REESE*LIBRARY*

OF THE UNIVERSITY
OF CALIFORNIA

HUMAN PHYSIOLOGY,

FOR THE USE OF

ELEMENTARY SCHOOLS.

BY CHARLES A. LEE M. D.5

LATE PROFESSOR OF MATERIA MEDICA AND MEDICAL JURISPRUDENCE, IN
THE UNIVERSITY OF THE CITY OF NEW YORK.

" The proper study of Mankind is Man.

ITH

TJHIV

NEW YORK:
TURNER, HUGHES, & HAYDEN,

NO. 10 JOHN ST.
RALEIGH, N. C.-TURNER & HUGHES.

1843.

iOLOGY
J3RARY

G

Entered, according to Act of Congress, in the year 1838,

BY J. ORVILLE TAYLOR,
In the Clerk's office of the District Court of the Southern

District of New York.

/

STEREOTYPED BY SMITH & WRIGHT, 21G WILLIAM ST. N. Y.

Piercy & Reed, Printers, 9 Spruce St. N. York.

TO

CHARLES ANTHON, L. L. D.

JAY PROFESSOR OF LANGUAGES

IN COLUMBIA COLLEGE,

THIS HUMBLE ESSAY,

IS BY PERMISSION,

GRATEFULLY INSCRIBED,

IN TESTIMONY OF PROFOUND RESPECT.

PREFACE TO THE SECOND EDITION.

In presenting to the public the present stereotype edi-
tion of this work, it is proper to state, that no labor or
expense has been spared to render it still more worthy
of the kind approbation with which it has been received.
A large proportion of it has been entirely re-written,
many corrections have been made, and numerous and
highly valuable illustrations introduced ; these improve-
ments, together with the questions at the end of each
chapter, cannot but render the work better adapted to
the objects for which it was written.

The author flatters himself that this treatise will be
found to contain the substance of what is yet known on
the subject of Human Physiology, and most that is
valuable, which is scattered through many learned and
ponderous volumes. In preparing it, more than fifty
different works have been consulted, from all of which
the author has freely taken whatever he found adapted
to his purpose. Originality has not been aimed at, as it
was precluded by the very nature of the subject ; in-
deed it would have been unsuited to the object in view.

Vlll PREFACE.

From the rapid sale of the first edition, and the nu-
merous orders for the work from all parts of the United
States, it may safely be concluded, that Physiology is
henceforth to be one of the common branches of know-
ledge taught in our schools, academies, and other semi-
naries of learning. Indeed it is remarkable, that
sciences, so closely connected with the health and hap-
piness of our race, as those which teach us the structure
and functions of the human body, should so long have
been confined to those who intend to pursue the
practice of medicine and surgery as a profession, espe-
cially when the practical application of such knowledge
is daily and hourly of the utmost importance to every
individual, connected as it is, with the preservation of
health and of life. That such studies are not above the
comprehension of children I can testify, not only from
my own observation, but from the experience of numer-
ous teachers, such as those whose names are appended
to the testimonials, on the first pages of this work. If
this is not sufficient, I have to commend to the attention
of the reader, the following extract from a lecture of
Mr. George Combe, the distinguished phrenologist of
Edinburgh, which he was so kind as to communicate to
me by letter :

" I take the liberty to urge very earnestly on your at-
tention, not only the advantage, but the necessity of in-
troducing instruction in anatomy and physiology into
popular education. The great laws of health cannot be
understood, nor can their importance be appreciated

PREFACE. iX

without this knowledge. I do not mean that you should
teach your children all the minute details of these
sciences, which would be necessary if you intended
them for the practice of medicine and surgery : all I
desire is, that the structure of the leading organs of the
body should be explained so far as to render the func-
tions of them intelligible, and that on this knowledge
should be founded a clear and practical elucidation of
the laws of health. I can certify, from observation,
that this instruction may be communicated to children
of ten years of age, and upwards, with great success.
The structure addresses their observing faculties, and
an explanation of the functions is as interesting to them
as a romantic story."

In treating of physiological subjects, I have unavoid-
ably employed some technical terms, but only in cases
where there was an evident advantage attending
their use; but in all such cases the exact meaning
of the term has been assigned it. This explanation
saves the necessity of a glossary, which was appended
to the first edition, and it is, therefore, omitted in the
present.

It will be perceived that the present edition contains
more anatomy than the former. This has arisen from
the full conviction, that in order to understand the
functions of an organ, its structure must first be learn-
ed To aid in the accomplishment of this object, nu-
meious well-executed wood cuts have been introduced,
alike creditable to the artist and useful to the learner.

Vlll PREFACE.

From the rapid sale of the first edition, and the nu-
merous orders for the work from all parts of the United
States, it may safely be concluded, that Physiology is
henceforth to be one of the common branches of know-
ledge taught in our schools, academies, and other semi-
naries of learning. Indeed it is remarkable, that
sciences, so closely connected with the health and hap-
piness of our race, as those which teach us the structure
and functions of the human body, should so long have
been confined to those who intend to pursue the
practice of medicine and surgery as a profession, espe-
cially when the practical application of such knowledge
is daily and hourly of the utmost importance to every
individual, connected as it is, with the preservation of
health and of life. That such studies are not above the
comprehension of children I can testify, not only from
my own observation, but from the experience of numer-
ous teachers, such as those whose names are appended
to the testimonials, on the first pages of this work. If
this is not sufficient, I have to commend to the attention
of the reader, the following extract from a lecture of
Mr. George Combe, the distinguished phrenologist of
Edinburgh, which he was so kind as to communicate to
me by letter :

" I take the liberty to urge very earnestly on your at-
tention, not only the advantage, but the necessity of in-
troducing instruction in anatomy and physiology into
popular education. The great laws of health cannot be
understood, nor can their importance be appreciated

PREFACE. il

without this knowledge. I do not mean that you should
teach your children all the minute details of these
sciences, which would be necessary if you intended
them for the practice of medicine and surgery : all I
desire is, that the structure of the leading organs of the
body should be explained so far as to render the func-
tions of them intelligible, and that on this knowledge
should be founded a clear and practical elucidation of
the laws of health. I can certify, from observation,
that this instruction may be communicated to children
of ten years of age, and upwards, with great success.
The structure addresses their observing faculties, and
an explanation of the functions is as interesting to them
as a romantic story."

In treating of physiological subjects, I have unavoid-
ably employed some technical terms, but only in cases
where there was an evident advantage attending
their use; but in all such cases the exact meaning
of the term has been assigned it. This explanation
saves the necessity of a glossary, which was appended
to the first edition, and it is, therefore, omitted in the
present.

It will be perceived that the present edition contains
more anatomy than the former. This has arisen from
the full conviction, that in order to understand the
functions of an organ, its structure must first be learn-
ed To aid in the accomplishment of this object, nu- "
meious well-executed wood cuts have been introduced,
alike creditable to the artist and useful to the learner.

X PREFACE.

The work is, therefore, presented to the public in its
present shape, with the hope and belief, that it will
subserve the cause of human knowledge and happi-
ness.

NEW YORK, April, 1839.

CONTENTS.

CHAP. I. — Organic and Inorganic Bodies . . . . 13

CHAP. II. — Division of the Animal Kingdom ... 20

CHAP. III.— Structure of the Human Body .... 24

CHAP. IV. — Structure of the Human Body continued . . 39

CHAP. V.— Chemistry of the Human Body ... 56

CHAP. VI.— The Human Skeleton 63

CHAP. VII. — Properties of Animal Bodies . 95
CHAP. VIII.— Relation of Animal Bodies to Heat, Light, and

Electricity 105

CHAP. IX.— The Nervous System . . . ' . . 110

CHAP. X.— Intellectual and Moral Faculties ... 123

CHAP. XI. — The Spinal Marrow and its Functions . 135

CHAP. XII. — The Nerves and their Functions . . . 144

CHAP. XIII.— The five Senses— Sense of Touch . . 156

CHAP. XIV.— Sense of Taste 167

CHAP. XV.— Sense of Smell 177

CHAP. XVI.— Sense of Sight 190

CHAP. XVII.— Sense of Hearing 225

CHAP. XVIII.— Respiration . 237

CHAP. XIX.— The Circulation of the Blood . . . .256

CHAP. XX. — Nutritive Functions — Digestion . . . 274

CHAP. XXI.— Secretion 286

CHAP. XXII.— Absorption 292

CHAP. XXIII.— Nutrition 298

CHAP. XXIV.— Animal Heat ...... 304

CHAP. XXV.— The Voice 312

CHAP. XXVI. — Locomotion, and its Organs, . . . 319

CHAP. XXVII.— The Teeth* 326

CHAP. XXXIII.— Sleep and Death 331

* Written by Solomon Brown, A. M. Scientific and Practical Dentist of this city.

HUMAN PHYSIOLOGY.

CHAPTER I.

DEFINITION ; ORGANIC AND INORGANIC BODIES.

1. PHYSIOLOGY is " the science of life," or that branch
of knowledge which explains the uses of the various. organs
of living beings. Vegetable physiology treats of the func-
tions of plants ; and Comparative physiology, of those of the
inferior orders of animals ; while Human physiology treats
exclusively of man.

2. The kingdom of nature embraces three great classes,
ANIMALS, VEGETABLES, and MINERALS. According to a more
scientific arrangement, it is composed of organic and inor-
ganic bodies. By' organic bodies, we mean those which
possess organs or instruments for the performance of certain
functions ; and by inorganic, those which do not. It is by
a knowledge of these works of God, that we derive our ideas
of his power, wisdom, and goodness.

3. Organized bodies are divided into two great classes,
animals and vegetables ; which differ from inorganic matter
in several respects, the most important of which are the
following : —

4. Organized bodies have a certain determinate form,
peculiar to the species to which they belong. Every species
of plant or animal may be known by its external shape ; as

2

14 PHYSIOLOGY.

a horse, a cow, a tree, or a rose. They differ so much from
all other kinds, that we are seldom in danger of mistaking
them. This will not apply to inorganic bodies, except,
perhaps, to a few minerals which crystallize in a certain
shape.

5. In organized bodies, we find the parts of which they
are composed, distinguished by round or oval forms ; as the
body and leaves of trees ; the petals of flowers ; the bodies
and limbs of animals. We scarcely ever see straight lines,
or sharp angles among them, as in mineral substances.

Every species of animal or vegetable has its own proper
size, from which it varies but little. But minerals may be
large or small ; the substance called granite, for example,
may make a pebble or a mountain.

6. Inorganic bodies contain either a single element, as
carbon, sulphur, &c., or several of the elementary or simple
substances, which are fifty -two in number, as lime, silex, and
magnesia ; while in organized bodies, we find at least three
of these elements, as carbon, hydrogen, and oxygen in veget-
ables ; and the same, with the addition of azote or nitrogen
in animals. In organic bodies, there have been discovered
in all eighteen simple substances, though they generally con-
tain but three or four.

7. But these two classes of substances, not only differ as
to the number of the elements which enter into their com-
position, they also differ, as to the mode in which these
elements are combined. Thus in minerals, two element-
ary substances unite and form a compound, and this again,
combines either with another simple substance, or with a
compound composed of two other simple substances. Thus,
for example, carbonate of ammonia is composed of car-
bon, oxygen, hydrogen, and nitrogen, but combined as
follows : —

The carbon and oxygen unite to form carbonic acid ; the
hydrogen and nitrogen, to form ammonia ; these two com-
pounds thus uniting, form carbonate of ammonia.

ORGANIC AND INORGANIC BODIES. 15

In animals, we find the same simple elements uniting, each
with all the others, forming the peculiar principles of organic
bodies, such as fibrin, gelatine, &c.

8. Organized bodies contain small particles of matter of
a round or oval shape, both among their solid and fluid parts.
These are supposed, according to their different arrangement,
to make up all the elementary forms of organized bodies ; as
when arranged in lines, they form nerves, tendons, and
muscles ; in sheets, the various membranes and coats of ves-
sels ; and in masses, the solid substance of the glands, as the
liver, kidneys, and pancreas.

9. There are but few changes in inorganic bodies. The
elements of which they are composed remain at rest. Rocks
and mountains are the same now, as they were five thousand
years ago. But in organized bodies, compounds are con-
tinually forming to be again separated ; animals feed on
vegetables, and vegetables on animals ;

" See dying vegetables life sustain;
See life dissolving, vegetate again ;
All forms that perish, other forms supply-—
By turns we catch the vital breath and die."

10. In organized bodies the parts are mutually dependen
on each other for support. If we cut off the limb of a tree,
it dies, because it can receive no sap ; if we amputate a
finger, it mortifies, because the circulation of the blood has
ceased ; but if we break off a piece of marble, it will remain
unchanged as long as the original mass.

11. Inorganic substances exist either in solid, liquid, or
gaseous forms. They are wholly solid, liquid, or gaseous.
But organic matter always presents a combination of solid
and fluid parts. We find fluids circulating in regular ves-
sels, and the solids and fluids mutually dependent on each
other for support. In vegetables, we discover various parts,

16 PHYSIOLOGY.

such as wood, bark, leaves, roots, and flowers ; and in ani-
mals, muscles, nerves, tendons, vessels — all of which are
organs, or instruments for the accomplishment of certain
purposes. Inorganic bodies are formed of homogeneous parts,
or parts perfectly similar.

12. Organic bodies are composed of two kinds of elements,
chemical, such as oxygen, carbon, and hydrogen, which exist
in minerals ; and organic, or proximate, such as albumen, gel-
atine, fibrin, &c., such as are never found in inorganic mat-
ter. It is because these organic substances are produced by
the peculiar forces of organic life, and not by chemical laws,
that we cannot decompose and then re-form them, out of
the same elements, as we can minerals. For example, we
can dissolve alum, salt, or copperas, and then by evapora-
tion, crystalize them in the same shape again.

13. The general properties of organic or inorganic bodies
differ in many particulars. In the first place there is a
constant warfare going on, between the chemical and phys-
ical laws, which govern inorganic matter, and the vital laws
which maintain animal life. This conflict commences at
the first period of our existence, and is kept up to the moment
of our dissolution. Life is enabled, for wise purposes, to
wrest portions of matter from the domain of the laws of
matter, for a certain indefinite period ; for a while, the
vital powers maintain a successful contest, but at last they
have to yield, and death gives over the body to the action
of the chemical forces.

14. This power of resisting the mechanical and chemical
laws of matter, is shown by the faculty which animal bodies
possess of maintaining the same degree of temperature, amid
the great changes from heat to cold to which they are exposed ;
in the power of changing to chyle and blood, the various
forms of food on which they subsist ; and also in their power
of forming from these the various tissues and organs of which
they are composed, and all in opposition to the general laws
of matter.

ORGANIC AND INORGANIC BODIES. 17

15. The growth of organized bodies proceeds from within,
that of inorganic matter from without. If minerals increase
in size, it is by attracting matter to their external surface,
while animals and « vegetables grow by a process, called
nutrition ; that is, laying hold of nutritious substances and
converting them to their own nature, by means of internal
organs.

16. Organized bodies possess the power of being affected
with disease and recovering from it. They also have a
determinate duration, beyond which they do not often live.
This period varies for each species of animal and vegetable.
Some insects live but a single day ; most plants live but a
single year ; but some trees, such as the oak and cedar, are
supposed to live more than two thousand years. The average
duration of human life in this country is not over thirty years.

17. But the great distinction between a living being and
an inorganic body is, that the former carries on a number of
processes, not performed by the latter. A plant, for example,
absorbs food, converts it into its own proper substance,
arranges it into bark, wood, leaves, and other organized
structures, grows, arrives at maturity, generates and main-
tains a certain degree of heat, decays, and finally perishes.
No such phenomena are exhibited by a stone, or other inor-
ganic bodies. These processes, therefore, are called vital, be-
cause they are peculiar to a state of life, and afford characters
by which a living being is distinguished from all others.

18. Organized beings are divided into two classes, animals
and vegetables, differing from each other in several well-
known features.

19. Sensation and voluntary motion are possessed by ani-
mals, but not by vegetables. Had animals no sensibility or
feeling, they could not know their wants ; and if they knew
them but had not the power of motion, they would perish for
want of food ; hence the necessity of these two faculties
being joined together.

20. An animal, like a plant, receives food, transforms it into

2*

18 PHYSIOLOGY.

its own proper substance, and builds it up into certain struc-
tures ; it also generates and maintains a certain degree of
temperature, and after having arrived at maturity decays
and dies ; but in addition to these vital processes which are
similar in both, the animal possesses the faculty of feeling
and moving spontaneously, or according to the dictates of
its will, a property peculiar to itself.

21. Vegetables are nourished by the substances immedi-
ately around them, such as air, water, and the saline proper-
ties of the soil. They draw their support from without, by
absorption at their surface, or by means of roots. But
animals draw their nutriment from a great variety of sources,
and they are furnished with an internal cavity to receive
and prepare it for the purposes of nourishment.

22. Vegetable matter is composed chiefly of three elements,
viz. carbon, hydrogen, and oxygen ; besides these, animal
matter contains azote, which gives the peculiar smell that we
perceive on burning flesh, hair, bones, or feathers. Eighteen
simple substances, however, have been found in vegetables,
in very small quantities ; such as lime, sulphur, iodine, silex,
potash, soda, &c.

23. Animals and vegetables both consist of solid and fluid
parts ; the fluids, however, in animals, exist in much the
largest proportion. This is the reason why decomposition
occurs more rapidly in animals than in vegetables. Veget-
ables, abounding in fluids, decay sooner than those of a more
solid or fibrous texture.

24. Though the differences between animals and veget-
ables, are in general sufficiently obvious and striking, yet
in some few instances, their distinguishing characteristics
are not so evident. This is apparent from the fact, that
some animals have been mistaken for vegetables, and some
vegetables for animals. Some animals we find to be as
firmly attached to the soil, as most vegetables are, as is the
case in many of the zoophytes, or lowest order of animals,
as the sponge, coral, &c. ; while on the other hand, some

ORGANIC AND INORGANIC BODIES. 19

vegetables float in the water, as many kinds of sea-weed,
and are never attached to the soil.

Questions. — What is physiology ? What does vegetable physiology
treat of? What human ? What classes does the kingdom of nature
embrace ? What other division ? What is meant by organic bodies ?
What by inorganic ? How are organic bodies divided ? How do or-
ganic and inorganic bodies differ from each other ? How do they
differ as to form ? — as to size ? — as to their number of elements ? — as to
their mode of combination ? — as to the shape of their particles ? — as to
the changes they undergo ?— as to the mutual dependence of parts ? — as
to the kinds of elements ? — as to their general properties ? How as to
their mode of growth ? of disease ? What is the grand distinction
between the two classes of bodies ? How are organized beings divid-
ed? How do animals and vegetables differ? How are vegetables
nourished? What is vegetable matter composed of ? Do animals or
vegetables possess the greatest amount of fluids ? What animals have
been mistaken for vegetables ?

CHAPTER II.

»

DIVISION OF THE ANIMAL KINGDOM.

1. CUVIEE has divided animals into four great groups.
1. The vertebral. 2. The molluscous. 3. The articulated.
4. The radiated. The three last are destitute of vertebrae,
or a connected series of bones to form a spinal column.
They are, therefore, called invertebrated, while the term
vertebrated is applied to the former. The vertebral are
again divided into four classes, viz. 1. Mammalia. 2. Birds.
3. Reptiles. 4. Fishes. These are also distinguished by
the terms warm, and cold-blooded ; the warm-blooded, in-
cluding the two former, which possess a temperature con-
siderably above that in which they live ; while the two
latter, or the cold-blooded animals, are but little warmer
than that of the medium by which they are surrounded.
The mammalia are divided into nine orders ; Birds into
six ; while Reptiles include Tortoises, Lizards, Serpents,
and Frogs. Fishes are divided into the Cartilaginous and
Bony.

2. Molluscous animals, as the name signifies, are. those
which have no bones corresponding to those of the higher
orders of animals. They include all those animals with soft
bodies, which dwell in calcareous habitations, constructed by
themselves ; many of them are accordingly called shell-fish,
such as the oyster, muscle, clam, &c. This division also
embraces the snail, slug, and the nautilus. The articulated
class includes such animals as are furnished with joints,
with a hard external crust, or skeleton, to which are attach-
ed the organs of motion. It embraces the annelides, or red-
blooded worms, the Crustacea, (the lobster and crab,) Spiders,
and Insects. The Radiated class includes the Zoophytes, or
Plant animals, so called from their resemblance to the veget-

PHYSIOLOGY. 21

able kingdom. Most of these are of a soft texture, as the
Polypus, so well known from its being capable of existing
when turned inside out, and of reproducing any part of Its
body when destroyed by accident. To this class belongs
the Sponge, and the numerous families of the Coral.

3. The mammalia are placed at the head of the animal
kingdom ; not only because it is the class to which man
himself belongs, but because it also enjoys the most numerous
faculties, the most delicate sensations, the most varied powers
of motion, and the highest degree of intelligence.

4. The peculiar characters of these different classes must
be learned from works which treat especially of Comparative
Anatomy. It will be proper, however, in this place, to
point out some of the peculiarities which distinguish man.

5. In structure and external shape, man bears considerable
resemblance to some varieties of the ape tribe, particularly
the ourang outang. But we find his position to be upright ;
his foot is large, and the leg placed vertically upon it ; while
the toes are short and but slightly flexible, and the great
toe is horizontal with the others, so that his feet is well
adapted to support the body, but cannot be used for seizing
or climbing. Apes have thumbs both upon their hands as
well as feet, so that they can seize with both equally well.
The head of man is also very large and heavy, owing to the
magnitude of the brain, and the smallness of the cavities of
the bones ; yet the means of supporting it, except in a per-
pendicular position are very small, as the ligament of the
neck, which in quadrupeds is very thick, in him is almost
wanting.

6. Besides this, the spinal column is so constructed, that
its flexure forwards is not prevented, so that should he at-
tempt to walk on all-fours, his mouth and eyes would be
directed towards the earth, and he could not see before him,
while in an erect attitude he preserves the use of his hands,
and at the same time his organs of sense are most favorably
situated for observation.

22 PHYSIOLOGY.

7. Though man surpasses all other animals in dexterity, yet
there are many that exceed him in strength, swiftness, and
the acuteness of many of the senses. The eagle excells him
in acuteness of vision, the grey hound in delicacy of smell,
and a vast number of animals in strength, yet reason makes
up for all other deficiences. Though physically defenceless,
yet the whole brute creation is subjected to his control.

8. It was formerly supposed that man, because gifted with
the highest mental endowments possessed the largest of all
brains. But as elephants and whales surpass him in this
respect, and the sagacious monkey and dog have smaller
brains ,than the comparatively stupid ass, hog, and ox, the
opinion was • relinquished, and man was said only to have
the largest brain in proportion to the size of his body. But
more extensive observation proved that canary and other
birds, and some varieties of the monkey tribe, have larger
brains than man in proportion to the body, and several
mammalia to equal him in this particular ; and as rats and
mice too, surpass the dog,1 horse, and elephant in the com-
parative bulk of their brains ; this opinion gave way to the
one now generally adopted by physiologists, viz. that man
possesses the largest brain in comparison with the nerves
arising from it.

9. In consequence of the great size of his brain, man has
a larger facial angle, which is the space included by lines
drawn from the centre of the ear to the root of the nose, and
from thence to the forehead. In the best formed human
heads, this angle is equal to 80 or 90 degrees. In man also,
the chin is more prominent, and the lower front teeth more
perpendicular ; his teeth also are of the same length, which
is not the case in the inferior animals. Man only can adapt
himself to the great varieties of climate, and of food, which
exist on the surface of the earth.

10. Lastly, man is possessed of faculties that enable him
to trace effects to their causes, to distinguish between virtue
and vice, to reflect upon events that have passed, to anti-

STRUCTURE OF THE HUMAIty^DY. 23

cipate the issues of the future ; and, abo

mind to the Supreme Intelligence, the

whom all nature owes her existence, and to

more or less clearness of conviction, he feels conscious of

responsibility.

Questions. — How is the animal kingdom divided ? .What is meant
by vertebrated, and what by invertebrate^ animals ? How are the
vertebral divided ? What is understood by a warm-blooded animal ?
What by a cold-blooded ? Into how many orders are the mammalia
divided ? Birds ? Reptiles ? What are molluscous animals ? What
does the articulated class include ? What the radiated ? What class
is placed at the head of the animal kingdom? — and why ? What
species of animals does man most resemble ? How does he differ from
the ape tribe ? Is man excelled in any respect by the inferior animals ?
Mention some of the peculiarities of man.

CHAPTER III.

STRUCTURE OF THE HUMAN BODY.

1. THE human body is composed of solids and fluids.
These terms, however, are merely relative. There is no
fluid which does not contain some solid matter in solution ;
and no solid however dense, which does not contain some
fluid. The nature of both fluids and solids is essentially the
same, for we see one readily passing into the other ; indeed
no fluid long remains a fluid, and no solid a solid ; but the
fluid is constantly passing into the solid, and the solid into
the fluid.

. 2. The relative proportion of the fluids in the human
body much exceeds that of the solids, the excess being about
8 to 1. But the excess varies according to the age. The
younger the age, the greater the preponderance of the fluids.
As age increases, the fluids gradually diminish, till in old
age, they become so much lessened, that the body assumes
a dry, wrinkled, shriveled and stiff appearance. In this
manner we explain the softness and roundness of the body
in infancy and youth, and its hard, unequal and angular
surface in advanced life.

3. The fluids, then, are very important, as they furnish
not only the material out of which every part of the body is
formed, but they also furnish the medium by which the
noxious and useless matter is carried out of the system.
Every part of the body is a laboratory in which complicated
and translorrhing changes are constantly going on ; the
fluids are the materials on which these changes are wrought,
and the vital forces are the agents by which they are effect-
ed. The fluids either contribute to form the blood, or they

STRUCTURE OP THE HUMAN BODY. 25

Constitute the blood, or having performed some special office,
is moistening the various surfaces, are returned to the blood ;
icnce according to their nature, they are called aqueous,
ilbuminous, mucous, serous, &c.

4. The solids are composed of the same chemical prin-
;iples as the fluids, and by analysis are reduced to the same
iltimate elements. In the formation of solids, the particles
if matter are supposed to be arranged in one of two modes,
riz., either in the form of minute threads or fibres, or of thin
dates or laminae ; hence every solid of the body is said to
v fibrous, or laminated. These fibres, or laminae are vari-
ously interwoven, and interlaced, so as to form a net-work ;
tnd the spaces included between them are called areolae, or
ells. According to some microscopical observers, the ulti-
mate animal solid is a minute sphere or globule of matter,
lot exceeding an eighth thousandth part of an inch in diam-
iter,

5. The fibrous or laminated matter is often so arranged
s to form a structure, possessing distinct and peculiar
Toperties ; and each of these modifications is considered a
eparate form of organized matter, and is called a primary
Issue. These tissues have been variously classified by dif-
srent anatomists and physiologists, some making them to
onsist of five, viz., the membranous, the cartilaginous, the
sseous, the muscular, and the nervous; while others make
ut three, the cellular, the muscular, and the nervous. An-
ther arrangement is into filaments, fibres, tissues, organs,
pparatuses, and systems.

6. A filament is made up of a series of minute or primi-
ive molecules, arranged in a row. A fibre is composed of
everal of these filaments united together, as the muscular
nd nervous fibres. A tissue is supposed to be composed of
bres disposed in planes, forming in this manner an expan-
ion, or when crossing each other, forming spongy solids,
rith cells interspersed throughout. In this" way are the
ellular, serous, and mucous membranes formed. When

3

26 PHYSIOLOGY.

these tissues are so arranged as to form a piece of animal
mechanism, designed for the performance of a certain office,
they form what is called an organ, as the lungs, brain, liver,
&c. The action of this organ is called its function. The
liver, for example, is an organ ; the conversion of the blood
which passes through it into bile, is its function. When
several organs are associated together for the accomplish-
ment of a common object, such an assemblage is called an
apparatus. The apparatus of digestion consists of the mouth,
teeth, esophagus, stomach, intestinal canal, liver, pancreas,
lacteals, &c., as all these concur in the process of digestion.
By system, is understood an assemblage of organs, possessing
a similar structure, as the nervous system, the muscular
system, &c.

7. Membrane may be considered as the first or primary
tissue. It is the simplest form of organized substance, and
is extensively employed in the composition of the body. In-
deed, it is the principal material used in forming covering,
containing, protecting, and fixing every other component
part of it. It is this which contains in its cells the earthy
matter which goes to form the bones ; the canals in which
are deposited the substance which composes the muscular
and nervous tissues ; which forms a covering for the whole
body ; which lines all its internal surfaces ; surrounds all
its internal organs ; which makes up the solid portion of
every part of the system; forming the tubes and vessels,
such as the arteries and veins ; it connects all parts of the
body together, and fixes them in their several situations ; in
short, it is the substratum, or mould, in which all the other
particles are deposited, thus giving form and outline to the
whole body, so that if every other kind of animal matter
were removed, this tissue alone would preserve the exact
figure and present a perfect skeleton of the whole, and of every
one of its parts.

8. There are several kinds of membrane ; the simplest form
of which, and that from which all the others arc supposed to

STRUCTURE OF THE HUMAN BODY. 27

be produced, is termed the cellular. It is this which I have
already alluded to as entering into the compositions of every
organ, and forming the basis of the solid structure of the
body. Into its cells all other kinds of animal matter are de-
posited as phosphate of lime and gelatine, which form the bones.
It forms sheaths for the muscles and nerves ; composes a great-
er part of the ligaments, tendons, and cartilages, and even the
hair and nails, thus constituting not only the basis of all the
solids, but serving as a bond of union by which the organs
are connected together. By its softness and elasticity, and
the oily fluid by which its cells are filled, it also promotes
the mobility of the parts on one another. It possesses the
property of contractility, and is composed chiefly of gelatine.
9. One remarkable circumstance connected with this tis-
sue is, that as it exists throughout the body, it forms a con-
nected whole, or an immense net-work, every where accessi-
ble to air. This is shown by forcing air into its cells, in
any part of the body ; which is found gradually to penetrate
and pervade every part till the whole body is inflated.
Butchers often avail themselves of a knowledge of this fact,
by blowing their meat, or in other words, inflating animals
by making a puncture in some part where the cellular tissue
is loose, and from this one aperture forcing the air to the
most distant parts of the body, in order to give the meat a
fat appearance. If we raise up a portion of cellular mem-
brane, in the form of a thin slice, it appears as a semi-trans-
parent and colourless substance, composed of minute threads
which are seen to cross each other in every possible direction,
leaving spaces between them, and thus forming a mesh,
similar to the spider's web. As to the precise form of these
cells or cavities we have no accurate knowledge. They are
generally supposed to be narrow spans with acute angles, the
sides of which are flattened, and when not forcibly expanded,
we may suppose to be in contact. Some physiologists in-
deed deny that any cavities at all exist, but the weight of
evidence is altogether in favour of their existence.

28 PHYSIOLOGY,

A single film of the cellular tissue lifted up, and slightly distended.

10. In health, the spaces between these lines are filled with
a thin exhalation of a watery nature, which serves to keep
the tissue always soft and moist. This is composed of the
thinner part of the blood, which is poured out by a process
called secretion, but is speedily taken up again by absorption.
These two operations exactly balance each other in health,
but when from any cause the equilibrium is disturbed, the
fluid accumulates, constituting the disease called dropsy.
This is often relieved by the operation of tapping, or draw-
ing off the water. Cellular membrane is dense or loose,
coarse or fine, according to its situation and office. Where
it is subject to pressure, as in the palm of the hand and sole
of the foot, it is dense and firm ; around the internal organs
it is more loose and delicate. Although cellular tissue en-
ters into the composition of all the organs, it never loses its
own character, nor participates in the functions of the organ,
of which it forms a part. Though present in the nerves it
does not share in their sensibility, and though it accompa-
nies every muscle and every muscular fibre, it nowhere par-
takes of the irritability which belongs to these organs. The
microscope shows that the minute particles of this tissue are
of a globular figure, arranged like strings of pearls, as repre-
sented in the following cut.

STRUCTURE OF THE HUMAN BODY.

29

A portion of cellular tissue, very highly magnified, showing tho
strings of globules of which its ultimate fibres are supposed to consist.

11. The principal varieties of membrane, which are formed
by the cellular tissue, are thefadipose, the serous, the mucous,
the dermoid, the fibrous, the cartilaginous, and the osseous.
The adipose is that tissue which contains the fat which is so
disposed as to form distinct bags in which the fat is con-
tained. Now it should be recollected, that while the cells of
the cellular tissue are continuous over the whole body, each
adipose vesicle is a distinct bag, having no communication
whatever with any other. While also, the cellular tissue is
universally disposed, the adipose is placed only in particular

2 2

1, A portion of adipose tissue : 2. minute bags containing the fat ;
3. a cluster of the bags, separated and suspended.

3*

30 PHYSIOLOGY.

parts of the body, principally beneath the skin and the ab-
dominal muscles, and around the heart, kidneys, &c. while
none is ever found in the cranium, the brain, the eye, the
ear, the nose, and several other organs.

12. The Serous Membranes.-fThese line all the closed
cavities, or sacs of the body, and are reflected over the or-
gans contained in them; Thus the cavities of the (brain and
chest, the abdomen and joints, are lined by serous membrane.
By its external surface, it is united to the walls of the cavity,
or the substance of the organ it invests ; by its internal sur-
face it is free and unattached ; whence this surface is in con-
tact only with itself, forming a close cavity, having no com-
munication with the external air.

13. If it were possible therefore to dissect serous 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 these 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 analagoua
to that portion of the serous membrane which adheres to and
invests the organ, whilst the external portion of the cap
represents the lining of the cavity in which that organ is
said to be contained. Hence it will readily be understood
that the serous membranes never open, or allow of any per-
foration for the passage of blood-vessels, nerves, or ducts, to
or from the enclosed organs ; but that they are always re-
flected over them, forming a sheath around them, and accom-
panying them in their course. It also follows as a necessary
consequence, that their free surfaces completely isolate the
parts between which they intervene.

144' The serous membranes are of a whitish, shining col-
our, and smooth on their free or inner surface* They are
kept constantly moist by a fluid which is exhaled in a
gaseous state from the serum of the blood, whence they
derive their name. They are also elastic and extensible,
and are said to be destitute of blood-vessels and nerves;

STRUCTURE OF THE HUMAN BODY. 31

being composed of condensed cellular membrane. Accord,
ing to Rudolphi, serous membranes line not only the closed
cavities of the body, but the interior of the vessels also,
and the canals which open outwardly, as the alimentary
canal and the air passages, forming a cuticle over the mu-
cous membranes, which line these passages. \he uses of
the serous membranes are to separate different organs, to
diminish friction, and to facilitate the motion or gliding of
these parts upon one another, by means of thin smooth,
moist, and polished surfaces?!

15. Mucous Membranes.-?YhesQ membranes are also
another form of the cellular structure, and derive their name
from the nature of the fluid, which it is their office to secrete
by means of numerous minute glands imbedded in their sub-
stance. As serous membranes form a shut sac, completely
excluding the air, mucous membranes on the contrary, line
the various cavities, which are exposed to the air, such as
the mouth, the nostrils, the windpipe, the gullet, the stomach,
the intestines, and the urinary organs. Their internal sur-
face, or that by which they are attached to the passages they
line, is smooth and dense, while their external surface, or that
which is exposed to the contact of the air, is soft and pulpy>
like the pile of velvet, or the rind of a ripe peach.

82 PHYSIOLOGY.

A portion of the stomach, showing its internal surface or mucous coat.

16^ The mucous coat is the seat of some of the most im-
portant functions of the economy ; in the lungs, of respira-
tion ; in the stomach, of digestion. ; and in the mouth and
nose, of taste and smell, &c., and forms, with scarcely an
exception, a continuous wholeJ That portion which lines
the eyes and eye-lids, is connected with that which lines the
nostrils, by means of the nasal canal ; while that which lines
the mouth, meets in the throat with that which comes
down from the nose. In the fauces it divides, and while one
portion goes down the windpipe into the lungs, the other
passes down the esophagus into the stomach, forming a lining
for the whole tract of the intestinal canal.

17. Mucous membranes are of a loose, spongy texture, of
a reddish colour, and are largely supplied with blood-vessels
and nerves. They are also numerously supplied with small
glandular bodies called mucous glands or folicles. (The
chief use of these membranes is, to sheath and protect the
inner surfaces of the body, as the skin does the outer, and by
means of the mucus, with which they are always covered in
a state of health, to guard them against the contact of irri-
tating substances.

STRUCTURE OF THE HUMAN BODY. 33

18. We find a remarkable sympathy existing between all
the mucous membranes ; accordingly their diseases, particu-
larly the catarrhal affections, to which they are often sub-
ject, are very apt to spread in -them. By reason of this sym.
pathy, the state of one part of these membranes may be as-
certained by examining another part ; the state of the tongue
for example, indicates the condition of that of the stomach
and intestinal canal. There is also an extraordinary sym-
pathy between the mucous membranes and the respiratory
organs.

19. Dermoid Membraite. — This membrane, called also
cutis or skin, is not only directly Continuous with the mu-
cous membranesTJthat line the internal passages, but is also
analagous in its structure. We see them passing into each
other at the orifices of the internal canals, as in the lips, nos-
trils, eye-lids, external ear, &c. We find it varying in thick-
ness according to its situation ; in the face and body being
thin and delicate, and on the palms of the hands and soles of
the feet, considerably firmer and thicker. The skin is
abundantly supplied with blood-vessels and nerves ; so nume-
rous indeed, that the finest needle cannot enter the skin
without piercing many of both, which is proved by the bleed-
ing, as well as the pain which follow.

20. The skin, in man, is made up of four parts, or layers^
the cuticle, rete-mucosum, corpus papillare, and corium. It
is covered externally by the;fcuticleSor epidermis, which is
destitute of nerves and blood-vessels, insensible, and probably
inorganic. It is the cuticle which is raised by the applica-
tion of a blister, or by a burn or scald, fit is supposed to be
a secretion from the true skin which concretes on the surface
becomes dry, and thus offers protection to the parts beneath,
and also serves to prevent excessive absorption or the escape
of the fluids by evaporation.^ It is pierced by little pores, for
the passage of hairs, sweat, -&nd the fluids, taken up by ab-
sorption, although Humboldt asserts that he could not discover
them with a miscroscope which magnified 312,000 times.

34 PHYSIOLOGY.

21. The next layer of the skin is the fate mucosum, or
mucous web.) It has been supposed to consist chiefly of
mucus, as it is of a soft pulpy texture. It is the/seat of the
coloring matter in the different races$ In the European, it
is white, in the African black, and in the Mulatto and Malay,
copper-coloured. In the Ethiopian race, it is much thicker
than in the light-coloured varieties of the human species, and
may easily be separated both from the cutis and cuticle, and
made to appear as a distinct membrane.

22. The dark color of the skin in the inhabitants of the
torrid zone, is ascribed by most physiologists, to the influence
of the sun upon the surface of the body ; but the tinge pro-
duced on the skin by exposure to a bright light, appears
to have no connection with the permanent colour of the
negro. Dr. Bostock states, that the blackest complexions
are not found in the hottest regions, and that there are
some tribes nearly under the equator, whose skin is
whiter than that of many Europeans. Besides, the tinge
produced by the sun is not transmitted from parents to
their offspring, whereas the children of negroes are equally
black in whatever climate they are born, and their com-
plexion is not altered by any number of generations. When
a person is tanned, as it is called, by the influence of the
sun, it is the cuticle only which is affected ; if this be
removed by a blister, in a few days new cuticle will be
formed, and the skin in that place will appear as white as it
ever did.

23. Albinos. — In the Caucasian race, from which Europe-
ans and Americans have descended, there is usually a mix-
ture of red or brown, with white in the complexion ; but
where the skin is of a uniform, clear, pearly whiteness, the
individuals are called Albinos, from albus, white. In these
persons, the hair is generally white, corresponding with the
colour of the skin, while the eye is without that substance
which gives the various colours to the iris. The iris, in such

STRUCTURE OE THE HUMAN BODY. 35

cases, is generally of a bright rose-colour, and the eyes are
so sensible to light, that they cannot be kept open in the
sun-shine, although in the shade, or dusk of the evening, the
vision is perfect. It is now well ascertained that the red-
ness of the eye and the whiteness of the skin in albinos
depends on the same physical defect in their organization,
and that it is owing to the absence of the colouring mat-
ter in the rete mucosum. In the eye, this matter, spread
over the retina, is called Pigmentum nigrum, or the black
paint.

24. What is called thefCorpus papillarej is merely a col-
lection of small papillae, formed by the extremities of nerves
and blood-vessels, and lying immediately under the mucous
web, &c. It is|m this layer that the sense of touch resides ;
the papillae can easily be seen when the cuticle has been
removed by a blister.

25. The Cutis vera, or true sldn, is the innermost of the
four layers above mentioned, flt is a firm stratum of dense
fibres intersecting each other in every direction, and having
holes for the passage of vessels and nerves^

26. The true skin is composed chiefly of gelatine, and hence
is ijsed for the manufacture of glue^ Gelatine combined
with tannin, which is a proximate vegetable principle ob-
tained from oak and other barks, forms a compound that is
insoluble in water ; and it is to this circumstance that
leather owes the properties it possesses. Leather, then, may
be considered as the product of the union of tannin and
gelatine.

27. Though the skin consists of four distinct strata, yet
it is only^rom one-sixth to one-fourth of an inch in diameter.
The true skin is united to the structure below by cellular
membrane, and this, with the layers above described, consti-
tute the common integument. The following sketch repre-
sents the several layers entering into the composition of the
skin.

36

PHYSIOLOGY,

1. Cuticle.

2. Rete inucosura.

3. Corpus papillare.

4. Cutis vera.

5. Cellular membrane.

6. Faniculus carnosus.

(There are in certain parts of the body, and especially in
animals, muscular fibres passing up through the cellular
membrane, and inserted obliquely into the cutis verq) as at
6 in the plate. These form the muscular web, or paniculus
carnosus. It is this which raises the feathers in birds and
which in the hedgehog and porcupine rolls up the body, and
erects the spines ; and by means of this, animals shake off
flies from their skin.

28. The skin is defended from the action of moisture, and
is also \kept soft and pliant by an oily fluid, which is separ-
ated from the blood by numerous sebaceous follicles.^ We
find these the most numerous where there are folds of the
skin, or hairs, or where the surface is exposed to friction.
We sometimes see the oily matter secreted by these glands
assume a dark appearance, in the form of black specks, scat-
tered over the face, which are called by many worms, because
when pressed out they assume that aspect.

29. The hair is usually treated of by physiologists as an
appendage to the skin, fine hair takes its origin from the
cellular membrane in the form of bulbs, each bulb consisting
of two parts ; an outer, which is vascular, and from which
the hair obtains its nourishment ; an inner, which is mem-
braneous, and which forms a sheath or tube to the hair during
its passage through the skin. ..The external covering of
each hair is of a horny structure, while the central part is

STRUCTURE OF THE HUMAN BODY.

37

soft and pulpy, and is called medulla, or pith. The colour
of the hair varies in different individuals, and isfgenerally
supposed to depend on the fluids contained in the pith! The
hair, it is said, has been known in several instances to have
changed from black to grey in the course of a single night,
from the effects of grief, fear, or some other great mental
agitation. Vauquelin supposes that as the colouring matter
of the hair is destroyed by acids, this phenomenon is owing
to the production of some acid in the system. Others sup-
pose that the effect depends upon the sudden stagnation of
the vessels which secrete the colouring matter, while the
absorbents continue to act and remove that which already
exists. There are probably two causes which act in chang-
ing the hair to grey ; (the first is a defective -secretion of a
colouring fluid, and the second, the canals which convey the
fluid into the hair become obliterated) In the first case, the
hair will remain ; in the last, it inevitably dies and drops
out.

38 PHYSIOLOGY.

30. The figure on the last page represents the pulp of a
iiair injected ; 1, cut surface of hair ; 2, the pulp ; 3, inject-
ed vessel ramifying in it. The figure on the right shows
the hair in its fallicle, though the drawing was made from
the whisker of a Walrus ; 2, the cutis ; 3, external sheath of
the fallicle ; 4, internal sheath continuous with the cuticle ;
5, pulp ; 6, shaft of hair ; 7, large nerve going to it.

31. The nails are also an appendage to the skin. Their
chief use seems to be to support the pulp of the finger while
it is exercising touch. Animals are provided with struc-
tures analogous in their physical and vital properties, such
as horns, beaks, hoofs, nails, spurs, scales, &c. Some physi-
ologists consider the teeth as belonging to the same class.
The various and peculiar functions of the skin, so important
to be understood in order to the preservation of the health,
will be fully described hereafter.

Questions. — Of what is the human body composed ? What is said
of the identity of solids and fluids ? What proportion do the fluids
bear to the solids ? How modified by age ? What purposes do the
fluids serve ? What is said of the solids ? How are their particles
arranged to form the different organs ? How are the areolae formed ?
Of what shape is the ultimate animal solid ? What is a primary tissue ?
How many primary tissues are there ? What is a filament ? — a fibre
— a tissue — an organ — a function ? Give an example ? What is an
apparatus ? — a system ? — membrane ? What are its uses ? What is
the simplest form of membrane ? — its use ? What property does it
possess ? What its chemical composition ? What remarkable circum-
stance connected with it ? What is the seat of dropsy ? What varie-
ties of membrane are formed by the cellular tissue ? Describe the
adipose ? What are serous membranes ? — where found ? — their use ?
structure ? What are mucous membranes ? Describe their structure,
situation, use, &c. What is the skin a continuation of ? Of how many
parts is it composed ? What is the external layer called ? — what is its
use ? What is the layer next ta the cuticle called ? Of what is it the
seat ? — the next layer ? — its use ? Describe the cutis vera ? What is
it used for ? How thick is the skin in ma-n ? By what contrivance is
the skin susceptible of motion ? How is the skin kept soft and pliant ?
What is said of the hair ? — what is its structure ? — what is its colour
owing to ? What causes it to turn grey ? What is said of the nails ?

CHAPTER IV.

STRUCTURE OF THE HUMAN BODY CONTINUED.

1. ANOTHER form of cellular structure is called fibrous,
from the arrangement of its component parts, which consist
of longitudinal fibres, plainly visible to the naked eye, placed
parallel to each other and closely united. These fibres are
sometimes so combined as to form a thin, smooth, dense, and
strong membrane, like that which covers the external surface
of bones, termed periosteum, or the internal surface of the
skull, (dura mater.) At other times it forms a firm sheath,
which dips down between the muscles, separating them from
each other, or it may be spread over them, binding them
firmly down in their placejk

2. In the loins and along the back bone there is a strong
binder of this kind, which greatly facilitates the motions of
•the body and powerfully contributes to the action of the
muscles. Where this is weak, a belt round the waist is of
considerable service, but in a well-formed person it is a
clumsy substitute of art for nature, and ultimately tends to
weaken the back, for exercise strengthens and invigorates all
parts of the frame, while artificial substitutes invariably
weaken the parts they are supposed to strengthen.

3. It also constitutes the strong, tough, and flexible band,
used for tying parts firmly together, termed ligaments, such
as are found about the joints, connecting the bones ) and it
also forms those white cords in which muscles terminate,
called tendons, which serve to attach the muscles to the
bones, thus acting as mechanical instruments of motion.
This tissue forms a firm covering or envelope to the bones,
muscles, tendons, cartilages, the eye, kidneys, spleen, and
most of the organs of the body.

40 PHYSIOLOGY.

4. Every joint is enclosed by a firm fibrous bag, called
the capsidar ligament, the internal surface of which secretes a
fluid, termed synovia, which lubricates the joints, and serves
the same purpose that oil does in a piece of machiner>\ . At
the wrist and ankle, and along the fingers and toes, the liga-
ments form strong bandages to bi'nd down the muscles and
tendons, and enables them to act with greater precision and
steadiness ; otherwise when the muscle contracted, the ten-
dons would start out like the string of a bow, and thus not
only destroy the symmetry of the parts, but entirely prevent
motion, When sprained by over exertion or accident, an
artificial bandage becomes ncccssar^; we then find how su-
perior the natural ligaments are to any artificial bandage that
can be contrived.

5. Tendon or Sinew. — This well-known structure is
plainly perceptible(at the wrist, on the back of the hand, at
the heel, &c. (They have a white, pearly lustre, possess
great strength, but little elasticity. They are composed
of bundles of parallel threads, bound * together by trans-
verse threads, and they vary both in figure and extent ; some
being cylindrical and tapering to the point of insertion,
and in others forming broad expansions., So insensible are
tendons, that when ruptured, as the tendon of Achilles at the
heel, not the slightest pain is felt, but the person feels that he
has received a smart blow, or that a part of the floor has given
way under him.^

0. Where force is to be exerted upon some distinct point, it
is transmitted along a tendon, as forces in machinery are by
ropes?* When a tendon passes over a joint, a bone is formed
sometimes where it crosses, as the knee-pan in front of the
knee joint ; which is a bone placed directly in the centre of
the tendon, and (serves, to throw the force farther -from the
centre of motion, thereby increasing the lever, and conse-
quently the effect.) Similar bones are often found in the
tendons of the feet.

STRUCTURE OF THE HUMAN BODY 41

7. Another primary tissue, or modification of cellular
structure, is termed the cartilaginous. (This seems to be a
substance intermediate between membrane and bonej It is
firm, smooth, highly elastic, of a pearly white colour, and ex-
cept bone, the hardest part of the animal frame. It is des-
titute of red vessels, and neither nerves nor lymphatics have
been discerned in it ; though as it becomes highly sensible,
like the fibrous tissue, by disease, it no doubt is supplied with
nerves*} It is placed at the ends of the bones, particularly
about the joints, where by its smooth surface, it facilitates
motion, and by its yielding nature, prevents the shock or jar
which would be produced were the same kind and degree of
motion effected by a rigid and inflexible substance. Where
strength and flexibility are required to be united * we there
find cartilage, as in the spinal column, between the ribs and
breast bone, in the larynx, the ear, nosej&c.

Portions of cartilage seen in section.

8. ClBy immersing cartilage in nitric acid and then in wa-
ter for some little time, we find its intimate structure so un-
folded, that we can perceive it to be composed of an infinite
number of minute fibres, arranged perpendicularly like the pile
of velvet^ Thus we see that in the construction of the joints,
millions and millions of springs of the most curious and ex-
cellent contrivance stand perpendicular to the direction of
the force applied, bend to pressure, and on its removal, regain

42 PHYSIOLOGY.

their form by their elasticity. When we stand in the erect
posture, the number of minute but efficient springs on which
the weight of the body rests, in the several joints of the back,
in the hip, knee, and ankle joints, infinitely surpasses the
powers of the human mind to calculate or even to imagine.

9. There is a peculiar tissue, allied to ligament in its tex-
ture, distinguished by a high degree of elasticity, fibrous
structure, and tawny colour, and is hence often called elastic
tissue. This structure is very conspicuous in the neck of
those animals, which have to support a heavy load horizon-
talljl at the the extremity of a long neck, as in the elephant,
the deer, and our domestic cattle. Had their heads been
supported merely by muscular action, as that is liable to fa-
tigue and requires intervals of rest, as well as the exercise of
volition, the postures could not have been sustained for any
length of time without pain and exhaustion. This tissue,
which is liable to none of these objections, is accordingly
| substituted for muscular power, in fixing the forms, preserv-
ing the attitudes, and contributing to motionj The strong
fibrous band, stretching along the back part of the neck to
the head of these animals, enables them with perfect ease to
support the head. It is the elasticity of this membrane
which causes the head of these animals to be bent back after
death, the action of the muscles having ceased. It also re-
tracts and retains the sharp claws of the cat tribe within
their sheath when not in use. A ligament of this tissue also
retains the wings of birds in a bent position when they are
in a state of rest.

10.-|TAe osseous fabric$—The osseous or bony tissue is
another form of cellular matter. The bones constitute the
hardest and the most solid parts of the whole system, and are
the principal parts thatjgive it form and stability, forming as
it were, the frame work of the animal machine,/ The num-
ber of bones in the human adult, including the teeth, is; 245.
When we examine the broken surface of a bone, with a mi-
croscope/we find it abundantly supplied with minute blood-

STRUCTURE OF THE HUMAN BODY. 43

vessels]! without any appearance of fibres or plates. The
different densities of bones (depends on the different mechani-
cal arrangements of the parts composing them^

11. The bones not only constitute the frame work of the
human fabric, but they also protect the vital organs, as the
heart and lungs, the brain and spinal marrow, and also con-
stitute a series of levers, by means of which, through the
agency of muscles, locomotion is performed. The bones in
man also furnish cavities for the secure lodgment of the deli-
cate organs of the senses, as the orbits of the eye, ear, mouth,
and nostrils. In man, and the higher order of animals, the
bones are for the most part in the interior of the body, and
when near the surface, as in the skull, they are covered by
muscles or membranes; bufin the Crustacea, insects, &c., the
bones compose an external case within which all the soft
parts are containe(Jf

12/If we divide any of the long bones longitudinally, we find
two kinds of structure, the hard or compact, and the alveolar
or spongy/ Indeed there is no bone that does not exhibit to
some extent both of these structures ; the compact forming
its external, and the spongy its internal part. These two
formations are clearly seen in the bones which compose the
skull, (as in the following cut,) with the spongy or cancel-

a. External plate. 5. c. Internal plates.

lated structure between them. This will serve to illustrate
the structure of all the flat bo/ies.

i

13. The above cut represents a section of the thigh bone.

44 PHYSIOLOGY.

a. a. the extremities having a shell or thin plate of compact
texture, crowded with small cells, diminishing in size, but in-
creasing in number as they approach the articulation ; c, the
cavity for containing the marrow ; 6. b. the walls of the shaft
very firm and solid. The compact part is thickest near the
middle of the bone where the greatest strength is required.
This structure admirably combines the greatest degree of
strength, with the least degree of weight aud expense of ma-
terial. It tfan be mathematically demonstrated that the re-
sistance of a cylindrical body, such as a pillar or mast, to a
force applied transversely is increased in proportion to its
diameter. The same quantity of matter, therefore, placed in
the circumference of a circle produces a stronger bone than
if united in the centre with proportionally diminished diame-
ter.

14. How admirably adapted is the arrangement of the
parts of the long bones to the purposes for which they are
destined. Their extremities are the fixed points from which
the muscles re-act, and where greater space was required for
the insertion of the tendons ; their diameter is on this ac-
count considerably increased, and their osseous matter*is
disposed in nearly an equal degree through their whole sub-
stance ; while in the middle of the bone, which is more
exposed to external violence^ and where nothing was want-
ing but mere strength, the bony plates are all consolidated
together into a compact dense ring, leaving the centre
nearly hollow.

15. While the long bones of the lower extremities are
adapted for the support of the body, and its various progres-
sive motions, those of the upper extremities are equally
fitted for acting upon contiguous bodies, being so attached to
the trunk as to be easily applied to them in all directions.

{The flat bones on the other hand offer an extensive sur-
face of defence, as those of the skull, or for the origin and
insertion of muscles, as the shoulder blade.^ The rounded
bones composing the spinal column and the angular bones of

STRUCTURE OP THE HUMAN BODY. . 45

the wrist and ankle, have the bony matter extended over a
considerable space, in order in the most era^fijfcbfenner to
combine the properties of lightness and strength. The
whole assemblage constitutes an apparatus which is capable
of executing all the various movements that are necessary for
the purposes of life, with a degree of precision and velocity
that is truly wonderful.

16. {The bones are covered with a fibrous sheathing of
dense membrane, called periosteum, which seems to nourish
the bone, for where it is abraded the bone perishes^ fit con-
tains an abundance of blood-vessels which run from it into
the bone ; besides these, a large blood-vessel enters the shafts
of the long bones near the centre, and branches out in each
direction, while numerous others enter at their extremities^
These blood-vessels, though generally too minute to convey
the red particles of the blood, yet they readily transmit the
colouring matter of madder. Numerous experiments have
proved that when animals are supplied with food mixed with
that substance, in a few days |he bones are coloured red, or
of a pinkish colourjland on the discontinuance of it, in a
short time their natural colour is restored, showing the
rapidity with which deposition and absorption are carried
on in the healthy state. This is shown in cases of fracture,
where the broken ends of a bone become speedily united. I
have lately had a case of fractured thigh bone in a child,
where it became united with considerable firmness in one
week.

17. stfarroiv is a species of fat deposited in the central
canals of the cylindrical bones, and in the lattice work of
the spongy bones!/ £t is contained in the cells of a delicate
membranous web) and ;has been supposed by some to serve
as a reservoir of nourishment, and by others, to keep the
bones from becoming dry and brittle^ ^t is found in greater
quantity in thef adult and aged than in the youn^; in the
latter, indeed, its place is occupied by a gelatinous fluid.

18. Chemical examination shows that{ bone is composed

46 PHYSIOLOGY.

of earthy and animal matter, the former constituting about
two-thirds, the remaining! one-third being animal matterl
As we find portions of both these substances in the minutest
particles of bones, both are therefore considered essential to
its composition, and existing in a state of chemical union,
and not as a mere mechanical mixture. These two sub-
stances can be readily separated from each other. ' If we
immerse bones for some time in diluted nitric acid, or muri-
atic acid, though they retain their size and form, their
weight is considerably diminished, and they are rendered
soft, pliable, and elastic. The earthy portion, phosphate of
lime, has been dissolved, and is held in solution in the fluid,
and the animal portion, gelatine, remains uninjured^

Membranous, or gelatinous portion of bone ; the earthy portion being
so completely removed, that it is capable of being tied in a knot.

19. If bones are subjected to a strong heat, as in a char-
coal fire, on cooling they appear to have undergone no alter-
ation in figure or bulk ; but they are rendered white as
chalk ; their weight is lessened, and they become very
brittle. In this case, the animal matter has been wholly
consumed by the fire, while the earthy part remains un-
changed ; in the former case, the very reverse happened ;
the animal matter remaining, and the earthy being removed.

3*

STRUCTURE OF THE HUMAN BODY. 47

Earthy portion of bone.

20. {The proportion between the animal and earthy sub-
stances varies in different individuals, and in the same indi-
vidual at different periods of life, and under various condi-
tions of health} In youth, the former, in old age, the latter
predominates. The earthy matter is sometimes so deficient
that jthe bones have not the necessary degree of firmness
and rigidity. |*The consequence is, that those parts of the
skeleton which have to support any considerable weight
bend under it, as the spine, the bones of the pelvis, and the
lower limbsy This is one cause of spinal distortions, though
they are generally caused by debility of the muscles from
want of proper exercise. In many cases of the former kind,
by the subsequent deposition of earthy matter, the bones be-
come sufficiently dense and compact ; but the distortion
remains fixed and permanent, and mechanical means, such
as pulleys, screws, inclined planes, &c., only serve to torture
the patient, without affording the slightest prospect of a
cure. No one who understands physiology will attempt to
correct such distortions by mechanical means. |Where
there is a deficiency of animal matter, the bones want a
poper degree of tenacity, and are therefore easily fractured
by slight blows or fallsj

21. The ends of the bones which are used for motion, as
already mentioned, are tipped with cartilage or gristle, which
is very smooth and hard ; and it is constantly wet, in a state
of health, by a fluid which answers the same purpose as oil
in machinery, or tar upon wagon wheels. The joints are

48 PHYSIOLOGY.

enclosed in membranous bags, and in health the fluid which
moistens them is of just the right quantity and quality ; but
if we do not take proper exercise, or if we take food or drink
that is too heating or irritating, the joints grow stiff, or
rheumatism or gout may be the consequence.

22. In those parts where bones are to be formed, a mould of
gristle or cartilage is first deposited, of the exact shape that
the future bone is to take ; and as bony particles are secret,
ed by the blood, the cartilage is taken up by the absorbent
vessels. In the long round bones, this process begins in the
middle, and in the flat bones, like the shoulder blade, or those
of the skull, it begins in the centre and extends gradually
towards the circumference^ But in the skull, all the bones
are not completely formed, till several months after birth.

23. The bones are variously connected by joints or arti-
culations, which admit of different degrees of motion, both
in extent and variety. Some of these connections allow
free, easy, and conspicuous motion, as the shoulder and hip
joints, which are called ball and socket joints ; in others,
there is motion in only two directions, as the knee, elbow,
wrist, and ankle. These are called hinge-joints, from their
resemblance to a hinge. Some bones, like those of the skull,
though connected by a kind of articulation, are nevertheless
immoveable.

24. Another form of animal matter, differing essentially
from those we have been considering is, muscular tissue.
This is familiar to all under the name of flesh. It is a sub-
stance of a peculiar nature, arranged in fibres of extreme
delicacy. |It is distinguished from every other texture in
the body, by an innate power of contraction j on examin-
ing it with microscopes of great magnifying power, it is
found to b^[ composed of filaments so fine as the one forty
thousandth part of an inch in diameter] These filaments
collected together, form fibres, which are plainly perceptible
in boiled fleshv {A collection of these fibres form a bundle,
and these bundles collectively constitute a muscle ; and

STRUCTURE OF THE HUMAN BODY. 49

muscles appear coarse or fine according to the size of these
btuxDejp

25. frhese fibres appear to be very uniform as to shape,
size, and general appearance, being delicate, soft, flattened,
and though consisting only of a tender pulp, still solid,/ (The
fibrous and fascicular arrangement appears to be chiefly con-
fined to muscles of voluntary action, as they are scarcely
perceptible in the heart, and not at all in the alimentary
canal, or urinary bladderjl In the stomachs of birds, how-
ever, the fibrous structure is very distinct, especially in
hawks and owls.

The appearance of the ultimate fibres and of their transverse lines, as
seen under the microscope of Mr. Lister, when the object is magnified

500 diameters.

26. The muscular fibres are every where penetrated by
cellular tissue and numerous blood-vessels and nerves. /The
colour of the muscle of course varies, according to the quan-
tity and quality of the blood.) In adult animals it is of various
shades of red ; in young animals, of a cream colour, as in
veal ; in birds, it varies in different muscles ; in fowls, for
example, it is white, on the breast, and a deep brown on the
legs ; whilefin fishes, it is bluish, or white,)&c.

27. No part of the body except, perhaps, the organs of
sense, is so abundantly supplied with blood-vessels and

6

50 PHYSIOLOGY.

nerves, as the muscular tissue. There is reason to believe
that every filament, however fine, is provided with the ulti-
mate branch of an artery, vein, and nerve. f*The direction
of the fibres of muscles varies ; in some, being parallel ; in
others, radiating in different directions. In some instances,
they form nearly or quite a circle, as the muscle which
closes the eye, and those of the intestinal canal ; in others,
they are penniform, or having their fibres disposed like those
forming the feathery part of a quill jj

Two portions of muscle ; one of which, cr, is covered with mem-
brane ; the other, b, is uncovered ; c, the muscular fibres terminating in
tendon.

27. [Muscular tissue is supposed to consist chiefly of
Jibrin, though some chemists state that it contains albumen,
gelatine, and osmazomefc These latter substances however,
are probably obtained from the cellular tissue which encloses
and dips down between the fibres of muscles. Fibrin con-
tains a larger proportion of azote, the element peculiar to the
animal body, than any other animal substance. The flesh
of young animals affords a large proportion of gelatine, while

STRUCTURE OP THE HUMAN BODY. 51

it is deficient in fibrin — in adult animals, the fibrin pre-
dominates, and the gelatine is deficient.

28. |The peculiar property of muscular tissue is vital, and
consists in the power of diminishing its length, or shortening
on the application of stimulus J All the motions of the body
are performed by means of it, and without its incessant
action, respiration, digestion, nor circulation could be carried
on for a moment. Tendons, ligaments, cartilages, and bones
seem to be mechanical contrivances to aid the muscles in
accomplishing their varied purposes, so that the only source
of motion in the body is muscular tissue, and the only mode
in which motion is generated is by contractility^

29. The last primary tissue which we have to describe, is
termed nervous. ^It consists of a soft and pulpy matter, of a
brownish white colour, and appears to be composed of solid,
elongated threads, differing in thickness from that of a hair
to the finest fibre of silk^j Like the muscles, the nerves are
enclosed in a sheath of condensed cellular membrane, called
neurilema, or nerve coat^ and like them also, each nerve is
composed of many bundles ; these of many fibres ; and the
fibres of many filaments. In one respect the nervous fibres
differ from the muscular, and that is, while the muscular fi-
bres generally run parallel to each other, those of the nerves
cross and penetrate each other, so as to form an intimate in-,
terlacement, as represented on the following page. When we
come to describe the vascular system, it will be seen that
either all the vessels proceed from one large trunk, which
goes on progressively to divide and subdivide, until its
branches become so minute as to be invisible ; or that they
arise by numerous and invisible branches, which unite to
form larger and larger vessels, until they ultimately consti-
tute only a few trunks. But the muscular and nervous fila-
ments never divide and subdivide in this manner. It is the
opinion of the best anatomists, that there is a diameter be-
yond which they no longer dimmish. That diameter they
maintain is quite uniform in each.

62

PHYSIOLOGY.

Nervous fibres, deprived of their neurilema and unravelled, showing
the smaller threads, or filaments, of which the fibres consist.

30. The nervous tissue is also abundantly supplied with
blood-vessels, like the muscular ; so that there is not a fibre
or filament, howev.er minute, which is not supplied by a dis-
tinct blood-vessel./ /The nervous structure forms the brain,

STRUCTURE OF THE HUMAN BODY. 53

spinal marrow, nerves and their ganglions/ The nervous tis-
sue appears to consist of two substances, which as far as the
eye can distinguish, appear to be entirely distinct from each
other. vThe one is called cineritious, or gray, from its col-
our ; from its position, cortical, and from its consistence pulpjrj
This last appears to be composed chiefly of blood-vessels.
The other is termed white, or medullary. It is of firmer
consistence than the pulpy. This is decidedly fibrous in its
nature. In every part of the nervous system which consti-
tutes a distinct nervous apparatus, both substances are con-
joined. Neither the pulpy, nor the fibrous alone, forms a
distinct organ ; the union of both is necessary to constitute
an instrument capable of performing a specific function.

Ultimate fibres of nerve highly magnified ; showing the strings of
globules of which they consist.

31. Much controversy exists in relation to the shape of
the ultimate particles of nervous matter ; but while micro-
scopical observations differ as much as they have done hith-
erto, the question may fairly be considered as unsettled,
ffhe common opinion is, that the ultimate filaments of which
they are composed, are formed of globules of extreme minute-
ness,) But then, when we consider the peculiar difficulties
attending investigations of this nature, that they require un-
wearied perseverance, extreme accuracy, great patience, and
a dexterity with the hand, united with a delicate discrimina-
tion of the eye, that belong to few ; and when we consider
moreover, that these very endowments can only be acquired

5*

PHYSIOLOGY.

by long practice, we shall be led to pause, before we adopt
the opinions of every microscopical enthusiast who enters on
this very extensive, and deeply fascinating field of discovery.

Portion of the trunk of a nerve dividing into two branches.

Questions. — Describe the fibrous structure. What are its uses?
What are ligaments ? What is a capsular ligament ? What use do
ligaments serve ? When sprained, what is a good remedy ? What is
a tendon or sinew ? Where are they found ? What their use ? Of
what composed ? Have they much sensibility ? Why are bones
sometimes placed in a tendon ? What use does the knee-pan serve ?
Describe the cartilaginous tissue. What are its uses ? How may its
structure be shown ? What is the elastic tissue ? Where is it found ?
What are its uses ? What constitutes the most solid portion of the sys-

STRUCTURE OF THE HUMAN BODY. 55

tern ? What are the uses of the bones ? How many are there in the
human skeleton ? Is bone supplied with blood-vessels ? What is the
different density of bones owing to ? What situation do the bones
occupy in man ? In the Crustacea and insects ? Describe the structure
of the long bones 1 — of the flat bones ? What is the chief use of the
Hat bones? What covering have the bones ? What is the structure
of the periosteum ? What its use ? How are the bones nourished ?
What effect has madder upon bones when taken internally ? What is
marrow ? Where is it deposited ? What its use ? At what period of
life is it most abundant ? What is the composition of bone. What pro-
portion is animal matter ? What earthy ? How are these different sub-
stances shown ? Are their proportions affected by age or health ?
What is the consequence when the earthy matter is deficient ? What
when the animal ? How are spinal distortions best remedied ? How
is bone formed ? Are all the bones formed at the time of birth? What
is muscular tissue ? By what property is it distinguished ? — Of what
composed? What are fibres ? What bundles? How do the fibres
appear? Do all muscles possess the fibrous arrangement? To what is
the colour of muscle owing ? Of what colour is the muscle of fishes ?
Of what shape are muscles ? What is the chemical composition of
muscular tissue ? Does age affect the quantity of fibrin in animals ?
What peculiar property does muscular fibre possess ? What its use ?
Describe the nervous tissue. What is the neurilema ? Does nervous
tissue abound with blood-vessels ? What does it form ? How many
kinds of substance is contained in it,? What is the cineritious ? What
their cortical portion ? Does either- alone form any organ ? What is
said of the shape of the ultimate particles of matter ?

CHAPTER V.

CHEMISTRY OF THE HUMAN BODY.

Ultimate and Organic Elements.

l.fBy the chemical composition of the. body, is meant
those ultimate elements of which it is made ;^ such asjbxygen,
carbon, hydrogen, and azote.j By the organic composition,
we mean the proximate elements, which are formed out of
these by the power of the living principle ; such as albumen,
Jibrin, gelatine$&c.

S.^The ultimate elements of animal matter have been
divided into non-metallic, and metallic substances ; the former
consisting of oxygen, hydrogen, carbon, azote, phosphorus,
sulphur, chlorine, and fluorine ; the latter, 1, the bases of the
alkalies, viz., potassium, sodium, and calcium ; 2, the bases
of the earths, magnesium, silicium, and aluminum ; 3, the
ponderous metals, iron, manganese, and copper.}

Of the first class, or the non-metallic substances, oxygen,
hydrogen, carbon and azote exist in much the largest pro-
portion, and are in fact the only essential elements of animal
matter.

3.| All the solids and fluids of the body contain oxygen.,
It is essential to all the proximate elements. United with
hydrogen, it forms water, which is calculated to constitute
nine-tenths of the whole weight of the body. In union with
carbon, it forms carbonic acid, which exists in the blood, and
is thrown out by the lungs and skin.

3. Oxygen forms with phosphorus, phosphoric acid, which
with lime constitutes the earthy portion of the bones ; it also
exists in some of the secretions. In union with their metalic
bases, it forms potash, soda, and lime. It also is a consti-

CHEMISTRY OF THE HUMAN BODY. 57

tuent part of albumen, fibrin, gelatine, and mucus. Oxygen
is derived partly from the air we breathe, and partly from
our food and drinks. It is given off in all the secretions
and excretions. The air contained in the swimming bladder
of fishes, is pure oxygen.

4. ^Hydrogen exists in all the fluids and most of the solids,
constituting as it does one element of water. In venous
blood, it exists in a larger proportion than in arterial blood,
which contains more oxygen. In the bile, it is very abund-
ant, and in fat and oil, is one of the essential elements. It
is this gas which often causes so much distress in a weak
state of the stomach. Hydrogen is introduced into the
system by means of food and drinks, and is discharged in
the same manner as oxygen^

5. {Carbon abounds in the vegetable as well as animal
kingdom. In oil, fat, albumen, gelatine, fibrin, and mucus,
it always forms a part. In bile, and in venous blood, it
exists largely. If we burn a piece of animal substance,
what is left is found to be chiefly carbon. We obtain it
from our food, and give it off by breathing and the secretions.
It is carbon that makes venous blood darker than arterial,
and the change from purple to bright crimson which takes
place in the lungs, id supposed to be owing chiefly to the
fact, that the excess of carbon contained in venous blood is
discharged by respirationj

Q.^Azote exists in large quantities in all animal matter.
It also exists to some extent in a few vegetables, but it is an
essential element in animal substances. It is more abund-
ant in fibrin, of which the muscular flesh is chiefly formed,
than in any other portions of the body, though it is found
in the brain and nerves. The peculiar smell of burning
animal matter is owing to azote. When animal substances
putrefy, it combines with hydrogen, and forms ammonia or
hartshorn^

7. Azote is chiefly taken into the system by means of
animal food. It is also taken into the blood by respiration,

58 PHYSIOLOGY.

as it forms a constituent part of the atmosphere. This,
however, is denied by some chemists. It is discharged from
the system in the same manner as oxygen, hydrogen, and
carbon ; though chiefly through the kidneys.

8. Phosphorus exists both in animal and vegetable sub-
stances. Nearly every part of animal bodies contain it,
though it is found more abundantly in the bones. It gener-
ally exists in combination with oxygen, forming phosphoric
acid. It is discharged mostly through the kidneys. The
spontaneous combustion of human bodies, of which we have
some well-attested cases of drunkards, is supposed to be owing
to an accumulation of phosphorus in the system, from some
unknown cause.

9./Sulphur is always united, in animal substances, with
other elements, as soda and potash. It is found in albumen,
in the hair and nails, and in muscular flesh. It is given off
by the intestines and by the skin.

10. Chlorine is found in most of the animal fluids com-
bined with hydrogen. This forms hydrochloric acid. In
the blood it is combined with soda and potash. It is found
also in the gastric juice, in sweat, milk, saliva, &c.

11. Potash exists more abundantly in plants than in ani-
mals. It is, however, contained in the blood, bile, urine,
sweat, milk, &c.

12. Soda is more abundant in animals than plants. It
exists in the same fluids in which potash is found ; also in
bones and muscular flesh. It is always combined with some
acid.

13. Lime forms a large part of the bones, in union with
phosphoric or carbonic acid. Silex exists in human hair,
and in some of the secretions. Magnesia is contained in
bones, and in some animal fluids, as milk. It is also found
in the brain. Iron forms the colouring principle of the red
globules of the blood, and is therefore pretty extensively
found in animal bodies. *

CHEMISTRY OF THE HUMAN BODY 59

14. fThe organic or proximate elements of the body are
formed from the ultimate elements already described^ We
cannot explain their formation on any chemical or mechan-
ical laws, but refer them solely to the influence of the vital
forces.

15. These proximate elements are mostly formed from a
combination of oxygen, carbon, hydrogen, and azote, and are

jdivided into two classes, acids and oxyds)

16. The acids found in the human system are the acetic,
oxalic, the benzoic, and the uri% The three first are also
found in the vegetable kingdom, and are composed of oxygen,
hydrogen, and carbon. When these organic elements are
made of three simple elements, they are called ternary
oxyds; such are sugar, resin, and the fixed and volatile
oils.

17. Milk contains a considerable quantity of sugar. It
can be obtained from whey by evaporating it slowly to the
consistence of a syrup, and then allowing it to cool. It may
then be purified by the white of an egg, or albumen, and
crystalized again. It has a different taste from the sugar
of the cane.

18. The bile contains a peculiar resin. Fat and the mar-
row of the bones contain fixed oils. Butfthe most important
compounds of the body are albumen, fibrin, gelatine, mucus,
and osmazomej

19. tAUwmen exists in the body, both in a solid and fluid
formj Combined with water it forms the white of eggs ;
hence its name, fit exists most abundantly in the serum,
but is found in all the fluids of the body. It is transparent,
without colour, taste, or smell, and coagulates by heat, acids,
and alcohol;

20. Solid albumen is also a white and tasteless substance.
It forms the basis of the nerves and brain, and is contained
in the skin, hair, nails, glands, and vessels. Tumours and
wens are mostly composed of albumen. It is composed of

60 PHYSIOLOGY.

Carbon 52 parts; Oxygen 23 parts ; Hydrogen 7 parts;
Azote 15 parts.

2l.{Fibrin is the basis of muscular fleshj and enters
largely into the formation of the blood, chyle, and lymph. It
is owing to the presence of fibrin that blood coagulates when
removed from the body. Fibrin is a solid, white substance,
of a fibrous structure, destitute of smell and taste, and in-
soluble in water.

22. Fibrin may be obtained by washing the thick part of
the blood with cold water, and thus separating the colouring
matter, or the red globules/ It differs from albumen by
possessing the property of coagulating at all temperatures.

jFibrin is composed of Carbon 43 parts ; Oxygen 19 parts ;
Hydrogen 7 parts; Azote 19 parts J It contains more azote
and less oxygen than albumen.

23. Gelatine is found in none of the fluids of the human
*ody. lit is, however, found in nearly all the solids* It is
known from all the other animal principles/by its readily
dissolving in warm water, forming a kind of jelly) /When
dry, it forms a hard, shining, brittle substance, called glue.
This is mostly prepared^ from the skins and hoofs of animals,
by boiling them in water, and then evaporating the solution.
Isinglass is obtained from the sounds of the sturgeon, and is
a very T>ure gelatine.

24. (Gelatine exists largely in the skin, cartilages, liga-
ments, tendons, and bones, and it forms the basis of the
cellular tissue/ As it does not exist in the blood, it is pro-
bably a modification of albumen. It is composed of Carbon
47 parts ; Oxygen 27 parts ; Hydrogen 7 parts ; Azote 16
parts.

25. It appears that gelatine contains less carbon than
albumen, by 5 or 6 per cent., and a larger proportion of
oxygen in the same ratio. ftfow, if we suppose, that near
the skin, and in the various tissues of the body, the albumen
of the blood gives off a portion of its carbon, a part of which

; CHEMISTRY OF THE HUMAN BODY. 61

is taken up by the veins, and a part thrown off by the skin,
lungs, and various secretions, we shall see how gelatine may
be formed out of albumen^

26.fOsmazome is an element which exists in all the animal
fluids^ and in some of the solids, as the brain and muscular
fbre. It is of a reddish brown colour, of an aromatic smell
and agreeable taste^ fit is this which gives the strong flav-
our of roasted meat, and the peculiar taste of the various
kinds of animal food. It is supposed to be tonic and stimu-
lating, but to possess no nutritive properties^

27. pfwcws is that bland fluid which moistens the surface
of all the mucous membranes^' '£n some of the hard parts
of the body, which are destitute of sensibility, it is found to
exist in considerable quantities, as in the nails, hair, and
cuticle of man, and in the scales, feathers, and wool of dif-
ferent animals. That part of the skin called rete mucoscum,
is supposed to be compacted mucus. Mucus is transparent,
has no colour or taste, and has a ropy and viscid consist-
ence. When dry, it is insoluble in water. It contains
much azote\

28. uThere are some other substances found in the human
body, such as caseine, or that principle of the milk which
forms the basis of cheese, curd, &c. ; but they are not of
sufficient importance to need a particular description^

Questions. — What is meant by the chemical composition of the
body ? What are some of the ultimate elements ? What are some
of the proximate elements ? How have the ultimate elements been
divided ? Is oxygen essential to all the proximate elements ? What
is said of hydrogen ? — Of carbon ? — Of Azote ? How do oxygen,
hydrogen, and azote get into the system ? Is phosphorus found in
animal bodies ? What other elements are met with in animals ? How
are the organic elements' of the body formed ? How divided ? What
acids are found in animal bodies?^ What are the most important
compounds in the body ? What is said of albumen ? In what is it
found ? What is fibrin the basis of? How may it be obtained from

62 PHYSIOLOGY.

blood ? Of what is it composed ? Where is gelatine found in the
animal body ? How known from the other animal principles ? What
does it form when dried ? Of what is glue prepared ? In what does
gelatine exist ? How may we account for the productions of gela-
tine ? What is osmazome ? What peculiar properties has it ? What
is mucus ? Where found, what is its use ? Are any other substances
found in the human body ?

CHAPTER VI.

THE HUMAN SKELETON*

1. OF all the wonderful works of the great Architect, none
bears such convincing proofs of divine wisdom and good-
ness as the mechanism of ^he human body. Every part,
down to the minutest fibre or blood-vessel, bears the impress
of the Creator's hand, and the marks of design and contri-
vance are so obvious throughout, as to lead the mind irre-
sistibly to an all-wise, Omnipotent designer !

2. The human skeleton consists of about (252 bones, in-
cluding the sesamoid, the teeth, and the small bones of the
ear ; though they are generally reckoned at 21 1/. They are
divided into those of the head, trunk, and extremities, • some
of them being single, others in pairs. (VVhen the bones com-
posing the skeleton are connected together by natural liga-
ments, they form what is called a natural skeleton; when by
wires, it is termed an artificial skeleton. The latter is the
common and most useful mode of articulation to the anato-
mist, as the joints can be easily moved and examined. The
skeleton has been called the bony frame work of the body,
because by its form and solidity, it not only retains every
part of the fabric in its proper shape, but also affords a hard
surface for the attachment of muscles, and the protection of
many important organs.) If we suppose a plane to pass
down from the top of the head through the middle of the skele-
ton, the latter will be divided into two equal portions, called
the right and left side of the body, which are perfectly alike
in shape and size. ^Those bones which are situated in the
centre, such as the spine and breast bone, and are inter-
sected by it, are said to be symmetrical,' because they are
divided equally ; the others, such as the bones of the arm
and leg, are in pairs.

64

PHYSIOLOGY.

THE HUMAN SKELETON.

t

£ The bone* of the head are 55 in number, a* follow* :

Fronlal, (On Front!*, a,) . . .1

Parictala, (Own Parictalia, ft,)

Temporal ..... 2

Occipital, (OB Occl[>iti«> ... 1

Bphenoidal, (Os Sphertoldc*, <*,) . . 1
Ethmoid, (Os Ethmoidcs) ... 1
Nasal, (Oeaa Naai, «,) • • • • 2

Malar, (Onsa malarum /,) • • 2

Lrfchrymal, (Oasa Luchrymalia,) . . 2
Upper Jaw bones, (Ossa maxillaria superiora) 2
Palate bones, (Otsa palatina) . . 2

Inferior turbinatcd bones, (Ossa turblnata) . 2
Vomer, ...... 1

Lower Jaw, (Oa maxillare inferius, A,) 1

Teeth, (Denies) .... 32

Tongue bone (Oa hyoldes) . . I

Total, 55 55

To these are sometimes added the proper bones of the car, contained in the tempo-
ral bone*.

Mallei, (hammer) . 2

Incudes, (anvil) . 2

Stapedes, (stirrup) . 2

Orbicularla, (round bones) 2

Total, "8 •

4. The trunk contains 57 boncs,'viz:

Vertebras, (a,) . . 21
Ribs, Co*to, «,/,#,) . 24

Breast bone, (Sternum, c, dt) 2
Hip bone*, (Otwa innoruinata, i,) 2
Rump bones, (Os sacrum, &,) 1
Coccygcal bones, (Ossa coceygln) 4

Total, 5T 57

5. The upper extremities contain 08 bonea/viz:

Collarbones, (Clavlculffi, «,) \' . 2

' Shoulder blades, (Bcapultu, b,) fjf . 2

Arm bones, (O«»a humeri, c,) fi,» . 2

Fore arm boneu, Radii ct ulnte, d, c,) . , 4

WrlHt bones, (O««a carpi,/,) . . 18

Hand bones, (Onsa mctacarpl, g, . . 8
Finger bones, (Phalanges digitorum maima, A, t, A,) 24

Thumb bones, (Onapolicis, /,)
Sessumoid bones, (Ossa vessamoidua)

i;
4

Total 68
6 The inferior cjxtntmiti^s contain 64 bones, viz:

Thigh bones, (Osoafemoris, a,) ; ; ... f
Knee-pans, (Patelie, ft,) . . ;r.* f

Shin bones, (Tibiw, c,) .... 2
SmalllKmoofthelegs, (Fibula) JM»;v . ' f
TarHal,(0»w tarsi, e,) . . . .14

Metalareal, (O«rfa metatarsi,/,) . . 10

Toe bones, (Phalanges digitorum pudli, A, i, A,) 28
Sessamoid, (Ossa sessamoldca) . 4

Total, "64

154

Grand Total "235"

66

PHYSIOLOGY.

THE HUMAN SKELETON. 67

7' The second plate represents a back view of the male skeleton,
while the first is a front view.

a. The parietal bone.

b. The occipital bone.

c. The temporal bone.

d. The cheek bone.

e. The lower jaw bone.

Neck and Trunk.

a. The bones of the neck.

b. The bones of the back.

c. The bones of the loins.

d. The hip bones.

e. The sacrum.

Upper Extremity.

a. The collar bones.

b. The blade bone.

c. The upper bone of the arm.

d. The radius.

e. The ulna.

f. The bones of the wrist.

g. The bones of the hands.

h. The first row of finger bones.
z. The second row of finger bones.
k. The bones of the thumb.

Lower Extremity.

a. The thigh bone.

b. The large bone of the leg.

c. The small bone of the leg.

d. The heel bone.

e. The bones of the instep.
/. The bones of the toes.

8. It does not fall within the plan of the present work to
give a description of the individual bones which go to make
up the skeleton ; this must be sought in treatises on anatomy.
Still there are many points connected with the subject of ex-
treme interest to every reflecting mind, to which the atten-
tion of the young may be profitably directed, particularly as
connected with the marks of wisdom and design in the Al-
mighty architect. If our curiosity is excited to see a piece
of ingenious machinery, or a new engine, shall we neglect to
raise the covering which displays in the body the most strik-
ing proofs of design, surpassing all art in simplicity and
effectiveness, and without any thing useless or superfluous.

68 PHYSIOLOGY.

9. If we compare the human body, as a work of art, with
any forms of human architecture, how vastly superior does
it appear. A watch, or a musical automaton are highly in-
genious specimens of inventive skill; but where is the
watch or the automaton that can, without repair, for the
space of 80 or 100 years, continue to perform its movements
with regularity and precision. And yet how much less
complicated is their machinery, how vastly more solid, and
durable the materials out of which they are formed !

10. If we examine a ship, we find it built for passive mo-
tion, and for resisting force externally applied ; a house or a
bridge is constructed for solidity and firmness, on the prin-
ciple of gravitation ; a railroad car is built for rapid motion,
and its wheels so adjusted, that they may not run off the
track ; but in the human body, we find not only securi-
ties n gainst the gravitation of the parts, provisions to with-
stand shocks and injuries from without, but at the same time,
the frame work is calculated to sustain an internal impulse
from the muscular force which moves the bones as levers, or
like a hydraulic engine, propels the fluids through the body.

11. The human fabric is admirably adapted to resist the
influences to which it is subjected ; in other words, there is
a nice balance between the power of exertion and the capa-
bility of resistance. A deer or a giraffe is never injured by
any leap which their muscular powers enable them to make,
because the inert power of resisting the shock, bears a rela-
tion to the muscular power with which they spring ; and so
it is in man. The elasticity of his limbs is proportioned very
accurately to his activity ; he readily resists shocks and im-
pulses upon the lower extremities, because they are adapted
to this end ; but if the same are applied to the upper, the
bones are broken or displaced, because they are adapted
rather for extensive and rapid motion, than for resisting vio-
lent shocks.

12. It has been truly remarked that the foundation of the
Eddystone light-house, the perfection of human architecture

THE HUMAN SKELETON. 69

and ingenuity, is not formed on principles so correct, as those
which have directed the arrangement of the bones of the feet ;
that the most perfect pillar is not adjusted with the accuracy
of the hollow bones which support our weight ; that the in-
sertion of a ship's mast into the hull is a clumsy contrivance
compared with the connexions of the human spine and pel-
vis ; and that the tendons are composed in a manner supe
rior to the improved chain cables of Bloxham.

13. As the head is the noblest part, and the brain the
most essential organ of the animal system, let us first direct
our attention to it. The brain is liable to injuries, not only
by sharp bodies touching and entering it, but by a blow upon
the head, which shall vibrate through it, without the instru-
ment piercing the skull ; and such a blow would more effec-
tually destroy a man's senses, than even if a sword pene-
trated into its substance. It is obvious, that if the bony
case were soft it would be easily pierced ; if of a brittle
nature, it would be easily cracked, and if very firm and solid,
like metal, it would ring and vibrate, and thus communicate
the concussion to the brain.

14. To obviate these dangers,(we find the skull composed
of two plates of bone, one external, which is fibrous and
tough, and one internal, so dense and hard, that it is called
by anatomists the glassy tdble% Now, as the brain is liable
to be hurt both by sharp and blunt instruments, the inner
table is hard and brittle, calculated to resist any thing pene-
trating ; while the outer table is tough to give consistence,
and stifle the vibration which would take place, if the whole
texture were uniform. This may be illustrated by an ex-
ample. If a soldier's head be covered with a steel helmet
or cap, the blow of a sword, which does not penetrate, will
yet bring him to the ground ; but if it be lined with leather
and covered with hair, the vibration is not transmitted to
the brain, and the wearer escapes without injury.

70 PHYSIOLOGY.

a, the external, 6, c, the internal table ; the intermediate cellular
texture, being soft and spongy, and conveying vessels and nerves from
one part to another.

15. It is worthy of particular remark, how the changes
in the structure of the bones of the skull are adapted to the
changes in the mind at different periods of life. /At birth,
the skull is soft and yielding, there being considerable inter-
vals between the adjacent bones of which it is composed ;
during childhood, it is highly elastic, so that the heedlessness
of that period may not endanger concussion, to which it is
so often exposed from falls ; and during youth and up to
manhood, the parts which are exposed to the contact of ex-
ternal bodies, are thicker, and the bones are still not firmly
consolidated at their sutures or seams, by which they are
united. As old age approaches, man grows more timid, and
is little disposed to feats of agility or activity ; something
teaches him that falls or blows, which could once be borne
with impunity, can no longer be encountered with safety ;
and if we examine the skull, we find the two layers of bone
consolidated into one. The result of which is, that con-
cussion at this period would be far more dangerous than in
early life, or at the age of manhood.

16. The sutures, or joinings of the bones of the skull, in-
terrupts, in a measure, the shock of the vibration produced
by external violence, and also prevent fractures from extend-
ing as far as they otherwise would do, in ofl'e continued bony
substance/ No one can examine the joinings of two of the
bones of the cranium, without admiring the minute dove-
tailing by which one portion of the bone is inserted into,
and surrounded by the other, whilst that other pushes its
processes out between those of the first in the same manner ;

THE HUMAN SKELETON. 71

and the fibres of the two bones are thus interlaced, as you
might interlace your fingers. But f this dove-tailing exists
only in the external plate^ on the internal surface the bones
are simply laid in contact.

17. Sir Charles Bell compares the human skull to the
dome of a building, which is acknowledged to be one of
the most difficult pieces of architecture. The dome of St.
Sophia, in Constantinople, built in the time of the Emperor
Justinian, fell three times during its erection ; and the dome
of the Cathedral of Florence, stood unfinished 120 years for
want of an architect. " Yet," says this writer, " we may,
in one sense say, that every builder who tried it, as well as
every labourer employed, had the most perfect model in his
own head." The difficulty in constructing a dome, is the
tendency of the weight of its upper part, to disengage the
stones from each other which form the lower circle, and
crowd out the circular wall on which it rests. This is
guarded against, either by soldering the stones into each
other, or by hooping them together by strong iron hoops.
The dome of St. Paul's, in London, is secured by several
strong double iron chains, linked together at the bottom and
along the sides of the cone. Now, In the bones which com-
pose the dome of the cranium, we find the edge of a bone at
the suture lying over the adjoining bone at one part .and
under it at another ; which, with the dove-tailing above-
mentioned, holds each bone securely in its placej But while
a dome is calculated to resist one kind of force, viz. that
acting perpendicularly, or in the direction of gravity, the
skull is equally calculated to resist forces operating in all
directions. Thus it can be shown, that no other form of
equal strength could be devised. When we reflect on the
strength displayed by the arched film of an egg-shell, we
need not wonder at the severity of blows which the cranium
can withstand.

72 PHYSIOLOGY.

a, a, the coronal, suture, from the Latin corona, crown, so called
from its situation on that part of the head, upon which the ancients
placed the laurel, or olive crown, given to the victors in their games.
It connects the frontal to the parietal bones ; 6, the sagittal suture,
from a Latin word, signifying arrow, from its straight course. It runs
from the middle of the frontal to the angle of the occipital bone, con.
necting the two parietals ; c, the lambdoidal suture, extending from
tne sagittal suture down to the base of the brain on each side ; e, et
the scaly overlapping of the temporal upon the parietal bones ; hence
called squamons suture.

18. The frontal bone is one of the most important in the
skull. It has been compared to a clam-shell from its shape,
and it forms the fore-head, part of the temples, and the roof
of the orbits of the eyes. Like the other bones, it is com-
posed of two plates, which often recede from each other,
immediately over the nose to a considerable distance, leaving
a space between them called the frontal sinuses. These
cavities communicate with the nose, and are supposed to
increase the intensity of the sound of the voice, and also to
render it more melodious. The change of voice, observable
in a person affected with a cold, is owing to a closure of the
passage between the nose and cavity, preventing the access

THE HUMAN SKELETON, 73

of the sound to this reverberating sinus. Snuff-taking, it
has been supposed, injures the voice by obstructing this
canal.

A front view of the frontal bone ; <z, a, fronted sinuses ; 6, the tern-
poral arch, beneath which lies the temporal muscle, which closes the
lower jaw ; d, the supra-orbitary hole for a psssage of a branch of the
fifth pair of nerves.

19. The shape of the head, as well as its size, varies great-
ly in different individuals. There are also national peculi-
arities in the form of the head, constituting a well-marked
national feature. Thus the Caucasian race, to whom we
belong, is distinguished by the beautiful oval form of the
head. To this race the most civilized nations belong, and
those which have ruled over the others. The Mongolian
race, which inhabits China and Japan, is known by its
prominent cheek bones, flat face, narrow and oblique eyes,
straight and black hair, thin beard, and olive complexion.

2*0. The negro race has a compressed skull, and a flat-
tened nose, a prominent mouth, and thick lips ; thus bearing
some resemblance in features to the monkey tribe. The
North American Indian has a very singular shaped head ;
it being high from the ear upward, and short from the front
to the back. The fore-head is not as largely developed as

74 PHYSIOLOGY.

in the Caucasian. The head of the Hindoo is much smaller
than that of the European, while that of the New-Hollander
is but little superior to that of the ourang outang, who roams
the same forests with himself. The New Zealanders have
heads nearly as large as the European ; but the fore-head
is low, and the great preponderance of size is in the back
part of the head,

21. The heads of the ancient Egyptians, as appears from
an examination of mummies, ^closely resembled in shape and
size those of modern Europeans. Some of our North American
Indians are in the habit of flattening their heads by binding
a piece of board on the fore as well as back part of the head,
in infancy. From this custom, one tribe among the Rocky
Mountains, has received the name of Flat Head Indians.
The Choctaw tribe were formerly in the habit of flattening
their heads in the same way ; but for some years past, they
have discontinued the practice. The heads of the different
European nations differ somewhat from each other ; but a
common type characterizes them all.

22. Not only the size, but the textwe of skulls among dif-
ferent nations varies. The grain of the New Holland skulls
is extremely rough and coarse ; that of the Hindoos, fine,
smooth, and compact, more closely resembling ivory. The
Swiss skulls are open and soft in the grain, while the Greek
are closer, and finer.- It has been suggested that there may
possibly be a corresponding quality of brain in the individu-
als, which may influence the mental, and consequently the
national character. This difference is generally attributed
to the effects of temperament.

23. (The bones of the cranium increase in extent, thick-
ness, and weight, from the commencement till the termina-
tion of their development in adult age ; but after this time,
and till old age, they always diminish in these three rela-
tionsv In advanced life, we often find them reduced to a
mere shell, and perhaps perforated in some places. They
thus become much lighter than in middle life. Meckel found

THE HUMAN SKELETON. 75

the skull of a female, seventy years of age, weigh but four-
teen ounces, while that of a girl, twenty years of age,
weighed twenty-four ounces. In the early periods of life,
the whole form of the head is much rounder than at an
advanced age ; owing, perhaps, to the small development of
the face, which the skull envelopes in every direction.

24. The size of the cavity formed by the bones of the
skull, is always proportional to the size of the organs it
lodges and protects. The shape and size of the cranium de-
pend on the brain, and not of the brain on the cranium. The
soft parts model and adapt to themselves the hard, and not
the hard, the soft> *The brain is formed before the case
which contains it, and it is not till after several years that
the bones of the cranium become perfectly consolidated. In
a child of ten years of age, afflicted with dropsy in the head
from infancy, and which was exhibited a year or two since
in this city as a great curiosity, although the head measured
thirty-two inches in circumference above the ears, yet nearly
the whole surface was protected by a bony covering.

25 The Spine. — However admirably the skull may
appear to be adapted to the objects for which it was obviously
designed, the spine exhibits no less evidence of wisdom and
skill in the divine Architect. In addition to the firmness
which was required in the joinings of the bones of the cra-
nium, a new principle is now introduced, viz. the attainment
of mobility or pliancy. -The spinal column indeed serves
three important purposes ; it is the great bond of union be-
tween all the parts of the skeleton ; it forms a tube for the
safe lodgment of the spinal marrow ; and lastly, it is a pillar
to sustain the hear&

26. In order (o accomplish these various purposes, the
back bone, so called, is composed of/twenty-four distinct
bones, or \vertebra, from vertere, to turn, ns the body turns on
them, which are /arranged into three classes, the cervical,
dorsal, and lumbar, The first seven are the cervical, because
they belong to the neck ; the next twelve are the dorsal, be-

76

PHYSIOLOGY.

cause they belong to the back ; and the last five are the
lumbar, because they are situated in the loins. The bones
comprising these classes, differ somewhat from each other in
shape ; a description of the dorsal pieces will prove sufficient
for our purpose.

A lateral view of the spine divided into its cervical, dorsal, and lura
bar portions.

27. Each of these twelve bones consists of a body, four
articulating processes, two transverse processes, and one spi-
nous process. The body is formed of soft and spongy bone,
which is circular before, flat towards the sides, hollowed out
behind into a crescent shape for containing the spinal mar-
row, and concave above and below for the accommodation
of the intervertebral substance. On the side of the bone are

THE HUMAN SKELETON. 77

situated the four articulating processes, each bone being con-
nected with the two immediately adjoining it. Two of these
processes are situated near its upper surface to articulate
with corresponding processes belonging to the bone above,
and two are placed near its under surface to join with those
of the bone below. The two superior articulating processes
of one vertebrae are thus connected with the two inferior
articulating processes of another, and these points of union
not only co-operate with the intervertebral cartilages in
keeping these two vertebrae together, but permit a slight
rotatory motion of the one upon the other* The spinous
process projects directly backwards from the body of the ver-
tebrae, and may be felt externally by passing the hand along
the spine ; the two transverse stand out on either side, and
have the ends of the ribs attached to them.

A vertebra of the neck ; a, body of the bone ; 6, the spinal process ;
c, d, the transverse processes double, showing circular holes for the
passage of the vertebral artery ; e, e. the superior ; /, /, the articular,
or oblique processes ; g, the spinal hole for the spinal marrow. The
roots of the articular processes are hollowed out above and below
into notches ; and these, when the bones are fitted together, form aper-
tures on each side of the spine, through which the nerves pass out from
the spinal canal.

7*

78

PHYSIOLOGY.

A vertebra of the loins ; a, a, their bodies, larger and more spongy
than those of the others ; b, b, 6, the superior ; c, c, c, the inferior ar-
ticular processes, strong and deep, the superior concave ; the inferior
convex ; d, d, d, the transverse processes, small and long, serving as
levers for the attachment of muscles ; e, e, the spinous processes,
strong, horizontal, and flattened at the sides; /, the spinal foramen.

28. The vertebrae, as I have stated, are not in contact,
but separated by a considerable interval, which is filled by a
peculiar gristly substance of a highly elastic nature, which
is pressed out from betwixt the bones, and therefore permits
them to approach, and play a little in the motions of the
body. This compressible cushion of cartilage and ligament
serves indeed the triple purpose of uniting the bones to each
other, of diminishing and diffusing the shock in walking or
leaping, and of admitting a greater extent of motion than if
the bones were in more immediate contact. These separate
vertebras are firmly bound to each other in such a way as to

THE HUMAN SKELETON. 79

admit of flexion and extension, and a certain degree of rota-
tion, while by their solidity and firm attachment to each
other, great strength is secured.

29. We can now readily perceive how great the influence
of these twenty-four joinings must be in giving elasticity to
the whole column, and how much this must tend to the pro-
tection of the brain. Indeed, were it not for the interposi-
tion of this elastic material, every motion of the body would
produce a jar to the delicate texture of the brain, and we
should suffer almost as much in alighting on our feet, as in
falling on our head.

30. But there is another very curious provision for the
protection of the brain, and that is the curved form of the
spine. By looking at the cut, you see that it is shaped like
an italic f. Now, suppose it were straight, and stood per-
pendicularly, it is evident that when we alighted on our feet
it would recoil with a sudden jerk, like a straight steel
spring pressed between the hands, from its extremities. In
such a case, the weight bearing equally, the spine would
neither yield to one side or the other, and consequently, there
would be a resistance, from the pressure on all sides being
balanced. |But shaped as it is, we find it constantly yielding
in the direction of its curves ; the pressure is of necessity
more on one side of the column than on the other, and its
elasticity is immediately in operation without a jerk. It
yields, recoils, and so forms the most perfect spring, admirably
calculated to carry the head without jar or injury of any
kind,

3 jl When we reflect that the spinal column is composed
of so many separate parts, so nicely adapted to each other,
and kept in place by such a complicated array of ligaments,
tendons, and muscles, we might expect that injuries and dis-
eases of the structure would be very frequent. But fortu-
nately this is not the case, except where undue restraint and
confinement are imposed ; and it is only within a few years

80 PHYSIOLOGY.

since at change has been introduced into the system of edu-
cation for young ladies," that the spine disease, so called, has
become a common affection.

32. Every one who has paid the least attention to physi-
ology, is aware that a certain degree of exercise is as neces-
sary to the growth and strength of the body, and of every
part of it, as nourishment itself; and that if such exercise
be withheld during the period of growth, the body never ac-
quires its due form and proportions, and often is permanently
crippled. How cruel it is, then, to repress that overflow of
life and energy, which nature has given to young creatures,
to prompt them to that exertion which is necessary to the
full development of their physical powers ; and instead of
allowing the young of both sexes to jump, and skip, and
dance, and play, as nature dictates, to curb all propensity
to such vulgar activity, for fear that they may not receive
the praise of being well-bred. How preposterous, unnatural,
and ruinous is the practice of confining delicate females for
hours together every day to sedentary employment, the sure
consequence of which will be, weakness of the body generally,
and of the back in particular, especially if the seat be a stool
which has no back, or even a narrow chair with a perpen-
dicular back.

33. The effect of such a practice is, that in consequence
of the fatigue induced by such a posture, the spine gives way
in some part and bends, and in a little time the curvature
becomes permanent. And often when a bend has taken
place in one direction, there immediately follows an opposite
bend above or below, to keep the centre of gravity of the
body always directly over the base ; the curve accordingly
thus becomes double, like an italic f, and the distortion is
rendered complete.

34. The means employed to remedy this affection almost
invariably make it worse. In the first place, strong, stiff
stays are put on, to support the back, as it is said ; and so.
they do, perhaps, while they are on ; but as they supersede

THE HUMAN SKELETON. 6 81

the action of the muscles, placed there by nature as the sup.
ports, they cause these to lose their strength | and when the
stays are withdrawn, the muscles are found toolitttK%t«ij3*
port the body. Other mechanical expedients maynowDe
employed, the back may be forcibly stretched by pullies, or
the patient may be kept all day and night lying on an inclin-
ed plane. The victim of fashion may next, perhaps, be
placed under the charge of a regular spine doctor, who, by
means of pulleys, screws, paddings, stays, and close confine-
ment, destroys what little chance there still remains of a
cure. A decline now sets in, and the sufferer sinks into an
early grave.

35. Dr. Arnott justly remarks, — " it would be accounted
madness to attempt to improve the strength and shape of a
young race horse or grey hound, by binding tight splints or
stays round its beautiful young body, and then tying it up
in a stall ; but this is the kind of absurdity and cruelty
which has been so commonly practised in this country to-
wards what may well be called the most faultless of created
beings." /This disease may always be prevented by suitable
exercise, and the same remedy so applied, as directly to ,
strengthen the affected part, will hold out the best prospect
of a cure. Boys never suffer from the spine disease, because
steel and whalebone in them are never made to perform the
office which God designed for the bones and muscles.

36. The Chest.— The thorax, or chest extends above from
the first bone of the neck, by which it is connected with the
head, to the diaphragm below, by which it is divided from
the abdomen. It is composed of bones, muscles, and car-
tilages, so disposed as to sustain and protect the most vital
parts, the heart and lungs, and to turn and twist with perfect
facility in every motion of the body, and to be constantly in
motion in the act of respiration, without the least cessation
during a whole life. In front, the chest is bounded by the
sternum, or breast-bone ; behind by the spinal column, or
back-bone, and at the sides by the ribs. Below, the

82 PHYSIOLOGY.

diaphragm forms a membranous partition between it and
the cavity of the abdomen. It is conical in shape, with its
apex above, where, indeed, it is so contracted, that there is
barely room in the aperture to contain the tubes which go
to the lungs and stomach, and for the larger blood-vessels
that go and come from the heart.

Thorax or chest ; a, the sternum ; b, 6, the spine ; c, c, the ribs, the
cartilages being in front.

37. The ribs are 24 in number,- twelve on each side, of
which/ the seven upper are united to the sternum by car-
tilage, and are called true rib&Ahe cartilages of the other
five are united with each other, and are not attached to the
sternum ; these are called false ribsfc all of them are con-
nected behind to the spinal column. The ribs increase in
length as far as the seventh, by which the cavity of the
chest is enlarged ; from the seventh, they successively dimin-
ish in length, thus diminishing the cavity. The direction

THE HUMAN SKELETON

83

of the ribs from above downwards is oblique, forming, as it
were, a bundle of hoops playing on each other.

38. The curve of the ribs diminishes considerably from
the first to the twelfth ; the sfecond, however, is usually more
curved than the first. The inferior ribs are very flat ; the
twelfth is sometimes straight. The external surface of each
rib is convex, the internal concave. Each rib on its outer
surface near the spine presents an oblique ridge, occasioned
by the insertion of a muscle ; and at this point there is a
curvature somewhat abrupt, called the angle of the rib.

Fourth rib ; a, vertebral extremity, called the head, which is connect,
ed with the bodies of the two contiguous dorsal vertebrae. At i, the
bone is contracted, forming the neck ; c, is the tubercle at the back of
the rib, which is articulated with the transverse process of the ver-
tebrae ; d, the angle ; e, the sternal extremity ; /, a groove for the inter-
costal vessels. This will serve for a general description of the ribs.

Twelfth rib, nearly straight.

r*

39. Sternum. —-Between the forward ends of the ribs,

directly in front of the chest, lies the sternum, or breast-
bone.) fit is light and spongy, depending chiefly for its
strength on the numerous ligaments which cover it. In tho
child, it is divided into eight pieces by cartilaginous portions,

84

PHYSIOLOGY.

which as life advances, are reduced to three ; and, in old
age, are united into one. It terminates below in a sharp-
pointed cartilage, which lies over the stomach, and may be
felt externally. It is somewhat hollowed beneath at its
upper end for the passage of the treachea or wind-pipe,
which lies directly under it ; and on each side there are
seven oval depressions for admitting the cartilaginous ex-
tremities of the first seven ribs.

40. The sternum in this cut consists of two bones. The
first is broad and thick above, and contracts as it descends.
It is convex before and concave behind. At the upper angle
a, the collar-bone is articulated ; b, the articular surface for
the cartilage of the first rib ; 6, for second rib ; e, d, e, f, g,
mark the articular surfaces of the 3d, 4th, 5th, 6th, and 7th
ribs ; h, the ensiform cartilage, terminates the lower extrem-

THE HUMAN SKELETON. 86

ity of the sternum. In old people, this cartilage is often
changed into bone.

41. The manner in which the ribs are attached to the
sternum by means of slips of elastic cartilage, is worthy of
particular notice, fit is to this circumstance that it is
owing, that the ribs are so seldom injured by blows and falls ;
for if they were wholly bone from one extremity to the other,
life would be endangered by any accidental fracture, and
even the rubs and jolts to which we are continually exposed,
would be too much for their delicate and brittle texture.
When we lean forward or to one side, the ribs accommodate
themselves not by a change of form in the bones, but by the
bending of the cartilages. It is owing to this elasticity that
the blows of boxers so seldom succeed in fracturing the ribs ;
as they yield in proportion to the violence of the force in-
flicted. But this is not the case in old age. Then the car-
tilages of the ribs become bony, and the whole arch unyield-
ing and inelastic ; so that blows which formerly would have
caused little or no injury, are now attended with fracture of
the rib. The influence of the elastic structure of the ribs,
in the action of breathing, is highly interesting and import-
ant, and will be fully explained when we come to treat of
Respiration. <

42. (The next division of the trunk is called the pelvis or
fom'n,1 which{consists of a circle of large firm bones, situated
between the lower portion of the trunk and the inferior
extremities? They are the sacrum, the coccyx, the ilium, the
ischium, and the pubis. The ilium forms the upper, the
ischium the lower, while the pubis is situated at the fore part
of the pelvis ; and each one of these bones contributes to
form the large and deep socket, for the head of the thigh
bone. {The pelvis not only affords lodgment for the organs
contained within its cavity, but it also sustains the entire
weight of the body, and furnishes sockets for the heads of the
thigh bones to roll in, and a broad surface for numerous mus-
cles to spring from,

8

PHYSIOLOGY.

The pelvis.

/

43. The last division of the body comprehends the upper

and lower extremities), The upper consist of the shoulder,
arm, fore-arm, and hand. (~The bones composing the shoulder
are two, the clavicle, or collar bone, and the scapula, or the
blade bonej |jThe clavicle, named from its resemblance to a
key, resembles the italic s, and extends across the upper part
of the chest, from the shoulder to the breast bone, and it
serves not only to sustain the upper extremity and connect
it with the chest, but also to prevent its falling forward upon
the thorax, and to afford a fixed point for steadying the arm
in the performance of its various actions.

44. f The scapula, or shoulder blade, is a large, flat, trian-
gular bone placed upon the upper and back part of the chest,
and extends from the second to the seventh ribs. It lies em-
bedded in muscles, and has no connection with any other
bone except the clavicle at a single point. It is separated
from the thorax by a double layer of muscles, on which it is
placed as on a cushion^ fit serves for the attachment of six-
teen muscles which go £o the ribs, the bone of the tongue,
the arm, the head, and the spine. It thus serves not only as
a support, but a fulcrum for every action of the superior
extremity.

THE HUMAN SKELETON.

87

Scapula, a, superior angle ; d, the glenoid cavity, or socket for the
round head of the arm bone ; m, the aeromion process : w, the coracoid
process, which serve to protect the joint ; /, the base ; g, the costa, or
inferior border, and 7i, the superior border of the triangle ; Z, the spine ;
o, the semi-lunar notch, for the passage of an artery, vein, and nerve.

45. As a general rule, in the joints, strength and security
are sacrificed, in some degree, to obtain great freedom and
latitude of motion. Accordingly, we find that the shoulder
joint, which allows of more extensive motion than any other*
is also more frequently dislocated. In the hinge joints, such
as the knee and ankle, such an accident is comparatively
rare. Where a bone is dislocated, a regularly educated sur-
geon should, if possible, always be employed to reduce it, as
there is great danger in trusting to a natural bone-setter, so
called, who is entirely ignorant of the anatomy of the parts.

46. The os humeri, or arm bone, is of a cylindrical shape,
and forms at the elbow a perfect hinge-joint with the two

88 PHYSIOLOGY.

bones of the fore-arm, called radius and ulna.\ |This bone is
susceptible of all kinds of motion, elevation, depression, ad-
vancing, retreating, circumlocution, and rotation Its scap-
ular extremity is lodged in a strong membraneous bag, called
the capsular ligament, and when the arm is raised up, the
bone slides downward in the glenoid cavity, and thus distends
the lower part of the capsular ligament. In every motion of
the arm, except in carrying it backwards, the scapular
readily moves or follows it ; it is therefore during motions of
the latter kind, that dislocations of the joint are most apt to
occur. If, therefore, the scapula could always follow the
motions of the arm, it would rarely be forced out of its
socket, and then only by extreme violence.

47. In the fore-arm we find two kinds of motion, one at
the elbow, backward and forward, and also a rotary motion, by
which the palm is turned upward or downward, as occasion
requires. These motions are called supination and pronation.
Flexion and extension of the arm are performed by means of
the ulna, which being articulated, with the os humeri, by a
hinge joint, carries the radius along with it in all its move-
ments. Now while the larger part of the ulna is above, the
larger part of the radius is below, so that while the former
presents a large surface for articulation at the elbow, the lat-
ter does the same at the wrist, and this inverse arrangement
also contributes to the uniform diameter of the fore-arm.
While the fore-arm is thus attached to the os humeri, the
radius is attached to the wrist ; so that when we turn the
palm of the hand, the radius rolls on the ulna carrying the
hand with it. Indeed so admirable is this contrivance, that
both motions may be performed at the same time, for while
we are bending the arm, we may also be rotating or turning
it upon its axis. To facilitate these motions, it will be
observed that near the elbow, a tubercle of the radius plays
into a socket of the ulna, whilst near the wrist, the radius
finds the socket, and the ulna the tubercle.

THE HUMAN SKELETON.

89

gt the ulna ; a, the radius.

48. It has been remarked that the ulna has a hooked pro-
cess, the olecranon, e, which catches round the lower end of the
humerus; forming with it a hinge joint. The radius also, has
a neat, small, round head, &, bound to the ulna by ligaments,
which, as it turns, carries the hand, which is attached to its
lower extremity along with it. Now in animals that have
solid hoofs, such a motion would be useless and a source of
weakness, according!/ we find these bones united together
and consolidated in such animals. By an examination of
these bones alone^the anatomist is able to determine whether
the animal to which they belonged, perhaps thousands of
years ago, was carniverous or graminiverous, that is,
whether he was an animal or a vegetable feeder ; whether he
had claws or hoofs. If he finds merely the end of the radius,
and notices in it a smooth depression where it bears against
the humerus, and the smooth surface that turns on the cavity
of the ulna, he concludes at once, that the animal had a paw,
and a motion of the wrist which implies claws. It was in
this way that Cuvier and Buckland made those singular and
interesting discoveries in relation to antediluvian fossil
bones, which have given such importance to geological
researches.

49. But let us examine this point a little further. If the
8*

90 PHYSIOLOGY.

examination of a single bone, or even the end of a bone, like
that of the radius, shows that the animal to which it belonged
was carniverous, like the tiger, lion or leopard, it also shows
the form of all the other bones ; not only that the animal had
teeth to rend his prey, and claws to hold it, but a spinal col-
umn to admit of such motion, such writhing and turning as
is necessary to secure it, and such a stomach and intestines
as are adapted to digest it, in short, such as belong to the
carniverous class. How beautiful is that process of reason-
ing, and how interesting that science which enables us from
a small portion of a skeleton, to determine the existence of a
carniverous animal, of a fowl, or a bat, a lizard, or a fish ;
which teach us the wisdom and the extent of that plan, which
adapts the members of every creature to its proper office ;
which exhibits a system extending through the whole range
of animated beings, whose motions are conducted by the ope-
ration of muscles and bones.

50. Twenty-nine bones enter into the composition of the
human hand, of which eight constitute the wrist. The meta-
carpal bones support the fingers, and are four in number, the
thumb being directly articulated with the wrist. From this
arrangement there results great strength, mobility, and elas-
ticity. Indeed, it may be said, that on'the length, strength,
free lateral motion, and perfect mobility of the thumb, de-
pends the power of the human hand. In strength it is said
to be equal to that of all the fingers, hence it is called pollex,
from " pollere" to have much strength. If we examine the
thumb of the monkey, we find that it extends no farther than
to the root of the fingers, p^he fingers would be compara-
tively of little use, were it not for the fleshy bed of the
thumb. |

THE HUMAN SKELETON. 91

Bones of the hand.

51. (The bones of the lower extremity consist of the thigh,
leg and foot.! The thigh bone (os femora,) is the longest
bone of the human skeleton, and is remarkable for its great
strength, supporting, as it does, the whole body, and often
several hundred pounds in addition. ^ The hip joint is a perfect
specimen of the ball and socket joint. This is for the pur-
pose of giving great extent and variety of motion to the legs,
as in walking. The end of the hip bone is perfectly round
like a ball, and covered with a smooth, shining cartilage ;
and this is received into a deep cup, also lined with cartilage
and moistened with the synovial fluid. Besides all this,
there are strong ligaments all around, binding the bone
firmly in its place, so that it is a very rare thing for it to be
dislocated1.

52.^ The knee is a hinge joint of singular construction. The
rubbing parts are flat and shallow, and therefore would
easily get out of place, were it not for the very strong liga.
ments which surround it. When the ligaments on the inside
of the joint are too weak, a person is said to be knock-kneed,
because the knees knock together. In weakly children, this
deformity may frequently be cured by exercise. It can also
be shown that, owing to the air being completely shut out of
the joint, forming what is called a vacuum, the bones of the
knee are held together by a constant pressure of the atmos-
phere equal to sixty or seventy pounds. On the fore-part of

92 PHYSIOLOGY.

the knee, is a movable bone of a flat, round shape, called pa-
tella, or knee-pan, over which a cord or tendon passes, which
is made by a contraction of all the muscles on the fore part
of the thigh. This serves as a pulley, and enables the mus-
cles to act to greater advantage, by increasing the distance
of the rope from the centre of motion.

53. \ The leg below the knee, is composed of two bones,
tibia and fibula, of a three-cornered or angular shape,
like those of the fore-arm ; and the design no doubt is, to
form a pillar of greater strength than one bone would
make ; and also to furnish a greater surface for the origin
and attachment of the numerous muscles required for the
feet. ;f The ankle, like the wrist, the elbow, and the knee, is
a perfect hinge of great strength. In front of it there is a
narrow strap, or ligament, which binds down the cords
which go to move the toes. There is a small groove just
within the inner ankle, for the passage of a tendon, exactly
like a little pulley) The heel is a lever for those strong mus-
cles to act by, which form the calf of the leg. It is the ac-
tion of these muscles, pulling on the heel, that lifts the body,
in walking, dancing, standing on the toes, dec. In the negro,
the heel is longer than in any other race of mankind.

54. The bones of the foot are divided into the tarsus,
which is composed of seven bones, reaching from the heel
to the middle of the foot.) The metatarsus consists of five
long bones, parallel to each other, which extend from the
tarsus to the roots of the toes. The bones of the toes are
called phalanges, from being in the form of a phalanx.
There are in all thirty-six bones in the foot, and as each
bone forms a joint, and as each joint not only permits
motion, but bestows elasticity, the obvious design of this
number is to render the foot elastic, and thus save the body
from shocks... It should be recollected that each bone is
tipped with cartilage, that the fibres composing cartilage
are disposed longitudinally or perpendicularly to the surface
of the bone and the pressure made upon it ; thus acting like

THE HUMAN SKELETON.

93

an infinite number of springs of the most delicate structure.
Besides this, the foot is a double arch ; [it is arched from
the toes to the heel, and from side to side, and the bones are
so wedged together, and bound to each other by ligaments,
that solidity is combined with elasticity and lightness.^

55. In reviewing the human skeleton, we cannot but re-
mark the nice adaptation of all the parts to each other, and
to the shares which they have respectively to bear ; how
the objects of strength and lightness are combined, and how
the nature and strength of material in different parts are so
admirably adapted to the purposes which the parts are
designed to serve. No one can contemplate the marks of
wisdom and design displayed in the osseous fabric, without
being led insensibly to acknowledge the hand of an all-wise
and benevolent Master Builder.

94 PHYSIOLOGY.

Questions. — Of how many bones does the human skeleton consist ?
How are they divided ? What is a natural skeleton ? What an arti-
ficial ? What uses does the skeleton serve ? What bones are said to
be symmetrical ? How many bones are there in the head ? — -in the
trunk I — :in the upper extremities ?r-«r-m the lower ? How does the
skeleton compare with works of human art ? How is the brain pro-
tected from injuries ? How many plates do the bones of the skull
contain ? What changes does age produce in the bones of the
skull ? What are the sutures ? — what their use ? To what does
Sir Charles Bell compare the skull ? How does it resemble a dome ?
What are the principal sutures ? Describe the frontal bone. What
is said of the national peculiarities in the shape of the head ?
What shaped heads had the ancient Egyptians ? Does the texture
of skulls vary ? What changes occur in the thickness and weight
of the bones of the skull ? What is said of the cavity of the
cranium ? What is formed first, the brain or the skull ? What uses
does the spine serve ? Of how many bones does it consist 1 What
are they called ? How divided ? Describe a vertebra. What sort of
substance is placed between the vertebrae ? — its use ? Why is the
spine curved like an /? What is the spine disease? — its causes? —
its cure ? f What effect have mechanical remedies ? Do boys ever
have it? Describe the thorax. How many ribs are there? What
are true ribs ? What false ? Which are the largest ? Where is the
sternum situated ? Describe it. What is the use of the cartilages
between the sternum and ribs ? What is the next division of the
trunk ? What is the pelvis ? — Of how many bones composed ? What
its use ? The last division ? Where is the clavicle ? — its use ? DCS-
cribe the scapula, — its use ? Is great freedom of motion compatible
with great strength in a joint? Describe the os humeri. Of how
many kinds of motion susceptible ? Describe the fore arm ? — the radius ?
— the ulna. What is the contrivance for rotating the arm ? What is
the olecranon 1 — its use ? In graminivorous animals, how are these
bones constructed ? How can the anatomist tell to what kind of
animal any bone belongs? How many bones are there in the hand??-
— how many in the wrist ? ^ What is said of the thumb ? — Of the
fingers ? What are the bones of the lower extremity? Describe the
hip joint ? — the knee. Does the pressure of the atmosphere affect the
joints?' Describe the leg below the knee? — the ankle. How are the
bones of the foot divided? How many bones in the tarsus?— the
metatarsus ? — the phalanges lj— the foot ? What is the use of so many
bones ? What is the use of the arched form of the foot ?

CHAPTER VII.

- -

PROPERTIES OF ANIMAL BODIES.

1. There are various properties which distinguish living
from dead animal matter. jBoth, in common, possess certain
'physical properties, such as weight, extensibility, flexibility,
&c. ; but" Jiving matter has certain physiological or vital
properties peculiar to it.| It is these which bring it under
the influence of external agents.

2. ^A.11 the phenomena of life are the effect of impressions
made upon the various organs of the body, by external or
internal agents^ and each organ has its own proper sti-
mulus. Thus the eye is stimulated by light ; the ear by
sound, the nose by odours, the organs of taste by condi-
ments, &c.

3. (The chick in its shell is developed by the influence of
heat J the seed germinates under the combined effect of
warmth and moisture ; and so the growth of the human
body requires the application of the appropriate stimulants,
such as food, drink, air, exercise, &c.

4. Every tissue and organ has its own mode of activity.
For example, the lungs react under the influence of the air ;
the heart under that of the blood ; the muscles under that of
the will ; the stomach under that of food, &c. Every gland,
though supplied by the same blood, is excited to secrete or
form that particular fluid for which it was so designed ; and
why the liver does not secrete urine and the kidneys bile, it
were useless to inquire.

5. This property of living matter has three principal
modifications in the solids and fluids, which have been called

{sensitive, motive, and alterative.] fey the sensitive powers, are
meant sensibility and its modifications^ (he motive are con-
tractility and expansibility '$ jthe alterative are those which

96 PHYSIOLOGY.

preside over the formation and nutrition of the different
organs and tissues of the bod)|

6. [Sensibility belongs exclusively to animals provided with
a nervous system) It enables us to receive impressions
from external objects, or from changes going on in our own
bodies ; and to the accuracy of this power, we owe our
ability to guard ourselves against the influence of noxious
agents.

7. .' Sensibility may be divided into two kinds, general and
special^ By general sensibility is meant, that universal sense,
of which we are conscious over the whole body, in the
mouth, &c. The same also exists in the interior of the
body, and conveys to the mind a knowledge of the wants of
the system ; and when disease attacks any part, it immedi-
ately apprizes us of the danger, in order that we may take
early measures to remove itj (By special sensibility, we
mean that property which renders the eye sensible to light,
the ear to sound, &c. Every organ has its own special
sensibility

8. (The brain is the common centre of sensibility, both
general and special) No impression can be felt on any part
or organ, unless it has a connection with the brain. If the
nerves going from that organ are divided, or if their function
is lost from palsy or any cause whatever, there can be no
sensation perceived, as none is excited.

9. j|By perception is meant, the faculty which the brain
has of perceiving or taking notice of these impressions}!
Perception and thought then, are owing to the property of
matter, called sensibility. Without it, we would be like
stocks or stones, alike unconscious of pleasure or of pain.

10. According to some physiologists, there, is another
kind of sensibility, which is termed organic. This resides
in the several internal organs, where it is called into exer-
cise, and does not require the action of the brain.) It de-
pends for nervous influence upon the great sympathetic nerve.
That such a kind of sensibility exists is very probable, but

PROPERTIES OP ANIMAL BODIES. 97

we have no proof of its existence in our own feelings and
consciousness, as we have of the other kinds of sensibility.

11. p5y organic sensibility, we mean that the stomach is
sensible to food, the heart to the blood, ice. ; and that this
feeling is confined to the organ and not transmitted to the
brain. It presides over the process of digestion, circulation,
secretion, absorption, and nutrition.

12. Although the internal organs of the body are not
sensible to the presence of the fluids or solids with which
they are usually in contact, yet if foreign bodies are brought
in contact with them, or substances calculated to injure
them, we are immediately made sensible of it. Thus let a
person drink a quantity of brandy, or spirits, to which he
is not accustomed, and he will at once feel a sensation of
heat in the region of the stomach, altogether unnatural to
that organ. This proves that ardent spirits are not designed
for the drink of man, and are therefore hurtful.

13. Certain parts of the body, which, in a healthy state,
are nearly insensible ; yet, by disease,{become the seats of
acute pain) This is particularly the case with the bones,
cartilages, and ligaments — parts usually wholly destitute of
feeling.

14. ^Contractility, or the property of contracting, is the chief
motive power of the system^ It exists in various degrees, in
different kinds of animal matter. {That element which pos-
sesses it in the greatest degree is Jibrin p and those tissues
which have the most fibrin, have the greatest degree of con-
tractility. The same is true of muscles, for the heart, which
is in constant motion, is almost pure fibrin.

15. It is supposed that the coagulation of the blood is
owing to this contractile power of fibrin. In the living
vessels, the blood is kept fluid by the vital influence of the
walls of the vessels themselves ; but as soon as it is with-
drawn from this influence, the particles of fibrin immediately
rush together and form a solid mass.

16. Those tissues which contain but little fibrin and are

9

98 PHYSIOLOGY.

made up mostly of gelatine, as the membranes, cartilages,
skin, vessels, &c., have but a slight degree of contractility ;
that they possess it, in some measure, is evident from the
contraction of blood-vessels by the application of stimulants.

17. There are two modifications of contractility); one of
which depends for its exercise on the brain, and the other
does not. For example, if we wish to bend the arm, we have
but to transmit to the muscles of the arm, through the nerves
with which it is supplied from the brain, a volition, or act
of the will, to that effect, and the arm bends. Here we per-
ceive that the influence of the brain is necessary to contrac-
tility or motion.

18. {When certain muscles are deprived of this power of
contracting, they are said to be paralyzed, or the limb is
called paralytic.} (When they have it in excess, they are in
a state of spasm, or convulsion^ We see such a state often
brought on by excessive drinking. There is no cure for this
but by entirely breaking off the habit.

19. The other kind of contractility belongs to every part
of the body. It does not depend for its existence on the
brain, nor is it at all under the influence of the will, or
accompanied with consciousness. Thus the heart and the
stomach contract constantly under the application of their
proper stimuli, but the brain is not conscious of it ; their
action is entirely beyond its jurisdiction. This form of con-
tractility has been called insensible.

20. It is owing to the insensible, organic contractility,
that the blood circulates in the capulary vessels ; the lymph
and the chyle in the absorbents and lacteals, and all the
secreted fluids through the vessels that prepare them. In
all animals destitute of a heart, the fluids can only be moved
by this insensible contractile power. A similar force is
supposed to exist in the vessels of plants.

21. These two kinds of contractility, viz., the sensible
and insensible, have been compared to the hour and minute
hands on the dial of a clock, which are both moved by the

PROPERTIES OF ANIMAL BODIES. 99

same power ; yet the motion of one is insensible to the eye,
while that of the other is distinctly visible.

22. {By means of the alterative powers, all the changes
which take place in the composition of the solids and fluids
of the body are effected. By these, the food is changed into
chyme, and then into chyle ; chyle into blood, and blood into
bone, muscle, cartilage, &c. By these, animal heat is pre-
served uniform ; and the solids preserve their cohesion, and
the fluids their fluidity} In short, it is these powers that
for a time successfully resist the agency of chemical laws.

23. Some physiologists attempt to account for every thing
that takes place in the body, on chemical or mechanical
principles. But the vital laws, or organic forces, form com-
pounds which could never be produced by chemical affinity.
In fact, they are antagonistic forces, fighting against each
other. The chemist can decompose blood, bile, saliva, al-
bumen, gelatine, and fibrin, but he can not re-form one of
them. He can no more make a piece of bone, than he can
make a diamond.

24. The physical properties of the animal tissues are
usually reckoned as five in number, viz.^elasticity, extensibil-
ity, flexibility, imbibition, and evaporation.}

25. f Elasticity is one of the physical properties of animal
matter. It is that power which tends to restore parts that
have been stretched OF extended to their former state. It is
possessed in the greatest degree by the cellular tissue, which
enters largely into the composition of all the structures in
the body. All the organs and membranes of the body are
in a constant state of extension. All the hollow organs, as
the stomach, gall-bladder, and blood-vessels are kept distend-
ed by the volume of their contents. The extensor and
flexor muscles, when in a state of inaction, are in a state of
extension. If such were not the case, all the organs would
contract and shrink to a comparatively small size)

26. (When the stomach is empty, its sides contract till
jy almost touch each other. When a muscle is cut, the

100 PHYSIOLOGY.

wound gapes open, owing to the two parts receding. The
cartilages of the ribs are highly elastic, and this facilitates
much the function of respiration. The same is true of the
substance of the lungs themselves. The cartilages between
the bones and the spine are highly elastic. The loss of this
elasticity makes a difference of an inch or more between the
height of a man in the morning and at evening. It is
not unusual for a very tall person to lose an inch in height
by dancing all the evening. x During sleep, the force of
elasticity restores these cartilages to their usual dimen-
sions.

27. The elasticity *of the arteries contributes much to the
circulation of the blood. The blood as it is forced into these
vessels, is constantly reacted upon, by their elastic coats,
and in this way driven along towards their termination in
the capillary vessels. The same power assists in circulating
the lymph and chyle in the vessels which contain them. It
is the last function that ^ceases to act, and it is not wholly
destroyed even at death./

28 ^Flexibility and extensibility are properties existing in
various degrees in different parts of the body. The liga-
ments, or little bands, which tie together the bones, are more
flexible than any other part. By observing the astonishing
feats of the rope-dancer, we see how flexible these parts are.
The tendons which connect muscles with the bones they
move, are capable of little, if any extension. If they stretch-
ed, when the muscles to which they belong contract, the
(imbs would not move, and the moving force would thus be
lostj

29. Imbibition, is another power possessed by living animal
bodies. ^.It means the act of drinking in, or taking up fluids,
which may be in contact with any part.? For example, if a
certain fluid be placed in contact with an animal tissue, it.
will penetrate into the latter, as water would into a sponge,
and this property is possessed by all the soft tissues to a
greater or less extent. All the serous membranes absorb

PROPERTIES OF ANIMAL BODIES. 101

with great facility. The epidermis or cuticle of the skin
permits fluids to pass with difficulty. That water is taken
up in considerable quantity, however, is proved by the fact,
which has often been proved by experiment, that a man in-
creases in weight by remaining for a considerable time in a
warm bath.

30. The following experiments prove the nature of this
process. |lf we fill the intestine of a chicken with milk, and
place it in water, we shall see the milk pass through its
coats into the water, and the water will pass through in an
opposite direction to supply its place. In the same manner,
if a bladder be filled with hydrogen gas, and suspended in
the air, in a short time it will be found to be mixed with
atmospheric air, which has passed through its coats. The
result of all the experiments on this subject seems to show,
that when any cavity containing a fluid is immersed in
another fluid less dense than the former, there is a tendency
in tfye membrane to expel the denser, and absorb the thinner

31. Many of the animal tissues are indebted for their
physical properties to the water they imbibe. If they are
deprived of this water, they are unable to perform their
proper office and function, until they are again supplied with
it. Hence one important reason why the system craves
water, and why the want of it produces such distressing
effects.

32. (By the functions of man, we understand the opera-
tion of the various organs^ in other words, his vital actions.
fyife is made up of a constant series of these actions, from
the period of birth to the moment of dissolution. Physiol-
ogists have attempted to define life ; but the best definition we
can give is, that^t is an assemblage of actions^ Indeed, the
essential nature of life is an impenetrable mystery, and not
a proper subject for philosophical inquiry. As the fluids
are as mucK endowed with life as the solids, it cannot be
said that life is the "effect of organization ;" besides, a

9*

102 PHYSIOLOGY.

dead man has the same organization as when alive. It
is, therefore, far better to confess our ignorance, and say
with John Hunter, — " life is a property we do not under-
stand."

33. All the actions or functions of the body are mutually
dependent on each other. They constitute a circle, with-
out beginning or end. The motion of the blood depends on
the action of the heart and arteries ; the action of the heart
and arteries depends on the presence of blood. The heart
cannot act without the action of the lungs ; the lungs can-
not act without the action of the heart. Neither lungs nor
heart can act without the influence of the brain ; the brain
would have no influence, were it not for the action of the
lungs and heart.

34.^ Thus the steam of a steam-engine works a bellows
which blows a fire that produces the steam J It would be as
difficult in this case, as in that of the animal functions to
say, which of these might be easiest dispensed with. If we
spare the bellows, the fire will not burn ; if we spare the fire,
the steam will not be raised ; if we spare the steam, the bel-
lows will not be worked ; so that if we spare either fire, bel-
lows, or steam, the machinery must stop* So it is in the
human body.

35. The functions which fall within the scope of this
work to notice, may be divided into three classes ; l( vital ;
2, nutritive ; and 3, sensorial. ) {The vital functions are those
which are every moment essential to preserve lifejfc They
also may be considered as three in number, viz : innerva-
tion, circulation, and respiration ; or the functions of the
nervous system, those of the heart, and those of the lungs.

36. fThe nutritive functions preside over the growth and
nutrition of the body* By their influence, the food is as-
similated, and becomes a part of our structures ; while all
the waste materials and worn-out elements are expelled from
the system. It thus embraces four functions ; digestion,
absorption, nutrition, and secretion.

PROPERTIES OF ANIMAL BODIES. 103

37. fThe sensorial functions are sometimes called the
functions of relation, because it is through them that we
hold communication with the external world. They com-
prise the sensations, intellectual operations, and voluntary
motions^ (It is the sensorial functions that raise man above
all other animals| In proportion as they are more or
less perfect, organized beings ascend or descend in the
scale of existence. In the lower animals, they are limit-
ed to the circle of physical wants ; but in man, they con-
fer moral and intellectual faculties, which are his noblest
attributes.

38. These functions have the brain as their common
centre. They can be improved to an almost indefinite
degree by education and habit. We see this in the perfec-
tion which some of the senses acquire when others are lost ;
in the gigantic intellect of a Newton or a Locke, whose
mental efforts at first were probably as weak as those of
other men. In all such cases, individuals acquire superi-
ority chiefly by education and constant practice.

Questions. — How is living animal matter distinguished from dead ?
What properties are possessed in common ? What are th<3 phenomena
of life owing to ? What developes the chick ? What properties does
living matter possess ? What is understood by the sensitive powers ?
— the motive ? — the alterative ? What characterizes animals provided
with a nervous system ? How many kinds of sensibility are there ?
What is meant by general sensibility ? — by special ? What is tho
common centre of sensibility ? What is perception ? What is organic
sensibility ? Are the internal organs sensible to the presence of their
contents ? How are such parts affected by disease ? What is con-
tractility ? What element possesses it in a great degree ? How many
kinds of contractility are there ? When is a limb said to be paralytic ?
When in spasm ? What are the alterative powers ? What their use ?
Is the body under the influence of chemical laws f-" What are the
physical properties of the animal tissues ? What office does elasticity
perform ? Describe its operation in cartilages, arteries, &c. What
are the uses of flexibility and extensibility in the animal body ? What
is imbibition ? Do the serous membranes absorb ? • What experiment*

104 PHYSIOLOGY.

prove imbibition ? What are understood by the functions of man ?
What is life? Are the fluids alive as well as the solids J" Are the
functions of the body dependent on each other ?-' illustrate this de-
pendence ? How are the functions divided ? What are vital func-
tions ? — nutritive ? — sensorial ? What raises man above all other ani-
mals?

CHAPTER VIII.

BELATION OF ANIMAL BODIES TO HEAT, LIGHT, AND
ELECTRICITY.

1. The relations which animal bodies have to heat, light,
and electricity, are highly interesting, and worthy of particu-
lar notice. vTo a certain extent, all animal bodies have the
power of regulating their own temperature! Many of them
develope electricity ; and some of them, like the lightning-
bug, and other insects, can produce light. These are singu-
lar properties of living animal matter.

2. SThe heat of animal bodies is produced within them-
selves.; It is not received from without, nor can it be ; as
the natural temperature of the body is near 100 degrees ;
even when the temperature of the surrounding air is below
zero. How this is produced we shall inquire when we come
to treat especially of animal heat.

3. Plants have a lower temperature than animals, and the
higher animals are in the scale of organized beings, so much
the more animal heat do they produce. Thus the tempera-
ture of what are called the cold-blooded animals, such as
fishes, 6s not much above that of the water in which they
live ; and Although they do not often freeze to death in the
winter, yet they become so torpid as to be incapable of mo-
tion.

4. It is a favourite sport in New England in the winter
season, to hunt, -on skates, for the pickerel, and other fish,
which abound in the lakes and ponds ; and when found to
take them, by cutting through the ice with a hatchet ; and
to spear them by torchlight at night. Now had they the
faculty of producing animal heat, like quadrupeds, or birds,
or man, they would not be ^rendered torpid and incapable of

>tion by cold.

106 PHYSIOLOGY.

5. Living animal bodies have not only the faculty of pro-
ducing heat, but they can also resist heat of a much higher
temperature than their own bodies. The heat of the body
is kept at its usual standard of 98 degreesjby the exhalent
vessels of the skin, which absorb by means of the perspira-
tion tho excess of caloric, and fly off with it in a state of
vapour^

6. In very hot weather, those functions of the body, such
as digestion, nutrition, and secretion, on which tho produc-
tion of animal heat depends, are weakened by the excessive
heat, so that in fact less caloric is produced in the system
than in cold wcathcrX This is a wise provision of Providence,
that when much internal heat is wanted to guard against the
cold, it is produced ; when less is needed, on account of the
warmth, the system generates less.

7. Animal bodies are also capable of developing electricity ;
as most of the bodies which surround us are conductors of
the electric fluid, it generally passes off as fast as it is
formed. Sparks of fire, however, are often seen in winter,
on taking off in the dark, silk dresses or stockings, or flannel
drawers. Some physiologists maintain that the nervous
power is nothing but the electric fluid ; but though this may
not be admitted, there is a very close analogy between them.

8. It has also been found that needles plunged into the mid-
dle of a nerve, become magnetic, and are capable of att r;i i- 1 i n •;
light substances, such as pieces of paper ; and a physiologist
by the name of Weinhold says, that he has seen sparks
obtained by bringing tho divided ends of a nerve together.
Muller mentions in his late work on Physiology, that cffi-
cient galvanic piles can be constructed from organic sub-
stances, without any concurrence of metals. Concentrated
solutions of organic substances were spread upon thin paper,
and with disks of this, paper piles constructed, the t\\o l;nvrs
of different substances being separated by two thicknesses of
paper ; electricity was developed by these piles, and tested
by an electrometer. It would seem from these experiments,

RELATION OF ANIMAL BODIES TO HEAT, &C. 107

that the nervous system is capable of developing electricity,
under the influence of vitality.

9. Certain fishes, such as the torpedo, the electrical eel,
and live or six other species, are provided with special organs
for the production of electricity^ Tin the torpedo they consist
of a large number of prisms, of from three to six sides, stand-
ing close together, near the gills of the fish, and perpendicu-
lar to the surface. They are composed of membranous
tubes, divided into numerous transverse cells, abundantly
supplied with blood vessels and nerves. These vessels arc
filled with a fluid of an albuminous nature. These organs
are connected with the brain by three large nerves on each
side,)

10. In the gymnotus the electrical apparatus may be com-
pared to a battery of galvanic troughs. Two of these are
found on each side of the spine, separated from each other by
a long ligament, and extending the whole length of the fish.
They arc composed of horizontal membranous plates, sepa-
rated from one another by a small interval, and crossed in a
perpendicular direction by membranous partitions, so as to
form a great number of cells, which arc filled with a gelati-
nous fluid. These organs receive numerous branches and
nerves from the spinal marrow.

11. The resemblance of these organs to the galvanic pile
is very striking. The latter consists of alternate plates of
copper and zinc with a fluid between them. Thus we have
in these fishes alternate layers of membranous partitions and
albuminous fluid. But is is worthy of particular notice that
these organs lose their electric powers if tho nerves which
supply them arc divided. There can bo no doubt then, that
the electric shock which they give is a vital act, depending
on a nervous influence, and under the control of the animal's
will.

VJ. Tho sensation produced by the shock of an electrical
fish, is also similar to that of common electricity. It is pow-
erful enough to kill small fishes, and is the animal's weapon

108 PHYSIOLOGY.

of defence. Sparks also have been seen to attend the dis-
charges ; and the shock has been communicated through a
chain consisting of several persons with their hands joined.

13. Common electricity, and that produced by the organs
of electric animals, are generally believed to be different, but
it has lately been discovered by Dr. Davy, that the electric
organs of the torpedo affect the galvanometer, render needles
magnetic, and decompose waters

14. Many animals as well as plants are endowed with
phosphorescent properties. Every person almost, has seen
rotten wood, or dead fish, shine in the dark ; such are phos-
phorescent. ,This phenomenon is probably owing to the
fact, that during the decomposition of animal or vegetable
matter there is formed a highly inflammable compound of
carbon, hydrogen, and oxygen, which like phosphorous, burns
at the ordinary temperature of the air, with an evolution of
light.

15. But several living animals exhibit luminous appear-
ances. Many of the lower order of animals that inhabit the
sea, and some fishes, are phosphorescent.i It is this that
causes the luminous appearance of the ocean in warm cli-
mates. If a vessel be filled with sea*. water containing these
animalcula they immediately become phosphorescent, on
shaking the vessel.

16. It is not uncommon to find insects which have the
faculty of phosphorescence in a high degree. It is supposed
to reside in a peculiar albuminous principle, secreted by the
animal, and that it requires for its manifestation atmospheric
air and a certain degree of heat. It is evidently under the
control of the animal's will, and probably , depends on the
nervous action. Some say, however, that it is a peculiar
animal matter secreted at will, which, combining with the
oxygen of the air gives rise to the disengagement of light.

Questions. — Have bodies the faculty of regulating their own temper-

RELATION OF ANIMAL BODIES TO HEAT, &C. 109

ature ? ~* *What is said of animal heat ? What is the temperature of
cold blooded animals ? What preserves the heat of the body uniform ?
Is as much heat produced in the body in hot as in cold weather ? Do
animal bodies develope electricity. Can galvanic piles be made of ani-
mal substances alone fr -What kind of fish are electrical ? Describe the
electrical apparatus of the torpedo. What is a galvanic pile ? What
effects have the electrical discharges of the torpedo, &c. ? In what
respects like common electricity ? What is said of the phosphorescent
properties of animals ? What animals have this property ? What
does it depend on 1

10

CHAPTER IX.

THE NERVOUS SYSTEM.

The Brain, Spinal Marrow, and Nerves,

1. THERE is no subject, which falls within the range of
physiological enquiry, more interesting or more important,
than that of the nervous system, tt is this which furnishes
the material instrument of thought, the means by which we
become acquainted with the external world around us, and
also the channels by which the will sends forth its commands
to the instruments it employs in their execution.) Besides
this, it presides over and regulates the functions of the ani-
mal economy, and binds the various organs into one sympa-
thizing, harmonious whole.

2. The nervous system may be considered as embracing,
1st. the brain ; 2d. the medulla oblongata ; 3d. the spinal
marrow ; 4th. the nerves ; 5th. th» ganglia. These are all
embraced under two general departments, the first consisting
of the brain and its dependencies ; and the second, of the
ganglia and their nervous connections pi the first appertain-
ing particularly to animal life, conveying impressions calcu-
lated to produce sensations, and sending out volitions to its
servants, the organs destined to receive them ; while the
second supply those organs not under the influence of the
will, viz. of digestion, circulation, respiration, and the secre-
tions.

3. (These two grand divisions of the nervous system,
may be still further distinguished by the circumstance, that
the first, or cerebral department, is exactly symmetrical!
The nerves all go out in pairs from each side of fhe brain
and spinal cord, while the ganglionic system of nerves is dis-
tributed irregularly to all the internal organs. The nerves

THE NERVOUS SYSTEM. Ill

of the first kind, are either nerves of sensation or of motion.
These nerves, as discovered by Sir Charles Bell, are entirely
distinct, the one rarely, if ever, performing the function of
the other. Although these nerves are endowed with different
properties, the common function of both is, to give us correct
intelligence of the relative condition of our existence.
When these functions are interrupted, as in apoplexy, or
concussion of the brain, [the individual is deprived of all feel-
ing and sensibility, hence they are called the nervous depart-
ment of external or animal life.) The nervous filaments
which furnish the power of mptionJfarise from the anterior
column of the spinal marrowj ^diile those in which sensation
resides, are connected with the posterior column.)

44 The brain fills the~cavity of the cranium or skull, and
in an adult weighs between three and four pounds. Its
greatest length is about six inches, and its breadth five
inches, though its dimensions vary greatly in different per-
sons. In infancy its texture is soft, but it grows harder in
proportion to the age.^|rThe brain is chiefly composed of
two distinct parts, the cerebrum, or brain proper ; and the
cerebellum, or the little brain. These again are divided,
each into two distinct lobes^ The medulla oblongata is the
commencement of the spinal marrow.

5. fThe brain is surrounded by three membranes ; the two
inner ones thin and delicate ; the outer one thick and firm,
and called dura mater} It is a perpendicular fold of the dura
mater, and divides the brain into two hemispheres. It ad-
heres loosely to the bones of the skull ; the internal perios-
teum of which it forms.

6. The other two thin membranes are called arachnoid and
pia mater, ffhe first is a serous membrane, as the dura mater
isnjibrous membrane ; and forms a completely closed sac or
bag. This membrane, which derives its name from its
resemblance to a spider's web, spreads over the whole surface
of the brain, without dipping into any of its furrows or con-

.

112

PHYSIOLOGY.

volutions, and also forms a sheath for all nerves or blood-
vessels that pass out of, or into the brain. 1

a. The scalp, turned down.

b. The cut edge of the bones of the skull.

e. The external strong membrane of the brain, (dura mater) »ui
pended by a hook.

d. The left hemisphere of the brain, showing its convolutions.

e. The superior edge of the right hemisphere.
/. The fissure between the two hemispheres.

7., The pia mater is a loose cellular membrane, composed
chiefly of blood vessels, which dips into all the fissures, and
wraps round all the convolutions of the brain. The chief
use of these membranes seems to be to support the different
parts of the brain in their respective places, so that they may
not be injured by sudden shocks and jars, or by compression ;

THE NERVOUS SYSTEM.^ 113

to moisten the brain ; and furnish a medium o£-transmitting
blood vessels and absorbents^

8. |The outside surface of the brain is cut up, or inter-
sected by deep winding fissures, forming numerous irregular
eminences called convolutions. These fissures are generally
about an inch deep.) The brain on the outer surface, is to a
considerable depth of a grey or ash colour ; (hence it is called
me cineritious or ashy portion, and sometimes cortical, from
its position, like the bark surrounding a tree. The internal
portion is white, and is therefore called the medullary part of
the brain|

9. (The cortical part of the brain which is found on the
exterior surface, is on an average about one-sixth of an inch
in depth, and dips down every where between the convolu-
tions.v Besides its being of a greyish colour, it is of a firmer
consistence than the medullary matter. It is full of vessels,
and from this circumstance has been supposed to nourish the
medullary part.

10. *There are four cavities in the substance of the brain,
termed ventricle^ Of these the two lateral ventricles are the
largest. During life a serous exhalation is constantly going
on into their interior, and in health this fluid is absorbed or
taken up, as fast as it is secreted. In dropsy of the brain,
the water sometimes accumulates in these cavities in im-
mense quantities. Not long since, a child, about ten years
of age, was exhibited in this city, whose head measured two
feet and seven inches in circumference, just above the ears.
The head was so heavy he could not raise it from the pil-
low. This was owing to water in the ventricles. The med-
ullary or white matter of the brain occupies the interior part
of that organ. It makes up by far the largest portion, and
is fibrous in its structure.

11. rThe cerebellum or little brain, is situated at the base
and back part of the skull, and in weight it is only about one-
eighth or ninth part of that of the cerebrum. Like the large
brain, it is divided into two lateral halves. It is made up of

10*

114 PHYSIOLOGY.

several little lobes, and if the two hemispheres be divided by
a knife, a beautiful appearance is presented, resembling the
trunk and branches of a tree ; composed of the white and
grey matter of the brain. Trom its shape it has been called
arbor vita, or tree of life. |

12.V The Spinal marrow is a round cord of nervous matter
which passes down through the spine to the loins. It is di-
vided into two equal lateral parts, by a deep fissure or groove,
which runs through its whole length both on its front and
back surface./ Some say that it consists of four distinct
columns ; others that it is made up of six white strands, two
before, two behind, and two on the sides ; proceeding from
the cerebrum, the restiform bodies, and the cerebellum.

13. (There are forty-three pair of nerves, making 86 in all,
proceeding from the brain and spinal marrowy These
nerves run to every part of the system, conveying, as already
stated, all sensations and impressions to the brain, and also
volition from the brain, to all the voluntary muscles of the
body. Of these, two pair go from the cerebrum, viz., those
for smell and sight, or the olfactory and optic ; five pair go
from the pons varolii, which is that round mass of nerve,
which lies between, and seems to connect the cerebrum and
cerebellum. Of these, the third, fourth, and sixth pair go to
the muscles of the eye ; while the ffth and seventh are dis-
tributed over the face.

14. The remaining thirty-six pairs go out from the spinal
marrow, viz., Jive from the medulla oblongata ; eight from the
cervical ; twelve from the dorsal ; Jive from the lumbar ; and
six from the sacral portion of the spinal cord. These nerves
supply filaments to every muscular fibre in the system ; or
pass directly to the organs of sense without sending off twigs;
some of them are chiefly employed to form plexuses, or a net-
work of nervous threads, woven closely together, so that it
cannot be unravelled.

THE NERVOUS SYSTEM.

1. Hemispheres of the brain proper, or cerebrum.

2. Hemispheres of the smaller brain, or cerebellum.

3. Spinal cord continuous with the brain, and the spiual nerves pro-
ceeding from it on each side.

116 PHYSIOLOGY.

15. The chief net-ioorJcs or ganglia are four in number.
The first which is called cervical, is formed from the second,
third and fourth cervical nerves ; lies on the side of the neck
about its middle ; and it gives rise to four large nerves which
go to the head, neck and upper part of the chest. The
second plexus lies under the pit of the arm, and gives rise to
eight principal branches which go to the chest, shoulder and
arms. The other two plexuses lie in the pelvis, and give off
branches which supply the viscera contained in it, and also
the lower extremities^

16. A second division of the nervous system, as I have
stated, has been called by anatomists ganglionic, or the ner-
vous system of organic life. (A ganglion is a small grayish
white body, of a roundish or oval shape, varying in size,
from a pin's head to an almond) These ganglions are chief-
ly siliiated on the sides of the spinal column, throughout its
whole length, and are connected by nervous threads, which
pass from one to the other, and also with the nerves which
come out from the spine. {&ix of these ganglions are found
in the head ; three in the neck ; twelve in the dorsal region ;
Jive in the lumbar ; and three in the sacral region.)

17. The principal of the plexuses are formed by nervous
filaments proceeding from these ganglions. These are the
cardiac plexus, the pulmonary plexus, and the great solar
plexus. {"The whole ganglionic system of nerves is called
the great sympathetic nerve.) jThis is connected with the brain
by the sixth cerebral nerve and a branch of the fifth. It
also receives branches from the seventh, eighth, and ninth,
and all the spinal nerves, to the lower part of the spine, be-
low which it terminates^ We are now prepared to consider
the functions of the nervous system.

18. The brain being the centre of the nervous system, is
the most important organ of the human body; pfo the lowest
order of animals, we find but imperfect rudiments of a ner-
vous system } but as we ascend in the scale of animal exist-
ence, we find it more and more developed as we advance, till

THE NERVOUS SYSTEM. 117

at length we arrive at man, who possesses it in its highest
form of development. The functions over which the brain
presides, are (the sensations, the voluntary motions, and the
intellectual and moral faculties?)

19. (The mind itself is immaterial-*-a principle superadded
to matter ; but the brain is the instrument which it employs
in all its operations. Though it is not matter, yet it works
by means of matter. In like manner, the eye is not sight,
but the instrument of sight ; the ear is not hearing, but the
organ of hearing ; so the brain is not mind, but the organ
of mind. Revelation teaches us all we know, with respect
to the powers and capacities of mind, when separate from
the body.

20. The spinal marrow and the nerves are of subordinate
importance ; as organs of the nervous system, their use
seems to be, to transmit impressions from the organs of
sense to the brain ; or the influence of the brain in a con-
trary direction to the muscles which are employed for
motion.

21. tThe first class of functions which pertain to the brain
are the sensorial.t Though the brain is the actual seat of
all impressions, yet the organs of sense and the nerves seem
to be the immediate seats of sensation. Indeed, no sensation
can be excited in any part or organ, unless- its nervous con-
nection with the brain be entire. For example, the sense
of touch seems to reside in the ends of the fingers, and that
of sight in the eye, yet if the nerve which connects these
parts with the brain be divided, no impression is felt, no
sensation whatever is excited ; showing conclusively that it
is the brain that perceives all impressions made on the organs
of sense.

22. It is a curious fact connected with this subject, that
though the brain is the real seat of the sensation, yet it is
always referred to the part or organ, on which the impression
is made, so that there seems to be a double action, viz., from
the organ to the brain, and from the brain back again to the

118 PHYSIOLOGY.

organ. Thus it is not unusual to see persons who have lost
a limb complaining of pain, or some other sensation in the
part which has been cut off, and thus they often imagine
that the limb is entire. Here the sensation existed only in
the mind ; in the same manner ghosts, hobgoblins, and other
strange sights are seen ; but the sensation is only in the
brain.

23. That the brain is the real seat of all our sensations
may be proved from other facts. If a person receives a
blow upon the head so as to stun him, or deprive him of
consciousness, though the organs of sensation and the senses
are wholly uninjured, he takes no notice of any thing ; he
receives no sensations from any of his senses ; in fact, he is
said to be insensible. The same thing happens if he become
stupid by the use of alcohol, opium, or any narcotic. If the
quantity is not enough to produce entire torpor of the brain,
his senses are impaired, his reason is gone ; he is in short a
voluntary mad-man.

24. (During sleep, the senses are said to be locked up.
But though the eye is closed, the ear is open ; the nerves in
which the sense of touch resides, are still spread out upon
the skin, but yet no impressions are felt ; no sensations are
excited ; no notice is taken. The reason is, the brain is in
a state of repose ; the ship does not obey the rudder, be-
cause the man at the helm is asleep ; the steamboat is not in
motion, for although she has furnace, boilors, condensers,
paddle-wheels, and all, yet the steam is not up ; so in sleep,
the organs of sense are all sound, yet the brain, the rudder
of the mind, the moving agent of the animal machine, is
dormant ; the messages of its servants, the organs of sense,
are neither received, noticed, nor acted upon.

25. There is another curious circumstance connected
with the brain ; /it may be so much employed in thought,
or deep meditation, as not to notice the impressions made
on the senses^ In this case, a person is said to be absent-
minded. Though the eyes and ears are open, the brain is

THE NERVOUS SYSTEM. 119

too busy about other matters, to take notice of the impres-
sions made on them ; accordingly, there are instances known,
where persons have walked off a precipice, or into the water,
without noticing the danger till it was too late.

26. Sensations, then, are the more vivid ; and the impres-
sions which they make, more durable, in proportion to the
degree of attention with which the mind is directed towards
them ; or the degree of activity of the brain. To obtain
ideas, which are|the pictures of sensible objects painted on
the brain) we must therefore endeavour to concentrate the
whole attention upon the subject before us, or the impres-
sions we receive will be weak and speedily fade away. We
see a great difference in this respect in different persons.
Two individuals will travel together through the same coun-
try, and apparently take the same degree of interest in the
objects which come under their notice. Yet, while one of
these persons will be able to describe minutely every thing
he has seen, the other can give only a confused and indistinct
account of what he has observed. It is, therefore, not only
necessary in the acquisition of knowledge that objects should
make an impression on the sensual organs ; but the brain
must act upon them, and that not in a slight and careless
manner, but vividly and energetically.

27. It is possible even that sensations may be excited by
the action of the brain itself, without the intervention of any
sensible objects. AVe see this oftenfn diseases of the brain,
and especially in that form of insanity, called delirium ire-
mens, or drunken delirium.) Here, the wretched victim of
depraved habit sees serpents, and lizards, and bats, and all
creeping things, and devils, flying about ; and he hears sing-
ing and various sounds, to which he listens, and calls the
attention of others, and nothing can break the spell by which
he is bound, or dispel the illusory conviction, that what he
sees and hears is real and not imaginary.

28. Such illusory and false impressions, are no doubt
sometimes excited in the minds of those, who cannot be said

120 PHYSIOLOGY.

to labour under actual disease ; but their imaginations have
been excited by the influence of fear and superstition, and
the brain is accordingly excited to act in the same manner
as it would by the actual sight of some frightful object.
Thus a post will appear in the night, to be a robber ; a black
stump of a tree, a bear, or a tomb-stone, a ghost ; according
to the idea or apprehension at the time uppermost in the
mind.

29. But though the brain is the seat of sensation, yet it
is very remarkable that it is not itself sensible. Wounds
in its substance do not seem to excite pain* The whole of
the cerebrum as well as the cerebellum has been pared away,
and yet the animal appeared to suffer no pain ; but as soon
as that portion of the base of the brain which seems to be
the commencement of the spinal marrow, is touched, con-
vulsions immediately follow. The posterior surface of the
spinal marrow is also highly sensible. This is the substance
of what is yet known on the subject of sensation.

30. Voluntary motion, like sensation, has also its seat in
the brain. Though the muscles are the instruments of
motion, yet alfytheir voluntary motions are performed through
the influence of the brain, by an act of the will/ If the brain
is in a state of repose the body is at rest ; Jif the brain by
an act of violition sends a portion of nervous influence to a
voluntary muscle, it immediately contracts, and the limb or
organ to which it is attached, moves. All we are conscious
of in" this process, is, the act of the will and the motion, which
that act causes. The volition and the motion seem to be
at the same instant ; at least there is no perceptible interval
between them.

31. But though the voluntary muscles are excited to action
through the agency of the brain, yet they are not always
under the control of the will. 'In many diseases of the
brain : in lock jaw, hydrophobia,;and other disorders where
the whole nervous system is in a state of irritation, the
muscles are excited to violent spasmodic contraction, alto.

THE NERVOUS SYSTEM. 121

gether beyond the control of the will. Where convulsions
arise from sympathy, as in teething, or irritation of the
bowels, the painful impression is transmitted to the brain,
and hence reflected back upon the muscles. Thus pricking
the finger with a needle has thrown a nervous woman into
spasms, by exciting the brain to action.

32. If a nerve which supplies any voluntary muscle be
divided, that muscle will no longer contract. This proves
that the influence of the brain is necessary. ; In palsy, there
is generally some disease of the brain, as the rupture of a
small blood-vessel, or tumour growing in its substance. J Here
the power of the will, or the faculty of volition is not des-
troyed ; but the brain is unable to carry into execution the
command of the will, as when a person is very willing to
take a load upon his back, but he happens not to have suffi
cient strength to carry it,

33. During sleep, all voluntary motion is suspended, be.
cause the brain ceases to act. In those cases where persons
walk and talk in their sleep, the brain is not entirely dormant.
Some of the senses seem to be awake at times, while the
others are asleep. That is, those portions of the brain which
are excited to action by certain nerves of sense, are awake
and active, while other portions are dormant and at rest.
i*The brain needs repose and relaxation, as much as the
muscles. Periodical cessation of effort is necessary to both,
in order to a vigorous performance of their respective func-
tions.

Questions. — What functions belong to the nervous system ? What
does it embrace ? How many departments ? . What offices does each
perform ? What marks characterize each ? When their functions are
interrupted, what happens ? From what portion of the spinal mar-
row do the nerves of motion arise ? — the nerves of sensation ? Des.
cribe the brain ; — its divisions ; — its membranes ; — dura mater ; — pice
mater ; What are the convolutions of the brain ? How do the cine,
ritious and medullary portions differ from each other ? Which is ex
terior ? How many cavities in the brain ? What are they called '?

11

122 PHYSIOLOGY.

Describe the cerebellum, — the spinal marrow. How many pairs of
nerves are there ? How many nerves arise from the cerebrum ?--^-from
the pons varolii '?— - from the spinal marrow.?— from the medulla oblon-
gata ? How many principal ganglia :>r net-works of nerves It— their
situation ? What is a ganglion ? What are the principal ganglions
of the nervous Astern of organic life ? What is the sympathetic nerve ?
— where situated ?' What is the most important organ of the body?
What is said of the brain in the lower animals ? Over what functions
does the brain preside? Is it immaterial £ What is the first class
of functions over which it presides ? What is understood by sensorial
functions ? What becomes of the senses during sleep? — during absent-
mindedness ? What are ideas ? Is attej tion necessary in order to im-
press sensations durably on the mind ?' . ~May sensations be excited
without the intervention of sensible objects-t In what disease does this
happen ? Is the brain itself sensible f'* Where is the seat of voluntary
motion ? How is it performed ? What is volition ? Are motions
always under the control of the will T ' In what diseases is this not the
case ? What effect has the division of a nerve ? What happens in
palsy ? Why is voluntary motion suspended during sleep ?

CHAPTER X.

1

INTELLECTUAL AND MORAL FACULTIES.

J. THE great superiority of the intellectual faculties of
man over those of other animals, has led to a diligent exami-
nation, whether there be any thing in his anatomical struc-
ture which would seem to account for this superiority.
Aristotle noticed the great size of the human brain compared
with that of other animals, andjlaid it down as a general
principle, that the faculties referred to this organ were in
proportion to its size, compared with that of the whole bodyV
Though this rule will hold true in relation to some of the do-
mestic animals, yet it does not in relation to many others,
for accurate researches have shown that whil^in man the
ratio of the weight of the brain to that of the whole body is
as 1 to 28j?in the dog, it is as 1 to IGO^in the horse, as 1 to
400") (n the elephant, 1 to 500){n the "canary bird, 1 to IV
(and in one species of ape, 1 to 11.)

2. It is now generally admitted by physiologists,, that the
perfection of the sensitive functions does not depend on the
absolute size of the brain, nor on its proportion to the body
at large, but(upon the proportion between the size of the
brain, and the aggregate bulk of the nerves that proceed
from it ; in other words,fbetween the sensorial and nervous
organs^ For example, the absolute size of the brain of the
horse is only about half the size of the human brain, while
the mass of the nerves of the horse at their origin is no less
than ten times larger than that of man. Extensive observa-
tions prove that though most of the inferior animals have larger
nerves, and possess some of the nervous functions in a much
more acute state than mnn. yet man decidedly exceeds them
all in the comparative size of the brain, and in the perfection
of his intellectual faculties.

124 PHYSIOLOGY..

3. The brain then, is the organ of the intellectual and
moral faculties, the material instrument of the mind. \ This
is proved not only by comparative anatomy, and experiments
on animals, but by the history of injuries of the brain, com-
pared with those of other organs. We know that if the
nerves supplying any limb are severed, the will has no longer
any influence over it ; it is to all useful purposes a dead por.
tion of matter. The same is true of the spinal marrow. If
this be compressed by fracture or dislocation of the spine,
the whole body below that point, is deprived both of sensa-
tion and motion, but the mind loses none of its powers any
more than if a limb had been amputated.

4. If the brain is not the seat of the intellectual facilities,
neither are any of the other organs of the body. *. The
lungs, the liver, the spleen, the intestines, or the kidneys,
may be affected with gangrene, and still the mind remains
clear ; though from sympathy, inflammation of any organ
may cause delirium, or other mental affections. Neither
is the heart the seat of the mind ; for cronic disease of that
organ, does not impair the mental faculties. Besides the
functions of all these organs are known and cannot be mis-
taken.* If the brain is not the seat of the intellectual facul-
ties, they cannot be said to have any seat in the body.

5. But the effects of injuries of the brain are very diffe-
rent, for every cause which disturbs its action suddenly or
slowly, affects at the same time the mind. }j Inflammation of
the brain is always attended with delirium, or stupoij; pres-
sure on it, whether produced by depressed bone, foreign
bodies, a tumour, serum, blood or pus, always gives rise to
similar symptoms, and often destroy both sensation and
motion. In cases of apoplexy, where a person falls in a fit,
and becomes insensible, we find pressure on the brain from
effusion of blood or serum. In cases of lunatics, we find in
nearly all cronic cases, structural changes in the braird; but
if the case be recent, these changes though they probably
exist, yet may escape our imperfect means of investigation.
Alcohol, opium, and other narcotics affect the mind and the

INTELLECTUAL AND MORAL FACULTIES. 125

nerves through their influence upon the brain. Whenever
in fact, we see a person become stupid and insensible, we
may be certain that the brain has suffered some physical
change ; and where in cases of sickness, we see the mental
faculties unimpaired to the last, we may be equally sure, that
the brain is not affected.

6. The following facts also show that the brain is the or-
gan of the mind. A man received a blow on his head, and
immediately lost his mental faculties, and his bodily power.
His appetite and digestion were good ; the blood circulated
freely ; and his breathing and pulse were natural. He con-
tinued in this state more than a year, when a surgeon raised
up a piece of bone which had been driven in upon the brain.
His reason was immediately restored ; the next day he
spoke, and in a short time he recovered entirely ; but he
could recollect nothing of what had happened since the acci-
dent. Not long since a beggar exhibited himself in Paris,
who had lost a portion of his skull ; his brain was only cov-
ered by the skin and membranes. For a trifling sum he
would allow any one to press on this exposed part. As soon
as any pressure was made he became wholly unconscious ;
but his intellect was immediately restored when the pressure
was taken off.

7. (it has been objected to the brain's being considered the
seat of the mind, that in some cases, considerable disease
has been found affecting an entire hemisphere without the
mental faculties having suffered ; but experiments on animals
show that a sudden lesion of one hemisphere only, does not
immediately produce complete stupor, and that this effect
does not follow until both are removed ; so that it appears
that one hemisphere aids the other, and compensates for its
inaction in the operations of the mind.;

8. But though it is almost universally admitted, that the
brain is the seat of the higher intellectual faculties, yet some
physiologists, like Bichat, contend that the passions are
seated in the thoracic and abdominal viscera. It is, however,

11*

126 PHYSIOLOGY.

to be remarked, that the passions, by means of the change
which takes place in the brain, affect the whole nervous sys-
tem. We find, for example in nervous females, that the ex-
citing passions give rise to spasmodic action of certain mus-
cles, especially those supplied by nerves belonging to the
respiratory system ; hence the crying, sobbing, sighing, and
the spasmodic distortion of the features. In the depressing
passions, such as fear and terror, the muscles of the body lose
their tone, because the supply of nervous influence from the
brain is cut off; the limbs are not able to support the body ;
the features lose their expression ; and the loss of power may
be so great as to cause complete paralysis of the whole body.

9. In like manner is the heart affected by the exciting and
depressing passions. {It throbs irregularly under the influ-
ence of fear and terror ; it beats high and strong under the
influence of joy ; while its action is weakened under the
operation of grief and care ; in short, it is affected in a
greater or less degree by every emotion which agitates the
human breast. But this no more proves that the passions
are seated in the heart, than that they are seated in the eye,
because grief brings tears into that organ.) Neither has the
liver, as the ancients believed, any relation to the passions of
rage and vexation, although a fit of jaundice, may, in some
persons labouring under a disease of this organ, follow a
paroxysm of these passions. In other individuals, a fit of
dyspepsia may follow as a consequenee of the same emotions ;
or any other organ, may suffer, according as it is predis-
posed by debility, disease, or other causes. Such phenome-
na only prove that the whole body is bound up in one indis-
soluble bond of sympathy, or as St. Paul expresses it, "God
hath tempered the body together, that there should be no
schism in the body, but that the members should have the
same care one for another ; so that, whether one member suf-
fer, all the members suffer with it, or one member be honored,
all the members rejoice with it."

10. The brain, like all the other organs of the body, in-

INTELLECTUAL AND MORAL FACULTIES. 127

creases in volume, by the exercise of its functions. When
the mind is properly cultivated, the brain attains its full
growth and development ; and where suitable opportunities
of education have been enjoyed, the intellectual powers are
generally proportioned to the size of this organ. Majendi
says, "The volume of the brain is generally in direct pro-
portion to the capacity of the mind." This was also be-
lieved by the ancient Greeks ; for Jheir statuaries, or workers
in marble, made the heads of their Apollo, and other intel-
lectual gods and heroes, much larger than the heads of their
Hercules, and other heroes, who were remarkable only for
their great physical strength.) The heads of idiots are known
to be extremely small ; some, indeed, are not more than one-
fifth the average size.

11. That the brain is constructed with evident design,
and is composed of a number of curiously wrought parts, all
physiologists admit ; yet they have not been able thoroughly
to penetrate the intention with which they are formed, or to
agree with respect to the particular functions which each
part performs. ( It is, however, pretty well ascertained, that
the hemispheres of the large brain, or cerebral lobes, are the
instruments by which the intellectual operations are carried
on ; in other words, are the seats of the faculties of thinking,
memory, and the will ; while the central parts, such as the
optic lobes, and the medulla oblongata, are principally con-
cerned in sensation ; and that the cerebellum, or little brain,
is the chief sensorial agent in voluntary motion, and the seat
of the animal, or lower propensities}

12. Many cruel experiments have been made on living
animals, to determine the exact functions of particular parts
of the brain ; but so much violence is done in these experi-
ments, that but little dependence caif be placed on them.
Many attempts have been made to determine the exact place
in the brain where perception resides, but all such attempts
have been fruitless. /*That it is placed in the base of the
brain* or *!:•:-. medulla oblmgata, is very probable,1as most of

128 PHYSIOLOGY.

the nerves of sense terminate in that part ; but it is difficult
to prove this by actual experiment.

13. (The brain, like all the organs of the senses, is double ;
the one side, as in the eyes, ears, and limbs, being exactly
similar to the other ; so that it may be said, that we have
two brains as well as two optic nerves, and two eyes. As the
structure of the brain is fibrous, in order that the two sets
of fibres may co-operate, and constitute a single organ, they
pass obliquely across from one side of the brain to the other,
and these bridges constitute what are called the commissures
of the brain*. It follows from this, that if the right side of
the brain receives an injury, it will be felt on the opposite
side of the body. The following case proves this.

14. 1, A piece of wire pieroed the brain of a boy just over
the right eye ; he immediately lost all motion in the left arm
and leg, although his sense of feeling was as perfect as ever.
There are many such cases on record, which conclusively
show that the right side of the brain furnishes nerves of
sense and motion to the left side of the body ; and the left
side of the brain to the right side of the body. If, then, a
portion of brain is lost by a wound, on one side of the head
only, as has often happened, and the intellect does not suffer ;
as the brain is a double organ, it does not prove, that it is
not the seat of the mental faculties.

15. The office of the cerebellum is supposed by many to
be. to regulate and combine different motions/ For example,
if the cerebellum be wounded, the animal cannot walk with-
out staggering, and there will be a particular weakness on
that side which is wounded. When a person is intoxicated,
his inability of walking in a straight course, is supposed to
be owing to the influence of the alcohol on the cerebellum.
In experiments, where the cerebellum has been wounded or
divided,|the animal has rolled over and over, or whirled round
and round ; the eyes squinted ; and all power of regulating
its motions seems to have been lost.

16. Though man is infinitely exalted above the brute

INTELLECTUAL AND- MORAL FACULTIES. 129

creation, by the endowments of reason and a moral sense,
yet many of the inferior animals excel him in the perfection
of subordinate powers. In strength and swiftness, he is sur-
passed by many of the quadrupeds ; in powers of vision, the
eagle and other birds excel him ; in acuteness of hearing,
taste, and smell, a large number of animals are superior to
him. Man is indeed a stranger to those delicate percep-
tions, which teach the lower animals to seek the food which
is salutary, and avoid that which is injurious, and has to
depend upon a painful and hazardous experience for that
knowledge which the brutes possess by instinct.

17. " But he has gifts of infinitely higher value. | In the
fidelity and tenacity with which impressions are retained in
his memory ; in the facility and strength with which they
are associated ; in grasp of comprehension, in strength of
reasoning, in capacity of progressive improvement) he leaves
all other animals at an immeasurable distance behind. Ho
alone enjoys in perfection the gift of utterance ; he alone is
able to clothe his thoughts in words ; in him alone do we
find implanted the desire of examining every department of
nature, and the power of extending his views beyond the
confines of this globe."

18. " On him alone have the high privileges been bestow,
ed of recognising and adoring the Power, the Wisdom, and
the Goodness of the Author of the universe, from whom his
being has emanated, to whom he owes all the blessings which
attend it, and to whom he has been taught to look forward
to brighter skies, and to purer and more exalted conditions
of existence."

19. Phrenology. — The actual meaning of the term Phren-
ology, is '< a discourse about the mind," or, " the doctrine of
the mind.? It professes indeed to be a system of Mental
Philosophy, and as it is pretends to be founded in nature and
supported by facts, it certainly is not beneath the attention
of the candid inquirer after truth.

130 PHYSIOLOGY.

20. The chief doctrines which Phrenology claims to have
established are the following : — •

l.fThat the moral and the intellectual faculties are in-
nate.

2. That their exercise, or manifestation, depends on organ-
ization.

3. That the brain is the organ of all the propensities, sen-
timents, and faculties.

4. That the brain is composed of as many particular
organs as there are propensities, sentiments, and faculties,
which differ essentially from each other. These four pro-
positions may be said to constitute the phrenological doc-
trine, and they are sustained by such numerous experiments,
observations, and facts, that a large proportion of enlighten-
ed physiologists of the present day acquiesce in their cor-
rectness.j

21. jr Another and a different proposition, however, and one
which, by many, is erroneously supposed, alone, to constitute
Phrenology, is, that we are able to recognise on the exterior
of the skull, the seats of the particular organs, or intellectual
and moral faculties, and thus determine the character of in-
dividuals^ This proposition has not received that general
concurrence of Physiologists, in its support, which has at-
tended the former ; but there are so many zealous and able
inquirers now in the field, and such is the ardour in pursuit
of knowledge, connected with this subject, that a few years
at farthest, probably, will suffice to overthrow or establish it.

22. I have already mentioned some facts, to prove that
the brain is the organ of the mind, and that the condition
of that organ influences the mind ; let us now inquire whether
the mind, in every act, employs the whole brain as one organ,
or whether separate faculties of the mind are connected with
distinct portions of the brain as their respective organs 1

23. It is a well established fact in Physiology, that differ-
ent functions are never performed by the same organ, but
that each function has an organ for itself. .; Thus the eyes

INTELLECTUAL AND MORAL FACULTIES. 131

see, the ears hear, the tongue tastes, the nose smells, the
stomach digests food, the heart circulates the blood, the liver
secretes bile, &c. Even where the function is compound,
as in the tongue, where a feeling, taste, and motion are all
combined, we find a separate nerve for each function, and
the same occurs in every part of the body. Now, as no
nerve performs two functions, we may, reasoning from
analogy, conclude, that it is so in the brain ; different sen-
timents, different faculties, and different propensities, require
for their manifestation different organs or portions of cerebral
matter./

24. Again, the external senses have for their exercise, not
only separate and external organs, but also as many separate
internal organs. Hearing, seeing, smelling, &c., require
different portions of cerebral substance for their exercise ;
may we not then from analogy, be justified in the conclusion,

/that there are as many cerebral, or nervous systems, or
organs, as there are special internal senses, and particular
intellectual and moral faculties ?) ^The legitimate inference
then is, that each faculty does possess in the brain a nervous
organ appropriated to its production, the same as each of the
senses has its particular nervous organ.i

25. The structure of the brain is not homogeneous, but
differs greatly in different parts, both in composition, form,
colour, consistence, and arrangement. But what object
could there be in all this variety, if the brain acted as a
whole, and there was but a single intellectual principle or
faculty ? A difference of structure shows that there must be
a difference of function, and as the brain has been proved to
be the organ of the mind, it follows that different portions or
organs of the brain must be employed by the intellectual and
moral faculties.

26. The faculties do not all appear at once, nor do they fail
at once, but they appear in succession, and as a general rule,
the reflecting or reasoning faculties are the latest in arriving
at perfection. So also the organization of the brain is un-

132 PHYSIOLOGY.

folded in a slow and gradual manner, and the intellectual fac-
ulties appear in succession only as the structure is perfected.
For example, in infancy, the cerebellum forms one fifteenth
of the encephalic mass ; in adult age about one sixth. In
childhood the middle parts of the forehead preponderate ; in
later life, the upper lateral regions are more prominent,
which facts are also in accordance with the periods of unfold-
ing the knowing and reasoning faculties.

27. Genius is almost always partial ; that is, men gene-
rally have a taste or faculty, for one particular pursuit, or
study, in which alone they have the power of excelling. One
has a talent for poetry, another for mechanics, another for
drawing, music, or mathematics, and that is often developed
at a very early age, and without the advantages of educa-
tion, or particular instruction, and these persons may, in all
other pursuits, be below mediocrity. Indeed, nothing is
more common than to see in the same individuals some fac-
ulties acute and powerful, while others are feeble and defec-
tive ; having an extraordinary memory for dates, words,
places, &c., while as to other things it is deficient. Such
facts are not easily explained on the scheme of a single in-
tellectual faculty, and a single organ devoted to its exercise.

28. It is an observation of common notoriety, that when
the mind is fatigued with one kind of occupation or study, it
can engage, with vigour, in one of a different kind, requiring
the exercise of different faculties ; and thus, instead of fa-
tiguing, actually acts as a restorative. Could this happen, .
unless there were a plurality of faculties and organs of the
intellect ?

29. The phenomena of partial idiocy and partial insanity
are at variance with the doctrine of a single organ of mind.
We often see persons in a state of monomania, that is,\they
are rational enough on all subjects but one ; but in relation
to that, they are entirely mad.) Now, if the brain be suffi-
ciently sound to manifest all the other faculties in their per-
fect state, why is it not also able to manifest this ?

INTELLECTUAL AND MORAL FACULTIES. 133

30. Numerous cases are contained in medical works
where a wound of the brain was succeeded by the loss of a
single faculty, and sometimes by exciting inflammation, be«
stowed unwonted energy on a single faculty. Larrey, in his
surgical memoirs, mentions several cases of wounds made by
bayonets and swords penetrating the brain through the orbit
of the eye, which entailed the loss of memory for names, but
not of things, &c.

31. Such are a few of the arguments adduced by writers
on this subject, to prove that the brain is not only the organ
of the mind, but an apparatus, a congeries of organs, each of
which is the seat of a particular faculty, the organ of a par-
ticular function. The evidence to most minds will appear
satisfactory and conclusive on this point, though other facts
arid more extended investigations are needed to place the
science on a permanent foundation.)

Questions. — What was Aristotle's theory in relation to the size »f the
brain ? How does its size compare with that of the body in man ?
in the dog, the horse ? the elephant ? the canary bird ? the ape ? What
is now the received doctrine in relation to the size of the brain ? How
is it proved that the brain is the organ of the intellectual and moral
powers ? How do you prove that no other organ than the brain can be
the seat of the mind ? How does inflammation or injuries of the brain
affect the mind ? What cases prove this connection ? What objec-
tions have been raised to the brain being the organ of the mind ? What
is said of the passions being situated in the viscera of the chest or abdo-
men ? Does the affection of the heart by passion prove that it is the
seat of the mind*' Why not? Does the brain increase in size by ex-
ercise ? What was the opinion of the ancient Greeks on this subject ?
What is said of the functions of particular portions of the brain ? Is
much (Jependance to be placed on the experiments made on animals ?
Where is it supposed perception resides ? What are the commisseurs
of the brain ? When the brain is injured on the right side, which side
of the body is affected ? What accident proves that the opposite side is
affected ? What is the office of the cerebellum ? What effect do we
see in animals when they have been wounded ? Is man excelled by ani-
mals in the perfection of the sanies I Jn what respect does he excel all am.
12

134 PHYSIOLOGY.

raals ? What is Phrenology ? What are its chief doctrines ? What
is said of locating the organs on the exterior of the skull ? What facts
show that the brain does not act as as a whole in the intellectual opera,
tions? Have the external senses separate internal organs? What
may we infer from this ? Is the structure of the brain homogeneous ?•
Do the faculties all appear at the same time ?• Is genius generally
partial 7* ' When the mind is fatigued, what effect is experienced by
turning the attention to a different subject? What is monomania?
What do we infer from its existence ? What is the general conclusion
in relation to the chief doctrines of Phrenology ?

CHAPTER XL

THE SPINAL MARROW AND ITS FUNCTIONS.

1. WE have seen, that of all animals, the brain of man
has the greatest development, in proportion to the spinal
marrow and nerves ; if we descend to the lower animals,
such as reptiles and fishes, we shall find that the brain^pre-
sents merely a delicate, anterior termination of the spinal
cord, not much larger in diameter than the cord itself./ In
these animals, we find the instincts very limited, and the
displays of sagacity extremely obscure ; while they possess
great tenacity of life. Frogs, for example, continue to jump
about for many hours after their heart has been torn out ;
and the heart of the shark will palpitate as long after it has
been removed from the body. Turtles have been known to
live for months after the whole brain has been scooped out.
These facts prove, that such an imperfect development of
the cerebral mass, leaves the different systems of organs less
intimately connected and more independent of each other.

2. If we descend still lower in the scale of invertebrate
animals, we shall find the different parts still more independ-
ent of each other ; for if we divide their bodies, so that each
part will possess a nervous ganglion, it will become a separ-
ate individual, and exercise all the functions performed by
the entire animal ; and if we descend to zoophytes, we find
that in cutting them into threads, however minute, each
piece will retain life and continue to grow.

3. Medulla oblongata.— -J^here is no distinct line of demar-
cation between the medulla oblongata and the spinal corcf;
For this reason, they are considered and described as one
organ. The medulla oblongata, however, consisting of six
columns, gives rise to several nerves of distinct function, and

136 PHYSIOLOGY.

is supposed to be the point at which excitement to motion
commences and sensation terminates, and to possess the
power of originating motion in itselfj Mr. Mayo infers
this, from the fact that the brain proper, the optic tubercles,
and even the cerebellum may be removed by successive por-
tions, and still the animal live, and exhibit feeling and in-
stinct ; but if the medulla oblongata be removed, all con-
sciousness is immediately destroyed. Other physiologists
say, that it is the hemispheres of the cerebrum that take
cognizance of sensation, and the source from whence volition
proceeds ; and that though they may be removed, layer
after layer, without pain, yet by so doing, the senses are
destroyed, memory and intelligence abolished, and the animal
reduced to an automaton, destitute of design, apprehension,
and judgment. As all the nerves which supply the larynx,
lungs, heart, stomach, and external muscles of respiration
originate from it, its removal must instantly destroy life.

4. (The spinal cord passess down through the foramen
magnum, or great hole of the skull, and the canal of the ver-
tebra, till it reaches the second vertebra of the loins, where
it generally terminates in a tapering pointj Besides the
bony case in which it is lodged, the cord is enclosed by a
prolongation of the dura mater, which, however, does not
adhere immediately to the bone, as it does in the skull. It
also is supplied with extensions of the arachnoid and pia
mater ; between which, there is usually a quantity of serous
fluid, varying from two to six ounces, which seems to impart
a certain degree of support by its pressure and obviates the
effects of concussion J

5. The general form of the spinal cord is cylindrical,
though somewhat flattened, from its transverse diameter
being the greatest. Its thickness, however, is not uniform,
as it bulges out at the lower part of the neck, where the
nerves go off to the arms, and also at the lower part of the
back, from whence spring the nerves of the legsj. It is com-
posed of grey and white, or cineritious and medullary mat-

IE SPINAL MARROW AND ITS FUNCTIONS. 137

ter, like the brain ; the situation of the two is, however,
reversed ; the medullary matter being disposed in a thin
layer upon the surface, while the grey portions occupies the
centre. We, however, find the same arrangement in the
medulla oblongata, and the central parts of the cerebrum
and cerebellum. The chord, as t have already mention,
ed, is divided into two lateral halves by a groove in front
and a similar groove behind. Besides this, there are on
each side two lateral grooves faintly marked, from which
the anterior and posterior nerves have their origin, so that
in fact, the cord consists of four columns ; from the two
anterior of which, the nerves ofjnotion spring, and from the
two posterior those of sensation.^

a, Spinal marrow.
6, Fibres of sensation.
c, Fibres of motion.
e, Nerve.

6. There are thirty pairs of nerves that spring from the
spinal marrow, viz., eight from the region of the neck, twelve
from that of the back, and five from the pelvis. By examin-
ing the above cut, it will be seen that they arise by two
roots, one from the anterior, and one from the posterior
column. The fibres of the posterior swell out into a gang-
lion before they unite with the anterior.
12*

138 PHYSIOLOGY.

7. A few years ago, Sir Charles Bell discovered, that by
opening the spinal canal in a living animal, and dividing
the posterior roots of the nerves, the parts to which they are
distributed are deprived of feeling. The limb may be prick-
ed or lacerated in any way, without the animal manifesting
the least feeling, or indication of suffering, while at the same
time the power of motion remains. He also found that when
the posterior roots were divided, sensation was destroyed,
but motion remained. One of Majendie's experiments, is
interesting. Availing himself of the fact, that the introduc-
tion of nux vomica into the system, produces violent spasms,
tremors, and rigidity of the muscles : he administered it to an
animal, after having severed the anterior roots of the spinal
nerves. The consequence was, that while all the muscles,
whose nerves remained entire, were thrown into a state of
violent spasm ; those supplied with the nerves, whose roots
had been divided, remained unaffected.

8. The spinal cord then serves to connect the brain, which
is the common centre of sensation and voluntary motion,
with all the sensible parts of the body, and with the muscles,
the instruments of motion.) We may view it in this sense,
as forming a channel of communication for a bundle of
nerves running from the brain to every part of the system
to carry messages from the will, and to transmit intelligence
back again, as if all the roads and high-ways in the country
should terminate in one grand post-road, connecting them
with the seat of government.

9. To illustrate, suppose I seize a hot iron in my hand,
not knowing it to be heated ; the painful impression is im-
mediately transmitted along the sensiferous nerves to the
spinal cord, and through that to the brain. The brain takes
cognizance of it, and a mental determination is immediately
formed to drop the iron. The will sends back its command
through the anterior column of the spinal cord to the motific
nerves, distributed to the muscles, which go to the hand.
The muscles instantly obey ; the iron drops, and the whole

THE SPINAL MARROW AND ITS FUNCTIONS. 139

process occupies but an instant.?" Thus we have two channels
of nervous influence ; the one transmitting intelligence to
the mind, the other conveying the purposes of the will to the
muscles necessary to carry them into effect.

10. That such is the chief function of the spinal marrow,
is proved by the well-known fact, jthat if it is divided
in any part of its course, that portion of the body, as well
as the limbs, which are situated below the seat of the
injury, will be paralyzed ; that is, all sense and motion will
be lost, while the parts above the injury will be unaffected.
Jf the injury occur very high up in the neck instant death
will ensue,|because the nerves, which go the diaphragm and
are necessary to carry on breathing, are separated from their
connection with the brain. These leave the spine as high
as the third vertebra of the neck.

11. I have stated that it has been proved, that the
^principle of motion resides to some extent in the spinal

marrow itself. | This is shown by the following experiment.
If after the spinal cord be divided in the neck, and then lower
down in the back, we irritate any -of the muscles which are
supplied with nerves from this isolated segment, motion will
be produced. If the foot, or the hand be pricked, it will im-
mediately contract ; and this contraction is produced by the
irritation being transmitted to that portion of the spinal mar-
row, from whence the nerves of the part arise, and whose
connection with the brain has been severed, and then an im-
pulse is sent back again from this portion to the muscles of
the hand or foot which causes them to contract. Still, all
voluntary motion, as well as sensation, depend on the brain.

12. If the medulla oblongata is injured, breathing imme-
diately ceases. If the spinal marrow is severed opposite the
second bone of the neck, death also speedily follows ; because
the nerves of respiration are cut off from their connection
with the part above. If the spinal cord be divided, as low as
the fifth cervical bone, thcn(lif3 will not be immediately de-
stroyed ; but the breathing will be difficult ; because the dia.

140 PHYSIOLOGY.

phragm is paralyzed, and death sooner or later follows from
suffocation. $ If it be divided about the first dorsal vertebra,
then life may be maintained for a considerable time, although
the ribs cannot be elevated, as the intercostal muscles are
rendered paralytic.. Breathing is, however, kept up by the
action of the diaphragm. I have seen a man whose spine
was dislocated in this region, live seven or eight weeks. All
sensation and motion were lost in the parts below the seat of
the injury, but his reason and senses were perfect.

13. As the heart, lungs, larynx, and many of the most im-
portant organs of the body are supplied with nervous influ-
ence by the eighth pair of nerves, or par vagum, why is it
that a division of the spinal marrow causes death ? This
question is easily answered, by remembering that one of the
functions of the par vagum is, to convey to the brain the
sense of the want of air, or of respiration, and that this
stimulus reacts upon those parts of the spinal cord which give
rise to the respiratory nerves of the chest,} Now if this com-
munication be cut off, the influence of the brain, or the me-
dulla oblongata, cannot be transmitted so as to excite those
muscles which are employed in breathing.

14. That this is the true answer to the above question is
also shown by dividing the par vagum in the neck. This
causes palsy of the lungs, and also of the muscles which open
the larynx ; in consequence of which, the top of the wind-
pipe is immediately closed, and death follows from suffocation.
Besides this, it also prevents transmitting to the medulla o&-
longata, the sense of the want of respiration, and thus pre-
vents also the reaction of this part upon the spinal marrow.

15. Does the spinal marrow exert any influence upon the
circulation of the blood ? (It is ascertained that the action of
the heart is nearly independent of the spinal marrowj Its
nervous influence is derived from the par vagum and the
great sympathetic nerve, the former of which has but little
connection with the spinal cord. The whole spinal marrow
has been removed, and still the heart has continued to act.

THE SPINAL MARROW AND ITS FUNCTIONS. 141

Its action, however in such cases is much weakened. That
the heart is, however, in some measure influenced by the spi-
nal innervation, must be admitted.

16. /'What is called the capillary circulation, or that in the
small vessels, is much under the influence of the spinal mar-
row. ) It is found that when any part of it is destroyed, the
blood does not, circulate in the small vessels which derive
their nerves from the portion destroyed. In these cases, the
skin becomes purple, and dry ; perspiration ceases, the cuti-
cle peels off, and the part becomes sensibly colder. The
whole nervous system, however, is concerned in the produc-
tion of animal heat.

17^ Digestion is to a considerable degree under the influ-
ence of the spinal cord^ /In all cases of diseases of the spine,
the appetite is poor, and the digestive powers weak. Colic
and dyspepsia are frequent attendants upon such complaints.
If the eighth pair of nerves be divided, the stomach is imme-
diately paralyzed, and digestion interrupted.} This shows
that the stomach depends for nervous influence on the me.
dulla oblongata, and that it is derived through the medium of
the par vagum.

18. The spinal marrow exerts an important influence over
the kidneys, more so perhaps than over any of the abdominal
viscera. Some physiologists also think that it presides over
the functions of nutrition. What seems to confirm this
opinion, is the fact, that in the Crustacea, insects, and worms,-
which have the power of speedily reproducing any part that
is cut off, the spinal marrow preponderates over every other
portion of the nervous system. Nutrition is known to depend
chiefly on the influence of the great sympathetic nerve, but
its connections with the spinal marrow are so numerous and
intimate, that there can be little doubt, it derives a consider-
able portion of its nervous energy from the latter. The fol-
lowing cut represents the left side of the brain and spinal
marrow, shown by making a section of the cranium and the
spinal column, and removing the dura mater.

142

PHYSIOLOGY.

THE SPINAL MARROW AND ITS FUNCTIONS, 143

a. The convolutions of the cerebrum.

b. The laminae of the cerebellum.
e. The pons varolii.

g. The medulla oblongata.

c. d. f. The medulla spinalis, or spinal marrow, extending from the
first cervical to the first lumbar vertebra, and terminating in the cauda
equina. The cerebrum, it will be seen, is the largest portion of the
brain, and occupies the whole upper cavity of the skull. It rests an-
teriorily upon the arches of the orbits ; in the centre, upon the middle
fossae of the base of the skull, and posteriorily upon the tentorium
cercbclli.

Questions. — How do we find the brain developed in the lower ani-
mals ? Have they great tenacity of life /"? Will zoophytes live when
divided into pieces 1 What is the medulla oblongata ? What its func.
tion ? Describe the spinal cord ? — its membranes ? its shape ? — its
structure ? How many pair of nerves arise from it ? How many from
the neckf — the back/t— the loins £; What is the function of the ante-
rior roots ? — the posterior roots ? What is the use of the spinal cord ?
How is this illustrated ? How proved ? What follows, if the spinal
cord be severed opposite the second bone of the neck ? — the fifth ? — the
first dorsal ? Does the principle of motion reside to any extent in the
spinal cord itself ? What experiment proves this ? Why does a divi.
sion of the par vagum or eighth pair cause death ? Does the spinal mar-
row exert any influence on the circulation of the blood ?— on the capil-
lary circulation t<rt-on digestion ? What proves this ? Has it any in.
fluence over the kidneys ?-s-over nutrition ?

CHAPTER XII.

THE NERVES AND THEIR FUNCTIONS.

1. IN describing the nerves and their functions, it will be
necessary to classify them, or to reduce them to such arrange-
ment, as the present state of our knowledge on the subject
will admit. The following comes as near such a classifica-
tion as it is possible to make : — l\j Nerves of Special Seme.
2. Motific Nerves. 3. The Respiratory Nerves. 4. The
Regular Nerves, 5. The Ganglionic Nervesf

2. FIRST ORDER.— t-The nerves which contribute to the
senses of sight, hearing, and smell, constitute the first class,
and are called Nerves of Specific Sense ; Because they are in-
capable of communicating any other impressions|fthan such
as belong to the respective senses with which they are con-
nected. For example, the olfactory can only transmit ideas
of odours, the optic of colours, the auditory of vibrations,
no matter what the stimulants may be which excite them
to action. If we send an electric shock to the eye, it re-
ceives the impression of light ; to the ear, of sound ; and to
the nose, an odour is perceived : so also, if we press or strike
the ball of the eye, we experience a vivid sensation of light,
and the same phenomenon occurs when the eye is pierced by
the needle of the surgeon : so also, if we take two pieces of
different kinds of metal in the mouth, and placing one over,
and the other under the tongue — allow their edges to come
together, we perceive at once a peculiar taste, excited by
galvanism. Thus do these nerves communicate to the mind
that they are affected in the only manner of which they are
capable.

THE NERVES AND THEIR FUNCTIONS. 1-15

This cut represents a portion of nerve, showing the filaments of
which it is composed, and one of them drawn out.

3. First, or olfactory. — These nerves take their name
from " olfactus" the smell, as they are essential to this sense.
They are the softest nerves in the body, and more closely
connected with the hemispheres of the brain than any othei>
They lie immediately under the anterior lobes of the brain ;
and as they pass on, they swell into a bulb, from which
numerous fibres issue, and pass into the nose through a plate
of one of the bones of the skull. This plate is pierced with
so many holes for transmitting these twigs of the nerve, that
it has the appearance of a seive ; and from this circumstance
is called the ethmoid bone. The olfactory nerve is spread
out upon the lining membrane of the nose, and is merely
defended by a thin layer of mucus. It was necessary that
these nerves should come to the surface, in order to come in
contact with the vapours inhaled by the nostrils. In some
animals these nerves are very large, especially in ruminants,
but in others they are entirely wanting, as in whales. In
fishes, you may see the bulb of the olfactory placed immedi-
ately under the cup-like nostril. From the bulb, the nerve
runs backward along a canal filled with transparent fluid,
enters the skull, and joins the brain.

4. The second, or optic. -Z These are the largest of the
cerebral nerves, and can be traced as far back as the medulla
obfongata at the base of the brain. They pass along the base
of the brain, and just before they enter the orbits they unite
with each other^ or seem to decussate, or cross each other.
In some fishes, these nerves evidently cross without union ;
but in man, it is now pretty well established, that a semi-

»decussation takes place ; that is, one half of the right optic
nerve crosses to the opposite side, and joins a half of the
"

146 PHYSIOLOGY.

left nerve to proceed to the luft eye ; so that each eye receives
its optic nerve from both sides of the brain ; the right sup.
plying the right side of both eyes, as the left does its cor
responding side of both. After the nerve has entered tha
orbit, it proceeds forwards to the ball of the eye, and pene-.
trating the coats of that organ, expands into a very delicate
web, or nervous net-work, called the retina, which Jserves to
receive the image of objects falling upon it.)

"5. The auditory nerve.— jf he last nerve of specific sense,
runs along with another, the two together being known as
the seventh, of which the auditory forms the soft portion, or
portio mottis. It arises from the medulla oblongata, and
goes on in contact with the hard portion, or portio dura, to
the internal auditory passage, which they enter. Here the
soft portion spreads out into a great many small branches,
which are distributed over the surface of the internal por-
tions of the ear, and their extremities float in the water
contained in the labyrinth, from which they receive vibra-
tions which produce the impressions of sound)

6- Second order. — -The motif erous nerves^ which consti-
tute the second order, consist of three nerves ; the third, the
sixth, and the ninth, with perhaps a branch of the fifth.
These take their origin at the anterior columns, in the same
line with each other ; but fibrils of sensation afterwards join
them, so that they are analogous to the double-rooted nerves
of the spinal marrow.

76^Fhe third pair rise from the crura of the brain, and

pass forward to a hole in the bottom of the orbit, through

which they enter, and supply four of the six muscles which

/move the eye, and also the muscle which moves the upper

' eye-lid, thus placing these muscles under the command of

the wilj. Besides this, a small twig of the fifth nerve swells

out into a ganglion, and then joins a twig from the third,

which go on together, and penetrate the coats of the eye, to

which they impart sensibility, and are connected with the

functions of the irisJ It is worthy of remark, that here the

THE NERVES AND THEIR FUNCTIONS. 147

general law is kept, viz., that a ganglion is formed in the
sensific nerves, before they become associated with the fila-
ments of motion.

8. (The sixth pair arise near the last, and also enter the
orbitj^jhere they are entirely expended upon the muscle
which turns the eye towards the temple. Where this nerve
has been injured or lost its power, the eye is permanently
turned in towards the nose ; and such a person is said to be
cross-eyedt

9< The ninth pair arise from the pyramidal bodies, and
passing through holes in the occipital bone, proceed forwards
towards the angle of the jaw, by the side of the hyoid bone
of the tongue, and are distributed upon the muscles between
the lower jaw, hyoid bone, and tongue, the motions of which
it regulate^

10. THIRD ORDER. — This division embraces what Sir
Charles Bell calls thefyespirato7-y nerves) These are not only
connected with the function of respiration, but contribute also
to the expression of the passions and emotions of the mind.
They consist of the fourth ; the portio dura ; of the seventh,
or facial ; the eighth, or par wgum ; the phrenic ; and the
external respiratory. As the medulla oblongata, consists of
three columns ; the nerves of motion arise from the anterior,
those of sensation from the posterior ; while the respiratory
nerves, already mentioned, spring from the middle portion,
and all nearly on the same horizontal plane.

1 1 . (The fourth nerve supplies the superior oblique muscle
of the eye, which rising from the bottom of the orbit, runs
along the roof of that cavity, till it comes close to its brim,
where it terminates in a small tendon, which passes through
a loop or pulley, then turns back, and is inserted into the
posterior part of the ball, so that its contraction turns the
eye in towards the nose.) When the will ceases to control
the, movements of the eye, it comes under the action of the
superior oblique muscle. We see this, in acute bodily
pain, and at the point of death, when the voluntary muscles

PHYSIOLOGY.

have lost their power. This turning of the eye inward
is supposed to indicate great agony ; but it rather shows
that all sufficing has ceased, and that the powers and
aation and motion are lost If we raise the eye-lid of a
person asleep, we shall find the eye turned in the same direc-
tion ; also in fainting, and in cases of suspended animation.
The fourth nerve is partly then under the influence of the
will, and partly independent of it.\

12. (The seventh nerve, consists of two portions, one of
which, the auditory, has already been described. The other
portion is called /octal, because it is distributed over the face.
Its origin has already been stated, though it receives
from each column of the medulla oblongata ; so that its
function is complicated. It seems, in fact, to combine the
character of a regular nerve and one of instinctive motion ;
it enters the internal auditory passage in connection with
the nerve of hearing, then entering a canal in the temporal
bone, it comes out just before the ear, and spreads out over
the face in three principal branches, called pes auarima, 01
goose's foot, from its resemblance to that object

13.frhe ffih nerve is distributed to the same parts or
which* the/aciol is ramified on the fac^ the one serving foi
sensation, the other for expression. Thus when the facia
nerve is divided, or its functions destroyed by disease, the
side affected loses all power of expression, though &ensati»i
remains unaffected ; on the contrary, if we divide the fiftl
pair, sensation is entirely abolished, while expression ranuBs
The facial nerve not only communicates the purposes of tb<
will to the muscles of the face, but at the same time, i
them into action under the influence of instinct and
thy. On this subject a late writer remarks, « How eaqprts
sive is the face of man ? How clearly it announces tib
thoughts and sentiments of the mind ! How well deptdtei
are the passions on his countenance ! tumultuous rage, a&jac
fear, devoted lore, envy, hatred, grief, and every other
tion, in all their shades and diversities, are imprinted

THE NERVES AND THEIR FUNCTIv 149

in characters so clear that he that runs may read ! How
difficult, Bay, how impossible is it to hide or felsify tin ex*
ns which indicate the internal feelings! Thus con-
scious guilt shrinks from detection, innocence declares its
confidence, and hope anticipates with bright expectation."

14.^The e*gk& pair of nerves consist of three distinct por-
the Jirst of which, from its being distributed to the
tongue and throat is called gbsm-pkaryngeal ; the tecomi,
from its irregular coarse is called ragout, or the wandering
nerve ; and die Ikird, from its origin from the spinal marrow,
is called accessory. These different nerves join just as they
are about to escape from the skull, which they do in com.
pany with the internal jugular vein, and as soon as they
emerge they form connections with the great sympathetic^

lo^Tlie twgowi on leaving the skull, sends off branches
to the pharynx and esophagus, also to the larynx and the
M»dij which close the air passage, and the mucous mem.
brane covering it Its trunk runs down the neck included in
the same sheath with the carotid artery and jugular vein,
and enters the chest under the collar bone) {Here a branch
is siven off, which locks round the subclavian artery on one
side, and arch of the aorta on the other, and goes up to the
larynx hence it is called recurrent. J It supplies those mus-
cles particularly which open the air passage. The vagans
sends down twigs with the sympathetic which surround the
the divisions of the wind-pipe, and accompany them in all
their ramifications through the lungs. It also sends numer-
ous t \vigs to the heart, stomach, liver, pancreas, spleen, in.
testinal tube, and finally with the sympathetic nerve, and forms
those great nervous centres or ganglia in the abdomen, which
supply all the viscera of that cavity with nervous energy)

16. The phrenic nerve derives Its name from its distribu-
tion to the diaphragm, which at one time, was considered as
the seat of the soul. Jit passes out of the vertebral canal be-
tween the second, third, fourth, and sometimes fifth cervical

150 PHYSIOLOGY.

vertebrae ; it runs down the neck, and enters the chest on
the outer side of the internal jugular vein.

17. The external respiratory nerve is distributed to the
intercostal muscles, and those which extend from the ribs to
the shoulder, and which are occasionally employed in labo-
rious breathing. It is through the instrumentality of the
accessory, phrenic, and external respiratory, that the mus-
cles employed in respiration are brought into action, com-
bined and directed with the proper degree of force, velocity,
and extent, without the necessity of interference of the
mind. Though to a certain extent, they may be under the
influence of the will, yet it is only in a secondary degree.
No one, for example, can long suspend the movements of
respiration, for in a short time, instinctive feeling issues its
irresistible mandates, which neither requires the aid of erring
reason, nor brooks the capricious interference of the will.)

18. The influence of this order of nerves in the expression
of the passions, is strikingly depicted in Sir Charles Bell's
Treatise on the Nervous System. " In terror," he remarks,
" we can readily conceive why a man stands with his eyes
intently fixed on the object of his fears, the eye-brows eleva-
ted, and the eye-balls largely uncovered ; or, why with hesi.
tating and bewildered steps, his eyes are rapidly and wildly
in search of something. In this way we only perceive the
intense application of his mind to the objects of his appre-
hension, and its direct influence on the outward organs.
But when we observe him farther, there is a spasm in his
breast ; he cannot breathe freely ; the chest remains elevated,
and his respiration is short and rapid ; there is a gasping
and convulsive motion of his lips, a tremor on his hollow
cheeks, a gasping and catching of his throat ; his heart
knocks at his ribs, while yet there is no force in the circu-
lation, the lips and cheeks being ashy pale."

19. " To those I address, it is unnecessary to go farther
than to indicate that the nerves treated of in these papers
are the instruments of expression, from the smile upon the

THE NERVES AND THEIR FUNCTIONS. 151

infant's cheek to the last agony of life. It is when the
strong man is subdued by this mysterious influence of soul
on body, and when the passions may be truly said to tear
the breast, that we have the most afflicting picture of human
frailty, and the most unequivocal proof, that it is the order
of functions we have been considering that is thus affected.
In the first struggles of the infant to draw breath, in the
man recovering from a state of suffocation, and in the agony
of passion, when the breast labours from the influence at the
heart, the same system of parts is affected, the same nerves,
the same muscles, and the symptoms or characters have a
strict resemblance."

20. FOURTH ORDER. — Regular Nerves. — I have already
stated that there arelthirty pair of regular nerves which go
out from the spine/ each nerve being composed of two kinds
of fibres ; those of the anterior column being subsidiary to
motion, and those from the posterior to sensation. With
these, physiologists now class the ffih nerve. This large
nerve divides into three principal branches £t\\ejirst going to
the eye, is called optlialmic) jhe second to the upper jaw, is
called superior maxillaryjfaiid the third sent to the lower jaw,
is named inferior maxillar^ It is the third branch, how-
ever, which is truly a compound nerve, as its roots arise both
from the anterior and posterior columns. The inferior
maxillary branch, is a nerve of both sense and motion;
its filaments of motion supply the muscles which shut the
jaw, while those of sensation go to the tongue, salivary
glands, gums, teeth of the lower jaw, external ear, cheek,
chin, and lower lip. ^It is this nerve) which gives sensibility
to the face, and it is this which is the seat of that painful
affection called tic dolouroux, which is sometimes removed by
cutting the nerve affected. In the cat, the hare, and other
.animals with large whiskers, the filaments of this nerve can
be traced to the bulbs of the hairs, which accounts for the
delicate tact which these animals are endowed with, and by
means of which they are enabled to wind their way in the

152 PHYSIOLOGY.

dark, through intricate passages, with the greatest facility.
{The fifth nerve is associated with the organs of the senses
of smell, sight, and hearing ; it exercises that of touch, is
the immediate instrument of taste, and is affected in some
degree by pungent odorous substances, by light, and by
sound,!

21. Spinal nerves.-^The nerves of the spinal cord are all
similar in their construction, and in the functions which
they perform/ ^The two sets of filaments of which they are
composed, though enclosed in the same sheath, yet remain
entirely distinct throughout their entire course*? i^Fhey go
to every muscular fibre in the system, and spread out over
the entire surface of the body) which possesses, accordingly,
a more exquisite sensibility than the deep-seated parts.
Thus in amputating a limb, the chief pain is in cutting
through the external parts ; for the bone may be sawn
through, the muscles, tendons, and ligaments cut and la-
cerated, and even burnt with a red-hot iron^ and still the
patient experiences little or no suffering.

22. f The object of endowing the skin with such a high
degree of sensibility, is, doubtless, to warn us to avoid, not
only what is injurious to the skin itself, but also what might
endanger internal parts. It thus serves as a protector to
the whole body. The extremes of heat and cold, which
might prove injurious, produce their painful impressions^
mechanical causes rouse by their sharpness, roughness, or
hardness ; acrid and corrosive chemical agents induce un-
easy sensation — all which serve to admonish us to shun the
causes producing such effects, fit is remarkable to notice
how every part of the body is endowed with its own kind
of sensibility/' J The skin feels changes of temperature ; the
muscles experience only a sense of fatigue ; the eye is sen-
sible only to light ; the ear to sound ; the nose to odours ;
the heart to blood ; the stomach to food^ &c. ; and these
sensations are sent along up to the brain by little threads,
in close contact with other threads, which bring back the

THE NERVES AND THEIR FUNCTIONS.

158

commands of the will ! Truly may it be said, " man is fear-
fully and wonderfully made."

23.* The spinal nerves are classed according to the por-
tion of the spinal column from which they issue £ as the
neck, back, loins, and pelvis ; forming eight cervical, twelve
dorsal, five lumbar, and five sacral nerves ; all being con-
nected with the sympathetic. The four lower cervical and
first dorsal go to the arm-pit, where they form a complicated
plexus, from whence nerves issue to supply the arm and hand.
The dorsal nerves supply the integuments of the body, the
intercostal muscles, and those of the chest. The lumbar
and sacral nerves supply the muscles of the loins and abdo-
men, together with the lower limbs.

24. FIFTH ORDER. — Ganglionic Nerves. — We have now
considered, somewhat minutely, that portion of the nervous
system which is called the cerebro-spinal, embracing the
brain, the material instrument of thought, the source and
channels of voluntary motion, and of instinctive movements
and sympathy. iThe ganglionic nerves jjare|sometimes called
great sympathetic, or the great intercostal ?. but sympathy
has been shown to be chiefly independent of it, except so
far as it receives filaments from the cerebro-spinal nerves ;
and it is called great, not so much from its size, as from its
supposed importance.

A plexus of nerves.

154 PHYSIOLOGY.

25. The ganglionic, or great sympathetic nerve, consists in
a series or chain of ganglions, extending from the base of
the cranium to the extremity of the sacrum. They are
placed on the lateral part of the bodies of the vertebrae, and
are united to each other by intermediate nervous cords, and
send off continually filaments to all the adjacent organs.
With the exception of the neck, there is a ganglion for each
intervertebral space, both of the true vertebrae and sacrum.
Besides these, there are other ganglia situated around the
trunks of some of the large vessels of the abdomen^ These
ganglia are composed of a mixture of cineritious and medul-
lary matter, and are supposed to be the centres of peculiar
nervous power.

26.<JAs to the functions of this order of nerves, there is
good reason to believe that the peculiar vitality of every
organ in the body directly depends on them. Most physi-
ologists believe that they preside over the involuntary func-
tions, as secretion, nutrition, absorption, calorification, &c.
Others suppose that the office of the ganglions is to render
the organs, which are supplied with nerves from them, inde-
pendent of the will. As branches from them, accompany
the blood-vessels throughout their course, every part of the
body must, to a certain extent, be under their influence.

27. There have been three hypotheses prevalent in respect
to the functions of the nerves. The first, that the brain
secretes a fine fluid, which circulates through the nerves,
called animal spirits, and which is the medium of communi-
cation between the different parts of the nervous system ;
the second regards the nerves as cords, which transmit all
impressions by a kind of vibration ; and the third ascribes
nervous influence to electricity or galvanism. But there
is no proof whatever of the existence of any such fluid ;
the doctrine of vibrations is pretty much abandoned ; while
the. electrical hypothesis, though at first view perhaps
more plausible, has probably no better foundation to rest
upon.

THE NERVES AND THEIR FUNCTIONS. 155

Questions. — How are the nerves classified? What nerves consti
tute the first order ? Why called nerves of specific sense*? Describe
the first or olfactory. Is it large in animals ?^— in fishes ? — in whales ?
— Describe the second, or optic. Do the fibres cross each other ? — its
function ? Describe the auditory nerve. What nerves constitute the
second order ? Where do they arise ? Describe the third pair ; — their
function ? Describe the sixth pair ; — their function ? — The ninth pair ;
— their function HL.Wb.at compose the third order of nerves ? Describe
the fourth nerve \— its function ? Describe t^he seventh nerve ; — its
functioa#A'*niS fi%h nerve ; — its function -f^^stMuMn^&c. ? Des.
cribe the eighth pair of nerves. What are its three branches called ?
Describe the vagans ; — the recurrent ; — the phrenic ; — the external
respiratory ? What does Sir Charles Bell say of the influence of this
order of nerves ? \fwhat compose the fourth order of nerves ? Why is
the fifth nerve classed with the regular nerves ? Where does its first
branch go ; — its second ; — its third ? What nerve is afiected in tic
doloreaux ; — its function ? "Describe the spinal nerves ; — their mode
of origin ; — their distribution ? Why is the skin so sensible ? Has
any part of the body its own sensibility ? Illustrate this. How are the
spinal nerves classed ? What compose the fifth order ? What other
names for the ganglionic nerves ? Describe them. What is the func-
tion of the ganglionic nerves ? What hypotheses have prevailed in
relation to the functions of the nerves ?

CHAPTER XIII.

THE FIVE SENSES. SENSE OF TOUCH.

1 . \A sensation is the perception of an impression made on
some organ.' By our sensations we receive a knowledge of
what is passing within or without the body. They are ac-
cordingly{divided into internal and external^ fAn internal
sensation, is one which is produced by causes acting within
the system, as hunger and thirst / but an external sensation
is one that is occasioned by the impression of a body, exter-
nal to the part impressed, as sight, hearing} &c.

2. No sensation, we have seen, can be perceived unless it
is transmitted to the brain. When ideas, which have been
called '<fthe images of sensible objects,* are reflected upon
and compared with each other, we exert thought and judg-
ment ; and when they are recalled, we are said to exert the
memory. Thus are the senses avenues to knowledge, though
they do not give rise, as some have stated, to our intellect
and moral powers.) With every sense an animal discovers
a new world ; thus creation is to it increased or diminished,
accordingly as its senses are more or less numerous. A
sensation lasts a certain time after the exciting cause has
ceased. Thus if a piece of wood, with one end ignited is
whirled round, we see a luminous ring ; the sensation pro-
duced by the wood in each point of the circle continuing
till the wood arrives at that point again ; a rocket forms a
train.

3. {The external senses are Jive in number; touch, taste,
smell, hearing, and vision. ; These are all situated at the sur-
face of the body, so as to be capable of acting on external
bodies. (Most of them are under the control of the will ; at
least they may be exercised actively or passively^ and by

SENSE OP TOUCH. 157

directing the attention, the impression may be rendered more
vivid.

4. /The sense of touch is the general feeling or sensibility
produced by the skin, and which instructs us regarding the
general qualities of bodies.) It resides also to some extent
in mucous membranes, as in the mouth, throat, &c., although
in a very imperfect degree. For example, we cannot feel
the pulse by placing the tongue over it on the wrist, as any
one can ascertain by trying the experiment. fThe sense of
touch is distinguished by some writers from that of feeling,
but they are only modifications of the same sense.

5. I have already given some account of the structure of
the skin, and stated that it is Divided into four layers, viz.,
the (cuticle, mucous web, papillary body, and true skin } and
thatT^he cuticle is the thin, transparent pellicle^or membrane,
whichfforms the external incrustment of the body, protecting
those papillae, in which reside the sense of touch.) As no
blood-vessels or nerves have been traced in it, it is supposed
to be an unorganized texture, or an albuminous secretion,
poured out by the subjacent vessels, and hardened by the in-
fluence of the air. This accounts for its rapid formation,
when destroyed by a blister, burn, &c. When a part of the
body is exposed to irritation, the vessels which pour out the
lymph, from which the cuticle is derived, have their action
increased, and the cuticle either becomes thickened, as in
the palms of the hand and soles of the feet, or the effusion is
so abundant as to cause a separation between it and the true
skin, causing blisters.

6. Now, it is a general law, that pressure promotes ab-
sorption ; and we see this exemplified daily in cases of
tumours, abscesses, bandaging for dropsical effusions, &c.
Had this tissue been subjected to this general law^the fric-
tion and pressure to which the cuticle of the hands is ex-
posed in manual labour, and of the feet in walking, would,
in a short time, have entirely deprived them of protection,
instead of rendering their covering more dense and thicker,

14

158 PHYSIOLOGY.

that it may more effectually serve as a shield to the parts it
covers. As the cuticle is constantly renewed from its inter-
nal surface, it is also constantly peeling off in the form of a
fine powder, or thin scales. After scarlet fever, and other
diseases, attended with great heat of the skin, it is entirely
removed ; the old scarf-skin, as it is called, being thrown off
in large patches. We find a cuticle in all organized beings,
plants, as well as animals, though it differs greatly in struc-
ture and appearance. In many reptiles and crustaceous
animals it is entirely shed at certain periods, presenting an
exact mould of their bodies, their scales, and other external
parts, and even their eyes being exactly represented.

7. The mucous web has already been pretty fully described.
It is a soft pulpy net-work, and seems to consist chiefly of
the shaggy extremities of blood-vessels, interlaced and bound
together by delicate filaments of cellular membrane. ) It is
the seat of those minute globules which constitute the colour-
ing matter which vary in their tints in different races.
These tints are influenced in a greater or less degree by
climate, for we find in tropical countries the colours of both
plants and animals are more intense and brilliant than in
colder regions, and that exclusion from light produces a pale
blanched appearance, while exposure to it has a contrary
tendency ; but these variations are neither permanent nor
do they descend to the offspring.

8. The dermis, or true skin, is the thickest part of the
external integuments, and is composed of an infinite number
of plates, consisting of filaments inextricably wound together,
and abundantly supplied with blood-vessels and nerves J The
external surface of the cutis is every where studded by very
minute nipples or papillae, and in several parts, as the palms
of the hands and the ends of the fingers, they are arranged
in symmetrical rows, which form wavering lines, and separ-
ated by small crevices that admit of the flexions of the skin
and its adaptation to the surfaces of external objects.| These
papillae are the terminations of nerves and blood-vessels, and

SENSE OF TOUCH. 159

are the immediate instruments of touch. Although covered
by the cuticle and mucous web, yet the removal of these by
blisters or otherwise, does not increase the sense, but tends
to destroy and disturb it. From this arrangement, sensation
is communicated through the hair and nails, as well as the
cuticle. In animals, of the cat tribe, which are furnished
with whiskers, these serve as organs of touch, as their roots
terminate in these nervous papillae.

9. The property of touch belongs to every part of the
body, though ;|he hand is considered as its special organ.
The great number of bones of which it is composed, make it
susceptible of every variety of motion, by which it changes
its form, and adapts itself to the inequalities of the surfaces
of bodies. What is called the pulp of the fingers, seems

^composed chiefly of a tissue of blood-vessels and nerves,
covered by the cuticle and mucous web, and supported by
the nailsjj The delicacy of touch is vastly improved by
education and practice. This is shown in the case of the
blind, who often can distinguish by touch the different
colours, and even their different shades, t This will not ap.
pear impossible when we consider that difference of colour
may depend on the dispositions, arrangement, and number
of the little inequalities which roughen the surface of bodies,
even of such as appear the most polished, and thus fit them
to reflect certain rays of light, while they absorb the others.
That the exercise of this sense is a gratification to the
young, is apparent from the eagerness with which the child
stretches out his littlo hands to all the objects within his
reach, and the pleasure he seems to take in touching them,
in all their parts, and running over all their surfaces.

10. t have already mentioned that the external surface of
the body is endowed with this special sensibility^ not only
that it might furnish us with a knowledge of the characters
of external objects, and so lead us to avoid dangers which
surround us, but also to be a source of positive pleasure^
Though in the acuteness of the other senses many animals

160 PHYSIOLOGY.

surpass man, yet in the exquisite sensibility of his skin, man
stands unrivalled. " The skin of man," says Majendie, f is
more delicate, fuller of nerves than that of the mammiferae ;
its surface is covered only by the epidermis, insensible in-
deed, but so thin, that it does not intercept sensation, whilst
the hairs which cover so thickly the body of quadrupeds, the
feathers which clothe that of birds, quite deaden it.J The
hand of man, that admirable instrument of his intelligence,
of which the structure has appeared to some philosophers, to
explain sufficiently his superiority over all living species ;
the hand of man, naked, and divided into many moveable
parts, capable of changing every moment its form, of exactly
embracing the surface of bodies, is much fitter for as-
certaining their tangible qualities, than the foot of the quad-
ruped, inclosed in a horny substance, or than that of a bird,
covered with scales too thick not to blunt all sensation."

11. The hand then, is the chief organ of touch, and in the
ends of the fingers it resides in the greatest perfection. Thus
we see that t\\e\blind are able to read with facility by passing
their fingers over the letters, which are raised by a particu-
lar kind of type^ In this manner they acquire a knowledge
of geography, arithmetic, reading, and the usual branches of
education, not often met with even in those who have the
use of their eyes as well as their hands.

12. Buffon, the celebrated naturalist, thought so much of
the sense of touch, that he believed the cause, why one per-
son has more intellect than another is. his having made bet-
ter use of his hands from early infancy. Other philosophers,
as Majendie states, have ascribed man's superiority over ani-
mals, and his intelligence, to the fact that he possesses a
hand. But the hand is only the instrument of the mind, the
agent of the will ; it can only execute ; the mind must plan.
Besides, the idiot has sometimes the sense of touch more deli-
cate than the man of genius, or than the most skilful artist ;
while some of the most ingenious artists have by no means,
the most delicate touch. Galen truly says, that man had

SENSE OF TOUCH. 161

hands given him because he was the wisest creature ; but he
was not the wisest creature because he had hands.*

13. /The following cases prove that hands are not indispen-
sable to genius, and that the human mind can even triumph
over the imperfections of the body. A few years since a
Miss Biffin was exhibited in London, who was entirely destitute
of both upper and lower extremities ; and yet she was very
intelligent and ingenious. She could hem-stitch with the
greatest facility, turning the needle very rapidly in her
mouth, and inserting it by means of her teeth. She also
painted miniatures faithfully and beautifully, holding the
pencil between her head and neck. All her motions in fact
were confined to the tongue and the lips, and to the muscles
of the neck.

14. In the year 1825 there was a young artist in Paris,
who had no hands or arms, and only four toes on each foot ;
and yet he sketched and painted beautifully with his feet. I
have myself seen a young lady, born without arms, who had
acquired so much skill in the use of the scissors as to be able,
by holding them in her mouth, to cut likenesses, watch-pa-
pers, flowers, &c. She would also draw and write, and exe-
cute all kinds of needle work with her mouth. A boy was
not long since exhibited in the museum of this city, who
performed all these things with his toes. This shows that
other parts of the body besides the fingers, are capable of
acquiring great delicacy of touch.^

* On this subject Dr. Elliotson remarks, "As philosophers have
ascribed the superiority of man's intellect to his hand, and of the ele-
phant's to its trunk, the constructiveness of the beaver to its tail, and
the ferocity of the tiger to its teeth and claws, the poor man may be
excused who was lately executed at Chelmsford, and left the following
directions. " I, Edward Clarke, now in a few hours expecting to die,
do sincerely wish, as my last request, that three of my fingers be given
to my three children, as a warning to them, as my fingers were the
cause of bringing myself to the gallows, and my children to poverty."
14*

162 PHYSIOLOGY.

•

15j{ In animals, the organ of touch varies. In the ape
tribe it is similar to that of man. In some quadrupeds it
is seated in the lips, snout, or proboscis, as in the horse, the
hog, the mole, the rhinoceros, and the elephant. Indeed,
the trunk of the elephant comes very near to the human
hand in nicety of touch, and delicacy of perception. The
bat is remarkable for sensibility of touch. It has been found
that if its eyes were destroyed and its ears and nostrils shut
up, it would fly through intricate passages, without striking
against the walls, and avoid every object placed in its way.
This faculty is supposed to be owing to the great delicacy of
touch residing in the membrane of the wings, which feels
instantaneously any change produced in the resistance of the
air.

16.1 Ig insects, the antenna or feelers, are the organs of
touch. These are of a great variety of forms, very flexible ;
and constantly in motion, when the insect is walking. If
the feelers of an insect are cut off, it either remains motion-
less, or if it attempts to fly, it appears bewildered and lost.
It is by means of their feelers that bees are able to work in
a hive without light, and build their cells with the greatest
regularity ; by them also, they communicate to one another
their impressions and their wants. |

17. It is supposed that the different modes in which ants
touch each other with their feelers, when they happen to
meet, constitutes a kind of natural language, understood by
the whole tribe. It is evident that they could not co-operate
in their labours without some kind of language. When an
alarm is given in time of danger, one ant strikes his head
against the corselet of every ant which it chances to meet,
and these repeat the same act to all that fall in their way,
and so the news is quickly spread through the whole societyjf

18. Sentinels are always placed on the outside of ants'
nests to apprize the inhabitants of any danger. When an
enemy approaches, these guardians quickly enter the nest
and spread the news in the way just stated, and soon the

SENSE OF TOUCH. 163

whole swarm is in motion. While a larger proportion of
the ants rush out to repel the attack, others, who have the
office of guarding the eggs and the larva, or eggs, hasten to
remove their charge to places of greater security. These
acts all depend on the faculty of touch, so that it is as import-
ant to the lower animals as to man.

19. Sight, hearing, and touch, have been called intellec-
tual senses, because they are the means through which we
obtain our most valuable information, the witnesses that fur-
nish the evidence of the existence of external things. We
can have no doubt as to the evidence they deliver, if they all
agree in their report. We find however that if we depend
on either alone, we are liable to be deceived. (Sight is liable
to many illusions^ we may, under the influence of the ima-
gination, or of a diseased brain, imagine that^ve see a
thousand strange sights, ghosts, hobgoblins, spectres, and
devils ; or from similar causes, we may believe that we hear
strange and unearthly sounds ; but if we attempt to touch
the objects which appear to present themselves to our vision,
or which discourse such unnatural music, we find that they
vanish before us, like the ignis fatuus, or jack-o'lantern,
which we may chase " o'er bog, and o'er moor," but we can
never lay our hands upon it. I have often watched, with a
degree of wonder, the action of a patient labouring under
drunken delirium ; the unhappy maniac not only sees strange
objects about his bed, and flitting before his eyes, but he
hears them singing and talking to him ; he puts out his hand
to grasp them, — he grasps nothing, — still he is not unde-
ceived, nothing can make him believe that what he sees
and hears are only the phantoms of a diseased brain ; he per-
sists in endeavouring to seize, to touch the strange objects,
and only ceases, when after days and nights of incessant
vigilance, his strength exhausted, he either sleeps or dies !

20. Touch has, therefore, been relied on in every age, as
the most certain of our senses,"* and it is well to recollect that
the most important fact that ever occurred on the theatre of

164 PHYSIOLOGY.

this earth, vizjfthe resurrection of the Saviour^ is established
by the testimony of the three intellectual senses. In the
gospel of the evangelist St. John, we read, " But Thomas,
one of the twelve, called Didyrnus, was not with them when
Jesus came. The other disciples therefore said unto him, we
have seen the Lord. But he said unto them, except I shall
see in his hands the print of the nails, and put my finger into
the print of the nails, and thrust my hand into his side, I will
not believe. And after eight days again his disciples were
within, and Thomas with them ; then came Jesus, the door
being shut, and stood in the midst, and said, peace be unto
you. Then saith he to Thomas, reach hither thy finger, and
behold my hands ; and reach hither thy hand, and thrust it
into my side; and be not faithless but believing. And
Thomas answered and said unto him, my Lord and my God.
Jesus saith unto him, Thomas, because thou hast seen me,
thon hast believed ; blessed are they that have not seen, and
yet have believed." Thus was the fact of the resurrection
established by the evidence of so many of the senses, as to
render deception impossible.

21. In some instances the touch itself, is liable to error.
For example(if we roll a pea, or a bullet, between two fingers
crossed, we receive the impression of two distinct objects,
though we know there is only one ; and if we look at it, at
the same time, the illusion is not removed, though we see at
once that it is an illusion. }. The organs here are, however,
placed in an unnatural position. Another fallacy occurs
with respect to heat. If we place the hand in separate ves-
sels, the one containing warm, and the other very cold water,
and after some time withdraw the hands, and immediately
plunge them in the mixture of both waters, to the one hand
the mixture appears warm, and to the other cold. So in a
tropical country, if one person descends a high mountain
from the regions of perpetual snow, and meets at the middle,
another ascending from the hot valley below, he who is de-
scending will feel oppressed with heat, while the other is

SENSE OP TOUCH. 165

shivering with cold, and both sensations are produced by the
same temperature. Frozen mercury excites the same sensa-
tion as red hot iron. A piece of marble will feel colder than
a woollen garment, although both be of the same temperature,
because the marble is a better conductor of heat than wool-
len ; a deep cellar appears warm to us in winter, and cold in
summer, though its temperature is nearly the same all the
year round. During the voyages made by Captain Parry
to discover the north-west passage, it was found that after
having lived for some days in a temperature of 15 or 20 de-
grees below zero, it felt quite mild and comfortable when the
thermometer rose to zero and conversely. The sense, there-
fore, only gives us an idea of the relative, not the actual
heat of bodies/

22. (The sense of feeling may become blunted to, an extra-
ordinary degree) \Chabert, the Fire King, was said to have
been in the habit of swallowing forty grains of phosphorus
at once ; washing his hands in melted lead ; and drinking
boiling oil, without any apparent injury. There is a great
difference in the degree of sensibility of the mucous mem-
brane, in different individuals, some being able without in-
convenience, to swallow fluids of a temperature which
would be very uncomfortable to others/

23. The tactile power of the skin is not proportionate to
its sensibility. Thus the arm-pits, flanks, soies of the feet,
and other parts of the body, have slight power of distinguish-
ing objects by touch, although they are very sensible. It
would be difficult to make a person laugh by tickling the
ends of his fingers, and yet we have seen that their sense of
touch is more delicate than that of any other portion of the
skin. All the surfaces and solids of the body possess a kind
of sensibility, peculiar to themselves, and in disease may give
sensations, but this a different property from that of touch.

Questions. — What is a sensation ? How are they divided? What

166 PHYSIOLOGY.

is an internal? What an external sensation? What are ideas?
What is the office of the senses ? How many external senses are there ?
Are they under the control of the will ? What is touch ? Is touch the
same as feeling ? Of how many layers is the skin composed ? What
is the cuticle ? How formed ? Its use ? Is it subjected to the same
law as the other parts of the body are in relation to pressure? What
would have been the consequence ? Describe the mucous web. — The
true skin. Where is the sense of touch chiefly situated ? Describe the
papilla?. What is the pulp of the fingers chiefly composed of? Can
the blind distinguish colours by the touch ?'/How is this explained?
Why is the external surface endowed with special sensibility ? What
does Majendie say of the human skin ? By what process are the blind
enabled to read ? What cases show that the possession of a hand is not
necessary for the display of intellect and ingenuity ? What is the or-
gan of touch in animals ? — in insects ? What senses are liable to illu-
sions ? Which is the most certain of the senses ? What fact was
established by the senses of hearing, sight, and touch ? Is the touch
ever liable to error ;?Vln what cases? May the sense of feeling be-
come blunted ? What facts prove it ? Are the tactile powers of the
skin in proportion to its sensibility ?

CHAPTER XIV.

SENSE OP TASTE.

1. THE sense of taste is allied to that of smell and touch,
as it requires the immediate contact of the body with the
organ where the sense resides) (The quality of bodies,
which it teaches us, is called sapidity. The superior surface
of the tongue is the chief organ of taste ; though;the general
lining of the mouth and the upper part of the throat partici-
pate in the function^ fThe tongue is chiefly composed of
muscular fibres, running almost in every direction ; conse-
quently it possesses great versatility of motion, and can be
moulded into a great variety of shapes. It may be con-
sidered as a double organ, as it is formed of two symmetrical
halves, whose boundaries are marked by a slight groove in
its upper surface ; dividing it into right and left. From
this groove a membranous partition extends down through
its centre, and is attached to the froenum or bridle beneath.
The tongue is not only the organ of taste but also of articu-
lation, and also aids in mastication and deglutition^

2. The tongue is abundantly supplied with blood-vessels ;
and its nerves, as we have seen, are supplied from three
sources. There has existed great difference of opinion
among physiologists, as to which of these three is the special
nerve of taste. General opinion now holds the ffth, as the
proper nerve of taste, as well as of sensibility ; the ninth, as
that of voluntary motion ; and the eighth, as the means
whereby the organ is brought into association with the
throat, gullet, larynx, &cJ /jDr* Elliotson, however, and some
others, think that the glosso-pharyngeal is the nerve of
taste.

3*. When we examine the surface of the tongue, we find
it thickly studded with fine papillae, or viJli, giving the organ

168

a velvety appearance. There are three varieties of these
papillae. -The first are situated near the root of the tongue,
and belong' to the class of mucous follicles, whose office it is
to furnish this secretion. These are much larger than the
others, and are called lenticular, from being shaped like a
lens. It is these, together with the almonds of the throat,
or ears, as they are sometimes called, which afford the
mucus to lubricate the food in the act of deglutition, and
also to keep the tongue moist, and in a condition for the due
performance of its function.)

4. The other two sets of papillae are the instruments of
taste. The one set is named conical, or filiform, and con-
sists of small nipple-shaped bodies, broader at the base than
the top, and scattered over the whole surface of the tongue,
giving it its rough or shaggy appearance. The other set
of papillae is larger, and consisting of small rounded heads,
supported on short stalks, something in the shape of a mush-
room, they have been called fungiform. These are but few
compared with the former. These sensitive papillae are
supplied with numerous blood-vessels as is shown in the next
cut. In order for the exercise of taste, it is necessary for the
mucous membrane, to be in a state of integrity, for if it be
removed, we only experience a sensation of pain. The
animal papillae, which abound on the sides and tip of the
tongue, appear to be the most exquisitely sensible. Certain
bodies seem to affect one part of the more than another.
Acids, for example, act especially on the lips and teeth ; acrid
bodies, like mustard and cayenne pepper, on the pharynx.
We read of cases in medical works, where, after the tongue
has been removed by disease, or a surgical operation, persons
could still speak, spit, chew, swallow, and taste. In one
case, the individual could distinguish the bitterness of sal
ammonial, and the sweetness of sugar ; and Blumenbach
mentions a young man, who was born without a tongue, and
yet when blindfold, could distinguish between solutions of
salt and aloes put upon his palate.

SENSE OF TASTE.

169

An upright section of one of the papillae of the tongue very greatly
magnified, and split open, to show the nerves (engraved white) and the
blood-vessels (black.)

5. The process of taste, then, is as follows : — When a
fluid is taken into the mouth, these papillae dilate and erect
themselves, being endowed with the property of adapting
themselves to the active or passive condition of the sense of
tasteO If a solid portion of food is received, it is first touch-
ed by the tip of the tongue and brought into close contact
with the papillae ; when if it be dry or solid, it is carried to
the back of the tongue and moistened with saliva, which
thus becoming impregnated with its flavour, and flowing
over the sides of the tongue, gives to the papillae a percep-
tion of the savoury juices. The saliva, or spittle, it should
"be recollected, is secreted by the parotid and other salivary

15

170 PHYSIOLOGY.

glands, chiefly during the process of mastication, for the
purpose of moistening the food, while the mucous secretion
is to keep the tongue in a condition to receive the impression
of sapid bodies. For example, in sickness, and especially in
fevers, when the mouth is dry and parched, owing to a sup-
pression of this secretion, the taste is entirely lost, showing
that the membrane of the tongue must be kept moist in order
to the preservation of the taste.

6. Insoluble substances are totally insipid, because in order
to affect the nerves, the substance musH>e in such a state as
to penetrate the spongy papillae, (it is supposed that the
salts which enter into the composition of the saliva, are very
efficient agents in reducing substances to a proper condition
for making an impression on the gustatory organ^ In this
way, we can account for the fact, that metals, though in-
soluble in water, often impart a peculiar taste. The organs
of taste are also powerfully affected by metals, so applied tc
the mouth as to call forth electric action. If we place ont
kind of metal on the tongue and another under it, and then
bring their edges together, a strong sensation is experienced
If we touch the surface of the tongue with the point of a
wire, connected with the positive pole of a galvanic battery,
a sour taste is experienced ; while the negative pole excites
an alkaline taste. fThese phenomena may be owing either
to the electric action, disengaging from the saliva an acid
in one instance, or an alkali in the other, or the electric ex-
citement may call forth the special sensibility of the gusta-
tory organ, in the same manner as it causes the special
sensibility of the other organs. )

7. Savours, like odours, are innumerable, and as they dif-
fer so much from each other, it is impossible to classify them
in any satisfactory manner. We can readily understand
what is meant by the terms sweet, Utter, sour, saline, acr'uly
&c., yet each of them differs in intensity, as well as other
shades of character. For example, rectified sugar, brown
sugar, maple sugar, beet sugar, molasses, honey, &c., are all

SENSE OF TASTE. 171

sweet, but the taste of each is different. Linneus and Booer-
haave both made a classification of savours, but they have
never been generally adopted by physiologists. Adelon
divides them into two kinds, the agreeable and disagreeable.
But even this division is not founded in nature ; for we find
the old adage true, that " one man's meat is another man's
poison." iEvery person has some peculiarities of taste, dis
likes to particular articles of food, or shades of difference in
the appreciation of tastes, which may be constitutional, or
caused by association. Besides, the taste sometimes be-
comes unaccountably morbid or depraved. We often see
children devouring chalk, brick-dust, ashes, dirt, and slate-
pencils, when if, at other times, they were required to swal-
low such articles, as medicine, they would doubtless deem it
a peculiar hardship.

8. Savours differ as to the permanence or transientness
of impression which they leave upon the organs of taste.
(Aromatic and bitter substances particularly leave their taste
in the mouth for a long time after they have been swallow-
ed jj the physician, therefore, when he wishes to administer
some nauseous drug, forestalls the sense of taste, by direct-
ing one of these substances lo be held previously in the
mouth. There is a common experiment on this subject,
which has led to many bets, viz., giving to a person blind-
fold, brandy, rum, gin, or any other spirituous liquor in rapid
succession, and see whether he can tell one from another.
In a short time, the nerve becomes so impregnated with the
different substances, that all distinction becomes confounded
Tasters of wine, tea, &c., understand this principle ;Hbr w<
see them take up a small portion and move it over the wholt
surface of the mouth, so as to extend its action, and then
they wait for some time after the impression is made before
they taste of other samplesjfr When a person takes a medi
cinal draught, he gulps it down as quick as possible, in order
that it may come in contact with as small a portion as pos
sihle of the organ of taste..

172 PHYSIOLOGY.

9. The taste is greatly under the influence of habit. ( Many
articles which at first excite disgust, being taken through
fashion or necessity, at length become highly grateful. We
need only name tobacco, and perhaps ardent spirits. The
taste for these substances is altogether artificial, no one be-
ing fond of them, when taken for the first time. Such per-
version of taste often becomes national. Thus garlic forms
a constant ingredient in the dishes of some European coun-
tries. The most celebrated sauce of antiquity, was the
Roman garum, prepared from the half-putrid intestines of
fish. Another of their favourite condiments was assafoetida ;
and this is still in high repute among many of the orientals.
Rotten eggs are highly esteemed by the Siamese, and fish in
an advanced state of decomposition is highly relished in the
northern and western islands of Scotland. Dried, putrid
mutton is habitually eaten in Iceland, and epicures in every
country esteem game and venison a greater luxury, if in a
putrescent state. To be a fashionable epicure of the present
day, requires that the taste should be educated or trained,
like a sportsman's setter. It is then prepared to scent out,
with infallible certainty, what fashion has taught it to relish
as choice luxuries ; but which -simple, unadulterated taste,
rejects as fit only for the kennel or the carrion crow^

10. The gratification which we derive from eating de-
pends chiefly on the state of the stomach. If that is not in
a condition to digest food properly, no matter how much we
may generally relish any particular article ; it will, at such
times, invariably excite disrelish or even disgust. So also
when we sit down with a keen appetite to a meal, as our
hunger is appeased, the relish proportionally diminishes, till
at length we reach the point of satiety, and if we persist,
nausea and disgust are certain to succeed/ Here then, is
another wise provision, informing us with infallible cer-
tainty when we have taken sufficient food to supply the
wants of the system. The ancient Romans availed them-
selves of a knowledge of this law, and hence were in the habit

SENSE OF TASTE. 173

of leaving the table once or twice during a meal, and after
having, by means of an emetic, unloaded the stomach, of re-
turning again to the charge.

11. As a general rule, articles that are agreeable to the
taste, are safe and nutritious, though this is not invariably
the case. For example, prussic acid has a very agreeable
savour, as well as odour, and is accordingly used to impart fla-
vour to dishes and liqueurs, such as noyeau, yet prussic acid
is one of the most powerful poisons in nature. Many sub-
stances which at first are highly agreeable, in a short time
lose their relish ; we see that grocers understand this prin-
ciple, for instead of forbidding a new apprentice from eating
sugar, raisins, honey, and molasses, he tells him to eat all he
wants, knowing, that in a short time, his appetite will be
cloyed, and all temptation removed.

12. /Among animals, we find a great difference in the per-
fection of this sense; iSome enjoy it, doubtless, in as great,
if not a greater degree than man, as they are able by it to
distinguish plants that are nutritive and good for food, from
those which are poisonous; and accordingly it is a rare
thing for animals to die from eating such vegetables. Many
insects feed on the leaves of poisonous plants, and seme ani-
mals eat the leaves of the poison ivy without injury. There
is an insect which feeds on the leaves of the tobacco, and the
southern planter guards against its ravages by a process
called worming. The taste also in animals sometimes be-
comes morbid, as we see it happen among our own race.
Mr. Bennet, in his "Wanderings in New South Wales"
states, that serious losses happened to the farmers in that
country from the sheep acquiring the habit of licking and
devouring earth impregnated with saline matter. In a short
time, he says, their natural innocent dispositions become
changed, and they become carniverous and savage, and de-
vour the lambs. Thus out of a flock of twelve hundred
lambs, eight hundred were devoured by the sheep themselves.

13. The sense of taste is most delicate in youth. It is
15*

174 PHYSIOLOGY.

much impaired by the use of alcoholic drinks, tobacco, and
highly seasoned food >; so that the spirit-drinker, the tobacco-
chewer, and the epicure often lose this sense to such a de-
gree that they cannot relish plain dressed food. That man
relishes his food best who rarely uses powerful stimulants and
narcotics. Majendie says that man would probably excel
all the other animals in delicacy of taste, if he did not, at an
early period, impair its sensibility by strong drinks, or by
the use of spices, and other luxuries.

14. CThe taste may be improved by cultivation like any
of the other senses* Dr. Kitchener states that some epicures
are able to tell from what precise part of the Thames a sal.
mon had been caught, when presented at table. Many
gourmands pretend to be able to pronounce by sipping a few
drops of wine, the country whence it comes, as well as its
age ; to tell by the taste, whether birds put upon the table
are domesticated or wild, &c. Such acuteness of taste is
however, by no means desirable, as we are liable, in the
" rough and tumble" of life, to meet with so much that de-
mands obtuseness rather than refinement of feeling. The
epicure with his acuteness and delicacy of taste, is liable to
continual annoyances and discomforts, while the man of
simple and unsophisticated taste will receive gratification
and pleasure from the very same objects which excited dis-
gust in the former.

15. If we examine the lower animals, we shall find that in
none of them is the tongue precisely like that of man. The
resemblance is the nearest in apes ; but in them, even, it is
much elongated. In animals that chew the cud, or ruminants,
we find the tongue covered with a dense cuticle, studded
over with numerous pointed papillae, especially towards the
root. These projections, together with the waving ridges on
their palates, are of great use in collecting and swallowing
the tender herbage on which they feed. In the cat tribe,
the sharp, horny prickles on the tongue, enables them to take
a firm hold. In the lion and tiger these prickles are suffi-

SENSE OF TASTE. 175

cient to tear off the skin even of large animals. Ant-eaters
are furnished with a very long and slender tongue, covered
with a viscid, adhesive secretion, whereby they are able to
seize their prey, on thrusting it into an ant-hill*

16. Whales have an enormous tongue, though it has been
doubted whether it is endowed with the sense of taste. They
have, moreover, projecting downwards from the upper jaw, a
kindofpallisade, consisting of several hundred plates of whale-
bone, the outer edges of which are sharp, the inner fringed
with long hair like appendages, the spaces between the
plates being little more than half an inch. The length of
the plates sometimes exceeds twelve feet. This pallisade,
when the mouth is closed, is covered by the enormous fleshy
lower lip, but when open, it presents a kind of grating
through which the water loaded with medusa and other
small animals, flows* Captain Parry states that these medu-
sa or sea-blubber, so abound in the arctic seas, that when
the water is still, and the surface smooth, they present a
striking resemblance to a thick snow-fall, when the flakes are
large and the air calm. The soft, spongy texture which
forms the tongue of the whale, is thought to be better
adapted for licking the food from the hairy whale-bone roof,
and transferring it to the gullet, than to serve as an instru-
ment of taste.

17. The tongue of birds varies much in form and con-
sistence. In some, it is horny, as in the toucan, where it is
several inches in length and exceedingly narrow, like a long
strip of whale-bone ; or in the wood-pecker, to the tip of
whose tongue there is fixed a long, sharp, pointed, spear-like
body with serrated edges, for piercing and seizing on insects
burrowing beneath the bark of trees. Parrots, which belong
to the same class, have soft fleshy tongues well adapted to the
exercise of taste.

28. In reptiles also, we find great variety of forms and
applications of the tongue. In the crocodile it is small and
imrnoveable, so much so, as to lead some naturalists to deny

176 PHYSIOLOGY.

its existence. In serpents, it is forked, and susceptible of
considerable motion ; while in the frog, it is folded back in
the state of inactivity ; but when the animal is about to
seize an insect, it suddenly unfolds and projects it out of the
mouth. The tongue of a chameleon is contained within a
sheath, and admits of being projected to the extent of six
inches, and is besmeared with a glutinous secretion. In the
twinkling of an eye it is darted out to catch its food, which
consists chiefly of flies. Fishes have the mere rudiments of
a tongue, fixed near the throat, which is often furnished with
teeth. There is reason to believe that many of the inverte-
brated animals are endowed with taste, such as bees, wasps,
flies, and leeches.

Questions. — To what sense is that of taste allied ? What is sapid-
ity ? What is the chief organ of taste ? What other parts participate
in the function ? Describe the structure of the tongue. From what
source does the tongue derive its nerves ? Which is the nerve of
taste ? What are papillae ? How many kinds are there on the
tongue ? What is the office of the mucous papillae ? — Of the conical
and fungiform ? What is the process of taste ? Can insoluble sub-
stances be tasted ? Why not ? What are the use of the salts in the
saliva ? How do we taste metals ? How is the taste excited by gal-
vanism explained ? Are there many savours ? Name some. Can
they be classified ?*" Why not? What articles leave a. taste in the
mouth the longest ? What use can be made of this fact ? How do
tasters manage ? Is taste under the influence of habit ? . What facts
show this ? To what is the pleasure of eating owing ? How is this
shown ? Is the taste a sure guide to what is safe and nutritious ? Do
animals differ as to taste ? Do they possess it in as great perfection as
man ? Does it ever become morbid in them ? When is taste most
delicate ? How is it impaired ? May the taste be improved ? Are
the advantages or disadvantages the greatest, which attend great deli-
cacy of taste ? Have any of the lower animals a tongue like that of
man ? Describe some peculiarities ? What apparatus have whales
for eating small sea animals ? What is said of the tongue of birds ? —
of reptiles ? of fishes ? Do any of the invertebrated animals possess tha
faculty of taste ?

CHAPTER XV.

THE SENSE OF SMELL.

1. -TiiE sense of smell takes cognizance of the odorous
properties of bodies.) The seat, or organ, is the mucous
membrane, which lines the nasal cavities, and is called the
schneiderian, or pituitary membrane.; It is covered with
nervous papillae, similar to, but more delicate than those
which cover the organ of taste. \ These cavities open an-
teriorily through the external nostrils, and posteriorly into
the fauces or throat, to permit the air to traverse them in
its passage to the lungs. .The nasal organ seems to be
designed for the purpose of collecting the odorous particles ;
and it is divided into two similar cavities, by a bony parti-
tion, called the vomer, which is extended by means of cartilage
to the anterior extremity of the nose. Each nostril contains

Front view of the nasal fossae.

178

PHYSIOLOGY.

two convoluted or, turbinated bones, of a light spongy tex-
ture, one being situated above the other ; and they divide
the general cavity of the nostril into three passages.

2. In connection with the nostrils, there are several cavi-
ties, as in the frontal and upper jaw-bones, called sinuses.
These communicate with the nostrils, and as they extend
the surface on which the lining membrane is expanded, they
are supposed to contribute to the sense of smell, by affording
capacious receptacles for air, loaded with odorous particles.
Of the 14 bones which enter into the formation of the face,
11 assist in forming the cavities of the nostrils, as do also
three out of the eight bones that form the cranium. Be-

Nasal fossae seen from behind,

OF 111E

sides the cartilage which forms the septum erf the nose, two
others of an elastic nature constitute the wings ; and as they

admit of motion, several muscles are attached
order to regulate the external orifices in accordance with
different conditions of respiration, and also to enable us to
exercise the sense of smell with greater effect, when we wish
voluntarily to employ that function.

3. The membrane which lines the nasal fossae, resembles
the mucous membranes generally, and adheres firmly to the
bones and cartilages which it covers. Externally, this mem-
brane is continuous with the common integuments, and pos-
teriorly with the lining membrane of the throat. It varies
somewhat in appearance in different situations. In the
sinuses, it is thin, pale, and of a smooth surface ; but where
it constitutes the immediate seat of smell, it is thicker, more
vascular, and of a redder colour than mucous membrane in
other situations. It is studded with mucous follicles, which
yield the secretion with which it is moistened ; though it is
also bathed with the tears that spread out upon it, after
having been conveyed from the eye through the nasal ducts.
The nasal mucus seems as essential to the sense of smell, as
the secretion from the mucous membrane of the mouth to
that of taste. In those who use tobacco in the form of
snuff, this secretion often becomes so scanty or so changed
in quality, that the smell is much impaired, and sometimes
entirely lost : the voice also is seriously injured by the same
practice.

4. |The olfactory, or first nerve, is the sense of smell. This
is spread out on the thick vascular portion of membrane just
described. 'Twigs from the first and second branches of the
fifth, are plentifully ramified over the whole surface of the
pituitary membrane, imparting to it common sensibility.
The nose is also supplied with branches from the facial to
regulate the action of the muscles. Dr. Majendie says, that
the organ of smell ought to be described as a sort of sieve,
placed in the passage of the air, as it is introduced into the

180 PHYSIOLOGY.

chest, and intended to stop every foreign body that may be
mixed with the air, particularly the odours.

5. What is called odour, or smell, resides in nearly all
bodies, and is given off by moisture, heat, motion, or friction.
Those which do not possess this quality are called inodorous.
Those little particles which convey the odour, are scattered
through the air, and in breathing drawn into the upper part
of the nostrils, where the sense of smell principally resides.
If we breathe through the mouth, odours in general will not
be perceived, unless very pungent. The fluid which moistens
the lining membrane of the nose, is supposed not only to
render it more sensitive and delicate, but also to entangle
the odorous particles, and in this way detain them longer in
contact with the olfactory nerve. The constant evaporation
which takes place from the membrane, owing to the passage
of the air in respiration, requires that the secretion should
be constant as well as copious ; otherwise the membrane
would soon become dry and parched.

6. It is very difficult to describe an odour, except to those
who have smelled it, or something with which it may be
compared. We can say that odours are pleasant or dis-
agreeable ; that they are aromatic, or sweet, rancid, or fetid,
&c. ; but we can give no correct idea of the peculiar smell
of bodies, such as camphor, musk, garlic, the rose, &c., with-
out experiencing the sensation which their smell produces.

7. The odorous particles of bodies must be very small to
excite any sensation on the animal organs. A grain of
musk will, it is said, scent a room for years, and not lose any
of its weight ; Mr. Boyle asserts that the smell of cinnamon,
from Ceylon, is perceived at sea at the distance of twenty-
five miles from the island. Scales in which a few grains of
musk have been weighed, have been found to retain the smell
for twenty years, though during all this time, they must have
been constantly giving off odorous particles. Haller kept
some papers forty years, which had been perfumed by a single
grain of amber, and at the end of that time they did not

SENSE OF SMELL. 181

appear to have lost any of their odour. But these particles
cannot be as small as those of light, because we see that glass
is capable of retaining the former, but suffers the latter to
pass through it. The art of the perfumer consists in fixing
and preserving odours in the most agreeable and convenient
vehicles.

8. Odours differ very much as to the permanence of the
impression which they produce. While that of some is very
transient, in others the scent remains for hours after the
application of the substance. They also differ, as we have
seen, as to the extent to which their influence extends.
.Moisture in the atmosphere is favourable to the diffusion of
odours, which would seem to show that vapour is a good
conductor. For example, a flower garden is never more
grateful to the smell than in the morning, when the dew is
evaporating, or after a warm summer shower. So also the
plants of a green-house are more fragrant, just after they
have been watered. Some flowers give off their odour only
at certain times, generally after they are fully expanded, and
their parts in the greatest activity.

9. Though the air is the usual vehicle for odours, yet we
find that they adhere to solid bodies, and can even be con-
veyed through water. But though the whole art of per-
fumery is founded on this fact, it has been strenuously denied
that they could be conducted through water, and conse-
quently that fishes could smell. Some physiologists state
that fishes have no olfactory organ ; that the part commonly
considered as such is the organ of taste. This opinion is,
however, erroneous. " Not many naturalists of the present
day," says Dunglison, " will be hardy enough to deny, that
fishes have an organ, or sense of smell. At all events, few
anglers, who have used their oil of rhodium, or other attrac-
tive bait, will be disposed to give up the results of their
experience, without stronger grounds than any that have
been assigned by the advocates of that view of the subject."

10. Fishes are furnished with organs of smell, but they

16

182 PHYSIOLOGY.

have no communication with tho mouth or gullet. They

are in .ulaled cavities, covered with a valvular lid, and lined
wilh u plaited membrane, similar to tho under surface of
•oino inushrooniH. This Borvos to extend the surface, while
it is covered with a viscid mucus, fin tho cod-fish, the nerves

of smell are spread mil. iii ii cavity fill«'d wilh Hind, and
lar«',er HI;III Unit which contains the brain itself. "That the.
rod is ;niided by Ninrll in the selection of food," says Aitkin,
••must he well Known to every "lie who has taken it with

bait, in circumstances whore ho could watch tho conduct of
tho finh. If not very hungry, it may frequently bo observed
to approach tho bait, apparently attracted by tho Bight, till,
at a closer distance, it seems distinctly to smell at it ; and
if not satisfied, turns aside and neglects it." Every person
who has been in tho habit of fishing much, must have often
observed the siiiue tact, in catching common poiid-lish, such
as perch, roach, &u.

11. It was an opinion formerly entertained, that odours

possess nutritive |»ro|>erlies, as savoury smells seem to have

the effect of allaying hunger, or at least of satisfying tho
appetite in some degree. This effect, however, is best ex.
plained, by referring it to tho influence of odours on the

nervous system, Ms we sec the appetite often instantly des-
troyed by unwelcome news. In persons whoso digestive
organs are weak, tho appetite is often destroyed instantane-
ously by a nauseous odour. (We read that Democritus lived

three days on (he vapour of hot bread ; and I'.acou speaks
of a man, who was supported several days by inhaling tho
odour of a mixture of aromatic and aliuceous herbs. In
IMS, |)r. Wilkins, the Hishop of Chester, published a hook,
the object of vtluch was, to :.how that the moon is iiihabil-
nble, and that it is possible lor us to find a passage thither.
In this work, he says, •• If we must needs ("eed upon some-
thing, why may not smells nourish us ? Plutarch and rimy,
and divers oilier ancients tell us of a nation in India, that

lived only upon pleasing odours; and it is the common

• ::\ • <>i MI. 1. 1. 183

opinion of phyMd.m , that these do strangely both strengthen
and n |»;iir I IK: NpiritM."

lii. We read ;ui ;HIIU in • inn r.lolr m Fuller, who lived .'it
the name time with thu bimhop, in relation to thin suppoxed
nourinhing property of odours/ A poor man being very
hungry, ntuid 00 long in u cook'n Hhop, who wan dinning up
the meat, that his utomach was cuitiHficd with only thu smell
thereof. The choleric cook demanded of him to pay for hit*

bn::ik!;is( ; tin: poor man denied h;ivin;j li;id ;iny ; and (In:
controverHy was referred to tin: <l< < I»M of the next man
that should puns hy, who chanced to be the mont notorioun
idiot in the whole oily ; lie, on the r< -l.ilion of (he matter,
determined that the poor man's money whould be put between
two empty dishes, and that the cook should be recompensed
with the jingling of the money,* as he was satisfied with tho
cook's meat*

18. (The sense of smell is closely associated with that of
taste./ It seems indeed as a sentinel standing on guard, to
see that no enemy approaches tho citadel ;[ it tells us whether
the aliment placed before UH, is agreeable or disagreeable:

ofroiirse whether it will JHM'er or di:.;;i»m- with Hie .slomadi.

The taste and the smell ore hardly ever at loggerheads ; it
does, however, sometimes happen that a substance that is re-
pugnant to tho smell, is agreeable to tho taste. In such a
case they soon come to an understanding, and the smell
chooses, to make the best of it, and drop its repugnance. At
any rate, its aversion, some way or other, is soon neutral-
ized. (The smell is, ho\\i v. r more useful to animals, as a
M-rilinel, lh:iu i! is In IM:IM, who <• reason n more Hum a
in:ilrh lor Hie in., line! of the hrul.- rre.-iliois. In them, in-
deed, it rarely fails to guide aright. How wonderful is this
provimon which leads them with unerring certainty to choose
the innocent herb from the poisonous plant ; the nutritious
vegetable from that which in destitute of nutriment ; and to

* Dunglitori'fl Physiology.

184 PHYSIOLOGY.

reject instinctively, every thing which would prove noxious
or disagreeable. It is not, however, infallible even in the
brute creation ; for we see the flesh-fly attracted by a certain
species of mushroom which admits a cadaverous odour, simi-
lar to putrid flesh ; in these they deposit their eggs, which,
when hatched, perish for want of suitable food to nourish
them.

14. A singular custom, which prevails among shepherds
in some countries, shows that the sheep is more under the
guidance of smell than sight or any of the other senses.
" When a lamb has died," says Aitkin, «* the shepherd
wishes to put to the ewe another lamb that may have lost its
dam ; if she refuses to foster the stranger, he is sure to suc-
ceed by stripping off the skin of her own offspring, and tying
it on the back of the stranger, that she may smell the skin ;
she then entertains and treats it as her own. In this case
she neglects the sense of sight, for nothing can be more un-
couth than the object of her affections ; neither does she
attend to the evidence afforded by hearing ; however unlike
the bleating of the foster lamb may be to that to which she
was first accustomed, her smelling is satisfied, and she is con-
tent." The same practice succeeds with the cow.

15. In the elephant, the tapir, and the hog, as well as in
oxen, sheep, deer, and antelopes, we find the cavities of the
nose very capacious, and the surface of the pituitary mem-
brane vastly extended ; and accordingly the sense of smell is
proportionally acute. In France it is customary to employ
the hog to hunt for truffles, a species of edible mushroom
which grows at some distance below the surface of the
ground. By the sense of smell alone, he is accurately
guided to the spot where one is growing, and begins to turn
up the earth with his snout, in order to get at it. The vege-
table hunter, however, anticipates him, and driving away the
animal, digs down, and appropriates it to himself. In this
way he secures, in a short time, sufficient for a family din-
ner.

SENSE OF SMELL. 185

16. The delicacy of this sense in the greyhound is most
astonishing. He not only tracks the hare, the fox, or the
wolf with unerring certainty, long after their footsteps have
been imprinted, but even in -a large city, he will trace the
progress of his master through thoroughfares and thickly
crowded streets, distinguishing his footsteps from those of a
thousand passers-by, and amidst the odorous particles emanat-
ing from a thousand sources. When Hispaniola was first dis-
covered by the Spaniards, they employed the greyhound in
hunting the poor natives, who, unlike the more fortunate
Seminoles of Florida, could find no ever-glade, no fastness,
no retreat, which could save them from the unerring scent
of these animals.

J7. The organ of smell is universally found in birds,
though varying in size. Rapacious birds and waders, or
those that live on fish, have it more largely developed than
any others. Humboldt relates that in South America, when
the inhabitants wish to take the condor, they kill a horse or
cow, and in a short time, the odour of the dead animal
attracts those birds in great numbers, and even in places
where they were scarcely known to exist. Some of the
Roman historians tell us that vultures went from Asia to the
field of battle at Pharsalia, a distance of several hundred
miles, attracted thither by the smell of the dead. Pliny, the
natural historian, affirms that the vulture and the raven have
the sense of smell so delicate, that they can foretell the death
of a man three days beforehand.

18. Mr. Audubon, however, relates two experiments to
show that vultures are indebted to sight rather than smell, in
the discovery of their prey. He stuffed a deer's skin with
hay, allowed it to become as dry as leather, and placed it in a
field ; in a few minutes a vulture made for it, attacked it,
tore open the stitches, and pulled out the hay. He then put
a dead hog into a ditch, and covered it over with care ; it
soon putrefied and became intolerably offensive, but the vul-
tures, which were sailing about in all directions in search of

16*

186 PHYSIOLOGY.

food, never discovered it, although several dogs had been
attracted to it by the scent. His next experiment was to
stick a young pig, and cover it over with leaves ; vultures
soon saw the blood, descended to it, and by this means soon
discovered the pig, while it was still fresh. The general
opinion of physiologists at present is, that birds of prey,
have not so acute a sense of smell as has been generally sup-
posed, and that they are guided chiefly by sight.

19. It is stated by whale-fishermen, that in Greenland,
when a whale has been captured, although at the time
scarcely a single bird may be visible, yet in a short time,
immense numbers of gulls and other sea-birds hover about,
and hasten to the spot from every point of the compass. Al-
though these birds have the organ of smell, and conse-
quently the sense itself, largely developed, yet such facts may
be more satisfactorily explained, than by supposing that they
are able to smell the flesh of a dead whale, before putrefac-
tion has commenced, at a distance of many miles. A better
explanation cannot be given than is contained in the first
volume of " MacGillivray's History of British Birds." —
Speaking of ravens gathering together in immense numbers
over a dead carcass, in explanation of the phenomenon he
remarks, " A single raven might first perceive the carcass.
Ravens have character in their flight as men have in their
walk. A poet sauntering by a river, a conchologist or fish-
woman looking for shells along the shore, a sportsman
searching the fields, a footman going on a message, a lady
running home from a shower, or a gentleman retreating
from a mad bull, move each in a different manner, suiting
the action to the occasion. Ravens do the same, as well as
other birds ; so those at the next station, perhaps a mile dis-
tant, judging by the flight of their neighbours that they had
a prize in view, might naturally follow. In this manner the
intelligence might be communicated over a large extent of
country, and in a single day a great number might assemble.
We know from observation that ravens can perceive an

SENSE OF SMELL. 187

object at a great distance, but that they can smell food a
quarter of a mile off we have no proof whatever ; and as we
can account for the phenomenon by their sight, it is unne-
cessary to have recourse to their other faculties.'* Every
person who has seen the manner in which crows collect
together about a dead animal in the country, will be satis-
fied that the above is a correct explanation of the pheno-
menon.

20. The olfactory organs of reptiles are but slightly
developed. Frogs have two small holes, which serve as the
organs of smell. The pituitary membrane of the turtle is
of a very dark colour, and the nerve is of considerable size.
In serpents, they are more elongated, and in lizards still
more so. The animals of this class have no cavities corres-
ponding to the sinuses ; of course the sense of smell cannot
be very acute.

21. The smell can be greatly improved by education.
Humboldt states, that the Peruvian Indians can distinguish
in the middle of the night the different races by their smell ;
whether they are European, negro, or American Indian.
By habit, the perfumer acquires the faculty of distinguishing
the nicest shades of odours. We see the influence of educa-
tion, by the difference between a dog that has been trained
to the chase, and one that has not. In the blind, the sense
of smell is particularly acute. A boy in Edinburgh, who was
born blind and deaf, could tell the entrance of a stranger in-
to the room by the smell alone ; and he told one person from
another by smelling at him.

22. Dr. Good remarks, that " we occasionally meet among
mankind with a sort of sensation altogether wonderful and
inexplicable. There are some persons so peculiarly affected
by the presence of a particular object, that is neither seen,
tasted, smelt, heard, or touched, as not only to be conscious
of its presence, but to be in agony till it is removed. The
vicinity of a cat not unfrequently produces such an effect ;
and I have been a witness to the most decisive proofs of this

188 PHYSIOLOGY.

in several instances." There can be no doubt, I think, that
this peculiarity is referable to delicacy of smell. Dr. Dung-
lison states, that a gentleman, blind from birth, had an
extraordinary antipathy to cats. One day in company, he
suddenly leaped up, got upon an elevated seat, and exclaim-
ed, that there was a cat in the room, and begged them to
remove it. It was in vain that the company assured him
that he was mistaken. He persisted in his assertion and in
his state of agitation ; when, on opening the door of a small
closet in the room, it was found that a cat had been acci-
dentally shut up in it. !

Questions. — Define the sense of smell. Where is it seated ? De-
scribe the pituitary membrane ; — the nose. What cavities are concern-
ed in the sense of smell ? What is the object of such an extended sur-
face ? How many bones assist in forming the cavities of the nostrils ?
Why are they supplied with muscles ? Does the membrane that line
the nostrils resemble the other mucous membrane ? How is it moist-
ened? Do the tears answer any purpose except washing the eye?
What effect has snuff-taking on the sense of smell ? What is the
nerve of smell ? What other nerves send twigs to the nose ; — their func-
tion ? To what does Majendie compare the organ of smell ? What
is odour ? How given off from bodies ? Are odours easily described ?
What facts show that their particles are very minute ? What is the
art of perfumery ? Do odours differ as to the permanence of the im-
pression they produce ? What favours the diffusion of odours ? Can
odours be conveyed through water or other fluids ? Have fishes any
organ of smell ? What facts prove this ? What article renders bait
attractive to fish ? Were odours ever believed to be nutritious ? What
anecdotes in relation to this ? Are the senses of smell and taste asso-
ciated ? What is the use of smell? Are any substances disagreeable
to the smell and agreeable tp the taste ? Is smell more useful to ani-
mals than man ? Is it infallible in them ? What fact proves that it
is not ? What singular custom prevails among shepherds ? What
animals have the sense of smell the most acute ? How is the smell of
the hog employed in France ? What is said of this sense in the grey-
hound ? Was it ever employed to hunt savages ? When and where ?
Have birds any organ of smell ? What does Humboldt say of the
condor ? What experiments did Audabon try, to prove that birds of

SENSE OF SMELL. 189

prey are guided by sight instead of smell ? What do whale fishermen
say of birds in Greenland ? How does Mr. MacGilivray explain the
gathering together of so many birds over a dead carcase ? Have rep.
tiles any olfactory organs ? Can this sense be improved by education ?
What causes the singular antipathy t<f^ats, which we meet with in
some persons ?

CHAPTER XVI.

THE SENSE OF SIGHT.

1. THIS is the most refined and admirable of all our senses.
By it especially we hold converse with the external world ;
and without it, we should not only be deprived of a large
portion of the pleasures we now enjoy, but we should be un-
able to maintain our existence for any length of time. The
wisdom, power, and benevolence of God are chiefly mani-
fested to us through the sense of vision/5

2. The eye is the organ of sight, and the most beautiful
of all the organs of the senses. So admirable is its struc-
ture, so wonderful the provisions which adapt it to the pur —
poses for which it was designed by our Creator, that I shall
give as full a description of it as my limits will allow ; and
in order to an easy and clear comprehension of its structure
and function, I shall first describe the coats of the eye, in-
cluding the retina, or the expansion of the nerve of vision ;
then the humours of the eye, by the agency of which, the_
rays of light are concentrated so as to form an image upon
the retina ; and lastly, explain the laws of vision, the motions
of the eye, and the means of protection against injury.

3. The Coats of the Eye. — The coats of the eye are
generally reckoned as three in number, viz.» the sclerotic, the
choroid, and the retina ) besides these, there are the cornea,
the iris, and the ciliary processes, /which are viewed and des-
cribed as appendages to these coats.

4.1 The sclerotic,* or outer coat, is the firm, opaque, fibrous
substance which preserves the globular figure of the eye ; and
besides defending its internal delicate structure, serves for the
attachment of those muscles which move the eye. It invests

* From a Greek word, signifying hard.

SENSE OF SIGHT.

191

the eye on every side except the front, forming about four-
fifths of the external covering, and extending from the
entrance of the optic nerve, at its base, to the cornea. This
coat has almost the firmness of leather, and possessing but
li**1'} sensibility, it is rarely exposed to inflammation or other

Fig. 1. '

Plan of the eye, seen in section.

A, The Sclerotic Coat. F, The Aqueous Humour.

B, The Choroid Coat. G, The Iris.

C, The Retina. H, The Ciliary Processes.

D, The Optic Nerve. I, The Crystalline Lens.

E, The Cornea. K, The Vitreous Humour.

diseases* The sclerotic coat is much denser in the eyes of
fishes than in the eyes of creatures which live on the surface
of the earth. In the whale, it is more than an inch thick,
in order, that when he dives some hundreds of fathoms deep,
the pressure of the water on the eye may not be greater than
its structure can withstand. That this pressure is very great,
is shown by the common experiment of corking an empty
bottle tight, and then letting it down into the sea by a cord ;
the cork will always be found forced in, and the bottle full
of water ; the pressure being equal to the weight of the
column of water above it, of which it is the base. Dr. Buck-

PHYSIOLOGY.

land stales, that in one experiment, a copper cylinder, con-
taining atmospheric air, was crushed flat under a pressure
of 300 fathoms, and bottles filled with air were crushed in-
stantly. This shows the necessity of a strong sclerotic coat
in animals that dive far beneath the surface. .
Fig. 2.

Front and side view of the ball of the eye.

5. The Choraid Coat*-4This constitutes the second in-
vesting membrane of the eye, which is of a dark brown
colour, soft, cellular, and vascular. This coat is situated
on the inner surface of the sclerotic, to which it is slightly
attached by means of blood-vessels and nerves, of which in-
deed it seems to be chiefly composed J for, on injecting the
eye carefully with coloured wax, it assumes a uniform red
colour. The inner as well as outer surface of this mem-
brane is covered by the pigmentum nigrum, or black paint ;
which seems to absorb the rays of light immediately after
they have struck the sensible surface of the retina. This
pigment, sometimes called tapetum\ in animals that see best
at night, is wanting in albinos, as I have already stated ;
and it is owing to this cause that the iris and pupil appear
of a red colour,, and that their vision is so imperfect, that
they cannot view objects in a strong light ; and indeed can
scarcely see enough to go about in the day-time. In ani-
mals that prowl by night, this pigment is wanting, or of a

* Choroides, fleecy, like a lamb skin,
t Tapetwn, like cloth, or tapestry.

\

SENSE OF SIGHT. 193

bright green, or silvery whiteness, and the dark pigment is
peculiar to those animals that see in the brightest light of day.

Fig. 3.

The eye, after cutting away the sclerotic coat and cornea, to show
the vessels of the choroid coat ; magnified,

6. The Retina** — -This is the third and innermost mem-
brane of the eye, and is the expansion of the optic nerve,
and the immediate seat of vision. It is a soft, thin, and
transparent substance, extending from the optic nerve to the
crystalline lens, and lining the choroid coat throughout with-
out adhering firmly to it. The retina may be divided into
three layers, viz., serous, nervous, and vascular ; the former
of which passes on over the surface of the lens, and forms
part of its capsule. There is a small portion of the retina,
supposed to be near where the optic nerve pierces the
sclerotic coat, which is not susceptible of vision, as may
be shown by an experiment hereafter mentioned. It was
formerly supposed, that the retina was endowed with extreme
sensibility ; but it is now ascertained that it is almost insen-
sible to every stimulus but that of light. The same is true

* Retina, a net.
17

194 PHYSIOLOGY.

of the optic nerve. The ordinary sensibility of the eye is
derived from the branches of the fifth pair of nerves ; and
we have already seen that several pairs of nerves are sent to
its muscles.

7. The minuteness with which objects are painted on the
retina is indeed wonderful. Standing on an eminence, the
eye takes in a landscape of hundreds of miles in extent ; and
all this is painted on the retina, though, as an English writer
calculates, a portion of the castle of Edinburgh, 500 feet
long and 90 feet high, occupies on the retina only the twelve
hundred thousandth part of an inch, when seen at a certain
distance. " A whole printed sheet of newspaper," says
Arnott, " may be represented on the retina on less surface
than that of a finger nail, and yet not only shall every word
and letter be separately perceivable, but even any imperfec-
tion of a single letter ; or, more wonderful still, when at night
an eye is turned up to the blue vault of heaven, there is por-
trayed on the little concave of the retina, the boundless con-
cave of the sky, with every object in its just proportions.
There a moon in beautiful miniature may be sailing among
her white-edged clouds, and surrounded by a thousand twink-
ling stars, so that to an animalcule, supposed to be within
and near the pupil, the retina might appear another starry
firmament with all its glory. If the images in the human
eye be thus minute, what must they be in the little eye of a
canary bird, or of another animal smaller still ! How wonder-
ful are the works of nature !"

8. The Cornea is the term applied to the anterior tran-
sparent portion of the ball. It resembles a watch crystal in
shape, and it is received into a groove in the sclerotic coat,
in the same manner as a watch-glass is received into its
case, as in this cut. It is somewhat thicker than the sclerotic

SENSE OF SIGHT. 195

coat, and is composed of six concentric plates ; but its blood-
vessels are so small, that they exclude the red particles alto-
gether, and admit nothing but serum. Under the first plate,
little glands are found, perceptible only by aid of the micro-
scope, which are supposed to secrete an oil which gives the
eye its bright, sparkling appearance. In the last stage of
life, we find this fluid forming a thin pellicle over the cornea?.
I What is called the ciliary ligament, is the groove or circle,
where the cornea is inserted in the sclerotic coat^

9. \We find the tunics just described in the lower grades
of animals, as well as in man, differing of course in form,
density, &c., but always fitted to the circumstances of the
animal. Thus in soft, molluscous animals, the defensive coats
of the eye are soft also ; but then their eyes are placed on ten-
tacula, or feelers, so that they can retract them within their
shells.! In the articulata, as insects, the coverings of the eye
are firmer, and of a horny consistence. In the Crustacea, such
as crabs, lobsters, &c., the eyes are set in short bony cylinders,
and the cornea is often covered merely by a portion of skin,
which passes over it. In fishes, we see the cornea flat, on
account of the absence of the aqueous humour. In birds,
the cornea is conical, corresponding with the quantity of
aqueous humour ; and it is more prominent in rapacious
birds, such as the hawk, eagle, and kite, than in aquatic
birds. It is remarkable that the sclerotica in birds consists
of three different layers, the middle one of which is bone,
and composed of several plates, overlapping each other ;
designed doubtless to protect their eyes against each other's
sharp-pointed bills, which they have to encounter in their
attacks. In the higher animals, the coverings of the eye are
similar to those of man.

10. tThe Iris, is a circular membrane, which hangs sus-
pended like a curtain in the aqueous humour, and is attach-
ed to one of the coats of the eye at its circumference. It
derives its name iris, or rainbow, from the various colours it
has in different individuals, such as dark-brown, or black,

196

PHYSIOLOGY.

light-grey, °^ue> ana" several shades and combinations of
these. It is on this alone that the colour of the eye de-
pends. The colour depends indeed on the refraction of the
light, as it falls on the fleecy or velvet-like surface of the
membrane, and also upon the degree in which the black
paint which covers its back is seen through it ; according as
the iris is more or less transparent, will the " colour of the
eye" be lighter or darker.

11. In many of the lower animals, especially birds, the
iris assumes a still greater variety of colours. The round
hole in the centre of the iris is called the pupil, and it is the
dark pigment of the choroid coat, that we see through this
when we look into the eye of another. Aitkin says that this
name has been given to it, from the fact that when we look
into the eye, we see a small image of our own face, like a
very minute child or pupil. In albinos, and in animals that
see best in the dark, like owls, the dark pigment is wanting
not only on the choroid coat, but also on this membrane, and
as these parts are very vascular, the blood is seen imparting
a red colour to the eye.

12. The iris has the power of dilating or contracting in
order to admit more or less light according as it is needed..
This is effected by muscular fibres.) Of these, there are two
kinds. The first set converge from the circumference of the
iris to the circular margin of the pupil, and are called the
radiated muscles. When these contract they dilate the pupil.
The other set is composed of circular fibres which go round
the border, and indeed, form the pupil ; these are called
the orbicular muscle ; and when they contract diminish the
size of the pupil. Now, when more light enters the eye than
is wanted, the excited retina immediately gives warning of
the danger, and the nerves which are plentifully distributed
to the iris, stimulate the orbicular muscle to contract, and
the radiated one to relax, by which means the size of the pu-
pil is instantly lessened. On the contrary, when in the dark
or twilight, more light is needed, to transmit a distinct image

SENSE OF SIGHT. 197

of objects to the brain, the orbicular muscle relaxes, and the
radiated one contracts, so as to enlarge the pupil to its full
extent. Between these two muscles is a middle layer, com-
posed of a net- work of blood-vessels and nerves.

Fig. 4.

The cut marked I. represents the iris magnified as seen from the
front, showing the radiated muscle.

Cut II. is a back view of the same showing the orbicular muscle.

13. The iris then, regulates the quantity of light passing
through the pupil. The pupil during sleep is in an intermediate
state ; in inflammation of the brain it is generally contracted ;
but when the functions of the brain are interrupted by nar-
cotic poisons, the pressure of effused fluid, a tumour, or any
other cause, the pupil is dilated. The bella donna, or deadly
night-shade, is employed by surgeons for this purpose, when
they wish to couch, or perform other operations on the eye.
The contraction of the pupil is readily seen by holding a
candle close to the eye of a person, and then withdrawing it
slowly ; or by directing a person to look at a very near ob-
ject, and then at one more distant. Some persons can dilate
and contract the iris at pleasure. I possess this faculty to
a very great extent, and was conscious of it before I ac-
tually tried the experiment. The motion of the iris is not at
all associated with that of the lids, as Walker suggests in his
late excellent work on the Philosophy of Sight, the lids
remaining the whole time perfectly stationary. I am, when
contracting the iris, sensible of an effort similar to that of
examining a very near object, and when dilating it, like that
17*

198 PHYSIOLOGY.

of looking on one at a distance ; but it is not necessary
actually to look at any object in either case, nor do I attempt
it. If this does not prove that the muscles of the iris are
somewhat under the control of the will, then it cannot be
proved that any muscles of the body are so.

14. |The iris, in the lower animals, not only presents
great diversities in colour, as has been stated, but also in
form and mobility. In birds, and in the cat tribe, its mo-
tions are free and evidently voluntary ; but in reptiles, its
motions are obscure ; and in fishes imperceptible. In rumi-
nants, in the horse, the marmot, in the whale tribe, and in
owls, the goose, and the dove among birds, the pupil is elon-
gated transversely or sideways. In the horse, a small square
curtain hangs down, which intercepts a great portion of the
rays coming from above. In the cat tribe, including the
lion, the tiger, leopard, the lynx, the jaguar, &c. the pupil is
elongated vertically, as it is also in the crocodile* Now we
see a wise design in this arrangement, for in such animals as
have to watch their prey, which is generally placed more
above them, as on a tree, than at either side, the pupil is
elongated vertically, so as to admit of more extended vision
in such direction ; while in timid animals, like the ox, sheep,
and hare, who have to guard against the insidious approach
of enemies, while quietly grazing the fields, we find this ar-
rangement reversed, and the pupil admits the greatest num-
ber of lateral rays.

15. Ciliary Processes. — These are little folds or fringes of
the choroid coat, which, joining the sclerotica near the cornea,
(which union is termed the ciliary ligament) turn backwards
and inwards, in the form of a circular, plaited fringe, the lit-
tle threads of which are called the ciliary processes. They
are covered, like the choroid, with the black pigment, and
closely embrace the margin of the crystalline lens, forming
round it an opaque blackened partition, which absorbs all the
side rays of light, which might otherwise have disturbed the
clearness of vision. These threads or processes are plaited

SENSE OF SIGHT. 199

like the folds of a ruffle, of which there are about 70 in the
human eye, all arranged in a radiated manner round the lens,
as represented in the following cut.

Fig. 5.

Section of the eye magnified, showing the ciliary processes, the pig-
mentum nigrum, the retina, and the choroid coat.

16. The ciliary processes are thus cellular and vascular,
and some have thought muscular, in order to give support to
the weight of the crystalline and vitreous bodies, to keep
them from falling towards the iris, or into the aqueous hu-
mour. To accomplish this, we find them placed immme-
diately in front of the vitreous humour, and closely embrac-
ing the circumference of the crystalline lens, and then to
strengthen the slender materials of which it is formed, we
find it implanted in little furrows on the surface of the vit-
reous body, glued as it were to it, and adhering to it very
firmly. We know that very substantial fabrics are made by
plaiting and matting together very slender and flimsy sub-
stances, as straw, chip, and grass to form hats ; and it is on
this principle, doubtless, that the ciliary processes are im-
pacted or plaited together.

17. HUMOURS or THE EYE. — The humours of the eye

200 PHYSIOLOGY.

have been compared to the glasses of a telescope, and the
coats to the tube which keeps them in their places. They are
three in number, and though all are perfectly transparent,
they differ in density, and in the space which they respec-
tively occuptl

18. Aqueous Humour.-^-The aqueous humour is as clear aa
the purest water, from whence its name, although its specific
gravity is greater ; containing, as it does, a little albumen,
gelatine, and muriate of soda. It fills the entire space be-
tween the cornea and cyrstalline lens. The iris floats in it,
suspended like a curtain. The space between the iris and
the cornea is called the anterior chamber ; and that between
the iris and the crystalline lens, the posterior chamber of the
eye. This fluid is secreted by a very thin, transparent mem-
brane which encloses it, though some say it exhales from the
vessels of the iris, and its chief office is to distend the cor-
nea, and preserve the iris in a moist condition, fit for the dis-
charge of its appropriate functions. This fluid is also in a
constant state of secretion and absorption ; for when
entirely discharged, in extracting the lens, for cataract, we
find that in a few hours it will be restored again. In old
age, its quantity is lessened, and the eye becomes flatter,
needing the aid of convex glasses. Fishes have no aqueous
humour at all, as the water, in which they swim, answers the
same purpose, as this was designed for, in land animals.

19. Besides this, the aqueous humour probably aids in
adjusting the eye to different distances. As the lens lies im-
mediately behind it, it is evident that, when the quantity of
fluid is increased, it will press the lens back nearer the re-
tina, while, at the same time, it renders the cornea more
convex, and the reverse happens when the quantity is dimi-
nished. When the distemsion is very great, the pressure
causes a cloudiness or opacity of the cornea, thereby pro-
ducing blindness. This not unfrequently happens with
horses that have been fed during the winter on dry food,
either placed on a level with the head or above it. In the

SE-NSE OF SIGHT. 201

spring, when they are turned out to the green pasture, where
their diet is changed from dry to succulent, and where also
the head is held near the ground to collect the food, a con-
gestion of the aqueous humour is apt to occur, sufficient to
produce temporary blindness.

20. The Crystalline Lens.-^-This is placed immediately
behind the aqueous humour, a short distance back of the
pupil, and is a double convex lens, perfectly transparent. In
shape it closely resembles the common burning glass ; its
posterior surface is, however, a little more convex than the
exterior, and it approaches nearer to a sphere in infancy
than in old age* When the crystalline lens is first removed
from an eye* it looks like a mass of transparent crystal,
without any trace of organization. Near the surface it is
much softer than at the centre, which is harder and more
compact. It is also softer in the young than in the old. As
it consists chiefly of albumen, when exposed to heat, as of
boiling water, alcohol or acids, it becomes white, like the
white of an egg. If we examine it in this state, we shall
find that it consists of an immense number of concentric
plates or Lamella. More than two thousand of these have
been counted, disposed in the form of layers like the coat of
an onion, each layer consisting of an infinite number of
very minute filaments, wound round in different directions,
from various centres. The arrangement of these fibres
differs in various animals, but is uniform in every individual
of the same species. In fishes the lens is nearly spherical ;
in reptiles it is less so, and in birds and mammalia, it is still
more flattened. In amphibious animals, as turtles or frogs,
or those whose vision is adapted both for air and water, as
seals and whales, the lens is more convex than in those which
live entirely in the water. When this lens becomes so
opaque as to obstruct the passage of the light, either par-
tially or entirely, a person is said to have a cataract. This
can only be cured by a surgical operation.

202

PHYSIOLOGY.
Fig. 6.

Section of the eye magnified, showing the Crystalline Lens in its
proper situation, between the aqueous and vitreous humours.

21. The Vitreous Humour. — -The vitreous body or humour
is so called from its resemblance to melted glass. It is, like
the other humours, perfectly transparent, and occupies the
globe of the eye, of which it constitutes at least the poste-
rior two thirds. It is surrounded by the retina in nearly its
whole extent, to which, however, it does not adhere. It is
composed of a fluid, contained in cells, formed of a mem-
brane called the hyaloid, which communicate with each
other, so that if it is punctured, the fluid with ^hich it is
filled will escape, though slowly in consequence of the intri-
cacy of the cellular structure. On removing the vitreous
humour from the eye, it appears to be of about the consis-
tency of the white of an egg ; its use being to afford a sur-
face for the extension of the expanded retina, to keep the
lens at the requisite distance, and to transmit and refract the
rays of light.

SENSE OF SIGHT.
Fig. 7.

203

The vitreous humour and crystalline lens magnified, with the stains
of the pigmentum nigrum left by the ciliary processes.

22. Laws of Vision. — 4Light passes through the air, or
any medium of the same density, in straight lines ; but
when it passes from one medium into another, it is refracted,
or bent out of a straight Course, unless it strikes the new
medium in a perpendicular direction, when it passes directly
through. Air, water, glass, or any substance through which
light passes, is called a medium. When a ray of light passes
from a thinner or rarer medium, into one more dense, as
from air into water, it is bent towards a line drawn perpen-
dicularly to its surface. The contrary is the case when the
reverse happens. This is shown by plunging a straight
stick into the water, which will appear crooked. This may
be illustrated by the familiar experiment of taking an object,
such as a shilling, and fixing it at the bottom of an empty
basin, then retiring backwards until the brim of the basin
hides it ; then let water be poured into the vessel, and the
coin will again come to light, as in the following cut, (See
Fig. 8.)

Thus the ray of light from the coin will proceed in the di-
rection #, previous to the addition of the water, but when
water is poured into the vessel, the ray will be reflected
down to the eye, and the shilling will appear to occupy the

204

PHYSIOLOGY.
Fig. 8.

situation b. In the same way, when we look into a river,
the pebbles appear to be raised in the water, and it looks
shallower than it really is. From this circumstance, persona
have often been drowned.

23. Lenses.— -A. lens is usually made of glass, its surface
being ground into some of the following shapes :

The first of these on the left hand would be called a plain
lens ; the third, double convex ; the fourth, plano-convex ; the
fifth, double concave ; the sixth, plano-concave ; the seventh,
concavo-convex, fyc. Now, light in its passage through these
glasses, would be refracted in proportion to their greater or
less degrees of convexity or concavity ; but in passing
through a plain lens, like the first, the rays would not be
bent out of a straight course. For example, if you place
an object at the bottom of a tub of water, and place the eye
in a perpendicular direction over it, the object is seen pre-
cisely in its true situation ; but if you withdraw a short
distance, it will appear to be situated where it is not.

SENSE OF SIGHT.

205

A, a solid oblong piece of glass ; a, a, a stream of light, which
strikes the surface of the glass, b, c, and which, being perpendicular,
suffers it to pass through without refraction.

24. Now let us take a concave lens, and see what effect
that will have on the light.

Fig. 11.

A, a solid oblong piece of glass; a, a, a stream of light which strikes
the surface of the glass 6, c, and vyhich being concave, causes the light
in its passage through it to diverge.

25. Now try a convex lens, such as the crystalline humour
of the eye, and see how that will affect the rays of light.

We see that this form of glass causes the rays of light
18

206 PHYSIOLOGV.

a, a, to converge to a point, or focus at d ; and if it was still
more convex, they would come to a point still nearer. We
are now able fully to understand how it is that the humours,
or lenses of the eye collect the light from visible objects, and
converge them into an image upon the retina. fThese media,
we have seen, are four in number, viz., the cornea, the aqueous
humour, the crystalline lens, and the vitreous humour ; each
possessing a different density, different sphericity, and con-
sequently different refractive powers.

26. Now let us examine the principle on which an image
is formed. This may be shown by holding a common sun-
glass opposite a window in a room, and placing a sheet of
paper behind it. We immediately see depicted on the paper
a perfect image of the window, diminished according to the
convexity of the glass, but inverted. The greater the con-
convexity, the nearer must the paper be held to the glass to
receive the image, and the nearer to the window the glass is
held, the larger will the image appear.

Fig. 13

In this cut, rays of light pass from the candle, and the
hand A, B, and falling on the lens at C, are conveyed to the
paper D, which is consequently illumined with the object
in the same way as in the above experiment, the window
was painted on the paper. In like manner precisely, are
images painted on the retina, as is shown in the following
cut.

'SENSE OF SIGHT.
Fig. 14.

207

27. Thus the convergence of the rays begins in the aqueous
humour is perfected in the crystalline^ but when they strike
the vitreous humour, which is concave on its front surface,
and also less dense than the crystalline, they diverge or
spread out, and are thrown upon the back part of the eye.
The manner in which this is effected may easily be seen by
the following illustration.

Fig. 15.

o, the aqueous ; c, the crystalline ; t>, the vitreous humour.

In passing through the crystalline, the rays cross each othei,
so that those rays which pass from the lower part of an
object are presented uppermost in the bottom of the eye and
the reverse, so that the images of objects are always invert,
ed, or bottom side upwards. Any one can see this by cut.
ting out a circular portion of the outer coat, at the back
part of the eye of an ox or sheep recently killed, and holding
it up at a window ; he will then see, on its posterior sur-
face, a perfect but inverted representation of objects whether

208 PHYSIOLOGY.

stationary or in motion. Now, suppose a person was look*
ing at a church with a tree standing at its side, he would
have in each eye an actual inverted panorama of the objects,
painted in a more beautiful, correct, and delicate manner
than any effort of art can ever hope to exhibit, as follows.

Fig. 16.

28. But if the images of objects are inverted, why do we
see things erect ? Locke, Buffon, Diderot, and other great
philosophers, supposed that infants at first see things upside
down, and afterwards learn to correct their erroneous sensa-
tion, by comparing the information obtained by touch with
that acquired by sight. And not only this, they maintain-
ed that infants see every object double, and all at the same
distance, until experience corrects their errors. Berkeley,
however, contended, that we judge of the position of objects
by comparing them with our own ; and as we see ourselves
as well as every thing else wrong side up, or inverted, ex-
ternal bodies are in the same relation to us as if they were
erect. But in that case, the boy who stoops down and looks
at objects between his legs, ought certainly to see them
wrong side up ; but though a little confused perhaps at first,
he soon sees in that way as well as any other. This diffi-
culty is easily explained by what is called the law of visible
direction ; that is, each point of an object is seen perpendi-
cular to the point of the retina on which its image falls.
The surface of the retina being concave, and nearly as pos-

SENSE OP SIGHT. 209

sible spherical, these lines of visible direction meet and cross
at a point within the eye, which is called the centre of visible
direction ; the lines from the upper part of the image go to
the lower part of the object, and those from the lower part
of the image proceed to the upper part of the object. Thus
an inverted image necessarily produces an erect object, and
the external object is the thing to which the mind attends,
and not the object on the retina. The error of all these
philosophers has consisted in this, that they have imagined
a true picture to be formed on the retina, which is regarded
by the mind, and therefore seen inverted. But there is no
interior eye to see or take cognizance of this image ; but
the mind accurately refers the impression made on the
retina to the object producing it. In short, the mind stands
behind the retina and looks at objects as they are through
this screen, but it does not see the screen itself, but judges
of the position of objects by the direction in which the light
comes from them towards the eye ; and as Arnott well
remarks, — "no more deems an object to be placed low be.
cause its image may be low in the eye, than a man in a
room into which a sun-beam enters by a hole in the window-
shutter, deems the sun low because its image is on the
floor."

29. Again, why, as we have two eyes, does not every
object appear double ? fThe reason is, that in the two eyes
are corresponding points, so that when a similar impres-
sion is made on both, the sensation, or vision, is single.
Now, we have the faculty of so directing the axis of the
eyes, that the image of* an object falls exactly on the same
point in each ; but if from any cause there is the least dis-
turbance, then vision becomes double, as often happens to
the drunkard. This is easily known by slightly pressing
a finger on the ball of either eye, so as to prevent its following
the motion of the other. Persons who squint always have
double vision, but then they acquire the power of attending
to the sensation in one eye at a time. Animals that have
18*

210 PHYSIOLOGY.

the eyes placed on opposite sides of the head, possess in a
more remarkable degree the faculty of thus attending to one
thing at a time.

30. It follows then, that the eye itself does not see ; it is
only an instrument employed by the brain, or rather the
mind, whose servant the brain is. The optic nerve is the
channel by which the mind peruses the hand writing of na-
ture on the retina, and through which it transfers to that
material tablet its decisions and its creations. There is then
a portion, or rather an organ of the brain, where vision or
the mind's eye is seated ; and this portion is sometimes im-
perfectly constituted or organized, as Gall has proved to be
the case, in those who cannot distinguish colours. That
such is a true statement of facts, we learn from observing that
disease of a given portion of brain produces blindness, whilst
the eye remains perfectly healthy. Either this was the case
with Milton, or he was afflicted with amaurosis, or palsy of
the retina, for he says,

" These eyes, though clear
To outward view, of blemish, or of spot,
Bereft of light, their seeing have forgot!
Nor to their idle orbs doth sight appear
Of sun, or moon, or star throughout the year !"

We also have the power of internal vision when asleep ; and
those who have lost their eyes perceive spectral illusions, and
other similar phenomena, and they can alio conjure up the
figures and forms of various objects familiar to them before
they lost their vision. ^gg

31. {From the principles now laid down we can understand
why rivers appear shallower than they are, and why a stick
placed in the water appears crooked. In spearing of fish,
or shooting them in the water, every sportsman knows that
he must make suitable allowance for this refraction, for the fish
is always nearer to him than it appears. Birds that dive for
fish seem to understand that there is but small chance of
success if they dive obliquely into the water, so like skilful

SENSE OF SIGHT.

211

opticians, they hover over, and when they see their prey,
dart down perpendicularly, in which direction, as we have
seen, there is no refraction. There is a curious fish in the
East India waters called chactodon, about eight inches long,
that appears to understand optics remarkably well. When
it sees a fly, sitting on the plants that grow in shallow water,
it swims within five or six feet, and then with the dexterity
of a practical marksman, ejects from its tubular mouth a
single drop of water which never fails to strike the fly into
the sea, where it soon becomes its prey. Dunglison states
that Hommel, the Dutch governor, put some of these fish
into a tub of water, and then pinned a fly on a stick within
their reach. He daily saw the fish shoot at the fly, and they
never failed to hit their mark.

32. Short-sightedness. — -This generally arises from too
great convexity of the cornea, or excessive density in the
structure of the crystalline lens ; either of which will cause
the visual rays from near objects, to converge to a focus, be-
fore they reach the retina. This is remedied by concave
glasses^ which, as we have seen, cause the rays to diverge, as
is represented in the following cut.

Fig. 17.

A. a short-sighted eye ; B. an arrow which it attempts to perceive,
but is prevented by the convergence of the passage of the visual rays
to foci, at C., before they reach the retina at D. E. the same eye.

212 PHYSIOLOGY.

similarly situated, showing how by the intervention of a concave lens,
G., the rays are di-verged, and the image of the arrow, F., accurately
converged to the retina at A.

33. Long-sightedness is the opposite defect to this, and is
owing to a flattening of the cornea, and a relaxation in the
structure of the crystalline lens, by which its power of re-
fraction is lessened. ) In this case, the rays of light are car-
ried beyond tlie retina, and therefore do not form a distinct
image on it. pld persons usually are subject to this defect ;
the only remedy known is convex glasses.. Where persons
have been short-sighted in youth, as the eye grows flatter by
age, they at length are able to see well, without glasses of any
kind. This change in the shape of the eye is often denoted
by a tendency to hold a book at a greater distance when
reading. Glasses do for the eye that portion of the labour
of bending the rays of light, which it is not able to do for
itself. By adapting glasses to the successive changes which
age produces in the shape of the eye, the sight may be pro-
longed very often to the close of life. After the operation of
extracting the crystalline lens for cataract, or depressing it
by couching, very convex glasses are needed to remedy the
deficiency.

34. The sight is often injured by long-protracted attention
to minute and near objects ; as we see in the watch-maker
and engraver ; also by watching for objects at a distance ;
as in sailors, and keepers of telegraph stations ; in the one
case the eye becoming near, and in the other far-sighted.
During the arbitrary reign of Napoleon, the young men of
France often produced short-sightedness voluntarily, by wear-
ing very concave glasses, in order that they might be exempt
from military service.

35. Some persons are unable to tell one colour from
another. Sir David Brewster gives us the following exam-
ples. A Mr. Scott mistook pinJc for pale blue, and red for
green. His father, uncle, sister, and two sons, all mistook
these colours in the same way. A shoemaker named White,

SENSE OF SIGHT. 213

could only see two colours, black and white, and he could
never distinguish the cherries on a tree from the leaves. A
tailor at Plymouth could only see yellow and blue. On one
occasion he repaired a Hack silk garment with crimson, and
on another, he patched the elbow of a blue coat with a piece
of red cloth. M. Nicoll tells us of an officer in the British
navy, who purchased a blue uniform coat and waistcoat,
with red breeches to match. -The cause of this defect is

y

believed to be a malformation, or deficiency of that portion
of the brain which takes cognizance of colours^

36. The lowest order of animals have no organs of
vision, or if so, they have never been detected. Many in-
sects have two kinds of eyes, one kind on each side of the
head, and the other on the top, in a row, or in the form of a
triangle. The spider .has generally eight of these eyes on
the top of the head. [What are celled the compound eyes
are placed on the side of the head, and in the wasp and
dragon-fly they cover a large part of it. These eyes are
formed of a large number of separate cones or cylinders,
closely packed together, each being a distinct eye, and hex-
agonal, or six-sided in shape, like the cells of a honey-combl
The ant has about 50 ; the beetle 3,000 ; the silk-worm moth
upwards of 6,000 ; the dragon-fly 12,000 ; and some in-
sects as many as 20,000.

37. It is now ascertained, that each eye forming these
compound eyes of insects, consist of a distinct tube, furnished
with every thing necessary for complete vision. The object
of this wonderful arrangement seems to be to compensate for
want of motion, by the number of eyes, as the insect thus
supplied, has an eye pointed towards the object in whatever
direction it may appear, and may therefore be truly called
circumspect. If we examine the wasp and dragon-fly, we
shall find these compound eyes to cover a large portion of
each side of the head. By examining with the microscope,
we find each of these conical tubes covered with a cornea,
and containing a crystalline lens, and aqueous and vitreous

214 PHYSIOLOGY.

humour, an iris, a choroid coat, and a retina ; the pigment
running back around the lens, separating each cylindrical
compartment. They have no eye-lids, eye-lashes, or tears ;
but these are compensated for by the great hardness and in-
sensibility of the cornea.

Fig. 18.

Eye of the yellow beetle magnified, composed of 8,820 hexagonal
cylinders, the interior of each tube being round.

Fig. 19.

Eye of the phalaena or butterfly, magnified, consisting of 11,300
square sections. The eye of the mordella is similar, containing 25,088
prisms.

38. Motions of the Eye. — We have seen that the eye is a
perfect optical instrument, infinitely surpassing the boasted
specimens of human skill ; but without the power of motion,
of adapting it to the varied objects which surround us, we
should derive but a very small proportion of that gratification
and pleasure, of which it is now the source. We shall per-
ceive the great advantages we enjoy from this benevolent
provision, if we contemplate the movements of a telescope ;
how difficult it is to direct it to any object, so as to obtain a
view of it, and what complicated and cumbrous machinery
are required to effect it. But all the various motions of the
eye are produced by six little muscles !

SENSE OF SIGHT. 215

39. Four of the .muscles of the eye are called straight or
recti muscles ; the other two are named the oblique muscles.
'The first four arise from the back part of the orbit, and are
inserted by broad thin tendons into the four sides of the
globes near the junction of the cornea with the sclerotic
coat. The white pearly appearance of the eye is caused by
these tendons. The oblique muscles arise from the front and
inner side of the orbit, and pass to the eye-ball at right angles
from the straight muscles, one passing over its upper surface,
and the other upon its under surface, and both are inserted
into its outer side, one a little above its horizontal axis, the
other a little below it. The superior oblique muscle is, how-
ever, worthy of more particular notice, as no part of the
body exhibits clearer marks of design and contrivance. It
arises as I have said, from the bottom of the orbit, it proceeds
forwards and becomes tendinous, and when it reaches near
the margin of the orbit, it passes through a little cartilagi-
nous pulley, by which the direction of its action is changed,
precisely as we see done by a pulley among the ropes of a
ship ; after passing through this little loop, which is dense>
smooth, and elastic, and furnished with a lubricating fluid to
diminish friction, the tendon runs obliquely backwards and
towards the internal angle to be inserted into the ball. When
this muscle acts, the eye is rolled directly inwards. Thus
the muscle pulls in a direction contrary to its own action, as
when a man raises himself by a rope thrown over a beam.
The other, or inferior oblique muscle, rolls the eye outwards
towards the temple. When they both act together, the eye
is steadily carried forwards. The recti muscles move the
eye in four directions, upwards, downwards, to the right, and
to the left, each movement being affected by its appropriate
muscle. When the four act together, the eye is drawn back
towards the bottom of the orbit.

216 PHYSIOLOGY.

Fig. 20

Side view of the muscles of the eye in their natural positions, a. b.
c. d. the four straight muscles, a. is turned up to prevent the others
from being hidden, e. the superior oblique muscle, f. the optic nerve.
The other oblique muscle is not shown, but it lies on the other side of
the ball, and comes round, and is inserted near the superior oblique ; so
that they pull opposite ways, like two men sawing timber. By the com-
bined action of all these muscles, an infinite variety of motions of the
eye can be produced.

40. In order to facilitate the motions of the eye it is
lodged securely on a soft bed of fat. This is contained in
very large cells at the bottom of the orbits, and is more
fluid than fat in general, and is less affected than any other
part of the body by those causes, which produce general
emaciation. The eye-ball may therefore be said to move in
a fluid medium, fully adequate to give every necessary sup-
port, and at the same time affording the least possible resist-
ance.

41. Defences and Appendages of the Eye. — These are

SENSE OF SIGHT. 217

Ahe orbit, the eyebrows, the eyelashes, the eyelids, and the
lachrymal apparatus. The or&& is a four-sided vault, com-
posed of seven bones, and shaped like a pyramid or cone,
the apex pointing backwards. The eyeball and the orbit
seem exactly made for each other ; the one being globular,
the other rounded to receive it. At the bottom of the orbit
are holes for the passage of the blood-vessels and nerves.
Now this cavity is not scooped out of the skull, as a boy
would make a hole in a block of wood, but the seven bones,
which enter into its composition, are so curiously dove-tailed
together as just to leave this space for the reception of the
eye and its appendages. What mechanic could place
seven irregular, jagged bones together so as to form a smooth,
polished cavity, for such a delicate organ as the eye to roll
in ! So securely is the eye protected by its bony house or
encasement, that it is a very rare thing for it to be injured,
except by some sharp pointed object.

42. The eye then is surrounded on every side with bone,
except the front ; now, what have we here to serve as a
means of defence ? It would not have answered our pur-
pose to have had it entirely shut up in a box of bones, or
even to have left a little hole just to peep through. As we
cannot draw our heads into a shell when danger threatens,
like a snail or turtle, we are furnished with a couple of
moveable curtains or eyelids, placed before the eyes, which
we can let down or raise up just when we please. If the
eyes are " the windows of the soul," then I would call the
lids a pair of inimitable window shutters, for they exclude
the light whenever its presence would be disagreeable to us.

43. The eyelids are composed of a thin skin, externally ;
internally of cellular membrane, — its cells filled with a soft
semi-transparent fluid ; while their inner surface, in contact
with the eye, is lined with a delicate mucous membrane,
continuous with the skin, called conjunctiva) Besides these
there are beneath the skin, two sets of muscular fibres ; one
called orbicular t running round the lid horizontally, whose

19

218 PHYSIOLOGY.

contraction serves to close the eye ; the other lying beneath,
are the fibres of the levator muscle, which serves to : aise the
Ud, or open the Syel These two muscles are well exhibited
in the following cut :

Fig. 21.

Muscles of the eyelids, the elevator passing back into the orbit ; the
sphincter, or orbicular muscle surrounding the eye.

44. Around the margin of each lid, there is a delicate
elastic cartilage placed, which serves to preserve the shape
of the lid ; and into this, as is shown in the cut, the fibres
of the elevator muscle, are inserted. In contact and around
each cartilage, on its anterior surface, at the root of the eye-
lashes, is situated a row of little bags or follicles, which
secrete an oily fluid, to keep the parts soft and pliant, and
prevent the lids from sticking together. It is this matter
which we often find in the morning, collected on the margin
of the lids, or in the internal angle of the eye.

45. Now, mark this difference ; the levator muscle, which
rises from the bottom of the orbit, is entirely under the con-
trol of the will ; the orbicular muscle is not. See the ad-
vantage of this. If we had always to issue a command of
the will to shut the eyes, before going to sleep, I imagine
there are a good many in this lazy world who would forget
to shut their eyes, and so go to sleep with them wide open.
To what dangers would they be exposed, and what injuries
might they not sustain in consequence ! But watch a

SENSE OF SIGHT. 219

sleepy person. No sooner does he begin to grow drowsy,
than his eyes begin to close ; in other words, " they grow
heavy." If he wishes to keep awake he makes a desperate ef-
fort to open his lids ; and in the drunkard, whose involuntary
muscles overpower the voluntary ones, it is quite ludicrous to
watch the expression of countenance, and see how quick the
disobedient, rebel lids close, upon the oft-repeated efforts to
keep them open.

46. The opening and closure of the lids ordinarily occu-
pies about the eighth part of a second, so that there is no
interruption to the continuance of vision. Besides serving
as a curtain to protect the eye, the lids serve, by their mo-
tions to diffuse the tears and mucous secretions, thus keep-
ing the surface of the cornea moist, and wiping off any
foreign matter, as dust, that may be lodged on it. The eye-
lids when closed, do not entirely prevent the transmission of
light ; for when we have been refreshed by sleep, the stimulus
of the light falling upon the lids, is sufficient to arouse sen-
sibility and awake us.

47. It is a curious fact, that while the upper eye-lid falls,
the lower eye-lid is moved towards the nose, and thus aids
in collecting all offensive particles in the corner of the eye.
This can readily be shown by marking the edges of the lids
with a black spot ; when the lids are opened and closed, the
spot on the upper eye-lid will rise and fall perpendicularly,
while that on the lower one will play horizontally like a
weaver's shuttle. When any thing gets into the eye, there
is this continual play of the lids maintained, till the offend-
ing particles have been driven into the inner corner of the
eye, when relief is at once obtained. When the object is
very small, or not sufficiently irritating to excite these
muscles of the lids to action, it is common to p-lace an eye-
stone, which is a smooth piece of sulphate of lime in the
eye. This not only excites an abundant secretion of tears,
but also causes the necessary motions of the lids, by which
the object is soon washed into the angle of the «ye.

220 PHYSIOLOGY.

48. Many animals have what may be called a third eye-
lid, called the nicitating membrane. This slides from one
angle of the eye to the opposite side, under the lids, whether
open or shut. Its use is to clear away all matter which
might be irritating to the eye. Birds that see best by night,
such as owls, defend their eyes against the light of the sun,
by drawing this curtain over them.

49. The eye-lashes, or cilia, also aid in the protection of
the eye. They ward off insects, protect the eye from par-
ticles floating in the air, and also break the intensity of light
Indeed, when moist, as they often are with perspiration, the
little drops serve to decompose the rays of light, causing the
appearance of a luminous zone around the flame of a candle.
{The eye-brows are composed of loose cellular substance,
covered with skin, from which spring short bristly hairs
projecting outwards. Like all hairs, they penetrate little
follicles, and become besmeared with an oily secretion, which
preserves their glossiness^.so that the drops of sweat which
may accumulate on the brow are prevented from trickling
over the eye-lids, where they might interfere with vision/

50. Lachrymal Apparatus. — rlThe tears are secreted by the
lachrymal gland, which is a small spongy body of a flatten-
ed form, seated in the hollow of the bone, in the upper and
outer part of the orbit, just beneath the outer end of the
bone4 These serve as fountains, as well as laboratories or
distilleries, separating, as they do, a pure water from the red
blood, and discharging it by means of seven or eight little
tubes, upon the inner surface of the upper eye-lid, from
whence it is spread along with the mucus from the con-
junctiva over the eye, by the movements of the lids. But
what becomes of the tears ? ^In the inner corner of the eye
are two very minute apertures, one in each lid, which are
the orifices of two canals, which communicate with a pipe,
by which the superfluous moisture is drained off into the
nostrils. This process is constantly going on without notice
But when there is much irritation, then the natural chan

SENSE OF SIGHT

221

nels are insufficient for their escape, and the tears roll over
the cheek.

Fig. 22.

a, the eye-ball, and b, b, are the upper and lower sides. Now in order
to prevent dust and other bodies from working their way between the
call and the lid, through passages at c, c, into the socket of the eye,
where they would excite great inconvenience and pain, we find the
common skin of the eye-lids d, d, after covering their edges, turn in a
little way between the lid and the ball, and then turn back and are
reflected over the surface of the cornea ; where, to prevent the obstruc-
tion of vision, it becomes perfectly transparent.

Fig. 23.

The eye-lids separated, and viewed from behind ; a, the lachrymal
gland ; 6, the ducts from the lachrymal gland ; c, the mouths of these
ducts ; d, the puncta lachrymalia ; e, the meibomian glands, which
secrete the oily fluid.

19*

222 PHYSIOLOGY.

51. There is a striking proof of design in the manner in
which the opaque, lining membrane of the eye-lids becomes
transparent, as it is reflected over the cornea. But we can
illustrate this more clearly by means of the following dia-
gram.

Fig. 24.

The eye-lids viewed from before ; a, a, the lachrymal canals ; J, the
iarchrymal sack. The lachrymal sack is a bag of an oval shape, fixed
to the end of the double canal, and lies in a depression of the nasal
bones. It terminates in a tube called the duct, which passes through
a hole made for it, in the bones of the nose, and opens into the nos.
tril.

52. It is now well ascertained that a belief in superna-
tural appearances, and stories in relation to seeing ghosts,
hobgoblins, and spectres, have arisen from optical illusion.
We have seen how a person in delirium tremens, imagines
that he sees a thousand unreal objects, and hears a thousand
strange voices ; the same phenomenon, though less in degree,
may happen to a person in health, owing to an excitement
in some portion of the brain. I have heard an aged rela-
tive, who believed in witchcraft, tell of frequently having
seen the ghost of some deceased friend, and once of having
fired at a deer three times, in the twilight, while he was
cropping the tender grain just springing out of a newly

SENSE OF SIGHT. 223

sown field, without frightening the animal; and when at
length he suddenly disappeared, no tracks or traces of him
could be discovered on the soft mould. Nothing could con-
vince the old gentleman that his sight had deceived him,
that these objects had only existed in his brain.

53. One source of deception lies in the fact that, indirect
as well as direct vision is intermittent, as any one may
learn by attempting to read small print by moonshine, or in
twilight, or by looking at a single star for some time, when
it will be found to vanish often and reappear. In an ob-
scure light we find that a painful effort is required to distin-
guish objects ; and after all they appear and disappear, be-
cause the impression they make upon the retina is not
sufficiently vivid to be continuous. We can easily imagine
therefore, that in the dusk, to a person who is ignorant of
this fact, the sudden disappearance and reappearance of
objects must seem very extraordinary.

54. Dr. Paley remarks that, " were there no example in
the world of contrivance except that of the eye, it would be,
alone, sufficient to support the conclusions which we draw
from it, as to the necessity of an intelligent Creator." When
we look at a telescope, and see how it consists of a tube
composed of various pieces, containing several glasses or
lenses placed at different distances in order to refract the
rays of light, and bring them to a focus ; how, within it,
there is a partition of metal, through which is a round hole
in the centre for the purpose of lessening the surface of the
lens on which the rays of light strike ; and when, in addi-
tion to all this, we see the inside painted black, to absorb the
oblique and scattering rays that would otherwise render
objects confused and indistinct; when we see all these
things, we immediately say, here are marks of design, here
is evidence of wise and skilful contrivance ! and yet the
telescope is but a close imitation of the human eye, which
had God for its designer. When, also, we look at the ca-
mera obscura and see a tight, dark box, with a lens fitted in-

224 PHYSIOLOGY.

to it, through which the light, passing, falls upon a screen
behind, forming an inverted image of the object represented,
we say at once here is design ! But this instrument also is
copied from the human eye !

Questions. — What is said of the sense of sight ? What arc the coats
of the eye ? Describe the scelerotic ?— the choroid ? What is the pig-
mentum nigrum ? Is it ever absent ? Describe the retina ? Illustrate the
minuteness with which objects are painted on it ? Describe the cornea ?
— the ciliary ligament ? What is said of these tunics in the lower
order of animals ? What is the iris ? How does it contract and di-
late ? Are the muscles ever under the control of the will ? What is
said of the iris among the lower animals ? Describe the ciliary pro-
cesses ? What are the humours of the eye ? Describe the aqueous ?
the crystalline ? — the vitreous ? Explain some of the laws of vision ?
What is a lens ? How many, and what kinds of lenses are there ?
What effect on light has a concave ? a convex ? a plain lens ? Illus-
trate this by the humours of the eye. Are images erect on the retina ?
Where do the rays cross ? How do you explain why we do not see
objects inverted ? Why do we not see objects double ? Why do riv-
ers appear shallower than they are? To what is short-sightedness
owing ? How may it be corrected ? What is long-sightedness ? What
is the remedy ? Are there persons who cannot distinguish colours ?
To what is this owing ? What is said of compound eyes ? How
many muscles are there to move the eye 1 Describe them ; the recti ;
the oblique. What are the defences of the eye ? Describe the orbit ;
the eyelids ; the muscles of the lids. Are they voluntary muscles ?
How are objects carried into the angle of the eye ? What is the use
of eyelashes ? — of eyebrows ? How are the tears secreted ? How ,
carried out of the eye ? What has led to a belief in supernatural ap-
pearances ?

CHAPTER XVII.

THE SENSE OF HEARING

1. THROUGH the sense o£ hearing, we obtain a know-
ledge of ; the peculiar vibrations of sonorous bodies, which
constitute sounds^. The organ of hearing is very complica-
cated, like that of sight, and the precise office of the differ-
ent parts is not yet fully known ; it is, however generally
divided into the outer, the middle, and the inner part, and
the auditory nerve.

2. The External Ear. — /The outer part of the organ of
hearing consists of what is called the external ear, and the
cavity which leads to the ear-drum ; and is composed chiefly
of cartilage, covered with the skin, and supplied with blood-
vessels and nerves. Its use is to collect sound, or rather the
vibrations of the air, and transmit them through the tube
that leads to the ear-drum. For this purpose it is admirably
contrived ; its surface being smooth and folded into grooves,
which, assisted by a raised border and several concave
spaces, conduct whatever sounds fall upon it, with the great-
est certainty, directly to the drum of the ear. The external
ear is furnished with muscles, and savages are said to have
the power of raising or bringing forwards their ears, like a
horse, to catch sounds as they come from different direc-
tions ; but the habits of civilized life destroy this faculty.
The following cut represents the external ear, and the mus-
cles by which it is moved. (See Fig. !.)•

3. Various names are assigned to the different portions
of the external ear, such as helix to the outer border, scapha,
the large boat-like depression, &c. ; but passing these by, as
of little importance, we remark that the external ear is con-
fined to the class mammalia, nor does it always exist among
them, for the mole, the water-shrew, and other diving animals,

226

PHYSIOLOGY.

Fig. 1.

External Ear and Muscles.

seals and whales, are destitute of it. Indeed, as water is a
much better conductor of sound than air, there would seem
to be little occasion for the external ear in them ; but they
suffer in consequence, when they attempt to live with their
heads out of water. Owing to this obtuseness of hearing
in the whale, he is easily approached by the whaler, and be-
fore he hears the oars of his enemy, the harpoon is fixed
into his unwieldy carcass. In like manner, the walrus and
the seal remain unconscious of the footsteps of their foe, till
it is too late to retreat. In land animals that are timid, as
the hare and rabbit, the ear is very large, so that they may
be apprized of the approach of their enemy in time to flee
to a place of safety. I

4. The Tube of the External Ear. — This is the passage,
called by anatomists meaius auditorius externus, which ex-
tends from the outer ear to the tympanum or drum, which is
stretched across its inner end. This passage is about ten
lines, or nearly an inch in length ; and pursues a somewhat
winding course inwards, a little forwards and downwards ;
its external portion being composed of cartilage, and its in-
ternal of bone. The width, as well as tension of this tube,
are effected by the motions of the jaw, ns any one can learn

THE SENSE OF HEARING.

227

by placing his little finger in his ear, and then opening and
closing the mouth. This is, no doubt, one reason why a
person stands with his mouth open when he is listening at-
tentively. This tube being constantly open, is liable to the
entrance of foreign bodies, such as dust, insects, and the
like. But, like the eye, it is not left without means of de-
fence, for on its inside, there are numerous fine bristles,
which interlace and prevent the entrance of any thing but
sound ; while between the roots of these hairs, there are
numerous little glands, which secrete a nauseous bitter wax,
which by its ofFensiveness, either deters insects from enter-
ing, or if they do, entangles them, and thus prevents any
further advance. This wax often becomes hard, and ob.
structs the tube, causing more or less deafness. This form
of deafness is easily cured, although it may have existed
even for years. When the ear is dry, from a deficiency of
wax, the hearing also becomes imperfect, as also when it ia
thin and purulent^

Fig. 2.

General sectional view of the structure of the ear ; a, th? meatus

228 PHYSIOLOGY.

auditorius externus ; 6, the tympanum ; c, the malleus ; d, the incus ;
c, the os orbiculare ; /, the stapes ; g, the semicircular canals ; h, the

cochlea ; i, the meatus auditorius internus ; kt the eustachian tube.
/

5. Membrane of the Drum, stretched across the inner end
of the auditory tube, is a membrane, called by anatomists the
membrane of the tympanum, (membrana tympani,) or drum of
the ear. It is somewhat oval in shape, but hollowed out, or
depressed at the centre, where, as we shall presently see, it
is fastened to the end of a small bone. This membrane is
tense like a drum-head, thin, and transparent. Its use is to
convey the vibrations of the atmosphere to the expansion of
the optic nerve in the internal ear. It does not seem entire-
ly essential to the function of hearing, as the hearing some-
times remains after it is destroyed. When it is ruptured, a
person can force the air out of his ear ; but while it remains
entire, it is impossible for insects or other bodies to get into
the drum, as is generally believed. The drum is capable of
being rendered more or less tense, and thus of moderating
the intensity of vibrations transmitted to it.

6. The Drum. — What is called the drum, or tympanum,
is an irregular cylindrical cavity, separated from the external
passage by the membrane of the drum. It contains the little
bones of the ear, the openings to the labyrinth and other
parts of the organ. Anteriorly a passage leads from this
cavity, forwards and downwards to the throat, called the
Eustachian tube. Posteriorly there are several openings into
osseous cells, called the mastoid cells, which are situated in
that projecting process of bone immediately back of the ear.
This cavity then is filled with air.

7 Eustachian Tube.-^-l have stated that this tube leads from
the drum into the mouth, and serves for the introduction of
air into the internal ear. The necessity of such a contri-
vance is obvious from the fact, that sounds cannot be trans-
mitted through a vacuum, as is shown in the common ex-
periment of ringing a bell in an exhausted receiver, when
no sound is made. So in a drum, there is an air-hole, else

THE SENSE OF HEARING. 229

the sound would be flat, and the head liable to be ruptured.
When this tube is obstructed by the swelling of its lining
membrane from cold, or the accumulation of secretion in the
passage, deafness is the consequence. This passage is about
an inch and a half in length, and widens from the ear to the
throat like a trumpet. When deafness occurs from com-
plete closure of this tube, hearing may be restored by per-
forating the membrane of the drum. We may ascertain
with a good degree of certainty whether deafness arises from
this cause, by placing a watch between the teeth, if its mo-
tions are audible, we may conclude that the essential organ
of hearing is unaffected.

8. Bones of the .Ear.-— These are four in number, and are
so connected with each other in the drum, that they serve
to transmit vibrations of the membrane of the tympanum to
the internal ear/ From their shape, they are called the
mallet, the ajivil, the orbicular, and the stirrup bones, and are
exhibited in nearly the natural size in the following cut.
Mallens, Incus, and Orbiculare, Stapes.
Fig. 3.

Bones of the ear.

These bones are very hard and brittle, have no cartilage on
their articular surfaces like other bones ; neither are they
furnished with ligaments or synovia, but their dry and
polished surfaces are accurately fitted to each other in the
form of a bent lever ; and in this way, being connected and
held together by the little muscles, by which they are moved
and attached to each other, the intensity of vibration which
they receive from the membrane of the drum is not blunted.

20

230 PHYSIOLOGY.

The handle of the mallet is attached to the membrane of the
drum, and its other extremity rests on the anvil, which is
connected with the orbicular bone, the smallest in the body,
and not much larger than a grain of sand. This is inter-
posed between the round bone and the stapes, whose base
rests upon the membrane of the oval fenestra. Now the
contraction of the muscles which connect these bones, puts
the drum-head on the stretch, and thus adapts it for the ready
transmission of sound.?

9. Mastoid Cells. — These are seated in the hard portion
of the temporal bone, and are also filled with air. The ear
is thus surrounded with an atmosphere of its own. In the
elephant, the two tables of the skull are separated from each
other by a bony cellular structure to the extent of upwards
of a foot, and these cells are filled with air which communi-
cate with the drum of the ear. We find in the cat tribe, in
dogs, and in gnawing animals, that there is a hollow sphere
of very hard bone attached to the drum, shaped something
like a conch, and well adapted for reflecting the vibrations
of sound, and rendering them more intense, like the sound-
ing board of a piano-forte. A similar hard conch is found
in the whale tribe. The two tables of the skull in birds are
also widely separated, thus rendering them lighter, and as
the cells communicate with the drum, doubtless for the pur-
pose of increasing the volume of air for the reception of
vibration.

10. Petrous Portion. — The internal ear is situated in a
portion of the temporal bone, called petrous, from petra, a
rock, because of its solid structure. The object of this is
evident from the fact, that hard elastic substances transmit
vibrations of sound far better than matter of a softer texture.
This portion of the temporal possesses indeed almost an
ivory hardness, being the densest structure in the animal
body, next to the enamel of the teeth ; and in this solid body
the labyrinth of the ear is situated. Now in whales, the
skeleton is formed of loose spongy bones, with a considerable

THE SENSE OP HEARING.

231

quantity of oil, collected in their cells. To compensate for
this soft structure, whales are furnished with a sounding
board, or the dense conch, above mentioned. In fishes, we
often find several of these little bony concretions, of a smooth
and polished appearance, and hard and brittle as porcelain.
These are often seen in cutting up boiled fish, when placed
upon the table, but few are aware of the uses they serve in
perfecting the organ of hearing.

11. In order, however, to understand the precise function
of these bones, it will be necessary to examine a little more
into their situation and connection. In the following plan,
they are represented, greatly magnified, but each bone in its

natural position.

Fig. 4.

A, the malleus, or mallet, with its long handle running down, to
touch with its delicate extremity the membrane of the drum. B, is the
incus, or anvil, nicely fitted to the mallet, and showing C, the orbicular
bone placed between its termination, and D, the stirrup. The line a, b,
represents the centre of motion of the malleus, and c, d, the centre of
motion of the incus. Now this chain of bones acts on the principle of
a long lever, as a small motion at one end of a long pole serve to move
it through a wide space at the other. As Sir Charles Bell explains it,
the head of the malleus is so articulated with the body of the incus,
that the centre of motion of the incus is a line drawn through the centre
of its body, and consequently the extremity of the long process, to

232 PHYSIOLOGY.

which the orbicular and stirrup bones are attached, moves through a
greater space than that which receives the impulse of the head of the
malleus. Thus a very small degree of motion, communicated by the
head of the malleus to the body of the incus, is greatly increased in
the extremity of the long process of the incus ; and consequently this
mechanism assists greatly in giving strength to the vibrations trans-
mitted to the internal ear.

12^ Now in distinguishing low sounds, the drum head is
supposed to be put upon the stretch, chiefly by the aid of one
little muscle, called tensor tympani, which is attached to the
malleus, and the centre of the membrane, so that when it
acts, it pulls the long handle of that bone, and draws the tym-
panum inwards. Thus being made tense, it is prepared for
the reception of low sounds. When sounds are so acute as
to be painful, and we wish to diminish their intensity, this
muscle relaxes, and the tympanum becoming comparatively
flaccid, a deadened muffled impression is transmitted to the
brain, precisely as when we muffle a drum. This relaxation
is also aided by a muscle expressly prepared for that pur-
pose, called laxator tympani, which arises from the temporal
bone and is inserted into the handle of the malleus, so as to
pull it forwards^

13. \ We traced the progress of sound through the external
ear, the auditory passage, and the chain of bones, to the
stapes. Now, if the reader will look at plate II., he will see
that the base of the stirrup-bone is smooth and flat ;
this is placed directly upon the passage into the labyrinth,
called foramen ovale, as a seal is placed on an impression, or
a valve upon a hole. The cavities we have described are
filled with air, those now to be mentioned are filled with wa-
ter. The labyrinth then, which has been called the audience
chamber of the ear, consists of three parts, viz., the vesti-
bule or lobby, which may be compared to the porch of a
building ; three semi-circular canals shaped like three hoops
tied together at one point, and their opposite points widelj
separated ; and lastly, the cochlea, which closely resembler

THE SENSE OF HEARING. 233

a snail shell, consisting of two spiral canals, which wind
round a central pillar twice and a half, and also separated
by a spiral partition.!

Fig. 9.

Section of the Cochlea.

14. The stapes then rests upon the membrane which is
placed across the opening into the labyrinth. When the
tympanum, or drum-head, is impressed by the vibrations of
the air, the vibration is communicated to the little bones,
and through them to the membrane of the labyrinth, which
causes corresponding tremws in the fluid which fills its
winding canals, and the spiral passages of the cochlea ;
upon which the auditory nerve is spread out like a fine
pulpy web, in the same manner as the retina is spread out
upon the choroid coat of the eye, or the olfactory nerve
upon the mucous membrane of the nose, and thus is sound
conveyed by the nerve to the brain.

15. ffhe object of these spiral passages returning into
themselves is, doubtless, to furnish an extensive surface,
within a small space, for the expansion of the auditory
nerve, and also that the undulations of the fluid which fills
them after -passing from the oval fenestra along the winding

20*

234 PHYSIOLOGY.

passages, and up the spiral staircase of the cochlea, might
come down to the round fenestra, whose elastic membrane
would transmit the vibration in the opposite direction. —
When the sounds, therefore, have done their office, in order
that the hearing might not be rendered confused by a pro-
longed vibration of the fluid, as an echo is repeated between
two mountains, as they strike the above named membrane,
they are given off to the air in the tympanum, and there the
vibrations end ; for we have seen that it is probably the
bones in the tympanum chiefly, and not the air, which trans-
mits impressions to the fluids of the labyrinth, and that they
receive their impulse from the drum of the ear. ;

16. Sound.— fSound has no distinct existence, but is the
result of certain conditions of bodies. We see how, by
throwing a pebble into a lake of water at rest, the undula-
tions spread in every direction, in the form of a circle, until
the impulse is lost in the distance. So in air, frequent vi-
brations produce sound ; and hearing has been defined to be
that function by which we obtain a knowledge of the vibra-
tory motions of bodies. These motions produce waves or
undulations in the air, which are propagated in every direc-
tion, as the circular waves are produced in the lake, by
throwing in the pebble.!

17. Air is the common vehicle of sound, though all elastic
bodies are capable of conveying it. Water conveys sound
better than air, and some solid bodies better than either. If
two stones are struck together under water, a person whose
head is under the surface may hear the sound at a great dis-
tance. A blow struck with a hammer by a workman in a
diving bell, far below the surface of the water, is heard dis-
tinctly many fathoms above. So also if the ear be applied
to the end of a long stick of timber a slight scratch made at
the other extremity will be distinctly heard. The report of
a cannon is heard to a much greater distance over the frozen
surface of snow ; and, under such circumstances, firing has
been heard from one to two hundred miles. Savages are

THE SENSE OF HEARING. 235

acquainted with this fact, for they apply their ears to the
ground to hear the approaching footsteps of their enemy or
their prey. An easy way to tell whether a tea-kettle boils,
is to touch it with a stick, and place the other end to the
ear. On this principle, I suppose, watchmen strike the curb
stone with their clubs, as the sound is communicated much
farther than it was formerly by means of their rattle. So
also a musical box, when held in the hand is scarcely heard,
but when placed on a bureau or sounding board, it " dis-
courseth most eloquent music." The stethoscope now used
by physicians to assist in determining the nature of many
diseases is derived from a knowledge of this principle. It is
merely a cylinder of wood, about an inch in diameter, one
end of which is placed on the surface of the body over the
diseased part, and the other applied to the ear ; sound is thus
carried along the tube, and most important aid is derived to
the skilful physician, in ascertaining the nature and seat of
all diseases of the heart and lungs.

18. The transmission of sound is affected materially by
the condition of the atmosphere, with respect to tempera-
ture, moisture, &c. During the night, when the air is still,
and of uniform density and temperature, sounds are heard
to a great distance ; but when it is loaded with vapors, as in
a fall of snow or rain, sounds are more limited, and rendered
confused and indistinct.

19. The density of the air has a great effect upon the
transmission of sound. In a dry, cold atmosphere, at the
level of the sea, sounds are transmitted to vast distances,
while on high mountains, such as the Andes, or even Mont
Blanc, the report of a pistol is not louder than that of an
Indian cracker. The wind, also, has a great influence in
aiding or retarding the transmission of sound. Sound is
also reflected like light, and indeed is subject to the same
laws, for the angle of reflection is always equal to the angle
of incidence. Reflected sound is termed an echo. The
rolling of thunder is supposed to depend partly on the sound

236 PHYSIOLOGY.

being reflected from cloud to cloud, and through strata of
air of different densities, though it also arises from a dis-
charge of electricity, through a wide extent of air. In this
case, as the sound from the point nearest the hearer reaches
his ear first, and some moments elapse before that from the
more distant arrives, there must consequently be a continued
peal. Some of our large public houses and manufactories
are fitted with pipes for conveying intelligence to distant
apartments, attention being attracted by ringing a bell.

20. 1 It has been doubted whether sound can be propagated
from one medium to another, as from air to water. It is
now known, however, that if a musket is discharged over a
person who is under water, he will hear the report. The
question has also arisen, whether sound can be propagated
from water to the air again. This is easily proved by strik-
ing two stones together under water, although we are told
that persons in a diving-bell under water, could not hear a
musket discharged immediately over it. But here the sound
had to be communicated from jthe air to the water, and from
the water to the air again, itound travels at the rate of
eleven hundred and forty-two feet in a second, or a mile in
four seconds. As light travels much faster, we see the flash
of a gun before we hear the report. This will enable us to
tell in a thunder storm how far we are from a thunder-cloud ;
as we have only to allow eleven hundred feet for each se-
cond, between the time when the flash is seen and the report
heard, and one beat of the pulse for a second. In this way,
too, the distance of a ship of war at sea is often ascertained
by those on board of the vessel she is in pursuit of. Solids
and fluids convey sound not only more perfectly, but also
more rapidly than air. It is found that the velocity of
sound in water, is about four thousand nine hundred feet in
a second, being between four and five times more rapid than
it is through air. Sound passes through tin at the rate of
eight thousand one hundred and seventy-five feet, and through
iron, glass and wood, eighteen thousand five hundred and

THE SENSE OF HEARING. 237

thirty feet in a second. This explains why, when a gun is
fired at a distance over the surface of a frozen lake, we hear
two reports after we see the flash ; first a sharp and loud
one, transmitted by the solid ice, and then a weaker and
duller one, through the air. Franklin, however, found by
his experiments, that, after travelling about a mile through
the water, sound lost some of its intensity, which indeed
might be expected. Musical tones are said to be acute when
the intervals between the vibrations are short, and grave
when they are long. Thus a flute called an octave produces
a shriller sound than the common flute ; a fiddle than a bass
viol. The strings, too, of a violin, which are designed for
high or acute notes, are smaller than the others, that their
vibrations may be more rapid ; while those which make the
grave tones are large, and wound round sometimes with fine
wire, to increase the weight, and make them vibrate more
slowly. It is the quality and variety of the sounds which,
in musical tones, gives the hearer so much pleasure.

21. In the lower order of animals, hearing is performed
by means of an apparatus, much more simple than in man.
Some of them have merely a membranous sac, supplied with
nervous threads. This is even the case in fishes, which re-
quire neither tympanum nor bones, nor any of the accessory
parts found in land animals, as the undulations of water strike
with greater force upon the organ of hearing than those of
air. The apparatus of hearing in the frog is very singular,
and designed so as to enable the animal to hear both in air
and water.

22. /Animals with long ears are able to move them by
musclos for that purpose, and turn them to the point whence
the sound proceeds. This may be seen in the horse, which
turns his ear always in the direction of the sound. In stage
horses, we often see the leaders turn their ears forward,
while those behind turn theirs backward. Some men also
have the power of moving their ears!

23. Like all our other senses, that of hearing is capable

238 PHYSIOLOGY.

of much improvement by cultivation. The Indian in the
forest, accustomed to listen to the approach of his enemies,
or of his prey, acquires such acuteness of this sense, as to
hear sounds which would be inaudible to those who live amid
the din of civilized life. The blind also excel in the acute-
ness of hearing, and for this reason especially, acquire great
skill in performing on musical instruments. Shakspeare
thus describes a person destitute of musical taste.

" The man that hath no music in his soul,
Nor is not moved with concord of sweet sounds,
Is fit for treasons, stratagems, and spoils ;
The motions of his spirit are dull as night,
And his affections dark as Erebus ;
Let no such man be trusted."

Questions. — What are sounds ? Describe the external ear ; — the
tube of the external ear ; — the membrana tympani ; — the drum, or tym-
panum ; — the eustachian tube. How many little bones of the ear are
there ? Their names and office ? How are low sounds perceived ?
What is the use of the spiral passages ? How is sound conveyed ? Is
it conveyed by solids ; — by water ? What is the stethoscope ? Can
sound be propagated from one medium to another ? At what rate does
it travel ? How can we tell the distance of sound ? What effect has
the density of air on sound ? How is the lengthened peal of thunder
explained ? How is hearing performed in the lower order of animals ?
Can hearing be improved by cultivation ?

CHAPTER XVIII.

RESPIRATION.

1. BY Respiration, is meant/the process of taking air into
the lungs and throwing it out again. Inspiration is the act
of drawing the air in ; expiration, that of forcing it out.
Respiration is essential to all animal existence. It is in the
lungs that the last change is produced in the assimilation of
the food, by which it is converted into that vital fluid, which
carries life, and strength, and nourishment to every fibre in
the animal system.

2. The parts concerned in respiration may be arranged
into three divisions, viz., 1, the bones which form the respir-
atory cavity ; 2, the muscles by which these bones are moved,

Thorax, or chest; a, the sternum ; b, b, the spine ; c, c, the ribs,

240 PHYSIOLOGY.

and the size of the cavity regulated ; 3, the respiratory organs
contained within the cavity)

3. \The bones which enter into the composition of the
chest, are the sternum, or breast-bone ; twelve dorsal vertebrae,
and twenty four ribsf By examining the preceding plate,
Fig, 1., the sternum will be seen to terminate at its lower
part in a triangular piece of cartilage, which lies directly
over the stomach, and may be felt externally ;f the seven
uppermost, or true ribs, will be seen to extend the whole
distance from the spine to the sternum, strips of elastic car-
tilage being interposed between the breast-bone and their
anterior extremities, while the five lower, or false ribs, are
merely attached to each other by slips of cartilage ; the two
lower, indeed, float loosely, without any attachment to the
others, except by means of muscles?l

4. I have already stated that the ribs are attached to the
spine at an acute angle, so that they cannot be moved out
of their ordinary position, without enlarging the dimensions
of the chest. The articulation of the ribs, both at the spine
and sternum, is effected by means of cartilage, thus allowing
sufficient degree of motion for the purposes of respiration in
a healthy state. The chest expands during inspiration for
the reception of air ; and during expiration, it contracts to
expel air, which is no longer useful. There are, therefore,
two motions required, an upward and an outward ; the first
increases the distance between the spine and sternum ; the
last, that between the ribs. Now these motions are both
effected by the ribs, and they are so articulated, that they
cannot perform the one without the other. By looking at
the cut, then, it will readily be seen how where the ribs rise,
the sternum will be pushed out, and of course the cavity of
the chest enlarged.

5. The Muscles. — All the muscles which are attached to
the bones just described, aid more or less in respiration,

Ithough the intercostal muscles are those chiefly concerned^
These run from one rib to another, filling up the spaces be-

RESPIRATION. 3J-4I

tween them. These muscles, though thin, consist of a double
layer of fibres, the external and the internal, which pass in
inverse directions, one layer from above downwards, the other
from behind forwards, from edge to edge of the ribs, crossing
each other. Now, the first rib being fixed, the second move-
able, but less so than the third, the third less than the fourth,
and so on through the whole series ; the contraction of the
intercostals must consequently elevate the whole series, as
the upper ribs serve as fixed points for the action of the
muscles. )

6. The chief muscle, however, of respiration, is the
diaphragm. By the aid of this, the capacity of the chest is
enlarged downwards, as we have seen it to have been up-
wards and outwards by that of the ribs. fThe diaphragm,
or midriff, is a circular muscle, placed transversely across
the trunk, nearly at its centre, dividing the cavity of the
thorax from that of the abdomen. It is attached to the in-
side of the breast-bone and the cartilages of the false ribs,
and is fleshy all around its border, but tendinous towards its
centre ; the surface towards the abdomen is concave, and
that towards the chest convex. Even when it is not in
action, its upper surface forms an arch, the convexity of
which is towards the thorax, and reaches as high as the
fourth rib. The central, or tendinous portion of the dia-
phragm, is attached to the pericardium supporting the heart ;
and is nearly, or quite immoveable, in order to afford a fixed
point for the action of the muscular fibres, which constitute
its sides. Owing to this arrangement, its motions do not
interfere with those of the hearty

21

£42

PHYSIOLOGY,
Fig. 2.

View of the diaphragm ; 1, cavity of the thorax ; 2, diaphragm sep«
arating the cavity of the thorax from that of the abdomen ; 3, cavity
of the pelvis.

7.: During the act of inspiration, the diaphragm contracts;
the rhuscular fibres shorten themselves, and the muscle de-
scends, passing from the fourth rib to below the seventh,
losing the arched form, as represented in the cut. At the
same time, the muscles of the abdomen are protruded for-
wards, and the viscera in its cavity pushed downwards.
The degree in which the capacity of the chest is enlarged by
these movements is very satisfactorily shown in the follow
ing cut.

RESPIRATION.

243

Fig. 3.

Fig. 4.

Fig. Ill, diaphragm in its state of greatest descent in inspiration ;
2, muscles of the abdomen, showing the extent of their protrusion in
the action of inspiration. Fig IV, diaphragm in the state of its
greatest ascent in expiration ; 2, muscles of the abdomen in action
forcing the viscera and diaphragm upwards.

8. We have now seen how the capacity of the chest is
enlarged by inspiration, how is its capacity diminished by
expiration ? The descent of the ribs is occasioned by the
elasticity of the cartilages and ligaments which join them
to the sternum and the spine. Indeed the natural condition
of the chest is that which obtains after a full expiration ;
and therefore we may consider the bones which form the
walls of the chest, and the muscles which cover those bones,
as anatagonizing or opposite forces. fThe ribs, then, have a
natural tendency to fall, owing to their peculiar structure,
as well as their position ; while their expansion is effected
by the specific action of their muscles.) Besides this, when
the diaphragm relaxes, the abdominal muscles contract and
push the abdominal viscera, and the diaphragm also, up to-

244 PHYSIOLOGY.

wards the cavity of the chest ; and thus by the descent of
the ribs and the ascent of the diaphragm, the capacity of
the thorax is diminished, and the motion of expiration is
completed.

9. [The third division of our subject embraces the respir-
atory organs, or the lungs. These are of a spongy texture
and conical shape, and fill the cavity of the chest, being
composed chiefly of blood-vessels, and air-vessels, with a
small portion of cellular tissue.! They are called lights Jin
the lower animals. There are two lungs, one in the right,
the other in the left side of the thorax ; and each of these
lungs is divided into several lobes. /A serous membrane
called the pleura surrounds the lungs, and is reflected upon
the walls of the chest, so as to form a shut sac, into which
a thin watery fluid is constantly exhaled, to keep the sur-
faces moist and slipperyJ It is this membrane which is the
seat of pleurisy. There are two pleurae, each of which is
confined to its own side of the chest, lining its cavity, and
covering the lung, feehind the breast-bone, they form a
partition, called mediastinum^ between the sides of which,
the heart and pericardium are situated. The pleurae serve
to attach the lungs by their roots to their respective cavi-
ties, and to facilitate their movements, by means of the fluid
exhaled from their surfaces. Each lung is attached to the
spine by its roots, where blood-vessels, nerves, lymphatics,
and a branch of the windpipe enter it. (See Fig. 5.)

10. Thus we perceive that the chest is divided into Three
compartments,) one on each side, containing a lung ; ^the
middle one, the hearts Between these there is no communi-
cation ; so that if a fluid is thrown into one of them, it does
not find its way into the others. As the heart lies chiefly
on the left side, the lung of that side is smaller than the one
on the right, and divided into only two lobes, while the other
is divided into three. The lungs are the lightest texture in
the human body, owing to the air which they contain, and
their aspect varies with the age. In infancy they are of 9

RESPRIATION.
Fig. 5.

245

«, the cut edges of the ribs, forming the lateral boundaries of the
cavity of the thorax ; 6, the diaphragm, forming the inferior boundary
of the thorax, and the division between the thorax and the abdomen ;
c, the cut edges of the abdominal muscles, turned aside, exposing the
general cavity of the abdomen.

Fig. 1, the cut edge of the pericardium turned aside ; 2, the heart ;
3, the great vessels in immediate connexion with the heart ; 4, the
trachea, or wind-pipe ; 5, the lungs ; 6, the liver ; 7, the stomach ;
8, the large intestine ; 9, the small intestines ; 10, the urinasy bladder.

pale red, in youth of a darker colour, and in old age of a
livid blue.

11. The air enters the lungs through the trachea or wind.
21*

PHYSIOLOGY.

pipe. This is a tube, made up of little rings, cartilaginous
in front, and muscular or fibrous behind ; and is about eight
or ten inches in length. It lies immediately on the gullet or
€Bsophagust and extends from the larynx to the third vertebra
of the back.1 Here it divides into two branches, called
bronchia, one of which goes to the right, the other to the
left lobe of the lungs. The right branch divides again into
three principle branches, as soon as it enters the lung ; and
the left into two ; corresponding to the number of lobes in
each lung ; then they subdivide into an innumerable number
of small twigs, like the branch of a tree, until they termi-
nate in those small cells already mentioned. These cells are
about the one hundredth of an inch in diameter, p

12. The bronchial tubes then, terminate in minute vesi-
cles of unequal size, which are of a cylindrical and some-
what rounded figure. These vesicles are large enough to be
visible to the naked eye, and present something of the ap-
pearance of a cluster of currants attached to their stem, as
shown in the following cut :

Fig. 6.
View of the Bronchial Tubes, terminating in Air vesicles.

External view. — 1. Bronchial tube. |
2. Air vesicles. I

The Bronchial tube and Air
vesicles laid open.

\It should be borne in mind that the office of respiration is
to bring the blood in contact with the airjand, accordingly,
the lungs are so constructed as to allow the largest possible

RESPIRATION. 247

quantity of deteriorated blood, to enjoy the fullest intercourse
with the largest possible quantity of vital air ; and all the
mechanism of bones and muscles which I have described,
are only subservient to th s end. Now it has been calcula-
ted by Hales, that each air cell is the one hundredth part of
an inch in diameter, and that the amount of surface furnish-
ed by them, collectively, is \gual to twenty thousand square
inches. Other physiologists have calculated the surface to
be over fifteen hundred cubic feetjand Munroe states that it
is thirty times the surface of the numan body)

Fig. 7.

1. The larynx ; 2. The trachea ; 3. Right bronchia ; 4. Left
bronchia ; 5. Left lung divided into three lobes ; 7. Large bronchial
tubes ; 8. Small bronchial tubes ending in air cells or vesicles.

13. Such is the structure of the vessel which conveys the
air to the blood ; let us examine how the blood gets to the
air. (This is effected by means of the pulmonary artery,
which springs from the right ventricle of the heart, divides

248 PHYSIOLOGY.

into two branches, one for each lung, and again subdivides,
and ramifies through the organ in a manner precisely simi-
lar to the bronchial tubes./ Every bronchus, or branch of
the trachea, thus has a corresponding blood-vessel, which
tracks it throughout its entire course until it reaches the air
vesicles, upon the surface of which the minute vessels ex-
pand and ramify, forming a net-work so beautiful, that the
anatomist who first observed it, called it the rete mirabile, or.
the wonderful net-work. Thus the air is on one side, and
the blood on the other, of an immense surface of membrane,
finer than the most delicate lace or gauze ; and as such
membranes are permeable to air and other gases, the oxygen
of the air penetrates it and unites with the blood, while a
portion of carbon and water are given off by exhalation.
Thus does the blood lose its dark venous character, and as-
sume a florid, arterial hue, and become fitted to carry life
and vigour to every part of the system.

14. Thus we see that the lungs and all their complicated
machinery of bones, ligaments, muscles and cartilages, were
formed for the sake of these little air-cells ; for it is through
their agency that the blood undergoes the necessary changes
and alterations. When we reflect upon the relative extent
of the actual respiratory surface, compared with the dimen-
sions of the lungs themselves, that a stratum of blood seve-
ral hundred feet in surface, is exposed to a stratum of air
still more extensive, and all compressed within the corn-pass
of a few inches, we are filled with admiration and astonish-
ment at the wisdom displayed in such a structure, and search
in vain, among all the contrivances of human skill and
genius, for a counterpart !

15. We are now prepared to trace the successive acts of
respiration, accomplished^through the agency of the me-
chanism just described. [About one second and a half after
expiration, the muscles of inspiration begin to act, the inter-
costals contract, and, by elevating the ribs, increase the dis-
tance between the spine and sternum. As the ribs rise, the

RESPIRATION.

diaphragm descends, and thus the cavity of the chest is en-
larged in every direction. This expansion, like that of a
bellows, causes a vacuum, and as the lungs are passive, the
air consequently rushes in through the mouth and nostrils
to fill it, and this influx of air continues until the density of
the internal, is equal to that of the external air, when the
act of inspiration is at an end. Again, the intercostal
muscles relax, and the ribs, by their elasticity, are restored
to their natural position, while, at the same moment, the dia-
phragm relaxes, and allows the abdominal muscles to con-
tract and thrust it up into the chest. Thus the lungs being
pressed upon in every direction, below by the diaphragm,
before by the sternum and ribs, and behind by the spine and
ribs, the air within them is pressed out! Such is the beau-
tiful and complicated mechanism of respiration.

Fig. 8.

The cut upon the left represents the natural shape of the chest, and
that upon the right, the contracted state of it, owing to tight lacing.

16. Now we can easily understand how tight-lacing alters
the shape and diminishes the capacity of the chest. By
looking at the cut, we see that the figure of the chest is that
of an irregular cone, with a convex projection on each side,
and flattened before and behind. I By compressing it, how.
ever, by corsets, it is changed into' a cylinder, its lower part
being forced in, so that its transverse diameter is diminished

250 PHYSIOLOGY.

nearly, or quite, one half. Now, in this state of things, it
is very clear that the ribs cannot be raised upwards and
outwards, as they are in natural and free respiration, and,
consequently, the capacity of the chest cannot be enlarged
in these directions)1 How, then, is life supported ? Clearly
by the play of the diaphragm alone, which, by its descent,
enlarges the cavity of the chest in its long diameter. But
even the action of this muscle is cramped by this unnatural
practice ; for, as the compressing apparatus extends down
over the loins behind, and in front over all the soft parts, or
the organs below the chest, it acts like a solid wall, prevent,
ing, by its resistance, the protrusion of these organs, and
thus restrains the diaphragm above, in its attempt to de-
scend ; so that in fact, the beautiful mechanism, contrived
by a Supreme architect, for performing a function indispen-
sable to life, health, beauty and enjoyment, is confined,
in every direction, and life, consequently, sapped at its very
fountain head !

17. If an opening be made into the cavity of the
chest, Ahe lung upon that side immediately collapses, and is
no longer useful in breathing] How is this explained ? The
lungs have a constant tendency to collapse, and they are
only kept from doing so, by the pressure of the air contained
within them. If a hole be made in the walls of the chest,
so as to allow the atmospheric air to come in contact with
the external surface of the lungs, and thus make the pressure
on the external and internal surface equal, they immediately
collapse and shrink to that size which is natural to them,
and which they assume when removed from the chest. This
operation, of opening the cavity of the chest, has been pro-
posed as a remedy for consumption ; as the lung in a state
of rest would be more likely to heal than when in constant
motion.

18. The atmosphere is an invisible elastic fluid, surround-
ing the earth to the height of about forty miles. Water is
seven hundred times heavier than air ; (And yet a column of

RESPIRATION. 251

air a foot in diameter, and extending to the top of the at-
mosphere, would be equal in weight to a column of water of
the same diameter thirty-two feet high, or to a column of
mercury twenty-eight inches high. The pressure of the at-
mosphere then, upon the body of a common sized man, is
equal to between thirty and forty thousand pounds) Atmos-
pheric air is composed of oxygen, azote and carbonic acid,
in the proportion of (20 parts of oxygen, 78 of azote, and 2
of carbonic acid.\

19. ^Oxygen is an invisible air, or gas, and enters into the
composition of air, water, and all animal and vegetable sub-
stancesJ It is the supporter of combustion, and no animal
can live without it. What are called acids and oxyds in
chemistry, are oxygen combined with other substances, as
sulphur, salt, nitre, &c. f Azote can neither support combus .
tion nor respiration, at least in man ; though it is an ele-
ment in all animal matter, and in some vegetables.) In
these cases it is obtained, both from food and the air.

20. It is now fully ascertained, that while the chemical
composition of the blood is essentially changed, its weight
always remains the same ; as the carbon discharged is pre-
cisely equal to the united weight of the oxygen and azote
absorbed, and the same change is effected by the respiration
of all animals, whatever be their rank in the scale of organ-
ization. It is worthy of remark, that plants and animals
produce directly opposite changes in the chemical constitu-
tion of the air. The carbonic acid given off by animals is
composed of oxygen and carbon ; this is decomposed by
vegetables, which absorb the carbon and give off the oxygen
to the air, which in its turn is absorbed by animals, and car-
bonic acid given off: so these two great departments of
organized structure furnish food for each other^ renovating
the air, and preserving it in a state of constant purit$ The
immense quantity of oxyen given off by vegetables, may be
inferred from the following experiment. About fifty leaves
were enclosed in a jar of air ; the surface of the whole being

252 PHYSIOLOGY.

about 300 square inches ; by adding some carbonic acid to
the jar, in a short time 26 cubic inches of oxygen were
evolved. What then must be the amount given off by an
entire tree, especially in cities, where carbonic acid abounds ;
hence how important it is that cities should be thickly plant-
ed with trees, not only for the sake of ornament, but much
more for that of utility.

21. The quantity of oxygen consumed by a man in a
minute, is about 30 cubic inches. He breathes 20 times in
a minute ; and every time he breathes, takes into his lungs 15
cubic inches of atmospheric air, which contains three cubic
inches of oxygen, so that one half of that which is inspired
disappears in every act of respiration. This will amount to
about 2,000 cubic inches in an hour, ancU45,000 cubic inches
in 24 hours.y Thus one man will consume, in 24 hours, all
the oxygen contained in a space of 312 square feet ; or in 12
hours, in 156 square feet. And still our churches, and school-
rooms, and dwelling-houses, are constructed with no view to
a renovation of the air we breathe !

22. Dr. Southwood Smith has lately performed a series
of very interesting experiments, from which he deduces the
following general results : — " 1. The volume of air ordinarily
present in the lungs is about 12 pints. 2. The volume of
air received by the lungs at an ordinary inspiration is one
pint. 3. The volume of air expelled from the lungs at an
ordinary expiration, is a little less than one pint. 4. Of the
volume of air received by the lungs at one inspiration, only
one-fourth part is decomposed at one action of the heart, and
this is so decomposed in the five-sixth parts of one second
of time. 5. The blood circulates through the system, and
returns to the heart in 160 seconds of time, which is exactly
the time in which the whole volume of air in the lungs is de-
composed. These circuits are performed every eight minutes ;
540 circuits are performed every 24 hours. 6. The whole
volume of air decomposed in 24 hours is 221,882 cubic inches,
exactly 540 times the volume of the contents of the lungs.

RESPIRATION. 253

7. The quantity of blood that flows to the lungs to be acted
upon by the air at one action of the heart is two ounces, and
this is acted on in less than one second of time. 8. The
quantity of blood in the whole body of the human adult is
24 pounds avoirdupois, or 20 pints. 9. In 24 hours 57
hogsheads of air flow to the lungs. 10. In the same time,
24 hogsheads of blood are presented in the lungs to this quan-
tity of air. 11. In the mutual action that takes place be-
tween these quantities of air and blood, the air loses 328
ounces of oxygen, and the blood 10 ounces of carbon."

23. The blood, as it goes the round of the system, leav-
ing a little bony matter here, a little muscular there ; sup-
plying the nails, and the hair, and the skin, and every thing,
with the particles which, in the wear and tear of the ma-
chine, they have lost ; loses by degrees its bright arterial
colour, and by the time it comes round again to the lungs,
it is no longer fit to perform its duty ; it has been robbed of
all its principles most essential to life, and it must be re-
newed and prepared afresh, before it can be of any further
use. This is done in the lungs : and this process is what
physiologists call the vital part of respiration.

24. All animals have not lungs, (insects absorb the air
from the surface of the body^ so also do many of the family
of zoophytes. ^Some have feathery tufts, like a plume of
feathers, which they keep in constant motion') while the
common earth-worm, or \angle-worm, has a single row of
holes along its back, about one hundred and twenty in num-
ber, which open each of them into a small respiratory bag,
situated between the skin and the intestine/ The leech or
blood-sucker, and the lamprey eel, have the same kind of
apparatus for breathing.

25. (Infohes, the gills, which are their lungs, are made up
of an infinite number of little fibres, or filaments, set close
together, like the teeth of a fine comb, or the barbs of a
feather; and these are covered with innumerable small
processes, crowded together like the nap of velvet, and over

22

254 PHYSIOLOGY.

these are spread myriads of blood-vessels, like a fine net-
work. I The air which is contained in the water, is drawn
in witti it by the mouth, and forced, by the muscles of the
throat, through the opening leading to the gills, the filaments
of which are expanded and separated by the same process,
so that they receive the full action of the fluid as it passes
by them. When a fish is taken out of water, the reason he
cannot breathe is, that these filaments collapse, and adhere
together in a mass, and the air cannot separate them.

26. The seal, porpoise, dolphin and whale, belong to the
class mammalia, and therefore have to rise to the surface of
the water to get air to breathe. It is this necessity which
exposes the whale to the harpoon of the fisherman ; for
such are his strength and swiftness, that, could he live en-
tirely under water, he might defy the utmost ingenuity of
man to capture him.

Fig. 9.

The above cut shows the mode of respiration in fishes. The gills
are seen bent over in the form of a feather : d is the auricle of the
heart ; c, the ventricle ; /, the bronchial artery ; g, g, the gills. The

RESPIRATION. J 255

ft vv OF THE

heart of a fish throws the blood only to the gills, and not to the rest of
the body as in other animals. This is the reason why the gills are red,
while the other parts of a fish are white. Respiration in fishes is,
therefore, performed by taking water into the mouth, and forcing it
through the gills ; in this manner the air contained in the water is
brought in contact with the thin coats of the blood-vessels, through
which the oxygen is absorbed.

Questions. — What is meant by respiration ? — by inspiration ?— by
expiration? How are the parts concerned in respiration arranged?
What bones are concerned ? Describe the position of the ribs. What
muscles are chiefly concerned in respiration ? Describe the intercos-
tals, — the diaphragm. How does the diaphragm act in inspiration ?
In expiration ? What causes the deecant of the ribs in expiration ?
Describe the structure of the lungs. Whawcalled in the lower animals ?
What are the pleurae ? — the mediastinTfinipHow many compartments
is the chest divided into ?) In which iVjthe heart ? What is the
trachea ? What does it end in ? How large are the air cells ? What
is the office of respiration ? What amount of surface do the air cells
present ? How does the blood get in contact with the air ? Describe
the process of respiration. How does tight lacing injure the health ?
What happens if a hole is made into the cavity of the chest ? What
is the weight of the atmosphere equal to ? Of what gases is it com-
posed ? What effect do vegetables have on air ? What is oxygen ? —
azote ? What is the effect of respiration on air ? How much oxygen
is consumed by a man in twenty-four hours ? How do insects breathe?
— the earth-worm ? — fishes ? — birds ? — the whale ? &c.

!

CHAPTER XIX.

THE CIRCULATION OF THE BLOOD.

1. THAT the blood is constantly circulating throughout
the human body, was unknown till \Harveyjmade the disco-
very, two hundred years ago| Before this time, air was
supposed to circulate through the arteries, or air tubes ;
hence their name. The reason why this great truth was
not found out sooner, was, that/ on examining dead bodies,
the arteries were always found" empty of blood ; owing to
the contractile force with which they are endowed^

2. The circulation is called one of the vital functions,

t>ecause it is essential to lifel Its suspension for a short
ime throughout the body is certainly fatal. Hence we find
that diseases of the heart and great vessels are apt to termi-
nate in sudden death, while in other diseases the approach
of death is gradual.

3. Life, in all the organs, is maintained (by the presence
of arterial blood) Without it they could not be nourished,
nor could they perform their appropriate functions. The
moment any part of the body is deprived of blood, from that
time it ceases to grow ; it withers and decays, and soon be-
comes a mass of dead matter. If the arteries which supply
any of the limbs with blood are tied, the limb soon grows
black, and mortifies. In the same way, if we stop the cir-
culation of sap in a tree by girding or dividing the vessels
which convey this fluid to the branches, the tree immediate-
ly dies. Blades of grass and corn are often destroyed by
worms severing the same vessels with their teeth ; and
peach and other fruit trees, are generally short lived from
the same cause.

4. Some animals are destitute of a circulation, such as in-
sects, worms, &c. Air and food are essential to the existence

THE CIRCULATION OF THE BLOOD. 257

of life, but the food cannot be changed into blood before the
air has acted on it by one of its principles, oxygen. Now,
if these two principles are not introduced into the system in
the same place, but in separate organs, it is evident they
cannot be employed in nutrition till they are brought toge-
ther ; which is done in the lungs ; the blood is there fitted
to carry nourishment and life to every part of the system.
Every animal then, that has a local respiration, must also
have a circulation.

5. The organs of the circulation are the heart, arteries,
the veins, and the capillary vessels. The arteries and veins,
or the arterial and venous systems as they are called, have
been compared to two trees, the one scarlet and the other
purple, whose trunks are united at the heart, and whose
branches are connected at their extremities, thus forming a
regular circle. The blood is then forced out of the heart
by the contraction of that organ, into the arteries, by which
it is distributed throughout the body ; from whence it is re-
turned by the veins. Between the ends of the arteries and
the commencement of the veins, are the small hair-like ves-
sels called capillaries.

6. (The heart is a hollow organ of a muscular and fibrous
structure, and somewhat conical in shape. It is placed in
the fore part of the cavity of the chest, inclined to the left
side. It rests on the midriff or diaphragm, which is the
muscle that separates the chest from the abdomen ; and it is
supported also at its base which is uppermost, by means of
the large blood-vessels connected with itA JThe heart is sur-
rounded by a strong membranous bagN, called the pericar-
dium, by which it is, in a measure, protected. This bag is
the seat of dropsy of the heart, and is generally found to
contain more or less water after death J

7. (tn the human species, and throughout the class mam-
malia) the heart is a double organ ; consisting in fact of two
single hearts, each of which gives motion to a different kind
of blood. One of these, the right heart, receives the dark

'W 22*

258

PHYSIOLOGY.

venous blood which is returned from all parts of the body,
and sends it through the* lungs, from whence it returns to
the left side of the heart changed to bright arterial blood,
and is distributed by the aorta, or great artery, through the
system. The right heart then may be called the venous or
pulmonary heart, the left, the arterial heart. Both, however,
are so united together, as to form in appearance but one
heart.

Fig. 1.

View of the heart inclosed in its bag, or pericardium, which is a se-
rous membrane. It is here laid open and turned back.

8. Each of these hearts has two separate cavities ; one to
receive the blood, and the other to pump it out. The cavi-
ties which serve as receptacles, are called auricles, those

THE CIRCULATION OF THE BLOOD. 259

which, by contracting, force it out, are called ventricles.
The walls of the heart are composed of strong muscular or
fleshy fibres, crossing and interlacing one another, and those
of the ventricles are much thicker than those of the auri-
cles.

9.(jThe cavities in the right side of the heart are trian-
gular in shape, and those of the left, oval. Each cavity
will hold about two ounces of blood. } Between each of
these two cavities or chambers, there is a passage, which is
closed with a valve ; so that when the ventricles contract,
the blood, instead of passing through into the auricle, is
poured into the arteries^ /This valve is formed by the dou-
bling of a thin, transparent membrane, which lines the
cavities, and extends both through the veins and arteries.
The valve in the right side of the heart is called tricuspid,
and that in the left, bicuspid or mitred) ' V

10. There are also valves placed at the orifice of the
great arteries of the heart, the pulmonary and aorta, as they
are given off from the right and left ventricles. ^They differ
somewhat from the former, by being of a half-moon or semi-
lunar shape, and formed by folds of the lining membrane of
the arteries.) These are called sigmoid valves ; and their
use is f;o prevent the blood from flowing back from the arte-
ries into the ventricles) Where the vena cava, or the great
vein which returns all the blood, empties into the right
auricle of the heart, there is another valve, called the Eusta-
chian valve. (See Fig. 2.)

11. (The arteries are the vessels into which the blood is
immediately propelled by the action of the heart, and which
distribute it to all the parts of the bodvl The pulmonary
artery or the artery of the right side of the heart, circulates
dark-coloured or venous blood through the lungs, where by
exposure to the air, it becomes a bright scarlet. This is re-
turned into the left auricle, which forces it into the left ven-
tricle, whence it is sent through the aorta to every part of
the system.

260 PHYSIOLOGY.

Fig. 2.

View of the heart with its several chambers exposed and the ves.
sels in connection with them. 1. The superior vena cava. 2. The
inferior vena cava. 3. The chamber called the auricle. 4. The right
ventricle. 5. The line marking the passage between the two cham-
bers, and the points of attachment of one margin of the valve. 6. The
septum between the two ventricles. 7. The pulmonary artery, arising
from the right ventricle, and dividing at 8 into right and left, for the
corresponding lungs. 9. The four pulmonary veins, bringing the blood
from the lungs into 10, the left auricle. 11. The left ventricle. 12.
The aorta, arising from the left ventricle, and passing down behind the
heart, to distribute blood to every part of the system. Thus the blood
moves in a double circle, one from the heart to the body, and from the
body back to the heart, called the systemic circle ; the other, from
the heart to the lung, and from the lung back to the heart, called the
pulmonic circle.

12. The arteries are very strong and elastic, of a yellow-
ish white colour Jand have three coats, jthe outer one of which
is called cellular^lhe middle, the fibrous coat, and the inter-
nal, serous. It is very important that arteries should be
elastic and capable of stretching, because, if they were not,
every time a limb was broken, the artery would be ruptured,
and the person bleed to death. (See Fig. 3.)

13. JThe veins which return the blood to the heart consti-
tute two systems like the arteries ; the one brings all the
dark-coloured blood from the head, trunk and limbs, and in-
ternal organs, to the right side of the heart, into which it
opens by the two great trunks, called the upper and lower

THE CIRCULATION OP THE BLOOD.
Fig. 3.

261

The Arterial system.

vena cava. The other conveys the scarlet-coloured or arte-
rial blood, from the lungs to the left auricle, into which it
issues by four large trunks, called pulmonary veinsj The
veins are strong and flexible, but not elastic like arteries.
They are furnished with little valves placed at short dis-
tances from each other, so as to prevent the blood from flow-

262 PHYSIOLOGY.

ing back again. Like the arteries, they are supplied with
nerves from Hie great sympathetic nerve.

Fig. 4.

Portion of an artery, showing the several coats of which it is com-
posed, separated from each other. 1. The internal or serous coat ; 2.
The middle or fibrous coat; 3. The external or cellular coat.

14. The capillary system, so called from the vessels being
small, like hairs, presents two modifications. \The first con-
sists of little tubes, furnished with proper coats or walls,
which are the termination of the arteries and the commence-
ment of the veins. But a part of these small vessels do not
terminate in veins, but in the very substance of the flesh,
and the organs themselves. These are even smaller chan-
nels than the first, and permit only a single globule of blood
to pass out at a time. They are probably formed by the
fine arterial vessels, gradually losing their proper coats, and
becoming confounded with the cellular tissue/

15. In the capillary system, the functions of secretion,
nutrition, absorption and calorification, or the production of
animal heat, are performed. It is often divided into two
sections, the general and the pulmonary. The first has al-
ready been described. The other exists only in the lungs,
and connects the pulmonary arteries and veins. In this the
blood is changed from venous to arterial.

16. The account which has been given of the circulation
applies to the human species, mammalia and birds. ^Reptiles
have but one heart, containing one ventricle and one or two

THE CIRCULATION OP THE BLOOD. 263

auricles, which receive arterial blood from the lungs, and
venous blood from the body, and in its cavity both are
mixed together. I The main artery going from the heart, di-
vides into two branches, one of which goes to the lungs, the
other is distributed throughout the body. In some of the
other classes of animals, such as icorm^ there is no heart,
and the circulation consists in the passage of the blood from
the surface, where are seated the organs of respiration, to
all parts of the animal and back again, which is performed
exclusively by vessels^ I Fishes have a single heart, designed
only to circulate venous blood, which it conveys to the gills,
or lungs ; and from thence it is carried to every part of the
body, by an artery which rises from the gills themselves^
Shell-fish have also a single heart, but this only circulates
arterial blood.

17. The following facts were brought forward by Harvey
to prove the circulation of the blood. \If the chest of a
cold-blooded animal be opened, the heart will be seen dilating
and contractingf The valves are so situated throughout the
circulating system, as to promote the circulation. Between
the auricles and ventricles they are so placed as to allow the
blood to pass freely from the former into the latter, and to
prevent its return. The valves placed at the orifice of the
arteries, permits the blood to enter them from the ventricles,
but prevents it getting back into the heart. The valves in
the veins allow the blood to go towards the heart, but pre-
vent it from going in the other direction.

18. In bleeding, a bandage or ligature is placed round the
arm, above the point where the arm is to be opened. The
blood, in its return toward the heart, is interrupted, but the
artery which carries the blood to it is not compressed, be-
cause it lies deeper. Sometimes, however, the ligature is so
tight that the blood will not flow till it has been loosened.
If the vein be opened below the ligature it will bleed freely,
but no blood is obtained if it be opened above.

19. When a limb is amputated by a surgeon, he only ties

264

PHYSIOLOGY.

the arteries. The reason is, that as these convey the blood
from the heart, the patient would soon bleed to death unless
some means were adopted to prevent it. But, although the
veins are as large as the arteries, yet, as they carry the
blood back to the heart, they do not bleed, although they are
not tied.

Fig. 5.

The Venous System.

THE CIRCULATION OP THE BLOOD.

20. The blood can also be seen to move in the small ca-
pillaries by means of a microscope. The fine web of a
frog's foot is generally used for this purpose. Microscopi-
cal observations, however, should be received with great al-
lowance, for no two observers have ever found the same ap-
pearances. One makes out the globules of the blood to be
round, another square, and another tubular. Some physi-
ologists, it is to be feared, find just what they wish to find.
Owing to the refraction of light, the microscope is little to
be depended on in examining the minute structure of bodies.

21. ^IThe motion of the blood is chiefly owing to the ac-
tion of the heart. This contracts with great force, and in
the following manner.) The auricles both contract at the
same instant, forcing the blood which is received from the
lungs, and the general circulation, into the ventricles ; these
then contract at the same moment ; the right one sending
the blood through the lungs, the left one through the aorta.
This alternate action is constant, as long as life continues.
The reason why the auricles act together, and the ventricles
the same, is probably owing to the fact, that both have a
common septum or dividing wall, so that one cannot contract
without the other.

22. The ventricles contract more suddenly and powerfully
than the auricles, and they are three times as long in dila-
ting or expanding, as contracting. When the ventricles
contract, the apex or point of the heart rises up and strikes
against the left wall of the chest, between the sixth and
seventh ribs, and this can be felt by placing the hand on the
left side. The left ventricle has much thicker and stronger
walls than the right, because it has a greater distance to
throw the blood ; but the right ventricle will hold more than
the left, because the venous system is more capacious than
the arterial.

23. (The velocity of the blood in the arterial system grows
slower in proportion to its distance from the heart, while
that in the veins is accelerated the nearer it approaches the

23

266 PHYSIOLOGY.

heart.] The reason why the blood moves slower in the arte-
ries as it recedes from the heart, is owing, probably, to
friction, and the increased capacity of the vessels, for the
arterial system is compared to a cone, whose apex is at the
heart. The course of blood in the arteries is intermittent,
or by jets ; not that it does not flow all the time, but its flow
is more or less rapid, according as the ventricles are con-
tracting or dilating.

24^The force with which the blood is thrown from the
heart is variously estimated. Hales computed that the left
ventricle of a horse exerted a force equal to 113 pounds, and
that of a man at 51 pounds. Some think that the contrac-
tion must overcome the whole pressure of the air upon the
body, which is equal to forty thousand pounds. As we can-
not, however, correctly estimate the influence of breathing
and other causes, we cannot, with any degree of certainty,
tell what degree of power is exerted by the heart. Dr.
Arnott thinks, however, that the heart acts with a force of
about six pounds on every square inch, and as the left cham-
ber of the heart has about ten square inches, the whole force
exerted is sixty pounds. )

25. The Blood. — The blood is not necessarily red, it may
be white, as in the fish ; transparent, as in the insect; yel-
lowish, as in the reptile ; and indeed there is no animal in
which the blood is red in all the parts of its body.

26. In a short time after blood is taken from the body it
separates into two portions, by a process called coagulation,
vi2^1. a watery portion called serum, and a solid portion
called coagulum or clot ; the white substance which forms
the upper part of the clot is called fibrin, and the red mass
under it, the red particles. The fibrin is the material from
which all the solids of the body are formed^ (See Fig. 6.)

27. The red particles owe their colour, it is supposed, to
the presence of iron; though some say it depends on an ani-
mal substance of a gelatinous nature. These are usually
described as being minute globules, but the latest microsco-

THE CIRCULATION OP THE BLOOD. 267

Fig. 6.

A portion of fibrin, showing its fibrous structure and the net-like
arrangement of its fibres.

pic observations show that they are flattened cakes, having
rounded and slightly thickened margins, as shown in the
following cut :

Fig. 7.

1. A particle of human blood as it appears when transparent and
floating. 2. The same, seen as illuminated. 3. The same, one half
illuminated. 4. A particle of frog's blood floating. 5. The same,
seen edge-wavs. All these objects are magnified five hundred diam-
eters.

28. (The blood constitutes about one fifth part of the
weight of the whole bodyj; so that the whole quantity of
blood in the body of an adult may be estimated at between
thirty and forty pounds. ^A complete revolution of the
blood takes place every three minutes, and there are about
five hundred and fifty revolutions every twenty-four hours/
The contractions of the ventricles, or the pulse, is about
seventy-five times in a minute, in a grown person, and one
hundred and forty in an infant ; in old age about sixty.

268 PHYSIOLOGY.

Now as two ounces of blood are thrown out of the heart at
each beat, thirty-five pounds on an average, must pass through
the heart every three minutes ; seven hundred pounds every
hour; and sixteen thousand pounds, or eight tons, every
twenty-four hours.

29. Dr. Barry states, that the quicker the blood circu-
lates the sooner will ther machine wear out. Now, suppose
that the pulse of a temperate man be seventy in a minute,
and by the use of ardent spirits he forces it up to eighty-
five, then instead of living seventy years, his number of pul-
sations will be finished at the age of fifty-six ; thus cutting
short his life fourteen years.

30. The heart beats more than one hundred thousand
times in twenty-four hours, and sometimes continues to beat
thus for one hundred years. What other machine so com-
plicated, could last as long ? And still it is made of nothing
but flesh. How strange that it should act so long, without
growing weary ! Truly is it said, that " man is fearfully and
wonderfully made !"

31. Some physiologists consider the heart the only mo-
ving power of the circulation : Others think that the arte-
ries aid by their contractile power. Others still believe that
the capillary vessels have a kind of absorbing and propelling
force, independent of the heart and arteries, while a last
class ascribe the circulation to a self-moving power in the
blood itself. All these theories may have some truth in them,
but they err in being too exclusive.

32. That the heart is the chief moving power of the
blood is generally admitted. If the heart of a frog be ta-
ken from the body and placed in warm water, it will con-
continue to contract and dilate with great force for a con-
siderable time. This would seem to prove that its action
does not depend on the contact of air and blood. In ser-
pents the heart retains this power a long time after death;
and it has been known to contract at least four days after
life appeared extinct. The heart of a sturgeon was cut out

THE CIRCULATION OF THE BLOOD. 269

and laid on the ground, and after it ceased to beat it was
blown up and ordered to be dried. It was then hung up
when it began to move again and continued to beat, though
more slowly, for ten hours ; and it continued to contract till
it became so dry as to rustle iffith the motion. If the heart
of any animal be taken from the body immediately after
death and carefully washed, it will continue to act for some
time ; showing that this alternation of action is natural to
its irritable fibre, and results directly from its structure.

33. The arteries have not an equal power of contraction,
with the heart, though they are generally found more or less
contracted after death. The pulse, which may be felt by
placing the fingers on the side of the wrist, takes place at
the very instant the heart contracts, and is not probably
owing to the contraction or dilitation of the artery, but
chiefly to the jet of blood, which is sent along the tube.
When arteries are changed into bone, the pulse is still felt.
No pulse exists in animals destitute of a heart.

34. That the arteries are not only elastic, but contract so
as to assist the heart in circulating the blood, is evident from
the following facts. If an artery be laid bare, and two lig-
atures applied so as to cut off all communication, and then
a small opening made between the ligatures, the blood will
spirt out with considerable force, and the artery become
much contracted. When a person or animal is bleeding to
death, the arteries always contract in proportion to the loss
of blood ; after death they relax again. Arteries too will
contract by the application of stimulants or irritating sub-
stances.

35. Besides these facts to prove that arteries contract,
We may mention the following. We read of cases of pal-
sy, where in the paralytic limb no pulse could be felt, al-
though the heart beat as strongly as ever. We read of oth-
er cases where the arteries continued to beat after the pul-
sations of the heart ceased. In diseases of the heart, we
sometimes have a weak pulse, although the heart beats very

23*

S70 PHYSIOLOGY.

strongly. And in apoplexy the pulse is often strong, when
the heart acts feebly. Burns relates cases where the pulse
at the wrist did not correspond with the contractions of the
heart : and it cannot be denied that in some animals a cir-
culation exists, although they have no heart. Although fish-
es have a heart, their blood is moved through the body by
vessels. After the heart is taken out of the body, the blood
is still seen to flow in the small vessels.

36. I have stated that arteries contract by an irritating
substance being applied to them. Hartshorn, or ammonia,
will make an artery shrink so as to lose one eighth of its cir-
cumference. A partial enlargement of an artery takes place
in a living animal by exposing it, and rubbing it between
the finger and thumb, but in general no pulsation will be
seen in an artery thus exposed.

37. The capillary vessels have an action independent of
the heart. When the blood has reached the ends of the ar-
teries, or the capillary vessels, the force of the heart and ar-
teries is probably nearly, if not quite exhausted. Dr. Ar-
nott says that the blood is driven into them, by a force
equal to four pounds to the square inch. There is no doubt
that the action of the heart is sufficient to force the blood
through the arteries into the veins ; for when the heart acts
feebly the surface of the body is pale and cold. But the
blood is known to move in a backward or retrograde direc-
tion. When a leech is applied to the skin, the blood flows to
the spot from all quarters. In blushing, the capillaries of
the cheek dilate instantly and admit more blood ; under the
influence of fear they contract, and the face becomes pale ;
tears will gush from the eye in a moment and suddenly dis-
appear ; now all these things could not happen if these ves-
sels did not act independent of the heart.

38. It is probably capillary action which moves the fluids
in all animals that have no heart. Persons have lain in a
swoon apparently dead for days together and then revived.
In these cases life was preserved in the capillary circulation,

THE CIRCULATION OF THE BLOOD. 271

I have seen- a case of this kind, where a young lady of this
city, was kept a fortnight after she was supposed to have
died ; her looks being so natural that her parents were un-
willing to bury her, for fear she would come to life. Al-
though she lay in a room without a fire in the winter season,
yet her body retained its natural warmth for several days,
her cheeks their florid colour, and her limbs their usual flex,
ibility. These singular phenomena were perhaps owing to
a continuance of the capillary circulation.

f \

40 .(The capillary vessels Vre the last part of the body that
continues to act. After the breathing and the action of the
heart have ceased, they still continue to act like innumera-
ble little pumps, drawing the blood out of the arteries and
substance of the organs, and forcing it into the veins. As
nutrition and secretion are performed by that portion of the
capillary system which acts independently of the heart and
arteries, the continuance of action in this system accounts
for the growth of the beard and the hair, which takes place
after death. It is owing to *he same reason, that the arte-
ries are always found empty after death.

41. physiologists are not agreed as to the cause of the
motion of blood in the veins.^ The veins have thinner coats
than the arteries and are destitute of elasticity. As they are
wanting in elasticity, if they had no irritability, they could
not act upon the blood contained in them, and accordingly
could exert no active force in circulating the blood. But it
is found by experiments that the veins are not mere passive
tubes ; they possess a certain degree of contractile power, as
is shown in the shrinking of the veins on the back of the
hands in cold weather ; besides, if a vein be punctured be-
tween two ligatures, the blood will spirt out. £The veins
then assist the circulation by a sli ht degree of contractile
power)

42. Again : when the heart dilates, the blood is sucked
up in the veins precisely as it is in a pump. This is denied
by some, who KW. thai if the end of a syringe be placed in a

272 PHYSIOLOGY.

tube of eel-skin, or any thing which is not elastic, and you
attempt to pump the water out of it, supposing it to be filled,
the sides will be brought together, and the tube closed, so
that the water cannot escape. This, however, will not hap-
pen, if, as in the veins, the fluid is forced in at the other end.

43. The expansion of the chest in breathing, also aids in
circulating the blood in the veins. When the chest is dila-
ted, both air and blood rush into it. This may be seen by
watching the jugular veins in the neck, which empty them-
selves during inspiration. Dr. Barry placed one end of a
tube in the jugular vein, and the other in a coloured fluid.
During inspiration, the fluid was sucked from the vessel into
the vein ; during expiration, it remained stationary. It should
be remembered, that during one act of respiration, the heart
beats five or six times.

44. One other cause remains to circulate the blood in the
veins, and that is, the action of the muscles. When the
muscles contract, they press upon the veins in contact with,
or near them, and so force the blood along their cavities.
This can be seen in bleeding from the arm ; if a person
grasps a stick, the blood flows much more freely than when
the muscles are relaxed. It is in this way, that exercise
proves so beneficial to health, by promoting the circulation
of the blood through the system ; and we account in this
way also, for the fact that sedentary habits so often lay the
foundation for incurable diseases.

45. (The heart is not so dependent on the brain for its ac-
tion as many other organs. } ^lonsters, born without heads,
sometimes live for several days. Snakes have lived six
months without a head ; and any animal may live for some
time in the same condition, if the blood-vessels of the neck
are tied. If the breathing be kept up by artificial respiration,
life may be continued for a long time. I have myself kept
a child alive two hours, that had its neck broken, by keeping
up artificial breathing ; persons have been saved in the same
way, who had taken large doses of laudanum.

THE CIRCULATION OF THE BLOOD. 273

46.; In fainting, the heart ceases to act) It may be owing
to various causes, acting on the nervous system, or on the
blood-vessels. Mental emotion, loss of blood, or any thing
that renders the blood-vessels about the heart less full or
tense than usual, will cause a person to faint. This state is
soonest relieved bjflying dow^ probably because the action
of the heart is sufficient to force the blood along horizontal
tubes, but not to raise it in a perpendicular position. Where
blood has been lost in sufficient quantity to endanger life, it
has been supplied from the veins of another person, by a pro-
cess called transfusion.

Questions. — When was the circulation of the blood discovered?
and by whom ? Why not discovered before ? Why is the circulation
called a vital function ? How is life maintained ? Have all animals
a circulation &* Describe the structure of the heart. What is the peri-
cardium? In what animals is the heart double ? Describe the cavi-
ties of the heart — the valves. WThat is their use ? What are arteries ?
How many coats have they f; Describe the venous system. Have the
veins valves ?>' What is the capillary system ? Describe the circulation
in reptiles — worms — fishes. What facts did Harvey bring forward to
prove the circulation of the blood ? What is the motion of the blood
chiefly owing to ? Are the veniricles thicker than the auricles ? Why ?
What is said of the velocity of the blood? Of the force of the
heart ? Describe the composition of the blood ? What proportion of
the body does it constitute ? How long is the blood in performing a
revolution ? What is the last part of the body that continues to act ?
Why are the arteries found empty after death ? What circulates the
blood in the veins 1 What aids in this process ? Does the heart de-
pend on the brain for its action ? What facts connected with this sub.
ject ? What occurs in fainting ? What position is most favorable in
recovering from fainting ?

CHAPTER XX.

NUTRITIVE FUNCTIONS. — DIGESTION.

1. (j)igestion, absorption, secretion, and nutrition constitute
what are called the nutritive functions.} Digestion is that
process by which the food is brought into a state in which
it may be taken up by the lacteal vessels and carried into
the blood. (.The digestive apparatus consists of the mouth
and its appendages ; the pharynx ; esophagus ; the stomach
and intestines^ the whole tract making what is called the
alimentary canal. Besides these, there are the salivary
glands ; the liver ; the pancreas, or sweet-bread of animals ;
all of which aid in the process of digestion.

2. The parts which compose the mouth, are (the lips,
cheeks, palate, tongue, teeth, and salivary glands} There are
six salivary glands, which secrete saliva, viz.: the parotid;
sub-maxillary ; and the sub-lingual. The parotid gland is
situated on the cheek before the ear ; the sub-maxillary im-
mediately beneath the lower jaw ; and the sub-lingual under
the tongue. They all pour forth a fluid, during mastication,
into the mouth to moisten the food, and prepare it for the
change it is to undergo in the stomach. A swelling of the
parotid gland is called the mumps.

3. In a grown person, there are thirty-two teeth ; four in-
cisor, or cutting teeth, two canine or dog teeth, ten molar or
grinders in each jaw. The first set of teeth begin to come,
when the child is about six months old, and by the time it is
two years and a half old, it has twenty ; about the seventh
year, they all become loose and fall out, and their place is
supplied by another set. The teeth are the hardest part of
the body ; their internal parts resemble bone ; the external
consist of a very hard and highly polished substance, called
enamelt which is very durable.

NUTRITIVE FUNCTIONS DIGESTION.

Fig. 1.

275

Half of the lower jaw ; a, the base ; 6, the angle ; c, the ramus ; d,
the condjle ; e, the coronaid process ; h, the two incisors or cutting
teeth; i, one canine or dog tooth; k, two small molar; I, three large
molar or grinding teeth.

4. The jaws perform an important part, in fitting the food
for the stomach. The lower jaw only has motion ; being
moved by means of strong muscles, which rise from the tern-
pies and upper jaw ; and it not only moves directly upwards
and downwards, but sideways, so as to grind the food be-
tween the teeth, as grain is ground between two mill-stones.

5. The tongue is likewise very useful in the process of
mastication, as it removes the food from one part of the
mouth to another, so as to bring every portion bet \veen the
teeth ; and then it forms it into a suitable shape for swal-
lowing. The tongue is made up by different muscles, and is
supplied by nerves, chiefly from the eleventh pair.

6. The esophagus or meat-pipe, lies directly behind the
wind-pipe, and is about one inch in diameter. It connects
what is called the pharynx, with the stomach. All these or-
gans are lined by a soft, velvet-like membrane, termed mucous
membrane, because it is always covered in health, with a vi-
scid fluid, called mucus.

276 PHYSIOLOGY.

7. The stomach is the largest organ of digestion. It lies
immediately under the false ribs, on the left side, below the
midriff, and is shaped somewhat like a bag-pipe. It has two
openings, the upper one, which admits the food, is called car-
diac, and the lower one, the pyloric orifice. In a middle sized
man, this organ is about ten inches long, and three or four in
diameter, and holds from three to six pints.

8. The stomach has four distinct coats ; the inner one is
called mucous or villous ; being thin, soft, and spongy ; the
second vascular ; as it is made up chiefly of blood vessels ;
the third muscular; composed of muscular fibres, and very
strong ; the fourth serous ; as it secretes a serous or watery
fluid. The stomach is freely supplied with blood vessels and
nerves; the latter being furnished partly from the spinal
marrow, and partly from the brain.

Fig. 2.

The human stomach : a, the esophagus or gullet ; &, the cardiac por-
tion ; c, the left extremity ; d, the small extremity ; e, the pylorus tied ;
g g, the omentum or caul, which is attached to the outside of the
stomach, and falls over the intestines like a curtain.

NUTRITIVE FUNCTIONS DIGESTION. 277

9. The intestines in man, are from five to six times the
length of the body ; and are divided into large and small in-
testines ; the latter making about four fifths of the whole.
The small intestines are divided into duodenum, jejunum,
and Ueon. The duodenum is so called because it is about
twelve finger's-breadth in length ; the jejunum from its gene-
rally being found empty ; the ducts or canals from the liver
and pancreas enter the duodenum near the middle, and it is
abundantly supplied with lacteals. The different portions
of the large intestine are called coecum, colon, and rectum.

10. The liver is the largest gland in the body ; and it lies
directly under the ribs, on the right side, and reaching be-
low them. In a grown person, it is about ten inches in diam-
eter, and weighs not far from four pounds. It secretes the
bile, which is poured out into a bag called gall-bladder, con-
nected with it ; from thence it is carried into the duodenum.
The liver is found in all the vertebrated animals and in the
mollusca ; in birds, reptiles and fishes, its size is greater in
proportion to that of the body than in the human species.
It is attached to the diaphragm, which lies above it, by a
fold of the peritoneum, called the suspensory ligament of the
liver. •

11. The pancreas is a gland about five inches in length,
of a whitish colour, lying immediately behind the stomach.
It is supplied, like the stomach, with numerous blood-vessels
and nerves. It secretes a fluid, called the pancreatic fluid,
which is white, viscid, inodorous, slightly saline, and con-
tains a large proportion of albumen. This gland is found
in all the mammalia, in birds, and in amphibious animals, or
such as live both in air and water, like the frog ; but it is
much larger in animals that live on vegetables, than in those
that feed on flesh. Hence, the fluid which it secretes, is
supposed to aid in difficult digestion. (See Fig. 3.)

24

278

PHYSIOLOGY.
Fig. 3.

The above cut represents the whole tract of the intestinal canal, not
exactly in its natural position, but spread out so as to show the relative
proportions ; /, the aesophagus ; g, cardia ; h, pylorus ; i, i, the duodenum,
about twelve fingers' breadth in length ; &, hepatic duct ; /, gall blad~

I ^ •

NUTRITIVE FUNCTIONS DIGESTION. 279

der ; m, cystic duct ; n, ductus communis, formed by the union of both;
o, the opening of this duct into the duodenum ; p, pancreatic duct ; q,
its opening into the duodenum ; r, jejunum; s, ilium; these constitute
the small intestines, and are about twenty-six feet in length, or five
times the length of the body ; *, termination of ilium in the coecum ;
u, superior fold of valve of colon ; v, inferior do. ; w, coecum ; x, ver-
miform process ; y, y, colon ; z, rectum. The coecum, colon, and
rectum, form the large intestines, and are about six feet in length ; the
coecum being about 4 inches long, and the same in diameter. The
arrows show the direction which the food takes in digestion.

12. Hunger and thirst are sensations designed to teach us
the necessity of supplying those losses which the system is
constantly undergoing by the different secretions and excre-
tions, amounting to several pounds in the course of twenty,
four hours. The blood first feels the loss, and then the
solids, whose particles are continually taken up by the ab-
sorbents, and carried into the blood, and thus ejected from
the system ; and were not these losses supplied by the timely
introduction of food, the body would rapidly emaciate, till
death closed the scene. Hunger is supposed to be owing to
a peculiar affection of the nerves of the stomach ; for when
the nerve which goes from the brain to the stomach (the par-
vagum,) is divided, the sensation of hunger is lost, or at
least the appetite for food is destroyed.

13. While the food is undergoing the process of mastica-
tion, that is, of being divided and ground down by the tee!

it is thoroughly mixed with a quantity of saliva, amounting
it is supposed to between eight and ten ounces. The food
is thus brought into a condition to be easily swallowed, and
readily dissolved by the action of the stomach. It is very
important, therefore, that the food should be slowly chewed,
and reduced to as fine a state as possible in the mouth, in
order that digestion may be easy. Too great rapidity in
eating, probably lays the foundation of many cases of indi-
gestion.

14. After the food has been sufficiently masticated, it is
carried down the aesophagus into the stomach, first by the

280 PHYSIOLOGY.

contraction of the muscles of the pharynx, and then by a
successive contraction of the circular fibres of the gullet it-
self, from above downwards. That the morsel is not carried
down merely by its own weight, is proved by the fact, that
a man can swallow with his head downwards.

15. In the stomach, the food is converted into a soft, grey,
pulpy mass, called chyme. This process has been called
chymosis. It is produced by the motions of the stomach,
together with the agency of the secretions, which are thrown
out by the gastric vessels. These motions have been called
vermicular or worm-like ; and undulatory, or like wave suc-
ceeding wave. The crawling of a worm furnishes a very
good illustration of the successive contractions of the muscu-
lar fibres of the stomach, commencing, as they do, at the aeso-
phagus, and proceeding onwards to the pylorus, and so back
again. These motions of course bring every portion of the
contents of the stomach in contact with all parts of its sur-
face ; and so they become intimately mixed with the gastric
fluid.

16. The food is thus carried round the interior of the sto-
mach, from one extremity to the other ; and from one to
three minutes are employed in each revolution. In the mean
time, both orifices are closed ; so that the contents cannot
escape. During this process, the gastric fluid is secreted in
large quantities, and becomes mixed with the food as it
passes round. In a short time, the taste, smell, and other
sensible properties of the food, are entirely changed. This
is produced by the agency of the gastric juice, which sub-
verts the chemical affinities of the food ; and with its ele-
ments forms new combinations.

17. fThe gastric fluid is a clear, transparent fluid, produced
by arterial exhalation ; acid to the taste, slightly saline, and
free from odour.] It possesses the singular property of co-
agulating albumen ; resists the putrefaction of animal mat-
ter ; and dissolves nearly every kind of alimentary substance.
Its acid properties are owing to the muriatic and acetic acids

NUTRITIVE FUNCTIONS DIGESTION. 281

which it contains. The gastric fluid is found to contain
more acid, in proportion as the food is more difficult of
digestion. It is only secreted, when food is present in the
stomach.

18. The aliment then is converted into chyme, chiefly by
the gastric fluid ; aided, however, by the motions of the sto-
mach. This is proved by the fact, that this fluid will dis-
solve alimentary substances out of the stomach : the chyme
which is prepared by artificial digestion, presenting the same
sensible properties as that which is found in the stomach.
Such is the power of the gastric fluid, that it will dissolve
bones, not only in the stomach, but out of it. It curdles
milk ; and for this purpose the rennet, or stomach of the
calf, is used by farmers in making cheese. But every thing
which is coagulated in the stomach, is dissolved again, in its
conversion into chyme.

19. But digestion is a vital and not a chemical process.
Though aliment may be reduced to a substance resembling
chyme, by the action of gastric fluid out of the body ; yet
it is destitute of all those peculiar properties which assimi-
late it to the nature of a living animal. The food may
doubtless be brought to a fluid state by a chemical process,
and even alimentary principles may in the same way be
changed into each other, as starch into sugar and gum ; but
there is still another power, which may be called vitalizing
or organization, by which alimentary substances are brought
into such a condition as adapts them for an intimate union
with the living body. Such a power is beyond the reach of
chemical action.

20. The time which is required to change food into chyme,
varies according to the nature of the food. Animal food is
digested sooner than vegetable. The average time required,
is about three hours and a half. A good deal depends, also,
on the degree of mastication it has undergone. If swallowed
in large masses its solution must go on slowly.

21. As fast as the aliment is changed into chyme, it pass-

24*

282 PHYSIOLOGY.

es out of the stomach into the duodenum, and it generally
stays in the stomach until it has undergone this change.
Indigestible substances have thus been vomited up, more
than a week after they were swallowed. All fluids which
are swallowed, are supposed to be taken up by absorption.

22. If the par-vagum, or nerve which goes from the brain
to the stomach, be divided, digestion is impaired or suspend.
ed. The same happens under the influence of mental emo-
tions, such as grief, anger, &c. Some physiologists have
thought that this nerve presides over the secretion of the
gastric juice ; others, that it stimulates the muscular motions
of the stomach ; while a third class consider it to be the
seat of sensation in the stomach, giving rise to hunger and
thirst. But it is not yet fully settled what particular influ-
ence this nerve exerts over digestion.

23. The chyme, on passing from the stomach, is received
into the duodenum. This, like the stomach, has a serous,
muscular, and mucous coat, and has a mucous, as well as se-
rous, secretion. In this portion of intestine, the chyme in
its passage meets with the pancreatic and the biliary fluids ;
the irritating properties of the acid chyme, cause these
fluids to be poured out in great abundance, as well as the
other secretions ; and these are thoroughly mixed with
the chyme by the contraction of the intestine. It now be-
comes of a yellowish, instead of a gray colour ; its acid
properties disappear, and large quantities of albumen are
developed. This is supposed, by some, to be derived from
the pancreatic fluid, which contains a large proportion of it.

24. As it becomes intimately mixed with the biliary and
pancreatic secretions, the substance called chyle is produced.
Though some say it is not to be found in the duodenum — but
only the elements out of which it is formed. But albumen,
which is the basis of chyle, exists abundantly in the duode
num ; and so also do particles of fibrin. By the microscope,
globules also may be detected in the chyme, similar to those
which are found in the chyle.

NUTRITIVE FUNCTIONS DIGESTION. 283

25. It would seem, then, that the great business of diges-
tion is to change the food into albuminous matter, which
forms the basis of the chyle as well as the blood ; and it is
certain that no albumen is formed in the stomach ; though
the change which the food there undergoes, is an approach
to the nature of albumen. As the bile is alkaline, it doubt-
less combines with, and neutralizes the acid properties of
the chyme, which would precipitate the mucus of the bile,
and leave it in a state of coagulation.

26. Chyle then is the fluid, which is taken up by the ab-
sorbent vessels, called lacteals, whether it exists ready formed
in the chyme, or is manufactured out of it, by the action of
these vessels themselves. It is usually of a milk white co-
lour, but varies in appearance in different animals ; and ac-
cording to the nature of the food. In animals that feed on
flesh, it is opaque ; in such as live on vegetables, it is trans-
parent ; in birds and fishes, thin, serous, and clear like wa-
ter. It is saltish, and somewhat sweet to the taste ; heavier
than water but less so than blood. It coagulates on stand-
ing, like blood, and separates into three portions ; a fluid, a
coagulum, and a fatty substance. The fluid portion is chief-
ly of albumen and coagulates like the serum of the blood by
heat, acids, and alcohol ; the coagulum consists of fibrin,
and a coloring matter, which is white.

27. Whatever the food may consist of, physiologists are
now pretty well agreed, that the chyle will always be com-
posed of Jlbrin, albumen, a fat matter, muriate of soda, and
phosphate of lime, though in variable proportions. Food
that contains much azote, such as that of animals, it is sup-
posed will form chyle, which contains a greater portion of

Jibrin than that of vegetables, as azote is one of the chief ele-
ments of fibrin. Dr. Marcet states that chyle produced from
vegetable aliments contains three times as much carbon as
that formed out of animal substances. It is certain that
chyle from animal food is milky ; and that from vegetables
transparent. As both however are composed of the same

284

PHYSIOLOGY.

essential elements, we may be assured, that man can live on
either animal or vegetable diet, as it may be most conve-
nient. As the most important part of digestion seems to be
completed in the small intestines, we shall not follow the pro-
cess any farther.

28. A few years since, a man in the United States army
received a gun-shot wound, which made a hole in his sto-
mach ; and which left an opening into the cavity of that or-
gan, so that the whole process of digestion could be seen, as
it was going on. Dr. Beaumont, a physician in the army,
availed himself of this singular case, and performed many
curious experiments which occupied him for several years.
The following are the most important inferences, which he
drew from his experiments.

29. " Animal and farinaceous aliments are more easy of

digestion than vegetables. Digestion is fa<
nuteness of division and tenderness of fibre ;
portance of thoroughly chewing the food,
principles of aliment are always the same,

itated by mi-
icnce the im-
The ultimate
-om whatever

kind of food they may be obtained, whether v sgetable or an

imal. The quantity of food generally take
mach, is greater than the system requires. S

sier of digestion than fluid. Stimulating cond ments, such as
spices, are hurtful to a healthy stomach.
30. The continued use of ardent spirits a

diseases of the stomach. Hunger is the eff
tension of the vessels, which secrete the gast
temperature of the stomach is 100 degrees
The gastric juice dissolves the food, and alters

It also coagulates, or renders solid, albumen,
dissolves it.

31. The gastric juice is a clear and transp irent fluid ;
little saltish, and somewhat sour to the taste. When pure,
it suffers no change by keeping. Gentle exen ise assists the
digestion of the food. Water, ardent spirits, a id most other
fluids are not affected by the gastric juice, >ut disappear
from the stomach soon after they are receivedl

into the sto-
id food is ea-

ays produces
ct of the dis-
c juice. The
' Fahrenheit.
ts properties,
nd afterwards

NUTRITIVE FUNCTIONS DIGESTION. 285

Questions. — What constitute the nutritive functions ? What the di-
gestive apparatus? What the mouth? How many salivary glands
are there ? How many teeth are there in an adult ? How divided ?
When do they begin to appear ? When are they shed ? What is the
outside of the tooth called ? How is the tongue useful in mastication ?
Describe the esophagus — the stomach — the intestines — the liver — the
pancreas — hunger and thirst. Describe the process of digestion. What
is the gastric juice ? Chyme ? Chyle ? What is rennet— what used
for ? Is digestion a chemical process ? How long does it generally
take to convert food into chyme ? What influence has the par vaguin
nerve on digestion ? Where do the pancreatic and biliary fluids enter
the intestines ? their use ? Is the nature of chyle changed by the kind
of food ? Of what is it always composed ? What are the principle re-
sults of Beaumont's experiments in relation to digestion ?

CHAPTER XXI .

SECRETION.

1. Secretion is one of the most obscure and mysterious
functions in the animal economy. /To secrete means to sepa-
rate ;ybut most of the fluids formed by this process, did not
previously exist in the blood, but only the elements out of
which they are made. It is purely a vital and not a mechan-
ical process, like straining through a seive, to which some
have compared it : and the vessels by which it is accom-
plished may well be called the architects and chemists of the
system ; for out of the same material, the blood, they con.
struct a variety of wonderful fabrids, and chemical com-
pounds.

2. We see the same wonderful power possessed also by
vegetables— ffor, out of the same materials, the olive pre-
pares its oil ; the cocoa-nut its milk ; the cane its sugar ; the
poppy its narcotic juice ; the henbane its poison ; the oak
its green pulpy leaves, its light pith, and its dense woody fi-
brej all composed of the same, few simple elements, only ar-
ranged in different order and proportions.

3. fin like manner, we find the vessels in animal bodies,
capable of forming all the various textures and substances
which make up the frame ; the cellular tissue ; the mem-
branes ; the ligaments ; the cartilages ; the bones ; the mar-
row ; the muscles, with their tendons ; the lubricating fluid
of the joints ; the pulp of the brain ; the transparent jelly of
the eye ; in short, all the textures of the various organs of
which the body is composed ; and still all are made out of
the same blood ; and consist of the same ultimate elements.^

4. (The most simple form of secretion, however, seems to
be, the mere separation of some principle, which previously
existed in the blood \ as senim is deposited in most of the ca-
vities, by a kind of exhalation. Some other principles also

SECRETION. 287

exist in the, blood, which are found in the secretions, as/-
brin, a fatty substance ; and some of the elements of the
bile. Some physiologists believe, that many of the secre-
tions do exist ready formed in the blood, but cannot be de-
tected by analysis. In proof of this, two ounces of bile have
been injected into the veins of a dog, but the blood of the
animal, which was analyzed a few moments after, exhibited
not a trace of bile.

5. That secretion is a vital process and not a chemical
one, is evident from the fact^that it is so much under the
influence of the nervous system. For example, sorrow and
grief change the qualities of the bile : a fit of anger some-
times causes an excessive flow of it : it will also change the
nature of milk to such a degree, as to produce colic, vomit-
ing, and even convulsions in the infant that swallows i^
Grief will also suspend the secretion of the gastric fluid, and
thus destroy the appetite ; while fear causes a cold sweat to
break out, all over the surface of the body. If the nerves go.
ing to any organ are divided, the function of secretion will
be suspended. It is doubtless owing in a great degree to the
changeful states of the nervous system, that the secretions
vary so much in quality as well as quantity at different pe-
riods.

6. Though we are able to understand but little of the true
nature of secretion, we know that there are three kinds of se-
cretory organs, v'i2^, exlialent vessels ; follicles ; and glands.^)

l.The exhalents are believed to be the termination of the arte-
ries, or capillaries^ and they are of two kinds, internal and
external ; the former terminating on all the surfaces within
the body ; and the latter on the outside. (Their use is to
soften and lubricate these parts)

7. The fluid, which is thrown out by the serous mem-
brane which surrounds the brain, the lungs, and the contents
of the abdomen, as well as into the cavities of the joints, is
very similar to the water of the blood, and its use is, to keep
the parts in a moist state, and enable the organs to move ea-

288 PHYSIOLOGY.

sily on each other. \Fat is also a secretion^ which is thrown
out in a fluid state, from the cellular tissue, into little cells'!
and it is mostly found immediately under the skin, between
that and the flesh. Its use seems to be, to lubricate the so.
lids and facilitate their movements ; to form a cushion around
the body, and protect it from external injuries as well as the
extremes of heat and cold.

8. During sickness, when we take little or no food into
the stomach, Hife is supported by the absorption of the fat,
which is taken up by little vessels and again poured into the
blood^ to nourish the body ; also in animals which lie in
their burrows, in a half torpid state during the winter, their
nourishment is derived from the same source.

Q.fMarrow which fills all the cavities of the long bones,
is very much like fat, and this also is a secretion from a thin,
delicate membrane, that lines the cavities of the bones^
These are the principal internal exhalations, or secretions.

10. The external secretions are two in number ; (/the first
and most important from the skin is called, when insensible,
perspiration ; and when it is visible, is called sweat ; the se-
cond is from the lungs, and can be seen in the form of a va-
pour in a frosty morning? The fluid which escapes from the
skin, is chiefly water, containing a little acid and some salts,
with a small quantity of animal matter.

11. The skin is covered with an innumerable number of
pores, so small indeed, as to be invisible to the naked eye,
through which the insensible perspiration is constantly pour-
ing,£amounting in weight to more than one half of all the
food and drink taken into the stomach, and much exceeding
that lost by all the other excretions^

12. From a vast number of experiments performed by dif-
ferent persons, it appears that the largest amount of insensi-
ble perspiration amounts to five pounds in twenty. four hours,
and the smallest to thirty-two ounces. Now, when we con.
sider that the skin, serves as one of the chief outlets, by
which the old and useless particles are got rid of, out of the

SECRETION. 289

blood, and that checked perspiration is one of the most pow-
erful causes of disease and death,(we shall see how important
it is to keep the pores of the skin free, by frequent washing
and bathing at all seasons of the year^

13. When the surface also is chilled by cold, and reaction
does not follow, the blood-vessels become contracted all over
the skin, and the blood retreats to the inner parts of the
body ; the 29 ounces of waste and noxious matter, which
ought to be discharged, are kept in the system, and sickness
is the consequence. Accordingly, we find that it is a good
remedy, in most cases of disease, to excite a perspiration and
keep it up for some time.

14. The uses of transpiration by the skin, are,(not only
to carry out of the body the noxious properties of the blood,
but also to render the skin soft and pliable, the sense of
touch delicate, and also to cool the body when exposed to
great heat]

15. The exhalation from the lungs closely resembles that
from the skin. It was once supposed to be formed in the
lungs, by the union of hydrogen from the blood, and oxy-
gen from the air, thus forming water ; but it is the opinion
of most physiologists at present, (that it is either the watery
part of the mucus secreted by the mucous coat of the lungs
and air passages, or that it is given off directly from the

16. (The Follicles, are small sacks or bags, found in the
skin, and the mucous membranes.) The pores which we see
on the skin are only the outlets of these follicles. Their use
is to secrete an oily matter to mix with the perspiration, and
help to keep the skin soft and moist ; when these outlets are
closed, sometimes there appear small black specks on the skin,
sometimes called worms, but they are nothing more than
hardened mucus. Every hair has a follicle at its root, and
the wax which collects in the ears, is secreted by follicles.

17. The chief agents of secretion in the body, are the
glands,: which are bodies of various size, generally of a

25

290 PHYSIOLOGY.

rounded form ; and the fluids they secrete, are very different
from each other, and also from the blood which furnishes the
same materials to all. For instance, the liver secretes the
yellow, ropy fluid, called bile ; the kidneys, secrete urine ; the
lachrymal gland, which is placed immediately over the eye
in the orbit, secretes the tears ; and the spittle or saliva is
poured out from the salivary glands.

18. ( Glands are formed of a large number of arteries, veins,
nerves, and lymphatics, disposed in a peculiar manner, and
connected together by a tissue of cellular membrane) When
in a cavity, they are covered on their external surface by a
coat, derived from the membrane that lines the cavity, and
they are also provided with a canal, called excretory duct,
which is lined with mucous membrane. There are seven
kinds of glandular secretions.

19. The secreted fluids have been divided |into serous or
watery, albuminous mucous, oily, and the mixed j( such as sa-
liva, bile, tears, dec. They have also been divided into recre-
mentitious and the excrementitious, or those which are des-
tined to be absorbed and returned into the mass of the blood,
and which are deposited in cavities that have no external
opening ; and the second, those which are designed, after
their formation, to be expelled from the system.

20. When any substance is taken up by the absorbents,
and carried into the blood, which cannot be converted to any
useful purpose in the system/it is immediately discharged by
means of the secretions. Not many years ago, a man was
carried into a London hospital, who was picked up drunk in
the streets. He lived but a short time, and on examining
his brain, nearly a half a gill of fluid strongly impregnated
with gin, was found in the ventricles. This was secreted.

21. Unless the secretions all go on, we cannot enjoy good
health. If that from the skin is stopped, fever, or some in-
ternal inflammation is the consequence. If the bile ceases
to flow, we cannot properly digest our food ; and so if any
of the others are interrupted, some serious disease will be the

SECRETION. 291

result. The use of ardent spirits deranges all the secretions,
and this is one reason why they shorten life so much.

Questions. — What is Secretion ? Is it a vital process ? Have vege-
tables the same property of secretion,/? 'Illustrate this. What is the use
of this function ? What is the most simple form of secretion ? How
is it proved that secretion is a vital process ? How many kinds of se.
cretory organs are there £ What are exhalents ? — their use ? What
is fat ? How is life supported in sickness ? What is marrow ? What
are the external secretions ? How much does the insensible perspira-
tion amount to in 24 hours ? What important inference do we derive
from this in relation to health ? What is use of transpiration by the
skin ? What is the exhalation from the lungs owing to ? What are
follicles ? What are the chief agents of secretion ? What are glands
composed of? — their structure ? How are the secreted fluids divided ?
What becomes of useless substances carried by absorption into the
blood ? Can health be maintained if the secretions be checked ?/ ^-r-

CHAPTER XXIL

ABSORPTION.

1. (ABSORPTION is another function of the animal body,
immediately connected with nutrition.^ By it is meant that
process by which food and drinks, designed for the nourish-
ment and growth of the body, are taken up and carried into
the blood ; and also those particles and materials that have
been already deposited, and have become either useless or
injurious, are conveyed into the general mass of the circula-
ting fluids, and thus removed from the system. The first is
effected by the lacteal vessels ; the second by the lymphatics.

2. The absorbent system, so called, consists of the lym-
phatic vessels, the lymphatic glands, and the thoracic duct)

[ The lymphatic vessels arise, not only from all the mucous
surfaces, but also from the whole surface of the body} the
intimate tissue of every structure ; and from all cavities,
such as the chest, abdomen, the joints, the pericardium, and
even the ventricles of the brain. jThey are exceedingly
small at their origin, but by uniting, form larger and larger
trunks as they proceed, which is generally in the course of
the veins, till they finally discharge their contents, either in-
to the thoracic duct, or some of the large veins near the
heart. Throughout their whole extent, they are provided
with numerous valves, which, when they are distended with
lymph, causes them to resemble a string of beads.^)

3. Every part of the body is supposed to be furnished
with absorbent vessels, with the exception of the nails, the
hair, the cuticle, and the enamel of the teeth. And even in
these, it is not impossible that they may exist ; only they
are too small to be detected.

4. (The lymphatics of the small intestines, called lacteals,/
are the agents of digestive absorption. $They arise from the

ABSORPTIO

surface of the mucous coat, pass between the serous and
muscular coats, and proceed to the small glands or ganglions
of the mesentery/ As they emerge from these, they increase
rapidly in size, till they finally unite in a large trunk, which
passes up along the spine, and at last empties its contents
into the left subclavian vein near the heart. Many physi-
ologists are of opinion that the lacteals not only terminate
in the thoracic duct, but also in numerous veins in the ab-
domen.

5. The chyle, which is the fluid taken up by the lacteals,
does not exist ready formed in the chyme, but isfformed or
manufactured out of the nutrient principles contained in it,
by a specific action of the lacteal vessels themselves} In
like manner, the sap which is contained in vegetables, does
not previously exist ready made in the materials which are
absorbed from the ground, but is formed by the peculiar ac-
tion of the roots. No chyle has ever been found in the
intestines.

6. As the chyle passes on towards the heart, it undergoes
important changes. /It loses some of its albuminous quali-
ties ; while its fatty matter, its fibrin, and cruor, considera-
bly increase)) Its tendency to coagulate, also becomes
greater as it approaches the venous system, and it becomes
clearer and more transparent. What is the precise nature
of the change which the chyle undergoes in passing through
the glands is unknown.

7. Absorption not only takes place from the small intes-
tines, but from the whole tract of the intestinal canal, inclu-
ding the mouth and sesophagus. But those vessels which
absorb chyle, are /chiefly found in the small intestines. It
is highly probable that alimentary substances may be directly
absorbed from the intestines, without undergoing any pre-
vious change or assimilation, like alcohol or water ; but that
in their passage through the absorbent system, they undergo
a species of digestion, and become in a good degree fitted
for the replenishment of the blood. To this, however, alco.

25*

294 PHYSIOLOGY.

hol is an exception, as it frequently, if not always, passes
into the blood unchanged.

8. Various medicinal substances are absorbed, and enter
the circulation, nearly or wholly unchanged. ^Colouring
matter, such as madder, is taken up and carried into the
blood, and even tinges the bones. ^ Odoriferous particles,
such as of garlic, camphor, asparagus, &c., are also readily
absorbed, and in this way the blood derives its saline proper-
ties. It is pretty well established, that articles not of an
alimentary nature, which are absorbed, are chiefly taken up
by the veins, while the lacteals absorb chyle more readily
than any other substances.

9. Absorption takes place from the external surface or
skin. This is proved by many facts. Thirst may be
quenched by applying moist cloths to the skin, or by bath-
ing. The body increases in weight by the use of the bath ;
and it has been found that the hand, immersed to the wrist
in warm water, will absorb from 90 to 100 grains of fluid
in the space of one hour. The saliva has become bitter by
the absorption of sea water ; and it is stated that patients
have been supported by baths of milk or broth.

10. Medicinal substances are often absorbed by the skin.
Mercury, Spanish fly, morphine, and many other articles are
frequently introduced into the system through the skin.
Metallic quicksilver has been found in the bones of persons
who had been subjected to mecurial frictions ; and it has
also been obtained by distilling the blood of rabbits, dogs,
and cats, which had been rubbed with this mineral. Gases
are also absorbed by the skin.

11. As every part of the body is subject to constant re.
novation and change, absorption must be (continually going
on among the particles and substance of which each organ
is composed.^ This is called interstitial absorption. It is
this which counterbalances the action of the nutrient ves-
sels, and preserves tjie form and size of every part of the
body, p hen it is too active, the body emaciatesjfc *vhen it

ABSORPTION. 295

is deficient, plethora is the result. In the later periods of
life it is more active than nutrition, and the body dwindles
in size ; in youth the reverse is the case.

12. Foreign bodies, introduced into the substance of or-
gans, are also absorbed. Wens and tumours of considera-
ble size, often disappear from the same cause. Instances
are known where the absorbent vessels have set to work and
removed the whole bone of a limb ; and but lately a case
occurred in Boston, in which every particle of bone in the
arm was thus taken up and carried away, after a fracture
had occurred. How admirable is that arrangement by
which the vessels of absorption and secretion so act as to
balance each other ; and how soon would a loss of this
balance produce derangement, disease, and even death.

13. Another form of absorption is called respiratory,
which we have already considered under the subject of res-
piration. We understand by it£merely the introduction of
oxygen into the blood, through the pulmonary cells) Sub-
stances, however, in a state of vapour, or fine dust, are also
readily imbibed when drawn into the lungs ; such as metal-
lic vapours, oderiferous particles, marsh and other effluvia.
It is in this way, probably, that contagious diseases are
caught.

14. It is by means of what physiologists call recrementi-
tidl absorption, §hat fluids are removed from the system
which are secreted upon surfaces that have no external out-
let £ as in the cavity of the chest, abdomen, brain, &c.
These fluids are various : such as the serous fluids ; the sy-
novia of the joints ; the fat ; the marrow, and the humours
of the eye. It is this which prevents dropsies in these vari-
ous cavities ; and also removes them when already existing.
This form of absorption is also proved by the fact, that fo-
reign substances, placed in contact with these surfaces, in a
short time disappear.

15. Another variety of absorption has been called
menttiicd ; as{it relates to the fluids which have been excrel

296 PHYSIOLOGY.

These are liable to be absorbed ; at least the more fluid parts
of them, by which they are again carried into the mass of
the circulating fluids, and such parts selected as are fit for
the uses of the animal economy, such is the case with the
fluids exhaled by the skin ; the mucous membranes ; the
saliva ; the bile ; the gastric and pancreatic fluids ; the milk,
&c. Thus, has it been remarked, does nature choose to
subject the materials of decomposition to a careful revision,
before rejecting them finally from the body.

16. All these varieties of absorption are constantly going
on from the moment of birth to that of dissolution, and all
the fluids which are absorbed, are changed in their charac-
ter, and fitted to repair the wastes of the system. Thus,
by absorption in the lungs, oxygen is converted into one of
the elements of the blood; in the intestines, chyme is
changed into chyle ; in the tissues of the organs, solid par-
ticles are converted into fluid lymph ; and from the cavities
secreted and excreted fluids are again taken up and thrown
into the circulation, to be once more revised and elaborated.

17. iFrogs, and several other amphibious animals, are fur-
nished with large receptacles for the lymph, situated imme-
diately under the skin, which exhibit distinct and regular
pulsations like those of the heart. The use of these lympha.
tic hearts is evidently to propel the lymph along the lympha-
tic vessels. The frog has four of these organs ; the two
posterior being situated behind the joint of the hip ; and the
two anterior ones on each side of the third vertebra. These
organs have also been discovered in the toad, salamander,
and lizard.

Questions — What is meant by absorption ? What composes the ab-
sorbent system ? Where do the lymphatic vessels arise ? Describe
their structure. Are they found in every part of the body ,.5 What are
the agents of digestive absorption ? Describe the lacteals. What is
chyle? Does it exist ready formed in chyme$ What changes does
it undergo in its passage to the heart ? Where are the chyliferous

ABSORPTION. 297

vessels chiefly found ? Are alimentary substances absorbed without be.
ing previously changed into chyle $-:^ Is alcohol digested T^Are medi-
cinal substances absorbed ?; How is this proved ? Does absorption take
place from the skin T,»: What is interstitial absorption? What is ema-
ciation owing to ? — plethora ? Are foreign bodies absorbed when in-
troduced into the substance of organs tj , --Are the bones ever absorbed 1) *
What is respiratory absorption ? What is recrementitial absorption ?
What excrementitial ? Are these processes always going on I., What
peculiarity is there in the lymphatic system of frogs ?

CHAPTER XXIII.

NUTRITION.

1. NUTRITION may be considered as (the completion of
the functions of digestion.) It is that process by which the
waste of the organs is repaired, and by which their develop-
ment and growth are maintained. Respiration, digestion,
circulation, absorption, and secretion, are but separate links
in the chain of nutrition ; which would be instantly de-
stroyed by the absence of any one of them.

2. In the construction of a machine, or an instrument,
designed to last for many years, Ihe mechanist seeks for^the
most durable materials.} In making a watch, for instance,
he forms the wheels of brass, the spring and barrel-chain of
steel, and for the pivot, which is subject to incessant friction,
he employs the hardest of all materials — the diamond. The
necessity for this arises from the fact, tha^such instruments
do not contain, within themselves, the power of repairing
their own lossesj

3. But far different is the case with the animal machine.
fin order to qualify it for exercising the functions of life, it

must be so constructed as to render it capable of continual
alterations, displacements and adjustments ; and these sub-
ject to continual variation, according to the stage of growth,
and also to the different circumstances in which it may be
placed j Instead, therefore, of a few elementary bodies, or
their simpler combinations, nature has employed such com-
pounds as admit of greater change, and a more variable
proportion of ingredients, and greater diversity in the mode
of combination. It is nutrition that moulds these plastic
materials, and forms these ever-changing compounds ; and
so preserves the animal machine, amid all the varying
changes of condition to which it is subject.

NUTRITION. 299

4. No one can doubt that the system is continually un-
dergoing changes. vThis is proved by the losses to which it
is subjected ; by the necessity of frequent supplies of ali-
ment ; by the rapid wasting of flesh on the withdrawal of
food ; and by the emaciation caused by sickness and old age.
It is also shewn by an experiment, which has often been
made, viz. of giving madder to animals mixed with their
food ; which in a short time tinges their bones of a red
colour. If the madder be withdrawn, the red colour in a few
days disappears from the bones ; evidently from the effects
of absorption^

5. Every part of the body is subject to this constant
change of matter. While one set of vessels, the lympha-
tics, are taking to pieces and carrying away the various
oarts of which the machine is composed, another set, viz.,
|He capillaries, are constantly at work, repairing the loss,]
depositing bone, muscle, cartilage, nerve, tendon, fat, mem.
brane, ligament, hair, nails, <Szc. where each is wanted, and
this with such regularity and order, as to preserve the shape,
size, and appearance of every organ, so that, though after an
interval of a few years there may not remain in the body a
single particle of which, at the former period, it was made
up ; still, the individual preserves the same form and features ;
his personal identity is never lost.

6. [Those animals, which are the most complicated in
their structure, and are distinguished by the greatest variety
of vital manifestationsjare subject to the most rapid changes
of matter. Such animals require more frequent, and more
abundant supplies of food, and in proportion as they are ex-
posed to a greater number of external impressions, so will
be the rapidity in this change of matter. The frog, for in-
stance, has been dug from the earth many feet below its sur-
face ; and even taken from cavities in solid limestone, where
he had been shut up probably for centuries, and still exhibit-
ed signs of life when exposed to the open air. As he was so
situated as to lose nothing, by secretion or evaporation, of

300 PHYSIOLOGY.

course he required nothing to supply any loss, but how the
vital principle was preserved for such a length of time, is a
mystery not easy to be explained.

7. \phe blood contains all the materials of nutrition.) The
process by which the food is changed into blood has been al-
ready explained. As it goes the round of circulation, the
nutrient capillary vessels select and secrete those parts which
are similar to the nature of the structure, and the other por-
tions pass on ; so that every tissue takes up and converts to
its own use the very principles which it requires for its
growth ; or in other words, as the vital current approaches
each organ, the particles appropriate to it, feel its attractive
force ; obey it ; quit the stream ; mingle with the substance
of its tissue, and are changed into its own true and proper
nature.

8. (Before the body has attained its full growth, \he func-
tion or nutrition is very active ; a large amount of food is
taken, being not only sufficient to supply the place of what
is lost by the action of the absorbents, but also to contribute
to the growth of the body. In middle age, nutrition and ab-
sorption are more equal ; but (In old age the absorbents are
more active than the nutrient vessels); /the size consequently
diminishes ; the parts grow weaker ; the bones more brittle ;
the body bends forward ; and every function exhibits marks
of decay and dissolution)

9. A few years ago, a man by the name of Calvin Edson,
of Vermont, commonly called the living skeleton, exhibited
himself through the country for money. From having been
a large man, he had wasted away by degrees, so that instead
of his usual weight, he weighed but sixty pounds. He had
been gradually losing flesh for eighteen years ; and he attri-
buted it to having taken cold from sleeping on the ground.
This emaciation was owing to the absorbent vessels being
more active than those of nutrition ; whatever may have
been the cause of the loss of balance.

NUTRITION. 301

10. On the other hand, when the nutrient vessels are the
most active, the person grows fleshy and corpulent, as in the
case of Daniel Lambert, who weighed seven hundred and
thirty-nine pounds at the age of forty ; or in that of a Lon-
don butcher, who weighed eight hundred pounds. There are
several cases on record, where men weighed eight hundred
pounds.

11. (The degree of nutrition, depends much on the quanti-
ty and quality of the foody A person who confines himself
chiefly to animal diet, and drinks freely of ale and other malt
liquors, will usually grow fat ; but this does not indicate
strength but weakness. \.t shows that there is not only a
weakness of the absorbents, which are not ab'e to take up
and remove the fat ; but also a muscular debility, and a want
of force in the circulation. Motion is impeded ; the heart
is loaded and oppressed ; the breathing is laborious ; the
blood accumulates in the brain, and the person is every mo-
ment exposed to apoplexy.) In all such cases, a sparing diet
of vegetables, with proper exercise, will prove an effectual
remedy. By sweating, horse-riding, and a«Jow diet, jockeys
have not unfrequently reduced themselves 15 or 20 pounds,
in a week or ten days.

12. Large accumulations of fat, it is said, sometimes take
place, as the sudden effect of the influence of the atmosphere.
Thus, in the short space of twenty-four hours, it is stated by
writers on natural history, that a mist will occasionally fatten
thrushes, robins, &c., to such a degree, than they can hard-
ly get out of the way of the sportsman's gun. This however
is not fat, but the appearance is owing to a fulness of the
vessels, from a suspension of evaporation.

13. The hump of the camel appearsfto form a sort of re-
serve, by which, the Arabs say, he is nourished, during his
long journeys.^ In a period of plenty, the rapid secretion of
fat converts it into a pyramid, equalling a fourth of the ani-
mal's entire bulk ; but a journey through the desert gradual-
ly lowers it, so that it becomes scarcely visible. The camel

26

302 PHYSIOLOGY.

then gives out, and can travel no further till the store is re-
plenished by rest and food.*

14. (Tumours, wens, and other morbid growths are the con-
sequence of an error in nutrition^) The nutritious vessels de-
posite/oJ where it is not wanted, and occasionally bony mat-
ter, where fibrin should be left or something else. In this
way only can we account for the bony concretions and
scales which are sometimes met with about the heart and
blood-vessels ; for the chalky deposits about the joints, in
cases of gout and rheumatism, and even for horny projec.
tions, which have in a few cases been known to sprout out
from the head. A few years ago, there were exhibited in
London, several individuals called the porcupine family, who
were all covered with dark colored horny excrescences ; which
they shed annually in the autumn or winter. These curious
organic peculiarities, resembled the quills of the porcupine,
and were two or three inches in length. But these are only
exceptions to the usual regularity of nature's operations, and
ought, instead of lessening, to increase our admiration at the
admirable symmetry and uniformity that prevail, through
every department of organized being.

15. (The activity of muscular nutrition, depends much on
exercise) The arm of a blacksmith, or a stone-cutter, for
instance, is generally large and brawny, because their mus-
cles are almost in constant use. The same is true of the
muscles of the leg, in rope-dancers and tumblers, also in
great walkers. Let any one examine the muscles of the Ra-
vel Family, so celebrated for strength and agility in all gym-
nastic exercises, and he will find them not only unusually de-
veloped, but also hard and firm. If a person meet with an
accident so that he is unable to walk, although his appetite
remains, his muscles dwindle away for want of exercise. If
then, a person who leads a sedentary life be corpulent, the
excess is not to be considered sound muscle or flesh, but fat,
which, I have before stated, is a sign of weakness.

* Burkhardt's travels.

NUTRITION. 303

Questions. — What is nutrition ? What is sought for in constructing
a machine ? Why the necessity for this ? How is it in the animal
machine ? Is the system constantly undergoing changes t^ How is
this shown ? What vessels repair the losses of the system ? What ani-
mals are subject to the most rapid changes of matter ? What contains
the materials of nutrition ? When is nutrition most active ? — when
least so ? What is the consequence ? What does the degree of nutri-
tion depend on ? Does fatness indicate strength ff Why not ? What
use does the hump of the camel serve ? What are tumours and wens
owing to ? What causes muscular nutrition ?

CHAPTER XXIV.

ANIMAL HEAT.

1. ^Calorification, is a function of animal bodies, not yet
thoroughly understood.) We see certain phenomena, but the
causes are hidden from our view. It is very doubtful wheth-
er we shall ever be able to penetrate the veil which con-
ceals the wonderful operations of vital chemistry ; and per-
haps it would lead to no useful result if we could ; should
we ever attain to the knowledge of all the natural laws of
life, we shall then be assured that it is only in consequence
of their violation that man pays, by suffering, sickness and
premature death, the penalty of their transgression.

2. What causes the temperature of the body to be main-
tained at an average of ninety -eight degrees, and this, too,
under all climates, and at all seasons ? \In the first place,
respiration is much concerned in the production of animal
heat.) It was once indeed believed, that the chief office of
respiration was to cool the blood ; and that the heart was the
great furnace of the system, where all the heat was pro-
duced.

3. (When it was discovered that both in combustion and
respiration, carbonic acid was produced, and oxygen ab-
sorbed, it was at once surmised, that breathing must be a kind
of combustion by which all the heat of the body is generat-
ed.^ But it was objected to this, (that if the heat was all pro-
duced in the lungs, why were not the lungs hotter than the
other parts of the body^)as those parts of a stove in contact
with the fuel, are hotter than those at a distance.

4. This objection to Mr. Black's hypothesis, led Mr.
Crawford to propose the following solution. Although ani-
mal heat is produced in the lungs by the process of respira-
tion, yet as arterial blood has a greater capacity for caloric

ANIMAL HEAT. 305

than venous, that is, requires more caloric to preserve it at
the same temperature, the heat becomes latent in saturating
this increased capacity of arterial blood ; and is gradually
given off in every part of the body, as the blood assumes the
venous character./ But unfortunately for this theory, it has
been ascertained that there is no difference, and that arterial
and venous blood have an equal capacity for heat.

5. But however it may be explained, no one can doubt,
that calorification is closely connected with respiration. If
the latter is increased by any cause, the heat of the body is
also increased. When it is impeded, as in asthma, fainting,
breathing deleterious gases, and suffocationf the animal heat
is sensibly diminished J Those animals whose respiratory ap-
paratus is the most perfect and the best developed, have the
highest temperature, as we see in birds, whose bodies are sev-
eral degrees warmer than the human species.

6. On the contrary, if we look at the cold-blooded ani-
mals, we shall find that a large proportion of them live in
water, where the supply of oxygen is but scanty, and that
their respiration is very imperfect); while in animals that
lie torpid during the winter, and are quite cold, respiration
is almost if not quite suspended. According to Majendie,
respiration produces (jour-fifths of the heat in herbivorous
animals ;){ three-fourths in carniverous, and the same in
birds.)

7. It is found by experiment, that arterial blood is warmer
than venous. \The blood is found to acquire one degree of
heat in passing through the lungs, and as the whole mass
of the blood passes through the lungs twenty times an hour,
it follows, that the system receives from respiration twenty
degrees of heat in an hour, or two hundred and forty degrees
every twelve hours! Respiration, then, is one of the chief
sources of animal neat.

8. Another theory in relation to animal heat is, that it is
produced by, or (depends on, nervous influence.! This is

26*

306 PHYSIOLOGY.

supported by a few experiments of Mr. Brodie,(who kept up
artificial respiration in animals after cutting off their heads.
He found that, notwithstanding, the usual changes took
place in the blood, and in the air introduced into the lungs,
yet the temperature fell even faster than in another animal
killed at the same time, in which respiration wae not kept
UD.J This experiment, however, is not conclusive, as an ani-
mal may be cooled by forcing too much air into the lungs ;
and if less be introduced the heat may be preserved for some
time.

9. Another theory is, that animal heat is generated in
the capillary system. /This is supported by the fact, that
some parts of the body are often hotter than others, as in
inflammation ; that it is always proportioned to the ener-
getic action of any organ, as the head becomes hotter by
hard study ; and; a glass of spirits excites a feeling of warmth
in the stomach./

10. ftt may be laid down as an axiom, or admitted truth,
that all movements among the particles 'of bodies which
cause a change of state, are attended with change of tem-
perature) This is the case in combustion, which is a
union of oxygen with the inflammable body, and the
production of carbonic acid ; and so also when two liquids
are mixed together, which chemically unite, heat is always
evolved. Now, in all the processes of nutrition, secretion,
digestion, respiration, &c., such changes are constantly
going on. In respiration, a part of the blood is thrown off
in a gaseous form, while a quantity of oxygen unites with
the remaining portion. This process, according to all the
known laws of caloric, must be attended with an elevation
of temperature. And this proves to be the fact.

11. By the function of nutrition, fluids are changed into
solids ; and by absorption, solids are changed into .fluids ; by
secretion, new chemical compounds are formed out of a few
simple elements contained in the blood ; and by digestion, a

ANIMAL HEAT. 307

new fluid, chyle, is formed out of the solids, which constitute
the food. By all these processes, animal heat must necessa-
rily be generated.

12. But in order to the production of animal heat, by the
action of the capillary vessels, two conditions are necessary.
(One is, the presence of arterial blood ; the other, the action
of the nervous system) £That arterial blood is necessary, is
shown by the operation of tying the vessels which supply a
limb with blood. } The consequence always is, that the tem-
perature immediately falls, and such limbs have to be wrap-
ped in cotton, and other means used to preserve a comforta-
ble degree of warmth. jThat nervous influence is also
productive of animal hea£ is shown by dividing, in like
manner, the nerves which go to any part.) The temperature
of a paralytic limb is always lower than that of the sound
one.

13.( It may be concluded then, that respiration, circula-
tion, and nervous influence^ all co-operate in producing
animal heat, or that they are conditions essential to this
phenomenon. We here also perceive a circle of actions ;
or a chain, composed of many links, no one of which can
be spared. Each one contributes to a result essential to
organic existence, and one of the most curious and wonder-
ful which the mind can contemplate.

14. If these principles be correct, we should expect to
find the greatest heat in those animals whose structure is
the most complex ; whose organic or vital actions are the
most intense ; and whose changes are the most rapid. Now
all these conditions belong to the warm-blooded animals es-
pecially, and particularly to (birds, j whose temperature
exceeds, by several degrees, thai of man. In them, as I
have already stated&respiration is more perfect, and the cir-
culation more rapid\

15. Upon the same principles, it would also follow, that
animal heat would be the higli3st in those portions of the
bodj/where the organic actions are most active^ And such

308 PHYSIOLOGY.

is actually the case. If a thermometer be placed oven the
chest, the stomach, or the liverjjit will indicate a higher
temperature by some degrees than exists in the extremities,
because it is near the seat of respiration, digestion, and the
largest secretory organ in the body. The temperature of
different parts of the animal body ranges from 91 to 100
degrees ; and in fever to 112, which is marked "fever heat"
on the thermometer.

16. Those animals that belong to the class mammalia,
and which livg in water, such as the whale, the dolphin, and
the porpoise/ have a temperature as high as that of manj
Captain Scoresby found the temperature of a whale, in the
Arctic Ocean, to be 104 degrees ; while that of the polar
bear and wolf were no greater. Warm-blooded animals are
generally covered with hair or feathers, to protect them
from the cold ; cold-blooded animals need no protection, as
they can live in a temperature as low as the freezing point
of water. Seals, bears and walruses in the Northern Ocean,
are protected by a coating of hair ; the whale is protected
by the great thickness of its skin and the stratum of fat im-
mediately beneath it. Dr. Edwards states that frogs, which
can live in water at 32 degrees, will die in a short time in
water at 105 degrees.

17. But this does not seem to be the case in all cold-
blooded animals. In some of the warm springs in Brazil,
which have a temperature of 88, many small fishes are
found; and also in a hot spring at the Manillas, which
raises the thermometer to 158 degrees ; and Humboldt, in
his travels, tells us that in the province of Quito, in South
America, he saw fishes thrown up from the bottom of a vol-
cano, along with water and heated vapour, which raised the
thermometer to 210, or only two degrees short of the boiling
point. Lord Bute saw beetles in the boiling springs of Al-
bano, which died when plunged into cold water ; and Dr.
Elliotson states that a gentleman of his acquaintance boiled
some honeycomb two years old, and after extracting all the

ANIMAL HEAT. 309

honey, threw the refuse into a stable, which was soon filled
with bees.

18. Warm-blooded animals have the faculty of preserv-
ing the same degree of heat in nearly every variety of cli-
mate. During Captain Parry's voyage to the Arctic seas,
in quest of the northwest passage, the crews of his vessels
were often exposed to a temperature of fifty degrees below
zero, or one hundred and fifty degrees below that of their
own bodies, and still they were able to resist it, and escape
being frost bitten. When the temperature was thirty-two
degrees below zero, they found that of an Arctic fox one
hundred and six degrees, which shows what a strong coun-
teracting energy there is in animals, against the effects of
cold.

19. The human body can also resist great heat as well as
cold. In summer we are often exposed, when in the sun, to
a temperature many degrees above that of the body, but the
heat of the body is not elevated. Chantry, the sculptor,
often entered his furnace when heated for drying his moulds,
when the thermometer in it stood at three hundred and
twenty ; and his workmen did the same when the tempera-
ture was three hundred and forty degrees. Dunglison
states that Chabert entered an oven with impunity, the
heat of which was from four hundred to six hundred de-
grees. In all these cases, where even water was boiled, and
meat cooked to a crisp, the heat of the body was raised but
a few degrees.

20. In these cases the heat of the body is kept down to
near the natural standard, by exhalation, or sweating. This
carries off the heat in a state of vapour as fast as it is pro-
duced. For the same reason, water cannot be heated above
two hundred and twelve degrees, as it then escapes in the
form of vapour. By evaporation, also, bottles of wine are
cooled in summer, by wrapping them round with wet
cloths. In India, it is said, that ice is produced in a simi-
lar manner. If an animal be saturated with moisture, and

310 PHYSIOLOGY.

placed in a hot oven, it soon dies, because the exhalation
from the body is prevented. It is for this reason, also, that
we feel the heat more in damp weather than in dry, although
the temperature be lower. Such weather is called sultry,
close, muggy, <$>c., because the saturation of the air by
moisture, prevents the escape of heat by evaporation from
our bodies.

21. In infancy, the faculty of generating animal heat is
much less than in adult age. This is the chief cause why
so many perish during the first years of life, and particular-
ly in winter, during the first few days. At this ^period, the
temperature of infants is only about ninety-three degrees,
and in some instances not more than eighty, and is rapidly
diminished by slight exposures. This shows the great im-
portance of guarding against the effect of cold, by proper
clothing, and a regulated temperature of houses. Man
has no natural protection against the influence of cold, but
reason was given him as a substitute. How few appear
to employ this faculty, in guarding against atmospheric
vicissitudes by a proper adaptation of the dress ; and in
consequence, how many, instead of consulting their health,
comfort, and usefulness, fall victims to negligence or fashion !

Questions. — What is calorification ? What are the causes of animal
heat ? Why was it surmised that respiration was concerned in this
process ? What objections to this ? What was Crawford's hypothesis ?
What occurs when respiration is impeded? What occurs in cold-
blooded animals ? How much heat, according to Magendie, is produced
by respiration in herbiverous animals ? — in carniverous ? — in birds 7^^-
Is arterial blood warmer than venous £> -.How much heat does the blood
acquire in passing through the lungs ? Hqw many degrees does the
system acquire from this source in 24 hours ^ '• What is Brodie's theory
with respect to animal heat ? What facts in favour of it ? What is
said of animal heat being generated in the capillary system ? What
axiom in relation to a change in the particles of bodies has a bearing
on this subject ? What conditions are necessary to the production of
animal heat by the action of the capillaries ? How is this proved ?

ANIMAL HEAT.

311

What functions co-operate in the production of animal heat ? In what
animals is heat the greatest ? Why ? In what parts of the body is it
the highest ? Why ? What is the temperature of the mammalia that
live in water ? What effect does a change of temperature have on
cold-blooded animals ? Can warm-blooded animals preserve the same
temperature in every climate ^HHow is this effected ? What effect
will checking evaporation hive ? Is the faculty of generating heat
less in infancy % What inference do we draw from this fact ?

"•«•*&

OF THE

n

CHAPTER XXV.

THE VOICE.

1. [The voice is a sound produced in the larynx, or wind-
pipe, by the passage of air, either to or from the lungsJ It
is generally caused in the act of respiration, and(its seat is
the larynx) which forms the very top of the wind-pipe, and
externally makes that prominence at the fore-part of the
neck, called Adam's apple. It is connected above with the
bone of the throat, by means of small muscles, and behind
with the esophagus, or passage to the stomach.

2. ^The larynx is composed of four cartilages, closely con-
nected by membranes ; these are called the thyroid, the cri-
coid, and the two arytenoid cartilages. The thyroid cartilage
is shaped somewhat like a shield, and hence its nam^J It
forms the front and lateral part of the larynx, being broader
in front than behind, and made up of two parts whictf join
in the front of the neck at an acute angle^f thus making the
prominence spoken of above, (it has two projections above,
and two below ; the former connect it with the bone of the
tongue, and are called the upper horns ; by the latter which
are called the lower horns, it is united with the cricoid carti-
lage, by means of ligamentsy

3. The cricoid cartilage is so called from its resemblance
to a ring. ^It lies immediately below the thyroid cartilage,
being broad at its sides, narrow in front, and connected with
the thyroid cartilage behind by a still broader surface 1 In
front it is not connected with the thyroid cartilage ; but the
space is occupied by the lining membrane of the larynx,
covered with the common integuments.

4. (The aryt.enoid cartilages are much smaller than the oth-
ers, and are situated at the back part of the larynx, in con-
nection with the cricoid cartilage.)) (They have small mus-

THE VOICE. 313

eles attached to them, by which they are moved sideways,
and it is by these motions that the opening in the larynx,
called the glottis, is enlarged or contracted/? Two fibrous
ligaments connect these cartilages with the thyroid ; these
two are called vocal chords, as they are supposed to be
particularly concerned in the production of voice. They
pass from the artenoid cartilages to the angle formed by the
two side pieces of the thyroid, and are about half an inch in
length. The opening between them is called glottis, rima~
glottidis, or chink of the glottis.

5. JThe epiglottis is the little moveable cartilage ; which
lies over the top of the wind-pipe, at the root of the tongue,
and has been compared to a trap-door^ It prevents the food
from passing into the wind-pipe when we swallow. From
its elasticity, its position is usually perpendicular, except in
the very act of swallowing, when the tongue is carried back-
wards, so as to bring it exactly over the opening ; this pre-
vents the passage of foreign bodies into the lungs.

6. The larynx is abundantly supplied with nerves which
are given off from the eighth pair. \The thyroid gland is a
body consisting of two lobes, lying one on each side, and
somewhat below the larynx^ the use of which is unknown ;/
it is the seat of the disease called goitre, or(swelled neck} so
common in Switzerland, and some other countries.

7. Such is the description of the organs immediately con-
cerned in the voice ; (the whole vocal apparatus, however,
comprises the muscles concerned in breathing, the mouth,
and nasal cavities, as well as the parts above mentioned.; It
is essential to the production of voice that the air should
pass from the lungs through the larynx ; for if an opening
be made in the wind. pipe, so that the air escapes, the voice
is lost. I lately witnessed this in a man who undertook to
destroy his life by cutting his throat. He succeeded in cut-
ting the wind-pipe completely off, but as no large blood ves-
sels were divided, he got well. This man could not utter a

27

314 PHYSIOLOGY.

syllable, not even in a whisper, until the wind-pipe healed
up ; his voice was then restored to its former condition.

8. Volition is necessary to the production of voice. If
the nerves going to the larynx are cut^ the voice will be
lost.A Palsy of the muscles of the larynx, also causes dumb-
ness ; and fear effects the voice by paralyzing muscular ef-
fort. The epiglottis is found not to be concerned in the pro-
duction of the voice, as it may be removed without affecting
it ; its sole office being to guard the wind-pipe against the in-
troduction of foreign substances.

9. It has been proved by experiments, that mearly all the
larynx except the chorda vocales, or vocal chords, may be
removed without destroying the voice.} These are the small
ligaments that pass from the arytenoid cartilages to the thy-
roid cartilages, and are usually called the inferior ligaments,
or the lower vocal chords.

10. \It is now ascertained that these chords perform the
principal part in the production of the voice.^ In what way
this is done, is not precisely known ; but, we may suppose
that the air in passing from the lungs in expiration, is forced
out of small cavities, as the air-cells and minute branches of
the wind-pipe, into the main channel ; it it is thence sent
through a narrow passage, on each side of which is a vibra-
tory chord ; the vibrations of which, by the action of the air
produces voice or sound.

11. It has been said that if this theory of the voice be cor-
rect, there ought to be sound produced by forcing air through
the wind-pipe of a dead animal. But this takes for granted
what is not true, namely, that the voice is the result of a
purely mechanical process ; instead of which, it is a vital
function, performed by living agents, and therefore under
the control of voluntary action.

12. In producing sound, there can be no doubt that nume-
rous Toluntary muscles are put in action, bringing the ary-
tenoid cartilages in contact with each other, thus putting
upon the stretch the lower vocal chords which are attached

THE VOICE. 315

to them. It is therefore by no means strange that vocal
sound cannot be made by forcing air through the larynx of
a dead animal.

13. It has often been disputed whether the larynx was a
wind or stringed instrument. Most physiologists at the pre-
sent time, regard it as a wind instrument of the reed kind,
such as the clarionet, hautboy, &c., and they differ chiefly
in explaining the various modifications of the tone and qua-
lity of the voice) There is, however, great reason to believe
that it partakes of the character of both.

14. ^The strength of the voice depends on the extent of the
vibrations, of course on the size of the larynx, and partly
also on the force with which the air is sent from the lungs)
Thus the voice of men is much stronger than that of wo-
men and children ; and that of a well person stronger than
that of a feeble individual. The change of voice at the pe.
riod of manhood, is owing \o the increase in size of the la-

15.1 The tone of the voice can be almost infinitely varied :
indeecf, nothing can exceed the human organ of voice in va-
riety and execution. We may perhaps safely calculate the
number of changes that can be produced in the organ, at
least to*be equal to the number of muscles employed, togeth-
er with all the combinations of which they are capable.^
Now, the muscles immediately concerned in the function of
voice su'^seven pair. Besides these, however, there are fif-
teen other pair, which are connected with the larynx, and
have more or less to do in regulating the motions of the car-
tilages, keeping them steady or moving them in different di-
rections]

16. Now, if there were only seven pair of muscles con-
cerned, the different movements which their varied action
would produce, will amount to more than sixteen thousand.
Taking the whole number of muscles into account, the dif-
ferent combinations will be more thanQww thousand million^
But besides these, there are the midriff^ or diaphragm, the ab-

318 PHYSIOLOGY.

What does the whole vocal apparatus comprise ? What is essential
to the production of voice ? What effect has cutting the nerves which
go to the larynx ? What part of the larynx can be removed without
effecting the voice ? What are chiefly concerned in the production of

voice ? Is the larynx a wind or stringed instrument ? What does the
strength of the voice depend on ? What is a change of voice owing
to ? What is said of the tone of the voice ? How many muscles are con-
cerned ? How many combinations can they produce ? How are acute
sounds produced ? How grave ones ? What is ventriloquism ? What
is natural voice ? What acquired ? Why are deaf children dumb ?
Why are idiots ? What is whistling ? — whispering ? — sighing, &c.1
What is said of singing ?

CHAPTER XXVI.

LOCOMOTION AND ITS ORGANS.

\f MAN is distinguished from the vegetable world, not
only by his possessing a nervous system, organs of sense,
and voice, but also by the power of locomotion) or (nioving
from place to place^) QThis power connects mm with the
external world, enlarges his sphere of action and increases
his means of acquiring knowledge. It implies that he has
a will, and that these motive organs are under the influence
of volition •) else he would be the sport of chance and wan-
der about without a motive)

2. Many of the functions of the body are not under the
control of the will ; such are/ digestion, absorption, circula-
tion, respiration, and secretion J which go on as well when
we are asleep as when awake. 'They are possessed, at least
some of them, by vegetables as well as animals, and are
therefore called organic functions.

3. The agents of locomotion are th/ bones and muscles $
but they would be useless for motion were they not suppliecf
with nerves of voluntary motion, and thus brought under
the influence of the will. The bones are tied together by
means of strong fibrous ligaments or cords, allowing the
joints great freedom and extent of motion, as we see in the
shoulder and hip joints.

4. We then have the bones, which act as levers ; the
muscles are the moving power, and the brain and nerves
are the vital agents, which set the machinery in motion.
(Muscles alone have the power of contraction^and it is one
of the most remarkable properties of life. Were it not for
this, the food could not be digested, the blood could not be

320 PHYSIOLOGY.

circulated, and the iris could not guard the eye against the
admission of too much light, which would speedily destroy
the vision.

5. The shape of muscles is various/some are round, some
flat, and the fibres of which they are composed, are con-
nected by means of cellular membrane. Some are penni-
form, or made of bundles of fibres, diverging from a central
line, like the feathers of a quilly Muscles compose a large
part of the bulk of the body ; and when they contract, the
fibres shorten and become harder, as may easily be perceived
by placing one hand on the middle of the arm and bending
the elbow, or on the temple and closing firmly the lower
jaw.

6. The force with which a muscle contracts^aepends on
the physical condition of the muscle and the entergy of the
brain^ When the fibres of the muscle are large and firm,
they will contract with more force than when they are small,
soft, and delicate. We see some persons, who labour under
great mental excitement, perform astonishing feats of
strength, although, perhaps, they may not have muscles of
the ordinary size.

7. |lhe knee-pan has often been split in two by the con-
traction of the muscles of the leg ; a horse has been known
to break its under jaw by biting a piece of iron. Men have
been known to lift eight and nine hundred pounds weight ;
to break ropes two inches in circumference, and to bend a
round piece of iron, a yard long, and three inches in circum-
ference, to a right angle, by striking it across the left arm,
between the shoulder and the wrist, with the right handy*

8. The force of muscular contraction is greatly increased
\by exercise.} The strength of an active man labouring to

the greatest possible advantage, is estimatedfto be sufficient
to raise ten pounds, ten feet in a second, for ten hours in a
dayV or to raise one hundred pounds, one foot in a second,

* Sec Dunglison's Physiology.

LOCOMOTION AND ITS ORGANS. 321

or thirty-six thousand feet in a day ; or three millions, six
hundred thousand pounds, or four hundred and thirty-two
thousand gallons, one foot in a day. The weakest men in
health can generally lift about one hundred and twenty-five
pounds, and the strongest of ordinary men four hundred
pounds. The daily work of a horse is equal to that of five
or six men.

9. There is much difference in the velocity of muscular
contraction, as it is regulated entirely by the will. The
swiftest race-horse on record was capable of going a mile in
a minute ; yet this is trifling compared with the velocity of
birds, or even of many small insects, fit has been ascer-
tained that a pigeon-hawk can fly one hundred miles in an
hour ; the eider-duck ninety miles an hour, and the common
crow, twenty-five miles an hour. The swallow flies ninety-
two miles an hour, and the swift is said to fly two hundred
and fifty miles in the same space of time\

10. A falcon belonging to Henry IV. of France, escaped
from Fontainbleau, and in twenty-four hours after was in
Malta, a distance of one thousand three hundred and fifty
miles, making a velocity of fifty-seven miles an hour, sup-
posing him to have been on the wing all the time ; but as
such birds do not fly by night, his flight was probably at the
rate of seventy-five miles per hour. This will give us some
idea of the wonderful velocity of the contractions of the
muscles of the wings of birds of rapid flight.

11. But this rapidity of motion is much under the influ-
ence of habit. How awkward are the first attempts at
writing, drawing, dancing, or playing on musical instru-
ments, and with what ease and grace are they performed
after a little practice. The same is true with regard to
public speaking, or any thing which requires voluntary mo-
tion, i

12. pt is a law of the human system; that relaxation must
follow contraction,^-or rest, exercise ; and although the du-
ration of action of the voluntary muscles is in a great de-

322 PHYSIOLOGY.

gree under the control of the will, yet it cannot be continued
long. This duration will be shorter in proportion as the
contraction is violent or moderate. f All muscles do not act
at the same time, for as some are contracting, such as the
flexors, or those that bend the limbs, the extensors, or those
that straighten them, are relaxed^

13 Pit is by the constant action of the musclesV that the
body is^kept in an erect position. If a person gets asleep
while sitting or standing up, the head 'falls forwards, and if
he did not wake, the body would fall likewise. The same
happens when a person is deprived of sense, by a fit of
apoplexy or palsy, or by the intemperate use of ardent
spirits.

14. We see that it requires a long time for children to
learn to walk securely. fThe reason is, that the base of sup-
port for the body is small $ being only the space between
the feet and that on which the feet rest. The larger the
base, the easier it is to maintain an erect position ; so that
persons with small feet do not stand as firmly as those with
large ones. This accounts for the difficulty of standing on
our toes, or of walking on a rope. It is practice and in-
stinct which teaches children where to place their feet in
order to be most secure when erect ; their muscles also are
still weak, for want of exercise.

15. Walking consists in a succession of steps. tWe first
balance the body on one foot, then bending the opposite foot
on the leg, and the leg on the thigh, we bend the thigh on
the pelvis, and so shorten the limb. In this way the leg is
brought forward, and the foot is then brought to the ground
resting first on the heel ; the body is then partially rotated
on the head of the thigh bone, and the other leg is raised,
bent, and carried forward in the same manner, and the foot
placed in advance of the other J The legs thus act as levers
to propel the body along, and the longer the levers the more
rapid will space be measured overA

16. The utility of walkingj'excels that of all other modee

LOCOMOTION AND ITS ORGANS. 323

^V

of progression J While the able pedestrian is independent
of stage coaclies and hired horses, he alone fully enjoys the
scenes through which he passes, and is free to dispose of his
time as he pleases. To counteract these advantages, greater
fatigue is doubtless attendant on walking ; but this fatigue
is really the result of previous inactivity ; for daily exercise,
gradually increased by rendering walking more easy and
agreeable, and inducing its more frequent practice, dimi-
nishes fatigue in such a degree, that very great distances
may be accomplished with pleasure, instead of painful exer-
tion.

17. The power of walking great distances, without fa-
tigue is unfortunately in this country a rare accomplish-
ment. A good walker will do six miles an hour, for one hour,
on a good road. If in good training, he may do twelve
miles in two hours. Eighteen miles in three hours have
been achieved, though rarely. At the rate of five miles an
hour, pedestrians of the first class will do forty miles in
eight hourgjjtnd perhaps fifty in ten. Captain Barclay
walked 180 miles without resting ; and also 1000 miles in
1000 successive hours.

18. {in the act of leaping, the whole body is raised from
the ground, and for a short time suspended in the air. It is
performed by bending the head upon the body, the body on
the thighs, these on the legs, and the legs on the feet. The
feet do not stand firmly on the ground, as in walking, but
the heel is raised, or perhaps slightly touches the ground.
The muscles are all in a state of flexion) They are sudden-
ly contracted at the same instant ; the consequence is, that
the feet are raised from the ground and carried forward, and
the body with them, until it is brought to the earth by the
force of gravitation!) (The distance passed over, is in pro-
portion to the power and suddenness with which the muscles
contract.^

19. The muscles which form the calf of the leg, act with
the greatest powef in leaping, tas they have to raise the whole

324 PHYSIOLOGY.

body. | Their (great strength is shown by raising the body
upon thV toes, together with a large additional weighty and
this power is not only owing to their great size, but also to
the manner in which they are inserted into the heel, thus
having the advantage of the long arm of a lever.

20. iThe muscular powers exhibited by many small ani-
mals and insects is astonishing. Small animals can leap
much farther than large ones, according to their size. The
flea and the locust leap two hundred times their own length,
as if a man should leap twelve hundred feet high. Others
leap three hundred times their length, and if man was as
strong in proportion, he ought to leap more than a quarter
of a mile. We read of an English mechanic, who made a
golden chain as long as the finger, with a lock and key,
which was dragged by a flea, and of another flea dragging
a silver cannon on wheels, that was twenty-four times its
own weight. This cannon was charged with powder and
fired without the flea seeming to be alarmed. A cockroach,
or an ant is six times as strong, for its size, as a horse ; and,
if an elephant were as strong in proportion, he would be
able to tear up rocks and level mountains]

21. popping is merely leaping on on/ foot. As but half
the muscular power is exerted, a man ought to be able to
leap twice as far as he can hop. Running consists of a
succession of low leaps, performed by each leg alternately./
It differs from walking, in the body being thrown forward at
each step, and the hind foot being raised before the fore foot
touches the ground. A person cannot stop running instant,
ly, as he can walking, because his velocity is so great as to
carry him forward a certain distance, whether he uses his
muscles or not, and thus occasions him to fall.

22. The practice of running may be carried to a great
degree of perfection. A quarter of a mile in a minute is
good running ; and a mile in four minutes, at four starts, is
excellent. A mile was perhaps never run in four minutes ;
but it has been done in four minutes and a half. A mile in

LOCOMOTION AND ITS ORGANS. 325

five minutes is called very good running ; two miles in ten
minutes is but rarely accomplished. Ten miles an hour is
done by all the best runners. Forty miles, in four hours
and three quarters has been done by one individual. Some
Indians, it is said, will run at this rate for several hours, but
it is very doubtful.

23. Swimming is very much like leaping ; at least the
same muscles are brought into action in the lower limbs)
While the hands are brought to a point before the head, the
legs are drawn up and suddenly extended, as in leaping. By
the resistance of the water, the body is projected forwards.
The hands are now carried, with a circular motion, the
palms being turned outwards, till they reach the sides of the
body, and thus the impulse through the water is kept up by
a constant succession of these movements. A boat is pro-
pelled on the same principle. Indeed the body may be coin-
pared to the boat itself, and the hands and feet to the oars.
A good swimmer ought to make three miles an hour.

24. The human body is very nearly of the same specific
gravity as water ; (that is, it is of the same weight as a body
of water of the same bulk^ Dr. Franklin says if a person
avoids struggling and plunging, he may lie on his back with
his mouth and face out of water, without difficulty, even if
he cannot swim. As swimming therefore, is a highly useful
art, and an agreeable and healthy exercise, it should be made
a necessary part of the education of boys.

25. The importance of gymnastic exercises will only be
questioned by those who are not aware that the health and
vigour of all the bodily organs depend on the proportioned
exercise of each. (Such exercises ensure the development
of all the locomotive organs ; and they prevent or correct
all the deformities to which those organs are liabl|. They
are the best calculated to produce strength and activity, and
to bestow invariable health. At the same time they confer
beauty of form, and contribute to impart an elegant air and
graceful manners.

28

CHAPTER XXVII.

THE TEETH.

1. (is the teeth are the only bones in the human frame
whicfc. are exposed to the immediate action of foreign bodies,
they mfrrit distinct and special consideration in this treatise
on the General Physiology of man) /^The most remarkable
fact in their history is, that unlike the other bones, the teeth
which make their appearance in infancy, are removed at the
age of seven or thereabouts, and another set come forward
to supply their places.)

2. /The first set called temporary teeth, are just twenty in
number, ten in each jaw. The two front teeth above and be-
low, are known as central incisors, because they serve to cut
the food. The teeth adjoining these are denominated lateral
incisors, next to which come the canine or dog teeth, of
which those in the upper jaw are called eye teeth. Back of
these at either extremity of each dental arch are two larger
teeth known as grinders from the fact that they operate like
mill-stones, in reducing the food to very minute particles in
preparation for quick and easy digestion^

3., 'The second or permanent set has twelve additional
teeth, six above and six below, making thirty-two in all.
The two next back of each eye tooth, are styled bicuspids,
because they terminate in two points ; and the four extreme
grinders are sometimes called wisdom teeth, because they do
not generally appear until the individual arrives at mature
age. Thus, there are twelve grinders or molar teeth in the
second set instead of eight as in the first set ; and there are
eight bicuspids which are not found among the temporary
teeth at all J

4. feach tooth consists of two distinct parts, called the
crown and root / the former being that portion which pro-

THE TEETH. 327

jecte from the gum into the cavity of the mouth, and the lat-
ter that which is buried in the socket. } The incisors, eye
teeth and bicuspids have one root each, the upper grinders
three and the lower grinders two. The roots of the wisdom
teeth are commonly compressed into one mass having little
or no divergency, and in rare instances the bicuspids have
two distinct fangs, while the upper molars have been known
to have four or five distinct roots.

5. {fevery human tooth is composed of two distinctly or-
ganised substances, namely the enamel covering the crown,
and the osseous or bony portion which constitutes the re-
remainder of the tooth.,) The osseous part is scarcely distin-
guishable from other bony structures excepting from its
greater density. The enamel on the contrary, is remarka-
ble for its extreme hardness resulting from its chrystaline
structure. It consists of needle-formed crystals, one ex-
tremity of which rests upon the bone beneath, while the
otheiys presented to the food.

6.( The teeth are found by chemical analysis to consist of
nearly the same elementary substances as the other bones ;
namely, phosphorus, lime, magnesia, soda, carbon, oxygen,
chlorine, gelatine and watery (As the teeth are a part of the
living system, they are supplied with nerves, blood vessels
and absorbents, not only by a central cavity extending from
the point of each root to the middle of the crown, but by a
membranous sheath enveloping the root called the periosteum,
as is true of the other bones.)

7. frhe teeth are firmly attached to the jaw or maxillary
bone, by means of sockets called alveoli^ fin case of extrac-
tion the alveoli yield to moderate pressure and suffer the
teeth to escape without any injury to the adjacent parts)^
and as soon as the teeth are removed the investigating bone
is sufficient to produce immediate absorbtion.

8. iThe first set of teeth begin to make their appearance
through the gums, between the sixth and eighth month} and
before the infant arrives at the thirtieth month all the teeth

328 PHYSIOLOGY.

have assumed their natural position. iThe second dentition
commences about the seventh year, and is commonly per-
fected before the fourteenth/ Yi % A.. * j (l ^utM^r-

9. V^Vhen the teeth are so rnucTr crowo'ed as to'disturo
their regular arrangement ; or when they press so hard upon
each other as to destroy the enamel, one or more should be
removed without delay. If this precaution should be ne-
glected, an unsightly mal-arrangement, or inevitable destruc-
tion of several of the teeth, will be the melancholy result.
The removal of a sound tooth causes very little pain com-
pared with the agony attending those which are suffered to
become diseased.

10. It is impossible, under ordinary circumstances, to
preserve the teeth for many years without keeping them
very clean. Food lodges between them at every meal, and
undergoes decomposition if not removed. A. substance, called
tartar, or salivary calculus, which is deposited from the
saliva, adheres to the teeth, becomes very hard, and finally
assumes a dark colour, if not constantly washed away with
a brush and water. If food be suffered to putrefy in spaces
between the teeth the process of mortification is extended to
the teeth themselves ; and if tartar collect in solid masses,
the teeth become loose in their sockets and are thus utterly
lost.

11. In order to keep the teeth and gums perfectly clean
and healthy, it is necessary to wash them with a stiff brush
and water several times in a day. No person of ordinary
neatness would consent to eat with knives, forks and spoons,
unless they were cleansed after every meal. The teeth are
more liable to accumulate filth than any of these domestic
utensils, and therefore need at least equally frequent washing.
In the morning, after each meal, and before retiring to rest,
are not too many times to purify the teeth with a brush and
water, and once in each week with good tooth powder.

12. The Dentifrice or Tooth Powder, which I would re.
commend in preference to all others which I have ever seen,

THE TEETH. 329

is composed of the following ingredients, well pulverised in
a mortar, and intimately mixed together :

Loaf sugar, half an ounce,

Cinnamon, half an ounce,

Gum Kino, quarter of an ounce,

Peruvian bark, three ounces,

Prepared chalk, six ounces,

Armenian Bole, five and a half ounces ;
making one pound avoirdupoise.

13. In addition to the above described dentifrice, every
person should be provided with a good tooth brush, which
should be laid aside as useless whenever it loses its stiffness
and elasticity. A piece of gloss-silk, well waxed, should be
employed to cleanse the open spaces between the teeth, inas-
much as these are not easily cleansed with the brush alone.
If tooth-picks are used at all, they should be made of wood
or quill, since those formed of any of the metals, particularly
of steel or iron, are quite too hard, and therefore destructive
to the teeth and gums.

14. If brushing the teeth and using the other methods of
keeping them in order as above described, should fail of
effecting the desired purpose, the assistance of the dentist
should be put in requisition. With his scaling instruments,
he can effectually remove every vestige of tartar, together
with any other impurities lodged upon the teeth. Above all,
abstain from the use of all kinds of powders and washes
which render the teeth white by chemical action. These
contain acid in one form or another, and are therefore de-
structive to the teeth.

15. Persons desirous of preserving their teeth in a sound
and healthy state for many years, should consult their gene-
ral health in all their habits of life, especially in relation to
food and drinks. Neither solid nor fluid aliment should be
taken into the mouth at either very high or very low tem-
perature, because sudden transitions from heat to cold, or
from cold to heat, are liable to crack the enamel of the teeth

28*

330 PHYSIOLOGY.

by unequal expansion and contraction, as is readily ascer-
tained by the assistance of the microscope. Teeth thus
injured, almost always decay in consequence of the exposure
of the bony substance of the tooth to the action of corro-
sive fluids.)

16. (There are three prevalent general causes of the de-
struction of human teeth, besides occasional accident : viz.
accumulation of tartar, ulceration of the fangs, and dental
gangrene/ Ulcers of the fangs extend to the alveoli or
sockets, which are also destroyed, together with the invest-
ing gum. The well informed dentist can best prescribe and
apply the proper remedies for all these forms of dental dis-
ease.

CHAPTER XXVIII.

SLEEP AND DEATH.

1. \SLEEP is the periodical and temporary suspension of
those functions that connect us with the external world.
Man is so constituted, that the functions of sensibility, vol-
untary motion, and the intellectual faculties cannot be in-
dulged for any length of time without fatigue. The nervous
energy, which seems essential to their exercise, becomes ex-
hausted ; the muscles can no longer contract ; the external
senses cannot receive impressions ; the brain, and conse-
quently the mind, becomes torpid ; and a person sinks into
a state of torpor and inaction, called sleep.

S.rThe approach of sleep is announced by an internal
sensation, termed drowsiness,} which gradually increases in
strength, till at length it becomes irresistible. Great languor
of the muscles and heaviness of the eyes are experienced ;
the sight yields first ; next the smell ; then the hearing ; and
lastly, the sense of touch ; while at the same time, all the
internal sensations, such as hunger and thirst, are no longer
felt. The will ceases to control the functions that are under
its influence, till finally all power of volition is wholly lost.
Respiration is still carried on, but chiefly by means of the
diaphragm, which is an involuntary muscle ; it is, however,
somewhat slower, as well as the circulation, than in the
waking condition. ,

3. During perfect sleepj the functions of the brain are en-
tirely suspended. In such a state, dreams do not happen ;
for as the brain is in a state of complete inaction, the intel-
iectual operations are consequently dormant. {When the
brain is not in a state of complete repose, objects and images
may float confusedly through the mindj which are often the
result of external impressions imperfectly perceived, as they
excite but an imperfect reaction in the brain.

332 PHYSIOLOGY.

4. /The organic or nutritial functions continue during
sleep, but with diminished energy.) The circulation and
respiration are not only slower, but digestion is retarded,
and secretion, nutrition, and calorification, are less active
than when awake. The temperature of the body is also
lowered during sleep, which may perhaps be owing to the
facts above mentioned.

5. \!The duration of sleep is influenced by a variety of
circumstances^ (The average time of ^regular, periodical
sleep, in adults, is from five to eight hourjf. Infants require
twice as much sleep as grown persons. The- quantity of
sleep required,/depends very much upon habi$ It is said of
Pichegru, one of Buonaparte's generals, that, for a whole
year, he had not more than one hour of sleep in twenty-four
hours. Buonaparte himself, when on active duty, seldom
slept more than three hours in twenty-four ; often but one
hour. Men of active minds, who are engaged in a series
of interesting employments, sleep much less than the lazy
and the listless. The intellectual and moral faculties seem
to require a longer period of repose than the functions of
voluntary motion.

6. Thoughfthe night is the proper season for sleep, owing
to the absence of light, diminished warmth, its comparative
stillness, as well as the exhaustion caused by the labours of
the day, yet some animals, which pursue their prey by night,
sleep during the day, as the cat, fox, wolf, otter, owl, and
bat. Hybernating animals sleep for several months during
the winter, such as the bear, hedge-hog, marmot, &c. Some
birds, also, such as bats and swallows, sleep during the win-
ter, or hybernate. During this state their temperature is di-
minished, their secretions nearly checked, their excretions
suppressed, their respiration slow, and scarcely perceptible,
their circulation very languid, and sensibility to external im-
pressions entirely suspended. The arterial blood of hyber-
nating animals, differs but little from venous blood.

7. Dreams are now considered by physiologists to be

SLEEP AND DEATH. 333

to an irregular action of the brain, in which the con-
trolling power of the will is lost, and the memory and the
imagination bear unlimited sway^ Indeed all the faculties
of the mind may be in exercise. The mind reasons, judges,
wills, and experiences all the various emotions. We seem
to hear, see, walk, talk, and perform the usual offices of rffe.
Sometimes the voluntary muscles are thrown into action,
and the dreamer moves, speaks, groans, cries, or sings ; but
the moment consciousness is roused, he is awake. Dreams,
therefore, have well been said to be " a portion of animal
life, escaping from the torpor in which the rest of it lies
buried."

8. Before the functions of the brain were understood,
(_dreams were regarded as supernatural^ and even now are
considered in this light by the ignorant and superstitious.
Mr. Baxter, as well as Bishop Newton divided them intent wo
kinds, good and evz7,j[because they believed that good and
evil spirits were concerned in their production, according as
one or the other obtained the ascendaricyj) It is supposed
that animals dream, especially the dog ; are they subject to
supernatural influence 1

9. /It is a singular circumstance in relation to our dreams,
that we mistake our ideas for actual perceptions, and sup-
pose that the train of images that passes through our minds,
represents scenes which really exist] rThis is doubtless owing
to the fact that, during sleep, the senses do not admit exter-
nal impressions, and of course we are unable to compare the
ideas that arise in our minds with sensible impressions, and
thus perceive the difference between them) Our only con.
sciousness consists in the images and ideas actually present
in the mind ; and it is therefore unavoidable that we should
believe that our ideas represent objects actually existing.

10. There is a kind of dreaming, in some cases of imper-
fect sleep, ^where the will retains its power over the muscles
of voluntary motion, while the external senses remain buried

334 PHYSIOLOGY.

in partial or complete repose. This is called somnambulism
or sleep-walking. j

11. Many remarkable cases of somnambulism have been
lately published, as the effects of animal magnetism ; but in
many of these, it is to be feared, credulity existed on one
side, and imposition was practised on the other. That som-
nambulism, or a state nearly similar, is brought about by the
practices of magnetizers in persons of acute sensibility, and
highly excitable nervous temperament, would seem scarcely
to admit of a doubt. Still, all such cases should be regarded
with great circumspection, and every means employed to
detect imposition and fraud.

12.\Somnambulism seems to differ from the waking state,
only in consciousness being absentJ The person appears to
enjoy the full exercise of all his faculties ; he can converse,
walk, sing, compose verses, and perform various operations ;
and yet in the waking state he has no recollection of what
has occurred. In this respect somnambulism differs from
dreaming, and resembles a morbid state ; indeed, it is a state
of disease analagous to trance, catalepsy, or epilepsy.

13. | A state, the reverse of somnambulism, is called incu-
bus, or nightmare. In this affection, a person feels a sense
of weight and suffocation, as if there was a heavy load on
his stomach or chest, and imagines that some frightful object
is seated there]. This is owing to some oppression of the
digestive, circulatory, and respiratory organs, most usually
occasioned by a late, hearty supper of indigestible food.

/Frightful dreams denote ill health; and are often caused by
\L- derangement of some important organ, as of the heart,
stomach, or liver, exciting the brain to sympathetic action.
To dream immediately on going to sleep, is always a mark
of disease.

14. There is still another state which bears a close resem-
blance to somnambulism, and this is termed revery, absence
of mind, or brown study. In this, the attention is so com-

SLEEP AND DEATH. 336

pletely riveted to some particular subject, that the person is
entirely insensible to the presence of surrounding objects.

15. One great object of education is to give the will power
over the attention.) The mind that cannot command this
faculty^is in a deplorable condition for all the higher pur-
poses of reflection and knowledge for which it is intende^l
Without it, perception exercises itself in vain ; the memory
can lay up no store of ideas ; the judgment draw forth no
comparisons ; the imagination must become blighted and
barren ; and in proportion as a person has no command
over his attention, in that degree must he be an idiot.

16. It is the will of Providence that all organized beings
must perish. For a while, life maintains a successful con-
flict with the chemical laws of matter ; but at length its re-
sistance becomes weaker and weaker, till, sooner or later,
those functions cease which have enabled us to withstand
the destructive influences by which we are surrounded.

17. (The duration of life varies, not only in the animal but
in the vegetable kingdom.) (As a general rule, where the
growth is slow, the period of decrease is proportionably
slow ; and where it is rapid, decay as rapidly supervenes^
The gourd that sprang up in a night, perished also in a
night.

18. ^There are two kinds of death, natural and accidental.)
Natural death, or that of old age, is caused by a gradual
decay and wearing out of all the organsjj£accidental death,
or such as is occasioned by accident, cuts off* existence pre-
maturelyy The natural period of life differs in different
individuals ^being influenced by a variety of circumstances ;
such as the original constitution ; habits of life ; and the
health of the locality where a person is situated?

19. \he natural period of life, has not materially differed
since the time of the floody " The days of our years," says
the Psalmist, " are threescore and ten ; and if by reason of
strength they be fourscore years, yet is their strength labour
and sorrow, for it is soon cut off and we fly away." This

33G PHYSIOLOGY.

description is as applicable now, as it was four thousand
years ago.

20. Those who die from old age are few ; being, in the
city of New York, but one in thirty-four. In New En-
gland, generally, the proportion is rather greater. The
mean duration of life in New York is but twenty.five years j
while the average rate of mortality, According to population,
is one in thirty-five) The diseases to which man is subject,
from the earliest fb the latest period of his existence, are
numerous, and many of them of a fatal character. Syden-
ham estimates that two thirds of mankind die of acute dis-
eases ; and that of the remaining, one third, or two ninths
of the whole, die of consumption, leaving only one ninth to
perish from other chronic maladies, and from pure old age.

20. As age approaches, the functions are all performed
with less energy. The teeth fall out, and their sockets are
absorbed ; respiration is not as readily accomplished ; the
valves of the heart, and the coats of many of the arteries
become changed into bone, thus obstructing the circulation,
and often causing an intermittent pulse j nutrition Ian-
guishes ; the senses are blunted ; animal heat diminishes, so
that warmer clothing is demanded ; the muscular system
loses its power, and the body bends forward ; the limbs totter,
the mental as well as corporeal faculties often fail ; and the
individual is reduced to second childhood, so well described
by Shakspeare.

" Last scene of all,

That ends this strange, eventful history,
Is second childishness, and mere oblivion ;
Sans teeth, Sans eyes, Sans taste, Sans everything."

As the other functions cease their office, sensibility gradual-
ly becomes extinct, and life almost imperceptibly takes its
flight.

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