.

Sporules, 785.

Spurzheim, 584, 725.

Stahl, 1156.

Standing, 247.

Stapes, 631.

Stark, 319.

Stellated structure, 533.

Steno's duct, 612.

Stevens, 343.

Stigmata, 1097.

Stimuli, 93, 203.

Stomach, 39, 338.

Straight muscles of the eye, 668.

Stuart, 198.

Sublingual gland, 612.

Submaxillary gland, 612.

Sudoriferous ducts, 555 (note).

Sugar, 316.

Sugar of milk, 520.

Sulphur, 270.

Surfaces, liquid of, -515.

Sutures, 233.

Swammerdam, 198, 1154.

Swimming bladder, 1061.

Symmetrical system of nerves, 722.

Sympathetic nerves, 747.

Sympathy, 735.

Syngenesis, 823, 826.

Synovia, 170.

Systemic circulation, 439,

Systole of the heart, 441.

Tabula vitrea, 231.
Tannin, test of gelatin, 282.
Tapetum, 928.
Tapir, 972.
Tardigrada, 963.
Tarsus, 653.
Taste, 20, 604, 613.
Teeth, 328, 568, 902, 916.
Temperaments, .52, 859.
Temperature, animal, 489.

sensation of, .595.

influence on digestion, 348, 386.

requisite for sensation, 688.

Tendons, 34, 35, 156, 163, 213.

Tendinous sheaths, 160.

Testes, 80.5, 849.

Thackrah. 386 (note), 402 (note).

Thaumatrope, 681.

Thenard, 367, 407.

Theology, natural, 74.

Thilenius, 142 (note).

Thirst, 325, 596.

Thomson, A. 794.

Thomson, 287, .558 (note).

Thoracic duct, 545.

Thorax, bones of, 23-5.

Thumb, 258.

Thymus, 495, 851.

Thyroid gland, 495, 761.

Tiedemann, 347, 368, 372 (note), 378,

Tingling, 597.

Todd, 340 (note).

Touch, 16, .593.

Tone, 175.

Tongue, 329, 606, 610, 1018.

Tonicity, 175, 224.

Torpedo, 1070.

Tortoise, 1027.

Tracheae, 766, 1097,

Tragus, 626.

Transfusion of blood, 447.

Travers, 669.

Tremulous action of muscles, 22.5.

Treviranus, 1.

Tuberculum Loweri, 412.

Tunica albuginea, 652, 797.

conjunctiva, 653.

granulosa, 804.

' Ruyschiana, 928.

vaginalis, 797.

Turbinated bones, 617.
Turner, 387.
Turtle, 1027.
Tympanic bone, 924.
Tympanum, 629, 630.

Umbilical cord, 851.
Upper extremities, 254.

516

INDEX.

Urachus, 848.
Urea, 407, 525, 559.
Urethra, 808.
Urine, 556, 557.
Uroline, 407.
Uterus, 816, 817.
Utero-gestation, 785, 829.
Utricle, 634, 1067.
Utricali, 505.
Uvea, 646.
Uvula, 609.

Vagina, 817.

Valentin, 588 (note), 809 (note).

Vallisneri, 817.

Valves, 438, 444.

ofheart, 410, 411.

of lacteals, 378.

Valvulas mitrales, 410.

Valvulss semilunares, 411.

Vampire bat, 938.

Van Helmont, 101.

Vanhorne, 1154.

Varieties in human race, 53, 869.

Vas deferens, 797.

Vasa inferentia, 543.

Vascular area, 841, 850.

Vascular layer, 837.

Vascularity, 113, 435.

Vauquelin, 399, 520.

Vegetable food, 314.

Velpeau, 833 (note).

Velum pendulum palati, 609.

Veins, 42, 425.

Velocity of sound, 624.

Vena portae, 427.

Vena terminalis, 1020.

Venous absorption, 45 (note), 549.

Venous system, 425.

Ventricles, 409.

of the br-ain, 583.

of the heart, 455.

Ventriculus succenturiatus, 1009.
Vernix caseosa, 843.
Vertebra, 236.
Vertebrata, 68.
Verumontanum, 807.
VeS ALIUS, 1143.
Vesicula alba, 844.

intestinalis, 847.

seminalis, 811.

Vessels, 131.
Vestibule, 632.

Vibrations, 692.
VicQ D'AzYR, 82.
Villi, 187, 532.
Vis a tergo, 465.
Vis insita of Haller, 93.
Vis medicatrix, 101.
Vision, 17, 640, 660.
Vital powers, 89, 92, 103.
Vital principle, 86, 100, 106.
Vitality of the blood, 389.
Vitelline sac, 844.
Vitreous humor, 648.
Vitrine auditive, 632.
Vocal ligaments, 762.
organs, 900.

VOGEL, 386.

VoisiN, 364 (note).

Voice, 24, 756.

Volition, 577, 709. '

Voluntary motion, 13, 23, 25, 378, 709.

Vomer, 617.

Vowel sounds, 770.

Walking, 251.
Walrus, 951.
Weasel, 945.
Wedembyer, 432 (note).
Weber, 594.
Weinholt, 407.
Wells, 399.
Wendt, 183 (note).
Wenzell, 585.
Whale, 1002.
Wharton's duct, 612.
Wheatstone, 615, 757.
Whytt, 1158.
Williams, 488 (note).
Willis, 764.
Withers, 976.
Wolff, 847.
Wolffian bodies, 847.

WOLLASTON, 225.

Woodpecker, 1023.
Worms, 1092, 1112.
Wounds of arteries, 447.
Wrist, 256.

WURZER, 407.

Young, 395, 396, 397, 436, 511, 639,
668, 755.

Zoology, 3, 5, 60.
Zoophytes, 1105.

THE END.

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