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The American Science Series.,

BRIEFER COURSE.

ASTRONOMY. By Simon Newcomb, Supt. Amen-
can Nautical Almanac, and Edwakd S. Holden,
Director of the Washburn Observatory. $1.40.

THE HUMAN BODY. By H. Newell Martin,
Professor in the Johns Hopkins University. $1.50.

ZOOLOGY. By A. S. Packard, Jr., Professor of
Zoology and Geology in Brown University, Editor
of the American Naturalist. $1.40.

POLITICAL ECONOMY. By Francis A. Walker,
President Massachusetts Institute of Technology.

$1.50.

BOTANY. By C. E. Bessev, Professor in the Iowa
Agricultural College, and late Lecturer in the Uni-
versity of California. $1.35.

HENRY HOLT & CO., Publishers,

NEW YORK.

AMERICAN SCIENCE SERIES, BRIEFER COURSE

THE HUMAN BODY

ELEMENT A R Y TEXT-BOOK OF ANA TOMY,
PHYSIOLOGY AND HYGIENE

INCLUDING A SPECIAL ACCOUNT OF THE ACTION UPON THE

BODY OF ALCOHOL AND OTHER STIMULANTS

AND NARCOTICS

BY

H. NEWELL MARTIN, D.Sc., M.D., M.A., F.R.S.

Professor of Biology in the Jolms Hopkins University
FOURTH EDITION, REVISED

NEW YORK
HENRY HOLT AND COMPANY

1891

QP36

mi

Copyright, 1883, 1864,

BY

HENRY HOLT & OO.

WT .^

PREFACE.

This elementary textbook of Physiology has been pre-
pared in response to many requests for a textbook
framed on the same plan as the "Human Body," but
abridged for the use of students younger, or having less
time to give to the surject, than those for whom that book
was designed. This demand, and the fact that a second
edition of the " Human Body" was called for within twelve
months of its publication, have shown me that I was not
wrong in believing that the teachers of Elementary Physi-
ology in the United States were ready and anxious for a
textbook in which the subject was treated from a scientific
standpoint, and not presented merely as a set of facts,
useful to know, which pupils were to learn by heart like the
multiplication table.

That some instruction in at least one branch of Natural
Science should form a part of the regular educational cur-
riculum is now so generally admitted that there is no need
to insist upon it. But if this instruction simply means
teaching by rote certain facts, no matter how important
these facts may be, the proper function of Natural Science
in a system of education is missed. Mere training of the
memory (no unimportant matter) is otherwise sufficiently

iv PREFACE.

provided for in the usual school and college course of study:
the true use of Natural Science in general education is
different. It should prepare the student in another way
for the work of subsequent daily life, by training the ob-
serving and reasoning faculties.

As a department of science, modern Physiology is con-
trolled mainly by two leading generalisations — the doctrine
of the " Conservation of Energy" and that of the " Physio-
logical division of labor." I have endeavored in this, as in
the larger book, to keep prominent these leading principles ;
and, so far as is possible in an elementary book, to exhibit
the ascertained facts of Physiology as illustrations of or de-
ductions from them.

The anatomical and physiological facts which can be
described in books of the size of the present, must be pretty
much the same in all. Apart from the attempt above men-
tioned to make elementary Physiology a more useful edu-
cational instrument than it has frequently hitherto been,
the present volume differs from most others of its grade in
having, as foot-notes or as appendices to the chapters, simple
practical directions, assisting a teacher to demonstrate to
his class certain fundamental things. The demonstrations
and experiments described necessitate the infliction of pain
on no animal, and require the death of no creature higher
than a frog, except such superfluous kittens, puppies and
rats as would be killed in any case, and usually by methods
much less merciful than those prescribed in the following
pages. The practical directions are, for the most part,
reprints from a series of such which I drew up some years
ago for a class composed of Baltimore teachers; those ex-
periments which required costly apparatus have, of course,
been omitted. The interest which my "Teachers' Class"
took in its work, and the good use its members subsequently
made of it, have encouraged me to believe that others
might be glad of a few hints as to things suitable to show
to young students of Physiology.

PREFACE. V

It may be well to anticipate a possible objection. A few
persons, some of tbem worthy of respect, assert that no ex-
periments on an animal can be shown to a class without
hardening the hearts of operator and spectators; even when,
in accordance with the directions given in the following
pages, the animal is anaesthetised and while in that condi-
tion is killed or its brain destroyed. This from an experi-
ence of more than fifteen years in the teaching of practical
physiology, I know to be not so. So far as the experiments
described in the present book are concerned, their effect is
most certainly humanizing. Young people are apt to be,
not callous, but thoughtless as to the infliction of pain.
When they see their teacher take trouble to kill even a frog
painlessly, they have brought to their attention in a way
sure to impress them, the fact that the susceptibility of the
lower animals to pain is a reality, and its infliction some-
thing to be avoided whenever possible.

As the question of size is no unimportant one in
relation to textbooks designed for junior students with
many other subjects to learn, I may be permitted to say that
though tins volume contains more pages than most of those
with which it will have to compete, I believe it is not really
larger* The extra pages are due, in part to the above-
mentioned appendices to the chapters, and in part to the
great number and large size of the figures. My publishers
had on hand electrotypes of the figures of the octavo edi-
tion, and have been able to utilize them in illustrating this
briefer one much better than most textbooks of its scope,
without proportionately increasing its price.

If I had relied solely on my own judgment the ques-
tions at the foot of each page would have been omitted. But
it was strongly represented to me by those whose opinion
I had reason to value, that such questions were useful
in enabling a student to test whether he had mastered his
lesson, and that teachers who disliked such prearranged
questions could and would ignore them. I hope that

VI PREFACE.

the pupils will use the questions and that their teachers will
not.

Before concluding, I must express my sincere thanks to
Miss Frances T. Bauman, who has given me the benefit of
her many years' experience as an eminently successful
teacher. She kindly read a large portion of the manuscript,
and gave me much advice of which I have been glad to
avail myself. I have also to acknowledge my indebtedness
to Mr. W. H. Howell, Fellow of the Johns Hopkins Uni-
versity, who has corrected most of the procf-sheets, and
prepared the index.

H. Newell Martin.

Johns Hopkins University,
August 10, 1883.

PREFACE TO THE SECOND EDITION.

The second edition of this book differs from the first for
the most part only in verbal alterations or typographical
corrections. Chapter XXIII., however, is entirely new,
and deals in some detail with the important question of
the influence on health of alcohol and various narcotics.

H. N. M.

March 26, 1884.

CONTENTS.

CHAPTER I.

THE GENERAL STRUCTURE AND ARRANGEMENT OF THE HUMAN

BODY.

PAGE

Human Physiology — Hygiene — Anatomy — Histology — Tissues —
Organs — The general plan on which the body is constructed
— Man is a vertebrate animal — The two chief cavities of the
body — The limbs — Man's place among vertebrates — Sum-
mary 1

CHAPTER II.

THE MICHOSCOPICAL AND CHEMICAL COMPOSITION OF THE BODY.

What the tissues are like — Cells and fibres — The physiological
division of labor and its results — The chemical composition
of the body — Albumens, fats, and carbohydrates 15

CHAPTER III.

THE SKELETON.

Bone, cartilage, and connective tissue — Articulations and joints
— The bony skeleton — Uses of the mode of structure of the
spinal column — Comparison of the skeletons of the upper
and lower limbs — Peculiarities of the human skeleton 23

CHAPTER IV.

THE STRUCTURE, COMPOSITION, AND HYGIENE OF BONES.

Gross structure of bones — The humerus — Why many bones are
hollow — Histology of bone — Chemical composition of bone
— Hygiene of the bony skeleton — Fractures 47

viii CONTENTS.

CHAPTER V.

JOINTS.

PARE

Muscles and joints — Structure of the liip joint — Ball and socket
joints — Hinge joints — Pivot joints — Gliding joints— Disloca-
tions— Sprains 59

CHAPTER VI.

THE MUSCLES.

The parts of a muscle — The origin and insertion of muscles —
Varieties of muscles — How muscles are controlled— Gross
structure of a muscle — Histology of muscle — Plain muscular
tissue— The muscular tissue of the heart — The chemical
composition of muscle — Beef tea and meat extracts 67

CHAPTER VII.

MOTION AND LOCOMOTION.

The special physiology of muscles — Levers in the body — Pulleys
in the body — Standing — Walking — Running— Hygiene of
the muscles— Exercise 80

CHAPTER VIII.

WHY WE EAT AND BREATHE.

How it is that the body can do work — The conservation of en-
ergy— Illustrations — Why we need food — Why the body is
warm — The influence of starvation upon muscular work and
animal heat — Oxidations in the body — The oxygen food of
the body — Appendix 93

CHAPTER IX.

NUTRITION.

The wastes of the body — Receptive and excretory organs — The
organs and processes concerned in nutrition 105

CHAPTER X.

FOODS.

Foods as tissue formers — What foods must contain— The special
importance of albuminous foods — The dependence of animals

CONTENTS. IX

on plants— Non-oxidizable foods — Definition of foods — Ali-
mentary principles — The nutritive value of various foods-
Alcohol— Tea and coffee— Cooking— The advantages of a
mixed diet 110

CHAPTER XI.

THE DIGESTIVE ORGANS.

General arrangement of the alimentary canal— Glands— The
mouth— The teeth — Hygiene of the teeth— The tongue— A
furred tongue — The salivary glands— The tonsils— The
pharynx— The gullet — The stomach — Palpitation of the
heart— The small intestine — The large intestine— The liver
— The pancreas 128

CHAPTER XII.

DIGESTION.

The object of digestion— Uses of saliva— Swallowing— The gas-
tric juice — Chyme — Chyle — The pancreatic secretion — The
bile and its uses — The intestinal secretions — Indigestible sub-
stances— Dyspepsia — Appetite — Absorption from the ali-
mentary canal — The lacteals — Appendix 152

CHAPTER XIII.

BLOOD AND LYMPH.

Why we need blood — Histology of blood— The blood corpuscles
— H&miaglobin — the coagulation of blood — Uses of coagu-
lation— Blood serum — Blood gases — Summary — Hygienic
remarks — Quantity of blood in the body — The lymph —
Dialysis — The lymphatic or absorbent vessels — Summary —
Appendix 174

CHAPTER XIV.

THE ANATOMY OF THE CIRCULATORY ORGANS.

The organs of circulation — Functions of the main parts of the
vascular system — The pericardium — The heart — The vessels
connected with the heart — How the heart is nourished —
The valves of the heart — The main arteries of the body
— The properties of the arteries — The capillaries — The veins
— The course of the blood — The portal circulation — Arterial
and venous blood — Appendix 192

X CONTENTS.

CHAPTER XV.

THE WORKING OF THE HEART AND BLOOD VESSELS.

PA3E

The beat of the heart — Events occurring in each beat — Use of the
papillary muscles — Sounds of the beart — Function of the
auricles — Work done daily by the heart — The pulse — Blood-
flow in capillaries and veins — Why there is no pulse in these
vessels — The muscles of the arteries — Taking cold— Bathing
— Appendix 216

CHAPTER XVI.

THE OBJECT AND THE MECHANICS OP RESPIRATION.

The object of respiration — The respiratory apparatus — The
windpipe — Bronchitis — The lungs — The pleura — Pleurisy
— Why the lungs remain expanded — How the air is renewed
in the lungs — The respiratory movements — The respiratory
sounds — Hygienic remarks— Appendix 233

CHAPTER XVII.

THE CHEMISTRY OP RESPIRATION AND VENTILATION.

The quantity of air breathed daily — Changes produced in Hie air
by being breathed — Ventilation — When breathed air be-
comes unwholesome — How to ventilate — Changes under-
gone by the blood in the lungs — Appendix 250

CHAPTER XVIII.

THE KIDNEYS AND THE SKIN.

General arrangement of the nitrogen -execreting organs — Gross
structure of 'the kidney — Histology of the kidney — The
renal secretion— The skin — Hairs — Nails — The sweat glands
— The sebaceous glands— Hygiene of the skin — Bathing —
Appendix 261

CHAPTER XIX.

WHY WE NEED A NERVOUS SYSTEM — ITS ANATOMY.

The harmonious co-operation of the organs of the body — Co-
ordination— Nerve trunks and nerve centres — The cerebro-
spinal centre — The spinal cord — The brain — The cranial
nerves — The sympathetic nervous system — The histology of
nerve centres and nerve trunks — Appendix 279

CONTENTS. XI

CHAPTER XX.

THE GENERAL PHYSIOLOGY OF THE NERVOD8 SYSTEM.

PAGE

The properties of the nervous system — Functions of nerve
centres and nerve trunks — Sensory and motor nerves — Classi-
fication of nerve centres — Functions of the cerebrum — Of
the cerebellum — Reflex nerve centres — Automatic ' nerve
centres — Habits — Hygiene of the brain — Appendix 301

CHAPTER XXI.

THE SENSES.

Common sensation and special senses— Hunger and thirst — The
visual apparatus and its appendages — The globe of the eye
— The retina — The blind spot — The formation of images on
the retina — Short sight and long sight — Hygiene of the eyes
— Hearing — The tympanum — The internal ear — Touch —
The localization of skin sensations — The temperature sense
—Smell— Taste 314

CHAPTER XXII.

VOICE AND SPEECH.

The production of voice — The pitch of the voice — Speech —
Structure of the larynx— The vocal chords — Range of the
human voice — Vowels— Semi-vowels — Consonants 335

CHAPTER XXIII.

ALCOHOL AND OTTIER NARCOTICS.

Introductory — Is alcohol a food? — Composition and properties
of alcohol — Alcoholic beverages — The direct physiological
action of pure alcohol — Action of diluted alcohol — Absorp-
tion of alcohol — Primary effects of a moderate dose of
alcohol — Secondary effects of alcohol — Minor diseased con-
ditions produced by alcohol — Acute alcoholic diseases —
Delirium tremens — Dipsomania — Chronic alcoholic diseases
— Deteriorations of tissue due to alcohol — Organs impaired
or destroyed by alcohol — Moral deterioration produced by
alcohol — Opium and morphia — Chloral — Tobacco 343

THE HUMAN BODY.

CHAPTER I.

THE GENERAL STRUCTURE AND ARRANGEMENT OF
THE HUMAN BODY.

Human Physiology is that department of science
which has for its object the discovery and accurate de-
scription of the properties and actions of the living
healthy human body, and the detection of the uses, or
(as physiologists call them) the functions, of its various
parts. Physiologists endeavor to find out what the
body, as a whole, does while alive, and what each part of
it does, and how it does it; also under what conditions
the work of the body is best performed; and, in connec-
tion with this last aim, to furnish the basis of Hygiene,
the science which is concerned with the laws and condi-
tions of health.

What is human physiology? What is a function? What do
physiologists endeavor to discover? What is meant by Hygiene?

1

2 THE HUMAN BOLT.

Anatomy. — Clearly, the first step to be taken towards
finding out the use and mode of working of each part
of the body is to find out what the parts are ; this study
is known as Human Anatomy. Examined merely from
the exterior, the body is quite a complicated structure :
we can all sec for ourselves, head and neck, trunk and
limbs, and even many smaller but quite distinct parts
entering into the formation of these larger ones, as eyes,
nose, ears, and mouth ; arm, forearm, and hand ; thigh,
leg, and foot. This knowledge of its complexity, which
we may all arrive at by looking on the outside of the body,
is vastly extended when it is dissected and its interior
examined ; we then learn that it is made up of many
hundreds of diverse parts, each having its own structure,
and form, and purpose, but all harmoniously working
together in health.

Summary. — Anatomy is concerned with the form and
structure and connections of the parts of the body.
Physiology with the uses of the parts, and the ways in
which they work. Hygiene with the conditions of life
which promote the health of the body.

Microscopic Anatomy or Histology. — When we exam-
ine the body from its exterior, we observe that a number
of different materials enter into its formation. Hairs,
nails, skin, and teeth arc quite different substances ; by
feeling through the skin we find harder and softer solid

What is human anatomy? Give illustrations of the complexity
of the body in structure? Is its internal structure as varied as its
external?

State in a few words the subject matters of the sciences of Human
Anatomy, Physiology, and Hygiene.

Give examples of the variety of substances entering into the com-
position of the body. What mav we feel through tlie skin ?

MICROSCOPIC AXATOMY OR 3IST0L0GY. 3

masses under it ; while the blood which flows from a cut
finger, and the saliva which moistens the mouth, show
clearly that liquids exist in the body.

If we were to go farther and examine closely, outside
and inside, any one part of the body, the hand for in-
stance, we should find it made up of quite a number of
different materials. On its exterior we see skin and
nails ; if the skin were dissected off we should find under
it more or less yellowish-white fat ; beneath the fat would
lie a number of red soft masses, the muscles (answering to
what we call the lean of meat) ; under the muscles, again,
would be hard, rigid, whitish bones ; at the finger joints,
where the ends of different bones lie close together, Ave
should find them covered by still another substance, gristle
or cartilage. Finally, binding skin and fat and muscles
and bone together, we should discover a tough stringy mate-
rial, quite different from all of them, and which, since it
unites all the rest, is called connective tissue. If we took
any other portion of the body we should arrive at a similar
result ; it, too, would be made up of a number of different
materials, which materials might, as in the case of the
foot, be identical with those found in the hand but ar-
ranged together in a different way so as to perform another
function (just as wood and nails may be used to build a
house or a bridge, but are put together in a different man-
ner in the two cases) ; or we might, as in the eye, find in
addition to some materials found in the hand others quite
unlike any of them.

What different materials do we see on looking at a Land ? What
others would be found on dissecting away the skin ? What is the
technical name for the lean of meat ? What is the technical name
of gristle ? What is connective tissue ? Are other parts of the body
besides the hand made up of different substances ? Illustrate by an
example ?

4 THE HUMAN BODY.

The branch of anatomy which deals with the charac-
ters of the materials nsed in the construction of the parts
of the body is called histology, or, since it is mainly carried
on with the aid of the microscope, microscopic anatomy.

Tissues. — Each of the different primary building ma-
terials which can be distinguished, either with or without
the microscope, as entering into the construction of the
body, is called a tissue ; we speak, for example, of muscu-
lar tissue, fatty tissue, bony tissue, cartilaginous tissue,
and so forth ; each tissue has certain properties in which
it differs from all the rest, and which it preserves in what-
ever part of the body it may be found. It also is charac-
terized by certain appearances when examined with a mi-
croscope, which are the same for the same tissue no matter
where it is found. The total number of important tissues
is not great ; the variety in structure and use which we
find in the parts of the body depends mainly on the
diverse ways in which the same tissues are combined
together, over and over again, in different parts.

Organs. — A portion of the body composed of several
tissues, and specially fitted for the performance of a par-
ticular duty or function, is called an organ ; thus, the hand
is an organ of prehension ; the eye, the organ of sight ;
the stomach, an organ of digestion; and so forth.

Summary. — The human body is made up of a limited
number of tissues ;* each tissue has a characteristic ap-

What is histology? Give another name for it.

What is a tissue? Give examples. How do tissues differ? Are
there a large number of important 1 issues ? How is the variety in
structure of the parts of the body produced?

What is an organ? Give examples. Of what is the body made
up ?

* The various tissues of the body will be considered in more detail subsequently:
the more important are— 1. Bony tissue. 2. Cartilaginous tissue. 3. White fibrous

TISSUES AND ORGANS. g

pearance, by which it can be recognized with the micro-
scope, and some one or more distinctive properties which
fit it for some special use ; thus, it may be very tough, and
suited for binding other parts together ; or rigid, and
adapted to preserve the shape of the body ; or have the
power of changing its length and be useful for moving
parts to which its ends are attached.

The tissues are variously combined to form the organs
of the body, of which there are very many, differing in size,
shape, and structure ; some organs contain only a few tis-
sues ; others, a great many ; some possess only tissues
which are found also in other organs, others contain one
or more tissues peculiar to themselves ; but wherever an
organ is found, it is constructed and placed with reference
to the performance of some duty ; the organs are the ma-
chines which are found in the factory represented by the
body, and the tissues arc the materials used in building
the machines; or, using another illustration, we may, with
Longfellow, compare the body to a dwelling-house ; and
then go on to liken the tissues to the brick, stone, mortar,
wood, iron, and glass, used in building it; and the organs
to the walls, floors, ceilings, doors, and windows, which,
made by combining the primary building materials in
different ways, have each a purpose of their own, and all
together make the house.

How are tissues recognized ? Give examples of differences in
properties of various tissues.

How do organs differ from one another ? In what do all organs
agree ? Illustrate the relation of organs and tissues to the body as a
whole ?

connective tissue. 4. Yellow elastic tissue. 5. Glandular tissue, of which there are
many varieties. 6. Respiratory tissues. 7. Fatty tissue. 8. Sense-organ or irritable
tissues. 9. Nerve cell tissue. 10. Nerve fiber tissue. 11. Striped muscular tissue.
13. Uustriped muscular tissue. 13. Epidermic and epithelial tissue.

6 THE HUMAN BODY.

The general plan on which the Body is constructed. —
When we desire to gain a general idea of the structural
plan of any object we examine, if possible, sections made
through it in different directions ; the botanist cuts the
stem of the plant he is examining lengthwise and cross-
wise, and studies the surfaces thus laid bare ; a geologist,
investigating the structure of any portion of the earth's
crust, endeavors to find exposed surfaces in canons, in
railway cuttings, and so forth, where he may see the strata
exposed in their natural relative positions ; and the archi-
tect draws plans which show to his clients sections of the
building which he proposes to erect for them ; so, also, the
best method of getting a good general idea of the way in
which the parts of the human body are put together is
to study them as laid bare by cuts made in different direc-
tions ; this gives us a general outline and the details may
be filled in afterwards.

If the whole body were divided from the crown of
the head to the lower end of the trunk, and exactly in the
middle line, so as to separate it into right and left halves,
we should see something like Fig. 1, if we looked at the cut
surface of the right half. Such a section shows us, first,
that the body fundamentally consists of two tubes or cav-
ities, separated by a solid bony partition. The larger cav-
ity, b, c, known as the ventral or hamuli cavity, lies on
the front side, and contains the greater part of the organs

How do we start by preference to gain a knowledge of the struc-
tural plan of any mass of matter? Give examples. Apply to
the study of human anatomy.

What shoukl we. see on examining the cut surface of a human
body divided into right and left halves? What organs lie in the
haemal cavity? What in the neural? How far does the haemal
cavity extend toward the head ?

GENERAL PLAN OF BODY.

concerned in keeping up the
blood flow (organs of circula-
tion), in breathing (organs of
respiration) and in digesting
food (organs of digestion). It
does not reach up into the neck,
but is entirely confined to the
trunk. The smaller cavity, a,
a', is tubular in the trunk region,
but passes on through the neck,
and widens out in the skull; it
is known as the dorsal or neural
cavity, and contains the most
important nervous organs, the
brain, N', and spinal cord, N.
In the partition between the two
cavities is a stout bony column,
the backbone or spine, e, e,
which is made up of a number of
short thick bones piled one on
the top of another.

Man is a vertebrate animal.
— The presence of these two
chambers with the solid par-
tition between them is a prim-
ary fact in tbe anatomy of
the body ; it shows that man is
a vertebrate animal, that is to
say, is a back-boned animal,
and belongs to the same great

What lies between the hoemal and
neural cavities? Of what is the spine
composed?

Fig. 1.— Diagrammatic longitud-
inal section of the body, a, the
neural tube, with its upper enlarge-
ment in the skull cavity at a'; iV,
the spinal cord; N', the brain; ee,
vertebrae forming the solid parti-
tion between the dorsal and vent-
ral cavities; b, the pleural, and, c,
the abdominal division of the
ventral cavity, separated from one
another by the diaphragm, d; i,
the nasal, and o. the mouth cham-
ber, opening behind into the
pharynx, from which one tube
leads to the lungs, I, and another
to the stomach,/,- h, the heart; k,
a kidney ; s, ' the sympathetic
nervous chain. From the stomach,
/. the intestinal tube leads through
the abdominal cavity to the pos-
terior opening of the alimentary
canal.

8 THE HUMAN BODY.

group as fishes, reptiles, birds, and beasts* : sea ane-
mones, clams, and insects are invertebrate animals, and
built on quite different plans ; sections made through
any of them from the head to the opposite end, would
show nothing like those two main cavities with a backbone
between them which exist in our own bodies.

Contents of the two chief cavities of the body. — Exam-
ination of Fig. 1 shows that the ventral cavity is entirely
closed itself, though some tilings which lie in it are hollow
and communicate with the exterior. On the head we
find the nose, i, and the mouth, o, opening on the ven-
tral side ; that is on that surface of the body next which
the haemal cavity lies. The nose chamber joins the mouth
chamber at the throat, and from the throat two tubes
run down through the neck and enter the ventral cavity.
One of these tubes, placed on the ventral side of the other,
is the windpipe, and ieads to the lungs, I ; the other is the
gullet, and leads to the stomach, f. From the stomach,
another tube, the intestine, leads to the outside again at
the lower or posterior! end of the trunk. Mouth, throat,

What fact in man's anatomy makes him a vertebrate animal?
Name some other vertebrate animals. Name some invertebrates.
How would sections made through invertebrates differ essentially
from similar sections made througb a man?

Is the ventral cavity open? Do any smaller cavities in it open on
the exterior of the body? What openings do we find on the bead?
What is the windpipe? To where does it lead? What is the intes-
tine? What parts constitute the alimentary canal? Does this canal
lie entirely within the haemal cavity?

* The main groups in which animals are arranged are— 1. Yertebrata, or backboned
animals. 2, MoUueea, including snails, slugs, clams, oysters. &c. 3. Arthropoda,
including flies, moths, beetles, centipedes, lobsters, spiders, &c. 4. Vermes, includ-
ing worms of various kinds. 5. Echinodermata (hedgehog-skinned animals), in-
cluding sea urchins, star fishes, &c. 6. Calertterala, the sea-anemones and their
allies. 7. The Protozoa ; all microscopic and very simple in structure.

t In anatomy the head end of an animal is spoken of as anterior, and the oppo-
site end as posterior, no matter what may be the natural standing position of the
creature.

TWO CHIEF CAVITIES OF THE BODY.

gullet, stomach, and intestine, together form the aliment-
ary canal, which, as we see, begins on the head quite
above or anterior to the ventral cavity ; then, at the bot-
tom of the neck, enters the ventral cavity and runs on
through it, to }>ass out again posteriorly; just as a tube
might pass quite through a box, in at one end and out at
the other, without opening into it at all. In addition to
the lungs and the greater part of the alimentary canal,
the ventral cavity contains several other things of which
we shall have more to say presently ; among the more
important of them are, the heart, h; the kidneys, h ; the
sympathetic nerve centers, s; and several large organs
making juices which are conveyed by tubes into the ali-
mentary canal and assist in digesting our food.

Fig. 2.— A diagrammatic section across the body in the chest region, x, the dorsal
lube, which contains the spinal cord; the black muss surrounding it is a vertebra:
a, the gullet, a part of the alimentary canal; h, the heart; sy, sympathetic nervous
system; 11. lungs; the dotted lines around them are the pleune; rr, ribs; si, the
breastbone.

If we examined a section made across the trunk of the
body, say about the level of the middle^f the chest (Fig.
2), we would find, on the dorsal side, the neural tube, x,
cut across, and in it the spinal cord, which is not repre-

Name some organs, in addition to parts of the alimentary canal,
which are found in the ventral cavity. Describe what would be
seen on a section made across the body about the middle of the
chest.

10 THE HUMAN BODY.

sented in the figure. The thick black mass below the
neural tube is part of the spinal column ; bounded by this
dorsally, by a rib, r, r, on each side, and by the breastbone,
st, on the ventral side (below in the figure) is the haemal
cavity, containing the lungs, I, Ij the heart, hj the gul-
let, a; and the sympathetic centers, sy.

Fig. 3. — A section across the forearm a short distance below the elbow-joint. R
and U, its two supporting bones, the radius and ulna; e, the epidermis and d, the
dermis, of the skin: the latter is continuous below with bands of connective tissue,
s, which penetrate between and invest the muscles, which are indicated by numbers,
n, n, nerves and vessels.

The Limbs. — If, instead of the trunk of the body, our
section were made across one of the limbs, we should find
no such arrangement of cavities on each side of a bony
axis. The limbs have a supporting axis made of one or
more bones (as seen at U and R, Fig. 3, which represents
a section made across the forearm near the elbow joint),
but around this axis soft parts, chiefly muscles, are closely
packed ; and the whole, like the trunk, is enveloped by
skin. The only cavities in the limbs are branching tubes,
which are filled during life either with blood, or a watery-
looking licpiid known as lymph. These tubes, the blood
and lymph vessels respectively, are not, however, character-
istic of the limbs, for they also exist in abundance in head,
neck and trunk.

How do the limbs differ from the trunk? How is each limb
supported? Describe the parts exposed on a cross section of the
forearm? What cavities exist in a limb? What do they contain?
Are they found in other parts of the body?

MAN'S PLACE AMONG VERTEBRATES. \\

Man's place among Vertebrates. — It must be clear to
every one that although man's structural plan in its broad
features, simply indicates that he is a vertebrate animal,
yet he is much more like some vertebrates than others.
The hair covering more or less of his body, and the organs
which produce milk for the nourishment of the infant by
its mother, are absent entirely in fishes, reptiles, and birds,
but are possessed by ordinary four-footed beasts and by
whales, bats, and monkeys. The organs which form milk
are the mammary glands, and all kinds of animals whose
females possess them are known as Mammalia *; man is,
therefore, a Mammal. In internal structure one of the
most important characters of the Mammalia is the pres-
ence of a cross-partition, called th(
phragm, which separates the heemal
terior and a posterior division. Thii
d in Fig. 1, where it is seen to divide
into an upper and a lower story ; the^
the chest or thorax cavity ; the lower
abdominal cavity. The chest contains the heart, lungs,
and most of the gullet ; the abdomen contains the lower

In what external characters does the human body differ from
that of fishes, reptiles, and birds? Name some animals which agree
with mankind in the possession of these characters ? What are
the mammary glands? What is meant by Mammalia? To what di-
vision of vertebrate animals does man belong?

Point out a fact in internal structure in which the Mammalia
differ from other vertebrates? Where does the diaphragm lie? What
is the name of the cavity above it? What is the name of the cavity
below it? Name some organs lying in the thorax. Some placed in
the abdomen. Some which run throuirh both.

* Zoologists classify vertebrate animals in five groups. 1. Pisas, including all
true fishes, as sharks, eels, salmons, shad, perch, &c. but excluding the so-called
shellfish, as oysters, clams, and lobsters, which are not vertebrates at all. 2. Am-
phibia, frogs, toads, newts, salamanders &c. 3. ReptUia, lizards, alligators, turtles,
snakes. 4. Jives, birds. 5. Mammalia.

12

THE UUMAX BODY.

end of the gullet (which pierces the diaphragm), the
stomach, (ho intestine, the kidneys, and most of the
organs making digestive liquids. The sympathetic nerve

Fig. 4.— The body opened from the front to show the contents of its ventral
cavity, lu. lungs; h, heart, partly covered by other things; le. W, right and left
liver lobes respectively; ma, stomach; ne, the great omentum, a membrane con-
taining fat wiiieii hangs down from the posterior bolder of the stomach and
covers the intestines; mi, spleen: zz. diaphragm.

ZOOLOGICAL POSITION OF MAN 13

centers run through both abdomen and chest, and extend
beyond the hitter into the neck.

The ventral cavity, opened from the front, but with its
contents undisturbed, is shown in figure 4. We there see
the edge of the diaphragm, z, z; above this, in the chest,
the lungs, In, hi, and the heart, h ; the latter partly covered
by other things. Below the diaphragm is the abdominal
cavity, containing in its upper part the liver, le, le'; the
stomach, ma ; and the spleen, mi; hanging down like an
apron from the lower border of the stomach is the omen-
tum, ne, ne, which lies over and conceals the intestines.

Summary. — Man is a vertebrate animal, because his
body presents dorsal and ventral cavities separated from
one another by a hard partition ; the dorsal cavity con-
tains the brain and spinal cord, and reaches into the he;*d;
the ventral cavity stops at the bottom of the neck and
contains the main organs of circulation, respiration, and
digestion.

Man belongs to that subdivision of vertebrates known
as Mammalia (1) because more or less of his surface is
covered by hair ; (2) because of the presence of mammary
glands ; (3) because the ventral cavity is completely sep-
arated by the diaphragm into thorax and abdomen.

That man is intellectually incomparably superior to
any other animal, and stands supreme in the world, can

Name the parts seen when the front wall of a man's trunk is cut
away. Describe the relative positions of these parts.

On what anatomical grounds do we call man a vertebrate animal?
What lies in the dorsal or neural cavity? How far does the upper end
of this cavity reach? What organs lie in the ventral cavity? Where
does its upper limit lie? Why is man a Mammal? In what is man
superior to any other animal? From what point of view have anato-
mists to regard man's body? What sort of facts do they take into
account in assigning man's position among animals?

14 THE HUMAN BODY.

be doubted by no one; still greater is his supremacy when
we consider his power of forming conceptions of right and
wrong, and his knowledge of moral responsibility. But
anatomists have only to deal with man's body as a mate-
rial object, and as such they classify it among other ani-
mal bodies according to the greater or less resemblances
or differences which are found between it and them.*

* It will be found very useful to accompany the teaching of this chapter with
a demonstration on the body of a dead rat, kitten, or puppy. On opening the
body the chest and abdominal cavities will be readily shown, and also the main
organs in them. Then, on opening the skull, the brain will be seen, and on
cutting across the spinal column with strong scissors, the slender soft spinal
cord lying in its tube will come into view.

CHAPTER II.

THE MICROSCOPICAL AND CHEMICAL COMPOSITION OF
THE BODY.

What the tissues are like. — Having gained some idea
of how the larger parts of the body are arranged we may
next inquire what the tissues, its smallest parts which are
combined to make the larger, are like. a k

The simjflest tissues are known as cells : * '?££

they are so small that a separated cell can | ' \

only be seen with the help of a microscope. 'm! ,
In a fully formed cell (Fig. 5) we find three % .£*jgf

parts : (1) a cell body made up of a soft
granular substance ; (2) a smaller and less </{jf
granular cell nucleus imbedded in the cell ^-.: x h.
body; and (3) a tiny dot, the nucleolus, e^^C^M <
lying in the nucleus. Cells vary much in ^:,'::%-?
form and size, though all are very small. A 0

good many, like those represented at b, no. 5 -Forms
float in our blood, and are more or less £ody"s from the
rounded. In other places cells are flattened to form thin
scales as those in Fig. 6, which represents cells scraped

Of what arc the larger parts of the body made up? What are
the simplest tissues? What instrument must we employ in order to
see them? Describe the structure of a cell. Describe some differ-
ent forms of cells.

* So called from an old belief that they were little bags or chambers. Most
cells are really solid or semi-solid throughout.

[151

10

THE HUMAN BODY.

from the inside of the wall of the abdomen. Elsewhere
we find cells elongated, as c, Fig. 5 ; if this goes on to any
great extent we get a long slender thread which is called
a fiber ; but very often fibers are made by a number of
cells, all elongating a little and then
joining together end to end. Ex-
amples of fibers are shown in Figs. 35
and 85. Speaking in general terms,
we may say that the whole body con-
sists of tiny cells, either rounded and
thick, flat and thin, or elongated to
form fibers. Just as a Avail is built
of distinct bricks or stones, so an
organ is made up of a number of cells.
All the solid parts of the body are
either cells or fibers which have grown
from cells, except something which corresponds pretty
closely to the mortar which lies between the bricks of a
wall and holds them together. This latter material,
known in the body as intercellular substance, is in some
places abundant, in others scanty or absent.

Wherever found, the intercellular substance is made
by the cells which lie imbedded in it ; they pass it out
from their surfaces and repair it when necessary, and in
this respect it differs very essentially from the mortar
which a mason lays between his bricks.

Summary. — Cells are thus at bottom the things which

Fig 6.— Flat cells from
the surface of the lining
membrane of the abdo-
men ; a, cell body ; 6, nu-
cleus; c, nucleoli.

"What are fibers ? How are they made ? In what respect may an
organ be compared to a brick wall ? What corresponds to the mortar
of the wall ? What makes the intercellular substance? How?

State briefly the relationship of its cells to the structure and work-
ing of the body.

MICROSCOPIC' COMPOSITION OF TI1E BODY. Yl

make up the body and do its work ; their forms and the
way they are arranged together determine the form of the
organs ; the things which the kinds of cells found in
it can do, determine the faculties of each organ. Some
cells can make a great deal of hard intercellular substance,
and are employed to construct tlie skeleton ; others can
change their shape and are used to form the organs which
move the body ; others can elaborate peculiar solvent
liquids and are used in the organs of digestion ; and so on
through all the parts. Anatomy in the long run is a study
of the forms which cells and intercellular substances may
assume ; and physiology a study of what the cells and in-
tercellular substances of the body can do.

The physiological division of labor. — In a tribe of
wandering savages, living by the chase, we find that each
man has no special occupation of his own ; he collects his
own food, provides his own shelter, defends himself from
wild beasts and his fellow-men. In a civilized nation, on
the contrary, we find that most men have some one par-
ticular business : farmers raise crop? and cattle ; cooks
prepare food ; tailors make clothes ; and policemen and
soldiers protect the properly and lives of the rest of the
community ; in other words, we find a division of labor.
Just as the more minute the division of employments in it
is, the more advanced a nation is in civilization, so an
animal is higher or lower just as the duties necessary for
maintaining its existence are distributed among different

What determines the form of an organ ? What its faculties ?
Give examples of the employment of cells with different powers to do
different things. What is Anatomy really ? What Physiology ?

Explain what is meant hy the physiological division of labor. In
what class of nations is the division most minute ? What decides
whether an animal is higher or lower than another ?

2

18 TEE EUMAN BODY,

tissues and organs. In the lowest animals every cell is
concerned in feeling, and moving, and catching food, and
digesting, and breathing; in higher animals different cells
are set apart in different organs for the execution of each
of these separate functions.

Results of a division of labor. — From the division of
employments in advanced communities, several important
consequences result. In the first place, when every one
devotes his time mainly to one kind of work, all kinds of
work are better done : the man who always makes boots
becomes much more expert than the man who is engaged
on other things also : he can not only make more boots in
a given time, but he can make better boots ; and so in
other cases. In the second place, when various employ-
ments are distributed among different persons there arises
a necessity for a new kind of industry in order to convey
that part of the special produce of any given individual
which may be in excess of the needs of himself and his
family to others who may want it, and to bring him in
return such of their excess production as he may need.
The conveyance of food from the country to cities, and of
manufactures to agricultural districts, are examples of
this sort of labor in civilized communities. Finally, there
is developed a necessity for arrangements by which, at
any given time, the activity of individuals shall be regu-
lated in accordance with the wants of the whole community
or of the world at large. This sort of regulation is still

What do we find all cells doing in the lowest animals? How do
higher animals differ in this respect?

How does a division of labor influence the quantity of work done
by a man? How the quality? Illustrate. What new kinds of
employment arise when a division of labor becomes developed in a
nation ? Illustrate.

MICROSCOPIC COMPOSITION OF TUE BODY. 19

very imperfectly carried out even in the most advanced
communities, and we accordingly hear from time to time
of the over-production of this or that article ; but it is in
part effected through the agency of capitalists who control
the activities of many individuals in accordance with what
they think to be the quantity of various articles likely to
he required from time to time.

Exactly similar phenomena result from the division of
physiological labor in the human body. Each tissue and
organ doing one special work for the whole body, and rely-
ing on the others for their aid in turn, every sort of
necessary work is better performed ; the tissue or organ,
having nothing else to look after, is constructed with
reference only to its own particular duty, and is capable of
doing it extremely well. This, however, necessitates a
distributing mechanism by which the excess products, if
any, of the various organs, shall be carried to others which
require them ; and a regulating mechanism by which the
activities of each shall be controlled in accordance with
the needs of the whole body at the time being. We accord-
ingly find a set of organs, the heart and blood-vessels, which
carry blood from place to place all over the body, the
blood getting in its course something from and giving
something to each organ it flows through ; and a set of
nervous organs which ramify in every direction and regu-
late the activity of all the more important parts.

The chemical composition of the body. — If we go be-
yond the tissues to seek the ultimate constituents of the
body, we must lay aside the microscope, and call in cheni-

How does the division of duties in it affect the human body?
What is the object of the distributing mechanism? What of the
regulating? What are the distributing organs in the body called?
What is the object of the nerve organs?

20 THE HUMAN BODY.

istry to our aid, to discover what elements and compounds
make up the cells and intercellular substance.

Elements found in the body. — Of the many elements dis-
covered by chemists, only sixteen have been found in the
healthy human body.* Very few exist in it uncombined.
Some oxygen is dissolved in the blood; and that gas is also
found, mixed with nitrogen, in the lungs.

Chemical compounds existing in the body. — These are
so numerous that it would be a long task to enumerate
them, but some require mention : they may be divided
into organic and inorganic. In a general way we may say
that the organic constituents of the body, if all water were
separated from them, would burn if put in a fire; and the
inorganic components could not be made to burn.

Inorganic constituents of the body. — Of the inorganic
constituents of the body, water and common salt are the
most important; they are found in all the organs and
liquids of the body. Phosphate and carbonate of lime are
found in large proportions in the bones and teeth; and
free hydrochloric acid (spirits of salts or muriatic acid)
may always be found in healthy gastric juice, which dis-
solves some kinds of food in the stomach.

Organic constituents of the body. — All organic con-
stituents of the body contain carbon, hydrogen, and

How mauy chemical elements exist in the body? Are most of
them free or combined with others? Name those found free.

Into what main groups may be divided the chemical compounds
existing in the body? Name some of the chief inorganic compounds
helping to build the body. Where are they found in it?

What do all organic substances in the body contain?

* The elements found in the body in health are— carbon, hydrogen, nitrogen,
oxygen, sulphur, phosphorus, chlorine, fluorine, silicon, sodium, potassium,
lithium, calcium, magnesium, iron, and manganese.

CHEMICAL COMPOSITION OF THE BODY. 21

oxygen; some contain nitrogen also. There are three chief
kinds of them, viz.: albumens, fats, and carbohydrates.

Albuminous or proteid substances. — These are by far
the most characteristic organic compounds existing in the
body; they are only known as obtained from living beings,
having never yet been artificially constructed in the labo-
ratory; a good example is found in the white of an egg,
which consists chiefly of albumen dissolved in water. All
the tissues of the body which have any marked physiolog-
ical property contain some albuminous substance, only
such things as hairs, nails, and teeth being devoid of
them. All albuminous bodies contain nitrogen, carbon,
hydrogen, and oxygen; most of them sulphur and phos-
phorus in addition. The more important ones found in
the body are, (1) Serum albumen, which is very like egg
albumen, and is found dissolved in the blood; (2) Fibrin,
which forms in blood when it clots; (3) Myosin, found in
the muscles and " setting" or coagulating after death, when
it causes the death stiffening; (4) Casein, found in milk,
and forming the main bulk of cheese.

Fats belong to the organic compounds in the body
which contain no nitrogen ; they consist solely of carbon,
hydrogen, and oxygen. The chief fats in the body are
palmatin, stearin, and olein ; by proper treatment each
can be split up into glycerine and a fatty acid; palmitic,
stearic, or oleic acid as the case may be.

What is found in addition in some of them ? How many chief
varieties of organic compounds are there in the body? Name them.

Give another name for albuminous substances. Can they be made
artificially? Give an example of an albumen. What elements do
albumens contain ? Name the more importaut albumens of the body ?
Where are they found ?

What elements do fats contain ? Name the chief fats of the body.
Into what may they be decomposed?

22 THE HUMAN BODY.

The carbohydrates also consist entirely of carbon,
hydrogen, and oxygen ; they belong to the same class of
substances as starch and sugar. The most important car-
bohydrate in the body is glycogen, a sort of starch found
stored up in the liver and muscles. Glucose or grape
sugar also exists in the body ; and lactose or milk sugar
is found in milk.

What elements do carbohydrates contain ? Name the most im-
portant found in the body ? Where is glycogen found ? Where
milk sugar ?

CHAPTER III.
THE SKELETON.

The skeleton * of the human body is composed of
three materials : lone, cartilage, and connective tissue.

The bones form the main supporting framework of the
body, and determine its shape ; they provide levers on
which the muscles moving the body pull, and are arranged
so as to surround cavities in which, soft, delicate organs,
as brain, spinal cord, and heart, may lie in safety.

Cartilage finishes off many bones at joints, forming
elastic pads with smooth surfaces ; it is also used instead
of bones in some parts of the skeleton where considerable
flexibility is required. Cartilage affords one of the best
tissues of the body for the examination of intercellular
substance. A thin slice of it highly magnified, Fig. 7,
shows the cartilage cells, a, b, scattered through an almost
structureless material. Very young cartilage consists of

Of what is the skeleton made up ? "What functions do the bones
fulfill ? Where is cartilage found ? "What are its purposes ? What
is seen when a thin slice of cartilage is highly magnified ? Of what
does young cartilage consist.

* There are two kinds of skeleton met with in the animal kingdom ; the external
skeleton or exoskeleton, and the internal skeleton or endoskeleton. The exoskeleton
is made by the skin, either in it or on it ; examples are found in the shells of clams
and lobstero : the scales of fishes and snakes ; the tortoise-shell of turtles ; the
feathers of birds; the hair and claws of beasts. In man the exoskeleton is only
slightly developed; hair, nails and teeth belong to it.

T23]

24

THE HUMAN BODY.

the cells only, but these lay down around them more and
intercellular substance, until at last it forms the main bulk

Fig. 7.— A thin slice of cartilage highly magnified.

of the cartilage, and gives this the elasticity and flexibility
for which it is used in the body.

Connective Tissue occurs partly in the form of stout
cords — ligaments — which bind different bones together ;
or which, called tendons, attach muscles to bones. It
also supplements the coarser bony skeleton by a finer
one, which extends as a fine network through all the soft
parts of the body, making a sort of microscopic skeleton

What is a ligament? A tendon? Of what are ligaments and
tendons composed ? Where else do we find connective tissue ?

TEE SKELETON.

25

for its cells, and being
laid down as a soft
packing material, a good
deal like raw cotton,
in the crevices between
different organs, as
shown at s, Fig. 3,
where it is seen between
the muscles of the fore-
arm. This tissue is, in
fact, so widely spread
over the body, from the
skin outside to the
lining of the alimentary
canal within, that if we
could employ a solvent
wdiich would corrode
away all the rest, and
leave only the connec- "fc
tive tissue, a very per-
fect model of all the
organs would be left ;
something like a skele-
ton leaf, but far more
minute in its tracery.

Articulations and
Joints. — If the pieces
forming the hard frame

For what purposes ?
What would be left if all
materials composing the
body except its connective
tissue were dissolved away ?

Pro. 8.— The bony and cartilaginous
skeleton.

2Q TUB HUMAN BOUT.

work of the body were put together like the beams
and planks of a frame house, the whole mass would
be rigid and immovable ; we could not raise a hand to the
mouth, or put one foot before another. In order to attain
mobility the bony skeleton is made up of more than two
hundred separate pieces, joined together; the points
where they meet are culled articulations. An articulation
at which a considerable range of movement is permitted
is called a joint. The ends of bones which rub over one
another in a joint are always covered by a very smooth
layer of cartilage.

The bony skeleton (Fig. 8) consists of an axial skeleton,
supporting head, neck, and trunk, and an appendicular
skeleton, supporting the limbs and attaching them to the
trunk.

The Axial Skeleton. — The fundamental portion of this
is the backbone, spinal column, or spine, partly seen at e
and c, Fig. 8, and represented isolated from the rest of the
bones and viewed from the left side in Fig. 9. It forms
an axis, on which the rest of the body is carried. On the
upper end of the vertebral column is the skull, a, b, Fig.
8, and attached by ligaments to the under surface of the
skull is the hyoid bone, to which the root of the tongue is
fastened.

Attached to the sides of part of the spine are the dor-
sal ends of the ribs, slender bones which curve round the

Why is the skeleton made up of separate bones ? What are
articulations? What is a joint? What covers the end of a bone in a
joint ?

What are the chief divisions of the bony skeleton ? What parts
of the body does the axial skeleton support ? What is the appen-
dicular skeleton?

What is the fundamental portion of the axial skeleton? What
does it bear on its upper end? What is the hyoid bone ?

What are the ribs? Where are their ends fixed ?

PECTORAL ARCH.

27

sides of the chest and are united in
front to the sternum, or breastbone, d,
Fig. 8.

Skull, hyoid bone, vertebral column,
ribs, and sternum together form the
axial skeleton.

The appendicular skeleton consists
of the pectoral and pelvic girdles, at-
taching the limb bones to the axial
skeleton ; and of the bones of the limbs
themselves.

The pectoral arch or girdle consists
on each side of a clavicle or collar-bone,
u, and a scapula or shoulder-blade,
which latter is a flat, triangular bone,
lying on the back of the chest outside
the ribs. The clavicle is a slender curved
bone like an italic /"in form. Its outer
end is attached to the scapula, and
its inner end to the top of the sternum.
It serves to brace out and support the
shoulder-joint, and to prevent it from
falling downwards and inwards toward
the front of the chest. It is absent
in beasts which use their fore limbs
for walking only, as horses, dogs, and
cattle, but is well developed in mon- Fig. 9.— side view of the

spinal column.

keys and bats.

Coll

Name the parts which make up the axial skeleton ?

Of what main divisions does the appendicular skeleton consist?
What bones exist in the pectoral arch ? Where does each lie? What
is its shape ? Name some animals which have no collar bones, and
some which have them.

28 TEE HUMAN BODY.

The skeleton of the upper limb consists of : (1) The
arm bone, or humerus, t, Fig. 8, which extends from the
shoulder to the elbow, and meets the scapula at the
shoulder-joint ; (2) of two forearm bones, the radius, g,
and ulna, f, the radius being on the thumb side ; and (3)
of twenty-seven hand bones. Of the hand bones eight,
the carpal tones, h, lie in the wrist ; five, the metacarpal
hones, i, in the palm of the hand ; and fourteen, the pha-
langes, h, in the thumb and fingers — two for the thumb,
and three for each finger.

The pelvic arch or girdle consists of a single bone, the
os innominatum, s, on each side ; this is firmly fixed at
its dorsal end to the lower part of the back-bone, meets
its fellow ventrally at the lower end of the abdomen, and
bears a deep socket on its outer side, into which the upper
end of the thigh-bone fits.

The skeleton of the lower limb consists of : (1) The
thigh-bone or femur, r, the longest bone in the body,
bearing above a hemispherical knob fitting into a hollow
on the outside of the os innominatum, with which it forms
the hip-joint ; (2) of two bones, tibia and fibula, I and m,
in the lower leg, the former on the great toe side ; (3) of

How many bones are there in the upper limb? Which of these
lies between the elbow and shoulder joints? With what bone does it
articulate above? Name the forearm bones. Which of them lies to
the outer side when the palm of the hand is turned forward? How
many bones are there in the hand? Where are the carpal bones?
How many of them are there? The metacarpal bones ; position and
number? The phalanges of the hand ; position and number ?

How many bones form the pelvic arch? What are they named?
To what are their dorsai ends attached? Where do they meet one
another ? What bone of the leg forms a joint with the innominate
bone ?

What is the first bone in the skeleton of the lower limb ? How
does it end above ? With what bones does it articulate ? At what
joints ? What bones extend from the knee to the ankle joint ?
Which of them is on the inner side of the leg ?

SKELETON OF FOOT.

29

the knee-cap or patella, q, in front of the knee-joint ; (4)
of twenty-six foot bones. Of the foot bones seven, the
tarsal hones, n, lie below the ankle-joint ; five, the meta-
tarsal hones, o, succeed these in the front half of the sole

Fig. 10.— The last lumbar vertebra and the sacrum seen from the ventral side.
Fsa, anterior sacral foramina.

of the foot ; and fourteen phalanges, p, are found in the
toes ; two in the great toe and three in each of the others.

"Where is the patella? How many bones are there in each foot?
Into what groups are the foot bones classified? Where are the
tarsal bones? How many ? The metatarsal? How many ? The
phalanges ? How many ?

30 TEE HUMAN BODY.

The vertebral column. — (Fig. 9.) The upper portion
of the spine consists of twenty-four separate bones, each
called a vertebra; these are piled one above the other, and
separated by elastic pads made of cartilage and connective
tissue. Seven vertebrae {cervical, C 1-7) are found in the
neck ; twelve {dorsal, D 1-12) lie at the back of the chest
and carry the ribs ; and five {lumbar, L 1-5) are in the
loins.

Below the separate vertebras comes the sacrum, (S 1),
which is shown as seen from its ventral aspect in Fig. 10,
along with the lowest lumbar vertebra. In childhood the
sacrum consists of five distinct vertebra?, but these grow
together afterwards, though cross ridges remain indicating
the original lines of separation. Succeeding the sacrum
and forming the lower end of the spine is the coccyx {Co,
1-4, Fig. 9), a single bone in adults, though consisting of
four pieces in children.

The structure of a vertebra. — Those vertebrae which
remain permanently separate resemble one another in
general form, with the exception of the uppermost two.
As an example we may take the eleventh from the skull,
that is the fourth dorsal vertebra (Figs. 11 and 12).

In it we find (1) a thick bony mass, C, rounded on the
sides and flattened above and below where it is turned
toward its neighbors ; this part is the centrum or body of

Of what is the upper portion of the backbone composed? What
are the bones forming it called? What lies between them? How
many vertebrae in the neck ? In the chest region? In the loins?

Of what parts is the lower portion of the vertebral column com-
posed? How many vertebrae form the sacrum? At what period of
life are they separate? How is this original separation indicated on
the sacrum of adults? How many vertebrae are united to form the
coccyx?

What vertebras differ essentially in form from the rest? Describe
a typical vertebra.

A VERTEBRA.

31

the vertebra ; the series of vertebral bodies forms the bony
partition (e, e, Fig. 1) already mentioned as existing in the
trunk between the neural and haemal cavities. (2) An
arch attached to the dorsal side of the centrum ; it is the
neural arch, A, and with the centrum incloses the neural
ring {Fv). The vertebrae being piled one above the other
the successive neural rings form the neural tube, in the

Fig. 11.

Fig. 12.

Fig. 11. — A dorsal vertebra seen from behind, i.e., the end turned from the
head.

Fig. 12.— Two dorsal vertebrae viewed from the left side, and in their natural
relative positions. C, the body; A, neural arch; Fv, the neural ring; Ps, spi-
nous process ; Pax. anterior articular process : Pai, posterior articular process :
Pt, transverse process ; Ft. facet for articulation with the tubercle of a rib ;
Fee, Fci, articular surfaces on the centrum for articulation with a rib.

cavity of which the spinal cord lies. (3) Projecting from
the body and arch are several processes ; one reaching out
from the dorsal side of the arch is the spinous jjrocess ;
the row of spinous processes which may be felt through
the skin along the middle of the back has given the name
of spinal column to the whole backbone.

What constitutes the hard partition between the dorsal and ventral
cavities of the trunk? How is the neural tube formed? Why is
the spinal column so named ?

s

32

THE HUMAN BODY.

Where the arch joins the centrum it is narrowed to a
stalk or pedicle, li, Fig. 12. When the vertebrae are placed
together in their natural relative positions, apertures {Fi),
leading into the neural canal, are left between their nar-
rower portions ; through these apertures (called the inter-
vertebral foramina) nerves pass out from the spinal cord.

The atlas and axis. — The first and second cervical ver-
tebra? differ considerably from the others. The first,
called the atlas (Fig. 13), carries the head ; it has a very

Aa Fas

Fas

Frt

Pai

Fig. 13. Fig. 14.

Fig. 13.— The atlas. Fig. 14.— The axis. Aa, body of atlas. D, odontoid pro
cess of axis ; Fas, facet on upper side of atlas with which the skull articulates ;
and in Fig. 13, anterior articular surface of axis; L, transverse ligament; Frt,
vertebral foramen.

small body and a very large neural ring. A ligament, L,
divides the ring into a ventral and a dorsal portion ; the
spinal cord "passes through the latter and a bony peg, D,
lies in the former. The peg is the odontoid or tooth-like
process. This reaches up from the second cervical or axis
vertebra (Fig. 14) and forms a pivot around which the atlas,

How are the intervertebral foramina formed? What is their pur-
pose?

What is the first cervical vertebra called? Describe its general
form. How is its neural ring divided? What lies in each division?
What is the second cervical vertebra named? What is the odontoid
process? Around what pivot does the head rotate when the face is
turned on either side?

SPINAL COLUMN. 33

carrying the skull with it, rotates when .the head is
turned from side to side.

On the anterior (upper) surface of the atlas are a pair
of shallow hollows, Fas; into these fit a pair of knobs,
found towards the back of the under surface of the skull
(Fig. 20), which glide in the hullows during nodding
movements of the head.

"Uses of the mode of structure of the spinal column. —
When the backbone is viewed from one side (Fig. 9) it is
seen to present four curvatures ; one in the neck, convex
ventrally, is followed by a curve in the opposite direction
in the dorsal region; in the loins the curvature is again
convex ventrally, and opposite the sacrum and coccyx the
reverse is the case. These curves add greatly to the
springiness of the spine, and prevent the transmission of
sudden jars along it.* The compressible elastic pads placed
between the centra of the vertebras promote the same end ;
the skull, containing the soft brain (which would be
readily injured by mechanical violence) and the spinal
cord, contained in the backbone itself, are thus protected
from jarring in running, jumping, &c.

The compressible pads between the bodies of the verte-
brae allow of a certain range of movement between each
pair, so that the column as a whole may be bent to a con-
How is the skull articulated to the backbone?
How many curvatures are there in the backbone? What is their
direction?

What results from the curvatures of the spinal column? "What is
the object of the pads between the vertebra'.'

* Take a straight bat tolerably flexible and elastic bar, as a lath, or, better still, a
thin steel rod. Hold it vertical, with one end restini: on the tlnor. and give a smart
blow on the upper end ; the jar will be sudden and violent. Now bend the rod and
hit it again ; the jar will be much less, as the curved rod yields sonu-what to the
blow on its top.

3

34 THE HUMAN BODY.

siderable extent in any direction. On the other hand,
these ])ads so limit the movement that no sharp bend can
occur at any one pointy such a.s might tear or bruise the
spinal cord lying in the neural canal.

The sacral vertebrae grow together firmly to give a
solid support to the pelvic arch, which transmits the
weight of all the rest of the body to the lower limbs when
we stand.

Summary. — The back-bone is rigid enough to sup-
port all the rest of the body ; flexible enough to bend
considerably in any desired direction, yet not sharply at
any one point ; and elastic enough to destroy or greatly
diminish any sudden jar or jerk which it may receive. It
is one of the most beautiful pieces of mechanism in the
body.

The ribs are twelve in number on each side (Fig. 15).
They are slender curved bones embracing the sides of the
chest, and attached at one end to the dorsal vertebrae.
Ventrally each rib ends in a costal cartilage; the carti-
lages of the seven upper pairs are directly articulated to
the sides of the breast-bone. The eighth, ninth, and
tenth cartilages join those of the ribs above them ; the
eleventh and twelfth are not attached to the rest of the
skeleton at their ventral ends, and are known as the free
or floating ribs.

How is it that we can bend the backbone? How is the extent of
bending at any one point limited? Why?

Why do the sacral vertebra? grow together?

State briefly the mechanical properties of the vertebral column.

How many ribs are there? What is their shape ? To what are
their dorsal ends attached? How does each rib end ventrally? To
what are the costal cartilages of the first seven ribs attached? To
what the next three costal cartilages? Which are the floating ribs?
Why so called?

THE SKULL.

35

Fro. 15.— The ribs of the left side, with the dorsal and two lumbar vertebrae,
the rib cartilages, and the sternum.

The skull (Fig. 16) is composed of twenty-eight bones :
eight of these, forming the cranium, are so arranged aa

How many bones in the skull?

86

tm hum ax mdy.

to surround the brain and protect the ears ; six lie inside
the ears ; and the remaining fourteen support the face,

Fio. in. — A side view of the skull. O, occipital bone ; T, temporal • Pr, parie-
tal ; F, frontal ; S, sphenoid ; Z, malar ; Mx, maxilla ; N, nasal ; E, ethmoid ; L,
lachrymal ; Md. inferior maxilla,

surround the month and nose, and (with the aid of some
of the cranial bones) form the eye-sockets.

How many in the cranium? What purposes do the cranial hones
fulfill? How many lie inside the ears? How many bones in the
luce? What parts do the face bones support and protect?

CHAMUM. 37

The cranium is a box with a thick floor (Fig. 1), con-
tinuing forwards the partition which in the trunk separates
the neural from the haemal cavity. On its under side
(Fig. 20) are many small apertures through which nerves
and blood-vessels ]iass in or out, and one larger one, the
foramen magnum, through which the spinal cord passes
in to join the brain.

The cranial bones (Fig. 1G) are the following : 1. Tlie
occipital bone, 0, unpaired, and having in it the fora-
men magnum. It lies at the back of the skull. 2. The
frontal bone, F, also unpaired, lies in the forehead. 3.
The parietal bones, Pr, two in number, meet one another
above the middle of the crown of the head, and form a
great part of the roof and sides of the skull. 4. The tem-
poral bones, T, one on each side, opposite the temples ; on
the exterior of each temporal bone is a large aperture
leading into the ear cavity, which is contained in this
bone. 5. The sphenoid bone, unpaired, and lying in the
middle of the base of the skull, but sending out a wing, S,
which reaches some way up each side, just in front of the
temporal. C. TJte ethmoid bone, E, forms the partition be-
tween the brain and nose chambers, and part of that be-
tween the nose and the eye socket.

The facial skeleton. — The majority of the face bones
are in pairs, but two are single; one of these is the loiver
jaw bone or mandible, Md, Fig. 1G ; the other is the vomer,

With what is the floor of the cranium continuous? Where does
the cranium present holes through it? What are most (if these aper-
tures for? What is the largest aperture called? What enters tbe
brain case through it?

Name the cranial bones. State where each lies. Through which
does the foramen magnum pass? Which contains the ear chamber?
Which of them are unpaired?

£g TEE EUMAN BODY.

which forms part of the partition between the two
nostrils.

The paired face bones are : 1. The maxilla or upper
jaio-bones, Mx, which carry the upper teeth and form
most of the hard palate separating the mouth from the
nose. 2. TJie palate bones, completing the bony palate, and
behind which the nostril chambers communicate by the
posterior nares (Fig. 20) with the throat cavity, so that air
can pass in or out through them in breathing. 3. TJie
malar or cheek-bones, Z. 4. TJie nasal bones, N, roofing in
the upper part of the nose. 5. The lachrymal or tear-
bones, L, small and thin, lying between the eye-socket and
the nose. 6. The inferior turbinate or spongy bones, which
lie inside the nose, one on the outer side of each nostril
chamber.

The cranial sutures. — All the bones of the skull, except
the lower jawbone, are immovably joined together. In the
case of most of the cranial bones this occurs by a dove-
tailing, like that used by cabinet-makers. Each bone has
its edges notched, and the notches fit accurately into hol-
lows on the bone it articulates with ; this kind of articula-
tion is called a suture ; it is well seen in Fig. 1G, between
the parietal bone and those in front of, behind, and
below it.

Comparison of the upper and lower limbs and their
supporting arches. The bones of these have already

Name the unpaired face bones.

Where does each lie? Name the paired face bones. State the
position of each in the skull. What bone carries the lower teeth?
Which the upper? What bones form the hard palate? By what
openings do the nose chambers communicate with the throat? Behind
what bone do these openings lie?

What cranial bone is movable? How are most of the cranial
bones joined together? Describe a suture?

SKELETONS OF LIMBS.

0 P

Fig. 17.— The skeleton of the arm and leg. H, the humerus; Cd, its articular
head which fits into the glenoid fossa of the scapula; U, the ulna; i?, the ra-
dius; 0, the olecranon; Fe, the femur; P, the patella; Fi, the fibula; T, the
tibia.

been enumerated, but certain resemblances and differ-
ences between the skeletons of the two limbs (Fig. 17)
are worth noting. In general plan it is clear that they

40 THE HUMAN BODY.

correspond pretty closely to one another; the pectoral
arch answers to the pelvic; the humerus to the femur;
the radius and ulna are represented by the tibia and
fibula ; five metacarpal bones correspond to five meta-
tarsal, and fourteen phalanges in the digits of the hand to
fourteen in the digits of the foot ; elbow and knee-joints,
and wrist and ankle arc comparable. There is, however,
in the arm no separate bone at the elbow answering to the
patella at the knee ; but the ulna bears above a bony
process, 0, which is in early life a separate bone and
represents the patella. There are in the adult carpus
eight bones, in the tarsus but seven ; here again we find,
however, that originally the astragalus, Ta (Fig. 19), of
the tarsus consists of two bones. The elbow-joint bends
ventrally and the knee-joint dorsal ly.

When we compare the limbs as a whole greater differ-
ences come to light, differences which are related to their
different uses. The arms, serving as prehensile organs,
have all their parts as movable as is consistent with the
requisite strength ; the lower limbs, having to carry all the
weight of the body, have their parts more firmly knit
together. Accordingly we find the shoulder girdle, C, S

Do the upper and lcwei limbs correspond in general plan of struc-
ture ? What in the lower limb answers to the pectoral girdle ?
What to the humerus ? What bones to those of the forearm ? What
to the metacarpal ? Bo the phalanges of the hand and foot agree in
number ? What joints in the leg answer to elbow and wrist ?

What bone in the leg is not represented by a separate bone in the
arm of adults? What in the arm corresponds to this leg bone? Is it
ever a separate bone? Which has more bones, hand or foot? How
many bones are there in the tiirsus in infancy? How many after-
wards unite to form one? What is the bone formed by this union
named? How do elbow and knee joints differ as to the direction in
which they bend?

Why are the arms made as movable as possible? Why are the
lower limb bones more firmly knit?

SHOULDER AND PELVIS.

41

Fig. 18, only directly attached to the axial skeleton by the
ventral ends of the collar bones, and free to make consid-

Fig. 18.— The skeleton of the trunk and the limb arches seen from the front.
C, clavicle ; 8, scapula ; Oc, innominate bone attached to the side of the saerum
dorsally and meeting its fellow at the pubic symphysis in the ventral median line.

erable movements, as in "shrugging the shoulders." The
pelvic girdle, Oc, on the contrary, is firmly and immova-
bly attached to the sides of the sacrum.

How is the shoulder girdle united to the axial skeleton?
Can it move? Give an instance? How is the pelvic attached? I?
it movable?

42

THE HUMAN BODY.

The socket on the outer end of the shoulder-blade, with
which the humerus forms the shoulder-joint, is very shal-
low, and allows of much freer movement than is permitted
by the deeper socket of the pelvis, into which the top of
the thigh bone fits.

If we hold one humerus tightly and do not allow it to
rotate, we can still move the forearm bones so as to turn
the palm of the hand up or down ; no such movement is
possible between tibia and fibula.

i

Sfhl 3

Fig. 19. — The bones of the foot. Ca, Calcaneum, or heel bone; Ta, articular
surface for tibia on the astragalus; Cb, the cuboid bone.

In the foot the bones are much less movable than in
the hand, and are so arranged as to make a springy arch
(Fig. 19) which bears behind on the heel bone, Ca, and in
front on the far ends, Os, of the metatarsal bones ; over
the crown of the arch at Ta is the surface with which the
leg-bones articulate, and on which the weight of the body
bears when we stand.

Which is deeper, the socket on shoulder-blade for humerus, or on
pelvic girdle for femur?

Can the foot be turned round so as to bring its sole upwards?
Can the hand so as to bring the palm up?

Are the hand or the foot bones more movable? How are the foot
bones arranged? On what points does the arch of the foot bear? Qn
what part of the arch is the weight of the body borne?

PECULIARITIES OF THE HUMAN SKELETON. 43

The toes are far less mobile than the fingers, the
difference between great toe and thumb being especially
marked. The thumb can be made to meet each of the
finger-tips, and so the hand can seize and manipulate very
small objects, while this power of opposing the great toe
to the others is nearly absent in the foot of civilized man.
In infants, and in savages who have never worn boots, the
great toe is often much more movable, though it never
acts so completely like a thumb as it does in most apes,
whose feet are used for prehension nearly as much as their
hands. Our own toes can by practice be made much more
movable than they usually are ; persons born without
hands have learned to write and paint with the toes.

Peculiarities of the Human Skeleton. — There are some
interesting points in the structure of the human skeleton,
connected with our power of maintaining the erect posture,
and of progressing on the feet so that the hands are left
free for grasping. In no other vertebrate is the division
of labor between the anterior and posterior limbs carried
so far; the highest apes often use the hand in locomotion
and the foot for prehension. As characteristic of man's
skeleton we may note:

1. The skull is nearly balanced* on the top of the verte-
bral column (Fig. 20) so that but little effort is needed to

Are toes or fingers more mobile ? How does the thumb differ in
this respect from the great toe? Wbat reason have we to think that
the shoe has produced this effect ? In what animals is the great toe
more movable? What power have their feet in consequence? Can
we make our toes more movable by practice ? Illustrate.

With wbat facts are the more marked peculiarities of the human
skeleton connected? In what living creature is the division of
labor between arms and legs carried farthest ?

Does the skull of man nearly balance on its support?

* The balance is, however, not quite complete. When any one goes to sleep in
an ill-ventilated lecture room he is usually a wakened by a sharp jerki lowq wan Is of

44

THE HUMAN BODY.

keep the head erect. In four-footed beasts the skull, being
carried on the front end of a horizontal backbone, needs
special ligaments and considera-
ble muscular effort to support it ;
in apes the skull does not nearly
balance on the top of the spine ;
its face is much heavier than its
back part, while in men the face
bones are relatively smaller and
the cranium larger. To keep the
head erect and look things
straight in the face " like a man "
is far more fatiguing to monkeys,
and they cannot maintain that
position long.

Fig. 20.— The base of the skull. _, „. . ...

The lower jaw has been removed. 1. 1 he human SDllial Column,

At the lower part of the figure is

the hard palate forming the roof "when Viewed from the front, IS
of the mouth and surrounded by

the upper set of teeth. Above seen to widen gradually from the

this are the paired openings of ° J

f^SS na mV°* ?..Bh£rt neck to the sacrum, and so to

way above the middle of the fig-
ure is the large median foramen
mag?ium, with the bony convex-
ities (or occipital condyles! which
articulate with, the atlas, on its
sides. It will be seen that the
part of the skull behind the
occipital condyles is about equal
in size to that in front of them ;
in an ape the portion in front of

the occipital condyles would be greatly to its spring and elasticity;

much larger than that behind . , , . , , . . , -, . ,

them. were it a straight rigid rod the

brain, concealed in the skull at its top, would be jarred at
every step.

How do four-footed beasts differ in this respect? Do apes' skulls
balance as well as man's? Why not? What is the result of this
want of balance?

What is observed when the human spinal column is viewed from
the front? What is gained by its gradual widening from above
down? What feature in our spines is peculiarly human? What
benefit results from it?

his chin. The muscles concerned in holding the head erect having relaxed their
vigilance the greater weight of Hie ti'wut li..., jL ilje skull exerts its effect.

be well fitted to sustain the
weight of the head, upper limbs,
&c., carried by it. Its curvatures,
which are peculiarly human, add

PECULIARITIES OF SKELETON. 45

3. The pelvis, to the sides of which the lower limbs are
attached, is proportionately very broad in man, so that the
balance of the trunk on the legs is not easily upset when
the body is bent towards one side.

4. The lower limbs are proportionately very long in
man. This makes progression on them more rapid by
allowing a longer stride, and also makes it difficult to go
on " all fours " except by creeping on the hands and
knees. The arms of some apes are as long, and of others
longer, than their legs.

5. The arched instep and broad sole of the human
foot are very characteristic. Most beasts, as horses, walk
on the tips of their toes, the hoof being really a very big
nail ; others, as bears, place the heel also on the ground,
but have a much less developed tarsal arch than
man. The vaulted human tarsus, made up of a number
of small bones, each of which can glide a little over its
neighbors, but none of which can move much, is admira-
bly calculated to break any jar which might be trans-
mitted to the spinal column by the contact of the sole
with the ground at each step.* A well arched instep is

What feature characterizes the human pelvis? What benefit
results from it? Which limbs are longest in man? What ends are
gained by the considerable length of the legs? Why do infants crawl
on the hands and knees instead of the hands and feet? Which limbs
are longest in apes?

"What structural points in the foot are especially human? What
part of the foot do horses put on the ground? Name an animal
which puts the heel also on the ground when it walks. How does
the bear's tarsal arch differ from man's?

What benefit results from the form and structure of the human
tarsus? How? Why is a well-arched instep beautiful?

* A carriage spring consists of two curved elastic steel bars fastened together at
their ends, and with their concave sides turned towards one another. The axle of
the wheel is attached to the middle of the lower bar. and the weight of the carriage

46 THE HUMAN BODY.

therefore rightly considered a beauty; it makes the gait
easier and more graceful.

bears on the middle of the upper. When the wheel jolts over a stone the jerk is
transmitted to the elastic arches, which each flatten a little, and so instead of a
sudden jerk a gentle sway is transmitted to the carriage. The tarsal arch of the
human foot acts like the upper half of a carriage spring.

CHAPTER IV.

THE STRUCTURE, COMPOSITION AND HYGIENE OF

BONES.

The gross structure of bones. — Although the bones
differ very much in shape all are alike in microscopic
structure and in chemical composition. When alive they
have a bluish-white color, with a pinkish hue when blood
is flowing through them ; they possess considerable flexi-
bility and elasticity, which may be best observed in a long
slender bone, as a rib.*

To get a general idea of the structure of a bone we
may select the humerus (Fig. 21). When fresh this is
closely invested on its outside by a tough membrane, the
periosteum, composed of connective tissue and containing
many blood-vessels. On its under side new bony tissue is de-
posited as long as the bone is growing thicker, and through-
out life it is concerned in the nourishment of the bone,

How do bones differ from one another? In what respects do all
bones agree? What is the color of a living bone? Name some mechan-
ical properties of bone. In what bones may such properties be most
readily seen?

What covers a bone on the exterior? What is it composed of?
Does it contain bloodvessels?

*The rib of a sheep or a rabbit when thoroughly boiled can be readily scraped
Clean and preserved, and serves admirably to show the flexibility and elasticity of
bone.

[47]

48

THE HUMAN BODY.

Fig. 21.— The right humerus, seen
from the front. For description, see
test.

which dies if it be stripped
off.* The periosteum covers
the humerus except on its
ends {Cp, Tr, Cpl) at the
shoulder and elbow-joints ;
there the bone is covered by
a thin layer of gristle or car-
tilage. Very early in life the
whole humerus consists of
cartilage ; this is afterwards
absorbed and replaced by
bone, leaving only a thin
layer of articular cartilage
on each end.

The bone itself consists
of a central nearly cylindrical
portion or shaft (extending
between the dotted lines X
and Z) and two articular ex-
tremities. These extremities
are enlarged to give a wider

What are the functions of the
periosteum? Where is the perios-
teum absent? Of what does the
humerus consist in very early in
life? What happens to most of its
cartilage afterwards ? Where is
some cartilage left?

AVhat are the main divisions of
the humerus? What is the general
form of its shaft ? Why are its ar-
ticular extremities large?

* Cases have been recorded in which a
considerable portion of a bone or even the
whole bone has been removed during life,
and the periosteum (left but slightly in-
jured) has formed a new boae in place of
the old.

STRUCT 'URE OF BONES.

49

$::

bearing surface in the joints, and also to provide space
on which to attach the muscles which move the bone ; the
various knobs on the extremities, and
the rough patches on the shaft, all mark
areas where muscles were fixed. Ǥ

Internal structure. — If the humerus
were divided lengthwise we would find
that its shaft was hollow ; the space is
known as the medullary cavity, and in
life is filled with soft fatty marrow. Fig.
22 represents such a longitudinal section.
We see in it that the marrow cavity ends
near the articular extremities ; and that
in these the bone has a loose, spongy text-
ure, except a thin dense layer on the sur-
face. In the shaft the compact outer
layer is much the thicker, the spongy
portion only forming a thin stratum next
the medullary cavity.* To the unas-
sisted eye the spongy bone appears made
up of a trellis-work of thin bony plates
which intersect in all directions and sur-
round cavities about the size of the

What do the knobs and rough patches on the
bone indicate?

What should we find on dividing the hu-
merus lengthwise? What is its shaft cavity
called? What does it contain? Where does
the marrow cavity end? What is the texture of
the articular extremities of the bone? How
does the shaft differ in structure from the ex-
tremities of the femur? What does the spongy SJjSi 6 hard bone; c,
i , r_ i-i_ a i oj spongy bone a, carti-

bone look like? lage

Fig. 22.— The humerus
cut open, a, marrow

* These facts may readily be demonstrated by sawing in two lengthwise the
bones out of a leg of mutton.

50 THE HVMAN BODY.

head of a small pin. In these spaces there is found dur-
ing life a substance known as the red marrow, which is
quite different from the yellow fatty marrow of the medul-
lary cavity.*

Why bones are hollow. — If the bones were solid they
would be extremely heavy and unnecessarily strong for
the common purposes of life, unless only the same amount
of material were used in their construction, and then they
would be either loose in texture and easily broken, or,
if dense, they would be thin rods and not give sufficient
surface for the attachment of muscles. It is a well-known
principle in practical mechanics that the same amount of
material will bear a greater strain if in the form of a tube
than in that of a solid rod of the same length ; hence iron
pillars are cast hollow; to fill them up solidly would make
them enormously heavier without anything like a propor-
tionate increase in strength. Take a glass tube one foot
long and a piece of glass rod of the same length and
weight; support each at its ends and hang weights on the
middle until it breaks; the tube will be found to bear a
very much greater strain before yielding. We see an ap-
plication of this same method of utilizing a given amount
of material to the best advantage for support, in the hol-
low stalks of grass, wheat, and barley.

Varieties of structure found in different bones. — Bones
which, like the humerus and femur, present a shaft and

What lies in the cavities of the spongy hone ?

Why are most hones hollow? Which will hear most weight, a
tuhe or a solid rod of the same material, weight, and length ? Give
illustrations. Why are grass stalks hollow ?

* Many of the bones of birds are thin-walled tubes of dense bone : the central
cavity contains air and no marrow, and communicates by tubes with the lungs.
Examine the humerus of a pigeon or a rooster.

HISTOLOGY OF BONE. 51

articular extremities, are called long hones ; other examples
are tibia and fibula, radius and ulna, metacarpal and meta-
tarsal bones, and the phalanges of fingers and toes. Tab-
ular bones form thin plates, like those of the roof of the
skull, and the shoulder-blades. Short bones are rounded
or angular, and not much longer in one diameter than
another ; as the carpal and tarsal (Fig. 19) bones. Irregu-
lar bones include all which do not fit well into any of the
above classes ; they usually lie in the middle line of the
body and are divisible into similar right and left halves ;
the vertebras are good examples.

All bones are covered by periosteum except where they
enter into the formation of a joint, but in the human
body only the long bones possess a medullary cavity con-
taining yellow marrow. The rest are filled up by spongy
bone, covered by a thin layer of dense, and have red mar-
row in their spaces.

The histology ol bone. — The microscope shows that
compact bone is only so to the naked eye ; even a hand
lens shows minute holes in it; it but differs from spongy
bone in the fact that its cavities are much smaller, and the
hard bony plates between tnem thicker, ii a thin trans-
verse section of the shaft ot long bone (Fig. 23) be exam-
ined with a microscope magnifying about twenty diameters,
even its densest part will be seen to show numerous open-
ings which become gradually larger near the medullary

What is a long bone? Give examples. A tabular bone? Exam-
ples. A sbort bone? Examples. An irregular bone? Examples.

With what is most of the surface of bones covered? Where is the
periosteum absent? What bones contain yellow marrow? What do
the others contain?

Does compact bone contain any cavities? How may these be
seen? How does it differ from spongy bone? What is seen when a
thin slice of bone is magnified twenty times ? Where do the apertures
in it become larger?

52

THE HUMAN BODY.

cavity and pass insensibly into the spaces of the spongy
bone around it. These openings are the cross sections of

Fig. 23.— yl, a transverse section of the ulna, natural size ; showing the medul-
lary cavity. B, the more deeply 3haded part of A magnified twenty diameters.

tubes known as the Haversian canals, which run all
through the bone, the majority of them in the direction of
its long axis, though numerous cross branches unite them.
The outermost Haversian canals open on the surface of
the bone beneath the periosteum ; from there blood-ves-
sels pass in, and, traversing the whole bone in these chan-
nels, convey materials for its growth and nourishment.

What are the Haversian canals? Where do the outer ones open?
What enters them? Where do the blood-vessels of a bone run?
What do they carry?

HISTOLOGY OF BONE.

53

Around each Haversian canal is a series of plates or
laiiirUie, each canal and its lamellae forming an Haversian
system ; the entire bone is made up of a number of such
systems, with the addition of a few lamellae lying in the
corners between them, and some which run around the
whole bone on its outer surface. In the spongy bone the
Haversian canals are very large, containing red marrow as
well as blood-vessels, and the lamellae around each are few
in number.

Fig. 24. — A email piece of bone, ground very thin and highly magnified.

If a bit of bone be still more magnified (Fig. 2-i) we
find that very small cavities lie between the lamellae; they

What lies around each Haversian canal? What is an Haversian
system? Of "what does a hone consist in addition to Haversian sys-
tems? Are the Haversian canals comparatively large or small in
spongy hone? What do the spaces of spongy hone contain in addi-
tion to hlood-vessels?

What spaces lie heWeen the lamellae of an Haversian system?

54 THE HUMAN BODY.

are called lacunce ; from each lacuna radiate many ex-
tremely fine tubes, the canaliculi, so that each lacuna with
its canaliculi looks something like a small animal with a
great many legs. The innermost canaliculi open into the
Haversian canal of the system to which they belong, and
those of various lacuna? communicate with one another, so
that a set of passages is provided through which liquid
which transudes from the blood-vessel in the Haversian
canal can ooze all through the bone.

In a living bene a nucleated cell lies in each lacuna.
These cells, the bone corpuscles, are the remnants of those
which made the bone, all whose hard parts are but in-
tercellular substance: a sort of skeleton is made by each
cell around itself, and this adheres to the skeletons of the
rest, and thus the whole bone is built.

Chemical composition of bone. — Apart from the bone
corpuscles and the soft contents of the Haversian canals
and of the spaces of the cancellated bone, the hard bony
substance proper is composed of animal and mineral mat-
ters so intimately combined that the smallest distinguish-
able bit of bone contains both. The mineral matters give
the bone its hardness and stiffness, and form about two-
thirds of its weight when dried. They may be removed
by soaking the bone in diluted muriatic acid,* and the

What radiate from the lacunae? Into what do the innermost
canaliculi of an Haversian system open? How is nourishing liquid
from the hlood carried throughout a bone?

What lies in each lacuna of a living bone? What are the bone
corpuscles? What is the hard part of bone? How is a whole bone
made up ?

Of what primary constituents is bone composed? Is there any
fragment of bone that does not contain both ? What qualities do its
mineral parts give to a bone? How much of a dry bone consists of
mineral matter? How may the mineral parts be removed?

* Add a couple of ounces of muriatic acid to a pint of water and place a

CHEMISTRY OF BONE. 55

animal or organic part of the bone is then left as a tough,
flexible mass, retaining perfectly the shape of the original
bone.

When long boiled in water the greater part of the
animal portion of bone is turned into gelatine and dis-
solved in the water; most of the gelatine which we buy in
the shops is obtained by boiling fresh bones in a closed
vessel under a high pressure; the water then gets much
hotter than when boiled in the air, and dissolves out the
gelatine more quickly; when a shin of beef is used to
make soup the bones are put in as well as the softer parts,
and the whole is kept boiling for hours so as to get some
of the gelatine out of the bones. The animal matter of
bone gives it its toughness and flexibility.

The earthy portion may be obtained free from the
animal by calcining a bone in a bright fire. The residue
is a white and very brittle mass, which retains perfectly
the shape of the original bone. It is readily powdered and
then forms bone ash, which consists chiefly of phosphate
and carbonate of calcium; most of the phosphorus of
commerce is obtained from it. If the burning be imper-
fect the animal matter is charred but not altogether burnt
away, and a black mass, known as animal charcoal or
" bone black,*' is left.

What then remains behind? What are its properties? Has it still
the shape of the bone? What happens when a bone is boiled for
hours? How is the gelatine of commerce obtained? Why do we
use bones in making soup? What properties does its animal matter
confer on bones?

How may we get the mineral part of bone free from the animal ?
What are its properties when isolated? What is bone ash? From
what is phosphorus prepared ? What is animal charcoal?

sheep's rib in the mixture for four or five days, having previously scraped the
bone quite clean. It will be found so flexible that, a knot may be tied on it; the
specimen may be preserved in strong brine or dilute alcohol from year to year
for exhibition to a class.

56 THE HUMAN BODY.

Hygiene of the bony skeleton. — In early life the animal
matter of the bones is present in larger proportion than
later; hence the bones of children are tougher, more
pliable, and not so easily broken. The bones of a young
child are tolerably flexible and are capable of being dis-
torted by any long-continued strain ; therefore children
should never be placed on a bench so high that the feet
have no support ; if this is frequently done the thigh
bones will almost certainly become bent over the edge of
the seat by the weight of the lower legs and the feet, and
a permanent distortion may be produced. For the same
reason it is important that a child be made to sit straight,
when writing or drawing, to avoid the risk of producing a
lateral curvature of the spinal column ; and young chil-
dren should not be made to walk too early lest they become
bow-legged, their bones not being rigid enough to bear
the weight of the body. How easily the bones yield to
prolonged pressure in early life is well illustrated by the
distorted feet of Chinese ladies ; and by the extraordinary
forms (Fig. 25) which some races produce in their skulls
by tying boards or bandages qn the heads of the children,
A distorted foot, even in the United States, is no uncommon
thing in these days of tight boots and high heels. The
latter are especially bad, as, instead of allowing the weight
of the body to bear properly directly downwards on the
crown of the arch of the instep, they throw it forwards,
and violently force the fore part of the foot into the toe of

How do the bones of children differ in composition from those of
adults? How in properties? Why should children have a seat allow-
ing the feet to be supported? Why should young persons be taught
to sit erect while writing? What will happen if young children are
encouraged to walk too much? Why? Give instances of the readi-
ness with which bones can be distorted in early life. Why are high-
heeled boots hurtful?

HYGIENE OF SKELETON. 57

the boot. This not only crushes the toes and leads to
deformities,, corns, and bunions, but makes the gait stiff,
inelastic and ungraceful.

Fro. 35. — Skull of a child of the tribe of Chinook Indians (inhabiting the neigh-
borhood of the Columbia river), distorted by tight bandaging so as to assume the
shape considered elegant aud fashionable by the tribe.

In advanced life the animal matter of the bones is
present in deficient amount, and hence they are brittle
and easily broken.

An infant has its bones but very imperfectly hardened
by mineral matter. Hence the great importance of sup-
plying it with food containing phosphate of lime, which
is the chief mineral constituent of bone. Of all common
articles of diet, milk contains most phosphate of lime :
hence one great reason of its value as a food for children.

Fracture. — When a bone is broken it is said to be frac-
tured ; when it is a clean break the fracture is simple J
when the bone is more or less broken up into bits on each
side of the break the fracture is comminuted j when the

"Why are the bones of an old person easily broken? Why should
milk form part of a child's diet ?

What is a fracture? A simple fracture? A comminuted fracture,'
A. compound fracture?

58 TEE HUMAN BODY.

Boft parts also are lacerated, so that there is an opening
from the skin to the broken bone, the fracture is com-
pound.

Once a bone is broken the muscles attached to it are
apt to pull its ends out of place; hence it requires to be
" set/' and then kept in position by splints or bandages; this
frequently needs much skill and a thorough knowledge of
the anatomy of the body. A medical man should be sum-
moned at once, as the parts around the break commonly
swell very rapidly and make the exact nature of the frac-
ture hard to detect, and also the replacement of the dis-
placed ends more difficult.

Why does a broken bone need "setting"? What is the object of
"splints"? Why should skilled assistance be obtained as soon as
possible after a bone has been fractured ?

Appendix to Chapter IV.

When giving lessons on Chapters III and IV, it is very desirable
for a teacher to have at hand an articulated human skeleton. This
may be purchased for about f 40.00 from Henry Ward, Rochester,
N. Y., and will last for an indefinite number of years. When the
school funds do not permit the purchase of a skeleton, one can almost
certainly be borrowed from some medical man or medical school for
a few days. When there are several public schools in a city it would
probably be possible to induce the school commissioners to purchase
a skeleton to be used by the schools in turn.

The mover

CHAPTER V.
JOINTS.

The movements of the body are brought about by means
of soft reddish organs known as the muscles; the lean of
meat is muscle, so every one knows what a dead muscle
looks like.* Muscles have the power of shortening with
considerable force ; when they do so they pull their ends
towards one another and swell out in the middle ; in
other words, they become shorter and thicker. With few
exceptions the ends of a muscle are attached to separate
bones f between which a joint lies, and when the muscle
shortens, or, in physiological language, contracts, it pro-
duces movement at the joint. The joints and muscles thus
form the chief motor apparatuses of the body.

"What organs produce the movements of the body? What is the
technical name of the lean <>f meat".' What power do muscles pos-
sess? What happens when they exert it? To what are the ends of
most muscles attached? What happens when the muscle contracts/
Name the chief motor apparatuses of the body?

* In many animals some muscles are much redder than others, and it is then
found that the deeper colore! are those which are kept most constantly in use ; the
leg muscles of a chicken, for example, are redder than those of the wings and
breast, and as the coloring matter is turned brown by heat, they form the "dark
meat" after cooking ; in birds which fly a great deal the breast muscles | which
chiefly move the wing?) are also dark. The heart, which is a muscle always at
work, is deep red, even in fishes, most of whose muscles are pale.

t As an example of a muscle not attached to the skeleton, we may take the orbic-
ularis oris, which forms a ring around the mouth-opening beneath the skin of the
lips ; when it contracts it closes the mouth, or if it contracts more forcibly purses
out the lips. The orbicularis palpebrarum forms a similar ring around the eye
opening, and when it contracts closes the eye.

62 THE HUMAN BODY.

on the head of the thigh-hone lies close against that lining
the acetabulum, so that practically there is no cavity left
in the joint. This close contact is not maintained by the
ligaments (which are much too loose, and serve mainly to
prevent such excessive movement as might roll the femur
cpiite out of its socket), but by the many strong muscles
which pass between pelvis and thigh-bone and hold
both firmly together. In addition, the pressure of the
atmosphere is transmitted by the skin and muscles to
the exterior of the air-tight joint, and helps to keep its
surfaces together. If all the muscles be cut away from
around the hip-joint of a dead body, it is found that the
head of the femur is still held in its place by the pressure
of the air ; and so firmly that the weight of the whole
limb will not draw it out ; but if a hole be pierced into the
bottom of the acetabulum, and air be thus let into the
joint, then the thigh-bone falls out of place as far as the
ligaments will let it.

In all joints we find the same essential parts ; bones,
articular cartilages, synovial membrane, synovial liquid,
and ligaments.*

Ball and socket joints. — Such a joint as that at the hip

Is there in health any definite space between the bones of the hip-
joint? What is the chief use of the ligaments? How are the bones
held together? What in addition to muscles helps to keep the bones
of the joint in contact? Describe an experiment illustrating the
effect of atmospheric pressure in keeping the bones together?

What essential parts are found m all joints?

What is such a joint as the hip- joint called?

* The structure of joints can be readily seen in those of a fresh calf's or
sheep's foot. The synovial membrane is so thin and so closely adherent to the
parts it lines that a microscope is needed for its demonstration ; but all the
other parts are readily made out.

BALL AND SOCKET JOINTS. 63

is called a ball and socket joint, and allows of a greater
variety of movement than any other kind. Through
movements taking place at it the thigh can (1) he flexed,
that is, bent so that the knee approaches the chest, and
(•2) extended or straightened again ; it can (3) be abducted
so that the knee is moved away from the middle line of
the body, and (4) adducted or brought back again ; by
movement at the hip the limb can also (5) be circum-
ducted, so that, with knee and ankle joints held rigid, the
whole leg is made to describe a cone, of which the apex is
at the hip-joint and the base at the foot ; and finally (6)
rotated so that the whole limb can be rolled to and fro a
little about its own long axis. All ball and sockets joints
allow all these movements to a greater or less extent.

Another important ball and socket joint is that be-
tween the upper end of the humerus and the hollow
{glenoid fossa) near the upper outer corner of the shoulder
blade. The glenoid fossa being much shallower than the
acetabulum the range of movement possible at the shoulder,
is greater than at the hip-joint.

Hinge-joints. — In this form the bony cavities and pro-
jections are not spherical, but are grooved and ridged so
that one bone can glide over the other in one plane only,
to and fro, like a door on its hinges.

The knee is a hinge-joint ; it can only be bent and
straightened, in technical language, flexed and extended.

"What kind of joints allow of the freest movement? "What is
meant by flexion of the thigh? By extension? By abduction? By
adduction? By circumduction? By rotation? What movements
do all ball and socket joints permit?

What sort of a joint is that at the shoulder? Why is more move-
ment possible at it than at the hip-joint?

What is a hinge-joint? Give an illustration.

Name other hinge-joints.

64 THE HUMAN BODY.

Between the phalanges of the fingers we find also hinge-
joints ; another is found between the lower jaw and the
cranium, allowing us to open and close the mouth.
The latter is not, however, a perfect hinge-joint ; it per-
mits also of slight lateral movements, and a gliding motion
by which the lower jaw can be thrust forward so as to
bring the lower range of teeth outside the upper.*

Pivot-joints. — In this form one bone rotates about
another. A good example is found between the first and sec-
ond cervical vertebrae (Figs. 13, 14). The odontoid process
of the axis reaches up into the neural arch of the atlas,
and, kept in place there by the transverse ligament which
does not let it press against the spinal cord, forms a pivot
around which the atlas rotates, carrying the skull with it
when we turn the head to right or left.

A more complicated kind of pivot-joint is found in the
forearm. Lay the forearm and hand flat on a table, palm
uppermost; without moving the shoulder-joint at all the
hand can then be turned over so that its back is upward.
In this movement the radius, which carries the hand,
crosses over the ulna. When the palm is turned up
(supination) the radius and ulna are parallel (Fig. 27, A),
and the radius on the outside ; place a finger of the other

Is the joint of the lower jaw with the skull a perfect hinge joint?
What movements can take place at it?

What is a pivot- joint? Name an instance from the spinal column.
Describe the joint between atlas and axis. What happens to the head
when the atlas rotates on the odontoid process of the axis?

Where do we find another kind of pivot-joint? Illustrate its
action. What happens when we turn the hand so that the palm
instead of being up shall be down? How can we observe the relative
change in position of radius and ulna while making this movement?

* The object of these minor movements is to allow us to chew our foo<1 ; in car-
nivora, as cats, which bite, but do not chew, the Jower jaw forms a perfect hinge-
joint with the cranium.

DISLOCATIONS.

65

hand on it near the wrist, and then turn the hand over ;
the lower end of the radius will be found to cross over the
ulna and to be on its inner side (Fig. 27, B), when the
movement is completed ; in this
position the hand is said to be R
in pronation.

The lower end of the hume-
rus (Fig. 21) has a large artic-
ular surface ; on the inner two-
thirds of this, Tr, the ulna fits,
and the grooves and ridges of
the bones interlocking form a
hinge-joint, allowing us only to
bend or straighten the elbow-
jomt. The radius fits on the
rounded outer third, Cpl, and
rotates there when the hand
is turned over, the ulna form-
ing a fixed bar around which it
moves.

Gliding joints as a rule per-
mit of but little movement.
Examples are found between the closely-packed bones of
the carpus and tarsus (Fig. 19), which slide a little over
one another when subjected to pressure.

Dislocations. — When a bone is displaced at a joint or
dislocated, the ligaments are more or less torn and other

B A

Ficj. 27.— A, arm in supination ;
B. arm in pronation ; II, humerus ;
K, radius ; {/ulna.

What movement is allowed between ulna and humerus? What
between radius and humerus? Around what does the radius rotate
when we turn the hand over?

Do gliding joints allow free movement? Give instances of gliding
joints.

What is a dislocation? What parts are injured when a joint is
dislocated ?

66 TUB KVMAlt BOD?.

surrounding soft parts injured. This generally leads to
inflammation and swelling, which make it difficult to find
out in what direction the hone has been displaced, and
also greatly add to the difficulty of replacing it, or, in sur-
gical language, of reducing the dislocation. The muscles
attached to it are, moreover, apt to pull the dislocated
bone more and more out of place. Medical aid should
therefore be obtained as soon as possible ; in most cases
the reduction of a dislocation can only be attempted with
safety by one who knows the forms of the bones and pos-
sesses sufficient anatomical knowledge to recognize the
direction of the displacement.*

A sprain is an injury to a joint, accompanied by strain-
ing, twisting, or tearing of the ligaments, but without dis-
location of the bones. A sprained joint should get imme-
diate and complete rest, continued for weeks if neces-
sary ; if there be much swelling or continued pain, medical
advice should be obtained. Perhaps a greater number of
permanent injuries result from neglected sprains than from
broken bones.

What results from this injury ? What is meant by " reducing a
dislocation ?" Why should medical aid be obtained as soon as possi-
ble after a joint has been dislocated ?

Wliat is a sprain ? How should a sprained joint be treated ?
What should be done at once if there is much swelling or continued
pain ? Are neglected sprains apt to lead to permanent injury ?

* Dislocations of the fingers can usnaily be reduced by strong pulling, aided by a
little pressure on the parts of the bones nearest the joint. The reduction of a dis-
location of the thumb is much more difficult, and can rarely be accomplished with-
out skilled assistance.

EXPLANATION OF PLATE II.

A view of the muscles situated on the front surface of the body,
seen in their natural position. It must be understood that beneath
these muscles many others are situated, which cannot be represented
in the figure.

Muscles of the Face, Head, and Neck:

1. Muscle of the Forehead. This, together with a muscle at the back of the

head, has the power of moving the scalp.

2. Muscle that closes the Eyelids. The muscle that raises the upper eyelid

so as to open the eye. is situated within the orbit, and consequently
cannot be seen in this figure.

3. 4, 5. Muscles that raise the Upper Lip and angle of the Mouth.

6, 7. Muscles that depress the Lower Lip and angle of the Mouth. By the
action of the muscles which raise the upper lip, and those that depress
the lower lip, the lips are separated.

8. Muscle that draws the Lips together.

9. Muscle of the Temple (Temporal Muscle).

10. Miisseter Muscle. 9 and 10 are the two chief muscles of mastication, for

when they contract, the movable lower jaw is elevated, so as to crush
the food between the teeth in the upper and lower jaws.

11. Muscle that compresses the Nostril. Close to its outer side is a small

muscle that dilates the nostril.

12. Muscle that wrinkles the Skin of the Neck, and assists in depressing the

lower jaw.

13. Muscle that assists in steadying the Head, and also in moving it from side

to side.

14. Muscles that depress the Windpipe and Organ of Voice. The muscles

that elevate the same parts are placed beneath the lower jaw, and can-
not be seen in the figure.

Muscles that connect the upper extremity to the trunk. Portions
of four of these muscles arc represented in the figure, viz. :

15. Muscle that elevates the Shoulder. Trapezius Muscle.

17. Great Muscle of the Chest, which draws the Arm in front of the Chest

(Great Pectoral Muscle).

18. Broad Muscle of the Back, which draws the Arm downwards across the

back of the Body (Latissimus Dorsi).

19. Serrated Muscle extends between the Ribs and Shoulder-blade, and draws

the shoulder forwards and rotates it, a movement which takes place in
the elevation of the arm above the head (Serratus magnus)

At the lower part of the trunk, on each side, may be seen the large
muscle which, from the oblique direction of its fibres, is called,
30. Outer Oblique Muscle of the Abdomen.

Several muscles lie beneath it. The outline of one of these,

21. Straight Muscle of the Abdomen, may be seen beneath the expanded

tendon of insertion of the oblique muscle. These abdominal muscles,
by their contraction, possess the power of compressing the contents of
the abdomen.

Muscles of the upper extremity.
16. Muscle that elevates the Arm (Deltoid Muscle).

22. Biceps or Two-headed Muscle (see also page 70).

23. Anterior Muscle of the Arm. This and the Biceps are for the purpose of

bending the Fore Arm

24. Triceps, or Three-headed Muscle. This counteracts the last two muscles,

for it extends the Fore-arm.

25. Muscles that bend the Wrist and Fingers, and pronate the Fore-arm and

Hand— that is, turn the Hand with the palm downwards. They are
called the Flexor and Pronator Muscles.

26. Muscles that extend the Wrist and Fingers, and supinate the Fore-arm

and Hand— that is, turn the Hand with its palm upwards. They are
called the Extensor and Supinator Muscles.

27. Muscles that constitute the ball of the Thumb. They move it in different

directions.

28. Muscles that move the Little Finger.

Muscles which connect the lower extremity to the pelvic bone.
Several are represented in the figure.

29. Muscle usually stated to have the power of crossing one Leg over the

other, hence called the Tailor's Muscle, or Sartorius; its real action is
to assist in bending the knee. ^

30. Muscles that draw the Thighs together (Adductor Muscles).

31. Muscles that extend or straighten the Leg (Extensor Muscles). The

muscles that bend the leg are placed on the back of the thigh, so that
they cannot be seen in the figure.

Muscles of the leg and foot:

32. Muscles that bend the Foot upon the Leg, and extend the Toes.

33. Muscles that raise the Heel— these form the prominence of the calf of the

Leg.

34. Muscles that turn the Foot outwards.

35. A band of membrane which retains in position the tendons which pass

from the leg to the foot.

36. A short muscle which extends the Toes.

The muscles which turn the foot inwards, so as to counteract the
last named muscles, lie beneatli the great muscles of the calf, which
consequently conceal them. The foot possesses numerous muscles,
which act upon the toes, so as to move them about in various direc-
tions. These are principally placed on the sole of the foot, so that
they cannot be seen in the figure. Only one muscle, 36, which assists
in extending the toes, is placed on the back of the foot.

PLATE II.— THE SUPERFICIAL MUSCLES Or" THE FRONT OF THI

70 THE HUMAN BODY.

seen and felt on the biceps in front of the humerus when
the elbow is bent, or in the ball of the thumb when that
digit is moved so as to touch the little finger ; when a muscle
contracts its belly may also be felt to grow harder. The
swelling and. hardening of a contracted muscle are daily
illustrated when one schoolboy invites another to feel his
" biceps."

The Origin and Insertion of Muscles. — Almost invaria-
bly that part of the skeleton to which one end of a mus-

Fig. 29.— The biceps muscle and the arm-bones, to illustrate how, tinder ordi-
nary circumstances, the elbow joint is flexed when the muscle contracts.

cle is fixed is more easily moved than that part on which
it pulls by its other tendon ; the less movable attachment
is the origin, the other the insertion of the muscle. Tak-
ing the biceps of the arm, we find that when the belly of
the muscle contracts and pulls on its upper and lower
tendons, the result is commonly that only the forearm is
moved, the elbow joint being bent as shown in Fig. 29.

How may ils thickening be recognized? What change besides
thickening and shortening occurs in the belly of a contracted muscle?
Give an example.

What is meant by the origin of a muscle? What by the insertion*?
Give an example.

VARIETIES OF MUSCLES.

71

The shoulder is so much more firm that it serves as a
fixed point, and so that end of the biceps is the origin of
the muscle, and the radial attachment its insertion. The
distinction is, however, only relative : if the radius were
held immovable the muscle would move the shoulder
towards the radius, instead of the
radius towards the shoulder ; as, for
example, in going up a rope " hand
over hand."

Varieties of Muscles. — Many muscles
have the simple typical form of a belly
tapering towards each end, as A, Fig.
30 ; others divide at one end, and are
called two-headed, or biceps muscles,
and there are even three-headed or
triceps muscles. On the other hand,
some muscles have no tendon at all at
one end, the belly running right up to the bone to which
it is fixed, and some have no tendon at either end. Some-
times a tendon runs along the side of a
muscle, and the fibres of the latter are at-
tached to it obliquely (B, Fig. 30) ; such
a muscle is called penniform or feather-
like, from a fancied resemblance to the
vane of a feather ; or a tendon may run gastric mubCle-
down the middle of the muscle (0), which is then called
bipenniform. Sometimes a tendon is found in the mid-
dle of the belly as w^ll as at each end (Fig. 31) ; such a

Fig. 30.— Diagrams il-
lustrating, a. typical mus-
cle with a central belly
and two terminal ten-
dons, b, a penniform
muscle; c, a bipenniform
muscle.

Is the origin of a muscle under all circumstances its most fixed
end? Give an example.

What is the simple typical form of a muscle? What is a biceps
muscle? What a triceps? Have all muscles tendons at each end? At
either end? Describe a penniform muscle. A bipenniform.

72 THE HUMAN BODY.

muscle is called two-bellied or digastric. Running along
the front of the abdomen, from the pelvis to the chest,
on each side of the middle line, is a long muscle, the
straight muscle of the abdomen (rectus abdominis) ; it is
polygastric, consisting of four bellies separated by short
tendons. Many muscles are not rounded, but form wide,
flat masses, as those which lie beneath the skin on the sides,
of the abdomen.

How the muscles are controlled.— Most of the muscles
of the body are paired in a double sense. In the first
place, to nearly every one answers a corresponding muscle
on the opposite side of the body,* its true mate ; in addi-
tion, most are paiitd with, or rather pitted against, an
antagonist ; for example, to the biceps muscle (Fig. 29)
which lies in front of the humerus and bends the elbow
joint, corresponds the triceps muscle which lie* behind
the arm bone and extends the elbow ; when the biceps
contracts the triceps relaxes, and vice versa. This orderly
working is carried out by means of the brain and spinal
cord, which, through the neives, govern the muscles and
regulate their activity. In convulsions these controlling
organs are out of gear, and the muscles are excited to con-
tract in all sorts of irregular and useless ways ; antagonists
pulling against one another at the same moment the whole
bodv is made rigid.

A digastric. Where do we find a polygastric muscle? How is
the rectus abdominis muscle constituted ? Where are flat wide
muscles found ?

In what two wavs are muscles paired? Give an example of antag-
onistic muscles. What happens !o the triceps when the biceps con-
tracts? How is the orderly working of the muscles guided and con-
trolled? What parts are out of working order in a fit of convulsions?
Why do the limbs often become stiff in convulsions?

* The single muscles cross the middle line and are made up of similar right
a»d left halves; examples are orbicularis oris and the diaphragm.

THE GROSS STRUCTURE OF A MUSCLE. 73

The Gross Structure of a Muscle. — Each muscle is an
organ composed of several tissues. Its essential constitu-
ent is a number of fibres consisting of striped muscular
tissue. These are supported and protected by connective
tissue; intertwined with blood and lymph vessels, which
convey nourishment and carry off waste matters ; and
penetrated by nerves which govern their activity.

A loose sheath of connective tissue, the perimysium,
envelopes the whole muscle in a sort of case ; from it
partitions run in and sub-
divide the belly of the mus-
cle into bundles or fasciculi
which run from tendon to
tendon, or the whole length
of the muscle when it has
no tendons. The coarse-
ness or fineness of meat de-
pends on the size of these **»■ frA sma!1" bi^ of "l"scl! com.'

•i posed of four primary fasciculi. A, nat-

fftsripnli ivlnVli mnv Tip ural size : .B, the same magnified, showing
idhUCllll, WI11CU lint) ue the secondary fasciculi of which the pri-

readily seen in a piece of ■«*■» «"»!»■*■
boiled beef. In good carving, meat is cut across the
fasciculi, or "across the grain," as it is then more easily
broken up by the teeth ; the polygonal areas seen on
the surface of a slice of beef are cross sections of the
fasciculi. The larger fasciculi are subdivided by fine
partitions of connective tissue into smaller (Fig. 32), each
consisting of a few muscular fibres enveloped in a close

Is a muscle an organ or a tissue? What is the chief tissue in it
called? What things exist in it besides striped muscular tissue? What
is the use of each?

What is the perimysium? How is a muscle divided into fasciculi?
How far do the fasciculi extend? When is meat coarse in texture?
Why is beef carved across the grain? Of what are the fasciculi com-
posed?

74

THE HUMAN BODY.

network of minute blood-vessels. Where a muscle tapers
the muscle fibres in the fasciculi are less numerous and when
a tendon is formed they disappear alto-
gether, leaving only the connective tissue.

Histology of Muscle. — The striped mus-
cular tissue, which gives the muscle its
power of contracting, is found when ex-
amined by the microscope to be made up
of extremely slender muscular fibres, each
about one inch in length, but most of
them less than jfa of an inch across.

Each muscular fibre has externally a
thin sheath or envelope, the sarcolemma,
which envelops the contracting part of the
fibre. This latter is soft and almost
Pm. a3.— Asmaii semi-fluid, and under a microscope is seen

piece of muscular , . - .„

fibre highly mag- to present a striped appeanince, as it

nified. At a the x x .

fibre has been made up ot alternating dimmer and

crushed and twist-

ed so as to tear brighter transverse bands (Fig. 33).

its contents, while ° \ o /

the tougher sar- After death the semi-solid contents of the

colemma. else-

Spited to the wit nbre son(lify and death -stiffening is pro-
LmfLse untSIobrn duced ; at the same time the fibre often

and conspicuous. ^j^ up ^ & lmmber 0f Yery fine

threads or fibrillar, which were formerly regarded as true
constituents of the living muscular fibre.

Plain muscular tissue. — The muscles hitherto spoken of

Of what is a tendon made ?

Of what is striped muscular tissue composed ? Describe the form
and size of muscular fibres?

What is the sarcolemma? What is the consistency of the con-
tractile part of a living muscular fibre? What appearance does it
present under the microscope? What is the cause of death stiffening ?
What arefibrillre?

What do we mean by voluntary muscles?

PLAIN MUSCULAR TISSUE. 75

are all more or less under the control of the will ; we
can make them contract or prevent this as we choose ;
they are therefore often called the voluntary muscles.*
There are in the body other muscles whose contractions

Fiq. 34.— The muscular coat of the stomach.

we cannot control, and which are hence called involuntary
muscles ; they are not attached to the skeleton directly,
nor concerned in our ordinary movements, but lie in the

What by involuntary? Which kind is attached to the skeleton?
Where do we find the involuntary muscles?

*No sharp line can be drawn between voluntary and involuntary muscles; the
muscles of respiration are to a certain extent under the control of the will ; any one
can draw a long breath when he chooses. But in ordinary quiet breathing we are
quite unconscious of their working, and even when we pay heed to it our control of
them is limited ; no one can hold his breath long enough to suffocate himself. In-
deed, any one of the striped muscles may be thrown into activity, independently of
or even against the will, as we see in the "fidgets" of nervousness, and the irre-
pressible trembling of extreme terror. Functionally, when we call any muscle vol-
untary, we mean that it may be controlled by the will, but not that it necessarily
always is so. Structurally, the heart occupies an intermediate place : its striped
fibres resemble much more those of voluntary than of invo.untary muscles, but its
beat is not at all subject to the will ; though, as the exception proving the rule, it
may he noted that there is an apparently well-authenticated case of a person wb.0
could by an act of will stop his heart.

76

THE BUM AH BODY.

walls of various hollow organs of the body, as the stomach
(Fig. 34), the intestines, and the arteries ; by their con-
tractions they move things contained in those cavities
Like the voluntary muscles, the involuntary consist of
contractile elements, with accessory con-
nective tissue, blood-vessels, and nerves ;
but their fibres have a very different appear-
ance under the microscope. They are not
cross-striped, but are made up of elongated
cells united by a small amount of cement-
ing material. Each cell (Fig. 35), is flat-
fish, and tapers off toward its ends ; in its
centre is a nucleus with one or two nucle-
oli. The cells have the power of shortening
in the direction of their long axes.

Heart muscle. — The muscular tissue of
the heart is not under the control of the
will ; it, however, is cross-striped, and more
like the voluntary than the ordinary in-
voluntary muscle, though it differs in some
Fig. 35.— Unetriped respects from both.

muscltj-cclls.

Speaking generally, we may say that
the movements necessary for the nutrition of the body are
not left for us to look after ourselves, but are carried on
by muscles which work involuntarily ; the blood is
pumped round by the heart, and food churned up in the

What is their function? What are they composed of ? What is
seen when a cell from an involuntary muscle is examined with the
microscope?

Is the heart muscle voluntary? In what respect does it resemble
voluntary muscle?

What movements of the body docs nature not leave to our own
control? Give examples.

THE CHEMICAL COMPOSITION OF MUSCLE. 77

stomach and passed along the intestines, whether we
think about it or not.

The chemical composition of muscle. — Muscle contains
about 75 per cent, of water ; and a considerable quantity
of salines. Living, resting muscle is alkaline to test
paper ; hard-worked or dying muscle is acid. Its chief
organic constituents are proteid or albuminous substances
(p. 21), and of these the most abundant in a per-
fectly fresh muscle is myosin. Soon after death the
myosin clots. Dilute acids dissolve myosin and turn it
into syntonin, which used to be thought the chief pro-
teid of muscle.

Beef tea. — When lean meat is heated its myosin is
converted into a solid insoluble substance much like the
white of a hard-boiled egg. Hence, when a muscle is
boiled most of its proteid is coagulated and stays in the
meat instead of passing out into the soup. Even if beef
be soaked first in cold water this is still the case, as myo-
sin is not soluble in water.* It follows that beef tea as
ordinarily made contains little but the flavoring matters and
salts of the beef, and some gelatin dissolved out from the
connective tissue of the muscle. The flavoring matters

"What proportion of water does muscle contain? What other in-
organic compounds do we rind in it? What is the reaction of living
muscle? How is this changed by work or death? What are its main
jiganic constituents?- Name the most abundant of these? What
change occurs in it after death? What is syntonin?

"What happens to the myosin when muscle is heated? When we
boil meat does its myosin become dissolved in the soup? Can we get
the myosin out of beef by soaking it in cold water? "What things are
found in ordinary beef tea?

* To get over this difficulty, various methods of making beef tea have been
suggested, in which the chopped meat is soaked an hour or two in strong brine
or in very dilute muriatic acid. In these ways the myosin can be dissolved out
of the beef; but the product has such an unpleasant taste that no one is likely
to swallow it, and least of all a sick person.

78 THE HUMAN BODY.

make it deceptively taste as if it were a strong solution of
the whole meat, whereas, it contains but a small propor-
tion of the really nutritious parts, which are chiefly left
behind in tasteless shrunken shreds, when the liquor is
poured off. Some things dissolved out of the meat make
beef tea a stimulant to the nervous system and the heart,
but its nutritive value is small, and it cannot be relied upon
to keep up a sick person's strength for any length of time.

Liebig's extract of meat is essentially but a concentrated
beef tea; from its stimulating effect it is often useful to
persons in feeble health, but other food should be given
with it. It contains all the flavoring matters of the meat,
and its proper use is for making gravies and flavoring
soups; the erroneousness of the common belief that it is
a highly nutritious food cannot be too strongly insisted
upon, as sick persons may be starved on it if ignorantly
used.

Various meat extracts are now prepared by subjecting
beef to chemical processes in which it undergoes changes
like those experienced in digestion. The myosin is thus
made soluble in water and uncoagulable by heat, and a real
concentrated meat extract is obtained. Before relying on
any one of them for the feeding of an invalid, it would,
however, be well to insist on having a statement of its

Why does beef tea taste as if all the " strength " of the meat were
in it? Where do the chief nutritious parts remain when beef tea is
strained off the meat ? What is the action of beef lea on the system?

What is Liebig's extract of meat? Why is it sometimes useful to
invalids? What should be given them in addition? What is its
proper use? Why is it important to know that it is not a nutritious
food?

How are some other meat extracts made? How is the myosin
changed in preparing them? Are they all to be relied on indiscrimi-
nately? What should he done before trusting the nutrition Qf a
feeble person to any one of them ?

MEAT EXTRACTS. 79

method of preparation, and then to consult a physician, or
some one else who has the requisite knowledge, in order to
ascertain if the method is such as might be expected to
really attain the end desired.

A

CHAPTER VII.
MOTION AND LOCOMOTION.

The special physiology of muscles. — The distinctive prop-
erties of* muscle are everywhere the same ; it has the power
of contracting ; but the uses of different muscles are very
varied by reason of the different parts to which they are
attached. Some are muscles of respiration, others of
swallowing; some bend joints and are called flexors, others
straighten them and are called extensors, and so on.
The determination of the exact use of any particular
muscle is known as its special physiology, as distinguished
from its general physiology, or properties as a muscle,
without reference to its use as a muscle in a particular
place. We may here consider the special physiology of the
muscles concerned in standing and walking.

Levers in the body. — In nearly all cases the voluntary
muscles carry out their special functions with the co-oper-
ation of the skeleton ; most of them are joined to bones
at each end and when they contract move the bones,

In what respect are all muscles alike? Have all muscles the same
uses? Give instances of the employment of muscles for different pur-
poses. What is meant by the special physiology of a muscle? What
by its general physiologv?

With what do the voluntary muscles co-operate? To what are the
ends of nearly all muscles attached? What happens when a muscle
contracts?

[80]

THE DIFFERENT KINDS OF LEVERS. 81

and, secondarily, the soft parts attached to these. When
muscles move bones the latter are almost invariably to be
regarded as levers whose fulcra lie at the joint where the
movement takes place. Examples of the three forms of
levers recognized in mechanics are found in the human
body.

Levers of the first order. — In this form (Fig. 3G), the
fulcrum or fixed supporting point, F, lies between the
weight to be moved and the moving power. The distance

F

P J^ W

Fig. 36.— A lever of the first order. F, fulcrum ; P, power ; TF, resistance or
-*- ight.

PF from the power to the fulcrum is called the power-
arm of the lever, and the distance WF is the weight-
arm. When power-arm and weight-arm are equal (as in
an ordinary pair of scales), no mechanical advantage is
gained ; to lift a pound at W, P must be pressed down
with a force greater than a pound ; and the end W will
go up just as far as the end P goes down. If PF be
longer than WF then a small weight at P will balance a
larger one at W, the gain being greater the greater the
difference in the length of the arms, but the distance
through which W is moved will be less than that
through which P moves ; for example, if PF be twice as

How are the bones moved by muscles to be regarded? Where
do the fulcra of these levers lie? How many kinds of levers are
founrl in the body?

Describe a lever of the first order. Define power-arm and weight-
arm. When is a mechanical advantage gained by such a lever?

G

82 TEE EUMAN BODY.

long as W F then half a pound at P would balance
against a pound at W, and just over half a pound laid on
the end P would lift a pound on the end W, but FT would
only go up half as far as P went down. On the other
hand, if the weight-arm were longer than the power-arm
there would be a loss in force, but a gain in the distance
through which the weight was moved.

Examples of levers of the first order are not numer-
ous in the human body. One is found in nodding
movements of the head, the fulcrum being where the
occipital bone articulates with the atlas (Fig. 20). When
the chin is raised the power is applied to the skull behind
the fulcrum by muscles passing from the spinal column

P

F

W

Pig. 37.— A lever of the second order. F. fnfcnim ; P, power : W, weight
The arrows indicate the direction in which the forces act.

to the back of the head ; the resistance to be overcome is
the excess in weight of the part of the head in front of
the fulcrum over that behind it, and is not great, as the
head is nearly balanced on the top of the spine. To let
the chin drop does not necessitate any muscular effort.

Levers of the second order. — In this form of lever
(Fig. 37), the weight or resistance acts between the ful-
crum and the power. The power-arm PF is accordingly

What is lost when power is gained?

Are there many levers of the first order in the body? Give an
example of one, describing the action.
Describe a lever of the second order.

LEVERS IK THE BODY. 83

always longer than the weight-arm, WF, and so a com-
paratively weak force can overcome a considerable resist-
ance. There is, however, a loss in rapidity and extent of
movement, since it is obvious that when /■* is raised a
certain distance W will be raised less. As an example of
this kind of lever Ave may take the act of standing on
the toes. Here the foot is the lever, and the fulcrum is
where its fore part rests on the ground ; the weight is
that of the body, and acts downwards through the ankle
joint at Ta, Fig. 19 ; the power is the great muscle of the
calf of the leg pulling by its tendon, which is fixed to the
end of the heel bone, Ca.

Levers of the third order.— In these (Fig. 38), the
power is applied between the fulcrum and the weight ;
hence the power-arm FFt is always shorter than the

W

F

Fig. 38.— a lever of the third order. F, fnlcrnm ; P, power ; W, weight.

weight-arm, WF. The moving force acts at a mechani-
cal disadvantage, but swiftness and range of movement
are gained ; this is the form of lever most commonly used
in the body. For example, when the forearm is bent up
towards the arm the fulcrum is the elbow joint (Fig. 29) ;

What is the mechanical gain in such levers? What is the loss?
Give an example of employment of a lever of the second order in
the body, pointing out fulcrum, point of action of the weight, and
point of application of the power.

Describe a lever of the third order. What is lost and what
gained by it? Is it often used in the body? Give an example

84 THE HUMAN BODY.

the power is applied at the insertion of the biceps muscle
into the radius ; the weight is that of the forearm and
hand and whatever may be held in the latter, and acts at
the centre of gravity of the whole, somewhere on the far
side of the point of application of the power. Usually
(as in this case), the power-arm is very short, so as to gain
speed and extent of movement, the muscles being strong
enough to work at a considerable mechanical disadvantage.
The limbs are thus also made much more shapely than
would be the case were the power applied near or beyond
the weight.

Pulleys in the body — Fixed pulleys are used in the
body ; they give rise to no loss or gain of power, but
serve to change the direction in which certain muscles
pull. One of the muscles of the eye-ball, for example,
has its origin at the back of the eye-socket, from
there it passes to the front and ends, before it reaches the
eye-ball, in a long tendon. This tendon passes on to the
margin of the frontal bone, which arches over the front
of the eye-socket, and there passes through a ring
and turns back to the eye-ball. The direction in which
the muscle moves the eye is thus quite different from
what it would be if the tendon went directly to the eye-
ball.

Standing. — We only slowly learn to stand in the year
or two after birth, and though we finally come to do it
without conscious attention, standing always requires the
co»-operation of many muscles, guided and controlled by

Why is the power-arm in the hody usually short?
What kind of pulley is used in the body? Is any mechanical ad
vantage gained from it? What is it used for? Give an example.
Is standing a simple process?

STANDING. 85

the nervous system. The influence of the latter is shown
by the fall which follows a severe blow on the head, which
has fractured no bone and injured no muscle; "the con-
cussion of the brain" stuns the man, and until it has
passed off he cannot stand.

When we stand erect, with the arms close by the sides
and the feet together, the centre of gravity of the whole
adult body lies at the articulation between the sacrum
and the last lumbar vertebra, and a perpendicular
drawn from it will reach the ground between the feet.
In any position in which this perpendicular falls within
the space bounded by a line drawn close around both feet,
we can stand. When the feet are together the area enclosed
by this line is small, and a slight sway of the trunk
would throw a perpendicular dropped from the centre of
gravity of the body outside it ; the more one foot is in
front of the other the greater the sway back or forward
which will be compatible with safety, and the greater the
lateral distance between the feet the greater the lateral
sway which, is possible without falling. Consequently,
when a man wants to stand very firmly he advances one
foot obliquely, so as to increase his base of support both
from before back, and from side to side.

In consequence of the flexibility of its joints a dead
body cannot be balanced on its feet as a statue can.
When we stand, the ankle, knee, and hip-joints, if not
braced by the muscles, would give way, and the head also

Illustrate the influence of the nervous system in connection with
standing.

Where is the centre of gravity of the body when we stand erect?
Where does a perpendicular from it reach the ground? Why do we
separate the feet when we want to stand firmly?

Why cannot a dead body be balanced on its feet? What prevents
our knee, and hip-joints from bending when we stand?

86

IRE HUMAN BODY.

(L

i

fall forward on the chest. But (Fig. 39) muscles, 1, in
front of the ankle-joint, and others, I, behind it, both
contracting at the same time, keep the
joint from yielding ; similarly muscles
(2) in front of the knee and hip-joints
are opposed by others (II) behind
them, and when we stand both con-
tract to a certain extent and keep those
joints rigid ; and the muscles (III),
rl which run from the pelvis to the back

of the head similarly pull against
others, 3 and 4, which run from the
pelvis to the lower end of the breast-
bone, and from the upper end of the
breastbone to the anterior part of the
skull, and their balanced contraction
keeps the head erect. Since the degree
to which each muscle concerned con-
tracts when we stand must be accu-
rately adjusted to the contraction of
its antagonist on the opposite side of
the joint, we may easily comprehend
why it takes us some time to learn to
stand, and why a stunned man, whose
",„„ muscles have lost guidance from the

Fig. 39.— Diagram lllus-

InatitSic^rabdk (1S nervous system, falls.

ffind Phrj0intraBdab? Locomotion includes all movements

JSuSZ^ngS of the body in space, dependent on

the body erect. .^ ^ unaided muscular efforts,

such as walking, running, leaping, and swimming.

Explain how the different joints concerned are "braced" in stand-
in?1. Why does it take a child some time to learn to stand?
° What, is meant in physiology by locomotion?

WALKING. 87

Walking. — In walking, the body never entirely quits
the ground, the heel of the advanced foot reaching this
before the toe of the rear foot has been raised from it. In
each step the advanced leg supports the body, and the
foot behind at the beginning of the step propels it.

A little attention will enable any one to analyze the
act of walking for himself. Stand with the heels to-
gether and take a step, commencing with the left foot. The
whole body is at first inclined forwards, the movement
taking place mainly at the ankle joints. This throws the
centre of gravity in front of the base formed by the
feet, and a fall would result were not the left foot simul-
taneously raised by bending the knee a little, and swung
forwards, the toes just clear of the ground and the sole
nearly parallel to it. When the step is completed the left
knee is straightened and the foot placed on the ground,
the heel touching first ; the base is thus extended in the
direction of the stride and the fall prevented. Meanwhile
the right leg is kept straight but inclined forwards, carry-
ing the trunk during the step while the left foot is off the
ground ; at the same time the right foot is raised, com-
mencing with the heel ; when the step of the left leg is
completed only the great toe of the right is in contact
with the support. "With this toe a push is given which
.sends the body swinging forward, supported on the left
leg, which now in turn is kept rigid except at the ankle
joint ; the right knee is immediately afterwards bent and
that leg swings forwards, its foot just clear of the ground,
as the left did before. The body meanwhile is supported

Is the body ever off the ground iu walking? Describe the act of
walking.

88 THE HUMAN BODY.

on the left leg alone. When the right leg completes its step
its knee is straightened and the foot thus brought, heel
first, on the ground ; while it is swinging forwards the left
foot is gradually raised, and at the end of the step its great
toe alone is on the ground ; with this a push is given as
before with that of the right foot, and the left leg then
swings forward to make the next step. Walking may, it
fact, be briefly described as the act of continually falling
forwards and preventing the completion of the fall by
thrusting out a leg to meet the ground in front.

During each step the body sways a little from side to
side, as it is alternately borne by the right and left legs.
It also sways up and down a little ; a man standing with
his heels together is taller than when one foot is advanced,
just as a pair of compasses held erect on its points is high-
er when its legs are together than when they straddled
apart ; in that period of each step when the advancing
trunk is balanced vertically over one leg, the walker's trunk
is more elevated than when the front foot also is on the
ground. Women, accordingly, often find that a dress
which clears the ground when they are standing sweeps
the pavement when they walk.

The length of each step is primarily dependent on the
length of the legs, though it can be largely controlled by
special muscular effort, as we see in a regiment of soldiers,
all of whom have been taught to take the same stride, no
matter how their legs vary in length. In natural easy
walking, little muscular effort is employed to carry the
rear leg forward after it has given its push ; it swings on

At what part of a step is a man tallest ? Give illustrations.
What primarily determines the length of a person's step? Can
this leue;th be controlled? Illustrate.

HYGIENE OF THE MUSCLES. 89

like a pendulum once its foot is raised from the ground.
As short pendulums swing faster than long ones the natu-
ral step of short-legged people is quicker than that of
long-legged.

Running differs from walking in several respects.
There is a moment when hoth feet are off the ground ;
the toes alone come in contact with it at each step ; and
the knee joint is not straight at the end of the step. In
running, when the rear foot is to leave the ground the
knee is suddenly straightened, and the ankle-joint extend-
ed so as to push the toes forcibly on the support and pow-
erfully impel the whole body forwards and upwards. The
knee is then considerably flexed and the foot raised some
way from the ground, and this occurs before the toes of the
front foot reach the support. The raised leg in each step is
forcibly drawn forward by its muscles and not allowed to
swing passively as in quiet walking. This increases the
rate at which the steps follow one another, and the stride
is increased by the sort of one-legged jump that occurs
through the jerk given by the straightening knee of the
rear leg, just before it leaves the ground.

Hygiene of the Muscles. — The healthy working of the
muscles is dependent on a healthy state of the body in
general ; this is indispensable that they may be sufficiently
supplied with proper nourishment, and have their wastes
promptly carried away. Hence good food and pure air are
necessary for a vigorous muscular system. Muscles also

Why do short-legged persons tend to take a quicker step than
others?

How does running differ from walking? Describe the act of run-
ning. How is the number of steps taken in a giveu time increased in
running? How is the stride increased?

How does the state of general health influence the muscular sys-
tem? Why does an athlete need good food and air?

90 THE HUMAN BODY.

should not he exposed to any considerable continued
pressure, since this interferes with the flow of blood
and lymph through them which is essential for their nu-
trition.

Exercise is necessary for the best development of the
muscles. A muscle long left unused diminishes in bulk
and degenerates in quality, as is well seen when a muscle is
paralyzed and remains permanently inactive because of
disease of its nerve ; although at first the muscle itself
may be perfectly healthy, it alters in a few weeks, and
when the nerve is repaired the muscle may in turn be in-
capable of activity. The same fact is illustrated by the
feeble and wasted state of the muscles of a limb which
has been kept motionless in splints for a long time : when
the splints are removed it is only after careful and per-
sistent exercise that the long idle muscles regain their
former size and power. The great muscles of the
" brawn v arm" of the blacksmith illustrate the converse
fact — the growth of muscles when exercised.

Exercise, to be useful, must be judicious; taken to
the point of extreme fatigue, day after day, it does harm.
When a muscle is worked its substance is used up ; at
the same time and afterwards more blood flows to it,
and if the exercise is not too violent and the intervals of
rest are long enough, the repair and growth will keep pace
with or exceed the wasting: but excessive work and too
short rest will lead to diminution and enfeeblement of the
muscle just as certainly as too little exercise.

Few persons can profitably attempt to work hard daily

Why should muscles not be exposed to continuous pressure?

What happens when a muscle is not used? Illustrate by examples.
Why are the muscles of a blacksmith's arm large?

When does exercise do harm? Why? Can most persons work
hard with both brain and muscle at the same time?

Varieties of exercise. 91

with both brain and muscle, but all should regularly use
both; choosing which to work with, and which to simply
exercise. The best earthly life, that of the healthy mind in
the healthy body, can only so be attained. For persons of
average physique, engaged in study or business pursuits of
a sedentary nature, the minimum of daily exercise should
be an amount equivalent to a five-mile walk.

Time for Exercise. — Since extra muscular work means
extra muscular waste, and should be accompanied by an
abundant supply of food materials to the muscles, violent
exercise should not be taken after a long fast. Neither
should it be taken immediately after a meal ; a great deal
of blood is then needed in the digestive organs to provide
materials for digesting the food, and this blood cannot be
sent off to the muscles without the risk of an attack of
indigestion. Strong and hearty young people may take a
long walk before breakfast, but others had better wait un-
til after eating something before engaging in any kind of
hard work.

Varieties of Exercise. — In walking and running the
muscles chiefly employed are those of the lower limbs and
trunk ; these exercises leave the muscles of the chest and
arms imperfectly worked. Rowing is better, since in
it nearly all the muscles are used. No one exercise em-
ploys in proper proportion all the muscles, and gymnasia
in which different feats of agility are practiced so as to
call different muscles into action have a deserved popu-

How can the highest development of man, regarded merely as a
thinking and moving machine, be attained?

Why should we not exercise when fasting? Why not soon after
eating?

What muscles are chiefly used in walking and running!' WhbL
are imperfectly exercised? Why are gymnasia useful?

92 THE HUMAN BODY.

larity. It should be borne in mind, however, that the
legs especially need strength; while in the arms delicacy
of movement is more important to most persons than great
strength: and the fact that gymnastics are usually practised
indoors is also a great drawback to their value. Out-of-
door exercise in good weather is better than any other, and
every one can at least take a walk. The daily "constitu-
tional " is very apt to become wearisome, especially to young
persons, and exercise loses half its value if unattended with
feelings of mental relaxation and pleasure. Active games,
for this reason, have a great value for young and healthy
persons; lawn-tennis, base-ball, and cricket are all attended
with pleasurable excitement, and are excellent also as ex-
ercising many muscles.

What is chiefly needed in the muscles of arms and legs respec-
tively? Point out conditions under which muscular exercise loses
much of its value. Why are athletic games especially useful ?

CHAPTER VIII.
WHY WE EAT AND BREATriE.

How is it that the body can do muscular work? — In the

muscles we possess a set of organs capable of moving the
body from place to place, of changing the relative positions
of its parts, and of lifting external objects: as long as we
are alive, more or fewer of our muscles are every moment
doing some mechanical work. This fact suggests the
question, where does this power of working come from ?
In a few words, the answer is, it comes from the burning
of parts of the body itself : in the burning, work-power or
energy is set free and some of this is used by the muscles.
The conservation of energy. — The different natural
forces known to us are not nearly so numerous as the
kinds of matter : we all, however, know several of them,
as light, heat, electricity, and mechanical work. One of
the greatest discoveries of the nineteenth century is that
these different natural forces, or forms of energy, can be
turned one into another, directly or indirectly : kinds of
energy are transmutable, while,- so far as we know at pres-

What are the functions of the muscles? Are all of our muscles ever
at rest at the same time 1

What question does the constant activity of our muscles suggest?
How may this question be briefly answered ?

Name some forms of energy. Can they be turned from one
form to another ?

94 THE HUMAN BODY.

cnt, kinds of matter are not. "We cannot, as the alchemists
hoped, turn iron or mercury into gold, but we can turn
light into heat, and heat into electrical force, or into me-
chanical work. When such transformations are made it is
always found that a definite amount of one kind of energy
disappears to give rise to a certain definite amount of an-
other. In other words, it has been discovered that energy
cannot be created : if we take a given epiantity of heat we
can turn some of it into mechanical work ; if we then
turn all this mechanical work back into heat we get
again exactly the quantity of heat which disappeared
when the mechanical work appeared : and so with all other
transformations of energy from one kind to another, and
back again. This fact that energy or work-power can he
turned from one hind into another, and often bach again,
but never created from nothing or finally destroyed, is
known as the Jaw of the conservation of energy.

Illustrations of the conservation of energy. — In a steam-
engine, heat, which is the best known kind of energy, is
produced in the furnace ; when the engine is at work all
of this energy does not leave it as heat ; some is turned into
mechanical work, and the more work the engine does the
greater is the difference between the heat generated in the
furnace and that leaving the machine. If, however, we
used the work to rub two rough surfaces together we
could get the heat back, and if (which of course is im-
possible in practice) we could avoid all friction between

Can matter be transmuted ? What is always found when energy
is transformed ?

Can man create energy ? Illustrate the fact that energy can be
changed in kind but not created. What is meant by the law of the
conservation of energy ?

Give an illustration of the conservation of energy

THE CONSERVATION OF ENERGY. 95

the moving parts of the machine, and have all parts of the
engine at the end of the experiment exactly at the same
temperature as at its beginning, the quantity of heat thus
obtained would be exactly equal to the difference between
that amount of heat originally generated in the furnace
of the engine, and the quantity which had been carried off
from it to the air since its fire was lighted. Having
turned some of the heat into mechanical work we could
thus turn the work back into heat again, and find it yield
exac^.y the amount which seemed lost.

Or we might use the engine to drive an electro-magnetic
machine and so turn part of the heat liberated in its fur-
nace, first into mechanical work, and this afterwards into
electricity; and if we chose to use the latter with the proper
apparatus, as now used for electric lighting, we could turn
more or less of it into light; and so have a great part of the
energy which first became conspicuous as heat in the engine
furnace, now manifested in the form of light at some dis-
tant point. In fact, starting with a given quantity of one
kind of energy, we may by proper contrivances turn all
or some of it into one or more other forms ; but if we col-
lected all the final forms and retransformed them into the
first, we should have exactly the amount of it which had
disappeared when the other kinds appeared.

Why we need food. — Energy, as we have seen, cannot be
created from nothing ; since the body constantly expends
energy, it must have a steady supply. This supply comes

Give an example of the transformation of heat into electrical
force. Of electrical force into li_rlit. Given a supply of one kind of
energy what can we do with it? What would we find if we collected
all the final manifestations of energy and turned them back into the
original form ?

Why must the body have a steady supply of energy J Where
does the supply come from ?

% TEE EUMAN BODT.

from the energy liberated when parts of the body are burned,
or, as the chemists say, oxidized, just as that used by a
locomotive comes from the burning or oxidation of coal or
wood in its furnace. In consequence of this constant oxi-
dation, which destroys the tissues of the body as coal is
destroyed in a furnace, new materials must constantly be
supplied to make up for those used for oxidation. These
new materials are provided in our food. One chief reason
of our needing to eat, is that we may replace the parts of
the body which have been burned in order to set free the
energy which we spend in our muscular movements.

Why the body is warm. — As a working steam-engine is
warm so are our bodies, because all the energy which is set
free when substances are burned in them, is not turned
into mechanical work, but some of it appears as heat.
This keeping warm is a very important matter, for experi-
ment shows that no tissue of the human body works well
when cooled down even a few degrees below 98.5° F.,
which is its natural healthy temperature. Careful experi-
ments prove that when a muscle does work it becomes
hotter, and we all know that exercise makes us warm.
This shows that the oxidation or burning which takes
place in a working muscle does not all become turned into
mechanical work, but a good share of it appears as heat.
What is true of muscle is true of all other organs of the
body: when they work, no matter what their kind of work,
their substance is oxidized, and some of the energy set free

What is the chemical term for burning? What does food supply?

Point out a chief reason for our need of eating?

Why are our bodies warm ? Why is it important that they should
be warm ? How is the temperature of a muscle affected when it
works ? Do other organs resemble muscles in this respect?

THE NECESSITY OF FOOD. 97

by the oxidation appears as heat, assisting to keep the
body warm, and at its best working temperature.

A second reason why we need food. — Since the body only
works well at a temperature which is higher than that of
the air around it (except <m a very hot day), and in health
always keeps at this temperature, it must lose heat nearly
all the time. At night each of us is, in health, just as warm
as in the morning ; and in the morning as when we went
to bed ; though we have lost heat to the air during the
day, and to the bedclothes at night. In order to keep our
bodies at the temperature most suitable to their activity,
they must, therefore, generate heat all the time, to com-
pensate for the giving of it from them to the outer world.
In this necessity of generating heat we find a second reason
for the need of food : we require daily to take into our-
selves things which can be burned (or oxidized) in the
body, and which in so doing will give off heat.

The influence of starvation upon muscular work and
animal heat. — When a man is deprived of food the supply
of things which can lie oxidized in his body is cut off. The
tissues and organs are used up and not renewed ; his tem-
perature falls, his muscles become weaker and weaker, and
at last he dies. The body does not live, and work, and
keep warm, by means of a peculiar vital force or energy
which inhabits it, but by utilizing the energy Tset free in it
by the oxidation of foods, or of tilings made in it from
foods. If the food supply be cut off, the body first uses up

What must we conclude from the fact that our bodies keep at
nearly the same temperature all the time? How do we know that
they generate heat? Give a reason for taking food, iu addition to its
use as a source of energy to be spent by the muscles.

What happens when a man is starving ? How does the body live,
and keep warm, anil work? What first happens when the food sup-
ply is stopped?

7

98 TttE HUM An BODY

any reserve of nutritious matter which may have been
stored up in it when the starvation commenced, and as
this is expended it becomes weaker and weaker until
death supervenes.*

How long a man, totally deprived of food, can keep
alive, will depend, partly, on how much reserve material,
capable of oxidation, he has stored up in him when the
starvation period commences ; but largely, also, on the ex-
tent to which he can spare himself muscular work and
loss of heat. The breathing movements and beat of the
heart must go on, but if the individual lies quiet in bed
he need do little or no other muscular work ; and if he is
well covered up with blankets, the loss of heat from the
body is slight and calls for but little oxidation of the tissues
to compensate for it.f Also, a fat person will survive starva-
tion longer than a lean one ; during the process his fat is
slowly burnt; but so long as it lasts he can supply his mus-
cles with something which can be oxidized to yield working
power, and he also, by its burning, can maintain his tem-
perature. Fat is, in fact, a sort of reserve fuel, laid up in
the body, and a man, in the strict sense of the word, can
hardly be said to begin to starve until his fat has nearly all
been used up. J

Upon what does the length of life of a man getting no food de-
pend? What expenditures of energy must go on all the time? How
does lying in bed diminish the expenditure of energy? Why will a
fat man deprived of food live longer than a lean one?

When does a fasting man really begin to starve?

* When warm-blooded animals are starved their temperature slowly falls; and
when it comes down to about 77° f. (23° c.) death occurs: the various tissues at
that temperature can no longer work so as to maintain life.

t Hence Dr. Tanner, and " fasting girls " keep in bed, warmly covered up,
most of the time: the losses of the body in mechanical work and heat are thus
reduced to a minimum, and consequently the oxidation of the food reserves stored
in the body at the beginning of the fast.

% Some warm-blooded animals, as uears, hibernate; that is, sleep all through

OXIDATIONS IN THE BODY. 99

Oxidations in the body. — In the preceding paragraphs
oxidation and burning have been used as equivalent
phrases : this is in accordance with the teachings of chem-
istry. To the chemist a substance is bunted when it is
combined with oxygen, whether this combination take place
slowly or rapidly. If the combination occur rapidly the
burning or oxidizing mass becomes very hot and also gives
off light: such a rapid and vigorous oxidation is called a com-
bustion ; no combustions take place in our bodies.

It has, however, been proved that whether the combi-
nation of oxygen with an oxidizable, or burnable, substance
takes place rapidly or slowly, at the end of the process ex-
actly the same amount of energy will have been set free in
each case. When the oxidation occurs in a few seconds the
oxidizing mass becomes very hot : when it occurs slowly, in
a few days or weeks, the mass will never be very hot, be-
cause the heat set free in the process is carried off nearly
as fast as it appears.

Illustrations of oxidations at a low temperature. — If a
piece of magnesium wire be ignited in the air it will
become white-hot, flame, and leave at the end of a few

"What docs a chemist mean when he says a substance is burned ?
What is a combustion ? Do combustions occur in our bodies ?

Does the quantity of energy liberated by the complete oxidation
of any substance vary with the rate of oxidation ?

Why is a slowly oxidizing mass of matter not very hot ?

Give an instance of the oxidation of the same substance at high
and low temperatures.

the winter and take no food. They feed well in the warm weather, and are quite
fat at the close of aHtumn, when they seek some sheltered place to winter in. This
shelter and their warm, furry coats make the loss of heat very little; the animal,
except for its breathing and the beat of its heart, hardly ever moves during the
winter, and even those necessary movements are ruduced to the least possible, the
breathing and heart-beat being much slower than during the summer. With return
of warm weather the creature wakes up again, but is then lean, having burnt up
to fat dunng ite winter Bleep.

100 THE HUMAN BODY.

seconds only a certain amount of incombustible rust or
magnesia, which consists of the metal combined with oxy-
gen ; under these circumstances it has been burnt or oxid-
ized quickly at a high temperature. The heat and light
evolved in the process represent the energy which is set
free by the metal and oxygen when they combine. We
can, however, oxidize the metal in a different way, attend-
ed with no evolution of light and no very perceptible rise
of temperature If, for instance, we leave it in wet air, it
will become gradually turned into magnesia without hav-
ing ever been hot to the touch or luminous to the eye.
The process then, however, takes days or weeks ; but in
this slow oxidation just as much energy is liberated as in
the former case, although now all takes the form of heat ;
and instead of being liberated in a short time is spread
over a much longer one, as the. gradual chemical combi-
nation takes place. The slowly oxidizing magnesium is, in
consequence, at no moment noticeably hot, since it loses its
heat to surrounding objects almost as fast as it generates
it. The oxidations occurring in our bodies are of this
slow kind. An ounce of arrowroot oxidized in a lire, and
in the human body, would liberate exactly as much ener-
gy in one case as the other, but the oxidation would take
place in a few minutes and at a high temperature in the
former, and slowly, at a lower temperature, in the latter.

Oxidation in the presence of moisture. — Wet wood or
wet coal we know will not burn, or can only be made to do
so with difficulty. Other kinds of burning or oxidation
are, however, well known, which take place in the pres-

How does the rate of oxidation differ in the two cases ? TTovv
does the oxidation of arrowroot burned in a fire differ from its oxida
tion in the living body?

Can oxklations occur in the presence of moisture V

OXLDA Tlom IN THE PRESENCE OF MOISTURE. 101

ence of moisture. The rusting of iron, for example, is
an oxidation or burning of the metal, and takes place
faster in damp air than in dry; during the slow rusting in
moisture just as much heat is set free as if the same com-
pound of iron and oxygen were prepared in a more rapid
way. Such experiments throw great light on the oxida-
tions which take place in our own bodies. All of them
are slow oxidations, which never at any one moment give
off a great amount of heat, and all occur in the damp
tissues.

Summary. (1) Energy can be turned from one form in-
to another ; as from heat into mechanical work by a steam-
engine. (2) Our bodies are constantly losing energy, partly
in muscular work, and partly as heat lost to surrounding
objects. (3) Energy cannot be created ; all that can be
done is to turn one kind of it into another kind: heat can
be turned into mechanical work (as in a locomotive) ; or
mechanical work into heat (as by friction) ; or heat into
electricity (as in a thermo-electric machine); and so forth.
(4) Since our bodies spend energy all our life long they
must be supplied with it from outside : they can turn into
other forms the energy which they receive, but they cannot
make it from nothing. (5) The chief forms of energy which
our bodies expend are muscular (t. e. mechanical) work,
and heat. (6) In ordinary machines, as a locomotive, the

Give an instance. Does the rate of oxidation or the presence
of moisture affect the amount of heat liberated ?

Of what kind are the oxidations which occur in our bodies ?

Give a summary of the contents of this chapter with reference to
the following points: (1) The transformation of energy; (2) The loss
of energy from the body ; (3) The fact that man cannot create ener-
gy but can transmute it ; (4) The fact that our bodies must be con-
stantly supplied with energy from outside ; (5) The chief forms of
energy spent by the body ; (6) The source of the energy spent by a
working steam-euginy.

102 THE HUMAN BODY.

source of the work done and the heat given off is the oxida-
tion of coal in a furnace. (?) Chemistry teaches us that just
the same amount of energy or work power is given off when
an ounce of any given substance is oxidized, whether the
oxidation occurs rapidly or slowly. (8) Chemistry also
teaches us that many oxidations, or burnings, occur in the
presence of water, and that in them just the same amount
of energy is set free as if the oxidation occurred in dry air.
(9) In our bodies substances are burnt slowly at a low
temperature and in the presence of moisture: in this burn-
ing energy is set free which the body uses for performing
its necessary work. (10) In the burning which the tissues
undergo while they work they are used up and destroyed.
(11) To compensate for the destruction of tissue which
accompanies and provides the power for every action of
the body, material must be taken into it from outside,
which wrili restore or repair the oxidized tissues. (12)
Such substances taken into the body from outside are
called ybo^s, and the constant oxidation of the body which
is necessitated by the performance of the functions essen-
tial to life, requires a supply of food from the outer world,
if life is to be maintained. (13) The body of a healthy
person has in it at any moment a certain reserve of oxid-
izable matters, which we may call stored-up food. The
most important of these reserve foods is fat. A fat man
can accordingly bear starvation longer than a lean one un-
der similar circumstances.

(7) The amount of energy given off when a substance is oxidized
at high or low temperatures; (8) The teachings of chemistry with
reference to oxidations in the presence of moisture ; (9) The con-
ditions under which substances are oxidized in our bodies ; (10) The
changes which oxidized tissues undergo; (11) Why we nee 1 to
take materia*! from the outer world into our bodies ; (12) What is
meant by food ; and wh}' we need foods ; (lo) What are reserve
foods. Illustrate.

THE OXYGEN FOOD OF THE BODY. 1Q3

The oxygen food of the body. — Hitherto we have only
considered the energy-supply of the body from one side ;
we have regarded it as dependent on the constant supply
of things which can be oxidized. But this is only half the
question : if substances are to be oxidized there must be a
provision of oxygen to oxidize them.

In order that a steam-engine may work and keep warm
it is not merely necessary that it have plenty of coal, but
it must also have a draught of air through its furnace.
Chemistry teaches us that the burning in this case consists
in the combination of a gas called oxygen, taken from the
air, with other things in the coals: when this combination
takes place a great deal of heat is given off. The same
thing is true of our bodies ; in order that food matters
may be burnt in them and enable us to work and keep
warm, they must be supplied witli oxygen; this they get
from the air by breathing. We all know that if his sup-
ply of air be cut off a man will die in a few minutes. His
food is no use to him unless he gets oxygen from the air to
combine with it ; while he usually has stored up in his
body an excess of food matters which will keep him alive
for some time if he gets a supply of oxygen, he has not
stored up in him any reserve, or, if any, but a very small
one, of oxygen, and so he dies very rapidly if his breathing
be prevented. In ordinary language we do not call oxygen
a food, but restrict that name to the solids and liquids which
we swallow : but inasmuch as it is a material which we
must take from the external universe into our bodies in or-

Why do we need oxygen ? What does a working steam-engine
need in addition to coal ? What happens in the furnace of an engine?
Why do we need to breathe ? What happens if a man's air supply
be stopped ? Why does a man die sooner of want of air than of want
of food ? Why is oxygen entitled to be called a food '/

104 THE HTTMAJf BODY.

der to keep us alive, oxygen is really a food as much as any
of the other substances which we take into our bodies
from outside, in order to keep them alive and at work.
Suffocation, as death from deficient air supply is named, is
really death from oxygen-starvation.

What is suffocation?

Appendix to Chapter VIII.

The liberation of energy by oxidation, or burning, at a low tem-
perature and in the presence of moisture, is such a fundamental fact
in physiology, and its essential agreement with ordinary combustion
so difficult to grasp by most pupils, who naturally associate burning
with a high temperature and luminosity, that it is worth while to il-
lustrate these facts by a few simple experiments.

1. Buy a coil of magnesium wire, which can be obtained at small
cost. Rub it clean with fine emery paper : cut it in two, apply a
lighted match to one half and show how it is rapidly consumed with
the evolution of light and heat, leaving behind only a white powder,
magnesia, which is oxidized magnesium. Put the other half away in
a bottle with a few drops of water. After a day or two its surface
will be covered by a layer of magnesia; if this be scraped off another
will succeed it ; and so on. This experiment shows that oxidation
may occur rapidly at a high temperature in a short time, or slowly
at a low temperature in a long time, but the ultimate product, in each
case, is the same.

2. In relation to a subsequent paragraph (p. 112) the magnesia ob-
tained by burning the wire in the air, may be kept, and attempts
made to ignite it: this will serve to show the uselessness of oxidized
substances to the body, as sources of energy : they cannot be any
more oxidized, and the best thing to do is to get rid of them.

3. Get a bundle of iron wire : rub it bright with emery or sand
paper. Place some in a warm dry bottle by the stove or fireplace.
Put the rest in a bottle containing a little water. Next day the first
specimen will be found bright, and the second covered with rust. This
shows that oxidation may sometimes occur better in the presence of
water than in its absence ; and serves as a text for pointing out how
oxidations occur in the moist tissues of the body.

CHAPTER IX.
NUTRITION.

The Wastes of the Body. — A man takes into his body
daily several pounds of foods of various kinds, as meats,
bread, vegetables, and water, yet he grows no heavier; it is,
therefore, clear that his body must in every twenty-four
hours return, on the average, to the outside world about as
great a weight of matter as it receives from it. Even in
childhood, while growth is taking place and the body be-
coming heavier, the gain is never nearly equal to the weight
of the foods swallowed. The materials given off daily from
the body to the external universe, and compensating more
or less accurately for the receipts from the outside world,
are its wastes, and are chiefly things which cannot be
burned. Much of the food taken in can be, and is, oxi-
dized to enable us to move and keep warm. When burned
it is of no further use to us, and would only clog up the
various organs, as the ashes and smoke of an engine would
soon put its fire out if they were allowed to accumulate in
the furnace. The chief wastes of the body are carbon di-
oxide gas, water, and a kind of ammonia called urea.

Receptive and Excretory Organs. — Those organs of the
body whose function it is to gather new material from
outside for its use are known as receptive organs. There

"What facts make it clear that a man must daily give off several
pounds weight of matter from his body? Does a child's increase in
weight equal the weight of the food it has eaten? What is meant by
the "wastes" of the body? How do most foods differ from wastes
in regard to oxidation ? Why must wastes be removed from the body ?
Name the chief wastes of the body.

What is meant by the receptive organs?

[105]

106 THE HUMAN BODY.

are two chief sets of these — one to receive oxidizable things,
and the other to receive oxygeu. The first set is represent-
ed by the alimentary canal, consisting of mouth, gullet,*
stomach, and intestines. It takes in food and drink. The
second set consists of the lungs, with the air passages lead-
ing to them ; their business, as receptive organs, is to
absorb oxygen.

The organs whose duty it is to get rid of waste materials
formed in the body are called excretory organs. The three
most important excretory organs are the lungs, the kidneys,
and the shin; the lungs pass carbon dioxide gas out to the
air, and also water ; the kidneys get rid of urea and water ;
and the skin, of water and a little urea.

The Intermediate Steps between Reception and Ex-
cretion.— Between the taking of oxidizable substances into
our mouths and oxygen into our lungs, on the one hand,
and the return of oxidized matters from our bodies to the
surrounding world on the other, a great many intermediate
steps take place. The alimentary canal (see Fig. 1) is a
tube which runs through the body but nowhere opens into
it ; so long as food lies in this tube it therefore does not
really form a part of the body, and is of no use to it : it
resembles coals in the tender of a locomotive, waiting to be
transferred to the furnace. In our bodies the furnace is
everywhere; wherever there is a living tissue things are

What are the functions of the two chief sets? Name those con-
cerned in receiving oxidizable things. Those whose business it is to
absorb oxvgen.

What is meant by the excretory organs? Name the most im-
portant. What does each get rid of?

Why is food in the stomach not really a pan of the body? To
what may we liken it? Where is the furnace of the body? Why
must food be carried all over the body?

* The technical name for the erullet is oesophagus.

JSUTMI10S. 107

burned to enable it to work; and the food or fuel must be
brought therefore, to every corner of our frames.

Digestion. — A great part of our food is solid, and could
not of itself get outside of the alimentary canal. To render
it available it must be dissolved so that it can souk through
the walls of the stomach and intestines. For this purpose
we find a set of digestive organs which make solvent juices
and pour them on the food which we swallow, and so get
it into a liquid state in which it can be absorbed.

Circulation. — The solution containing our digested food
if it simply soaked through the walls of the alimentary
canal, would be of no use to distant parts, as the brain, or
the muscles of the limbs. We find, therefore, in the body
a set of tubes containing blood, and called blood-vessels:
the blood is driven through these by a pump, the heart.
Much of the dissolved food passes into the blood-vessels of
the alimentary canal, and from them is carried by other
blood-vessels to every organ, no matter how remote. As
the blood flows unceasingly, round and round in its vessels,
from part to part, the organs concerned in moving and
conveying it are called circulatory organs, and the blood-
flow itself is known as tltc circulation.

Absorbents. — Some of the dissolved food is taken up
into another set of tubes in the walls of the alimentary
canal; these tubes carry it afterwards into the blood-vessels.
They are called the absorbents.

Why must many foods be dissolved? What is accomplished by
the digestive organs?

What are the blood-vessels? What enters those of the alimentary
canal? How are organs distant from the alimentary canal nourished"?
Why are the organs which keep up the blood-flow called circulatory
organs? What is meant by the circulation?

What are the absorbents? Where do they convey the foods
which they take up in the walls of the alimentary canal?

108 THE HUMAN BODY.

Respiration. — The blood in its course flows through the
lungs. It is necessary not merely that food, but oxygen also
should be carried to every part of the body. As the blood
traverses the lungs it picks up oxygen from the air in them;
this air is then renewed by taking a fresh breath, and so
on. The organs concerned in renewing the air in the
lungs are the respiratory organs, and the act of renewal is
respiration.

Assimilation. — As each organ works it oxidizes; some of
its substance is broken down by combination with oxygen
brought to it by the blood, and is thus converted into burnt
waste matter. The blood, as we have seen, brings, how-
ever, not merely oxygen, but also food matters in solution.
These ooze through the walls of the blood-vessels, and are
taken up by the living tissues and built into new tissues
like themselves, to replace the part which has been used
up and destroyed. This building and repair of tissues
and organs from the dissolved food obtained from the
blood is known as assimilation, — in plain English, "a
making alike." Each living tissue takes from the blood
foods which are not like itself, and builds them up into a
form of matter like its own. The converse process, which
accompanies all vital action, the breaking down into wastes
of a living tissue when it works, is called dissimilation,
or "a making unlike.5'

The Relation of the Circulatory Organs and the Absorb-
ents to Excretion. — It is as essential to the body that its
wastes be carried off from the organs, as that the used-up

What must be carried to all parts in addition to food ? Where
does the blood get oxygen? What is meant by the respiratory
organs? By respiration ?

What happens when an organ works? How are oxidized tissues
replaced? What is meant by assimilation ? By dissimilation?

What is needful to each organ in addition to a supply of fresh
material?

NUTRIT10X. 109

material be replaced by new. Kot merely must matter for
assimilation be provided, but the various waste products
must be removed. Here again tbe blood-vessels and ab-
sorbents come into play. Absorbents are found not only
in the walls of the alimentary canal, but all over the bodv.
The wastes of each working tissue are passed out into
them, and by them carried into the blood-vessels; these
in turn carry the wastes to the lungs, kidneys, and skin,
which get rid of them. The blood is thus as important
in relation to removing the waste matters of an organ as
in regard to supplying it with food and oxygen.

Nutrition. — From what has been said above it is clear
that the nourishment of the body is a very complicated
process. It implies — (1) the reception of food from out-
side ; (2) the digestion of food ; (3) the absorption of
digested food ; (4) the conveyance of absorbed food to all
parts by the blood: (5) the taking up of wastes from the
different organs ; (G) the conveyance of these wastes by the
blood to excretory organs which pass them out of the body ;
(7) the absorption of oxygen in the lungs, and its con-
veyance by the blood to every organ ; (8) assimilation or
the building up of new tissue from materials brought by
the blood ; and (9) disassimilation, or the breaking down
of working tissues by combination with oxygen.

In subsequent chapters we shall have to consider in
more detail, Digestion, Circulation, Absorption, Respira-
tion, and Excretion. The sum total of the actions of all
the organs concerned in the nourishment of the body is
known as the function of nutrition.

Where do we find absorbents in addition to those of the alimen-
tary canal? What is their function? What part does the blood
play in the removal of wastes?

Enumerate the processes concerned in the nourishing of the body

What is meant by the function of nutrition?

CHAPTER X.

FOODS.

Foods as Tissue Formers. — In the last chapter we have
considered foods merely as sources of energy, bat they are
also required to build up the substance of the body. From
birth to manhood we increase in bulk and weight, and
that not merely by accumulating water and such sub-
stances, but by forming more bone, more muscle, more
bruin, and so on, from the things which we eat. Even
after full growth, when the body ceases to gain weight,
the same constructive processes go on; the living tissues
are steadily oxidized and broken down as they work, and as
constantly reconstructed.

Foods are therefore needed, not only to supply the body
with work-power by their oxidation, but to supply material
from which new living tissue can be constructed.

What Foods must Contain. — Most foods serve for both
purposes, energy supply and tissue formation; they are
built up by the living cells into new tissue before they are
oxidized to set energy free. Our food must, therefore,
contain such substances as the body can utilize for tissue
formation.* The living tissues when analyzed are found

What use have foods besides supplying energy to the body?
Illustrate from the growth of a child. Why are foods needed for
construction after growth has censed?

What purposes do most foods serve? Are they usually oxidized
before making tissue? What sort of substances must our food
contain?

* Whether any food is ever oxidized in the body before being built up into
a tissue, as coal is burnt in an engine without ever forming part of the engine,
must still be regarded as an open question in physiology. The old doctrine that
some foods, as starch and sugar, were useful only to set free heat, and others,
as albumen and flesh, alone built tissue, must be given up. It 6eems certain

[110]

THE IMPORTANCE OF PROTEID FOODS. HI

to consist . ainly of carbon, hydrogen, nitrogen, and oxy-
gen, and we might at first suppose that these chemical ele-
ments in their uncombined form would serve to nourish
us. Experience, however, teaches that this is not the case.
Four fifths of the air is nitrogen, but we cannot feed on it;
hydrogen gas is of no use as a food; and a lump of char-
coal (carbon) might fill the stomach, but would not keep a
man from starving. Oxygen can be utilized when taken
by the lungs from the air; but all other elements to be of
use as food must be taken, not in their separate state,
but in the form of complex compounds, in which they are
chemically combined with other things; as, for example,
in starch, and sugar, and fat, and oil, and albuminous sub-
stances.

The Special Importance of Albuminous or Proteid Foods.
— All the active tissues of the body are found to yield on
chemical analysis large quantities of proteids. (See p. 21).
As the tissues work this proteid is broken down, and its
nitrogen carried off in the form of a peculiar ammoniacal
substance, urea; to repair the wasted living tissue new
proteids must be laid down in it. So far as we know at
present the human body (like that of most animals) is un-
able to make proteids out of other things; given one vari-

What elements do the tissues yield on analysis ? Can wc feed
on these elements in their uncombined state ? Name one -which is
absorbed in a free state and used. Whence is it derived ? What
organs receive it? Name substances containing the necessary elements
in combination and used as food.

What do we find in all the active tissues? What becomes of the
nitrogen of working tissues? Explain why proteids are an essential
article of diet.

that under some conditions sugar and starch may be used in building tissue,
though they cannot do it alone; but whether they are under any circumstances
ever burnt before making part of a tissue is not certain. On the other hand,
there is some reason to suspect that albuminous substances may, when eaten
in excess, be oxidized in the body without ever forming part of a living cell

112 THE HUMAN BODY.

ety of them it can turn it into other varieties, but it cannot
make proteids from things which are not proteids. Hence
these albuminous or proteid substances are an essential
article of diet.

The Limited Constructive Power of the Animal Body. —
From what has been said above it is clear that our bodies
are, on the whole, destructive rather than constructive in
relation to the outer world. They require for their nutri-
tion very complex chemical compounds (starch, sugar, fat,
proteids), build these up into living tissues, and then
oxidize the tissues and return the carbon, hydrogen, and
nitrogen, which were received from outside in the form of
complicated chemical molecules, to the outer world in the
form of much simpler chemical compounds, namely, carbon
dioxide, water, and urea. None of these latter substances
is capable of nourishing an animal ; it cannot from them
alone build up its tissues or set free energy.

How Plants Supply Food for Animals, and Animals
Food for Plants. — Since animals are essentially proteid con-
sumers, and destroyers also of other complex substances,
as starch and sugar, the question naturally suggests itself,
How is it, if animals are constantly consuming these
things, that the supply of them is kept up? For example,
the supply of proteids ; they cannot be made artificially
by any process known to us. The answer is, that animals
live on the things which plants make, and plants live on

Do our bodies on the whole build up or break down chemical
compounds? What class of compounds do they require for their
nutrition? What do they do with these compounds? What simple
compounds docs the hody return to the outer world? Can these
compounds feed any animal?

What facts suggest the question, How is the supply of pro-
teids and other complex foods kept up? How is the question
answered ?

NON-OXIDTZABLE FOODS. 113

the carbon dioxide and water and ammonia (urea) which
animals excrete.

As regards our own bodies the question might, indeed,
be apparently answered by saying that we get our proteids
from the flesh of the other animals which we eat. But,
then, we have to account for the possession of proteids by
those animals ; since they cannot make them from urea
and carbon dioxide and water any more than we can. The
animals whose flesh is used by us as food get their proteids fro in
plants, which are the great proteid formers of the world;
the most carnivorous animal really depends for its niost
essential foods upon the vegetable kingdom; the fox that
devours a hare, in the long run lives on the proteids of
the herbs that the hare had previously eaten.*

Non-Oxidizable Foods. — Besides our oxidizable foods a
large number of necessary food materials are not oxidizable,
or at least are not oxidized in the body. Typical instances
are afforded by water and common salt. The use of these is
in great part physical: the water, for instance, dissolves ma-
terials in the alimentary canal, and carries the solutions
through its walls into the blood and lymph vessels, so that
they can be conveyed from place to place; and it permits
interchanges by enabling the things it has dissolved to
soak through the walls of the vessels. The salines also
influence the solubility and chemical interchanges of other
things present with them. Fibrinogen, one of the proteids

Where does the proteid that a man eats in a piece of beef come
from? Explain.

What foods are necessary in addition to oxidizable? Give ex-
amples. What are their physical uses?

* Some animals are known which contain cblorophyl, the green coloring
matter of plant leaves; and it has recently been proved that these animals, like
plants, can, when exposed to the action of light, live on the waste products of
other animals.

114 THE HUMAN BODY.

which is carried in the blood all over the body to supply al-
buminous material to the tissues, is, for example, insoluble
in pure water, but dissolves readily if a small quantity of
common salt be present. Besides such uses, the non-oxidiz-
able foods have probably others, as what may be called
machinery formers. In the lime salts, which give their
hardness to the bones and teeth, we have an example of such
an employment of them; and to a less extent the same may
be true of other tissues. The body is a self-building and
self-repairing machine, and the material for this building
and repair, as well as the fuel or oxidizable foods which
yield the energy the machine expends, must be supplied in
the food. While experience shows us that even for
machinery construction oxidizable matters are largely
needed, it is nevertheless a gain to replace such substances
by non-oxidizable material when possible; just as, if prac-
ticable, it would be advantageous to construct an engine
out of a substance which would not rust, although other
conditions determine the selection of iron for building the
greater part of it.

Definition of Foods. — Foods are (1) substances which are
taken into the alimentary canal, which can be absorbed
from it, and after absorption serve to supply material for
the growth of the body, or for the 1'eplacement of matter
which has been removed from it; or (2) they are substances
which can be oxidized in the body to yield energy for its use;
or (3) substances, which by dissolving nutritive or ivaste

Illustrate the use of common salt in helping to keep important
substances in solution. Illustrate the employment of non-oxidizable
foods in constructing the body. What must foods supply to the
body besides fuel? Why? Are oxidizable foods used in machinery
construction? Give an example showing the gain of using non-
oxidizable matters when possible.

Give a definition of foods.

DEFISITIOX OF FOODS. 115

matters facilitate the transfer of material from the recep-
tive organs to the working, and from the working to the
excretory. Foods to replace matters which have been oxi-
dized must be themselves oxidizable; they are force gener-
ators, but may be and generally are also tissue formers: they
are nearly always complex organic substances derived from
other animals or from plants. Foods to replace matters
not oxidized in the body, as water and salt, are force regu-
lators, and are for the most part tolerably simple inorganic
compounds. Among the force regulators we must, how-
ever, include certain foods, which, although oxidized in the
body and serving as sources of energy, yet produce effects
totally disproportionate to the amount of energy which they
thus set free. Their influence as stimulants in exciting cer-
tain tissues to activity, or as agents checking the activity of
parts, is more marked than their direct action as force gener-
ators. As examples, we may take condiments: mustard and
pepper are not of much use as sources of energy, although
they no doubt yield some when oxidized; we take them for
their stimulating effect on the mouth and other parts of the
alimentary canal, by which they promote a greater flow
of the digestive secretions or an increased appetite for food.
Thein, again, the active principle of tea and coffee, is taken
for its stimulating effect on the nervous system rather than
for the amount of energy which is yielded by its own oxi-
dation.

To the above definition of a food should be added the
condition that, neither the substance itself nor any of the

What foods must be oxidizable? What are they called? Do they
also make tissue? Are they complex or simple? What i^ their source?
What is meant by force regulators? Examples? Are thejr chem-
ically complex or simple? What oxidizable foods are included
among the force regulators? How is their influence chiefly exhib-
ited? Give examples

116 THE HUMAN BODY,

products of its chemical transformation in the body shall he
injurious to the structure or action of any organ; other-
wise it would he a poison, not a food.

Alimentary Principles. — The substances which in ordi-
nary language we call foods are in nearly all cases mixtures
of several foodstuffs with substances which are not foods at
all. Bread, for example, contains water, salts, gluten (a
proteid), some fats, much starch, and a little sugar; all these
are true foodstuffs, but mixed with them is a quantity
of cellulose (the chief chemical constituent of the walls
which surround vegetable cells), and this is not a food, since
it is incapable of absorption from the alimentary canal.
Chemical examination of all the common articles of diet
shows that the actual number of important foodstuffs is
but small; they are repeated in various proportions in the
different foods we eat, mixed with small quantities of dif-
ferent flavoring substances, and so give us a pleasing
variety in our meals; but the essential substances are much
the same in the fare of the artisan and in the "delicacies
of the season." The chief foodstuffs, which are found re-
peated in many different foods, are known as "alimentary
principles," and the nutritive value of any article of diet
depends on the proportion of these foodstuffs which is
present, far more than on the various agreeable flavoring
matters which cause certain things to be especially sought
after, and to have a high market value. Alimentary prin-
ciples may be conveniently classified into proteids, albu-
minoids, hydrocarbons, carbohydrates, and inorganic bodies.

What is a poison?

What are ordinary foods? Give an example. Why is cellulose
not a food? What does chemical examination of ordinary foods
show? How do we get variety in our foods? What are "alimentary
principles"'? On what does the nutritive value of a food depend?
Into wiiat groups are alimentary principles classified?

ALIMENTARY PRINCIPLES. 117

Proteid Alimentary Principles. — Of the nitrogen-contain-
ing foodstuffs the most important are proteids: they form
an essential part of all diets, and are obtained both from
animals and plants. The most common and abundant are
myosin and syntonin, which exist in the lean of all meats;
egg albumen; casein, found in milk and cheese; gluten and
vegetable casein from various plants.

Albuminoid Alimentary Principles. — These also contain
nitrogen, but cannot entirely replace the proteids as foods;
though a man can manage with less proteids when he has
some albuminoids in addition. The most important is
gelatine, which is yielded by the connective tissue and bones
of animals when cooked. On the whole the albuminoids
are not foods of high value, and the calf s-foot jelly and
such compounds often given to invalids have not nearly the
nutritive value they are commonly supposed to possess.

Hydrocarbons {Fats coal Oils). — The most important of
these are stearin, palmatin, margarin, and olein, which exist
in various proportions in animal fats and vegetable oils; the
most fluid containing more olein : butter contains u pecu-
liar fat known as butyrin. All fats are compounds of
glycerine with fatty acids, and, speaking generally, any
such substance which is fusible at the temperature of the
body will be useful as a food. The stearin of beef and mut-
ton fats is not by itself fusible at the body temperature, but
is mixed in those foods with so much olein as to be melted

What nitrogen-containing substances form an essential article of
diet? Whence are they obtained? Name the most important proteid
foods.

What foods besides proteids contain nitrogen? To what extent
can they take the place of proteids? How is gelatin obtained? Should
we try to build up an invalid's strength on calf 's-foot jelly alone?
Give the reasons for your answer.

To what group of foods do fats and oils belong? Name the more
important. What is their chemical composition ? Why are some
tatty bodies not nutritious? Give an instance.

118 THE HUMAN BODY.

in the alimentary canal. Beeswax, on the other hand, is a
fat which will not melt in the intestines and so passes on
unabsorbed, although from its composition it would be use-
ful as a food could it be digested.

Carbohydrates. — These are mainly of vegetable origin.
The most important are starch, found in nearly all vege-
table foods; dextrin; gums; grape sugar (found in most
fruits); and cane sugar. Sugar of milk and glycogen are
alimentary principles of this group derived from animals.
All carbohydrates, like the fats, consist of carbon, bydrogen,
and oxygen; but the percentage of oxygen in them is much
higher than in fats. When oxidized tiny have therefore less
power of combining with additional oxygen than fats, and
so are not capable of yielding as much energy to the body.

Inorganic Foods. — The most important of these are
water; common salt; and the chlorides, phosphates, and
sulphates, of potassium, magnesium, and calcium. A suf-
ficient quantity of most of these substances, or of the ma-
terial for their formation, exists in all ordinary articles of
diet, so that we do not swallow most of them in a separate
form. Water and table salt form exceptions to the rule
that inorganic bodies are eaten imperceptibly along with
other things, since the body loses more of each daily than is
usually supplied in that way. It has been maintained that
salt as a separate article of diet is an unnecessary luxury,
and there seems to be some evidence that certain savage tribes
live without more than they get in the meat and vegetables

What is the chief source of carbohydrates? Name the most im
portant. Name carbohydrate foods derived from animals. How do
they resemble fats in composition, and how do they differ from them?
Can an ounce of starch yield as much energy to the body as an ounce
of fat? Give a reason lor your answer.

Name the more important inorganic foods. Why do we not require
to eat most of them separately ? What inorganic foods are taken in
a separate form ? Why ?

THE NUTRITIVE VALUE OF DIFFERENT FOODS. 119

which they eat. Such tribes are, however, said to suffer
especially from intestinal parasites; and there is no doubt
that to many animals as well as most men the absence of
salt from their diet is a terrible deprivation. Buffaloes and
other creatures are well known to travel miles to reach
" saltlicks;" of two sets of oxen, one allowed free access to
salt, and the other given none save what existed in its or-
dinary food, it was found after a few weeks that those given
salt were in much better condition. In man the desire for
salt is so great that in regions where it is scarce it is used as
money. In some parts of Africa a small quantity of salt will
buy a slave, and to say that a man commonly uses salt at his
meals is equivalent to stating that he is a luxurious mill-
ionaire. In British India, where the poorer natives regard
so few things as necessaries of life that it is hard to levy any
excise tax, a large part of the revenue is derived from a salt
tax, salt being something which even the poorest will buy.
As regards Europe, it has been found that youths in the
Austrian empire who have fled to the mountains and there
led a wild life to avoid the hated military conscription, will,
after a time, though able abundantly to supply themselves
with other food by hunting, come down to the villages to
purchase salt, at the risk of liberty and even of life.

The Nutritive Value of Different Foods. — All meats,
whether derived from beast, bird, or fish, are highly valu-
able foods. They contain abundant albumen, more or less
fat, and, when cooked, their connective tissue is in great part
turned into gelatin. Pork is the least easily digested form
of fresh meat, and contains a larger percentage of fat than
most. This fat, which, by its oxidation liberates much

Give illustrations of the strength of the desire for salt.
Why are meats valuable foods? How does pork differ from other
fresh meats? Why is pork not a good form of food for summer?

120 THE HUMAN BODY.

heat, makes it a good food in cold weather for persons with
a good digestion. Pigs are especially liable to a parasite,
called trichina, which lives in their muscles, and may be
transferred thence to man, sometimes causing death. Hence
pork should always be thoroughly cooked. Salted meats of
all kinds are less digestible and less nutritious than fresh.
Milk contains an albuminous substance (casein), also fats
(butter), and a sugar, known as sugar of milk, in addition
to useful mineral alimentary principles. It will support life
longer than any other single food. Cheese consists essen-
tially of the casein of milk: it is a very nutritive albuminous
food. Eggs contain albumens and fats, and have a high
nutritive value: they are more easily digested when cooked
soft than hard. Wheat contains more than a tenth of its
weight of proteids, more than half its weight of starch,
some sugar, and a little fat. The proteid of wheat flour is
mainly gluten, which when moistened with water forms a
tenacious mass, and this it is to which wheaten bread owes
its superiority. When the dough is made, yeast is added
to it and causes fermentation by which, among other
things, carbon dioxide gas is produced. This gas, im-
prisoned in the tenacious dough and expanded by heat dur-
ing baking, forms cavities in it. and causes the dough to
"rise" and make "light bread/' which is not only more
pleasant to eat but more easily digested than heavy. Some
grains contain a larger percentage of starch, but none have
so much gluten as wheat; when bread is made from them

Why should pork be well cooked? How do salted meats differ in
value as articles of diet from fresh? What foodstuffs exist iumilk?
What one food will support life longest? What is the chief aliment-
ary principle in cheese? What is the nutritive value of cheese? What
makes the value of eggs as foods? Are they more easily digested soft
or hard boiled? What foodstuffs exist in wheat? Why is wheaten
bread lighter than that made from other grains?

ALCOHOL. 121

the carbon dioxide gas escapes so readily from the less
tenacious dough that it does not expand the mass properly.
Corn contains less proteid, more starch, and more fat than
wheat. Rice is poor in proteids but very rich in starch.
Peas and beans are rich in proteids and contain about half
their weight of starch. Potatoes are a poor food. They
contain a great deal of water and only about one part of
proteids, and fifteen of starch in a hundred parts by weight.
Other fresh vegetables, as carrots, turnips, and cabbages,
are valuable mainly for the salts they contain ; their weight
is chiefly due to water, and they contain but little starch,
proteids, or fats. Fruits, like most fresh vegetables, are
mainly valuable for their saline constituents, the other food-
stuffs in them being only present in small proportion. Some
kind of fresh vegetable is, however, a necessary article of
diet, as shown by the scurvy which used to prevail among
sailors before fresh vegetables or lime-juice were supplied
to them.

Alcohol. — We shall learn later that all drinks containing
alcohol are dangerous (Chap. XXIII.), as tending to pro-
duce disease, or to make the body less able to resist it, and
more dangerous the more alcohol they contain. For the
present we confine ourselves to the question, Has alcohol a
just claim to be called a food ? Does it build tissue, or
strengthen the muscles, or help to maintain our animal
heat ? It may be useful sometimes as a medicine when
ordered by a physician, but is it useful to healthy persons
who can obtain and digest other foods ?

How does corn differ from wheat in composition? What aliment-
ary principles are scarce in rice? Which one is abundant? What
do potatoes contain? What is the main useful constituent of most
fresh vegetables? Of fruits? How may scurvy be prevented?

Why are all alcoholic drinks dangerous? What questions must
be answered before deciding if alcohol is a true food ?

122 THE HUMAN BODY.

Is Alcohol a Tissue-Forming Food ? — To this the answer
is certainly no; so far at least as useful tissue is concerned.
It often leads to excessive and harmful overgrowth of con-
nective tissue and fat, but it does not lead to development
of muscle or brain or gland.

Is Alcohol a Strengthening Food? — To this the answer is
also no. Alcohol in small do.-^es causes excitement of the
brain, and may for a short time cause it and the muscles to
overwork or to work when they should be resting: but as it
nourishes neither, the final result is bad. The brain and
muscle are left in an injured state. As regards the brain,
the consequence is often insanity (Chaj). XXIII. ). As
regards the muscles, very careful experiments have been
made on soldiers who were given definite tasks to accomplish.
The result was that on the days on which they were sup-
plied with spirits, they could neither use their muscles as
powerfully, nor for as long a time, as on the days when
they got no alcoholic drink.

Does Alcohol keep up the Heat of the Body ? — To this
question, also, the answer is no, though this may seem
strange in view of the fact that a drink is often taken
" to warm one up." The apparent inconsistency is easily
explained. Our feeling of being warm depends on the
nerves of the skin (p. 333). We have no nerves which tell
us whether heart or muscles or brain are warmer or cooler.
These inside parts are always hotter than the skin, and if
blood which has been made hot in them flows in large
quantity to the skin, we feel warmer because the skin is

What is said of alcohol as a tissue-forming food?

Is alcohol a strengthening food? How may it lead to overwork?
Results? What were the results of experiments made on soldiers as
to the action of alcohol on the muscles?

Does alcohol maintain the heat of the body? Why does a drink
sometimes make a person feel warmer?

TEA AND COFFEE. 123

heated. As alcoholic drinks make more blood flow through
the skin, they often make a mau feel warmer. But their
actual effect upon the temperature of the whole body is to
lower it. The more blood that flows through the skin,
the more heat is given off from the body to the air, and
the more blood, so cooled, is sent back to the internal
organs. The consequence is that alcohol cools the body as
a whole, though it may for a short time heat the skin.
That a large dose of alcohol leads to excessive loss of heat
from the body has been proved by many observations on
drunken men, and by experiments on the lower animals.

The action of alcohol as an excitant is so much more
marked than its efficacy as a source of energy that it is to
be regarded as a medicine rather than a true food, and the
best plan is to avoid it altogether in health.

Tea and Coffee arc to be regarded as stimulants rather
than nutritive foods. The amount of nourishment in a
cup of either is but little. Both have, however, a wonder-
ful influence in tranquillizing the nervous system and re-
moving the sense of fatigue; and when taken in moderate
doses usually leave none of the injurious after-effects of
alcohol. Some persons experience wakefulness or a feeling
of fulness in the head after taking coffee, and such should
of course avoid it. For relieving fatigue, tea and coffee are
far superior to alcohol. Sportsmen out for a long day's
shooting find cold tea superior to spirits ; military com-
manders find a ration of coffee far better than one of
whiskey for fat'gued trooj)s; and all arctic explorers have
come to a similar conclusion.

How is it that alcohol sometimes makes a person feel warmer?
How does it cool the body?

To what class of foods do tea and coffee belong? What results
do they produce? Why are they better than alcohol for similar
purposes? Give illustrations of the influence of tea and coffee in
removing the sensation of fatigue.

124 THE HUMAN BODY.

Cooking. — When meat is cooked most of its connective
tissue is turned into gelatin, and the whole mass becomes
softer and more readily broken up by the teeth. In boil-
ing meat it is a good plan to put it first into boiling water
which coagulates its surface layer of albumen, and this then
keeps in flavoring and other matters which would otherwise
pass out into the water. After the first few minutes the
cooking should be continued at a lower temperature; meat
boiled too fast is hard, tough, and stringy. In roasting or
baking meat, the same plan is advisable. Put it close to
the fire or in a hot oven for a short time, and then com-
plete the cooking more slowly at a lower temperature.

The cooking of vegetable foods is of considerable impor-
tance. Starch is the chief nutrient matter in most of them,
and raw starch is much less easily digested than cooked.
When starch is roasted it is turned into a substance known
as soluble starch, which is easily dissolved by the digestive
liquids, so there is a scientific foundation for the common
belief that the crust of a loaf is more digestible than the
crumb, and toast than fresh bread.

The Oxidizable Matters required daily by the Body. —
The necessary quantity of daily food depends upon that of
the material used by the body and passed out from it in each
twenty-four hours; this varies both in kind and amount
with the work done and the organs most used. In children
a certain excess is required to furnish material for growth.

What happens when meat is cooked ?

Why does a good cook first put meat that she is to boil into very
hot water? Why should the boiling be completed at a lower temper-
ature? How should meat be baked?

Why is it important to cook most vegetable foods ? Why is toast
more easily digested than fresh bread?

What determines the necessary amount of daily food? How does
it vary? Why do children require more in proportion to their size
than adults?

TllhJ ADVANTAGES OF A MIXED DIET. 125

It is impossible to state accurately beforehand just what
amount of food any individual will require, but a general
idea may be arrived at by taking the average daily losses, by
excretion, of a man, as determined by many experiments
made on different persons. Such experiments show that a
man of average size and doing ordinary work needs rather
more than 9| ounces ("274 grams) of carbon to replace his
loss of that element; and about ,"„ of an ounce of nitrogen
(20 grams). Some hydrogen is also required, as the body
daily loses more water than we take in our food; and this
extra amount implies a loss of hydrogen, combined with
oxygen in the body to form water.

The Advantages of a Mixed Diet. — Since proteid foods
contain carbon, nitrogen, and hydrogen, life may be main-
tained on them if the necessary salts, water, and oxygen be
also supplied; but such a diet would not be economical.
Ordinary proteids contain in 100 parts about 52 of carbon
and 15 of nitrogen, so a man fed on them alone would
get about 3| parts of carbon for every 1 of nitrogen. His
daily losses are not in this ratio, but about 13.7 parts of
carbon to 1 of nitrogen ; and to get enough carbon from
proteids far more than the necessary amount of nitro-
gen must be taken. Of dry proteids 1 pound 2}2 ounces
(527 grams) would yield the necessary carbon, but would
contain 2f ounces (79 grams) of nitrogen, or four times
more than is necessary to cover the daily losses of that
element from the body. Fed on a purely proteid diet a
man would, therefore, have to digest a vast quantity to get

What is the average daily loss of carbon from the body? Of
nitrogen ? Does a man need hydrogen also in his food ? Win ?

On what group of foodstuffs can life be maintained without any
others? Why is feeding entirely on albuminous substances not de-
sirable?

126 THE HUMAN BODY.

enough carbon, and in eating and absorbing it, and in
getting rid of the excess nitrogen (which is useless to him),
a great deal of useless labor must be thrust upon the
digestive and excretory organs. Were a man to live on
bread alone he would force much unnecessary work on his
organs. Bread contains little nitrogen in proportion to
its carbon, and to get enough nitrogen far more carbon
than could be utilized would have to be eaten, digested,
and excreted daily.

The human race has discovered this fact: men use,
where they have a choice, richly proteid substances to
supply the nitrogen needed, but derive the carbon mainly
from non-nitrogenous foods of the fatty or carbohy-
drate kinds, and so avoid excess of either nitrogen or
carbon. For instance, lean beef contains about J of its
weight of dry proteid, which proteid contains 15 per
cent of nitrogen. Consequently 1 pound 3 ounces of lean
meat would supply the nitrogen needed to compensate for
a day's losses. But the proteid contains 52 per cent of
carbon, so the amount of it in the above weight of fatless
meat would be 1070 grains (69 grams) or nearly 2| ounces,
leaving 3150 grains ('305 grams) or rather more than
seven ounces, to be got either from fats or carbohy-
drates. The necessary amount would be contained in
3940 grains (256 grams) or about 9 ounces of ordinary
fats, or in 7080 grains (460 grams), a little over a pound, of
starch; hence either of these with the above quantity of
lean meat would form a far better diet both for the purse
and the system than meat alone.

Explain why bread by itself would afford a bad diet.

Why do men use a mixed diet? Explain why lean meat aloue
would not be a good food. How could the deficient carbon of lean
beef be supplied?

THE ADVANTAGES OF A MIXED DIET. 12?

As already pointed out, nearly all common foods contain
several foodstuffs. Good butcher's meat, for example, con-
tains nearlv half its dry weight of fat : and bread in addition
to proteids contains starch, fats, and sugar. In neither of
them, however, are the foodstuffs mixed in the physiologically
best proportions, and the custom of consuming several of
them at each meal, or different ones at different meals dur-
ing the day, is not only agreeable to the palate but in a high
degree advantageous to the body. The strict vegetarians
who do not eat even such substances as eggs, cheese, and
milk, but confine themselves to a purely vegetable diet,
which is always poor in proteids, take daily far more car-
bon than they require, and are to be congratulated on their
excellent digestions which are able to stand the strain.
Those so-called vegetarians who use eggs, cheese, etc., can of
course get on very well, since such substances are extremely
rich in proteids, and supply all the nitrogen needed,
without the necessity of swallowing the vast bulk of food
which must be eaten in order to get it directly from plants.

Give illustratious of the fact that most foods contain more than
one foodstuff.

Why do we commonly use several foods at one meal ? What ele-
ment do strict vegetarians take in excess? How do nominal vegeta-
rians get their nitrogen ?

CHAPTER XL
THE DIGESTIVE ORGANS.

General Arrangement of the Alimentary Canal. — The ali-
mentary canal is a tube which runs through the body from
the lips to the posterior end of the trunk. It is lined by a
soft reddish mucous membrane (easily seen inside the mouth),
which is but a redder and moister sort of skin. Outside
the mucous membrane are connective tissue and muscular
layers, which strengthen the digestive tube and push the
swallowed food along it. The mucous membrane is con-
structed to absorb dissolved nutritive substances; it soaks
them up and passes them into blood or lymph vessels. Im-
bedded in this mucous membrane, or lying outside it, are
hollow organs called glands; these glands make liquids
which alter chemically many substances which we eat, and
turn them from things which cannot be absorbed by the
mucous membrane into things which can. The whole series
of changes which any food material undergoes, between its
reception by the mouth and its absorption by the aliment-
ary mucous membrane, is spoken of as its digestion.

Various foodstuffs undergo different kinds of changes

"What is the alimentary canal? By what is it lined? What are
found outside the mucous membrnne of the digestive tube? What
are their uses? Witli reference to what object is the alimentary
mucous membrane constructed? What does it do with the nutriment
it absorbs? What is the function of the glands of the alimentary
caual? What is meant by the digestion of a foodstuff?

[128]

THE KINDS OF GLANDS. 129

preliminary to absorption, and so we speak of different kinds
of digestions; as that of starch, of fats, of albuminous bodies,
and so forth.

Glands are hollow organs which make or secrete peculiar
fluids and poar them out on some free surface of the body.
They are very widely distributed; we find, for example,
digestive glands (of several kinds) opening into the digestive
tube, perspiratory glands opening in the skin, tear glands
or lachrymal glands pouring out their secretion on the eye-
ball. Different glands have their cavities lined by different
kinds of cells, and produce different secretions. In general
arrangement all glands are built on one or other of two
primary structural plans, known as the tubular and the
racemose.

The Kinds of Glands. — All portions of the body making
and pouring forth secretions are not technically called
glands. In the peritoneum, which lines the inside of the
abdominal cavity (p. 11), we find simply a thin membrane
{A, Eig. 40), having on its side nearer the cavity which it
surrounds a layer of cells, a, and on its deeper side a net-
work of very fine blood-vessels, c, supported by connective
tissue, d. Such simple, smooth, secreting surfaces are not
common; in most cases an extended area is required to
form the necessary amount of secretion, and if this were
attained simply by spreading out flat membranes, these,
from their number and extent, would be hard to pack con-
veniently in the body. Accordingly, in most cases, a large
area is obtained by folding the secreting surface in various

Why do we speak of different kinds of digestion? Illustrate.
What is a gland? Give examples of glands. How do glands differ?
What are the two chief types of glands named?

Name and describe a secreting surface which is not technically
called a gland. What is gained by folding a secreting surface?

130

ma HUMAN BODY.

Fig. 40. — Forms of Glands. A, a simple secreting surface : a, its epithelium;
b, basement membrane ; c, capillaries ; B. a simple tubular gland \.C, a secret-
ing surface, increased by protrusions ; E a simple racemose gland : D and O,
compound tubular glands; F, a compound racemose gland. In all but A, if, and
C the capillaries are omitted for the sake of clearness. H, half of a highly devel-
oped racemose gland ; c, its main duct.

F0RM8 OF GLANDS. 131

ways so that a wide surface can be packed m a small bulk,
just as a Chinese paper lantern when shut up occupies
much less space than when extended, although the actual
area of the paper in it remains of the same extent. In a
few cases the folding takes the form of protrusions into the
cavity of the secreting organ, as indicated at C, Fig. 40, but
much more commonly the surface extension is attained in
another way, the supporting or basement membrane, cov-
ered by its epithelium, being pitted in or involuted as at B.
Such a secreting organ is known as a true gland.

Forms of Glands. — In some cases the surface involutions
are uniform in diameter, or nearly so, throughout (B, Fig.
40). Such glands are known as tubular; examples are
found in the lining coat of the stomach (Fig. 48); also in
the skin (Fig. 76), where they form the siveat-glands. In
other cases the involution swells out at its deeper end and
becomes more or less sacculated (B); such glands are named
racemose or acinous. The small glands of the skin which
form the oily matter poured out on the hairs (p. 273) are
of this type. In both kinds the lining cells near the deeper
end are commonly different in character from the rest; and
around that part of the gland the finest and thinnest walled
blood-vessels form a closer network. These deeper cells
form the true secreting tissue of the gland, and the tube,
lined with different cells, leading from the secreting re*
cesses to the surface on which the secretion is poured out,
and serving merely to drain it off, is known as the duct of
the gland. When the duct is undivided the gland is simple;
but when, as is more usual, it is branched and each branch

"What is a tubular gland? Examples? A racemose gland?
Example? Where do we find the closest network of blood-vessels
in a gland? Which cells of a idand make its secretion? What is
meaut by the "duct" of a gland? What is a simple gland?

132 THE HUMAN BODY.

has a true secreting chamber at its end we get a compound
gland, tubular (G) or nicemose (F, H) as the case maybe.
In many cases the chief duct, in which the smaller ducts
unite, is of considerable length, so that the secretion is
poured out at some distance from the main mass of the
gland.

A fully formed gland, H, is thus a complex structure,
consisting primarily of a duct, c, ductules, dd, and secret-
ing recesses, ee. The ducts and ductules are lined with
cells which are merely protective, and differ in character
from the secreting cells which line the deepest parts. The
cells lining the ultimate recesses differ in different glands,
and produce different liquids; consequently, though all
glands are built on much the same plan, they make very
varied secretions, the nature of the secretion of any gland
depending on the properties of its cells.

The Complexity of the Alimentary Canal. — We may
now return to our immediate subject, the alimentary canal.
This is not a simple tube, but presents several dilatations on
its course; nor is it a comparatively straight tube, as dia-
grammatically represented in Fig. 1, but, being much longer
than the regions of the body which it traverses, much of it
is packed away by being coiled up in the abdominal cavity.

Subdivisions of the Alimentary Canal. — The mouth-
opening leads into a chamber containing the teeth and
tongue, and named the mouth-cliamber or buccal cavity.
This primary dilatation is separated by a constriction (the

A compound? How does it happen that the secretion is some-
times poured out at a distance from the main mass of the gland?

Describe a fully developed gland. How is it that glands make
such different secretions? On what does the nature of the secretion
of a gland depend?

How does the alimentary canal differ from a simple uniform tube?
Why is a great part of it coiled?

Into what does the opening between the lips lead?

THE MOUTH CA V1TT.

133

isthmus of the fauces) at the buck of the mouth, from
another, the pharynx or throat
chamber, which narrows again
at the top of the neck into
"the gullet or oesophagus, which
runs as a comparatively narrow
tube through the thorax, and
then, passing through the dia-
phragm, dilates in the upper ""
part of the abdominal cavity
to form the stomach (see Fig.
1). Beyond the stomach
the channel again narrows to
form a long and greatly coiled
tube, the small 'intestine, which
terminates by opening into the
large intestine, which, though
shorter is wider, and ends by
opening on the exterior.
The Mouth Cavity.— (Fig.

41) is bounded in front and Fig. 41.— The mouth, nose and

. . pharvnx, with the commencement of

On the Sides by the lips and the gullet and larynx, as exposed by

a section, a little to the left of the me-

cheeks, below by the tono-ue, dian plane of the head, a, vertebral

J ° ' column : 6. gullet : c, windpipe ; rf,

k, and above by the palate, laryiix; e. epiglottis^/ soft palate;

J -» 9. opening of Eustachian tube ; k,

which latter consists of an an- t0»f.'e: *. harfd palate: ». the sphe-

v,^ u ^o vx iin «ii noid bone on the base of the skull: n,

rprinr narr 7 snnnnvforl llr tne fore Part of the cranial cavit\
leriOl pait, I, SUppOlteCl D\ opq^ the 'turbinate bones of theout-

bone and Called the hard pal- er side of the left nostril chamber.

What is the isthmus of the fauces? Where does the gullet begin?
Through what regions of the body does it pass? Where does the
Btomach lie? What part of the alimentary canal succeeds the
stomach? Describe it briefly. How does it end? How does the
large intestine differ from the small? How does it end?

What are the boundaries of the mouth cavity? Of what parts
does the palate cousist?

134 THE HUMAN BODY.

ate, and a posterior, f, containing no bone, and called the
soft palate. The two can readily be distinguished by ap-
plying the tip of the tongue to the roof of the mouth and
drawing it backwards. The hard palate forms the parti-
tion between the mouth and nose. The soft palate arches
down at the back of the mouth, hanging like a curtain
between it and the pharynx, as can be seen on holding the
mouth open in front of a looking-glass. From the middle
of its free border a conical process, the uvula, hangs down.

The Teeth. — Immediately within the cheeks and lips are
two semicircles, formed by the borders of the upper and
lower jaw-bones, which are covered by the gums, except at
intervals along their edges where they contain sockets
in which teetli are implanted. During life two sets of
teeth are developed : the first or milk set appear soon after
birth and are shed during childhood, when the second or
permanent set appear.

The General Structure of a Tooth. — The teeth differ in
minor points from one another, but in all, three parts are
distinguishable ;* one, seen in the mouth, and called the
crown of the tooth; a second, imbedded in the jaw-bone,
and called the root or fang; and between the two, embraced
by the edge of the gum, a narrowed portion, the neck or
cervix. By differences in their forms and uses the
teeth are divided into incisors, canines, bicuspids, and

How can we feel the difference between them? "What cavities
does the hard palate separate? Where does the soft palate lie?
What is the uvula ?

What do we find inside the lips? Where are the gums? What
do the margins of the jaw bones contain ? What are the milk teeth ?
What the permanent?

What parts may we distinguish in every tooth? Into what
groups are teeth divided? Why?

* A number of teeth can be readily obtained from a dentist, and will be found
of great use in connection with this lesson.

CHARACTERS OF INDIVIDUAL TEETH.

135

molars, arranged in a definite order in each jaw. Begin-
ning at the middle line we meet in each half of each jaw,
successively, with two incisors, one canine, and two mo-
lars in the milk set; making twenty altogether in the two
jaws. The teeth of the permanent set are thirty-two in
number, eight in each half of each jaw, viz. — beginning at
the middle line — two incisors, one canine, two bicuspids,
and three molars. The bicuspids of the permanent set
replace the molars of the milk set, while the permanent
molars are new teeth added on as the jaw grows, and not
substituting any of the milk teeth. The hindmost perma-
nent molars are often called the wisdom teeth.

Characters of Individual Teeth. — The incisors or cutting

Fig. 43.

Fig. 45.

Fig. 42.— An incisor tooth.
Fig. 43. — A canine or eye tooth.

Fig. 44.— A bicuspid tooth seen from its outer side; the inner cusp is accord-
ingly not visible.

Fig. 45. — A molar tooth.

teeth (Fig. 42) are adapted for cutting the food. Their
crowns are chisel-shaped and have sharp horizontal cutting
edges which become worn away by use, so that they are
beveled off behind in the upper row and in the opposite

Enumerate the milk teeth in order. How many are there alto-
gether? Number of permanent teeth? Enumerate in order. What
permanent teeth replace the milk molars? What permanent teeth
replace no milk teeth? Which are the wisdom teeth?

Describe an incisor tooth.

136 THE HUMAN BODY

direction in the lower. Each has a single long fang. The
canines {dog teeth) (Fig. 43) are somewhat larger than the
incisors. Their crowns are thick and somewhat conical,
having a central point or cusp on the cutting edge. In
dogs and cats the canines are very long and pointed, and
adapted for seizing and holding prey. The bicuspids or
premolars (Fig. 44) are rather shorter than the canines and
their crowns are cuboidal. Each lias two cusps, an outer
towards the cheek, and an inner on the side turned towards
the interior of the mouth. The molar teeth or grinders
(Fig. 45) have large crowns with broad surfaces, on which
are four or five projecting tubercles which roughen them
and make them better adapted to crush the food. Each
has usually several fangs. The milk teeth differ only in
subsidiary points from those of the same names in the per-
manent set.

The Structure of a Tooth. — If a tooth be broken open
a cavity extending through both crown and fang will be
found in it. This is filled during life with a soft pulp, con-
taining blood-vessels and nerves, and is known as the
"pulp cavity." The hard parts of the tooth disposed
around the pulp cavity consist of three different tissues.
Of these, one immediately surrounds the cavity and makes
up most of the bulk of the tooth; it is dentine or ivory;
covering the dentine on the crown is enamel, the hardest

A canine. Name animals with specially developed canines. For
what do they use them? Give another name for a bicuspid tooth.
Describe one.

Describe a molar tooth. What is the object of the projections
on their crowns? How far do the milk teeth differ from the perma-
nent in form?

What do we find on breaking open a tooth? What is it called?
Why? What tissues form the hard parts of a tooth? Where docs
each lie?

HYGIENE OF THE TEETH. 137

tissue in the body,* and on the fang the cement, which is a
thin layer of bone.

The pulp cavity opens below by a narrow aperture at the
tip of the fang, or at the tip of each fang if the tooth has
more than one. Through these openings its blood-vessels
and nerves enter.

Hygiene of the Teeth. — The teeth should be thoroughly
cleansed night and morning, by means of a tooth-brush
dipped in tepid water ; once a day soap should be used, or
a little very finely powdered chalk sprinkled on the brush.
The weak alkali of the soap or chalk is useful. A large
proportion of a tooth consists of carbonate of calcium, which
readily dissolves in weak acids ; and decomposing food
particles lodged between the teeth develop acids, which
eat away the tooth slowly but surely. Hence all food
particles should be carefully removed from between the
teeth ; as this cannot always be effected completely it is
important to brush the teeth with alkaline substances
which will neutralize and render harmless any acid.f
Good manners forbid the public use of a tooth-pick, but
on the earliest privacy after a meal a wooden or quill
tooth-pick should be employed systematically and carefully
to dislodge all food remnants which may have remained
wedged between the teeth.

Where is the pulp cavity open? What things pass through the
opening?

When and how should the teeth be cleansed? What substance
forms a large part of the teeth? In what is this substance soluble?
Why should food particles be carefully removed from between the
teeth? Why are weak alkaline substances useful in cleaning the
teeth?

* Enamel will strike fire with flint.

+ Acid medicines should always be sucked up through a glass tube and
swallowed with as little contact as possible with the teeth After each dose
the mouth should be thoroughly rinsed with water.

138

THE HUMAN BODY.

Once a slight cavity has been formed, the process of
decay is apt to go on very fast ; first, because the ex-

Fig. 46.- The upper surface of the tongue. 1, 2, circumvallate papillae ; 3, fun-
giform papillae; 4, filiform papillae; 6, mucous glands.

posed deeper layer of the tootli is more easily dissolved
man its natural surface: and, second, because the little

TBB 1'OmUB. 139

pit forms a lodging-place for bits of food, which, in de-
composing, form acids and hasten the corrosion. Small
eroded cavities are very apt to be overlooked ; the teeth
should, therefore, be thoroughly examined two or three
times a year by a dentist.

y The Tongue (Fig. 46) is a muscular and highly mov-
able organ, covered by mucous membrane, and endowed not
only with a delicate sense of touch, but with the sense of
taste. Its root is attached to the hyoid bone (p. 26).
The mucous membrane covering the upper surface of the
tongue is roughened by numerous minute elevations or
papilla, of which there are three varieties. The circum-
vallate papilla (Fig. 46, 1 and 2) are the largest and fewest,
and lie near the root of the tongue, arranged in the form
of a V, with its open angle turned towards the lips. The
fungiform papillm are rounded masses attached by nar-
rower stems. They are found all over the middle and fore
part of the upper surface of the tongue, and during life
are readily recognized as red dots, more deeply colored
than the rest of the mucous membrane. The filiform
papillce are pointed elevations scattered all over the upper
surface of the tongue, except near its root. They are on
our tongues the smallest and most numerous.* v^

Wliy is decay of a tooth apt to go on fast once it has commenced?
VY"hy should the teeth be examined from time to time by a dentist?

Briefly describe the tongue. What sensations do we obtain
through it? To what is its root attached? What are found on the
mucous membrane of the upper surface of the tongue? Of how
many varieties? Which are largest and fewest? Where are they
found? HowT are they arranged? Describe the fungiform papillae.
Where are they found"? What do they look like when we examine
a person's tongue? Where are the filiform papillae found? What
is their form? What papillae on the human tongue are smallest?
Most numerous?

* The filiform papillae are very large on the tongue of the cat, where they
may readily be seen and felt. They are large in nearly all carnivorous animals,

140 THE HUMAN BODY.

What a "Furred Tongue" Indicates. — In health the
surface of the tongue is moist, covered by little "fur"
and, in childhood, of a red color. In adult life the natural
color of the tongue is less red, except around the edges
and tip ; a bright red glistening tongue is then usually a
symptom of disease. When the digestive organs are de-
ranged the tongue is commonly covered with a thick
yellowish coat, and there is frequently a " bad taste" in
the mouth.* The whole alimentary mucous membrane is
in close physiological connection ; and anything disorder-
ing the stomach is likely to produce a " furred tongue,"
which in most cases may be taken as indicating something
wrong with the deeper parts of the digestive tract.

The Salivary Glands. — The saliva, which is poured into
the mouth and moistens it, is secreted by three pairs of
glands, the parotid, the submaxillary, and the sublingual.
The parotid glands lie close in front of the ear ; each sends
its secretion into the mouth by a duct, which opens inside
the cheek opposite the second upper molar tooth. In the
disease known as mumps f the parotid glands are inflamed
and enlarged. The submaxillary glands lie between the
halves of the lower jaw-bone, and their ducts open beneath

Describe the surface of a healthy tongue. How does the tongue
of a healthy man differ in appearance from that of a healthy child?
When is the tongue apt to be "coated"? What does a furred
tongue usually indicate?

By what is the saliva secreted? Where does the parotid gland lie?
Where does its duct open? What change occurs in the parotid
glands during "mumps"? Where are the submaxillary glands?
Where do their ducts open?

serving to scrape or lick clean bones, etc. Tamed tigers have been known to
draw blood by licking the hand of their master.

* The fur of the tongue consists of some mucus, a few cells shed from its
surface, and numerous vegetable microscopic organisms belonging to the group
of Bacteria.

i Technically, parotitis.

TBE PBARTNX. 141

the tongue. The sublingual glands lie beneath the floor
of the mouth behind the submaxillary.

The Fauces is the name given to the passage which
can be seen at the back of the mouth leading from it
into the pharynx, below the soft palate.* It is bounded
above by the soft palate and uvula, below by the root of
the tongue, and on the sides by muscles, covered by mucous
membrane, which reach from the soft palate to the tongue.
The muscles cause elevations known as the pillars of the
fauces. Each elevation divides near the tongue, and in
the hollow between its divisions lies a tonsil (7, Fig. 46), a
soft rounded body about the size of an almond, and con-
taining numerous minute glands which form mucus.

Enlarged Tonsils. — The tonsils not unfrequently become
enlarged during a cold or sore throat, and then pressing on
the Eustachian tube (Chap. XXI), which leads from the
throat to the middle ear, keep it closed and produce
temporary deafness. Sometimes the enlargement is perma-
nent and causes much annoyance. The tonsils can, how-
ever, be readily removed without danger, and this is the
treatment usually adopted in such cases.

The Pharynx or Throat Cavity (Fig. 41). — This portion
of the alimentary canal may be described as a conical bag
with its broad end turned towards the base of the skull
and its other end turned downwards and narrowing into

Where do the sublingual glands lie?

What is meant by the fauces? How are they bounded? What
are the pillars of the fauces? What is a tonsil?

Why is temporary deafness not uncommon when we have a sore
throat? What is usually done when the tonsils are permanently
enlarged?

Briefly describe the pharynx.

* Observe for yourself with the help of a looking glass.

142 THE BVMAN BODY.

the gullet. Its front or ventral wall is imperfect, present-
ing apertures which lead into the nose, the mouth, and
(through the larynx and windpipe) into the lungs. Except
when food is being swallowed the soft palate hangs down
between the mouth and pharynx; during deglutition it is
raised into a horizontal position, and separates an upper or
respiratory portion of the pharynx from the rest. Through
this upper part air alone passes,* entering it from the pos-
terior ends of the two nostril chambers, while through the
lower portion both food and air pass, one on its way to the
gullet, b, Fig. 41; the other through the larynx, d, to the
windpipe, c; when a morsel of food "goes tho wrong way"
it takes the latter course. Opening into the upper portion
of the pharynx on each side is an Eustachian tube, g. At
the root of the tongue, over the opening of the larynx, is a
plate of cartilage, the epiglottis, e, which can be seen if the
mouth is widely opened and the back of the tongue pressed
down by some such thing as the handle of a spoon. Dur-
ing swallowing the epiglottis is pressed down like a lid over
the opening of the air-tube and helps to keep food from
entering it. The pharynx is lined by mucous membrane
and has muscles in its walls which, by their contractions,
drive the food on.

The (Esophagus or Gullet is a tube commencing at the

What apertures open into its ventral side? What is the usual
position of the soft palate? How is this position altered during
swallowing? What passes through the respiratory division of the
pharynx? What things pass through its lower division? What is
the destination of each? What is meant by saying a morsel lias
"gone the wrong way"? Where do the Eustachian tubes open?
What is the epiglottis? How may it be seen? What is its use?

* During a severe attack of vomiting the soft palate often only acts imper-
fectly in closing the passage between gullet and nostrils; hence some of the
ejected matter not unfrequently is expelled through the nose."

THE STOMACH.

143

lower termination of the pharynx and which, passing on

through the neck and chest, ends below the diaphragm in

the stomach. In the neck it lies close behind the windpipe.

The Stomach (Fig. 47) is a curved conical bag placed

Fig. 41.

Fkj. 48.

Fig. 47.— The stomach, d. lower end of the gullet ; a, position of the cardiac
aperture : b, the fundus ; c, the pylorus ; e, the first part of the umall intes-
tine ; along a, b, c, the great curvature ; between the pylorus and d, the lesser
curvature.

Fig. 48. — A thin section through the gastric mucous membrane, perpendicu-
lar to its surface, magnified about 25 diameters, o, a simple peptic gland; b, a
compound peptic gland ; c, a mucous gland.

transversely in the upper part of the abdominal cavity.*
Its larger end is turned to the left and lies close beneath
the diaphragm, and opening into its upper border, through
the cardiac orifice at a, is the gullet, d. The narrower right
end is continuous at c with the small intestine; the com-
munication between the two is the pyloric orifice. The

Describe the gullet. Where does it lie in the neck?

What is the stomach? Which end of it is larger? Where does
this end lie? What opens into it? What is the opening called?
What is continuous with the small end of the stomach? What is the
name of the aperture between the stomach and the small intestine?

♦The general anatomical arrangement of the stomach, and its connections
with the gullet and intestine, may be readily shown on the body of a puppy, kit-
ten, or rat, which has been killed by placing it for five minutes in a small box
containing also a sponge soaked with chloroform.

144 THE HUMAN BODY.

pyloric end of the stomach is separated from the diaphragm
by the liver (see Fig. 4). When moderately distended the
stomach is about twelve inches long, and about four inches
across at its widest part, and would contain about three
pints.

The Glands of the Stomach. — The mucous membrane
lining the stomach is seen, when its surface is examined
with a common magnifying glass, to be covered with shallow
pits. A more powerful microscope shows on the bottom
of each one of these pits the openings of several minute
tubes, the gastric glands, which lie imbedded in the mu-
cous membrane, packed closely, side by side (Fig. 48).
These glands secrete the gastric juice.

The Muscular Coat of the Stomach lies outside the mu-
cous membrane, and is made up (Fig. 34) of plain muscular
tissue, whose fibres run in different directions. By its
contractions it stirs up the food and mixes it with the gastric
juice. Around the pyloric orifice of the stomach is a thick
ring of muscle (the pyloric sphincter), which usually is
contracted, closing the passage between the stomach and
the «ommencement of the small intestine. During diges-
tion in the stomach the pyloric sphincter relaxes from time
to time, and allows food, more or less digested, to pass on
into the intestine.

Palpitation of the Heart. — The cardiac end of the stom-
ach lies close beneath the diaphragm, and the heart imrae-

What lies between the right end of the stomach and the dia
phragm? What is the size of Ihe stomach?

What may he seen on examining the mucous membrane of the
stomach with a hand lens? What does a more powerful magnify-
ing instrument show? What is the function of the gastric glands?

Describe the muscular coat of the stomach. What is its function?
What is the pyloric sphincter? Its function? What happens
when the pyloric sphincter relaxes during gastric digestion?

TUE SMALL INTESTINE.

145

diately above it. Over-distension of the stomach, due to
indigestion or flatulency, may press up the diaphragm
and interfere with the
proper working of the
thoracic organs, causing
feelings of oppression
in the chest, or palpita-
tion of the heart.

The Small Intestine
commences at the pylo-
rus and ends, after many
windings, in the large.
It is about twenty feet
(six meter.-) long and
about two inches (five
centimeters) wide at its
gastric end, narrowing
to about two thirds of
that width at its lower
portion. Externally
there are no lines of sub-
division on the small in-
testine, but anatomists FlG 49.-Diagram of abdominal part of
ni-KifTOwlu ^nonin^a ^f no al'mentary canal. C. the cardiac, and P, the
diuiuailiy uesuiue II db pyloric end of the stomach: D, the duode-
,.~«„;^+:„~ f i-1 ™ , * num; J, I, the convolutions of the small in-
COn&lStingOI txliee parts, testine: CC, the caecum with the vermiform
. , c , , appendix; AC, ascending, TC. transverse, and

the trst twelve inches -DC, descending colon; E, the rectum.

being the duodenum, the succeeding two fifths of the re-
mainder the jejunum, and the rest the ileum.

Why is it that an over-distended stomach sometimes causes palpi-
tation of the heart?

Where does the small intestine commence? Where does it end?
Describe its length and diameter. Of what divisions do anatomists
describe it as consisting?

146

THE HUMAN BODY.

The Mucous Coat of the Small Intestine. — This is pint,
soft, and extremely vascular. It is throughout a great por-
tion of the length of the tuhe raised up into permanent
transverse folds in the form of crescentic ridges, each fold
running transversely for a greater or less way round the in-
testine (Fig. 50). These folds are the valvules conniventes.
They are first found about two inches from the pylorus, and
are most thickly set and largest in the upper half of the
jejunum, in the lower half of which they become gradually
less conspicuous; they finally disappear altogether about the
middle of the ileum. The folds of the mucous membrane

Fio. 50.— A portion of the small intestine opened to show* the valvules conni-
ventes.

serve to greatly increase its surface both for absorption and
secretion, and they also delay the food in its passage; it
collects in the hollows between them, and so is longer ex-
posed to the action of the digestive liquids.

The Villi. — Examined closely with the eye or, better, with
a hand leus, the mucous membrane of the small intestine is
seen not to be smooth but shaggy, being covered everywhere
(both over the valvulae conniventes and between them) with
closely packed minute elevations standing up somewhat like

Give the general characteristics of the mucous membrane of the
small intestine. What are the valvular conniventes? Where do
they commence? Where are they most developed? Where do they
cease? What purposes do they subserve? What are the villi?

THE VILLI.

147

the "pile" on velvet and known as the villi (Fig. 51). In
structure a villus is somewhat complex. Covering it is a
single layer of cells, beneath which the villus may be re-
garded as made up of a framework of connective tissue sup-
porting the more essential constituents. Near the surface
is a network of plain muscular tissue. In the centre is an
offshoot of the lymphatic or absorbent system, sometimes

Fig. 51. — Villi of the small intestine; magnified about 80 diameters. In the
left-hand figure the laeteals. «, b, c. are filled with white injection; '/. blood-ves-
sels. In the right-hand figure the laeteals alone are represented, filled with a
dark injection. The epithelium covering the villi, and their muscular fibres are
omitted.

in the form of a single vessel with a closed dilated end, and
sometimes as a network formed by two main vessels with
cross-branches. During digestion these lymphatics are
filled with a milky white liquid absorbed from the intestines,
and they are accordingly called the laeteals. They com-
municate with larger branches in the outer coats of the in-

Describe the structure of a villus. What is found iu its lymphatics
during digestion?

148 THE HUMAN BODY.

testine, and these end in trunks which join the main lym-
phatic system. Finally, in each villus, outside its lacteals
and beneath its muscular layer, is a close network of blood-
vessels.

The Glands of the Small Intestine. — Opening on the
surface of the small intestine between the bases of the villi
are small glands, the crypts of Lieberkiihn. Each is a
simple unbranched tube, lined by a single layer of cells.

The Muscular Coat of the Small Intestine lying outside
the mucous coat, is composed of plain muscular tissue, dis-
posed in two layers: an inner circular, and an outer longi-
tudinal. By their combined and alternating contractions
they slowly force the digesting food along the tube.

In the duodenum are found in addition minute glands,
the glands of Brunner, which lie outside the mucous
membrane, and send their ducts through it to open on its
inner surface.

The Large Intestine (Fig. 49), forming the final portion
of the alimentary canal, is about 5 feet (1.5 meters) long,
and varies in diameter from 2^ to \% inches (6-4 centi-
meters). Anatomists describe it as consisting of the ccecum
(cc) with its vermiform appendix, the colon (ac, tc, dc),
and the rectum (e). The small intestine does not open into
the end of the large but into its side, some distance from
its closed upper end; the caecum is that part of the large
intestine which extends beyond the communication. From
it projects the vermiform appendix, a narrow tube not
thicker than a cedar pencil, and about 4 inches (10 centi-

Where do we find the crypts of Lieberkiihn? Describe them.
Where are the glands of Brunner?

Give the dimensions of the large intestine. Of what parts is it
made up? How does the small intestine open into it? What is the
caecum? The vermiform appendix? Its size?

THE LIVER 149

meters) long. The colon commences on the right side of
the abdominal cavity where the small intestine communi-
cates with the large, runs up for some way on that side
(ascending colon), then crosses the middle line (transverse
colon) below the stomach, and turns down (descending colon)
on the left side, and there makes an S-shaped bend known
as the sigmoid flexure; from this the rectum proceeds to
the opening by which the intestine communicates with the
exterior. The mucous coat of the large intestine possesses
no villi nor valvulaeconniventes; it contains numerous closely
set glands much like the crypts of Lieberkiihn of the small
intestine.

The Ileo-Colic Valve. — Where the small intestine joins
the large there is a valve formed by two flaps of the mucous
membrane sloping down into the colon, and so arranged as
to allow matters to pass readily from the ileum into the
large intestine, but not the other way.

The Liver. — Besides the secretions formed by the glands
imbedded in its walls, the small intestine receives those of
two large glands, the liver and pancreas, which lie in the
abdominal cavity. The ducts of both open, by a common
aperture, into the duodenum about 4 inches (10 centime-
ters) from the pylorus.

The liver is the largest gland in the body, weighing
from 50 to 60 ounces (1400 to 1700 gn.ms). It is

Describe the colon. What is the sigmoid flexure? What is the
terminal portion of the alimentary canal named? How does the
mucous lining of the large intestine differ from, and how does it re-
semble that of the small ?

Where is the ileocolic valve? How is it formed? What is its
function?

What large glands pour their secretion into the small intestine?
Where are they situated? Where do their ducts open?

What is the largest gland in the body? What is its weight?
Where is it placed?

150

TUB HUMAN BODY.

situated in the upper part of the abdominal cavity (le, W,
Fi°\ 4), rather more on the right than on the left side, imme
diately below the diaphragm. The liver is of dark reddish-
brown color, and of soft friable texture. The vessels carrying
blood to the liver (Fig. 52) are the portal vein, Vp, (p. 208)
and the hepatic artery; both enter it at a groove on its under

Fig. 52.— The under surface of the liver, d, right, and s, left lobe; Ffi.hepa
tic vein; Vp, portal vein; Vc, vena cava inferior; Dch, common bile duct; Dc
cystic duct; Dh, hepatic duct; Vf, gall-bladder.

side, and there also a duct passes out from each half of the
organ. The ducts unite to form the hepatic duct, Dh,
which meets the cystic duct, Dc, proceeding from the gall-
bladder, Vf, a pear-shaped sac in which the bile or gall
formed by the liver accumulates when food is not being di-
gested in the intestine. The common bile duct, Dch, formed

Describe the color and texture of the liver. What vessels bring:
blood to it? Describe the arrangement of its ducts. What is the
gall bladder? Where does the common bile duct open?

THE PANCREAS. 151

by the union of the hepatic and cystic ducts, opens into
the duodenum.

The Functions of the Liver. — The size of the liver is
related to the fact that the organ plays a double function;
on the one hand it is a digestive gland secreting bile; on the
other, its cells serve to store up, in the form of a kind of
animal starch, called glycogen, excess of starchy or sugary
food absorbed from the intestine during the digestion of a
meal, and then to gradually dole this out to the blood for
general use by the organs of the body until the next meal
is eaten.

The Pancreas or Sweetbread* is a compound racemose
gland. It is an elongated soft organ of a pinkish-yellow
color, lying along the lower border of the stomach. Its
right end is embraced by the duodenum which there
makes a curve to the left. A duct traverses it and joins
the common bile-duct close to its intestinal opening. The
pancreas secretes a watery-looking liquid, much like saliva
in appearance, which is of great importance in digestion.

With what fact is the large size of the liver connected? What are
its functions?

To what group of glands does the pancreas belong? Describe its
form and color. Where is it placed? What does its duct unite with?
What does its secretion look like? Is it of much value?

* Butchers sell two kinds of sweetbread, known as the belly sweetbread and
the neck or heart sweetbread. The former is the pancreas; the latter is the
thymus, an organ of doubtful function, found only in young animals, and lying
at the bottom of the neck and upper part of the chest in front of the windpipe.

CHAPTER XII.

DIGESTION.

The Object of Digestion. — Some of the foodstuffs which
we eat are already in solution and ready to soak at once
into the lymphatics and blood-vessels of the alimentary
canal; others, such as a lump of sugar, though not dis-
solved when put into the mouth, are readily soluble in the
liquids found in the alimentary canal and need no further
digestion. In the case of many most important foodstuffs,
however, special chemical changes have to be brought
about to make them soluble and capable of absorption.
The different secretions poured into the alimentary tube
act in various ways upon different foodstuffs, simply dis-
solving some and chemically changing others, until at last
all are got into a condition in which they can be taken up
into the lymph and blood-vessels for transference to distant
parts of the body.

The Saliva. — The first solvent poured upon the food is
the saliva, which, when it meets the food, is a mixture
of pure saliva with the mucus secreted by the membrane
lining the mouth. This mixed saliva is a colorless, cloudy,
feebly alkaline liquid.

The Uses of Saliva are mainly physical and mechanical.
It keeps the mouth moist and allows us to speak with corn-
Explain the object of digestion.

What is the first digestive liquid which the food meets -with?
How does it differ from pure saliva? Describe mixed saliva.

[152]

THE USES OF SALIVA. 153

fort ; most young orators know the distress occasioned by
the suppression of the salivary secretion through nervous-
ness, and the imperfect efficacy under such circumstances
of the traditional glass of water placed beside public
speakers. The saliva also enables us to swallow dry food;
such a thing as a cracker when chewed would give rise
merely to a heap of dust, impossible to swallow, were not
the mouth cavity kept moist.* The saliva also dissolves
such bodies as salt and sugar, when taken into the mouth
in a solid form, and enables us to taste them; undissolved
substances arc not tasted, a fact which any one can verify
for himself by wiping his tongue dry and placing a frag-
ment of sugar upon it. No sweetness will be felt until a
little moisture has exuded and dissolved part of the sugar.
Chemical Action of the Saliva. — In addition to such
actions the saliva, however, exerts a chemical one on an
important foodstuff. Starch (although it swells up greatly
in hot water) is insoluble and could not be absorbed from
the alimentary canal. The saliva has the power of turning
starch into the readily soluble and absorbable grape sugar,
the sugar of most fruits, f The starch is made to combine
with the elements of water, and the final result is grape
sugar.

Describe and illustrate the uses of saliva with reference (1) to
speech, (2) to swallowing, (3) to dissolving some foods.

What foodstuff does saliva act upon chemically? What change
is produced by its action?

* This fact used to be taken advantage of in the East Indian rice ordeal for
the detection of criminals. The guilty person believing firmly that he cannot
swallow the parched rice given him, and sure of detection, is apt to have his
salivary glands paralyzed by fear, and so does actually become unable to swal-
low the rice; while in those with clear consciences the nervous system, acting
normally, excites the usual reflex secretion, and the dry food causes no difficulty
of deglutition.

+ Grape sugar or glucose is now an extensively produced article of commerce,
being made for this purpose by the prolonged action of dilute acids upon
starchy substances.

154 THE HUMAJS BODY.

CH^O10 + 2H'0 = 2C6Hl208

Starch. Water. Grape Sugar.

The Influence of Saliva in Promoting Digestion in the
Stomach. — So fur as chemical changes are concerned the
saliva is but of secondary importance in digestion: its main
use is to facilitate swallowing. It only changes starch into
grape sugar (at least rapidly) when no acid is present, and
food passes from the mouth to the stomach where it is
mixed with the acid gastric juice, before the saliva has time
to do much. Indirectly, however, the saliva promotes di-
gestion in the stomach. Weak alkalies stimulate the gastric
glands to pour forth more abundant secretion,* and the
saliva, being alkaline, acts in this way. This is one reason
why food should be well chewed before being swallowed;
its taste, and the movements of the jaws, excite a more
abundant salivary secretion, and this alkaline saliva, when
swallowed, helps to stir the stomach up to work.

Swallowing or Deglutition. — A mouthful of solid food
is broken up by the teeth and rolled about the mouth by
the tongue until it is thoroughly mixed with saliva and
made into a soft pasty mass. The muscles of the cheeks
keep this from getting between them and the gums.f The
mass is finally sent on from the mouth to the stomach by

What is the chief use of saliva? Under what circumstances does
it change starch into sugar? In what portion of the digestive tract
is this action of the saliva stopped? "Why? How does the saliva
promote digestion in the stomach? Why should food he thoroughly
chewed before swallowing?

What is the technical term for swallowing? In how many stages
does swallowing occur?

* Hence the efficacy of a little carbonate of soda or apollinaris water taken
before meals, in some forms of dyspepsia.

+ Persons with facial paralysis have from time to time to press out with the
finger food which has collected outside the e;ums, where it can neither be chewed
uor swallowed.

DEGLUTITION. 155

the process of deglutition, which occurs in three stages.
The first stage includes the passage from the mouth into
the pharynx. The food being collected into a heap on the
tongue, the tip of that organ is placed against the front of
the hard palate, and then the rest of the tongue is raised
from before back, so as to compress the food mass between it
and the palate and drive it through the fauces. This much
of the act of swallowing is voluntary, or at least is under
the control of the will, although it commonly takes place
unconsciously. The second stage of deglutition is that in
which the food passes through the pharynx; it is the most
rapid part of its progress, since the pharynx has to be
emptied quickly so as to clear the opening of the air-pas-
sages for breathing purposes. The food mass, passing back
over the root of the tongue, pushes down the epiglottis ; at
the same time the larynx (or voice-box at the top of the
windpipe) is raised so as to meet the epiglottis, and thus
the passage to the lungs is closed.* The soft palate is, at
the same time, moved into a horizontal position, so as to
separate the upper (or respiratory) portion of the pharynx,
leading to the nose and the Eustachian tubes (see Fig. 41),
from its lower portion, which ends inferiorly in the gullet.
Finally the isthmus of the fauces is closed as soon as
the food has passed through, by the contraction of the
muscles on its sides, and the elevation of the root of the
tongue. All passages out of the pharynx except the gullet
being thus blocked, when the pharyngeal muscles contract

Describe the first stage. What is the second stage? Which
stage is most rapid? Why? How is the passage to the lungs
closed while food is passing through the pharynx? How is the
passage to the nose blocked? Describe the processes of the second
stage of deglutition.

* The raising of the larynx during swallowing can be readily felt by placing
the finger on its large cartilage forming "Adam's apple"' in the neck.

156 THE HUMAN BODY

the food can only be squeezed into the oesophagus. The
muscular movements concerned in this part of deglutition
are all excited without the intervention of the will; food
touching the mucous membrane of the pharynx produces
quite involuntarily the proper action of the swallowing
muscles.* Indeed, many persons after having got the
mouth completely empty cannot perform the movements
of the second stage of deglutition at all. On account of
the involuntary nature of the contractions of the pharynx
any food which has once entered it must be swallowed; the
isthmus of the fauces forms a sort of Rubicon; food that
has entered the pharynx must be swallowed, even although
the swallower learned immediately that he was taking poi-
son. The third stage of deglutition is that in which the
food is passing along the gullet, and is comparatively slow.
Even liquid substances do not fall or flow down this tube,
but have their passage controlled by its muscular coats,
which grip the successive portions swallowed and pass
them on. Hence the possibility of performing the appar-
ently wonderful feat of drinking a glass of water while
standing upon the head, often exhibited by jugglers; peo-
ple forgetting that one sees the same thing done every
day by horses and other animals which drink with the
pharyngeal end of the gullet lower than the stomach.

The Gastric Juice. — The food having entered the stom-
ach is exposed to the action of the gastric juice, which is a
thin colorless or pale yellow liquid of a strongly acid re-
action. It contains, beside water and some salts and mu-

How are the movements of the second stage of deglutition excited?
What is the third sta<re of deglutition? Is it fast or slow? How is
it that jugglers can drink while standing on the head?

Describe the gastric juice.

* The process is what is known as a reflex action. See Chap XX.

GASTRIC DIGESTION. 157

cus, free hydrochloric acid (about .02 per cent.), and a
substance called pepsin, which in acid liquids has the power
of converting ordinary proteids into closely allied bodies
called peptones. It also dissolves solid proteids, changing
them at the same time into peptones.

Peptones. — Ordinary proteids are typical examples of
what are called ''colloids;" that is to say, substances which
do not readily pass through moist animal membranes; pep-
tones are a kind of proteid which does readily pass through
such membranes, and are, therefore, capable of absorption
from the alimentary canal. (See Dialysis, p. 18G.)

Gastric Digestion. — In the stomach the onward progress
of the food is stayed for some time. The pyloric sphincter
remaining contracted closes the aperture leading into the
intestine, and the irregularly disposed muscular layers of
the stomach keep its semi-liquid contents in constant
movement, by which all portions are thoroughly mixed
with the secretion of its glands. In the stomach part of
the proteid of the food is dissolved and turned into pep-
tones. Certain mineral salts (as phosphate of lime, of
which there is always some in bread), which are insoluble
in water but soluble in dilute acids, are also dissolved in
the stomach. On the other hand, the gastric juice has no
action upon starch, nor does it digest oily substances. By
the solution of the white fibrous connective tissues the
disintegration of animal foods, commenced by the teeth, is

Name its more important constituents. What powers does pepsin
possess?

What are colloids? Give examples. How do peptones differ
from other proteids?

Does food pass on immediately from the stomach to the intestine?
How is it kept back? How is it mixed with the gastric juice? What
happens to proteid foods in the stomach? Name another substance
dissolved in the stomach. Name foodstuffs which are not changed
in the stomach. How are animal foods broken up in the stomach?

158 THE HUMAN BODY.

carried much further in the stomach; and the food- mass,
mixed with much gastric secretion, becomes reduced to the
consistency of a thick soup, usually of a grayish color. In
this state it is called chyme. jO

The Chyme contains, afreFan ordinary meal, a consid-
erable quantity of peptones, which are in great part gradually
absorbed into the blood and lymphatic vessels of the gastric
mucous membrane and carried off, along with other dissolved
and dialyzable bodies — for example, salts and sugar.
After the food has remained in the stomach some time (one
and a half to two hours) the chyme begins to be passed
on into the intestine in successive portions. The pyloric
sphincter relaxes at intervals, and the rest of the stomach,
contracting at the same moment, injects a quantity of
chyme into the duodenum; this is repeated frequently, the
larger undigested fragments being at first unable to pass the
orifice. At the end of three or four hours after an ordinary
meal the stomach is quite emptied, the pyloric sphincter
finally relaxing to such an extent as to allow any larger in-
digestible masses, which the gastric juice has not broken
down, to be squeezed into the intestine.*

The Chyle. — When the chyme passes into the duodenum
it finds preparation made for it. The pancreas commences
to secrete as soon as food enters the stomach; hence a
quantity of its secretion is already accumulated in the intes-
tine when the chyme enters. The gall-bladder is distended

"What is chyme? What things would be found in chyme after
an ordinary meal? When does chyme begin to be sent on to the in-
testine? How? How soon is the stomach completely emptied after a
meal? What has accumulated in the small intestine when the chyme
reaches it ?

* Several of the above facts were first observed on a Canadian trapper,
Alexi6 St. Martin, who as a result of a gunshot wound had a permanent opening
from the surface of the abdomen to the interior of the stomach.

THE PANCREATIC SECRETION. 159

with bile, secreted since the last meal; the acid chyme
stimulating the duodenal mucous membrane causes,
through the nervous system, a contraction of the muscular
coat of the gall-bladder, and so a gush of bile is poured out
on the chyme. From this time on both liver and pancreas
continue secreting actively for some hours, and pour their
products into the intestine. The glands of Brunner and
the crypts of Lieberkiihn are also set at work. All of these
secretions are alkaline, and they suffice very soon to more
than neutralize the acidity of the gastric juice, and so to
convert the acid chyme into alkaline chyle, which, as found
in the intestine after an ordinary meal, contains a great va-
riety of things: water, partly swallowed and partly derived
from the salivary and other secretions; some undigested
proteids; some unchanged starch; oils from the fats eaten:
peptones formed in the stomach but not yet absorbed; sal-
ines and sugar, which have also escaped complete absorp-
tion in the stomach; indigestible substances taken with the
food; all mixed with the secretions of the alimentary canal.
The Pancreatic Secretion is clear, watery, alkaline, and
much like saliva in appearance. The Germans call the
pancreas the "abdominal salivary gland." In digestive
properties, however, the pancreatic secretion is far more
important than the saliva, acting not only on starch but
on proteids and fats. On starch it acts like the saliva, but
more energetically. It produces changes in proteids simi-
lar to those effected in the stomach, but by the agency of a

How is an outpouring of bile on the chyme brought about ? Do
liver and pancreas cease secreting when the chyme enters the intes-
tine? What other glands are set to work? How is the acidity of
the chyme overcome? What is chyle? What does it usually con-
tain?

Describe the pancreatic secretion. What foodstuffs does it act
upon? Describe its action on starch. How does it change proteids?

160 FBE HUMAN BODY.

different substance, trypsin, which differs from pepsin in
acting in an alkaline instead of in an acid medium. On
fats it has a double action. To a certain extent it breaks
them up into fatty acids and glycerine.* Tbe fatty acid
then combines with some of the alkali present to make
a soap, which being soluble in water is capable of absorp-
tion, f Glycerine also is soluble in water and capable
of absorption. The greater part of the fats is not, how-
ever, so broken up, but simply mechanically separated
into little droplets which remain suspended in the chyle
and give it a whitish color; just as cream-drops are sus-
pended in milk, or olive oil in mayonnaise sauce. If oil be
shaken up with water, the two cannot be got to mix; immedi-
ately the shaking ceases the oil floats up to the top; but if
some raw egg be added a creamy mixture is readily formed
in which the oil remains for a long time evenly suspended
in the watery menstruum. The reason of this is that each
oil-droplet becomes surrounded by a delicate pellicle of
albumen, and is thus prevented from fusing with its neigh-
bors to make large drops which would soon float to tbe top.
Such a mixture is called an emulsion, and the albumen of
the pancreatic secretion emulsifies the oils in the chyle,
which becomes white (for the same reason as milk is that

How does trypsin differ from pepsin ? How does pancreatic secre-
tion break up some fats ? What digestive end is thus attained ?
How is most of the fat eaten acted upon by the pancreatic secretion ?
Why is the chyle white ? How may we mix oil with water '? Ex-
plain the process. What is an emulsion ? What emulsifies the oily
matters of the chyle ?

* (C,6?h650)3 f °3 + 3H*° = 3 (CisH35h [ °) + C3h: [ °3

1 Stearin + 3 Water = 3 Stearic acid -f- 1 Glycerine.
t Ordinary soap is a compound of a fatty acid with soda, colored and scented
by the addition of various substances. Soft soap is a compound of a fatty acid
with potash. Both dissolve in water, which the fats from which they are made
will not do

THE BILE. 161

color) because the innumerable tiny oil-drops floating in it
reflect all the light which falls on its surface.

^The Bile. — Human bile when quite fresh is a golden
brown liquid. It is alkaline, and besides coloring matters,
mineral salts and water, contains the sodium salts of two
nitrogenized acids, taurocholic and glycocliolic, the former
predominating in human bile.

The Uses of Bile. —Bile has no digestive action upon
starch or proteids. It does not break up fats, but to a
limited extent emulsifies them when shaken up with them
outside the body, though far less perfectly than the pancre-
atic secretion. It is even doubtful if this action is exerted
in the intestines at all. In many animals, as in man, the bile
and pancreatic ducts open together into the duodenum, so
that on killing the creature during digestion and finding
emulsified fats in the chyle it is impossible to say whether
or not the bile had a share in the process. In the rabbit,
however, the pancreatic duct opens into the intestine about
a foot farther from the stomach than the bile-duct, and it
is found that if a rabbit be killed after being fed with oil,
no milky chyle is found down to the point where the pan-
creatic duct opens. In this animal therefore the bile alone
does not emulsify fats, and since the bile is pretty much
the same in rabbits and other mammals it probably does not
emulsify fats in them either. From the inertness of bile
with respect to most foodstuffs it has been doubted if it is
of any digestive use at all, and whether it should not be
regarded merely as an excretion, poured into the aliment-
Describe fresh human bile. What is its reaction? Name its
chief constituents.

Name foods on which bile has no influence. How does it
act upon fats when shaken with them? Give a reason for doubt-
ing if it emulsifies fats in the intestine.

162 TBE BUM AN BODY.

ary canal to be got rid of. But there are many reasons
against such a view. In the first place, the entry of the
bile into the upper end of the small intestine, where it
has to traverse a course of more than twenty feet before
getting out of the body, makes it probable that bile has
some function to fulfill in the intestine. One use is
no doubt to assist by its alkalinity in overcoming the
acidity of the chyme, and so to allow the pancreatic secre-
tion to act upon proteids. Constipation is also apt to
occur in cases where the bile-duct is temporarily stopped,
so that the bile probably helps to excite the contrac-
tions of the muscular coats of the intestines; and it is
said that when the bile secretion is deficient putrefactive
changes are extremely apt to occur in the intestinal con-
tents. Apart from such secondary actions, however, the
bile probably has some influence in promoting the absorption
of fats. If one end of a very narrow glass tube moistened
with water be dipped in oil the latter will not rise in it, or
but a short way; but if the tube be moistened with bile
instead of water the oil will ascend higher. Again, oil
passes through a plug of porous clay kept moist with bile,
under a much lower pressure than through one wet with
water. Hence bile by moistening the cells lining the intes-
tine may facilitate the passage into the villi of oily sub-
stances. At any rate, experiment shows that if the bile be
prevented from entering the intestine of a dog the animal
eats an enormous amount of food compared with that
amount which it needed previously; and that of this food

Give reasons for believing that bile is not a mere excretion. How
does bile aid the digestive power of the pancreas? Point out other
uses of bile. Describe experiments which it-nd to prove that bile
helps in promoting the absorption of fatty matters from the intes-
tine.

INTESTINAL DIGESTION. 163

a great proportion of the fatty part passes out of the ali-
mentary canal unabsorbed. There is no doubt therefore
that the bile somehow aids in the absorption of fats.

The Succus Entericus or Intestinal Juice consists of the
mixed secretions of the glands of Brunner and the crypts
of Lieberkiihn. It is very difficult to obtain it pure, and
hence its digestive action is but imperfectly known.
It is alkaline and so helps to overcome the acidity of the
chyme and allow the trypsin of the pancreas to act on pro-
teids, and seems capable itself of dissolving some kinds of
proteids and turning them into peptones.

Intestinal Digestion. — Having considered separately the
digestive actions of the different secretions poured into the
small intestine, we may now consider their combined ac-
tion. The acid chyme entering the duodenum from the
stomach is more than neutralized by the alkaline secretions
which it meets in the small intestine; it is made alkaline.
This alkalinity allows the pancreatic secretion to finish the
solution and transformation into peptone of proteids which
have escaped conversion in the stomach. The pancreatic
secretion also continues that conversion of insoluble starch
into soluble and absorbable grape sugar, which had com-
menced in the mouth but was checked in the stomach.
The bile and pancreatic secretion together emulsify the
fats, with which they are thoroughly mixed by the contrac-
tions of the muscular coat of the intestine; they get them
into a state of very fine division in the form of microscopic
droplets, which are taken up by the cells lining the intes-
tine. To a certain extent the fats are also saponified. The

What does the succus entericus consist of? Why is its digestive
action hut little known? Point out some of its uses.
Describe the process of intestinal digestion.

164 2:## HUMAN BODY.

result of all these processes is a thiu, milky looking alka-
line liquid called cliyle.

Indigestible Substances. — With every meal several
things are eaten which arc not digestible at all. Among
them is elastic tissue, forming apart of the connective tissue
of all animal foods, and cellulose, which is the chief constit-
uent of the cases which envelope the cells of plants. The
mucus secreted by the membrane lining the alimentary
tract also contains an indigestible substance, mucin. These
three materials, together with some water, some undigested
foodstuffs, and some excretory substances found in the
various secretions poured into the alimentary canal, form
a residue which collects in the lower end of the large
intestine, and is from time to time expelled from the
body.

Dyspepsia is the common name of a variety of diseased
conditions attended with loss of appetite or troublesome
digestion. Being often unattended with acute pain, and
if it kills at all doing so very slowly, it is pre-eminently
suited for treatment by domestic quackery. In reality,
however, the immediate cause of the symptoms, and the
treatment called for, may vary widely; and the detection
of the cause and the choice of the proper remedial agents
often call for more than ordinary medical skill. A few of
the more common forms of dyspepsia may be mentioned
here, with their proximate causes, not in order to enable
people to undertake the rash experiment of dosing them-

Name some indigestible substances eaten in every ordinary meal.
Point out the source of each. What indigestible substance is added
in the alimentary canal? What substances are found in the lower
end of the large intestine?

What is meant by dyspepsia? Why is it not a wise thing for
people to try to treat it themselves without skilled advice?

DYSPEPSIA. 165

selves, but to show how wide a chance there is for any
unskilled treatment to miss its end and do more harm
than good.

Appetite is primarily due to a condition of the mucous
membrane of the stomach, which in health comes on after
a short fast and stimulates its sensory nerves ; and loss of
appetite may be due to any of several causes. The
stomach may be apathetic and lack its normal sensibility
so that the empty condition does not act, as it normally
does, as a sufficient excitant. When food is take.i it is a
further stimulus and may be enough ; in such cases "ap-
petite comes with eating." A bitter before a meal is useful
as an appetizer to patients of this sort. On the other
hand, the stomach may be too sensitive, and a voracious
appetite be felt before a meal, which is replaced by nausea,
or even vomiting, as soon as a few mouthfuls have been
swallowed ; the extra stimulus of the food then over-
stimulates the too irritable stomach, just as a draught
of mustard and warm water will a healthy one. The
proper treatment in such cases is a soothing one.* In
states of general debility, when the stomach is too feeble
to secrete under any stimulation, the administration of
weak acids and artificially prepared pepsin is needed, so as
to supply gastric juice from outside until the improved

Describe the symptoms of some chief forms of dyspepsia.

* When food is taken it ought to stimulate the sensory gastric nerves, so as
to excite the reflex centres for the secretory nerves and for the dilatation of
the blood-vessels of the organ; if it does not, the gastric juice will be imper-
fectly secreted. In such cases one may stimulate the secretory nerves by weak
alkalies (p. 154), as apollinaris water or a little carbonate of soda, before
meals; or give drugs, as strychnine, which increase the irritability of reflex
nerve-centres. The vascular dilatation may be helped by warm drinks, and this
ii probably the rationale of the glass of hot water after eating which has
recently been in vogue; the usual cup of hot coffee after dinner js a more
agreeable form of tlje same aid to digestion,

166 THE HUMAN BODY.

digestion strengthens the stomach up to the point of being
able to do its own work.

Enough has probably been said to show that dyspepsia
is not a disease, but a symptom accompanying many
diseased conditions, requiring special knowledge for their
treatment. From its nature — depriving the body of its
proper nourishment — it tends to intensify itself, and so
should never be neglected ; a stitch in time saves nine.

Absorption from the Alimentary Canal. — Through its
whole extent the mucous membrane lining the digestive
tube is traversed by very closely packed tubes of two
kinds, the blood and lymph vessels. Matters ready for
absorption pass through or between the cells covering the
surface of the mucous membrane, and then through the
very thin walls of the smallest blood and lymph vessels ;
and by these vessels are conveyed to larger channels with
thicker walls, which all ultimately lead to the heart. From
the heart the digested and absorbed food is distributed to
every organ of the body.

Absorption from the Mouth, Pharynx, and Gullet is but
slight. Some water, some common salt, some sugar, and
some grape sugar (made from starch by the action of saliva)
are no doubt taken up during the processes of chewing and
swallowing. But the time which elapses between taking a
mouthful of food and its transference to the stomach is
usually too short to allow the occurrence of any consid-
erable absorption.

Why should dyspepsia never be neglected?

What tubes are found in the mucous membrane of the alimentary
canal? How do dissolved foods enter them? Where are the ab-
sorbed matters carried? To what parts are they finally distributed?

What foodstuffs are partly absorbed in mouth, pharynx, aud
gullet? Why does not any great amount of absorption take place
in those parte t

PLATE III.— a general view of the lymphatic's "it absorbents. That portion of them
known as the lacteala is seen at d, passing from the small intestine e to the thoracic duct f.

EXPLANATION OF PLATE IIL

A General View of the Lymphatic or Absorbent System
op Vessels.

e, A portion of the small intestine from -which lacteals or chyle-
conveying vessels, d, proceed, their origin within the villi may he
seen magnified in fig. 51; /, the duct called thoracic, into which the
lacteals open. This duct passes up the back of the chest, and opens
into the great veins at g, on the left side of the neck: here the chyle
mingles with the venous blood. In the right upper, and lower limbs
the superficial lymphatic vessels II 1 1, which lie beneath the skin,
are represented. In the left upper and lower limbs the deep lym-
phatic vessels which accompany the deep blood-vessels are shown.
The lymphatic vessels of the lower limbs join the thoracic duct at the.
spot where the lacteals open into it: those from the left upper limb
and from the left side of the head and neck open into that duct at
the root of the neck. The lymphatics from the right upper limb and
from the right side of the head and neck join the great veins at n.
to to, enlargements called lymphatic glands, situated in the course of
the lymphatic vessels. These vessels convey a fluid called lymph,
which mingles with the blood in the great veins. A fuller account of
the lymphatic vessels in general, as distinguished from that section of
them known as the lacteals, will be found on p. 188.

ABSORPTION FROM THE STOMACH. 167

Absorption from the Stomach is more important. Food
stays there a considerable time, and a good deal of the
substances mentioned above as being absorbed to a slight
degree on their way to the stomach, are taken up to a
much greater extent by the mucous membrane of the
stomach itself and passed on into the general blood current.
In addition, a large proportion of albuminous food is
turned in the stomach into peptones, which can be and
are readily absorbed by the vessels of the gastric mucous
membrane.

Absorption from the Small Intestine is by far the most
important in bringing nutritive matters into the body.
The stomach is an organ rather of digestion than absorp-
tion; the small intestine, on the other hand, is specially
constructed to absorb. Its valvulse conniventes delay the
progress of the food mass which stagnates in the hollows
between them; and its innumerable villi, with their blood-
vessels and lymphatics (p. 147), reach out, like so many
rootlets, into the chyle and take it up.

The sugars reaching the small intestine or formed in it
are absorbed mainly by the blood vessels and carried to the
liver, where they are turned into glycogen (p. 151), which is
heaped up in the liver during digestion, and slowly given
out to the blood, as its sugar is used up gradually before
the next meal. The peptones passed into the intes-
tine from the stomach, or formed in it by the action of the

Why does more absorption take place from the stomach? Name
things absorbed from both mouth and stomach? "What food matters
are first absorbed from the stomach?

Where does the most important food absorption occur? What
structural peculiarities of the small intestine peculiarly fit it for ab-
sorbing?

What vessels absorb sugars in the small intestine? To what organ
are these sugars conveyed? What there becomes of them?

168 THE HUMAN BODY.

pancreatic secretion, are partly taken up by its lymphatics
and partly by its blood-vessels. The emulsified fats main-
ly pass into the lymphatics of the villi, and are carried off
by them.

The Lacteals. — The innumerable tiny fat drops drained
off by the intestinal lympbatics or lacteals after an
ordinary meal make their contents look white and milky,
hence the name.* During fasting the lymphatics of the
small intestine, like those in other parts of the body (see
Chap. XIII.) convey a clear colorless liquid.

Absorption from the Large Intestine. — In the duo-
denum the bulk of food entering from the stomach is
increased by the bile and pancreatic secretions poured out
on it. Thenceforth absorption overbalances excretion, and
the food-mass becomes less and less in bulk to the lower
end of the ileum. The contractions of the small intestine
drive on its continually diminishing contents, until they
reach the ileo-colic valve, through which they are ulti-
mately pressed. When the mass enters the large intestine
its nutritive portions have been almost entirely absorbed,
and it consists chiefly of some water, with the indigestible
portions of the food and of the secretions of the alimentary
canal. It contains cellulose, elastic tissue, mucin, and
somewhat altered bile pigments; commonly some fat if a
large quantity has been eaten; and some starch, if raw veg-

How are emulsified fats carried off?

What are the lacteals? Why so called? Under what conditions
do the lacteals not contain milky looking chyle?

In what part of the alimentary canal does absorption more than
balance the amount of liquid poured out on the food?

What are the constituents of the mass passing from the small into
the large intestine? What changes does' this mass undergo as it
passes along the large intestine?

* from Latin, lac, milk.

APPENDIX. 169

etables have formed part of the diet. In its progress
through the large intestine the food-mass loses still more
water, and the digestion of starch and the absorption of
fats is continued. Finally the residue, with some excre-
tory matters added to it in the large intestine, is expelled
from the body.

APPENDIX TO CHAPTER XII.

The digestion and absorption of food are such fundamental facts
in physiology that a thoroughly intelligent comprehension of them is
of great importance; at the same time they are so largely merely
chemico-physical phenomena that they are readily illustrated by a
few simple experiments. These described below take but little time
and cost but little money, while they cannot fail to be of value not
merely in interesting a class, but in giving its members a much better
idea of the way in which food is digested than they can get from
merely reading a book.

1. Anatomy of the Alimentary Canal. — Kill a rat by chloroform or
drowning. Dissect away the skin from the whole ventral aspect of
the body.

Note in the neck region the large salivary glands which meet in the
middle line: the posterior gland, close to the middle line, rounded
and compact, is the submaxillary ; on raising it, its duct will be seen
passing forwards to the mouth, into which it may be followed by
separating the halves of the lower jaw.

The large gland, composed of several loosely united lobes, and
reaching from the neighborhood of the ear to the submaxillary, is the
parotid. Its duct will be found passing forwards over the face to
the mouth, near the angle of which it passes in through the cheek
muscles.

In front of the submaxillary will be found a small gland, the sub-
lingual.

Remove the muscles, etc.. covering the larynx and trachea; cut
away the front and side walls of the chest and abdomen; remove
larynx, trachea, lungs, and heart.

The gullet, a slender muscular tube, will now be exposed in the
neck; trace it through the chest; note the relative positions of the
abdominal viscera as now exposed, before displacing any of them;
then turning the liver up out of the way, follow the gullet in the
abdomen until it ends in the stomach.

170 THE HTJMAX BODY.

Note the form of the latter organ; its projection {fundus) to the
left of the entry of the gullet; its great and small curvatures; its
narrower pyloric portion on the right, from which the small intestine
proceeds. Attached to the stomach, and hanging down over the other
abdominal viscera, notice a thin membrane, the omentum.

Follow and unravel the coils of the small intestine, spreading out
as far as possible the delicate membrane {mesentery) which slings it.
In the mesentery are numerous bands of fat, running in which will
be seen blood-vessels and lacteals.

The termination of the small intestine by opening into the side of
the large. Observe the cacum or blind end of the latter, projecting
on one side of the point of entry of the small intestine: on the other
side follow the large intestine until it ends at the anal aperture, cut-
ting away the front of the pelvis to follow its terminal portion {rec-
tum). The portion between the caecum and the rectum is the colon.

Spread out the portion of the mesentery lying in the concavity of
the first coil {duodenum) of the small intestine; in it will be seen a
thin branched glandular mass, the pancreas.

Observe the portal rein entering the under side of the liver by
several branches. Alongside it will be seen the gall-duct, formed by
the union of two main branches, and proceeding, as a slender tube,
to open into the duodenum about an inch and a half from the pyloric
orifice of the stomach.

Note the spleen: an elongated red body lying in the mesentery,
behind and to the left of the stomach.

Divide the gullet at the top of the neck, and the rectum close to
the anus, and severing mesenteric bands, etc., by which intermediate
portions of the alimentary canal are fixed, remove the whole tube;
then cutting away the mesentery, spread it out at full length, and
note the relative length and diameter of its various parts. The whole
is seven or eight times as long as the head and trunk of the animal,
and the small intestine forms by far the longest part of it.

Open the stomach; note that the mucous membrane lining the fun-
dus is thin and smooth, and is sharply marked off from the thick
corrugated mucous membrane lining the rest of the organ. (This is
not the case in the human stomach.) Pass probes through the car-
diac orifice into the gullet and through the pyloric orifice into the
duodenum.

Remove the liver; note its general form.

Obtain from your butcher an inch or two of the small intestine
of a recently killed calf. Place in 50 per cent, alcohol for twenty-
four hours. Then open under water and examine with a hand lens to
see the villi.

APPENDIX. 171

2. The Action of Saliva on Starch. — Make a thiu paste of good
arrowroot (which is almost pure starch) with hoiling water. Let it
cool.

a. Add two or three drops of this starch paste to half a test tube-
ful of cold water; next add three or four drops of solution of caustic
potash and two or three drops of dilute watery solution of blue vitriol
(cupric sulphate). Mix thoroughly and boil over a spirit lamp. No
orange-red precipitate will result. This shows that there is no grape
sugar in the starch paste.

b. Rinse the mouth thoroughly and then collect a small quantity of
saliva in a test tube. Dilute with water. Add caustic potash and
cupric sulphate solutions as above; mix thoroughly and boil. The
mixture will become violet, but give no orange-red precipitate, there-
fore there is no grape sugar in saliva.

c. Take now three drops of the starch paste and a teaspoonful of
saliva, mix with a half test tubeful of water. Place the mixture in
a moderately warm place for five minutes. Then add a few drops of
the caustic potash and cupric sulphate solutions; mix and boil. An
abundant orange or brick -red precipitate will be thrown down, prov-
ing the presence of grape sugar, which has been produced by the
action of the saliva on the starch.

3. Gastric Digestion. — a. Obtain a pig's stomach. Cut it open
and wash away its contents with a gentle stream of water. Then
dissect off the mucous membrane from its middle part, mince and
put aside for a couple of days in three or four ounces of glycerine.
The glycerine dissolves the pepsin. Then strain off the glycerine
through muslin.

b. Get a butcher to " whip" some fresh drawn blood for you with
a bunch of wire or twigs. The blood fibrin will collect on these
(p. 181), and when thoroughly washed with water, forms a good proteid
for digestion experiments. One lot of it thus obtained and washed
may be put aside in 50 per cent, alcohol, and will provide material for
digestion experiments for years.

c. Add a teaspoonful of muriatic acid to a pint of water.

d. Dilute a teaspoonful of the pepsin solution a with two table-
spoonfuls of water. Fill a test tube with the mixture; add a few
shreds of washed fibrin, and set aside in a warm but not hot place for
twenty-four hours. No change will occur, showing that pepsin alone
will not dissolve proteids.

e. Put some shreds of fibrin in a test tube of the mixture c in a
warm place for twenty-four hours. The fibrin will swell up and
become translucent, but will not dissolve. This shows that dilute
r.cids will not in a short time dissolve proteids.

172 THE HUMAN BODY,

f. Half fill a test tube with the mixture c, add a teaspoonful of
the pepsin solution a, and then a few shreds of fibrin. Place in a
■warm place for twenty-four hours. The fibrin will be more or less
completely dissolved at the end of that time. We thus find that
pepsin alone and dilute acid alone (at least in a moderate time) will
not dissolve proteids, but that acting together they quickly effect a
solution.

4. The Action of Bile on Fatty Substances. — a. Shake up some
olive oil with water in a test tube. The two liquids soon separate
when the shaking ceases.

b. Obtain an ox gall from the butcher. Cut it open and collect
the bile. (The bile of herbivorous animals differs from human bile
in being green in color.) Shake up some oil with bile instead of
water. A creamy emulsion is formed from which the oil only slowly
floats up to the top.

5. The Action of the Pancreatic Secretion on Fats. — a. Obtain
a pig's pancreas; mince, and extract with about its own bulk of water
for two or three hours. Strain off the watery infusion. Add to it
half its bulk of oil in a test tube and shake thoroughly. The oil will
be very thoroughly emulsified ; and separate very slowly on standing.

6. Action of Pancreatic Secretion on Starch. — With some of the
watery extract of pancreas perform the experiments described above
under heading 2; substituting pancreatic extract for saliva.

7. Action of Pancreatic Secretion on Proteids. — a. Obtain a fresh
pig's pancreas. Lay aside in a cool place for twenty-four hours.
Mince, and extract for two days with twice its bulk of glycerine.
Strain off the glycerine extract.

b. Dilute the glycerine extract with ten times its bulk of water.
Place part of this mixture in a test tube together with some fibrin
shreds, and put aside in a warm place. After twenty-four hours
none of the fibrin will have been dissolved.

c. To the diluted glycerine extract as above add a teaspoonful of
dilute acid (3 c). The fibrin will swell but not dissolve.

d. To another portion of the diluted glycerine extract add just
sufficient bicarbonate of soda to make it distinctly alkaline, as tested
by litmus paper. Tben put in some fibrin and set aside in a warm
place for a day. The fibrin will be more or less completely dissolved.
We thus find that the pancreas affords a substance which, in the
presence of weak alkalies, dissolves proteids.

The fat-absorbing power of the lymphatics of the small intestine
is very readily demonstrable, without giving pain to an animal or any
unnecessary destruction of life. In most families superfluous kittens
or puppies have to be killed at the time of birth. Feed a kitten or

APPENDIX. 173

puppy on rich milk, and three hours after place it in a hox or under a
hell-jar with a sponge soaked with ether or chloroform. When the
animal is completely insensible cut off its head, and then rapidly open
the abdomen and spread out the mesentery (the thin membrane which
slings the small intestine). In it will be seen a beautiful network of
lacteal vessels filled with milk-white liquid, some of which can be
collected if one of the lacteals be cut open. For comparison a kitten
or puppy may be used which has had no food for eight or ten hours.
The lacteals being then filled with clear, watery-Jooking lymph, will
he recognized with difficulty.

. CHAPTER XIII.
BLOOD AND LYMPH.

Why we need Blood. — Some very small animals of simple

structure require no blood ; every part catches its own food

and gives off its own wastes to the air or water in which

the creature lives. "When, however, an animal is larger and

more complex, made up of many organs, some of which are

far away from the surface of its body, this is impossible;

some organs arc therefore set apart to catch food, and

arrangements made to carry some of this food to the others.

In our own bodies many parts lie faraway from the stomach

and intestines which receive, digest, and absorb our food,

and from the lungs which take oxygen gas out of the air

we breathe; yet every part, bone and muscle, brain and

nerve, skin and gland, needs a steady supply of both of these

things to keep it alive. The division of labor, in accordance

with which some organs are especially set apart for the

purpose of receiving substances from the outside world

to build up, nourish, and repair the body, necessitates

an arrangement by which the matters received shall be

distributed to other parts. This distribution is accomplished

by the blood, which flows into every organ from the crown

of the head to the sole of the foot. Being pumped round

"What kind of animals do not need blood? How are their wants
supplied and their wastes removed? Why do we find special recep-
tive organs in larger animals? Illustrate from the human body,
What arrangement is necessitated by the fact that special organs are
set apart in the body for receiving food and oxygen? How is the
distribution effected?

[174]

THE BLOOD. 175

and round, from place to place, by the heart, the blood picks
up nourishing things in its course through the walls of
the alimentary canal, and oxygen as it flows through the
lungs; it then carries them to all other parts of the body.

The Removal of Wastes. — The rapidly flowing blood not
only conveys a supply of nutritive material for all the
organs, but is a sort of sewage stream that drains off their
wastes (p. 108), and carries them to the excretory organs, by
which they are sent entirely out of the body.

The blood is a middleman: on the one hand, between the
receiving organs (lungs and alimentary canal) and all the
rest; and on the other hand, between the excretory organs
and all the others. Each part is thus kept in a well-fed
and healthy state, though it may lie far distant from all
places where new materials first enter the body, and from
those where refuse and deleterious substances are finally
passed from it.

The Blood, as every one knows, is a red liquid which is
very widely distributed over the body, since it flows from
any part of the surface when the skin is cut through.
There are very few portions of the body into which blood
is not carried. One of them is the outer layer of the skin;*
hairs and nails, the hard parts of the teeth and most carti-
lages also contain no blood; these non-vascular tissues are

Where does the blood receive nutritive matters? Oxygen?
What does it do with them?

What part does the blood play in the removal of wastes?

State briefly the functions of the blood with reference to the
nutritive processes of the body

What is blood? How do we know that it is widely distributed?
Name parts into which blood does not flow. How are the non-vas-
cular tissues nourished?

* The absence of blood in the superficial layer of the skin may be readily
shown: take a fine needle threaded with silk; by taking shallow stitches a pat-
tern can be easily embroidered on the palm or back of the hand without draw
ing a drop of blood

176

THE HUMAN BODY.

nourished by liquid which soaks through the walls of
blood-vessels in neighboring parts.

The Histology of Blood. — Fresh blood is to the unassisted
eye a red opaque liquid showing no sign of being made up
of different parts; but when examined by a microscope it is

Fig. 53 —Blood-corpuscles. A, magnified about 400 diameters. The red
corpuscles have arranged themselves in rouleaux; a. a, colorless corpuscles;
B, red corpuscles more magnified and seen in focus; E, a red corpuscle slightly
out of focus. Near the right-hand top coiner is a red corpuscle seen in three-
quarter face, and at C one seen edgewise. F,G,H,I, white corpuscles highly
magnified.

seen to consist of a liquid, the blood-plasma, which has
floating in it countless multitudes of closely crowded and
extremely minute solid bodies known as blood-corpuscles.
The liquid is colorless and watery-looking; the corpuscles
are of two kinds, red and colorless. The red corpuscles are

Describe the appearance of fresh drawn blood. What is seen
when a drop is examined with a microscope? Describe the blood-
plasma Name the kinds of blood-corpusciea

TEE RED CORPUSCLES OF OTHER ANIMALS. 177

by far the most numerous and give the blood its color; they
are so tiny and so plentiful that about five millions of them
are contained in one small drop of blood. They are so
closely packed that the unaided eye cannot see the spaces
between them, and so the whole blood appears uniformly
red.

The Red Corpuscles of Human Blood (Fig. 53) are cir-
cular disks a little hollowed out on each face. Seen singly
with a microscope each is not red but pale yellow; it is
only when they are crowded in a heap that the mass looks
red; a drop of blood spread out very thin on glass, or mixed
with a tablespoonful of water, is pale yellow and not red.
Soon after blood is drawn most of the red corpuscles cohere
side by side in rows, something like piles of coin.

The Red Corpuscles of other Animals. — -The red corpus-
cles of most mammalia resemble those of man in being
circular biconcave pale yel-
low disks; those of camels,
and dromedaries, however,
are oval. The blood-cor-
puscles of dogs are so
like those of man in size
that they cannot be Fl° 54~Bed corpuscles of the Frog.

readily distinguished; but in most cases the size is suffi-
ciently different to enable a safe opinion to be formed. This

Which kind is most numerous? Give some idea of their num.
ber. Why does t he blood look uniformly red to the unaided eye?

Describe the form of human red blood-corpuscles. What is
the color of one seen by itselt with a microscope? How may we
show that blood looks red only when its corpuscles are crowded close
together? How do the red corpuscles become arranged soon after
blood is drawn ?

Describe the corpuscles of most mammalia. How do those of
camels and dromedaries differ from the corpuscles of other mam-
mals? Why cannot a dog's blood be easily distinguished from
human blood?

178 THE HUMAN BODY.

fact has often been used to further the ends of justice in
determining whether spots of blood on the clothes of a
suspected murderer were really due to the cause assigned
by him. The red blood-corpuscles of birds, reptiles, amphi-
bians, and fishes cannot be confounded with those of man,
since they are oval and contain a nucleus in the centre such
as is not found in our red corpuscles.

Haemoglobin. — Each red corpuscle is soft and jelly like.
Its chief constituent, besides water, is a substance called
hcem' -o-glo' -bin, which has the power of combining with
oxygen when in a place where that gas is plentiful, and of
giving it off again in a region where oxygen is absent or
present only in small quantity. Hence as the blood flows
through the lungs, which are constantly supplied with fresh
air, its corpuscles take up oxygen, which, as it flows on, is
carried by them to distant parts of the body where oxygen
is deficient, and there given up to the tissues. This oxygen-
carrying is the function of the red corpuscles.

Arterial and Venous Blood. — Haemoglobin itself is dark
purplish-red in color; haemoglobin combined with oxygen
is bright scarlet red. Accordingly, the blood which flows to
the lungs after giving up its oxygen is dark red in color,
and that which, having got a fresh supply of oxygen, flows
away from the lungs is bright scarlet. The bright red blood
is called arterial and the dark red venous.

Can the blood of most mammals bo certainly distinguished from
human blood ? Point out a use which has been made of this fact. How
do the red corpuscles of birds, reptiles, and fishes differ from human?

Describe the consistence of a red corpuscle. What are its chief
constituents? Point out an important property of haemoglobin. How
does this enable it to receive and distribute oxygen? What is the
function of the red corpuscles?

What is the color of haemoglobin? What of haemoglobin com-
bined with oxygen? What is the color of blood flowing to the
lungs? Why? The color of that flowing from the lungs? Why?
What is arterial blood? What veuous?

THE COAGULATION OF BLOOD.

179

The Colorless Blood Corpuscles are a little larger than
the red, but much less numerous (about 1 to 300). As
their name implies they contain no coloring matter. Each
is a cell with a nucleus, and has the wonderful property of
being able to change its own shape. Watched with a micro-
scope the corpuscle may be seen to alter its form slowly
(Fig. 55), or even to creep across the glass. These corpus-
cles are thus little, independently
moving cells which live in our blood.
The pus or "matter" which collects
in an abscess is chiefly made up of
colorless blood - corpuscles which
have bored through the walls of
the smallest blood-vessels. Their
movements are very like those of the
microscopic animal named amoeba,
and are accordingly called amoeboid.

The Coagulation of Blood. — When blood is first drawn
from the living body it is perfectly liquid, flowing in any
direction as readily as water. This condition is only tem-
porary; in a few minutes the blood becomes viscid and sticky,
and comes to resemble a thick red syrup; the viscidity be-
comes more and more marked, until, after the lapse of five
or six minutes, the whole mass sets into a jelly which ad-
heres to the vessel containing it, so that this may be in-
verted without any blood whatever being spilled. This
stage is known as that of gelatinization, and is also not per-

How do the colorless corpuscles d;ffer from the red in size and
number? What is each? What property does it possess? What is
seen when one is watched with the help* of a microscope? What is
pus? Why are the movements of the colorless corpuscles called
aniceboid ?

What is the consistency of fresh drawn blood? What change
occurs in it within a few minutes?

Fig. 55.— A white blood-
corpuscle, sketched at suc-
cessive intervals of a few
seconds to illustrate the
changes of form due to its
amoeboid movements.

180 THE HUMAN BODY.

manent. In a few minutes the top of the jelly-like mass
will be seen to be hollowed or "cupped," and in the con-
cavity will be found a small quantity of nearly colorless
liquid, the blood-serum. The jelly next shrinks so as to
pull itself loose from the sides and bottom of the vessel con-
taining it, and as it shrinks it squeezes out more and more
serum. Ultimately we get a solid dot, colored red and
smaller in size than the vessel in which the blood coagu-
lated, but retaining its form, and floating in a quantity of
pale yellow serum. The whole series of changes leading to
this result is known as the coagulation or clotting of the
blood.

Cause of Coagulation. — If a drop of fresh drawn blood
be spread out and watched with a powerful microscope, it
will be seen that its coagulation is due to the separation of
very fine solid threads which run in every direction through
the plasma and form a close network entangling all the
corpuscles. These threads are composed of an albuminous
substance known ?.s fibrin. When they first form, the
whole drop is much like a sponge soaked full of water
(represented by the serum) and having solid bodies (the
corpuscles) in its cavities. After the fibrin threads have
been formed they begin to shorten; hence the fibrinous
network tends to shrink in every direction, and this shrink-
age is greater the longer the clotted blood is kept. At first
the threads stick too firmly to the bottom and sides of the

"What is meant by the stage of gelatinization? What first follows
that stage? What next? What is the final result? What is the whole
process called?

What is seen on watching a drop of fresh drawn blood with the
aid of a good microscope? What are the separated threads composed
of? To what may we compare a drop of blood in the first formation
of the fibrin threads? "What do the threads do after their for-
mation?

WHIPPED BLOOD. Igl

vessel to be pulled away, and thus the first sign of the
contraction of the fibrin is seen in the cupping of the sur-
face of the gelatinized blood where the threads have no
solid attachment, and there the contracting mass presses
out from its meshes the first drops of serum. Finally the
contraction of the fibrin overcomes its adhesion to the vessel,
and the clot pulls itself loose on all sides, pressing out
more and more serum. The great majority of the red cor-
puscles are held back in the meshes of the fibrin.

Whipped Blood. — The essential point in coagulation
being the formation of fibrin in the plasma, and blood only
forming a certain amount of fibrin,* if this be removed as fast
a? it forms the remaining blood will not clot. The fibrin
maybe separated by what is known as "whipping" the
blood. For this purpose fresh drawn blood is stirred up
vigorously with a bunch of twigs or a bundle of wire, and
the sticky fibrin threads as they form adhere to these. If
the twigs be then withdrawn a quantity of stringy material
will be found attached to them. This is at first colored red
by adhering blood-corpuscles, but by washing in water pure
fibrin may be obtained perfectly white and in the form of
highly elastic threads. The blood from which the fibrin
has been in this way removed looks just like ordinary
blood, but has lost its power of coagulating spontaneously.,,^

Uses of Coagulation. — The living circulating blood^m^o
the healthy blood-vessels does not clot; it contains no solid

Why is the first sign of their contraction seen in the cupping ?
What is the final result of this contraction ? Why is the clot red ?

How can we prevent blood from clotting? How is blood
whipped ? What do we find on examining the twigs after whipping
blood ? How may we get the pure fibrin ? AVhat are its characters?
How does whipped blood differ from ordinary blood?

* Fibrin is formed from fibrinogen, a soluble albumen existing in blood-plasma.

182 THE HUMAN BODY.

fibrin, but this forms in it, sooner or later, when the blood
gets in any way out of the vessels or if the lining of these is
injured. By the clotting the mouths of the small vessels
opened in a wound are clogged up, and the bleeding, which
would otherwise go on indefinitely, is stopped. So too,
when a surgeon ties an artery, the tight ligature crushes or
tears its delicate inner surface, and the blood clots where
this is injured. The clot becomes more and more solid,
and by the time the ligature is removed has formed a firm
plug in the cut end of the artery, which prevents bleeding.

Blood Compared with Water. — " Leaving aside its color,
we all know that blood is f /ticker than water; this is true
not only in a metaphorical but in a literal sense. In the
first place, bulk for bulk, blood is heavier than wTater; ten
teaspoonfuls of blood weigh as much as ten and a half tea-
spoonfuls of water. Secondly, blood contains in it solid
corpuscles and when drawn from the body forms spon-
taneously a solid clot, while pure water has no solid bodies
floating in it, and can only be made solid by freezing.
Thirdly, the blood liquid itself, quite apart from the cor-
puscles, is thicker than pure water, because it contains a
great many things dissolved in it; things which are of great
importance, because they are the foods which the blood is
carrying to, and the wastes which it is carrying from, the
various organs of the body."

The Composition of Blood-Serum. — About one half of
the bulk of fresh blood is corpuscles and the other half

When does blood clot? Illustrate the uses of the coagulating
property of blood.

Compare blood with water, (1) as to the weight of equal bulks of the
two (specific gravity); (2) as to its microscopic structure; (3) as to its
tendency to solidify; (4) as to the composition of its plasma. Why
are the things dissolved in tlie plasma of great importance?

What is the relative proportion of corpuscles rnd plasma in blood?

THE COMPOSITION OF BLOOD-SERUM. 183

plasma. What the plasma contains we may learn by ex-
amining blood-serum, which is plasma minus fibrinogen.

Blood-serum is very different from water; if we keep on
boiling pure water in a saucepan it will all go off in steam
and leave nothing behind, but if we try to boil serum we
find that we cannot do it; before it gets as hot as boiling
water it sets into a stiff, solid mass just like the white of a
hard-boiled egg. In fact the serum contains dissolved in it
two albumens very like that in the white of an egg, and
coagulated in a similar way by boiling. About eight and a
half pounds of albuminous substances exist in one hundred
pounds of blood.

Blood-serum also contains considerable quantities of oily
and fatty matters, a little sugar, some common salt and
carbonate of soda, and small quantities of very many other
things, chiefly waste products from the various tissues.
Nine tenths of the blood-plasma is water.

Composition of the Red Corpuscles. — In the fresh moist
state these contain a little more than half their weight of
water. Nine-tenths of their solid part is haemoglobin ;
they also contain phosphorus and iron and potassium.

The Blood Gases. — Ordinary fresh or salt water has a
good deal of air dissolved in it, which fishes breathe. Blood
also contains a quantity of gases which it gives off when
exposed to a vacuum, about sixty pints of gas to a hundred

What may we learn by examining blood-serum? What is blood-
serum?

What happens "when we try to boil blood-?erum? Why does it
coagulate in heating? What proportion of albumen exists in blood?

What things are found in the blood-seruin in addition to water?
How much water is there in ten pints of blood-plasma?

How much solids do the red corpuscles coniain? What propor-
tion of these is haemoglobin? Name other things found in the red
corpuscles.

What do fishes breathe? What does blood give off when placed in
a vacuum? How many pints of gas for each ten pints of blood ?

184 THE HUMAN BODY.

pints of blood. In blood going to the lungs the main gas
is carbon dioxide (or carbonic acid), which is a waste product
of all tbe organs of the body. In blood coming from the
lungs the most abundant gas is oxygen.

Summary. — "Blood, (hen, is a very wonderful fluid:
wonderful for being made up of colored corpuscles and
colorless fluid, wonderful for its fibrin and power of clot-
ting, wonderful for the many substances, for the proteids,
for the asbes or minerals, for the rest of the tilings which
are locked up in the corpuscles and in the serum.

" But you will not wonder at it when you come to see that
the blood is the great circulating market of the body, in
which all the things that are wanted by all parts, by the
muscles, by the brain, by tbe skin, by tbe lungs, liver, and
kidneys, are bought and sold. What the muscle wants it
buys from the blood; what it has done with it sells back to
the blood; and so with every other organ and part. As
long as life lasts this buying and selling is forever going on,
and this is why the blood is forever on the move, sweeping
restlessly from place to place, bringing to each part the
things it wants, and carrying away those with which it has
done. When the blood ceases to move, the market is blocked,
the buying and selling cease, and all the organs die, starved
for the lack of the things which they want, choked by the
abundance of things for which they have no longer any
need." — Foster.

Hygienic Remarks. — The blood flowing from any organ
will have lost or gained, or gained some things and lost

What is the most abundant gas in blood going to the lungs?
What in that leaving those organs?

Why may blood be justly culled a wonderful fluid? Why is its
complexity not astonishing? Why is the blood always kept in move-
ment during life? What happens when the blood ceases to move?

HTQIENW REMARKS. 185

others, when compared with the blood which entered it. But
the losses and gains in particular parts of the body are in
such small proportion as, with the exception of the blood
gases, to elude analysis for the most part; and, the blood
from all parts being mixed up in the heart, they balance one
another and produce a tolerably constant average. In
health, however, the red corpuscles are present in greater
proportion to the plasma after a meal than before it.
Healthy sleep in proper amount also increases the proportion
of red corpuscles, and want of it diminishes their number,
as may be recognized in the pallid aspect of a person who
lias lost several night's rest. Fresh air and plenty of it
favors their increase. The proportion of these corpuscles has
a great importance, since they serve to carry oxygen, which
is necessary for the performance of its functions, all over
the body. Ancemia is a diseased condition characterized
by pallor due to deficiency of red blood-corpuscles, and ac-
companied by languor and listlessness. It is not unfrequent
in young girls on the verge of womanhood, and in persons
overworked and confined within doors. In such cases the
best remedies are open-air exercise and good food, though
medicines containing iron are often of great use.

The Quantity of Blood in the Body. — The total weight
of the blood is about one-thirteenth of that of the whole

What would we find on comparing the blood leaving an organ
with that which entered it? What losses and gains are most easily
detected? How is it that, the blood maintains a tolerably uniform
average composition ? How does a meal affect the proportion of red
corpuscles ? How does sleep ? Illustrate. What is the influence of
plenty of fresh air ? Why is the proportion of blood-corpuscles im-
portant ? What is anaemia ? What class of persons is apt to suffer
from it ? What are the best remedies for it ?

What is the proportion of the weight of blood to that of the
whole body ?

Salt

Sti£

j 86 THE HUMAN BODY.

body; a man of average size contains about twelve pounds
of blood.

The Lymph. — The blood lies everywhere in closed tubes,
and consequently does not come into direct contact with
any of the cells which make up the body, except those which
float in it and those which line the interior of the blood-
vessels. At two parts of its course, however, the vessels
through which it passes have extremely thin walls, and
through the walls of these capillaries liquid transudes
and bathes the various tissues. The transuded
liquid is called lymph ; the blood makes lymph,
and the lymph directly nourishes all the tis-
sues except those mentioned above, with which
the blood itself comes in contact.

Dialysis. — When two specimens of water

J L Fig.56— A dia-

containing different matters in solution are sram of a dialy-

° sing apparatus,

separated from one another by a moist animal fiq"^1""1^ and
membrane, an interchange of material will £ mo^inimli
take place under certain conditions. If A be membrane-
a vessel (Fig. 56), completely divided vertically by such a
membrane, and a solution of common salt- in water be
placed on the side b, and a solution of sugar in water on
the side c, it will be found after a time that some salt has
got into c and some sugar into b, although there are no
visible pores in the partition. Such an interchange is said
to be due to dialysis or osmosis, and if the process were

How much blood is there in an average sized man?

"Why does the blood not directly bathe most of the tissues? What
cells come in contact with it? What are the capillaries? What is
lymph? What is the nutritive function of lymph?

What happens when watery solutions of different substances
are separated by a moist animal membrane? Illustrate. What is
such an interchange called? What would be the result at the end of
some hours?

THE RENEWAL OF THE LYMPH. 187

allowed to go on for some hours the same proportions of
salt and sugar would be found in the solutions on each side
of the dividing membrane.

The Renewal of the Lymph. — Osmotic processes play a
great part in the nutritive processes of the body. The
lymph present in any organ gives up things to the cells
there and gets things from them; and so, although it may
have originally been tolerably like the liquid part or plasma
of the blood, it soon acquires a different chemical composi-
tion. Dialysis then commences between the lymph out-
side and the blood inside the capillaries, and the latter
gives up to the lymph new materials in place of those which
it has lost, and takes from it the waste products which it
has received from the tissues. When this blood, thus al-
tered by exchanges with the lymph, gets again to the stom-
ach and intestines, having lost some food materials, it is
poorer in these than the richly supplied lymph around their
cells, and takes up a supply by dialysis from it. When it
reaches the excretory organs it has previously picked up a
quantity of waste matters, and loses these by dialysis to the
lymph there present, which is specially poor in such mat-
ters, since the excretory organs constantly deprive it of
them. In consequence of the different wants and wastes
of various cells, and of the same cells at different times,
the lymph must vary considerably in composition in various
organs of the body, and the blood flowing through them
will in consequence get and lose different things in differ-
How does the lymph in an organ come to differ chemical!}- from
the blood plasma which supplied it? What results? What happens
when the blood thus changed reaches stomach or intestine ? What
when it reaches excretory organs ? Why does the lymph vary in
composition in different parts of the body ? How does this affect
the blood ?

188 THE HUMAN BODY,

ent places. But, receiving in its passage through one re-
gion what it loses in another, its average composition is
kept pretty constant; and, through interchange with it, the
average composition of the lymph also.

The Lymphatic Vessels or Absorbents. — The blood, on
the whole, loses more liquid to the lymph through the cap-
illary walls than it receives back at the same time. This de-
pends mainly on the fact that the pressure on the blood in-
side the vessels is greater than that on the lymph outside,
and so a certain amount of filtration of liquid from within
out occurs through the vascular wall, in addition to the
dialysis. The excess is collected from the various organs
of the body into a set of lymphatic vessels, which carry it
directly back into some of the larger blood-vessels near
where these empty into the heart; and as fast as this on-
ward flow of the lymph occurs under pressure from behind,
it is renewed in the different organs, fresh liquid filtering
through the capillaries to take its place as fast as the old is
drained off.

Since the lymphatic vessels may be said to take up or
absorb the excess of liquid drained from the blood and also
the effete matters of the various organs, they are frequently
called the absorbents.

Lacteals we have already learned to be only another
name for the absorbents of the small intestine (p. 147).

How is the average composition of the blood maintained? How
that of the lymph?

Give another name for the lymphatic vessels. Does the blood on
the whole gain or lose liquid to the lymph as it flows through the cap-
illaries ? Explain why. What becomes of the excess of liquid
drained off from the blood ?

Where do the lymphatic vessels convey it? What produces the
onward flow of lymph? How is the lymph thus drained off replaced?
Why are the lymphatics called absorbents?

What is meant by the lacteals?

HISTOLOGY AND CHEMISTRY OF LYMPH. 189

Histology of Lymph. — Pure lymph is a colorless, watery
looking liquid; examined with a microscope it is seen to
contain numerous pale corpuscles exactly like those of the
blood. It contains none of the red corpuscles.

Chemistry of Lymph. —Lymph is not quite so heavy as
blood, though heavier than water. It may be described as
blood minus its red corpuscles and considerably diluted,
but of course in various parts of the body it will contain
minute quantities of substances derived from neighboring
tissues.

Summary. — To sum up: the blood and lymph pro-
vide a liquid in which the tissues of the body live; the
lymph is derived from the blood, and affords the immedi-
ate nourishment of the great majority of the living cells of
the body; the excess of it is finally returned to the blood,
which indirectly nourishes the cells by keeping up the
stock of lymph. The lymph itself moves but slowly, but
it is constantly renovated by interchanges with the blood,
which is kept in rapid movement by the heart, and which,
besides containing a store of new food-matters for the lym ph,
absorbs the wastes which the various cells Have poured into
the latter.

What does lymph look like? What is seen when it i.~ examined
with a microscope?

How does lymph differ in density from blood and from water?
How may it be briefly described? What Hoes it contain in various
regions of the body?

What do the blood and lymph provide? Whence is the lymph de-
rived? What does it afford? What becomes of its excess? How
does the blood play a part in nourishing the cells of the body?
Which moves faster, lymph or blood? How is the lymph renovated ?
What keeps the blood in motion? What does the blood do besides
renewing the food-matters in the lymph?

190 THE HUMAN BODY,

APPENDIX TO CHAPTER XIII.

Many of the main facts pertaining to the structure and composi-
tion of blood may be easily demonstrated as follows:

1. Kill a frog with ether (note, p. 68); cut off its head, and collect
on a piece of glass a drop of the blood which flows out. Spread out
the drop so that it forms a thin layer. Hold the glass up against the
light, and examine the blood with a hand lens magnifying four or five
diameters. The corpuscles will be readily seen floating in the plasma.

2. Wind tightly a piece of twine around the last joint of a finger;
then, taking a needle, prick the skin near the root of the nail. A
large drop of blood will exude. Spread it out on a piece of glass
and examine, as described above for frog's blood. The corpuscles
will be seen floating in the blood liquid, but not so easily as in frog's
blood, since those of man are considerably smaller.

[3. If a compound microscope is available the form, size, and
color of human and frog red blood corpuscles can be demonstrated;
also the tendency of the human to aggregate in rolls, and the color,
form, size, and relative number of the colorless corpuscles. As any
one possessing a compound microscope is sure to know how to
mount a specimen of blood for examination with it, or, if not, to
have at hand some treatise on the use of the microscope giving the
necessary information, details need not be given here.]

4. Obtaining a large drop of human blood as above described (2)
—note: a, that as it flows from the wound it is perfectly liquid; b,
that it is red and very opaque; c, spread it out very thin on the glass:
note that it then looks yellow when held over a sheet of white paper;
d, mix a similar drop with a teaspoonful of water in a wineglass;
note that the mixture is yellowish, or, if not, becomes so on further
dilution.

5. Place another large drop of human blood, obtained as above
indicated, on a clean glass plate. To prevent drying up cover by
inverting over the drop a wine glass whose interior has been moistened
with water. In four or five minutes remove the wine-glass and note
that the blood drop has set into a firm jelly. Replace the moist
wine glass, and in half an hour examine again. The blood will then
have separated into a tiny red clot, lying in nearly colorless serum.

6. If a slaughter-house is accessible the clotting of blood may be
still better illustrated. Provide two large wide-necked glass bottles
and a bundle of twigs. When the butcher bleeds an animal collect
in one bottle some blood, taking care that nothing else (contents of

APPENDIX. \§\

the stomach, for example, when the animal is bled, as is often done,
by cutting off its head) gets mixed with it. Put this bottle aside
until the blood clots, and carry it home with the least possible
shaking. Next day the mass will exhibit a beautiful clot floating in
serum. The latter will probably be tinted red, as the jolting in
conveying the specimen from the slaughter-house shakes some of the
corpuscles out of the clot into the serum.

7. In the other uottle collect biooaand beat it vigorously with the
twigs for three or four minutes. Next day this specimen will not
.have clotted, but on the twigs will be found a quantity of stringy
elastic material (fibrin), which becomes pure wThite when thoroughly
washed with water.

8. Take some of the serum from specimen 6. Point out that it
does not coagulate spontaneously. Heat it in a test tube over a spirit
lamp; the albumen will be coagulated and the whole will become
solid.

9. Place a small quantity of whipped blood (7) on a piece of
platinum foil. Heat over a spirit lamp. After the drop dries it
blackens, showing that it contains much organic matter. As the
heating is continued this is burnt away, and a white ash, consisting
of the mineral constituents of the blood, is left.

CHAPTER XIV.
THE ANATOMY OF THE CIRCULATORY ORGANS.

The Organs of Circulation are the heart and the blood-
vessels; the blood-vessels are of three kinds, arteries, capil-
laries, and veins. The arteries carry blood from the heart
to the capillaries; the veins collect it from the capillaries
and return it to the heart. There are two distinct sets of
blood-vessels in the body, both connected with the heart;
one set carries blood to, through, and from the lungs, the
other guides its flow through all the remaining organs; the
former are known as the pulmonary , the latter as the sys-
temic blood-vessels.

General Statement. — During life the pumping of the
heart keeps the blood flowing rapidly through the paths
marked out for it by the blood-vessels ; these paths it never
leaves except in cases of disease or injury.

The blood-vessels form a continuous system of closed
tubes comparable in a certain way to the water-mains of a
city. These tubes begin at the heart, and are very much
branched except close to it, just as the water pipes are
single only where the main aqueduct leaves the reservoir,

Name the organs of circulation. Name the kinds of blood-ves-
sels. "What is the function of the arteries? Of the veins? How
many sets of blood-vessels are there in the body? What does each
set do? "What are they called?

What is brought about by the beat of the heart? Under what
circumstances may blood leave a blood channel ?

What do the blood-vessels form ? Illustrate their function by
comparison wilh the water-mains of a city.

[192]

PLATE IV.— THE CHIEF ARTERIES AND VEINS OF THE BODY.

EXPLANATION OF PLATE IV.

The Circulatory Organs.

The arteries (except the pulmonary) and the left side of the heart
are colored red; the veins, (except the pulmonary) and the right half
of the heart blue: on the limbs of the left side the arteries are omitted
and only the superficial veins are shown.

1. Aorta, near its origin from the left ventricle of the heart.

2. Lower end of aorta.

3. Iliac artery.

4. Femoral artery.

5. Popliteal artery; the continuation of the femoral which passes behind the

knee-joint.
6,7. The main trunks .anterior and posterior tibial arteries into which the
popliteal divides).

8. Subclavian artery.

9. Brachial artery.

10. Radial artery.

11. Ulnar artery.

12. Common carotid artery.

13. Facial artery.

14. Temporal artery.

15..Right side of Heart, with superior vena cava joining it above, and inferior
vena cava (16) passing up to it from below

17. Innominate vein, formed by the union of subclavian and jugular veins

,„ , I V'g aiHl left innominate veins unite to form the superior cava

18. Left internal jugular vein.

19. Axillary vein.

20. Basilic vein.

22. Cephalic vein.

23. Radial vein.

24. Ulnar vein.

25. Median vein.

26. Iliac vein.

27. Femoral vein

28. Long saphenous vein.

29. The kidney: attached to it are seen the renal arterv and vein.
80. Branches of the pulmonary arteries and veins in the lung.

FUNCTIONS OF THE VASCULAR SYSTEM. 193

and more and more divided the further one follows them
from that point, until, in the various houses, they end in
numerous but very much smaller tubes. The course of the
blood differs, however, essentially from that of the water
supplied to a city, for the water does not return to the
reservoir, whereas the blood is carried back to the heart:
instead of having a large supply of liquid stored up as in
a reservoir, there is at any one time only quite a small
amount in the heart, but this is steadily replaced by the in-
flow through the veins as fast as it is carried off by outflow
througl 1 the arteries.

General Functions of the Different Parts of the Vascular
System. — The blood vascular system is quite closed except at
two points, one on each side of the neck, where lymph vessels
pour the excess of lymph back into the veins. Valves at
these two points let lymph flow into the blood-vessels, but
will not allow blood to pass the other way. Accordingly
everything which leaves the blood must do so by oozing
through the walls of the blood-vessels, and everything
which enters it must do the same, except matters conveyed
in by the lymph at the points above mentioned. This inter-
change through the walls of the vessels takes place only in
the capillaries. In India where rain only falls at certain
seasons it is stored up in huge tanks, and during the subse-
quent dry months distributed over the fields by a set of
small ditches and channels, cut through them in all direc-
tions, and from which the liquid soaks through the sur-

How does the blood flow differ from that of water in the mains
of a city? How is the supply of blood in the heart kept up?

Where is the blood vascular system not closed? What occurs at its
openings? What is the function of the valves at these openings? How
must substances leave the blood ? How enter it? In what vessels does
interchange through the walls of the blood-vessels occur? Illustrate the
function of the capillaries by comparison with an irrigation system.

194

TBE BVMAK BODY.

rounding soil; this is known as irrigation, and the capillaries
may be said to form an irrigation system for the body. In
a certain sense also they may be compared to the water
spigots of a house, which lie at the end of the supply tubes,
the arteries; but, to make the comparison more accurate,
we would have to imagine instead of ordinary spigots bags
of very fine muslin through which the. water oozed when
the tap was turned on. The capillaries, though far the
smallest tubes in the vascular system, are
the really important parts ; the heart,
arteries, and veins are all merely ar-
rangements for keeping the capillaries
full, and renewing the blood within
them. It is while flowing through these
and soaking through their walls that the
blood does its physiological work.

Diagram of the Circulatory Organs. —
The general relationship of heart, arte-
ries, capillaries, and veins may be gath-
ered from the accompanying diagram
(Fig. 57). The heart is essentially a bag
with muscular walls, and internally di-
vided into four chambers (d. g, e, f).
Those at one end (d and e) receive blood
from vessels opening into them and
known as the veins. From there the blood passes on to
the remaining chambers (g and/), which have very mus-
cular walls and, forcibly contracting,drive the blood out into

By comparison with the water pipes of a house. "What is the
use of heart, arteries, and veins? AVhen does the blood do its physi-
ological work?

Sketch on the blackboard a diagram of the circulatory organs.
What is briefly the structure of the heart? Where does the blood
enter the heart? From what vessels? Where does it go next?

Fig. 57.— The heart
and blood-vessels dia-
grammatically repre-
sented.

THE POSITION OF THE HEART. \%

vessels (i and i) which communicate with them and
are known as the arteries. The big arteries divide into
smaller; these into smaller again (Plate IV), until the
branches become too small to be traced by the unaided eye,
and these smallest branches end in the capillaries, through
which the blood flows and enters the commencements of the
veins; the veins convey it again to the heart. At certain
points in the course of the blood-path valves are placed,
which prevent a back-flow. This alternating reception of
blood at one end of the heart and its ejection from the
other occurs about seventy times a minute during health.

The Position of the Heart.— The heart (h, Fig. 4) lies
in the chest, immediately above the diaphragm and opposite
the lower two thirds of the breast-bone. It is conical in
form, with its base or broader end turned upwards and pro-
jecting a little on the right of the sternum, while its nar-
row end or apex, turned downwards, projects to the left of
that bone, where it may be felt beating between the carti-
lages of the fifth and sixth ribs. The position of the organ
in the body is, therefore, oblique. It does not, however, lie
on the left side, as is so commonly believed, but very nearly
in the middle line, with the upper part inclined to the
right, and the lower (which may be more easily felt beat-
ing— hence the common belief) to the left,

The Pericardium. — The heart does not lie bare in the

What then happens to it? How are the small arteries formed?
In what vessels do they end? What becomes of blood which has
flowed through the capillaries? Where do the veins carry it? How
is back-flow prevented? How frequently does the heart receive and
pump out blood?

Where is the heart situated? What is its form? Where does its
base lie? Where its apex? Where may we feel the apex beat?
What is the origin of the common belief that the heart is on the left
side?

196 THE HUMAN BODY.

chest, but is surrounded by a loose bag composed of con-
nective tissue and called the pericardium. This bag, like
the heart, is conical but turned the other way, its broad
part being lowest and attached to the upper surface of the
diaphragm. Internally it is lined by a smooth serous mem-
brane like that lining the abdominal cavity, and a similar
layer (the visceral layer of the pericardium) covers the out-
side of the heart itself, adhering closely to it. In the space
between the serous membranes is a small quantity of liquid
which moistens the contiguous surfaces, and diminishes the
friction which would otherwise occur daring the movements
of the heart.

Suppose a pear put in a bag of about the same shape,
but larger, and turned the other way so that the big end
of the bag was round the small end of the pear; then you
will get a good idea of how the pericardium lies with refer-
ence to the heart. If the outside of the pear and the inside
of the bag were covered with paint, this would represent
the serous membrane, and a few drops of water between the
pear and the bag would represent the serous liquid. To
complete the comparison we may imagine the pear to
have eight or nine stalks which reached out from it through
the bag; these would answer to the blood-vessels entering
and leaving the heart.

Note. — Sometimes the pericardium becomes inflamed,
this affection being known as pericarditis. It is extremely
apt to occur in rheumatic fever, and extreme care should
be taken never, even for a moment, except under medical

What is the pericardium? "What is its form? What lines it?
What covers the outside of the heart? What lies between the visceral
layer of the pericardium and the outer bag? What is its use?

Illustrate the relations of heart and pericardium.

What is pericarditis? In what disease is it especially apt to occur?

CAVITIES OF THE HEART. 197

advice, to expose a patient to cold during that disease,
since any chill is then especially apt to set up pericarditis.
In the earlier stages of pericardiac inflammation the rub-
bing surfaces on the outside of the heart and the inside of
the pericardium become roughened, and their friction pro-
duces a sound which can be heard with a stethoscope. In
later stages great quantities of liquid may accumulate in
the pericardium so as to seriously impede the heart's beat.

The Cavities of the Heart.— On opening the heart (see
diagram, Fig. 57, p. 194) it is found to be subdivided by a
longitudinal partition or septum into completely separated
right and left halves, the partition running from about the
middle of the base to a point a little on the right of the apex.
Each of the chambers on the sides of the septum is again
incompletely divided transversely into a thinner basal por-
tion into which veins open, known as the auricle, and a
thicker apical portion from which arteries arise and called
the ventricle. The heart cavity thus consists of a right
auricle and ventricle and a left auricle and ventricle, each
auricle communicating by an auricula-ventricular orifice
with the ventricle on its own side; there is no direct com-
munication whatever through the septum between the op-
posite sides of the heart. To get from one side to the other
the blood must leave the heart and pass through a set of

"Why should a person with rheumatic fever never be exposed
to cold except under skilled advice? What can be heard with a
stethoscope in the early stages of pericarditis? What may occur in
its later stages?

What is seen on opening the heart? In what direction does the
septum run? What is an auricle? A ventricle? Enumerate the
chambers of the heart cavity. With what does each auricle com-
municate? Is there a direct connection between the right and left
sides of the heart? What must the blood do to get from one side of
the heart to the other?

198

THE HUM AX BODY.

capillaries, as may readily be seen by tracing the course of

the vessels in Fig. 57.

The Vessels connected with the Different Chambers of

the Heart. — One big ar-
tery, called the aorta,
springs from the left
ventricle ; it runs back
to the pelvis after giving
off very many branches
on its way and then di-
vides into an artery for
each leg. Its big branches
divide into smaller and
these into smaller again,
until they become too
small to be traced by the
unaided eye. They spread
through the whole body,
to muscles, and bones,
and skin, and brain, and
stomach, and intestines,

Fig. 58.— View or the Heaht and Great „n(3 ljvpr and kidneVS *
Vessels from before. dna HVC1, dlla Kiuiieys ,

The pulmonary artery has been cat short theV finally end ill the SV8-

close to its origin. 1, right ventricle; 2, left "

ventricle; 3, root of the pulmonary artery; 4, temiC Capillaries. The
4', arch of the aorta; 4", the descending thoracic

aorta; 5, part of the right auricle; 6, part of the systemic Veins Collect the

left auricle; 7,7', innominate veins joining to J

form the vena cava superior; 8, inferior vena K|nfwl fvnm rlin r>nr>i11'i

cava; 9, one of the large hepatic veins; X, uluuu Ilom TntJ Capilia

placed in the right auriculq-ventricular groove, • » ,, diffprpnr or-

points to the right or posterior coronary artery ; *-l^v ui nit; uintutJiiu ui

X, X, placed in the anterior interventricular , ,, ,,

groove, indicate the left or anterior coronary ganS, ana all tUeSe VemS
artery.

What artery arises from the left ventricle ? To what point does
it run? What does it <rivc off on its course? How does it end? What
becomes of its branches? In what do they end? What vessels col-
lect the blood from the systemic capillaries?

VESSELS CONNECTED WITH THE HEART. 199

unite to form the superior and inferior voice cava or
the upper and lower hollow veins. These carry the blood
to the right auricle ; thence it enters the right ventricle
from which arises one vessel, the pulmonary artery ; this
divides into a branch for each lung ; each branch splits up
into minute arteries in its own lung, and these end in the
pulmonary capillaries. From the pulmonary capillaries the
blood of each lung is collected into two pulmonary veins,
and the four pulmonary veins open into the left auricle.

Summary.— One artery, the aorta, arises from the left
ventricle. The blood carried out by the aorta comes back
by the upper and lower venae cavae to the right auricle; this
blood, then goes to the right ventricle and is sent thence
through the pulmonary artery, which splits up into branches
for the lungs. The blood, carried out by the pulmonary
artery from the right ventricle of the heart, returns to the
left auricle by four pulmonary veins, two from each lung ;
and then enters the left ventricle and begins its flow again
through the aorta.

How the Heart is Nourished. — The heart is a very hard-
worked organ, and needs an abundant supply of nourish-
ment. Its walls are much too thick to allow this to soak
in sufficient abundance all through them, from the blood
flowing through its cavities; accordingly they are perme-
ated by a very close network of capillary blood vessels.
These are supplied by the right and left coronary arteries

Where do the venae cavse carry it ? Where does it pass from the
right auricle? TVhat vessel arises from the right ventricle? Into
what does the pulmonary artery divide? "What happens to each
branch? How do the branches finally end? Into what is the blond
which flows through the pulmonary capillaries collected T How
many pulmonary veins are there? Where do they end?

State briefly the course of the blood How

200

THE HUMAN BODY.

(Fig. 58), which are the two very first branches of the
aorta, and the blood from them is collected by the coronary
veins nnd poured by them directly into the right auricle.

Fie;. 59.— The left ventricle and the commencement of the aorta laid open. Mpm,
Mpl. the papillary muscles. From their upper ends are seen the chordae tendineae
proceeding to the edges of the flaps of the mitral valve. The opening into the
auricle lies between these flaps. At the beginning of the aorta are seen its three
pouch-like semilunar valves.

What are the coronary arteries ? The coronary veins ?

AURICULO-VENTRICULAB VALVES. 201

The Auriculo- Ventricular Valves. — Between each auricle
of the heart and the ventricle of the same side are found
valves which allow blood to pass from the auricle to the
ventricle, but prevent any flow in the opposite direction.
These valves are known as the tricuspid and mitral valves.
The mitral valve (Fig. 59) consists of two flaps fixed by
their bases to the margins of the opening between the left
auricle and the left ventricle; their edges hang down into
the ventricle when the heart is empty. These edges are not
free, but have fixed to them a number of stout connective-
tissue cords, the chorda? tendinem, which are fixed below to
muscular elevations, the papillary muscles, Mpm and Mpl,
on the interior of the ventricle. The cords are long enough
to let the valve flaps rise into a horizontal position and so
to close the opening between auricle and ventricle, which
lies behind the opened aorta, Sp, represented in the figure.
The tricuspid valve is like the mitral, but with three flaps
instead of two.

Semilunar Valves. — These are six in number ; three at
the mouth of the aorta, Fig. 59, and three, quite like them,
at the mouth of the pulmonary artery. Each is a strong
crescentic pouch fixed by its more curved border, and with
its free edge turned away from the heart. When the valves
are in action their free edges meet across the vessel and
prevent blood from flowing back into the ventricle.

The Course of the Main Arteries of the Body (Fig. 60).
— The aorta after leaving the left ventricle makes an arch

What is found between each auricle and ventricle? "What are
they called? Describe the mitral valve. Where is it placed? What
are the chordae tendineae? The papillary muscles? How far will
the cords allow the valve flaps to rise? How does the tricuspid valve
differ from the mitral?

How many semilunar valves are there? Where are they placed'
Describe them. What is theu use?

202 THE HUMAN BODY.

(«a) with its convexity towards the head. From the heart
end of this arch arise the coronary arteries, which carry
blood into the walls of the heart. From the convexity of
the arch spring the three large trunks : the innominate
artery ; the left common carotid artery (as) ; and the left
subclavian artery (ssi). The innominate soon divides into
the right subclavian (sd), and the right common carotid (cd)
Each common carotid runs up the neck on its own side,
and divides into branches for the neck, face, scalp, and brain.
Each subclavian continues across the arm-pit as the axil-
lary artery (ax), and then runs down to near the elbow as
the brachial artery (b). Just above the elbow it divides
into the radial and ulnar arteries (r, u,) which supply the
fore-arm, and end in small branches for the hand

Beyond its arch the aorta runs back close to the spinal
column as the thoracic aorta (a/), which gives off branches
to the walls of th« chest and some organs in that cavity.
The vessel then passes through the diaphragm, and con-
tinues as the abdominal aorta (Aab) to the lower part of the
abdomen. The main branches of the abdominal aorta are:
(1) the cceliac axis, which divides into branches for the
stomach, liver, and spleen; (2) the upper and lower mesen-
teric arteries, which supply the intestines with blood; (3)
the renal arteries (k), which carry blood to the kidneys.

What is meant by the aortic arch? Wh;it are its first branches?
What brandies are given off from the upper side of the aortic
arch? Into what vessels does the innominate artery divide? To
what parts do the common carotid arteries carry blood? In what
does the subclavian artery terminate? What vessels supply the
fore-arm with blood? How do they end?

What is the thoracic aorta?

The abdominal aorta? Name the chief branches of the abdom-
inal aorta. What onrans are supplied by the cceliac axis? The
mesenteric arteries? The renal arteries?

Fig. 60.— The main arteries of the body. Crd and Ora, rig:ht and left coronary-
arteries of the heart, cut short near their origin: An, and a A. aortic arch; At,
thoracic aorta: Aab, abdominal aorta: K, renal artery: Sfl. right, and Sat, left
subclavian: Cd. right, and Cs. left carotid; Ax. axillary artery: B. brachial
artery; U, ulnar artery: R, radial artery: Ai. common iliac artery; I. external
iliac artery; C. femoral artery; Po, popliteal artery; Ta, anterior, and Tp, pos-
terior tibial arter}-; Pe, peroneal artery.

204 THE HUMAN BODY.

The two trunks into which the posterior end of the ab-
dominal aorta divides (Ai) are named the common iliac
arteries ; each gives off some branches in the pelvis, and
then continues along the thigh as the femoral artery (C);
this runs to the knee-joint, behind which it is called the
popliteal artery (Po). The popliteal artery divides into
the peroneal (Pe) and tibial (Ta, Tp) arteries, which sup-
ply the lower leg and the foot.

The Properties of the Arteries. — Two fundamental facts
must be borne in mind in connection with the arteries :
First, that they are highly elastic and extensible ; a large
artery is, in this respect, much like a piece of rubber tub-
ing of the same size. Second, the arteries have rings of
muscular tissue in their walls, and when the muscle con-
tracts the bore of the artery (and consequently the amount
of blood which flows through it) is diminished. When the
muscle relaxes, the bore of the artery is increased, and more
blood passes along it to the capillaries in which it ends.

The Capillaries. — The smallest arteries pass into the
capillaries, which have very thin walls, and form very close
networks in nearly all parts of the body ; their immense
number compensating for their smaller size. The average
diameter of a capillary vessel is so small that only two or
three blood-corpuscles can pass through it abreast, and in
many parts the capillaries lie so close together that a pin's

Into what vessels does the abdominal aorta ultimately divide?
What is the femoral artery derived from? To what point does it
run? What is the popliteal artery? Into what branches does the
popliteal artery divide? What parts do they supply with blood?

What main facts are to be borne in mind in connection with the
arteries? How is the quantity of blood which an artery will let pass
regulated?

What is found when the arteries are followed to the ends of their
smallest branches? Describe the structure, arrangement and size of-
the capillaries.

THE VEINS. 205

point could not be inserted between two of them, as, for
instance, in the deep layers of the skin which can hardly
be pricked anywhere with a needle without drawing blood.
It is while flowing in these delicate tubes that the blood
does its nutritive work, the arteries being merely supply-
tubes for the capillaries, through whose delicate walls
liquid containing nourishment exudes from the blood to
bathe the various tissues. Imagine a piece of the finest
lace, with all its threads consisting of hollow tubes, and
diminished twenty times in size, and you will have some
idea of the capillaries.

The Veins. — The first veins arise from the capillary net-
works in various organs, and like the last arteries are very
small. They soon increase in size by union, and so form
larger and larger trunks alongside the main artery of the
part, but there are many more large veins just beneath the
skin than there are large arteries. This is especially the
case in the limbs, the main veins of which are superficial,
and can in many persons be seen as faint blue lines through
the skin.

Why the large Arteries usually lie deep. — The heart
pumps the blood with great force into the arteries, and if
an artery is cut very rapid and dangerous bleeding occurs ;
the veins, if cut, do not bleed nearly so violently as an
artery of the same size. Hence it is less dangerous to have
a large vein than a large artery close under the skin.

Point out a fact illustrating the closeness of the capillaries in
many parts of the body. What does the blood do as it flows through
the capillaries?

Where do the first veins arise? What is their size? How do
they increase in size? Where do the larger veins lie? In what parts
of the body do we especially find larije veins close beneath the skin?

Why are the large arteries, as a rule, placed deeper than veins of
corresponding size?

206

THE HUMAN BODY

The Valves of the Veins. — Except the pulmonary artery
and the aorta, which have the semilunar valves, arteries have
no valves. Most veins, on the contrary, contain many valves
formed by pouches of their lining, which resemble in form,
the semilunar valves of the aorta and the pulmonary artery,

§tfi>

Fig. 61.— A small portion of the capillary network as seen in the frog's web when
magnified about 2.3 diameters, a, a small artery feeding the capillaries; v, v, small
veins carrying blood back from the latter.

What arteries have valves? Where are these valves placed?
How do veins differ from arteries in regard to the presence of valves
m them?

VALVES OF THE VEINS. 207

but are turned in the opposite direction, having the edge
nearest the heart free and the other fixed. These valves
permit blood to flow only towards the heart, for a current
in that direction, as in the upper diagram, Fig. 62,
presses the valve close against the side of the vessel, and
meets with no obstruction from it. Should any back-flow
be attempted, however, the current closes up the valve and
bars its own passage, as indicated in the lower figure.
These valves are most numerous in superficial veins and

those of muscular parts. Usually

the vein is a little dilated opposite
a valve, and hence in parts where
the valves are numerous gets a
knotted look. On tying a cord
tightly round the fore-arm, so as

, , ,i a 'l i i Fig. 62— Diagram to illus-

to Stop the flow 111 its SllbcutaneOUS trate the mode of action of

, . . ti , i • the valves of the veins. C. the

veins and Cause their dilatation, capillaiy, H, the heart end of

tlitj vessel

the points at which valves are

placed can be recognized by their swollen appearance. The
valves are most frequently found where two veins communi-
cate.

The Course of the Blood.— From what has been said it
is clear that the movement of the blood is a circulation.
Starting from any one chamber of the heart it will in time
return to it; but to do this it must pass through at least
two sets of capillaries; one of these is connected with the

In what direction do the valves of the veins allow the blood
to pass? Make a diagram illustrating the action of the valves.
In what veins are the valves most numerous? Why does a vein with
many valves appear knotted? How may we see the dilatations of
the veins opposite the valves? Where are the valves of the veins
most frequently placed?

If we followed the blood course steadily from one chamber of the
heart what would we find in time? Through what must blood pass
before returning to the chamber of the heart which it leaves?

208 THE HUMAN BODY.

aorta, and the other with the pulmonary artery, and in its
circuit the blood returns to the heart twice. Leaving the
left side it returns to the right, and leaving the right it
returns to the left; and there is no road for it from one
side of the heart to the other except through a capillary
network. Moreover, it always leaves from a ventricle
through an artery, and returns to an auricle through a
vein.

There is then really only one circulation; hut it is not
uncommon to speak of two, the flow from the left side of
the heart to the right through most of the body being
called the systc7nic or greater circulation, and from the
right to the left through the lungs the pulmonary or lesser
circulation. But since, after completing either of these
alone, the blood is not again at the point from which it
started, but is separated frcm it by the septum of the
heart, neither is a " circulation'' in the proper sense of the
word, for a, circulation implies that any object at the end
of its course is again exactly where it was at the com-
mencement.

The Portal Circulation. — A certain portion of the blood
which leaves the left ventricle of the heart through the
aorta has to pass through three sets of capillaries before it
can again return there. This is the portion which goes
through the stomach and intestines. After traversing the
capillaries of those organs it is collected into the portal

Through what does blood always leave the heart? To what does
it return? How many circulation* are there really? What is meant
by the systemic circulation? What by the pulmonary? Why is
neither a true " circulation" in the proper sense of the word?

How many sets of capillaries does some blood pass through in a
complete circulation? What portion of the blood is it? What vessel
does it enter after traversing the capillaries of the stomach and in-
testines?

THE PORTAL CIRCULATION.

209

vein, which enters the liver, and breaking up there into
finer and finer branches like an artery, ends in the
capillaries of that organ, forming
the second set which this blood
passes through on its course.
From these it is collected by the
hepatic veins, which pour it into
the inferior vena cava which cur-
ries it to the right auricle, so that
it has still to pass through the
pulmonary capillaries to get back
to the left side of the heart. The
portal vein is the only one in the
human body which thus like an
artery feeds a capillary network,
and the flow from the stomach
and intestines through the liver
to the inferior vena cava, is often
spoken of as the portal circulation.
Diagram of the Circulation. —
Since the two halves of the heart,
although placed in proximity in
the body, are actually completely
separated from one another by an
impervious partition, we may con-
veniently represent the course of the blood as in the ac-
companying diagram (Fig. 63), in which the right and

Fig. 63 Diagram of the
blood vascular systo m, show-
ing that it forms a single
closed circuit with two pumps
in it, represented by the right
and left halves of the heart,
which are separated in the
diagram, ra and rv, right auri-
cle and ventricle; la and Iv,
left auricle and ventricle ; ao,
aorta; sc, systemic capilla-
ries; vc, vena? cavae; pa, pul-
monary artery ;pc,pulm onary
capillaries; pv, pulmonary
veins.

Where does this vein carry it? In what does it end? Into
■what vessels is the blood of the capillaries of the liver collected?
Where do they convey it? What chamber of the heart does it.
first reach? Through what must it pass to get back to the left
ventricle? How does the portal vein differ from all others in the
body? What is meant by the portal circulation?

210 THE HUMAN BODY.

left halves of the heart are represented at different points
in the vascular system. Such a diagram makes it clear that
the heart is really two pumps working side by side, and
each engaged in forcing blood to the other. Starting from
the left auricle, la, and following the flow, we trace it
tli rough the left ventricle, and along the branches of
the aorta into the systemic capillaries, sc; thence it
passes back through the systemic veins, vc. Reaching
the right auricle, ra, it is sent into the right ventricle, rv,
and thence through the pulmonary artery, pa, to the lung
capillaries, pc, from which the pulmonary veins, pv, carry
it to the left auricle, which drives it into the left ventricle,
Iv, and this again into the aorta.

Arterial and Venous Blood. — The blood when flowing
in the pulmonary capillaries gives up carbon dioxide (a
waste product which it has gathered in its flow through
the other organs) to the air, and receives oxygen from it;
since its coloring matter (haemoglobin) forms a scarlet
compound with oxygen, the blood which flows to the left
auricle through the pulmonary veins is of a blight red
color. This color it maintains until it reaches the sys-
temic capillaries, but in these it loses much oxygen to
the surrounding tissues, and gains much carbon dioxide
from them. But the blood-coloring matter which has lost
its oxygen has a dark purple-black color, and since this
unoxidized or " reduced" haemoglobin is now in excess, the

Why are we justified in diagrammatically representing the heart
as made of two separated parts? Starting from the left auricle,
describe the course of the blood until it returns there.

What does the blood give up in the pulmonary capillaries? What
does it receive? Why is it bright red when it enters the left auricle?
How far in its course does it keep this color? What gases does the
blood gaiu and lose in the systemic capillaries?

APPENDIX. 211

blood returns to the right auricle of the heart by the
venae cavae of a dark purple-red color. This color it
keeps until it reaches the lungs, where the reduced haemo-
globin becomes again oxidized. The bright red blood,
rich in oxygen and poor in carbon dioxide, is known as
"arterial blood," and the dark red as "venous blood;"
and it must be borne in mind that the terms have this
peculiar technical meaning, and that the pulmonary veins
contain arterial blood, and the pulmonary arteries contain
venous blood. The change from arterial to venous takes
place in the systemic capillaries, and from venous to
arterial in the pulmonary capillaries.

What color is the blood wheu returned to the right auricle? Why?
What is muaut by arterial blood? By venous? What veins contain
arterial blood? What arteries venous? Where does the change
from arterial to venous occur? Where that from venous to arterial?

APPENDIX TO CHAPTER XrV.

1. In the following directions " dorsal " means the side of the heart
naturally turned towards the vertebral column, "ventral" the side
next the breast-bone; "right" and "left" refer to the proper right
and left of the heart when in its natural position in the body; " an-
terior" means more towards the head in the natural position of the
parts; and " posterior" the part turned away from the head.

2. Get your butcher to obtain for you a sheep's heart, not cut out
of the bag (pericardium), and still connected with the lungs. Impress
upon him that no hole must be punctured in the heart, such as is
usually made when a slaughtered sheep is cut up for market.

3. Place the heart and lungs on their dorsal sides on a table in
their normal relative positions, and with the windpipe directed away
from you. Note the loose bag {pericardium) in which the heart lies,
and the piece of midriff {diaphragm) which usually is found attached
to its posterior end.

4. Carefully dissecting away adherent fat, etc., trace the vessels

212 THE HUMAN BODY.

below named until they enter the pericardium. Be very careful not
to cut the veins, which, being thin, collapse when enrply, and may
be easily overlooked until injured. As each vein is found stuff it
with raw cotton, which makes its dissection much easier.

a. The vena cava inferior ; find it on the under (abdominal) side of
the diaphragm; thence follow it until it enters the pericardium, about
three inches further up; to follow it in this part of its course, turn
the right lung towards your left and the heart towards your right.

The vein just below the diaphragm may be seen to receive several
large vessels, the hepatic veins.

As it passes through the midriff, two veins from that organ enter it.

Between diaphragm and pericardium the inferior cava receives no
branch; but, lying on its left side, will be seen the lower end of the
right phrenic nerve, ending below in several branches to the diaphragm.

b. Superior vena cava : seek its lower end, entering the pericardium
about one iuch above the entry of the inferior cava; thence trace it
up to the point where it has been cut across; stuff and e'ean it.

c. Between the ends of the two venae cava? will be i-ecn l lie two
right pulmonary veins, proceeding from the lung and entering the
pericardium; clean and stuff them.

5. Turn the right lung and the heart back into their natural posi-
tions; clear away the loose fat in front of the pericardium, and seek
and clean the following vessels in the mass of tissue lying anterior to
the heart, and on the ventral side of the windpipe.

a. The aorta : immediately on leaving the pericardium this vessel
gives off a large branch; it then arches back and runs down behind
the heart and lungs, giving off several branches on its way.

b. The pulmonary artery : this will be found imbedded in fat on
the dorsal side of the aorta. After a course, outside the pericardium,
of about an inch, it ends by dividing into two large branches (right
and left pulmonary arteries), which subdivide into smaller vessels as
they enter the lungs.

c. Observe the thickness and firmness of the arterial walls as
compared with those of the veins; they stand out without being
stuffed.

6. Notice, on the ventral side of the left pulmonary artery, the
left pulmonary veins passing from the lung into the pericardium.

7. Up to this point the dissection may be made before the meeting
of the class; on the preparation demonstrate the anatomical facts
above noted and then proceed as follows:

8. Slit open the pericardiac bag, and note its smooth, moist, glis-
tening inner surface, and the similar character of the outer surface of
the heart. Cut away the pericardium carefully from the entrances
of the various vessels which you have already traced to it. As this

APPENDIX. 213

is done, you will notice that inside the pericardium the pulmonary
artery lies on the ventral side of the aorta.

9. Note the general form of the heart — that of a cone with its apex
turned towards the diaphragm. Very carefully dissect out the entry
of the pulmonary veins into the heart. It will probahly seem as if
the right pulmonary veins and the inferior cava opened into the same
portion of the organ, but it will be found subsequently (13. a.) that such
is not really the case. Note on the exterior of the organ the follow-
ing points:

a. Its upper flabby auricular portion into which the veins open,
and its denser lower ventricular part.

b. Running around the top of the ventricles is a band of fat, an
offshoot of which runs obliquely down the front of the heart, passing
to the right of its apex, and indicating externally the position of the
internal partition or septum which separates the right ventricle,
which does not reach the apex of the heart, from the left, which
does.

c. Note the fleshy "auricular appendages" — one (left) appearing
below the pulmonary artery; the other {right), between the aorta and
superior cava.

10. Dissect away very carefully the collection of fat around the
origins of the great arterial trunks and that around the base of the
ventricles. In the fat will be found —

a. A coronary artery arising from the aorta close to the heart,
opposite the right border of the pulmonary artery; it gives off a
branch which runs in the groove between right auricle and ventricle,
and then runs down the dorsal side of the heart on the ventricles.

b. The other coronary artery, considerably larger, arises from the
aorta dorsal to the pulmonary artery; its main branch runs along
the ventral edge of the ventricular septum.

c. The coronary reins and sinus: small coronary veins will be
seen accompanying the arteries; for the coronary sinus see 11. c.

11. Open the right ventricle by passing the blade of a scalpel
through the heart about an inch from the upper border of the ventri-
cle, and on the right of the band of fat marking externally the limits
of the ventricles, and noted above (9. b.), and then cut down towards
the apex, keeping on the right of this line; cut off the pulmonary
artery about an inch above its origin from the heart, and open the
right auricle by cutting a bit out of its wall, to the left of the
entrances of the venae cava?. On raising up by its point the wedge-
shaped flap cut from the wall of the ventricle, the cavity of the latter
will be exposed.

a. Pass the handle of a scalpel from the ventricle into the auricle;

214 THE HUMAN BODY.

and also from the ventricle into the pulmonary artery, and make out
thoroughly the relations of these openings.

b. Slit open the auricular appendage; note the fleshy projections
{columnce cameo?) ou its walls, and the smoothness of the rest of the
interior of the auricle. Observe the apertures of the tenm cava,
and note that the pulmonary veins do not open into this auricle.

c. Behind or below the entrance of the inferior cava, note the
entrance of the coronary sinus; pass a probe through the aperture
along the sinus and slit it open; notice the muscular layer covering
it in.

12. Raise up by its apex the flap cut out of the ventricular wall,
and if necessary prolong the cuts more towards the base of the ven-
tricle until the divisions of the tricuspid valve come into view.

a. Note the column* carneae on the wall of the ventricle, -and the
muscular cord (not found in the human heart) stretching across its
cavity. Also the prolongation of the ventricular cavity towards the
aperture of the pulmonary artery.

b. Cut away the right auricle, and examine carefully the tricuspid
valve, composed of three membranous flexible flaps, thinning away
towards their free edges; proceeding from near these edges are strong
tendinous cords {chorda tendinece), which are attached at their other ends
to muscular elevations {papillary muscles) of the wall of the ventricle.

c. Slit up the right ventricle until the origin of the pulmonary
artery comes into view. Looking carefully for the flaps of the semi-
lunar valves, prolong your cut between two of them so as to open
the bit of pulmonary artery still attached to the heart. Spread out
the artery and examine the valves.

d. Each flap makes, with the wall of the artery, a pouch, opposite
which the arterial wall is slightly dilated. The free edge of the
valve is turned from the heart, and has in its middle a little nodule
[corpus Aranlii).

13. Open the left ventricle in a manner similar to that employed
for the right. Then cpen the left auricle by cutting a bit out of its
wall above the appendage. Cut the aorta off about half an inch
above its origin from the heart. The aperture between left auricle
and left ventricle can now be examined ; also the passage from the
ventricle into the aorta, and the entry of the pulmonary veins into
the auricle ; and the septum between the auricles and that between
the ventricles.

a. Pass the handle of a scalpel from the ventricle into the auricle;
another from the ventricle into the aorta ; and pass also probes into
the points of entrance of the pulmonary veins. Observe that no
other veins open into this auricle.

APPENDIX. 215

b. Slit open the auricular appendage; note the fleshy projections
(columnce carnece) on its interior, and the general smoothness of the
rest of the inner wall of the auricle. Notice the columnce came/?
over the inner surface of the ventricular wall, also the considerable
thickness of the latter, as compared with that of the right ventricle or
of either of the auricles.

c. Carefully raise the wedge-shaped flap of the left ventricle, and
cut on towards the base of the heart, until the valve (mitral) between
auricle and ventricle is brought into view; one of its two flaps will
be seen to lie between the auriculo-ventricular opening and the origin
of the aorta.

Examine in these flaps their texture, the chorda? teudinese. the
colu mnae carueae, etc., as in the case of the right side of the heart (12).

d. Examine the semilunar valves at the exit of the aorta; then
cutting up carefully between two of them, examine the bit of aorta
still left attached to the heart, and note the valves more carefully as
described in 12. d. Note the origins of the coronary arteries in two
of the three dilatations (sinuses of Valsalva) of the aortic wall above
the semilunar flaps.

14. Examine a piece of aorta. Note that when empty it does not
collapse; the thickness of its wall; its extensibility in all directions;
its elasticity.

15. Compare with the artery the tkiu-walled flabby veins which
open into the heart.

CHAPTER XV.

THE WORKING OF THE HEART AND BLOOD-VESSELS.

The Beat of the Heart. — It is possible by methods known
to physiologists to open the chest of a living animal, such
as a rabbit, made insensible by chloroform, and see its
heart at work, alternately contracting and diminishing the
cavities within it, and relaxing and expanding them. It is
then observed that each beat commences at the mouths of
the veins which open into the auricles; and from there runs
over the rest of the auricles, and then over the ventricles;
the auricles beginning to dilate the moment the ventricles
start their contraction. Having finished their contraction,
the ventricles begin to dilate, and then for some time
neither they nor the auricles are contracting, but the
whole heart is expanding. The contraction of any part of
the heart is known as its sys'to-le, and the relaxation as its
di-as'to-le, and since the two sides of the heart work syn-
chronously, the auricles together and the ventricles to-
gether, we may describe a whole " cardiac period " or
"heart-beat" as made up successively of auricular systole,
ventricular systole, and pause. In the pause the heart, if
taken between the finger and thumb feels soft and flabby,

What is seen when the beating heart of a living animal is exposed?
When do the auricles begin to dilate? What is the state of the heart
for a short time after the end of a ventricular contraction? What is
meant by the systole of a part of the heart? What by the diastole? Of
what does a cardiac period consist? How does the heart feel to the
touch during the pause?

[216]

EVENTS DURING A CARDIAC PERIOD. 217

but during the systole it, especially in its ventricular por-
tion, becomes hard and rigid, and diminished in size so as
to force blood out of it.

The Cardiac Impulse. — The human heart lies with its
apex touching the chest-wall between the fifth and sixth
ribs on the left side of the breast-bone. At every beat a
sort of tap known as the "cardiac impulse," or "apex
beat," may be felt by placing the finger at that point.

Events occurring within the Heart during a Cardiac
Period. — Let us commence just after the end of the ventric-
ular systole. At this moment the semilunar valves at the
orifices of the aorta and the pulmonary artery are closed bo
that no blood can flow back from those vessels. The whole
heart, however, is soft and distensible, and yields readily to
blood flowing into its auricles from the pulmonary veins
and the hollow veins; this blood passes on through the open
mitral and tricuspid valves, and fills up the dilating ventri-
cles as well as the auricles. As the ventricles fill, back cur-
rents are set up along their walls, and carry up the flaps
of the auriculo-ventricular valves, so that by the end of the
pause they are nearly closed. At this moment the auricles
contract; this contraction commences at and narrows the
mouths of the veins so that blood cannot easily flow back
from the auricles into them; the flabby and dilating ventri-
cles oppose much less resistance, and so the general result is

How during the systole? How is its bulk changed in systole?

Where does the apex of the heart touch the chest-wall? What is
the cardiac impulse?

What is the position of the semilunar valves just after the end of
a ventricular systole? What results from their closure? In what
condition is the heart in general? What parts of it does blood enter?
From what vessels? What cavities does this blood till ? What hap-
pens as the ventricles fill ? What is the position of the valves at the
end of the pause ? Where does the auricular con traction commence ?
What is the main result of the auricular contraction?

218 THE HUMAN BODY.

that the contracting auricles send blood mainly into the
ventricles and hardly any back into the veins. The in-
creased current into the ventricles produces a greater back
current on the sides, which, as the auricles cease their con-
traction, and the filled ventricles become tense and press on
the blood inside them, completely closes the auriculo-ven-
tricular valves.

The auricular contraction now ceases, and the ventricu-
lar begins. The blood in eacli ventricle is imprisoned be-
tween the auriculo-ventricular valves behind and the semi-
lunar valves in front. The former cannot yield on account
of the chordae tendinese fixed to their edges; the semilunar
valves, on the other hand, can open outwards from the ven-
tricle and let the blood pass on; but they are kept tightly
shut by the pressure of the blood in the aorta and pulmo-
nary artery, just as the lock-gates of a canal are by the pres-
sure of the water on them. In order to open the canal-gates
water is let in or out of the lock until it stands at the same
level on each side of them; but they might be forced open
without this by applying sufficient power to overcome the
higher water pressure on one side. It is in this latter way
that the semilunar valves are opened.

The contracting ventricle tightens its grip on the blood
inside it. As it scjueezes harder and harder, at last the
pressure on the blood in it becomes greater than the pres-
sure exerted on the other side of the valves by the blood in

What is the consequence of the increased flow into the ventricles
due to the auricular contraction?

What happens when the ventricle begins to contract? Why can-
not the imprisoned blood escape back into the auricle? How are the
semilunar valves kept closed? Illustrate. How might we force open
the gates of a canal lock without bringing the water to the same level
on each side?

How are the semilunar valves opened?

USE OF PAPILLARY MUSCLES. 219

the arteries, the valves are forced open, and the blood begins
to pass out; the ventricle continues to contract until it has
obliterated its cavity and completely emptied itself. Then
it commences to relax, and blood to flow back into it from
the arteries. This back current, however, catches the pock-
ets of the semilunar valves, drives them back, and closes the
valve so as to form an impassable barrier, and so the blood
which has been forced out of the ventricle is hindered from
flowing directly back into it.

Use of the Papillary Muscles. — In order that the con-
tracting ventricles may not force blood back into the auri-
cles, it is essential that the flaps of the mitral and tricuspid
valves be held together across the openings which they
close, and not pushed back into the auricles. If they
were like swinging doors and opened both ways they
would be useless ; they must so far resemble an ordi-
nary door as only to open in one direction, namely, from
the auricle to the ventricle. At the commencement of the
ventricular systole this is provided for by the chordae tendin-
eae, which are of such a length and so arranged as to keep
the valve -flaps shut across the opening, and to maintain
their edges in contact. But, as the contracting ventricles
shorten, the chordae tendineae would be slackened and the
valve-flaps pushed up into the auricle. The little papil-
lary muscles prevent this. Shortening as the ventricular
systole proceeds, they keep the chordae taut and the valves
closed.

"What then happens? How long does the ventricle continue to
contract? What then follows? How are the semilunar valves closed?

What is essential in order that hlood may not be forced hack from
ventricle to auricle? Illustrate. How is the pushing back of the
valve-flaps between auricle and ventricle prevented at the beginning
of a ventricular systole? When would the chordae tendinere be slack-
ened? What would result? How is the slackening prevented?

220 THE HUMAN BODZ

Sounds of the Heart. — If the ear be placed on the chest
of another person over the heart region, two distinguisha-
ble sounds will be heard during each round of the heart's
work. They are known respectively as the first and second
sounds of the heart. The first is of lower pitch and lasts
longer than the second and sharper sound; vocally their
character may be tolerably imitated by the syllables tub, dilp.
The cause of the second sound is the closure, or, as one
might say, the "clicking up" of the semilunar valves.
The first sound takes place during the ventricular sys-
tole, and is probably due to vibrations of the tense ven-
tricular wall at that time. In many forms of heart disease
these sounds are modified or cloaked by additional sounds
which arise when the cardiac orifices are roughened, or nar-
rowed, or dilated, or the valves inefficient. A physician
often gets important information as to the nature of a heart
disease by studying these new or altered sounds.

Function of the Auricles. — The ventricles have to do the
work of pumping the blood through the blood-vessels.
Accordingly their walls are far thicker and more muscular
than those of the auricles; and the left ventricle, which has
to force the blood over most of the body, is stouter than the
right, which has only to send blood around the compara-
tively short pulmonary circuit. The circulation of the
blood is, in fact, maintained by the ventricles, and we have
to inquire what is the use of the auricles. Not unfre-

Whatdo we hear on listening over the heart region of a living per-
son's chest? What are the sounds called? How does the first differ
from the second? What words give some idea of their character?
What is the origin of the second sound? Of the first? What occurs
as regards the heart sounds in many forms of heart disease?

What work have the ventricles to do? How do their walls differ
from those of the auricles? Which ventricle has the thicker wall?
Why? What part of the heart maintains the blood flow?

WORK DONE BY THE BE ART. 221

quently the heart's action is described as if the auricles
first filled with blood, and then contracted and filled the
ventricles; and then the ventricles contracted and drove the
blood into the arteries. From the account given above,
however, it will be seen that the events are not accurately
so represented, but that during all the pause the blood
flows on through the auricles into the ventricles, which
latter are already nearly full when the auricles contract;
this contraction merely completes the rilling of the ventri-
cles, and finishes the closure of the auriculo-ventricular
valves. The main use of the auricles is to afford a reservoir
into which the veins may empty while the comparatively
long-lasting ventricular contraction is taking place.

The Work done daily by the Heart. — At each beat each
ventricle pumps on rather more than six ounces (say four-
teen tablespoonfuls) of blood. The elastic aorta and the
pulmonary artery are full, and resist the pumping of more
liquid into them, just as an elastic bag filled with Avater
could only have more sent into it by force; to get more in
one would have to stretch the bag more. The resistance
opposed by these arteries to receiving blood from the heart
has been measured in some of the lower animals, and calcu-
lations made from them to man. According to these the
work which the left ventricle does every day, sending 6£
ounces of blood seventy times a minute into the aorta, is
enough to lift one pound 325,584 feet high; and the work
done by the right ventricle would lift one pound 108,528

What parts of the heart does the blood enter during the pause?
What is the condition of the ventricles as regards fullness at the
end of the pause? What is done by the auricular contraction?
What is the chief use of the auricles?

How much blood does each ventricle pump out at every beat?
What resists the ventricular emptying? Illustrate. How much
work does a man's left ventricle do daily? How much the right?

222 THE HUMAN BODY.

feet. The work done daily by the ventricles of the heart
together is equal to that required to raise one pound 434,112
feet from the earth's surface, or, what comes to the same
thing, more than 193 tons one foot high.

If a man weighing 165 pounds climbed up a mountain
2644 feet high the muscles of his legs would probably be
greatly tired at the end of his journey, and yet in lifting
his body that height they would only have done as much
work as his heart does every day without fatigue in pump-
ing his blood.

No doubt the fact that more than half of every round
of the heart's activity is taken up by the pause during
which its muscles are relaxed and its cavities filling with
blood, has a great deal to do with the patient and tireless
manner in which it pumps along, minute after minute,
hour after hour, and day after day, from birth to death.

The Pulse. — When the left ventricle of the heart con-
tracts it forces on about six ounces of blood into the aorta,
which, with its branches, is already quite full of blood.
The elastic arteries are consequently stretched by the extra
blood, and the ringer laid on one feels it dilating; this dila-
tation of an artery following each beat of the heart is called
the pulse; it is easiest felt on arteries which lie near the
surface of the body, as the radial artery, near the wrist,
and the temporal artery, on the brow.

The arteries at their ends furthest from the heart lead

How much both ventricles together?

How high would a man have to climb in order to do as much
work by the muscles of his legs as the heart does in a day?

How may we account for the fact that the heart does not become
fatigued and unable to work?

What happens when the left ventricle of the heart contracts?
What results in the arteries? What is the pulse? Name arteries or
which the pulse is easily felt.

THE PULSE. 223

into capillaries; before the next heart-beat occurs they pass
on into these minute vessels as much blood as the aorta re-
ceived during the preceding ventricular systole; consequently
they shrink again during the pause, just as a piece of rubber
tubing with a small hole in it, when overfilled with water,
would gradually collapse as the water flowed out of it. The
next beat of the heart again overfills and expands the arteries,
and so on; at each heart-beat there is a dilatation of the
arteries due to the blood sent into them from the ventricle,
and between each beat there is a partial collapse of the ar-
teries, due to their emptying blood into the capillaries.

What may be learnt from the Pulse. — The pulse being
dependent on the heart's systole, "feeling the pulse" of
course primarily gives a convenient means of counting the
rate of beat of that organ. To the skilled touch, howrever,
it may tell a great deal more; as, for example, whether it is
a readily compressible or "soft pulse," showing that the
heart is not keeping the arteries properly filled up with
blood, or tense and rigid ("a hard pulse"), indicating that
the heart is keeping the arteries excessively filled, and is
working too violently, and so on. In healthy adults the
pulse rate may vary from sixty-five to seventy-five a minute,
the most common rate being seventy-two. In the same in-
dividual it is faster when standing than when sitting, and
when sitting than when lying down. Any exercise in-

Into what do the final arterial branches open? How much blood
is sent into the capillaries during a cardiac period? What change
takes place in the bulk of the arteries during the interval between
two ventricular contractions? Illustrate. What happens in the
arteries during each heart-beat? Why? What during each heart
pause? Why?

How may we conveniently count the rate of heart-beat? What
does a soft pulse indicate? A hard pulse? What is the most com-
mon pulse rate in health? Within what limits may it vary? How is
it influenced by the position of the body?

224 THE HUMAN BODY.

creases its rate temporarily and so does excitement; a sick
person's pulse should not therefore be felt when he is ner-
vous or excited (as the physician knows when he tries first
to get his patient calm and confident). In children the
pulse is quicker than in adults, and in old age slower than
in middle life.

The Flow of the Blood in the Capillaries and Veins. — The
blood leaves the heart intermittently and not in a regular
stream, a quantity being forced out at each systole of the
ventricles; before it reaches the capillaries, however, this
rhythmic movement is transformed into a steady flow, as
may readily be seen by examining with a microscope thin
transparent parts of various animals, as the web of a frog's
foot, a bat's wing, or the tail of a small fish. In consequence
of the steadiness with which the capillaries supply the veins
the flow in these latter is also unaffected directly by each
beat of the heart; if a vein be cut the blood wells out uni-
formly, while a cut artery spurts out with much more force,
and in jets which are more powerful at regular intervals
corresponding with the contractions of the ventricles.

The Circulation of the Blood as seen in the Frog's
Web. — There is no more fascinating or instructive spectacle
than the circulation of the blood as seen with the micro-
scope in the thin membrane between the toes of a frog's
hind limb. Upon focusing beneath the outer layer of the
skin a network of minute arteries, veins, and capillaries,

How by exercise? Why should an invalid's pulse not be felt
when he is excited? How does age affect ihe pulse rate?

In what manner does the blood leave the heart? How is its flow
altered before reaching the capillaries? How may this be observed?
Is the flow in the veins rhythmic or steady? Why? How does the
bleeding from a cut artery differ from that of a cut vein?

What comes into view on examining a frog's web with a micro-
scope?

BLOOD FLOW IN THE CAPILLARIES. 225

with the blood flowing through them, comes into view
(Fig. 61). The arteries, a, are readily recognized by the
fact that the flow in them is fastest and from larger to
smaller branches. The smallest are seen to end in capillar-
ies, which form networks, the channels of which are all
nearly equal in size. In the veins arising from the capil-
laries the flow is from smaller to larger trunks, and slower
than in the arteries, but faster than in the capillaries.

Why the Blood flows slowest in the Capillaries. — The
reason of the slower flow of the capillaries is that their
united area is considerably greater than that of the arteries
supplying them, so that the same quantity of blood flowing
through them in a given time has a wider channel to flow
in and therefore moves more slowly. The area of the veins
is smaller than that of all the capillaries, but greater than
that of the arteries, and so the rate of movement in them is
intermediate.

We may picture to ourselves the vascular system as a
double cone, widening from the ventricles to the capillaries,
and narrowing from the latter to the auricles. Just as
water forced in at a narrow end of this wTould flow quickest
there, slowest at the widest part, and quicker again where
it passed out the other narrow end, so the blood flows quick
in the aorta and hi. 'How veins,* and slow in the capillaries,

How may the arteries be recognized? In what are the smallest
arteries seen to end? Do the capillaries vary much in size? What
is the direction of flow in the veins? How does its rate differ
from that in the arteries? From that in the capillaries?

Why does blood flow slowest through the capillaries? Why in the
veins quicker than in the capillaries, but slower than in the arteries?

How may we picture the vascular system? Illustrate. How do
capillaries differ in size from the large arteries?

*A good illustration taken from physical geography is afforded by the Lake of
Geneva, in Switzerland. This is supplied at one end by a river which derives its
water from the melting glaciers of some of the Alps. From its other end the

226 THE HUMAN BODY.

which, though thousands of times smaller than the great
arteries and veins, are millions of times more numerous.
The channel through which the blood flows in them is,
therefore, when they are all taken together, very much
greater than that to which it is confined in the large arterial
and venous trunks.

Why there is no Pulse in the Capillaries and Veins. —
The heart sends blood into the arteries not steadily but
intermittently; each beat forces in some blood, and then
comes a pause before the next beat. Accordingly the flow
in the larger arteries is not even and continuous, but jerky,
as indicated by the pulse.

But in the capillaries the flow is quite steady, and yet the
capillaries are supplied by the smaller arteries. We have to
inquire how this is brought about.

The disappearance of the pulse is due to two things, (1)
the fact that in the tiny capillaries the blood meets with
considerable resistance to its flow, dependent on friction,
and (2) that the arteries are very elastic.

On account of friction in the capillaries the arteries have
difficulty in passing on blood through them; blood there-
fore accumulates in the aorta and its large branches and
stretches their elastic walls. The stretched arteries press
all the time on the blood inside them, and constantly keep
squeezing it on into the small arteries and the capillaries;

How in number? Is the total blood channel greater in arteries or
capillaries? In veins or capillaries?

Why is the blood-flow in the great arteries not steady? Name
vessels in which it is steady.

To what is the loss of pulse in the capillaries due? What results
from friction in the capillaries? What is done by the stretched
arteries?

water is carried off by the river Rhone. In the comparatively narrow inflowing
and outflowing rivers the current is rapid ; in the wide bed of the lake it is much
slower.

ABSENCE OF PULSE IN THE CAPILLARIES . 227

both while the heart is contracting and between two heart-
beats. The heart, in fact, keeps the big elastic arteries
over-disteuded with blood; before they have had time to
nearly empty, another systole occurs and fills them up tight
again: so all the while the walls of the arteries are stretched
and keep pressing on the blood inside them, and steadily
forcing it on into the capillaries. The heart keeps the
arteries over-full, and the stretched elastic arteries drive the
blood through the capillaries. As the arteries are always
stretched and always pressing on the blood the capillaries
receive a steady supply, and the flow through them is uni-
form. This even capillary flow passes on a steady blood
stream to the veins.*

The object of having no pulse in the capillaries is to
diminish the danger of their rupture. As we have seen,
materials from the blood have to ooze through their walls
to nourish the organs of the body, and wastes from the
organs to soak back into the blood that they may be carried
off. Their walls have therefore to be very thin; and if the

When? What does the heart do? What happens before the
arteries have had time to empty? What is the condition of the
arterial walls all through life? What results from their stretched
condition? What keeps the arteries tightly tilled? What sends
blood through the capillaries? How do the capillaries get a steady
blood supply? Why do we rind a uniform current in the veius?

What is gained by having no pulse in the capillaries? What
must food materials in the blood do before they can nourish the
body? What must the wastes of the organs do? Why must the
capillary walls be very thin?

* "Every inch of the arterial system may, in fact, be considered as convert-
ing a small fraction of the heart*s jerk into a steady pressure, and when all these
fractions are summed up together in the total length of the arterial system no
trace of the jerk is left. As the effect of each systole becomes diminished in
the smaller vessels by the causes above mentioned, that of this constant pres-
sure becomes more obvious, and gives rise to a steady passage of the fluid from
the arteries towards the veins. In this way, in fact, the arteries perform the
same functions as the air-reservoir of a fire-engine, which converts the jerk-
ing impulse given by the pumps into the steady flow of the delivery hose." —
Huxley.

228 THE HUMAN BODY.

blood were sent into them in sudden jets at each beat of
the heart, they would run much risk of being torn.

The Muscles of the Arteries. — The arteries have rings of
plain muscular fibre in their walls ; when these contract
they narrow the artery, and when they relax they allow it
to widen under the pressure of the blood in its interior. The
vessel then carries more blood to the capillaries of the organ
which it supplies. Blushing is due to a relaxation of the
muscular layer of the arteries of the face and neck, allow-
ing more blood to flow to the skin.

Why the Arteries have Muscles. — The amount of blood
in the body is not sufficient to allow of a full stream of
blood through all its organs at one time: the muscular fibres
controlling the diameter of the arteries are used to regulate
the blood-flow in such a manner that parts hard at work
shall get an abundant supply, and parts at rest shall only
get just enough to keep them nourished. Usually when
one set of organs is at work and its arteries dilated, others
are at rest and their arteries contracted. Few persons, for
example, feel inclined to do brain-work after a heavy meal;
for then a great part of the blood of the whole body is led
off into the dilated vessels of the digestive organs, and the
brain gets but a small supply. On the other hand, when the
brain is at work its vessels are dilated, and often the whole
head flushed; and when the muscles are exercised, a great
portion of the blood of the body is carried off to them ; there-

What would be apt to happen if blood were sent into them in
sudden jets?

How are the muscles of the arteries arranged? What results from
their contraction? From their relaxation? To what is blushing
due?

Why cannot all the organs have a full blood stream through them
at the same time? For what purpose are the muscular fibres in the
walls of arteries used? What is the usual condition of tilt' arteries
Of a resting organ?

TAKING COLD. 229

fore, hard thought or violent exercise soon after a meal is very
apt to produce an attack of indigestion by diverting the
blood from the abdominal organs, where it ought to be at
that time. Young persons whose organs have a super-
abundance of energy, enabling them to work under unfa-
vorable conditions, are less apt to suffer in such ways than
their elders. One sees boys running actively about after
eating, when older people feel a desire to sit quiet or even
to go to sleep.

Taking Cold. — When the skin is chilled its arteries con-
tract, as shown by the pallor of the surface. This throws
an undue amount of blood into internal parts, whose ves-
sels become gorged with blood or "congested," and con-
gestion very easily passes into inflammation. Consequently,
prolonged exposure of the surface to cold is very apt to be
followed by inflammation of parts inside the body, and
give rise to a so-called "cold" (which is really an inflam-
mation) of the mucous membranes of the head, or throat,
or lungs; or of the intestines, causing diarrhoea. In
fact, the common summer diarrhoea is far more often
due to a chill of the surface leading to intestinal inflam-
mation than to the fruits eaten in that season, which
are so often blamed for it. The best preventive is to
wear when exposed to sudden changes of temperature, a
woollen or at least a cotton garment over the trunk of the

Why is it not wise to take hard exercise or do severe mental work
soon after eating? Why do young persons suffer less from exercise
soon after dinner than do their elders?

What happens to its arteries when the skin is chilled' How does
this manifest itself? What is its result on the blood-supply of in-
ternal parts? What is congestion? Into what diseased state does it
otten pass?

What diseases are apt to follow a surface chill? What is the most
frequent cause of summer diarrhoea? What should be worn wher.
U»ble to exposure to considerable changes of temperature?

230 THE HUMAN BODY.

body; linen permits any change in the external tempera-
ture to act almost at once upon the skin. After an un-
avoidable exposure to cold or wet, the thing to be done is
of course to maintain the cutaneous circulation; movement
should be persisted in, and a thick dry outer covering put
on until warm and dry underclothing can be obtained.

In healthy persons, a temporary exposure to cold, as
a plunge in a bath, is good, since in them the sudden con-
traction of the cutaneous arteries soon passes off, and is
succeeded by a dilatation causing a warm healthy glow on
the surface. If the bather remain too long in cold water,
however, this reaction passes off, and is succeeded by a more
persistent chilliness of the surface, which may last all day.
The bath should therefore be left before this occurs; but
no absolute time can be stated, as the reaction is more
marked and lasts longer in strong persons and in those used
to cold bathing than in others.

Why does linen not form a good inner garment under such circum-
stances? What should be done after unavoidable exposure to cold
or wet?

Why is a plunge in a cold bath useful to healthy persons? What
results if a person remains too long in cold water? When should a
cold bath be left? What persons may remain longest with safety in
a cold bath?

APPENDIX TO CHAPTER XV.

1. A frog may be used to illustrate the beat of the heart. Ana-
tomically a frog's heart differs in many respects from that of a mam-
mal, but the phenomena of systole and diastole are essentially the same.

2. Etherize a frog as before described. Cut off its head. Check
bleeding and destroy its spinal cord by forcing a pointed wooden peg
along the spinal canal.

3. Laying the animal on its back, carefully divide with scissors
the skin along the middle line of the ventral surface for its whole
length. Make cross cuts at each end of this longitudinal one and
pin out the flaps of skin. ,

APPENDIX. 231

4. Next pick up with forceps the remaining tissues of the ventral
wall near its posterior end, and carefully divide them longitudinally
a little on the left side of the middle line; heing very careful not to
injure either the viscera in the cavity heneath or a large vein {ante-
rior abdominal) running along the wall in the middle line.

5. About the point where you see this vein passing from the wall
to enter among the viscera of the ventral cavity, youwill come to the
bony and cartilaginous tissues of the sternal region Raise the
posterior cartilage in your forceps, make a short transverse cut in
front of the vein, and, looking beneath the sternum, note the peri-
cardium with the heart beating inside it. Divide the fibrous bands
which pass from the pericardium to the sternum, and with scissors
cut away sternum, etc., taking great care not to injure the heart.

6. Push a rod about half an inch in diameter down the animal's
throat so as to stretch the parts, and then picking up the pericardium
in a pair of forceps, open it and gently cut it away from about the
heart; push aside any lobes of the liver which lie on the latter organ.
In the heart thus exposed note —

a. Its beat; a regularly alternating contraction (systole) and dila-
tation (diastole).

b. In consequence of the destruction of the spinal cord compara-
tively little blood now flows through the heart, but during the con-
traction you will be able to observe that the ventricular portion,
which will be readily recognized, becomes paler; and during dias-
tole again becomes deeply colored, getting more or less filled up with
blood which shows through its walls.

c. Observe that each contraction starts at the auricular end and
travels towards the ventricular; this may be more easily seen by-
and-by, when the heart begins to beat more slowly.

7. The specimen may be put aside under a bell-jar with a wet
sponge, or a piece of flannel soaked in water. If kept from drying
the heart will go on healing for hours.

8. To demonstrate the action of the valves of the heart, obtain two
uninjured sheep's hearts from a butcher. Remove them from the
pericardium, taking care not to injure the vessels.

9. Cut off the apex of one heart so as to open the ventricles. Then
fill up the stumps of the aorta and the pulmonary artery with water.
As the water is poured in the semilunar valves will be seen to close
up and block the passage to the ventricle, so that the stump of the
vessel remains full for some time. The valves rarely act quite per-
fectly in a heart removed from the body and treated as rbove, but
they will support the water column quite long enough to illustrate
their action.

232 the n tTMAtf Bob t.

10. Carefully cut the auricles away from the other sheep's heart,
taking great care not to injure the ventricles or the auriculo-ventric-
ular valves. Then holding the ventricles, apex down, in one hand,
pour water in a stream into them from a pitcher held about a foot
above them. As the ventricles fill, the flaps of the mitral and tricus-
pid valves will be seen to float up and close the auriculo-ventricular
orifice, illustrating their movement as the ventricle fills during its
diastole in the natural working of the heart.

11. The manner in which the elasticity of the arteries and the fric-
tion resistance to flow in the capillaries together serve to turn a
rhythmic into a steady flow may be readily demonstrated as follows:

Take an elastic bag such as is commonly sold with enema appara-
tus in drug-stores, and having an entry and exit tube provided with
valves In the exit tube place a piece of glass tubing six feet long.
Put the entry tube of the bag in a basin of water. On pumping, an
intermittent flow of water, corresponding to the strokes of the pump,
will be obtained from the glass tube. Connect a very fine glass
nozzle with the end of the long tube; on pumping, less water can
be forced through, and the outflow is still rhythmic.

12. Replace the glass tube by a rubber tube of the black, highly
elastic kind: on pumping we get again a rhythmic outflow. Now
connect your narrow nozzle to the end of the rubber tube, and pump:
the outflow will be nearly constant, because the rubber tube not being
able to empty itself as fast as the water is pumped into it, becomes
stretched, and in the interval between two strokes of the pump it
keeps on squeezing out the extra water accumulated in it. The
longer and more elastic the tube, the quicker and stronger the stroke
of the pump, and the narrower the exit, the more steady will be the
outflow. In the body the heart keeps the arteries very tightly
stretched all the time, and they keep up accordingly a steady flow
into the capillaries. The experiment shows that to get such a steady
flow two things are necessary : (1) that the tubes fed directly by the
heart shall be highly elastic, and (2) that there shall be considerable
resistance to the exit trom their outflow euua

CHAPTER XVI.
THE OBJECT AND THE MECHANICS OF RESPIRATION.

The Object of Respiration. — Blood is renewed, so far as
ordinary food materials are concerned, by substances either
directly absorbed by tbe blood-vessels of the alimentary
canal, or taken up by the lymphatics of the digestive tract
and afterwards poured into the blood. But in order that
energy may be set free for use by the tissues of the body
(Chap. VIII.), oxidations must occur, and the continuance
of these Tital oxidations depends on a constant supply of
oxygen. As their result, waste substances are produced,
which are no longer of use to the body, but detrimental to
it if present in large quantity. The most abundant of
these wastes is carbon dioxide gas.

The function of respiration has for its objects (1) to
renew the supply of oxygen in the blood, and (2) to get rid
of the carbon dioxide produced in the different organs.

The Respiratory Apparatus. — This consists primarily of
two elastic bags, the lungs, placed in the thorax, filled with
air, and communicating by the air -passages with the sur-

How is the blood renewed as regards ordinary food matters ?
What must occur that energy be set free for use by tbe body? What
is necessary that the oxidations may continue ? What do the oxida-
tions produce? Which is the most abundant waste substance of the
body ?

What are the objects of respiration ?

Of what does the respiratory apparatus primarily consist ?

[2331

234 THE HUMAN BODT.

rounding atmosphere. In the lungs the pulmonary capil-
lary blood-vessels form a very close network: through their
walls the blood gives off to the air in the lungs carbon
dioxide, and takes from this air oxygen. The air in the
lungs consequently needs renewal from time to time: other-
wise it would no longer have oxygen to give to the blood,
and would become so loaded with carbon dioxide as to
no longer take that waste product from it. This renewal
is effected by the working of a system of muscles, bones,
and cartilages whose co-operation brings about that alter-
nating expansion and contraction of the chest which we call
breathing. When the chest contracts, air deprived of its
oxygen and polluted with wastes is expelled from the lungs;
and when it expands, fresh air, rich in oxygen, and con-
taining hardly any carbon dioxide, is taken into them.

The respiratory organs are, therefore, (1) the lungs; (2)
the air-passages: (3) the vessels of the pulmonary circula-
tion, including the pulmonary artery bringing the blood to
the lungs, the pulmonary capillaries carrying it through
them, and the pulmonary veins conveying it from them;
(4) the muscles, bones, and gristles which are concerned in
producing the breathing movements.*

The Air-Passages. — Air reaches the pharynx through
the nose or mouth (Fig. 1) : on the ventral side of the pharynx

"What vessels form a close network in the lungs? What takes
place through the walls of these vessels? Why must the air in the
lungs be renewed? How is the renewal brought about? What is
breathing? "What happens when the chest contracts? What when
it expands ?

Enumerate the respiratory organs.

Through what passages does air reach the pharynx?

* To these should be added (5) the nerve centres and nerves which contro-
the muscles of respiration, and which will be subsequently considered (see
Chap. XX).

THE AIR- PASS AGE8.

235

(Fig. 41) is an aperture through which it passes into the
larynx or voice-box (a, Fig. 64), which lies in the upper
part of the neck. From the larynx air passes on through
the windpipe or trachea; this enters the chest, in the upper

Fig. 64.

Fig. 65.

Fig. 64. — The lungs and air-passages seen from the front. On the left of the
figure the pulmonary tissue has been dissected away to show the ramifications
of the bronchial tubes. «, larynx ; b. trachea; d, right bronchus. The left bron-
chus is seen entering the root of its lung.

Fig. 65. — A small bronchial tube, a, dividing into its terminal branches, c;
these have pouched or sacculated wails and end in the sacculated alveoli, b.

part of which it divides into a right and a left bronchus.
Each bronchus enters a lung, and divides in it into a vast
number of very small tubes, called the bronchial tubes.
The last and smallest bronchial tubes (a, Fig. 65) open
into subdivided elastic sacs, b, c, with pouched walls.

"What aperture is found on the ventral side of the pharynx?
Where does the larynx lie? Where does the air so from the larynx?
Into what does the trachea divide? Where? What are the bronchial
tubes? How do the final bronchial tubes terminate?

236 THE HUMAN BODY.

Structure of the Windpipe and its Branches. — The

trachea, bronchi, and bronchial tubes are lined by mucous
membrane, outside of which is a supporting stratum com-
posed of connective and plain muscular tissues. Their Avails
also contain cartilaginous rings or half-rings which keep
them open. Below the projection on the throat known as
Adam's apple (due to the larynx, see Chap. XXII.) there
may readily be felt in thin persons the stiff windpipe pass-
ing down to the top of the chest.

The Cilia of the Air-Passages. — The mucous membrane
of the trachea and its branches, down to almost the smallest,
has a layer of ciliated cells on its surface. Each of these
cells has on its end turned towards the cavity of the tube a
tuft of from twenty to thirty slender threads which are in
constant motion; they lash forcibly towards the throat,
move gently back again, and then once more violently to-
wards the outlet of the air- passage. These moving threads
are called cilia. Swaying in the mucus secreted by the
membrane which they line, they sweep it on to the throat,
where it is coughed or "hawked" up.

Imagine a man rowing in a boat at anchor. The
sweep of the oars will drive the water back and not the
boat forwards. So these little oars, the cilia, being an-
chored on the mucous membrane drive on the secretion
which bathes its surface.

With what are the windpipe and its branches lined? What lies
outside this lining? What do these walls also contain? What is
the use of the cartilages? What is " Adam's apple"? What may be
felt below it in front'of the neck?

What lines the mucous membrane of the windpipe and its sub.
divisions? What does each ciliated cell bear on its free end? How
do the threads move? What are they called? What is the use of
the cilia of the air-passages?

Illustrate how they push on the liquid they move in

THE LUNGS.

237

Bronchitis, or "a cold on the chest," is an inflamma-
tion of the membrane lining the bronchial tubes, in con-
sequence of which it swells, and secretes an extra amount
of mucus. The swelling and secretion tend to close the
tubes and interfere with the free passage of air in breathing.

The Lungs consist of the bronchial tubes and their ter-
minal dilatations, together with blood-vessels, lymphatics,
and nerves, all bound firmly together by elastic tissue.
The expansions called "air-cells" *at the end of each final
branch of a bronchial tube (Fig.
66) are relatively very large,
and their surface is still fur-
ther increased by the pouches
(a, b) which project from them.
Their walls are highly elastic,
and contain a close network of
capillary blood-vessels, supplied
by the pulmonary artery and
emptying into the pulmonary
veins. Through the extremely
thin lining of the air-cell, and

■ i , i • nl c ,, •!, • Fig. 66.— Two alveoli of the lung

the thin Wall 01 the Capillaries highly magnified. 6, 6, the air-cells,

,,,,.. . or hollow protrusions of the alveo-

lmbedded in It, OXygen IS ab- lus, opening into its central cavity;

c, terminal branches of bronchial

sorbed by the blood from the tube.

air in the air-cell and carbon dioxide given up to it. It

What is bronchitis? How does an attack of bronchitis interfere
with breathing?

Of what do the lungs consist? What are the air-cells? How is
their surface increased? What do their walls contain? By what are
their capillaries filled, and into what do they empty? What inter-
change between blood and air occurs in the air-cells of the lungs?

* Cell is here used in its primitive sense of a small chamber or cavity (Latin,
cellula), and not in its modern histological signification, as one of the distinct
pieces of living matter recognized by the microscope as serving to build up the
body by their accumulation and co-operation.

238 THE HUMAN BODY.

has been calculated that if the walls of the air-cells were
all spread out flat and placed side by side they would cover
an area of 2600 square feet. This great surface, therefore,
represents the area of the body by which oxygen is received
and carbon dioxide given off.

The Pleura. — The exterior of each lung, except where
its bronchus and blood-vessels enter it, is covered by a
thin elastic serous membrane, the pleura (Fig. 2). This
membrane also lines the inside of the chest. Its surface in
health is kept moistened by a small quantity of lymph.
In consequence of its smoothness and moisture, during the
breathing movements the chest wall and lung glide over
each other with hardly any friction.

Pleurisy is inflammation of the pleura. In its early
stages it is usually associated with sharp pain on drawing the
breath. Later on a large quantity of lymph is often poured
out by the inflamed pleura, filling up the cavity which
should be occupied by the lung, and pressing the latter up
into a small mass, very inefficient for breathing purposes.

The Elasticity of the Lungs. — The lungs are so elastic as
to be like a thin india-rubber bag. If we tie a tube tightly
into a bronchus and blow in air the lung will dilate, but as
soon as we cease blowing and leave the tube open, it will
shrink up again. Yet in the chest the lungs always remain
so expanded as to completely fill up all the space left for
them by the heart and other things contained in the
thorax. How is this ?

How large is the surface of the body set apart for oxygen recep-
tion and carbon dioxide elimination?

What is the pleura? What does it cover besides the outer surface
of each lung? What is its condition in health? What is its use?

What is pleurisy? What symptom usually accompanies its early
stages? What happens later?

What do the lungs resemble in their elasticity? How may this
elasticity be demonstrated? What is the natural condition of the
lungs in the chest?

EXPANSION OF THE LUNGS. 239

Why the Lungs remain expanded. — We may best under-
stand this by considering a thin india-rubber bag, such as a
toy balloon. If the neck of the bag is open it collapses.
Why ? Because the atmosphere, which pushes on all
things near the earth's surface with a pressure of about
15 lbs. on each square inch (1033 grams on each square cen-
timetre), presses equally on the outside and the inside of
the bag. These pressures balance one another, and the bag
collapses on account of its elastic contractility.

We can expand such a bag in two ways. We may blow
air into it forcibly, and so make the pressure inside suffi-
ciently greater than the opposing aerial pressure outside to
overcome the elasticity of the bag. But we can also dis-
tend the bag, not by increasing the aerial pressure inside it,
but by diminishing that outside it.

Suppose (Fig. 67) we tie our rubber bag (d) on the lower
end of the tube b, which, like the tube c, passes
air-tight through a cork, and then fit the cork
tightly into the glass bottle a. The air will
then press with its full weight on the inside of
the bag through b and on the outside of it
through c, and the bag will remain collapsed.
If now we suck air out through c we diminish
its pressure on the outside of the ba^ without fig. 67.— Dia-

r ° gram lllustrat-

altering the atmospheric pressure on its inside: j-efaVioifshlpTof
d will therefore begin to expand, because the thoraxgs in the
pressure inside it is no longer counterbalanced by the pres-
sure outside. The more air we suck out of c (that is, the more
we diminish the atmospheric pressure on the exterior of d)

Why does a thin rubber bag collapse when its neck is open?

How can we expand such an elastic bag? Describe a model illus-
trating the means by which the lungsare kept expanded in the chest-
and explain its action?

240 THE HUMAN BODY.

the more will the bag expand. Finally, if the rubber bag
is distensible enough, when all the air in the bottle is
sucked out d will be distended by the push of the air inside
it until it completely fills the bottle, whose walls prevent
it from going any farther. If now we open c and let in
the outside air, the bag will again collapse to its original
shrunken dimensions.

Application to the Lungs.— The above experiment illus-
trates very perfectly how the lungs are kept distended dur-
ing life. The chest is an air-tight chamber containing,
among other things, the elastic hollow lungs. On the
interior of the lungs the weight of the atmosphere presses
through the air-passages which lead to them, and answer
to the tube b in Fig. 67. Outside the lungs in the thorax
there is no air at all, and the uncounterpoised aerial pres-
sure inside them overcomes their tendency to shrink, and
expands them so as to completely fill all holes and corners
of the thoracic chamber not occupied by other organs. If,
however, we make a hole in the chest wall and let the air
press on the outside of the lungs they collapse at once.

How the Air is renewed in the Lungs. — Suppose in Fig.
67 that the bottle a has a movable bottom, by pulling down
which its capacity can be increased, and that all air has
been sucked out of the bottle through c, which is then
closed. The elastic bag will then be distended by the weight
of the atmosphere acting upon its interior so as to fill the
bottle and press against its sides. If now the movable
bottom of A be pulled down so as to make the cavity of the

Apply to the lungs the facts illustrated by the model represented
in figure 67.

Suppose we have a bottle like that in Fig. 67. but with a movable
bottom, what would happen when the bottom was pulled dowu V

RENEWAL OF AIR IN LUNGS.

241

bottle larger, the bag would have a larger space to fill.
The impediment on its outside being removed the
atmospheric pressure on its inside would expand it
still further, and the elastic bag would swell out to
fill the extra space. As the movable bottom was pulled
down, the bag would enlarge and receive fresh air

Fig. 68.— The skeleton of the thorax, a, </, vertebral column; b, first rib; c,
clavicle; d, third rib; »*, glenoid fossa.

through b. When the bottom was raised again the bag
would diminish, and some air be driven out of it through b.
It is in quite a similar way that the air is renewed in our
lungs by breathing. When we breathe-in, the thoracic
cavity is enlarged and air enters the lungs; when we

How would the bag inside it be affected?

What would the bag receive? What would happen when the
bottom was again raised? What happens when we breathe-in?

242 THE HUMAN BODY.

breathe-out, the thorax is diminished and air driven out
of the lungs.

Inspiration and Expiration. — The process of taking air
into the lungs is known as inspiration, that of expelling it
as expiration. On the average, fifteen to eighteen inspira-
tions and expirations occur in each minute. We therefore
breathe in and out about once for every four beats of the
heart.

The Structure of the Thorax. — The thorax is a conical
cavity with a rigid supporting skeleton (Fig. 68) formed by
the dorsal vertebra behind, the breast bone in front, and
the ribs and rib cartilages on the sides. Between and over
these lie muscles, and the whole is covered air-tight by the
skin outside and the pleura (p. 238) inside. Above, it is
closed by the muscles and other organs of the neck; and
below by a movable bottom, the diaphragm. The air-tight
chamber thus bounded can be enlarged in all three diame-
ters, but especially in the vertical, and in that running
from the spinal column to the breastbone (dorso-ventral
diameter).

The Vertical Enlargement of the Thorax. — This is
brought about by the contraction of the diaphragm, which
(as may be seen in Fig. 69), is a thin sheet of muscle, with
a fibrous membrane in its centre serving as a tendon. In rest
the diaphragm is dome-shaped, its concavity being turned
towards the abdomen. From the tendon on the crown of

What when we breathe-out?

What is inspiration? Expiration? How often does each occur in
a minute? Compare the rate of respiration and of the heart-beat?

What is the form of the thorax? What forms its skeleton? What
lie between and over its bones and cartilage? How is it closed air-
tight?

How is the chest closed above? How below? In what diameters
can the chest cavity be enlargi d?

Describe the diaphragm.

THE DIAPHRAGM.

243

the dome, striped muscular fibres radiate, downwards and
outwards, in all directions, and are fixed by their inferior
ends to the lower ribs, the breast-bone, and the vertebral
column. In inspiration (drawing a breath) the muscular

Fig. 69.— The lower half of the thorax, with four lumbar vertebrae, showing
the diaphragm from above. 1, 2, 3, central tendon; 4, 5, muscuiar part.

fibres, shortening, flatten the dome and so enlarge the
thoracic cavity at the expense of the abdominal. The con-
traction of the diaphragm thus greatly increases the size of
the thorax chamber by adding to its lowest and widest
part.

What happens to it during inspiration? What results'?

244

THE HUMAN BODY.

The Dorso-Ventral Enlargement of the Thorax. — The ribs
on the whole slope downwards (Fig. 15) from the vertebral
column to the breast-bone, the slope being most marked in
the lower ones. During inspiration
the breast-bone and the sternal ends
of the ribs attached to it are raised
by muscles which pull on them, and
so the distance between the sternum
and the vertebral column is in-
creased. That this must be so will
readily be seen by examining the
diagram Fig' 70, where ab represents
Fig. ro. — Diagram iiius- the vertebral column, c and d two

tratiner the dorso-ventral in- ., , , , . „,,

crease in the diameter of the 1'IDS, and SI the sternum. Ihe
thorax when the ribs are

raised. continuous lines represent the natu-

ral position of the ribs at rest in expiration, and the
dotted lines the position in inspiration. It is clear
that when their lower ends are raised so as to make
the bars lie in a more horizontal plane, the sternum is
pushed away from the spine, and so the extent of the
chest cavity between back-bone and breast-bone is in-
creased.

Expiration. — Inspiration requires a good deal of muscu-
lar effort. When the diaphragm contracts and flattens its
dome it has to push down the abdominal viscera on its
under side, and to press out the front wall of the abdomen
to make room for them. The ribs and breast-bone have
also to be pulled up out of their natural position of equilib^

What is the general direction of the ribs? How is it altered
during inspiration? What is the consequence? Illustrate by refer-
ence to a diagram.

Why does inspiration require muscular effort?

EXPIRATION. 245

rium. In ordinary expiration, on the contrary, but little
if any muscular effort is required.

As soon as the muscles which have raised the ribs and
sternum relax, these bones return to their natural uncon-
strained position; and the elastic abdominal wall presses
the abdominal viscera against the under side of the dia-
phragm and pushes that organ up again, as soon as its
muscular fibres cease contracting. In this way the chest
cavity is restored to its original capacity, and the air is
sent out of the lungs rather by the elasticity of the parts
which were stretched in inspiration, than by any special
expiratory muscles.

When, however, an expiration is violent (when, for ex-
ample, we try to empty our lungs of air as completely as
possible, or during a fit of coughing) special expiratory
muscles, which pull down the ribs and press up the dia-
phragm, are called into action.

The Respiratory Sounds. — The entry and exit of air are
accompanied by the respiratory sounds or murmurs, which
can be heard on applying the ear to the chest wall. The
character of these sounds is different and characteristic
over the trachea, the larger bronchial tubes, and portions
of lung from which large bronchial tubes are absent. They
are variously modified in pulmonary affections, and hence
the value of auscultation of the lungs in assisting the phy-
sician to form a diagnosis.

Hygienic Remarks.— Since the diaphragm when it con-
How does expiration differ from it in this respect?
Explain how the chest is brought back to its resting position after
an inspiration?

Give examples of violent expiration? How does it differ from
an ordinary expiration in the forces at work for its production?

What are the respiratory sounds? Where do their characters
differ? Why do physicians study them in lung diseases?

246

THE HUMAN BODY.

tracts pushes down the abdominal viscera lying against its
under side, these have to make room for themselves by
pushing out the soft front of the abdomen, which accord-
ingly protrudes when the diaphragm descends. Hence
breathing by the diaphragm is indicated on the exterior by

Fig. 71.

Fig. 71.— Torso of the Statue
known as Venus of Milo.

Fig. 72.
Fig. 72.— Paris Fashion, May,

movements of the abdomen, and is often called "abdominal
respiration," as distinguished from breathing by the ribs,
called "costal" or "chest breathing." In both sexes the
diaphragmatic breathing is the more important, but, as a
rule, men and children use the ribs less than adult women.

Why does the abdomen protrude during an inspiration? What is
meant by abdominal respiration? Why? What is costal respira
tion? Which form of breathing is most developed in women?

APPENDIX. 247

Since abdomen and chest alternately expand and contract
in healthy breathing, anything which impedes their free
movement is to be avoided: the tight lacing which used to
be thought elegant, and, indeed, is still indulged in by
some who think a distorted form beautiful, seriously im-
pedes one of the most important functions of the body,
leading not only to shortness of breath and an incapacity for
muscular exertion, but, as has been proved, in many cases
to actual disease. In extreme cases of tight lacing some
organs are often directly injured, weals of fibrous tissue
being, for example, not unfrequently found developed on
the liver from the constant pressure of the lower ribs forced
against it by a tight corset.

Why should conditions impeding the movement of chest and
abdomen be avoided? What is the result of tight lacing? What is
often found on examining after death the bodies of persons who
have practised tight lacing for a long time?

APPENDIX TO CHAPTER XVI.

1. A sheep's lungs with the windpipe attached may be readily ob-
tained from a butcher. It is best to secure it and the heart all in one
mass, as unless the heart be carefully removed holes are apt to be
cut in the lung.

2. Examine the windpipe, and trace it down to its division into the
bronchi. In the wall of the windpipe note the horse-shoe-shaped
cartilages which keep it open, and which are so arranged that the
dorsal aspect of the tube (which lies against the gullet) has no hard
parts in it.

3. Trace one bronchus to its lung, and then cutting away the lung
tissues follow the branching bronchial tubes through the organ.
Note the cartilages in their walls.

4. Carefully divide the other bronchus where it joins the wind-
pipe, and lay it and its lung aside. Then slit open the trachea, the
bronchus still attached to it and the bronchial tubes. Observe the
soft pale-red mucous membrane lining them.

248 THE HUMAN BODY.

5. In the bronchus which has still an uninjured lung attached to
it tie air-tight a few inches of glass or other tubing of convenient size.
On the end of the glass tube then slip a few inches of rubber tubing.
On blowing through the rubber tube the lung will be distended, and
as soon as the opening is left free it will collapse; in this way its
great extensibility and elasticity will be seen.

6. Blow up the lung moderately, and while it is distended tie a
string very tightly around the bit of rubber tubing. This will keep
the air from escaping; the distended lung can now be examined at
leisure, and its form, lobes, and the smooth moist pleura covering it
be better seen than when it is collapsed.

7. To construct the very instructive model depicted in Fig. 67.
obtain a wide-necked glass vessel, and a rubber toy balloon. Very
carefully untie and open the neck of the balloon, and tie into it
tightly a glass rod. Take a cork (one of rubber is best) which fits
the neck of the bottle tightly and is perforated by two holes; through
one of these holes pass the tube projecting from the neck of the
balloon in such way that the collapsed balloon is on the under side
of the cork. Through the other hole pass, airtight, a tube bent as
shown in the figure, and on the upper end of this slip a few inches
of rubber tubing. (This can be pinched or tied up at any time, and in
that way closed, and so forms a cheap substitute for the stopcock
represented in the figure)- When the cork is now secured firmly
in the bottle the apparatus is read}' for use as indicated on p. 239.

8. Substitute a lung for the rubber balloon in the above experi-
ment.

9. The action of the diaphragm may be illustrated by substituting
for the bottle of § 7 a bell-jar with a wide neck at its upper end.
Take a piece of sheet rubber somewhat larger than the bottom of the
bell-jar, and tie a button or marble in the centre of it. Lay the rub-
ber on the table, with the projection caused by the button down-
wards. On it place the bell-jar, stretch the rubber moderately tight,
turn its edges up around the margin of the bell jar, and tie very
tightly with waxed cord or copper wire. In the neck of the bell-
jar place a tight cork with tubes and rubber balloon, as described in
§7. Suck air out of the bottle until the balloon is fairly well ex-
panded; then tie the rubber tube. As the air is removed the pressure
of the atmosphere on its exterior will cause the rubber sheet to arch
up into the cavity of the bell jar so that it now fairly well represents
the diaphragm. The knob caused by the button serves as a handle
by which this artificial diaphragm may be pulled down, representing
inspiration; as it descends the balloon (lung) enlarges, and air enters
it from outside. When the button is let go the artificial diaphragm

APPENDIX. 249

ascends, the lung collapses, and air is forced out of it (expiration).
Then open the air tube leading into the bell-jar. The lung will col-
lapse, and the movements of the diaphragm have no influence
upon it.

10. The diaphragm itself may be readily seen on the body of any
small animal (rat, kitten, puppy), on removing the abdominal vis-
cera. The liver and stomach must be cut away with especial care.

a. When the above viscera are removed the vaulted diaphragm
will be seen, and through it the pink lungs.

b. Seizing some of the folds of peritoneum attached to the dia-
phragm, pull it down, imitating its contraction and flattening in in-
spiration. The lungs will be seen to follow it closely, expanding to
fill the space left by it in its descent.

c. Make a free opening into one side of the thorax. The corre-
sponding lung will collapse, and be no longer influenced by move-
ments of the diaphragm.

d. Now open the other side of the chest: its lung also shrinks up;
the structure of the diaphragm (its tendinous centre and muscular
peripheral regions) can now be better seen, as also the attachment of
the pericardium to its thoracic side.

11. The action of the microscopic cilia in driving along the mucus
in which they move may be demonstrated as follows:

a. Cut off a frog's head and destroy its spinal cord (p. 230)
Then cut out its gullet as completely as possible; slit this open and
spread it out, inner side up, on a piece of cork or board, and fix it
with pins stuck through its edges.

b. Prepare a very thin and small shaving of cork. Dissect the
skin off one thigh of the animal and wrap a bit of it round the shav-
ing of cork, with its underside outwards.

c. Place the light mass thus formed on the mucous membrane of
the gullet, near its mouth end. The little mass will slowly be moved
along to the stomach end of the gullet, and if returned to the mouth
end time after time will be swept along in the same direction. This
is due to the cilia which line the frog's gullet (they are not present
in that of man), and push along to the stomach the mucus bathing
them on which the little float swims.

d. Place the exposed gullet under a bell-jar with a wet sponge for
an hour or two. The mucus secreted by it will be found to have
been swept along to the end of it which joins the stomach.

CHAPTER XVII.

THE CHEMISTRY OF RESPIRATION AND VENTILATION.

Th© Quantity of Air breathed daily. — After an ordi-
nary expiration the chest cavity is by no means completely
collapsed. At this time the lungs still contain about 200
cubic inches of air. In the next inspiration 30 more cubic
inches are taken in, about the same amount sent out at the
following expiration, and so on throughout the day. Du-
ring quiet breathing the quantity of air in the lungs varies,
therefore, with each inspiration and expiration between 230
and 200 cubic inches. At each inspiration something over
a pint of fresh air is taken in, and at each expiration about
the same amount of vitiated air is expelled. As each of
us breathes at least fifteen times a minute, we thus use each
minute, and render impure, 15x30=450 cubic inches (15^
pints) of air. In an hoar the quantity would be 450x60
=27,000 cubic inches (930 pints), and in twenty-four
hours 27,000x24 = 048,000 cubic inches (22,320 pints) of
air, which would weigh about 28.7 lbs. We have next to

How much air do the lungs contain after an ordinary expiration?
How much do ihey receive at the next inspiration? How much is
sent out from them during expiration? Within what limits does the
quantity of air in the lungs vary during quiet breathing? What bulk
of air is taken in during an inspiration?

How often do we breathe? How much air does each one of us
render impure every minute? How much in an hour? How many
pints in a day? What does this quantity of air weigh?

[250]

CHANGES IN RESPIRED AIR. 251

see what it is that happens to this vast quantity of air
breathed daily by each one of us; what we have taken out
of it, and what we have given off to it.

The Changes produced in Air by being once breathed. —
These are fourfold — changes in its temperature, in its mois-
ture, in its chemical composition, and in its volume.

Temperature Changes. — The air taken into the lungs is
nearly always cooler than that expired, which has a tem-
perature of about 36° C. (97° P.). The temperature of a
room is usually about 21° C. (70° F.). The warmer the
inspired air, the less the heat which is lost to the body in
the breathing process.

Changes in Moisture. — Inspired air always contains more
or less water vapor, but is rarely saturated — that is, rarely
contains so much but it can take up more without showing
it as mist; the warmer air is, the more water vapor it re-
quires to saturate it. The expired air is nearly saturated
for the temperature at which it leaves the body, as is read-
ily shown by the vapor deposited when it is slightly cooled,
as when a mirror is breathed upon; or by the clouds seen
issuing from the nostrils on a frosty day, these being due
to the fact that the air as soon as it is cooled cannot hold
all the water vapor which it took up when warmed in the
body. We therefore conclude that air when breathed gains
water vapor and carries it off from the lungs. The quan-
tity of water thus removed from the body is about nine
ounces each twenty-four hours.

Chemical Changes. — The most important changes
brought about in the breathed air are those in its chemical

What changes are produced in the air on its being once breathed?
How does expired air differ in temperature from inspired?
How does expired air differ from inspired in moisture? How
much water is evaporated from the lungs daily?

252 THE HUMAN BODY.

composition. Pure air when completely dried consists in
100 parts of —

By Volume. By Weight.

Oxygen 20.8 23

Nitrogen 79.2 77

When breathed once, such air gains rather more than
4 volumes in 100 of carbon dioxide, and loses rather more
than 5 of oxygen. More accurately, 100 volumes of ex-
pired air, when dried, consist of —

Oxygen 15.4

Nitrogen 1. 2

Carbon dioxide 4.3

The expired air also contains volatile organic substances
in quantities too minute for chemical analysis, but readily
detected by the nose upon coming into a close room in
which a number of persons have been collected.

The Quantity of Oxygen taken up by the Lungs in a
Day. — We have already seen that the quantity of air breathed
in a day is 648,000 cubic inches. This loses 5.4 per cent,
of oxygen or 35,000 cubic inches, weighing 12,818 grains
(14; lbs.): the body therefore gains this amount of that gas
through the lungs daily.

The Amount of Carbon Dioxide passed out from the
Lungs in a Day. — This being 4.3 per cent, of the total bulk
of the air breathed, is 27,864 cubic inches; it weighs 14,105
grains or about 2 lbs.

We thus find that though each breath seems in itself a

What is the chemical composition of pure air by volume? By
weight ? What substances does air gain and lose when once breathed ?
What is the composition by volume of dried expired air? What
does dried expired air contain besides oxygen, nitrogen, and carbon
dioxide?

What bulk of oxygen does the air breathed in a day lose? What
Aveight? How much oxygen does the body take up daily by means
of the lungs?

What bulk of carbon dioxide is carried off by breathing in each
day ? What does it weigh ?

VENTILATION. 253

very little thing, on calculation it is obvious that the total
amount of matter received into the body from the lungs,
and that passed out of it by these organs, every day of our
lives is considerable. In a year each adult breathes about
10,000 lbs. of air ; from it he takes 657 lbs. of oxygen, and
to it he gives off 730 lbs. of carbon dioxide.

Changes of Volume in Air once breathed. — If the ex-
pired air be measured as it leaves the body its bulk will be
found greater than that of the inspired air, since it not
only has water vapor added to it, but is expanded in con-
sequence of its higher temperature. If, however, it be dried
and reduced to the same temperature as the inspired air,
its volume will be found diminished, since it has lost 5.4
volumes of oxygen for every 4.3 volumes of carbon dioxide
which it has gained.

Ventilation. — Since at each breath some oxygen is taken
from the air and some carbon dioxide given to it, w^ere
the atmosphere around a living man not renewed he would
at last be unable to get from the air the oxygen he required;
he would die of oxygen starvation or be suffocated, as such
a mode of death is called, as surely, though not quite so
fast, as if he were put under the receiver of an air-pump
and all the air around him removed. Hence the necessity
of ventilation to supply fresh air in place of that breathed,
and clearly the amount of fresh air requisite must be deter-
mined by the number of persons collected in a room: the
supply which would be ample for one person would be in-

"What weight of air is breathed yearly by an adult? How much
oxygen is taken from it? How much carbon dioxide is given to it?

How does the air expired differ in bulk from inspired? Why?
If the expired air be dried and cooled to the temperature of the in-
spired, what is found? Why?

Why would a man die if the air around him were not renewed!
What is suffocation? What is the object of ventilation?

254 TEE EUMAN BODY.

sufficient for two. Moreover, fires, gas, and lamps all use
up the oxygen of the air and give carbon dioxide to it, and
hence calculation must be made for them in arranging for
the ventilation of a building in which they are to be used.

When breathed Air becomes unwholesome. — In order
that air be unwholesome to breathe, it is by no means
necessary that it shall have lost so much of its oxygen as to
make it difficult for the body to get what it wants of that
gas. The evil results of insufficient air-supply are rarely
directly due to that cause even in the worst ventilated
room, for the blood flowing through the lirngs can take
what oxygen it wants from air containing comparatively
little of that gas. The headache and drowsiness which
come on from sitting in badly ventilated rooms, and the
want of energy and general ill-health which result from
permanently living in such, are dependent on a slow poison-
ing of the body by the reabsorption of matters eliminated
from the lungs in previous respirations. "What these are
is not accurately known; they doubtless belong to those
volatile bodies mentioned above as carried off in small
quantities in each breath, since observation shows that the
air becomes injurious long before the amount of carbon
dioxide in it is sufficient of itself to do any harm. Breath-
ing air containing one or two per cent, of that gas produced
by ordinary chemical methods does no particular injury,
but the breathing of air containing one per cent, of carbon

What conditions determine the supply of fresh air which should
be provided to a room?

Is air ever unwholesome while still capable of supplying the
oxygen which the body requires? What results from living in ill-
ventilated rooms? Why? Does air once breathed become injuri-
ous before the quantity of carbon dioxide in it is poisonous?
What percentage of pure carbon dioxide may be present in the air
breathed without doing harm?

VENTILATION. 255

dioxide produced by respiration is decidedly injurious,
because of the other things sent out of the lungs along with
it. Carbon dioxide, in any such percentage as is commonly
found in a room, is not poisonous, as used to be believed,
but as it is tolerably easily estimated in air, while the more
dangerous injurious substances evolved in breathing are not,
the purity or foulness of the air in a room is usually deter-
mined by finding the percentage of carbon dioxide in it;
but it must be borne in mind that to mean much this car-
bon dioxide must have been produced by breathing; other-
wise the amount of it present is no guide to the quantity
of the more important poisonous substances present. Of
course when a great deal of carbon dioxide is present the
air is irrespirable, as for example sometimes at the bottom
of wells or brewing- vats.

The Quantity of Fresh Air which should be allowed for
each Person in a Room. — In each minute a man breathes
out 450 cubic inches of air containing rather more than
4 per cent, of carbon dioxide. This mixed with three times
its bulk of pure air would give a little over one cubic
foot containing one per cent, of carbon dioxide. Such air
is no longer resp.irable with safety. The result of breath-
ing it for an hour or two is headache and drowsiness; of
breathing it for weeks or months several hours daily, a

What percentage of carbon dioxide produced bv breathing shows
that the air is unfit for use? Is the proportion of carbon "dioxide
found ordinarily in a room poisonous? Why is the percentage
of carbon dioxide in air usually employed in deciding whether
the air is fit to breathe? What must be borne in mind in deciding
from the percentage of carbon dioxide in it that air is no longer
wholesome? Is air containing much carbon dioxide fit to breathe?
Give an example.

What bulk of air does a man contaminate with carbon dioxide to
the extent of one per cent, in each minute? Is air so contaminated
fit to breathe? What are the consequences of breathing it for a few
hours? What of breathing it for months?

256 THE HUMAN BODY.

lowered tone of the whole body, less power of work, physi-
cal or mental, and less power of resisting disease. The ill
effects may not show themselves at once, and may accord-
ingly be overlooked or considered scientific whims by the
careless, but they are there ready to manifest themselves
nevertheless.

In order to have air to breathe in a fairly pure state
every man should have for his own allowance at least about
800 cubic feet of space to begin with, and the arrangements
for ventilation should at the very least renew this at the
rate of one cubic foot per minute. The nose is, however,
the best guide, and it is found that at least five times this
supply of fresh air is necessary to keep free from any odor
the room inhabited by one adult. If an inhabited room
smells " close" to one coming into it from ' ' out of doors,"
the air ^u it is unwholesome to breathe for any length of
time.

How to Ventilate. — Ventilation does not necessarily
mean draughts of cold air, as is too often supposed. In
warming by indirect radiation it may readily be secured by
fixing, in addition to the registers from which the fresh
warmed air reaches the room, corresponding openings at
the opposite side by which the old air may pass off to make
room for the new. An open fire in a room will always
keep up a current of air through it, and is one of the
most wholesome, though not most economical, methods of
warming an apartment.

Why are the injurious effects of impure air apt to be ignored?

What volume of air should be allowed to each adult? At what
rate should it be replenished? What supply of fresh air is needed to
keep an inhabited room free from odor? Is it safe to live in a room
which " smells close"?

How may ventilation be secured in heating by " indirect radia-
tion"? What are the advantages and what the disadvantages of an
open fire?

CHAXGES OF BLOOD IX THE L UXGS. 257

Stoves in a room unless constantly supplied with fresh
air from without dry its air to an unwholesome extent. If
no appliance for providing this supply exists in a room it
can usually he got, without a draught, by fixing a board
about four inches wide under the lower sash and shutting
the window down on it. Fresh air then comes in by the
opening between the two sashes and in a current directed
upwards, which gradually diffuses itself over the room
without being felt as a draught at any one point. In the
method of heating by direct radiation the apparatus em-
ployed provides of itself no means of drawing fresh air into
a room, as the draught up the chimney of an open fire-
place or of a stove does; and therefore special inlet and
outlet openings are very necessary. Since, fortunately,
few doors and windows fit quite tight, fresh air gets into
closed rooms in tolerable abundance for one or two in-
habitants.

Changes undergone by the Blood in the Lungs. — These
are the exact reverse of those exhibited by the breathed air
— what the air gains the blood loses, and vice versa. The
blood loses heat, and water, and carbon dioxide in the pnl-
monary capillaries, and gains oxygen. These gains and
losses are accompanied by a change of color from the dark
purple which the blood exhibits in the pulmonary artery,
to the bright scarlet it possesses in the pulmonary veins.

Why the Blood changes its Color as it flows through

"What are stoves apt to do? Point out a good way of supplying
fresh air to a room warmed by a stove? What are especially impor-
tant in a room heated by "direct radiation"? Why is it fortunate
that doors and windows do not fit air-tight?

What is the relationship between the gaius and losses of blood in
the pulmonary circulation, and the losses and gains of the breathed
air? What does the blood lose as it flows through the lungs? What
"ioes it gain? What change in the color of the blood accompanies
»'hese gains and losses?

258 THE HUMAN BODY.

the Pulmonary Capillaries. — The color of the blood depends
on its red corpuscles, since pure blood-plasma or blood-
serum is colorless or at most a very faint straw yellow.
Hence the color change which the blood experiences in
circulating through the lungs must be due to some change
in its red corpuscles. These consist chiefly of haemoglobin
(p. 178), and haemoglobin, as we have learned, is a sub-
stance which has the power of absorbing oxygen and form-
ing a bright scarlet compound called oxyhcemoglobin.
This oxyhemoglobin very easily gives up its oxygen when
it is placed under conditions where that gas is scarce: the
haemoglobin left behind has a dark purple color. The
blood leaving the lungs by the pulmonary veins is bright
red because all its haemoglobin has been turned into oxy-
hsemoglobin. From the left side of the heart it is conveyed
by the branches of the aorta to all the organs of the body.
These are constantly using oxygen, which is therefore very
scarce in them, and as the blood flows through its oxy-
hemoglobin is broken up, the oxygen taken away, and
dark purple-red haemoglobin left to be conveyed by the
veins to the right auricle of the heart. From there it
passes to the right ventricle and thence by the pulmonary
artery to the lungs, where it again picks up oxygen and

Why must the change in color of the blood during its pulmonary
circuit be due to a change in its red corpuscles? What is the chief
constituent of the red blood-corpuscles? What property does haemo-
globin possess with reference to oxygen? What is the color of oxy-
hsemoglobin?

When does oxyhemoglobin give off its oxygen? What is the
color of haemoglobin? Why is the blood in the pulmonary veins
bright red? Where is it conveyed? Why is oxygen scanty in most
organs of the body? What results as regards the oxyhamioglobin of
the blood? What is the color of the blood sent to the right auricle
of the heart? What is the subsequent course of this blood until it
reaches the lungs? What does it receive in the lungs? How is its
color altered in 'those organs?

APPENDIX. 259

becomes bright-red oxyhemoglobin. The red corpuscles
of the blood are so many little boxes in which oxygen is
packed away in the lungs for conveyance to distant parts
of the body.
"What is the function of the red blood-corpuscles?

APPENDIX TO CHAPTER XVIL

1. To show that air is warmed by breathing, breathe for a few
seconds on the bulb of a thermometer. The mercury will be seen to
rise rapidly in its stem.

2. To demonstrate that air gains water in the lungs, breathe on a
mirror, or on a knife-blade or other polished metallic surface.

3. The presence of carbon dioxide in expired air may be readily
demonstrated by expiring through a tube immersed in lime-water.
This may be obtained at any drug store; with carbon dioxide it gives
a white precipitate, which dissolves readily in a little vinegar.

4. To show that much less carbon dioxide exists in inspired air,
take a small bottle with a wide neck. Fit tightly into the neck of the
bottle a cork perforated by two holes. Through one hole pass a glass
tube reaching to near the bottom of the bottle, and through the other
one which ends just below the cork; on the outer end of this tube fit
a foot or so of rubber tubing. Remove the cork; half fill the bottle
with lime-water and then replace the cork. Suck air through the
rubber tubing. It will bubble through the lime-water, but (unless
the room is very badly ventilated) a great deal must be drawn through
the lime-water before as abundant a precipitate is produced as that
which results from blowing a small quantity of breathed air (3)
through the lime-water.

5. The influence of oxygen upon the color of the blood may be
illustrated as follows:

a. Take to a slaughter-house a glass jar or beaker (an ordinary
tumbler answers quite well), two bottles, an earthenware quart pitcher,
and a bundle of wire.

b. "When an animal is killed and bled, collect some blood in the
jar and let it clot.

c. Collect some more blood in the pitcher, and defibrinate by

260 THE HUMAN BODY.

thorough whipping with the bundle of wire. Half fill each bottle
with the defibrinated blood ; then cork the bottles.

d. Having brought home all the specimens, set them aside until the
next morning in a cool place. It will then be found that the blood
in each bottle is dark-colored or venous (having used up its own
oxygen and not being able to get more from the air), and that the
clot in the jar is bright scarlet (arterial-colored) above where it is in
contact with the air, but dark purple-red where it is immersed in
the serum.

e. Invert the clot: in an hour or two its previously dark original
under surface will have become bright red, while the original upper
surface, previously bright-colored and now immersed in the serum
away from the air, will have become venous in tint.

/. Take the cork out of one bottle; renew the air in it by blow-
ing. Placing a thumb on the neck of the bottle, thoroughly shake
up the blood with the air. Tlien renew the air again, and shake once
more; and so on for three or four times. At the end the blood shaken
up with air will be seen to have assumed a much brighter red color
than that kept shut up in the other bottle.

g. If the proper chemical apparatus and reagents are accessible,
the air in the bottle about to be shaken may be replaced by nitrogen,
hydrogen, or pure oxygen, and the procedures described in section
/ repeated. It will be found that only the oxygen brightens the
blood color. As any one possessing the chemical apparatus and
knowledge implied for the execution of this experiment will certainly
know how to replace the air by the gases above named, no further
details need be given.

CHAPTER XVIII.

THE KIDNEYS AND THE SKIN.

General Arrangement of the Nitrogen-excreting Or-
gans.— These organs are (1) the kidneys, the glands which
secrete the urine; (2) the ureters or ducts of the kidneys,
which carry the secretion to (3) the urinary Madder, a
reservoir in which it accumulates and from which it is ex-
pelled from time to time through (4) an exit tube, the
urethra. The general arrangement of these parts, as seen
from behind, is shown in Fig. 73. The kidneys, R, lie
at the back of the abdominal cavity, opposite the upper
lumbar vertebrae, one on each side of the middle line.
Each is a solid mass, with a convex outer and a concave
inner border, and its upper end a little larger than the
lower. From the abdominal aorta, A, a renal artery, Ar,
enters the inner border of each kidney, to break up within
it into finer branches, ultimately ending in capillaries.
The blood is collected from these into the renal veins, Vr,
one of which leaves each kidney and opens into the inferior
vena cava, Vc, which carries it, after having lost water and
urea in the kidney, back to the heart. From the concave

Name the chief organs concerned in removing from the body its
nitrogenous waste matters. Describe the general arrangement of
these organs. Describe the form of a kidney. What vessel supplies
it with blood? What vessel carries blood out of the kidney? What
has the blood carried off from a kidney lost while flowing through
that organ?

[261]

262

THE HUMAN BODY.

Fig. 73.-The renal organs, viewed from behind. B right kidney; A aorta ;
Ar, right renal artery; Vc, inferior vena cava; FT, nght renal vein, tf, ngnt
ureter; Vu, bladder; Ua, commencement of urethra.

STRUCTURE OF THE KIDNEYS. 263

border of each kidney proceeds also the ureter, U, a slender
tube opening below into the bladder, Vu, near its lower
end. From the bladder proceeds the urethra, at TJa. The
channel of each ureter passes very obliquely through the
wall of the bladder; accordingly if the pressure inside the
latter organ rises above that of the liquid in the ureter the
walls of the oblique passage are pressed together and it is
closed. Usually the bladder (which contains muscular
tissue in its walls) is relaxed, and the urine flows readily
into it from the ureters. The commencement of the
urethra being kept closed by elastic tissue around it (which
can voluntarily be reinforced by muscles which compress
the tube), the urine accumulates in the bladder. When
this latter contracts and presses on its contents the ureters
are closed in the way above indicated, the elasticity of the
fibres closing the urethral exit from the bladder is over-
come, and the liquid is forced out.

Naked Eye Structure of the Kidneys. — When a section
is made through a kidney from its outer to its inner border
(Fig. 74) it is seen that a deep fissure, the hilus, leads
into the latter. In the hilus the ureter widens out to form
the pelvis of the kidney, which breaks up into a number of
smaller divisions, the cups or calices. The cut surface of
the kidney proper is seen to consist of two distinct parts;
an outer or cortical portion, and an inner or medullary.
The medullary portion is less red and more glistening to
the eye, is finely striated in a radial direction, and does not

What is the ureter? Under what circumstances is its opening
into the bladder closed? What is the usual state of things?
How is the commencement of the urethra closed? What results?
What happens when the bladder contracts?

What is seen on a section made through a kidney? How is the
pelvis of the kidney formed? What are the calices? What is seen
on the cut surface of the kidney proper? How does the medullary
part differ in appearance from the cortical?

264

THE HUMAN BODY.

consist of one continuous mass, but of a number of conical
portions, the pyramids of MalpigM, 2', each of which is

Fig. 74 .—Section through the right kidney from its outer to its inner border.
1, cortex; 2, medulla; 2', pyramid of Malpighi; 2", pyramid of Ferrein; 5, small
branches of the renal artery entering between the pyramids; A, a branch of the
renal artery; C, the pelvis of the kidney; U, ureter; C, a calyx.

separated from its neighbors by a prolongation,*, of the
cortical substance. This, however, does not reach to the

Describe the pyramids of Malpigbi. What lies between them?

MINUTE STRUCTURE OF THE KIDNEY. 265

apex of the pyramid, which projects, as the papilla, into a
calyx of the ureter. At its outer end each pyramid separates
into smaller portions, 2", separated by thin layers of cortex
and gradually spreading everywhere into the latter. The
cortical substance is redder, more granular looking, and
less shiny than the medullary; it forms everywhere the
outer layer of the organ, besides dipping in between the
pyramids in the manner above described.

The renal artery divides in the hilus into branches (5)
which run into the kidney substance between the pyra-
mids, give off a few twigs to the pyramids, and end finally
in a much closer vascular network in the cortex.

The Minute Structure of the Kidney. — The kidneys are
compound tubular glands, being composed of branched
microscopic uriniferous tubules, lined by a single layer of
secreting cells, supported by connective tissue, and supplied
with blood-vessels, nerves, and lymphatics. The final
branches of each tubule end in a dilatation which contains
a knot of blood-vessels, through whose walls water and
salts filter into the tubule. As the water trickles along the
latter, the cells lining it pass out the nitrogenous wastes
of the blood brought there by the capillaries which wrap
closely around them. The tubules unite in the pyramids
to form fewer and larger ducts, which pour the secretion

How does the apex of a pyramid end? Where do we find the cor-
tical substance of the kidney?

Describe the general distribution of the renal artery and its
branches in the kidney. What part of the kidney contains most
capillary biood- vessels?

To what type of gland do the kidneys belong? Of what are they
made up? How do the uriniferous tubules end? What lies in each
dilatation? What filters from the blood-vessels of its dilatation into
the cavity of the tubule? What is added to this as it trickles along
the tubule? How is the nitrogenous waste of the body brought close
to the kidney tubules? What becomes of the tubules in the pyra-
mids? Where do the larger ducts convey the secretion?

266 TIIE HUMAN BODY.

into the calices of the pelvis of the ureter, and this tube
then conveys it to the bladder.

The Renal Secretion is less in bulk in warm weather,
when perspiration carries off a good deal of the excess
water of the blood, than in cold. On an average the kid-
neys eliminate from the body in twenty-four hours about
fifty ounces (2£ pints) of water, and 500 grains (1\ ounces)
of urea, which contain a little more than 230 grains of
nitrogen.

The Kidneys, being the chief organs for the excretion
of nitrogen, are among the most important organs of the
body. Any defect in their healthy activity leads to serious
interference with the working of many organs, due to the
accumulation in the body of nitrogenous waste products.*

The Skin, which covers the whole exterior of the body,
consists everywhere of two distinct layers: an outer, the
cuticle or epidermis; and a deeper, the dermis, cutis vera,
or corium. A blister is due to the accumulation of liquid
between these two layers. Hairs and nails are excessively
developed parts of the epidermis.

The Epidermis, Fig. 75, consists of cells, arranged in

Where does the ureter convey it?

Is the hulk of the renal secretion greater in summer or in winter?
Why? What is its average daily amount? How much urea does it
contain? How much nitrogen is contained in this quantity of urea?

Why are the kidneys important organs? What follows when
their physiological work is defective?

Of what two main parts does the skin consist? What is a hlister?
What are hairs and nails?

* BrighVs Disease, one of the commonest and most dangerous of maladies,
consists essentially in an alteration of the kidney structure, in consequence of
which these organs cease to eliminate urea from the blood, and drain off pure
albumen from it instead. The three most common causes of Bright's disease
are (1) an acute illness, as scarlet fever, of which it is a frequent result; (2) sud-
den exposure to cold when warm (this often drives blood in excessive amount
from the skin to internal organs and leads to k'dney disease); and (3) excessive
drinking of alcoholic liquids.

TEE EPIDERMIS.

267

many layers, and united by a small amount of cementing
substance. The deepest layer, d, is composed of elongated

UliK '}'

Fig. 75.— A section through the epidermis, somewhat diagrammatic, highly
magnified. Below is seen a papilla of the dermis, with its artery, /, and veins,
gg; a, the horny layer of the epidermis; b, the rete muscosum or Malpighian
layer; d, the layer of columnar epidermic cells in immediate contact with the
dermis; h, the duct of a sweat-gland.

or columnar cells, set on with their long axes perpendicular
Describe the epidermis.

268 THE HUMAN BODY.

to the corium beneath. It is succeeded by several strata of
roundish cells, b, which in the outer layers become more
and more flattened in a plane parallel to the surface. The
outermost epidermic stratum is composed of many layers of
very flattened cells from which the nuclei (conspicuous in
the deeper layers) have disappeared. These superficial cells
are dead, and are constantly being shed from the surface of
the body, while their place is taken by new cells, formed in
the deeper layers, pushed up to the surface, and flattened in
their progress. The change in the form of the cells as they
travel outwards is accompanied by chemical changes ; they
finally constitute a semi-transparent dry homy stratum, a,
distinct from a deeper, more opaque, and softer layer, b and
d, of the epidermis.

The rolls of material which are peeled off the skin on
rubbing it with a rough towel after a warm bath, are dead
outer scales of the horny stratum of the epidermis.

Nerves penetrate the epidermis, but no blood-vessels
enter it. In dark races the color is due to a pigment con-
tained chiefly in the deeper-placed cells of the epidermis.

The Corium, Cutis Vera, or True Skin, Fig. 76, consists
of a close feltwork of connective tissue, which, becoming
wider meshed below, passes gradually into the subcutane-
ous areolar tissue, in texture much like damp raw cotton,
which loosely attaches the skin to parts beneath. In tanning,
the cutis vera is turned into leather, its connective tissue

What portion of it is constantly being cast off from the body ?
What is meant by the horny stratum of the epidermis? Of what do
the rolls of matter consist which are peeled off the skin on vigorous
rubbing after a warm bath ?

Does the epidermis contain nerves? Blood-vessels?

Where does the coloring matter of the skin of negroes lie ?

Of what does the true skin consist ? Into what does it pass on its
deeper side ? What is turned into leather when an ox-hide is tanned?

THE CORIUM.

2G9

forming an insoluble and tough compound with the tannin
of the oak-bark employed. Wherever there are hairs bun-
dles of plain muscular tissue are found in the corium : it
contains also a close network of capillary blood-vessels, and

h

m

i I

fr

-A

ta

f

sc

Fig. 76. — A section through the skin and subcutaneous areolar tissue, h, horny
stratum, and in, deeper more opaque layer of the epidermis; d. dermis passing
below into sc, loose areolar tissue, with fat, /, in its meshes: above, dermic
papillae are seen, projecting into the epidermis which is moulded on them, a,
opening of a sweat-gland; <jl, the gland itself.

numerous lymphatics and nerves. In shaving, as long as

the razor keeps in the epidermis there is no bleeding ; but

a deeper cut shows at once the presence of blood-vessels in

the true skin.

How ? Where do -we find plain muscular tissue ir the corium '!
What bloodvessels are found in it ? What else ?

270 THE HUMAN BODY.

The Papillae of the Dermis. — The outer surface of the
corium is almost everywhere raised into minute elevations,
called papillm, on which the epidermis is molded, so that
its deep side presents pits corresponding to the projec-
tions of the dermis. In Fig. 75 is shown a papilla of the
corium containing a knot of blood-vessels, supplied by the
small artery, /, and having the blood carried off from them
by the two little veins, gg. Other papillae contain no
capillary loops, but, instead, special organs connected with
nerve-fibres, and supposed to be concerned in the sense of
touch. On the palm of the hand the dermic papillae are
especially well developed (as they are in most parts where
the sense of touch is acute), and are frequently compound
or branched at the tip. On this surface of the hand they
are arranged in rows; the epidermis fills up the hollows
between the papillae of the same row, but dips down be-
tween adjacent rows, and thus are produced the finer epi-
dermic ridges seen on the palms.* The wrinkles of old
persons are due to the absorption of subcutaneous fat and
of other soft parts beneath the skin, which, not shrinking
itself to the same extent, is thrown into folds.

Hairs, longer or shorter, are found all over the surface
of the body, except in a few regions, as the palms of the
hands and the soles of the feet. A hair is a slender thread
of epidermis, developed on a special dermic papilla placed

What are the papillae of the epidermis? Describe a papilla con-
taining blood-vessels. What is found in other papillae? Name a
region of the skin where the dermic papillae are especially de-
veloped. How are the ridges seen on the palm of the hand pro-
duced? To what are the wrinkles on the skin of elderly persons
due?

Name regions of the skin which have no hairs. What is a
hair?

* The more marked furrows on the palm, the so-called "lines of life" of
the gypsy's palmistry, have a different origin.

THE NAILS.

271

at the bottom of a depression, formed by a pitting-in of the

dermis. The depression is known as the hair follicle. The

part of the hair buried in the

follicle is culled its root; this

is succeeded by a stem, which

(in uncut hairs) tapers off to a

point. Each hair is made up

of a number of epidermic cells,

arranged together so as to form

a fibre.

Nails. — A nail is a part of
the epidermis, with its horny
stratum greatly developed. The
back part of the nail fits, into
a furrow of the dermis, and is
called its root. The visible part
consists of a bod]), attached to
the dermis beneath (which forms
the led of the nail), and of a
free edge. Near the root is a
little area, whiter than the rest
of the nail, called the lunula.
The whiteness is due in part to
the nail being really more
opaque there, and partly to the
fact that its bed, which seen
through the nail causes its pink
color, is in this region less vas-
cular.

The portion of the corium on which the nail is formed

What is a hair follicle? What is the root of a hair? The stem?
Of what is a hair composed?

What is a nail? Of what parts does it consist? What is the
lunula? Why is it paler in color than the rest of the nail?

Fig. 77— The root of a hair im
bedded in its follicle, o, stem of
haircut short; o, />, root of hair;
c, swollen part of root which fits
on i, the dermic papilla at the
bottom of the hair follicle; n, m. ?,
iayerof skin which turn in to line
and form the follicle; k. k, mouths
of ducts of sebaceous glands.

272

THE HUMAN BODY.

is called its matrix. Behind, this forms a groove lodging
the root of the nail, and it is by new cells added there that
the nail grows in length. The part of the matrix lying
beneath the body of the nail, and called its bed, is highly
vascular; new cells formed on its bed and added to its
under surface cause the nail to increase in thickness, as it
is pushed forward by the new growth at its root. The
free end of a nail is therefore ifcs thickest part. If a nail
is "cast" in consequence of an injury,
or torn off, a new one is produced, pro-
vided the matrix is not destroyed.

The Glands of the Skin are of two
kinds. The siceat glands or sudori-
parous glands, and the oil glands or
sebaceous glands.

The Sweat Glands (Fig. 78) are
microscopic tubes which reach from
the surface of the skin to the subcu-
taneous areolar tissue; then the tube
often branches, and is coiled up into
a little knot, intertwined with blood
capillaries. These glands are found all

Fig. ?8.— A sweat : °

gland, d, horny layer over the skin, but are most abundant on

of cuticle; c, Malpighian

cX^ftUTnfprope" the PalmS °f the h<™ds> tlie ^leS of the

£££* JK£ fe ^et, and the brow. Altogether, there are

low the dermis. ^^ twQ ^ & ha]f mil]ions of ^

The perspiration or sweat poured out by the sudoriparous

"What is the matrix of a nail? When does the nail grow longer?
What is the bed of a nail? How does a nail grow thicker? Which
is its thickest part? What is necessary in order that a " cast nail"
may be reproduced?

What glands are found in the skin? Describe a sweat gland.
Where are the sweat glands most numerous? How many are there
on the whole skin?

THE PERSPIRATION. 273

glands is a transparent colorless liquid, with a peculiar odor,
varying in different races, and in the same individual in
different regions of the body. Its quantity in twenty-four
hours is subject to great variations, but usually lies between
10,850 and 31,000 grains (or 25 and 71 ounces). The
amount is influenced mainly by the surrounding tempera-
ture, being greater when this is high; but it is also in-
creased by other things tending to raise the temperature
of the body, as muscular exercise.* The sweat may or
may not evaporate as fast as it is secreted; in the former
case it is known as insensible, in the latter as sensible per-
spiration. By far the most passes off in the insensible form,
drops of sweat only accumulating when the secretion is very
profuse, or the surrounding atmosphere is so humid that it
does not readily take up more moisture. The perspiration
in 1000 parts contains 990 of water to 10 of solids. Among
the latter is, in health, a little urea, some sodium chloride,
and other salts. In diseased conditions of the kidneys the
urea may be greatly increased, the skin supplementing to a
certain extent deficiencies of those organs.

The Sebaceous Glands nearly always open into hair fol-
licles. They are small compound racemose glands (p. 131).
Each presents a duct, opening near the mouth of the hair
follicle; when followed back this duct is found to divide
into several branches which end in globular expansions.

Describe the perspiration. How much is secreted daily? Point
out conditions influencing its amount. What is meant by " insensi-
ble perspiration"? Under what conditions do we find "sensible
perspiration"? What percentage of solids exists in the sweat?
What do they contain? When is the proportion of urea in the
perspiration apt to be increased?

Where do the sebaceous glands open? To what type of gland do
they belong?

* In fever the sweat glands are paralyzed, and we find a high temperature
of the body with a dry skin.

274 THE HUMAN BODY.

The latter are lined by secreting cells. The mouth of
the ducts of a sebaceous gland is seen on one side of the hair
follicle in Fig. 77.

The Sebaceous Secretion is oily and semi-fluid. In
healthy persons it lubricates the hairs and renders them
glossy even Avhen no " hair-oil " is used. It is also spread
more or less over all the surface of the skin, and makes the
cuticle less permeable by water, which in consequence does
not readily wet the healthy skin, but runs off it, as "off a
duck's back," though to a less marked extent.

The Skin as a Sense Organ. — Besides its functions as a
protective covering and an excretory organ, the skin is of
extreme importance, as being the seat of one of our most
important senses — the sense of touch. (Chap. XXI.)

Hygiene of the Skin. — The sebaceous secretion and the
solid residue left by evaporating sweat form a solid film
over the skin, which tends to choke the mouths of the sweat
glands (the so-called " pores " of the skin) and impede their
action. Yet these glands, minute though each is, have for
their function to separate daily from the body a great amount
of water* and some little urea and salines. Hence the
importance of personal cleanliness. The whole skin, except
that of the scalp, should be washed daily. Women cannot

Describe the structure of a sebaceous gland.

Describe the sebaceous secretion. Why is the hair of a healthy
person, using no hair-oil, glossy ? Why does water run off the skin?

Enumerate the chief functions of the skin.

How are the mouths of the sweat glands apt to be choked up ?
Point out functions of these glands.

How much of the skin should be washed daily ?

* The sweat glands not merely carry off some water from the body, but serve
also to regulate its temperature. When water evaporates from the surface of
any object it abstracts heat from that object; and when perspiration evapo-
rates it takes more heat from the skin.

HYGIENE OF THE SKIN. 275

well wash their hair every day, as it takes so long to dry;
but there is no reason why a man should not immerse his
head when he takes his hath. Except on parts of the skin
especially exposed to contamination, soap should only he
used occasionally — say once or twice a week: its employ-
ment is quite unm cessary for cleanliness, except on exposed
parts of the body, if frequent bathing is a habit and the
skin be well rubbed afterwards until dry. Soap nearly al-
ways contains an excess of alkali, which in itself injures some
skins, and, besides, is apt to combine chemically with the
sebaceous secretion and carry it too freely away. Persons
whose skin is injured by soap, will find in cornmeal a good
substitute. Xo doubt many folk go about in very good
health with very little washing ; contact with the clothes
and other external objects keeps the skin excretions from
accumulating to any very great extent. But apart from
the duty of personal cleanliness imposed on every one as a
member of society in daily intercourse with others, the mere
fact. that the healthy body can manage to get along under
unfavorable conditions is no reason for exposing it to them.
A clogged skin throws more work on the lungs and kid-
neys than their fair share, and the evil consequences vmay
be experienced any day when something else throws an-
other extra strain upon them.

Bathing. — One object of bathing is to cleanse the skin;

How often should soap be used in the bath? Why is the too fre-
quent use of soap not desirable? What is a good substitute for it in
eases where soap is injurious to the skin ? How does an unclean skin
influence internal organs? When are its results apt to show them-
selves?

The sweat glands secrete more vigorously when the body is heated, and the

evaporation of their secretion cools it. In most fevers the sweat glands are para-
lyzed: and the abnormally warm body is nut c<><>|h,1 i,y |,,s< 0f the beat, which
in health would have been carried off by the evaporating sweat.

276 THE HUMAN BODY.

but it is also useful to strengthen and invigorate the whole
frame. For strong healthy persons a cold bath is the best; in
severe weather the temperature of the water should be raised
to 15° C. (about 60° F.), at which it still feels quite cool to
the surface. The first effect of a cold bath is to contract
all the skin-vessels and make the surface pallid. This is
soon followed by a reaction, in which the skin becomes red
and full of blood, and a glow of warmth is felt in it. The
proper time to come out of the bath is while this reaction
lasts, and after emersion it should be promoted by a good
rub. If the stay in the cold water be too prolonged, the
state of reaction passes off, the skin again becomes pallid,
and the person probably feels cold, uncomfortable, and de-
pressed all day: such bathing is injurious instead of bene-
ficial; it lowers instead of stimulating the activities of the
body. How long one may remain in cold water with benefit,
depends greatly on the individual; a vigorous man can bear
and set up a healthy reaction after much longer immer-
sion than a feeble one; moreover, a person used to cold
bathing can with benefit remain in the water longer than
one not accustomed to it. Of course, apart from this, the
temperature of the water has a great importance. Water
which feels cold to the skin may, as shown by the ther-
mometer, vary within very wide limits of temperature.
The colder it is, the shorter the time which it is wise to
remain in it.

When to Bathe. — It is perfectly safe to bathe when warm,

What ends are obtained by bathing? What sort of a bath should
healthy persons take? What is the primary effect of a cold bath on
a healthy person? What follows next? When should one leave
a cold bath ? What happens if one stays too long in a cold bath ?
Point out conditions which influence the time of remaining with
benefit in a cold bath.

SHOWER BATHS AND WARM BATHS. 277

provided the skin is not perspiring profusely; the common
belief to the contrary notwithstanding. On the other hand,
no one should enter a cold bath when feeling chilly, or in
a depressed vital condition. It is not wise to take a cold
bath immediately after a meal, for the afterglow of the skin
tends to draw away too much blood from the digestive
organs, which are then actively at work. The best time for
a long bath is two or three hours after breakfast; but for a
brief daily dip there is no better time than while the body
is still warm from bed.

Shower Baths abstract less heat from the body than a)i
ordinary cold bath, and at the same time give it a greater
stimulus, tending to set up the warm reaction. Hence they
are valuable to persons in not very vigorous health.

Warm Baths, except occasionally for purposes of clean-
liness, are medical remedies, and not proper things for daily
use. While promoting the tendency to perspiration (which
it is often important to do in disease), they also, if often
repeated, lower the general vigor of the body. Persons in
feeble health, who cannot stand an ordinary daily cold bath,
may diminish the shock to the system by raising the tem-
perature of the water they bathe in to any point at which
it still feels cool to the skin.

Is it ever safe to bathe while warm? Point out conditions when
a cold bath should be avoided. Why is it not wise to take a cool
bath soon after a meal ? What is the best time for a prolonged cold
bath? What the best time for a brief daily dip ?

Why are shower baths better than immersion baths for persons
in enfeebled health?

Should healthy persons take daily warm baths? What is the con-
sequence of frequent warm baths?

How should persons in feeble health regidat0 the temperature of
their daily bath ?

278 THE HUMAN BODY.

APPENDIX TO CHAPTER XVIII.

To demonstrate the anatomy of the renal organs proceed as
follows :

1. Kill a rat in any merciful way; placing it under a bell-jar
with a sponge soaked in ether is a good method.

2. Open the abdomen of the animal, remove its alimentary canal,
and cut away (with stout scissors) the ventral portion of the pelvic
girdle. The dark-red kidneys will then be easily recognized on each
side of the dorsal part of the abdominal cavity, the right one nearer
the head than the left.

3. Dissect away neatly the connective tissue, etc., in front of the
vertebral column, so as to clean the inferior vena cava and the abdom-
inal aorta. Trace out the renal arteries and veins.

4. Find the ureter, a slender tube passing back from the kidney
towards the pelvis : it leaves the inner border of the kidney behind
the vein and artery; and lying, at first, at some distance from the
middle line, converges towards its fellow as it passes back.

5. Follow the ureters back until they reach the urinary bladder;
dissect away the tissues around the latter and note its form, etc.

6. Open the bladder; find the apertures of entry of the ureters,
and pass bristles through them into those tubes. Note the mucous
membrane lining the bladder.

?. Remove one kidney from the body and divide it from its outer
to near its inner border ; turn the two halves apart (still leaving them
connected by the tissues at the inner border), and examine the cut
surfaces.

8. Note at the inner border (hilus) the dilatation (pelvis) of the
ureter; the outer, darker, granular cortical portion of the kidney, and
the inner, paler, smoother medullary portion; the papilla formed by
a projection of the medullary substance at the hilus. contained in an
expansion (calyx) of the pelvis of the ureter.

9. Obtain a fresh sheep's kidney. Divide it by a section made
through it from its outer to its inner border. On the cut surfaces the
cortex and medulla will be more readily demonstrated than on the
rat's kidney. The pyramids of MalpigM will also be easily seen, and
the offshoots of the cortex exteudiug between them.

CHAPTER XIX.
WHY AVE NEED A NERVOUS SYSTEM. ITS ANATOMY.

The Harmonious Co-operation of the Organs of the
Body. — We have already learned that the hody consists of
a vast number of cells and fibres, combined to form organs;
and that each kind of cell or fibre and each organ has its
own peculiar structure, properties, and uses. Except in so
far as the blood, passing from organ to organ, carries mat-
ters from one to another, and indirectly enables each organ
to act upon the rest, we have as yet seen no means by which
all this collection of organs is made to work together, so
that each shall not merely look after itself, but regulate its
activity in relation to the needs or dangers of other parts
of the body.

That the organs do co-operate we all know. The lids
shut when an object threatens to touch the eye, and (with-
out our thinking about it at all) thrust themselves in the
way so as to protect the more tender eyeball. When we are
using the muscles of the legs vigorously the muscles of
respiration hurry their action, and, consequently, oxygen is
conveyed more rapidly to the blood for the supply of the
working leg muscles, and the carbon dioxide produced in
great quantity by these muscles is quickly removed. When
the sole of the foot is tickled the muscles of the thigh and

Of what is the body made up? How do the various kinds of
cells, fibres, and organs differ? How does the blood enable each organ
to influence the rest?

Give an example showing the cooperation of the organs of the
body. Give another example. A third.

280 THE HUMAN BODY.

leg, which are not directly interfered with at all, contract
and jerk the foot away from its tormentor. Everywhere
we find this co-operation among the organs; and it is only
by such co-operation that our oodies are able to continue
alive. In JEsop's fable we are told how the arms and jaws
declined to work any longer in providing and grinding food
for the lazy stomach, and how they soon came to grief in
consecpience. We might extend the fable, aud go on to
state how afterwards the stomach made up its mind to
digest and absorb just as much food as it wanted for itself,
and not bother about supplying those cantankerous arms
and jaws, and the moral would be the same: if the stomach
ceased to work for the other parts they soon would cease to
be able to send food to it, and so it would itself starve in turn.
How a Man differs from a Collection of Living Organs.
— Throughout the body, heart, lungs, stomach, intestines,
liver, muscles, and skin, all need one another's aid to
obtain food and oxygen, to remove wastes, and to avoid dan-
gers. This co-operation makes the individual human be-
ing; a mere mass of living organs, arranged together in the
form of man's body, but each acting without reference to
the rest, would no more make a man than a mob of strong
men would make an army. As in the mob the reckless
courage of some, the personal cowardice of others, the
uncontrolled ambition of a few, would make the crowd
nearly useless for military purposes in spite of the merits of
its individual members, so in the body; if the organs were

Is co-operatiou between its organs general throughout the body?
Is it important? Illustrate the importance of co-operation between
the parts of the body.

For what purposes do the different organs need one another's help?
Is the co-operation of organs necessary to make an individual human
being? Illustrate.

CO-ORDINATION. 281

not disciplined, controlled, and guided, so as to work to-
gether for the good of the whole, death would very soon
result. As a matter of fact this is the way in which death
almost always does hegin. The body is not built like the
deacon's "one-hoss shay," to run till every part of it gives
out at the same moment. Some important organ ceases to
do its part properly; as a consequence the whole complex
mechanism is thrown out of gear, and deatn results.

Co-ordination means controlling the activities of a num-
ber of working things (whether men, or organs, or ma-
chines) for the attainment of a definhe end. A pro-
miscuous and undirected crowd of competent bricklayers,
carpenters, hod-carriers, and so forth, would be quite in-
competent to build a house. There might be present
abundant energy and skill to construct walls and floors and
roof; but if each man worked for himself and took no heed
of the rest the result would be an odd building, if any at
all. Ilencc the whole work is placed under the control of
a master builder, who guides the activities of individ-
uals according to the needs of the moment: undirected
workmen, if conscientious, would work just as hard with-
out supervision, but they would work un profitably. The
healthy body may be regarded as made up of a number of
conscientious workers, the organs, who are concerned in
building it and keeping it in repair, each one acting so as
to co-operate with the rest for the attainment of the com-
mon end. The master builder, or "boss," if we may use

How does death usually begin? What happens when some im-
portant organ ceases to doits duty?

What is meant by co-ordination? Illustrate. How may the
healthy body be regarded when compared with the workmen con-
cerned in building a house?

THE HVMAN BODY.

such a word, is represented by the nervous system, which
is in communication with all the other organs, is influenced
by the condition and the needs of every part at each mo-
ment, and guides the activity of all the others accordingly.
Part of this control is exercised consciously and with the
co-operation cf the " will," but much more is carried on by
the nervous system without our knowing anything about it.
Nerve-Trunks and Nerve-Centres. — In dissecting the
body numerous white cords are found which at first sight
might be taken for tendons. That they are something else
soon becomes clear, since a great many of them have no
connection with muscles, and those which have, usually
enter near the middle of the belly of the muscle, instead of
being fixed to its ends as most tendons are. These cords
are nerve-trunks : followed from the middle line of the
body each (Fig. 79) will be found to break up into finer
and finer branches, until the subdivisions become too small
to be followed without the aid of a microscope. Traced
towards the middle of the body the trunk will, in most
cases, be found to increase by the union of others with it,
and ultimately to join a much larger mass of different
structure, from which other similar trunks spring. This
mass is nerve-centre. The end of a nerve attached to the
centre is, naturally, its central, and the other its distal or
peripheral end.

What is it in the body which represents the master builder?
What are the relations between the nervous system* and the other
organs of the body? Is the control of the nervous system always con-
sciously exercised?

How may we recognize that certain white cords found on dissect-
ing the body are not tendons? What are they? What is found when
nerve-trunks are traced towards the outer parts of tlie body? What
when traced in the opposite direction? What is a nerve-centre?
What is meant by the peripheral end of a nerve?

DIAGRAM OF THE NERVOUS SYSTEM. 283

FfG. 79,— Diagram illustrating the general arrangement of the nervous system,

2^4 THE HUMAN £01) F.

Nerve-centres give origin to nerve-trunks ; these radiate
all over the body, branching and becoming smaller and
smaller as they proceed from the centre ; finally they end
in or among the cells and fibres of the various organs.
The general arrangement of the nerve-centres and of the
larger nerve-trunks of the body is shown in Fig. 79.

The Main Nerve-Centres. — The great majority of the
nerve-trunks take their origin from the brain and spinal
cord, which together form the great cerebrospinal centre.
Some nerves, however, commence in rounded or oval
masses, which vary in size from that of the kernel of an
almond down to microscopic dimensions, and which are
widely distributed in the body. Each of these smaller
centres is called a ganglion. A considerable number of the
iargest ganglia are united directly to one another by nerve-
trunks, and give off nerves especially to blood-vessels and
to the organs in the thoracic and abdominal cavities. These
ganglia and their branches form the sympathetic nervous
system (Figs. 1 and 2), as distinguished from the cerebro-
spinal nervous system, consisting of the brain and spinal
cord and the nerves proceeding from and to them.

The Cerebro-Spinal Centre and its Membranes. — Lying
in the skull is the brain, and in the neural canal of the
vertebral column the spinal cord or spinal marrow,
the two being continuous through the foramen magnum

To what do nerve-centres give origin? What becomes of nerve-
trunks?

From what organs do most nerves arise? What is meant by the
cerebro-spinal centre? From what do those nerves arise which are
not directly connected with brain and spinal cord? What are the
smaller nerve-centres named? What is the sympathetic nervous sys,
tem? Where is the brain placed? What organ lies in the neural canal
of the backbone? Through what opening do brain and spinal cord
unite?

THE CEREBROSPINAL CENTRE.

285

(Fig. 20) of the occipital bone.
This cerebro-spinal centre con-
sists of similar right and left
halves, incompletely separated
by grooves and fissures. Brain
and spinal cord "are very soft
and easily crushed ; accordingly,
both are placed in almost com-
pletely closed bony cavities, and
are also enveloped by mem-
branes which give them sup-
port. These membranes are
three in number. Externally
is the dura mater, tough and
strong, and composed of con-
nective tissue. The innermost
enveloping membrane of the
cerebro-spinal centre, in imme-
diate contact with the proper
nervous parts, is the pia mater,
less dense and tough than the
dura mater. Covering the out-
side of the pia mater is a layer of
flat cells ; a similar layer lines
the inside of the dura mater,
and these two layers are de-
scribed as the third membrane

Why are brain and spinal cord
placed in bony chambers? How
many membranes also support them?
What is the outside membrane
named? What are its mechanical
properties? Of what is it composed?
Wbat is the pia mater?

286

Ttiti HUMAN BODY.

of the cerebrospinal centre, called the arachnoid. In the
space between the two layers of the arachnoid is a small
quantity of watery cerebrospinal liquid.

The Spinal Cord (Fig. 80) is nearly cylindrical in form,
being, however, a little wider from side to side than dorso-
ventrally, and tapering off at its posterior end. Its aver-
age diameter is about f inch and its length 17 inches.
It weighs 1| ounces. There is no marked limit be-

Fig. 81. — The spinal cord and nerve-roots. A, a small portion of the cord
seen from the ventral side; B, the same seen laterally; C, a cross-section of the
cord; D, the two roots of a spinal nerve; 1, anterior (ventral) fissure; 2, poste-
rior (dorsal) fissure ; 3, surface groove along the line of attachment of the
anterior nerve-roots; 4, line of origin of the posterior roots; 5. anterior root
filaments of a spinal nerve; 6, posterior root filaments; 6', ganglion of the pos-
terior root ; 7, 7', the first two divisions of the nerve-trunk after its formation
by the union of the two roots.

What is the arachnoid? What is the cerebrospinal liquid?
What is the general form of the spinal cord? Its average diame-
ter? Its length? Its weight? How does it connect with the brain?

THE SPINAL CORD AND THE SPINAL NERVES. 287

tween the spinal cord and the brain, the one passing
gradually into the other. In its course the cord presents
two expansions, an upper, 10 (Fig. 80), the cervical en-
largement, reaching from the third cervical to the first
dorsal vertebrae, and a lower or lumbar enlargement, 9,
opposite the last dorsal vertebra?.

Banning along the middle line on both tlic ventral and
the dorsal aspects of the cord are fissures which (C, Fig.
81) nearly divide it into right and left halves.

A transverse section, C, shows that the substance of the
cord is not alike throughout, but that its white superficial
layers envelop a central gray substance arranged somewhat
in the form of a capital EL Each half of the gray matter
is crescent-shaped, and the crescents are turned back to
back and united across the middle line by the gray com-
missure.

The Spinal Nerves. — Thirty-one pairs of spinal nerves
join the spinal cord in the neural canal of the vertebral
column, entering the canal through the intervertebral fora-
mina (p. 32). Each divides in the foramen into a dorsal
and ventral portion, known respectively'as the posterior
and anterior roots of the nerve (6 and 5, Fig. 81), and
these are attached to the sides of the cord. On each pos-
terior root is a spinal ganglion (6', Fig. 81), placed where

What expansions are seen in it? Where is each placed?

How are the right and left halves of the cord separated?

Is the spinal cord alike all through? What are the colors of its
outer and of it? inner portions? What is the form of the gray mat-
ter of the cord as seen on cross-sections? How are the crescents
united?

How many spinal nerves are there? What do they join? How
do they get into the neural canal? Where do they divide? What
are the divisions named? To what are they attached? What is
found, on each posterior root'

2S8

THE HUMAN BODY.

it joins the anterior root to make up the common nerve-
trunk. Immediately after its formation by the mixture of
fibres from both roots, the trunk begins to divide into
branches for the supply of some region of the body.

The Brain (Fig. 82) is far larger than the spinal cord
and more complex in structure. It weighs on the average
about 50 ounces in the adult. The brain consists of three
main masses, each with subsidiary parts, following one an-
other in series from before back, and respectively known
as the fore-brain, mid-brain, and hind-brain. In man
the fore-brain, A, weighing about 44 ounces, is much
larger than all the rest put together and laps over them.

Fig. 82. — Diagram illustrating the general relationships of the parts of the
brain. A, fore-brain; b, mid-brain; B, cerebellum; C, pons Varolii ; D, medulla
oblongata; B, C, and D together constitute the hind-brain.

What becomes of the common trunk formed by the mixture of
the roots?

Point out characters in which the brain differs from the spinal
cord. Wbat is its weight? Of what main divisions is the brain
Composed? Which is the largest division? Its weight?

THE FORE-BRAIN.

289

It is chiefly formed of two large convoluted masses, sepa-
rated from one another by a deep fissure, and known as
the cerebral hemispheres. The great size of these is very
characteristic of the human brain. Beneath each cere-
bral hemisphere is an olfactory lube (I, Fig. 84), incon-
spicuous in man but often larger than the cerebral hemi-
spheres, as in most fishes. The mid brain, b, forms a
connecting isthmus between the two other divisions. The
hind-brain consists of three main parts: on its dorsal side
is the cerebellum, B, Fig. 82; on the under side is the
pons Varolii, C, Fig. 82; and behind is the medulla ob-
longata, D, Fig. 82, which joins the spinal cord.

In nature the main divisions of the brain are not sepa-

Fig. 83.— The brain from the left side. Cb, the cerebral hemispheres forming
the main bulk of the fore-brain; CM, the cerebellum; Mo, the medulla oblon-
gata; P, the pons Varolii; *, the fissure of Sylvius.

By what is the fore-brain chiefly formed? What lies below the
cerebral hemispheres? Are the olfactory lobes ever larger than the
cerebral hemispheres? What does the mid-brain form? Name the
main divisions of the hind-brain? State their relative positions,
What part of the brain joins the spinal cord?

290 THE HUMAN BODY.

rated so much as has been represented in the diagram for
the sake of clearness, but lie close together as represented
in Fig. 83; and the mid- brain is entirely covered in on its
dorsal side. Nearly everywhere the surface of the
brain is folded, the folds, known as the convolutions,
being deeper and more numerous in the brain of man
than in that of the animals nearest allied to him zoologi-
cally.

The brain, like the spinal cord, consists of gray and
white nervous matter, but somewhat differently arranged;
for while the brain, like the cord, contains gray nerve-mat-
ter in its interior, a great part of its surface is also covered
with it. By the external convolutions of the cerebellum
and of the cerebral hemispheres the surface over which this
gray substance is spread is very much increased.

The Cranial Nerves. — Twelve pairs of nerves leave the
skull cavity by apertures in its base; they are known as the
cranial nerves. Most of them spring from the under side
of the brain, which is represented in Fig. 84. The first
pair, or olfactory nerves, are the nerves of smell; they arise
from the under sides of the olfactory lobes, /, and pass out
through the roof of the nose. The second pair, or optic
nerves, II, are the nerves of sight; they spring from the
mid-brain, and, under the name of the optic tracts, run
down to the under side of the fore-brain, where they unite

Is the surface of most of the brain smooth? What are the folds
called? How does a man's brain differ, as regards its convolutions,
from an ape's?

Of what does the brain consist? ITow does tlie arrangement of
white and gray matter in it differ from that of the spinal cord? How
is the surface bn which the gray matter is spread increased?

How many cranial nerves are there? Where do most of them
originate? Name the first pair. Where do they arise? Where do
Uiey pass out? Name the second pair. What are the optic tracts?

THE CRANIAL NERVES.

291

Fig. 84.— The base of the brain. The cerebral hemispheres are seen over-
lapping all the rest. I, olfactory lobes; II, optic tract passing to the optic
commissure from which the optic nerves proceed ; III. the third nerve or motor
oculi; IF, the fourth nerve or patheticus; V, the fifth nerve or trigeminalis;
VI, the sixth nerve or abducuns; VII, the seventh or facial nerve or portio dura;
VIII, the auditory nerve or portio mollis; IX, the ninth or glossopharyngeal;
X, the tenth or pneumogastric or vagus; XI, the spinal accessory; XII, the
hypoglossal; ncl, the first cervical spinal nerve.

to form the optic commissure, from which an optic nerve
proceeds to each eyeball.

All the remaining cranial nerves arise from the hind-
brain. The third pair, III., (motores oculi, or movers of the

What is the optic commissure? Where does each optic nerve go?
How many pairs of cranial nerves arise from the hind- bruin?
JTame the third pair. Whut is their distribution?

292 THE HUMAN BODY.

eyeball,) are distributed to most of the muscles which move
the eyeball and also to that which lifts the upper eyelid.

The fourth pair, IV, (pathetici,) are quite small; each
goes to one muscle of the eyeball.

The fifth pair of cranial nerves, V, (trigeminals,) re-
semble the spinal nerves in having two roots, one of which
possesses a ganglion (the Gasserian ganglion). Beyond
the ganglion the two roots form a common trunk which
divides into three main branches. The first of these, the
ophthalmic, is distributed to the muscles and skin over the
forehead and upper eyelid; and also gives branches to the
mucous membrane lining the nose, and to the integument
over that organ. The second division (superior maxillary
nerve) of the trigeminal gives branches to the skin over the
temple, to the cheek between the eyebrow and the angle of
the mouth, and to the upper teeth; as well as to the mu-
cous membrane of the nose, pharynx, soft palate and roof
of the mouth. The third division {inferior maxillary) is
the largest branch of the trigeminal. It is distributed to
the side of the head and the external ear, the lower lip
and lower part of the face, the mucous membrane of the
mouth and the anterior two thirds of the tongue, the lower
teeth, the salivary glands, and the muscles which move the
lower jaw in mastication.

The sixth pair of cranial nerves, VI, (abduccntes,) arc
distributed each to one muscle of the eyeball on its own
side.

What is the distribution of the fourth pair?

Name the fifth pair of cranial nerves. How do they resemble the
spinal nerves? What is the ganglion on one root called? Into how
many main branches does the common trunk divide? Name the first
branch. Slate its distribution. The second branch. Its distribu
tion. The third main branch. Its distribution.

Name the sixth pair of cranial nerves, Where do they go?

NERVOUS SYSTEM. 293

The seventh pair (facial nerves), VII, are distributed to
most of the muscles of the face and scalp.

The eighth pair (auditory nerves), VIII, are the nerves
of hearing, and are distributed to the inner part of the ear.

The ninth pair of cranial nerves (glosso-phar yngeal),
IX, are distributed chiefly to tongue and pharynx.

The tenth pair (pneumogastric nerves or vagi), X, give
branches to the pharynx, gullet and stomach, the larynx,
windpipe and lungs, and to the heart. The vagi run far-
ther through the body than any other cranial nerves.

The eleventh pair (spinal accessory nerves), XI, do not
arise mainly from the brain, but from the spinal cord by a
number of roots attached to its upper portion, between the
anterior and posterior roots of the proper spinal nerves.
Each enters the skull cavity alongside of the spinal cord
and, getting a few filaments from the medulla oblongata,
passes out by the same aperture as the glosso-pharyngeal
and pneumogastric nerves. Outside the skull the spinal
accessory divides into two branches, one of which joins the
pneumogastric trunk, while the other is distributed to
muscles about the shoulders.

The twelfth pair of cranial nerves (hypoylossi), XII, are
distributed mainly to the muscles of the tongue.

The Sympathetic Nervous System. — The ganglia which
form the main centres of the sympathetic nervous system

Name the seventh pair of cranial nerves. To what parts are
they distributed?

What is the eighth pair called? What are their functions? Where
do they end?

Name the ninth pair. State their distribution.

Name the tenth pair. State their distribution.

Name the eleventh pair. Where do they arise? How do they
get into the brain-case? With what nerves do they leave the brain-
case? State their distribution.

Name the twelfth pair of cranial nerves. State their distribution..

294 THE HUMAN BODY.

lie in two rows (s, Fig. 1, and sy, Fig. 2), one on each side
of the bodies of the vertebrae. Each ganglion is united by a
nerve-trunk with the one in front of it and the one behind it,
and so two chains are formed reaching from the base of the
skull to the coccyx. In the trunk region these chains lie in the
ventral cavity, their relative pDsition in which is indicated
by the dots sy in the diagrammatic transverse section repre-
sented on p. 9 in Fig. 2.

Each sympathetic ganglion is united by branches to
neighboring spinal nerves, and near the skull to various
cranial nerves also; from the ganglia and their uniting cords
arise numerous trunks, which in the thorax and abdomen
form networks, from which nerves are given off to the or-
gans situated in those cavities. Many sympathetic nerves
finally end in the walls of the blood-vessels of various or-
gans. To the naked eye they are commonly grayer in color
than the cerebro-spinal nerves.

By means of the junctions between the cranial and spinal
nerves and the sympathetic system the brain is enabled to
control the parts supplied by the sympathetic system.

The Three Kinds of Nerve Tissue. — The microscope
shows that the nervous organs contain tissues peculiar to
themselves, known as nerve-fibres and nerve-cells. The

How are the ganglia of the sympathetic system arranged?

How is eacli united to others? How far through the body do
the chains of sympathetic ganglia extend? Where are the sym-
pathetic chains situated in the trunk of the body?

How are the sympathetic ganglia united with spinal and cranial
nerves? What arise from the ganglia? What do they form iu the
trunk region of the body? Where do many sympathetic nerve-
fibres end? How do sympathetic nerves differ to the unaided eye
from spinal or cerebral nerves? How is the brain enabled to control
the parts supplied by the sympathetic system?

How many kinds of nerve-tissue are there? "What are the pecul-
iar nerve-tissues called ?

NMVB-FiB&m.

295

Cells are found in the centres only; while the fibres, of.
which there are two main varieties known as the zohite and
the gray, are found in both trunks and centres; the white
variety predominating in the cerebrospinal nerves and in
the white substance of the centres, and the gray in the sym
pathetic trunks and the gray portions of the central organs.
White Nerve-Fibres consist of extremely delicate threads,
about s-gVtf inch in diameter, but frequently of a length

Fig. 85.

Fig. 86.

Fig. 85.— White nerve-fibres soon after removal from the body and when they
have acquired their double contour.

Fig. 86.— Diagram illustrating the structure of a white or medullated nerve-
M>re. I, 1, primitive sheath; 2, 2, medullary sheath; 3, axis cylinder.

"Where only do we find nerve-cells? Where are nerve-fibres
found? How many main kinds of nerve-fibres are there? Name
them. Where do the white nerve-fibres predominate? Where the
gray?

Describe white nerve-fibres.

296 THE HUMAN BODY.

which is in proportion very great. Each is continuous
from a nerve-centre to the region in which it ends, so
that the fibres, e.g., which pass out from the spinal cord
and run on to the skin of the toes, are three to four
feet long. If a perfectly fresh white nerve-fibre he exam-
ined with the microscope it presents the appearance of a
homogeneous glassy thread ; but soon it acquires a charac-
teristic double border (Fig. 85) from the coagulation of a
portion of its substance, as a result of which three layers
are brought into view. Outside is a thin transparent en-
velope (1, Fig. 86) called the primitive sheath; inside this
is a fatty substance, 2, forming the medullary sheath (the
coagulation of which gives the fibre its double border), and
in the centre is a core, the axis cylinder, 3, which is the es-
sential part of the fibre, since near its ending the primitive
and medullary sheaths are frequently absent. At intervals
of about -£j inch along the fibre are found nuclei. These
are indications of the primitive cells which by their elon-
gation, fusion, and other modifications have built up the
nerve-fibre. In the course of a nerve-trunk its fibres rarely
divide; when a branch is given off some fibres merely sepa-
rate from the rest, much as a skein of silk might be sepa-
rated at one end into smaller bundles containing fewer
threads.

Gray Nerve-Fibres have no medullary sheath, and con-
sist merely of an axis cylinder and primitive sheath. Gray

Is each nerve-fibre continuous from centre to end? Point out
nerve-fibres three or four feet long. What is the appearance under
the microscope of a quite fresh white nerve-fibre? How does it soon
alter? Name the layers then seen and state their relative positions.
Which is the essential part of the nerve-fibre? Give a reason for
your statement. What are found at intervals along the nerve-fibre?
What do they indicate?

What occurs when a nerve-trunk branches?

NBRVE-CELLB.

297

fibres are especially abundant in the sympathetic trunks;
and they alone are found in the olfactory nerve.

Nerve-Cells. — As far as our knowledge at present goes,
all nerve -fibres begin as branches of nerve-cells.

Fig. 87.— Different forms of nerve-cells from the spinal cord. 1, a cell from
the anterior part of the gray matter, and believed to be connected with a motor
nerve-fibre; 2. a cell from the posterior part of the gray matter, believed to be
connected with sensory fibres.

At 1, Pig. 87, is shown a nerve-cell such as may be
found in the anterior part of the gray matter of the spinal
cord. It consists of the cell body, or cell protoplasm, con-
taining a large nucleus, in which is a nucleolus. From the

Describe a gray nerve-fibre. Where are they especially numerous?
Name a cranial nerve that consists entirely of them.
How do nerve-fibres begin ?
Of what does a nerve-cell consist ?

298 THE HUMAN BODY.

body of the cell arise several branches, the great majority
of which rapidly subdivide. One process of the cell (a),
although giving off several very fine branches, retains its
individuality, and is continued as the axis cylinder of a
nerve-fibre in an anterior spinal root. At 2, in Fig. 87, is
represented a nerve- cell from the posterior part of the gray
matter of the spinal cord. It also has an axis-cylinder
process, differing somewhat in its way of branching from 1,
but probably ultimately giving rise to one or more cylinder-
axes of sensory nerve-fibres. Cells such as those represented
in Fig. 87 are found also in many parts of the brain.

The Structure of Nerve-Centres. — These consist of white
and gray nerve-fibres, of nerve-cells, and of connective tis-
sue and blood-vessels, arranged together in different ways
in the different centres.

What arise from the protoplasm of a nerve-cell? What becomes
of most of the brandies? How does one branch of some nerve-
cells of the spinal cord differ from the remainder? As regards this
branch, how do otlier nerve-cells differ from the above?

Of what do nerve-centres consist?

APPENDIX TO CHAPTER XIX.

1. The co-operation of the parts of the body may be illustrated as
follows:

a. Feign a blow at a person's eye; the lids will close involuntarily,
even if he be told beforehand that he is not to be actually struck.

b. Count a boy's pulse and breathing while he is sitting quietly,
then let him run a hundred yards at full speed, and immediately
afterwards again count pulse and breathing movements. Both will
be found accelerated; the breathing, to carry off from the blood the
carbon dioxide given it by the working muscles, and to bring in new
oxygen to replace the large amount used by the working muscles;
the heart-beat, to renew more rapidly the blood-flow through the
muscles.

c. Tickle the inside of the nose with a feather. This, in itself.

APPENDIX. CHAPTER XIX. 299

does not interfere with the breathing muscles; but their action will
be almost at once so changed as to produce a sneeze, tending to clear
and protect the nose.

2. Kill a frog with ether (note, p. 68); open its abdomen and re-
move the viscera. At the back of the abdominal cavity will be seen
a bundle of white cords (nerve-trunks) passing back to each leg.
They soon unite into one main stem (the sciatic nerve), which may
be easily dissected along its course until it ends in fine branches in
the hind limb.

3. Kill a frog and expose the origin of the sciatic nerve as above.
With stout scissors then cut away bit by bit, and very carefully, the
bodies of the vertebrae (which will be seen projecting in the middle
line at the back of the abdominal cavity) until the neural canal is
laid open and the spinal cord exposed. You will probably fail the
first time, but on the second attempt succeed in doing this without
cutting the nerve trunks as they pass between the vertebrae to join
the spinal cord. On the specimen thus prepared the origin of the
nerves from the spinal cord, and their division into anterior and pos-
terior (ventral and dorsal) roots before they join the cord can be
demonstrated, also the ganglionic enlargements on the posterior
roots.

4. The general form, the cervical and lumbar enlargements, etc.,
of the spinal cord may be shown on a frog. Having killed the ani-
mal, remove the skin and muscles on the dorsal side of the spinal
column. With great care cut away the upper two thirds of the
neural arches of the vertebrae. Then remove the upper half of the
skull cavity. Gently raising piece by piece the exposed brain and
spinal cord, divide the nerves which spring from them and lift out
the whole cerebro-spinal centre and place it in alcohol for twenty-
four hours. Demonstrate the origin of nerves from both brain and
cord, the union of the brain and cord, etc. etc. The specimen may
be preserved in alcohol for future use.

5. A frog's brain differs in many important points from that of
man, as in the very small cerebellum, the comparatively small cere-
bral hemispheres, the comparatively large mid-brain and the ab-
sence of convolutions. To demonstrate the main anatomical fea-
tures of the brain that of a mammal is necessary.

a. Obtain a fresh calf's or sheep's head from a butcher. Dissect
away the skin and muscles covering the cranium. Then with a
small saw very carefully divide the bones in a circular direction,
so as to cut off those of the crown of the head. Next carefully
remove the loosened bones of the top of t lie skull, tearing them away

300 THE HUMAN BODY.

from the dura mater lining them. So far the specimen may he pre-
pared previous to the meeting of the class.

b. To the class demonstrate the tough dura mater enveloping the
brain; then cut it away, noting the processes which it sends between
the two cerebral hemispheres and between cerebellum and cerebral
hemispheres. Then cut the membrane away.

c. Note its glistening inner surface, due to the arachnoid lining
it; the pia mater full of blood-vessels and closely attached to the
brain; the glistening arachnoid layer covering the exterior of the
pia mater. Then put the specimen aside in alcohol for a day or
two. This will harden the brain substance.

d. When the brain has become somewhat hardened dissect away
the pia mater on one side. Show the cerebral hemispheres and
their surface convolutions, the cerebellum and its foldings, the
medulla oblongata beneath the cerebellum.

e. With bone forceps cut away the remainder of the sides and roof
of the skull. The'n raise the brain in front, and cutting through the
vessels, nerves, etc., which attach it to the base of the skull, en-
tirely remove it from the skull cavity. On it demonstrate the cere-
bral hemispheres (which overlap the cerebellum much less than
in man"), cerebellum, mid-brain, etc.

/. Attached to the base of the brain will be found the stumps of
some of the cranial nerves, though most of these will have been en-
tirely torn off unless the dissector has some technical skill. The
optic commissure, with the optic tracts leading to it and the stumps
of the optic nerves leading from it, will almost certainly be found.

g. Make sections across the brain in different directions to see the
gray matter spread over most of its surface, and the nodules of gray
matter imbedded in its interior.

CHAPTER XX.

THE GENERAL PHYSIOLOGY OF THE NERVOUS
SYSTEM.

The Properties of the Nervous System. — If one's finger
unexpectedly touches a very hot object, pain is felt and the
hand is suddenly snatched away ; that is to say, sensation
is aroused and certain muscles arc caused to contract. If,
however, the nerves passing from the arm to the spinal
cord have been divided, or if they have been rendered in-
capable of activity by disease, no such results follow. Pain
is not then felt on touching the hot body nor does any
movement of the limb occur ; even more, under such cir-
cumstances the strongest effort of the Will of the individual
is unable to cause any movement of his hand. If, again,
the nerves of the limb have connection with the spinal
cord, but parts of the cord are injured higher up, between
the brain and the point of junction of the nerves of the
arm with the cord, then contact with the hot object may
cause the hand to be snatched away, but no pain or other
sensation due to the contact will be felt, nor can the will
act upon the muscles of the arm, either to make them con-
tract or to prevent their contraction. From the compari-
son of what happens in such cases (which have been observed
again and again upon wounded or diseased persons), with
what occurs in the natural condition of things, several im-
portant conclusions may be reached:

What usually results when a hot object is unexpectedly touched?
Under what circumstances do these results not occur? Can the Will
cause movement of the muscles of an arm whose nerves have been
cut? When the arm-nerves are intact but the spinal cord is injured
near the brain, what happens on touching a hot body?

302 THE HUMAN BODY.

1. TJie feeling of pain does not reside in the burned part
itself; for it is found that applying a hot object to the skin
or pinching it arouses no sensation if the nerves between
the skin and the nerve-centres be diseased or divided.

2. The hot object when the nerves are intact originates
some change which, propagated along the nerves, excites a
condition of the nerve-centres accompanied by a feeling, in
this particular case a painful one. This is clear from the
fact that loss of sensation immediately follows division of
the nerves of the limb, but does not immediately follow the
injury of any of its other parts. The change propagated
along the nerve-trunks and causing them to excite the
nerve-centres is called a nervous impulse.

3. When a nerve in the shin is excited it does not direct-
ly call forth muscular contractions; for if so, touching the
hot object would cause the limb to be moved even when
the nerve had been divided high up in the arm, while, as a
matter of observation and experiment, we find that no such
result follows if the nerve-fibres have been cut in any part
of their course from the excited, or, in physiological phrase,
the stimulated, part to the spinal marrow. It is therefore
through the nerve-centres that the nervous impulse trans-
mitted from the excited part of the skin is " reflected" or
sent bach to act upon the muscles.

4. The preceding fact makes it probable that nerve-fibres

How do we know that our feeling of pain does not reside in a
burned or pinched part of the skin?

What does a touched hot ohject originate when the nerves are
healthy? What is a "nervous impulse"?

Does a skin-nerve when excited produce directly a muscular
movement? Give reason for your answer. What happens to the
nervous impulse transmitted from the excited part of the skin?

Is it probable that other nerve-fibres than those arising from the
Skin are. connected with the nerve-centres ?

FUNCTIONS OF NERVES AND NERVE-CENTRES. 303

pass from the centre to muscles as ivell as from the skin to
the centre. This is confirmed when we find that if the
nerves of the limb be divided the Will is unable to act
upon its muscles, showing that these are excited to con-
tract through their nerves. That the nerve-fibres con-
cerned in arousing sensation and muscular contractions are
distinct, is shown also by cases of disease in which the
sensibility of the limb is lost while the power of voluntarily
moving it remains; and by other cases in which the op-
posite is seen, objects touching the hand being felt, while it
cannot be moved by the Will. We conclude therefore that
certain nerve-fibres when stimulated transmit something (a
nervous impulse) to the centres, and that these, when ex-
cited by the nervous impulse conveyed to them, may radiate
impulses through other nerve-fibres to distant parts, the
centre serving as a connecting link between the fibres whicJi
carry impulses from without in, and those which convey
them from within out.

5. Further we conclude that the spinal cord can act as
an intermediary between the fibres carrying in nervous im-
pulses and those carrying them out, but that sensations can-
not be aroused by impulses reaching the spinal cord only,
nor has the Will its seat there ; volition and consciousness
are dependent upon states of the brain. This follows from
the unconscious movements of the limb which follow stimu-
lation of its skin after such injury to the spinal cord as
prevents the transmission of nervous impulses farther on;

Point out a fact tending to prove that the muscles are normally
excited to contraction through their nerves. State facts showing
that the nerves of sensation and those governing the muscles are
distinct. What purpose does the nerve-centre serve?

What further conclusions may we draw from the facts already
considered in this chapter? Give reasons for your answer.

304 THE HUMAN BODY.

from the absence, in such cases, of sensation in the part
whose nerves have been injured; and from the loss of the
power of voluntarily causing its muscles to contract.

6. Finally, we conclude that the spinal cord in addition
to being a centre for unconscious movements serves also to
I ran sin 1 1 nervous impulses to and from the brain; this is
confirmed by the histological observation that in addition
to the nerve-cells, which are the characteristic constituents
of nerve-centres, it contains the simply conductive nerve-
fibres, many of which pass on to the brain. In other words
the spinal cord, besides containing fibres which enter it
from, and pass from it to, the skin and muscles, contains
many fibres which unite it to other centres.

The Functions of Nerve-Centres and Nerve-Trunks. —
From what has been stated in the previous paragraphs it is
clear that we may distinctly separate the nerve-trunks from
the nerve-centres. The fibres serve simply to convey im-
pulses either from without to a centre or in the opposite
direction, while the centres conduct and do much more.
They take heed, some consciously and some unconsciously,
of the impulses carried to them by the ingoing nerve-fibres,
and then send out impulses along outgoing nerve-fibres;
these impulses call into action the proper organs for the
safety and well-being of the body in general. The centres
do not merely transmit and reflect, they also co-ordinate.

Classification of Nerve-Fibres. — The nerve-fibres of the
body fall into two great groups corresponding to those

For what is the spinal cord a centre? What else does it do?
How does histology support the belief that the spinal cord is both
a nerve-centre and a conductor of nervous impulses?

What is the function of nerve-fibres? What is done by nerve-
centres in addition to conducting nerve-impulses?

Into what main groups may nerve fibres be classified?

PSYCHIC NERVE-CENTRES. 305

which carry impulses to the centres and those which carry
them out from the centres. The former are called afferent
or sensory fibres and the latter efferent or mot or.

The posterior roots of the spinal nerves contain only
afferent, the anterior only efferent, nerve-fibres.

Classification of Nerve-Centres. — Nerve-centres are of
three kinds: (1) Automatic centres, which, without being
excited by the action of any sensory nerve or by the Will,
originate in themselves stimuli for efferent nerves. (2) Re-
flex centres, which act quite independently of the Will and
of consciousness, but are aroused by the action of a nervous
impulse conveyed to them by a sensory nerve, and in turn
excite one or more efferent nerves. (3) Conscious or psy-
chic centres, whose activity, however aroused, is accom-
panied by some kind of mental activity; as feeling, or
willing, or reasoning.

The Psychic Nerve-Centres lie in the fore-brain, and
mainly in the gray matter of its convolutions. If the cere-
bral hemispheres of a pigeon be destroyed and all the rest of
its body left intact, the animal can still control its muscles
so as to execute many movements, but it gives no sign of
consciousness. Left to itself it will stand still until it dies;
corn and drink placed before it arouse in it no idea of eat-
ing; it will die of starvation surrounded by food. Yet it
can move all its muscles, and if food is placed in its mouth
will swallow it. If its tail be pulled it will walk forward;

What fibres are found in the posterior spinal nerve-roots? What
in the anterior?

Name the main varieties of nerve-centres. What is done by
automatic centres? What by reflex? What is the characteristic
property of the psychic centres?

Where are the psychic nerve-centres located? What may be ob-
served in a pigeon whose cerebral hemispheres have been destroyed?

306 THE HUMAN BODY.

if it be put on its back it will get on its feet; if it be
thrown into the air it will fly until it strikes against some-
thing on which it can alight; if its feathers be ruffled it
will smooth them with its bill.

The difference between a pigeon in this state and an
uninjured pigeon lies in the absence of the power of form-
ing ideas or initiating movements. It has no thoughts, no
ideas, no Will. We cannot predict what an uninjured
pigeon will do under given circumstances: we can say be-
forehand what the pigeon with no cerebral hemispheres
will do; it is a mere machine or instrument, which can be
played upon. In such a pigeon the excitation of any given
sensory nerve or nerves excites unconscious nerve-centres
which set certain muscles at work, and the result of any
one stimulus is always the same invariable movement.
The animal exhibits no evidence of possessing any con-
sciousness ; it has no desires or emotions ; it is like a piano
which while untouched is silent, but when a given key is
struck emits always the same note ; so the pigeon without
its cerebral hemispheres stays quiet while left to itself, and
responds to any one given stimulus always in one invari-
able and predicable way.

Functions of the Cerebellum. — The cerebellum is the
great centre for co-ordinating the muscles of locomotion.
Each step we take implies the action of many muscles and
many thousands of muscular fibres; the actions of all must
be very precisely graded as to amount, and very accurately
arranged as to proper sequence. We do not, however, con-
sciously think about the muscles to be used in every move-
How does such a pigeon differ from an uninjured pigeon?
What is the main function of the cerebellum? AVliat is implied
in each step that we take?

FUNCTIONS OF THE CEREBELLUM. 307

ment of each step; if we do think at all about our walking
the cerebral hemispheres simply send a message to the cere-
bellum, and leave it (with the aid of the spinal cord) to
regulate all the details. When we walk without thinking
about it, the contact of the foot with the ground stimulates
sensory nerves of the sole, which then stimulate the locomotor
centres; these centres excite in proper order the nerves
which control the muscles; and the co-ordinated action of
the muscles produces the next step.

A pigeon with its cerebellum destroyed and all the rest
of its nervous system intact stands unsteadily, staggers when
it attempts to walk, and flutters uselessly when thrown
into the air. But, having its cerebrum, it wills and feels;
it does not stand quiet until touched; it initiates movements
when left to itself, though it cannot perform them properly.
It wills, and feels, and thinks, but cannot co-ordinate the
action of its muscles except for some simple movements,
regulated by the medulla oblongata or the spinal cord.

Automatic Nerve-Centres send out nervous impulses
through efferent nerves without waiting to be excited by
afferent nerves or by the Will. The most conspicuous are
the small nerve-centres buried in the heart, which excite its
beat even when it is separated from all the rest of the body.
Auother automatic centre is that which lies in the medulla
oblongata and stimulates the nerves which control the

Do we have to think about using each muscle concerned in walk-
ing? What happens when we think about our walking? What when
we walk without thinking about it ?

What do we see in a pigeon whose cerebellum has been destroyed?
Does it initiate movements? Does it execute them well? What is
its condition as regards willing, feeling, and thinking? What can
it not do?

What is done by automatic nerve-centres? Give examples of au-
tomatic nerve-centres.

308 THE HUMAN BODY.

muscles of respiration. When this centre is cut off from
all sensory nerves it still acts, and its activity goes on even
against the Will. We can voluntarily hold the breath for
a short time, but not long enough to kill ourselves by suffo-
cation. Although automatic nerve-centres act indepen-
dently of impulses carried to them by nerve-trunks, they
are nevertheless usually more or less subject to control by
them. For example, stimulating the branch of the pneu-
mogastric nerve (p. 293) which goes to the automatic heart
nerve-centres slows the beat of the organ; and a dash of
cold water on the skin makes us draw a deep breath.

Reflex Centres are aroused to activity by nervous im-
pulses conveyed to them through afferent nerves: they
then excite efferent nerves and produce a movement or a
secretion. Such nerve-centres do all the routine of the ad-
ministrative control of the organs of the body, without
troubling the psychic centres. They frequently act with-
out the intervention of consciousness at all, and often in
spite of the Will. When sugar is placed in the mouth it
excites its sensory nerves ; these stimulate a centre from
which nerves go to the salivary glands, and these nerves,
aroused by the centre, make the gland-cells secrete and pour
saliva into the mouth; no effort of the Will can stop this
reflex action, so called because a nervous impulse sent to a
centre by one set of nerve-fibres is turned back or reflected
from it along another set. When a morsel of food enters
the pharynx it excites the sensory nerves of the mucous

Can a man commit suicide by holding his breath? Are the
automatic centres entirely free from control ? Illustrate.

How are reflex centres excited ? What is the consequence of
their stimulation ? What sort of work in the body is executed by
reflex nerve-centres? Are we always conscious of their action ? Can
the Will always control them ? What happens when sugar is placed
on the tongue? Why is it called a "reflex action "?

USES OF AUTOMATIC NERVE-CENTRES. 309

membrane; these arouse a reflex centre of swallowing,
which sends out nervous impulses to the swallowing mus-
cles, and the food is sent on into the gullet whether we wish
it or not. Sneezing when something irritates the mucous
membrane of the nose, and coughing where some foreign
mass enters the larynx, are other instances of reflex actions.

The Use of Automatic and Reflex Centres is to relieve
the thinking centres of the vast amount of work which
would be thrown upon them if every action of the body
each moment had to be planned and willed. Were not the
unconscious regulating nerve-centres always at work the
mind would be overburdened by the mass of business which
it would have to look after every minute. No time would
be left for intellectual development if we had to think
about and to will each heart-beat, each inspiration and ex-
piration, and the swallowing of each mouthful of food.
Moreover, during sleep, so necessary for the rest and repair
of the psychic centres, the automatic and reflex centres
carry on the actions essential for the nutrition of the body
and the maintenance of life. If we had to reason concern-
ing each beat of the heart and decide if it was time for it
to occur and what force it should have, and then to make up
our minds whether to will it or not, we could never sleep.

Habits are Acquired Reflex Actions, distinguished from
primary or those born with us, such as sneezing, coughing,
and winking. Every time a nerve-centre acts in a given way
it tends to more easily act in that manner again; as a result

Give other examples of reflex actions.

What is the main use of the automatic and reflex nerve-centres?
What would result if the unconscious nerve-centres were not always
at work?

What are habits? What happens when a nerve-centre acts in a
given manner? What is the result?

310 THE HUMAN BODY.

many actions which are at first only performed with
trouble and thought are after a time executed easily and
unconsciously. The act of walking is a good instance; each
of us in infancy learned to walk with much pains and care,
thinking about each step. But the more we walked tbe
closer became ingrained in the nervous system the connec-
tion between the stimulation of nerves in the sole when a
foot touched the ground, and the sending out by the reflex
nerve-centres with which they were in connection, of
impulses to those muscles which had to make the next step.
At last the contact of the foot with the ground, stimu-
lating some sensory nerves, acts so readily on the " nerve-
centres of walking" that the cerebral hemispheres need
take no heed about it: we walk ahead while thinking
of something else. In other words we have acquired a
reflex action not born in us. Other instances will readily
come to mind: as the difficulty with which we learned to
ride, or swim, or skate, thinking about and willing each
movement; and the ease with which we do all these things
after a little practice. The trained lower nerve-centres then
do all the co-ordinating work and the Will has no more need
to trouble about the matter. A habit simply means that the
unconscious parts of the nervous system have been trained
to do certain things under given conditions, and can only be
restrained from doing them by a special effort of the con-
scious Will. A practised rider will keep his seat uncon-
sciously under all ordinary circumstances, and can only
fall off his horse by taking some trouble to do so, by will-
ing it in fact; an unskilled rider, on the other hand, must
exert all his attention to avoid falling. So with what in

Illustrate by the act of walking. Give other examples. What
does a "formed habit" really mean? Illustrate.

HYGIENE OF TEE BRAIN. 311

every-day language are called " habits": once we have repeat-
ed an action so often that our bodies almost unconsciously
do it, it becomes a habit, and needs special exercise of Will
to deviate from it. TVe thus find, in the tendency of the
nervous system to go on doing what it has been trained to
do, a physiological reason for endeavoring to form good
and to avoid bad habits of whatever sort, physiological,
business, social, or moral. Every thought, every action,
leaves in the nervous system its result for good or ill. The
more often we yield to temptation the stronger effort of
the Will is required to resist it. The knowledge that every
weak yielding degrades our nerve-organs and leaves its trail
in the brain, through whose action man is the "para-
gon of animals," while every resistance makes less close the
bond between the feeling and the act for all future time,
ought surely to "give us pause"; on the other hand, every
resistance of temptation helps to make subsequent resist-
ance easier.

Hygiene of the Brain. — The brain, like the muscles, is
improved and strengthened by exercise and injured by over-
work or idleness; and just as a man may specially develop
one set of muscles and neglect the rest until they degenerate,
so he may do with his brain; developing one set of intel-
lectual faculties and leaving the rest to lie fallow until, at
last, he almost loses the power of using them at all. The
fierceness of the battle of life nowadays especially tends to
produce such lopsided mental development. How often

What happens when we have very frequently repeated an action?
Point out why it is desirable, even on physiological grounds, to form
good habits. How does every thought or act influence the nervous
system? "What is the consequence of yielding to temptation? "What
of resisting it?

312 THE HUMAN BODY.

does one meet the business man, so absorbed in money-
getting that he has lost all power of appreciating any but
the lower sensuous pleasures; the intellectual joys of art,
science, and literature have no charm for him; he is a mere
money-making machine. One, also, not unfrequently
meets the scientific man with no apj^reciation of art or
literature; and literary men utterly incapable of sympathy
with science. A good collegiate education in early life,
on a broad basis of mathematics, literature, and natural
science, is the best security against such deformed mental
growth.

APPENDIX TO CHAPTER XX.

1. Place a frog on the table; note that it sits up and breathes
(as shown by the movements of its throat), and either stays still or
jumps around as it pleases; i.e., it has a Will of its own, and its actions
cannot be predicted.

2. Etherize two frogs (note, p. 68), removing them from the ether-
ized water the moment they become insensible. With strong sharp
scissors cut off from one frog (a) all the head in front of the anterior
margins of the tympanic membranes: in the other frog (b) remove
the head along a line joining the posterior borders of the tympanic
membranes. Place both frogs aside on a dish containing a little
water for half an hour. The quantity of water should be such that
while keeping the frogs moist it will not reach to the wounds.

3. The frog (a) which has lost its cerebral hemispheres, but re-
tained its mid brain, cerebellum, and medulla oblongata, will be
found after the above-stated time sitting up in a natural position, and
breathing. Left to itself it will, however, never walk or jump; it
shows no sign of possessing a will. Its heart continues to beat and
its respiratory muscles to contract, but left alone it stays where it is.
Turned upon its back it will regain its feet; and put into water it
will swim: its muscles, and the nerves controlling them, are, there-
fore, quite able to act. The animal stays still not because the parts of
its body necessary to produce movements are injured, but because it
can no longer will a movemeut. Such a frog shows very well the de-
pendence of volition upon the presence of the cerebral hemispheres.

APPENDIX. CHAPTER XX. 313

4. The frog (b) will have had its whole brain removed. Its heart
will continue to beat, but its breathing movements will cease, be-
cause the respiratory centre, which lies in the medulla oblongata, has
been cut away. It will also lie down squat, instead of sitting up
like a normal frog, because its most important muscle co-ordinating
centres have been removed with the mid-brain and cerebellum. Left
to itself the animal will, within half an hour of the removal of the
head, pull up its hind legs into their natural position, but after this
it will make no movement. It has no volition.

5. Such a frog can, however, perform many co-ordinated reflex
actions, which may be illustrated as follows: {a) Pinch a toe; it will
be pulled away, (b) Soak some blotting-paper in vinegar, and
then cut the paper into small pieces about £ inch square. Put these
bits of paper on different regions of the frog's skin, dipping the ani-
mal in clean wTater after each application, to wash away the vinegar.
It will be found that tbe brainless creature moves its limbs so as to
wipe away the acid paper placed on its skin. The frog without its
brain has no Will and no consciousness; but its spinal cord when ex-
cited by afferent nerves, whose ends the vinegar stimulates, excites
in turn efferent nerves which stimulate muscles, wrhose contrac-
tion produces a movement calculated to rub away the irritating
object.

6. Now run a stout pin down the frog's neural canal so as to de-
stroy its spinal cord. It will be found that no subsequent pinchiugof
the creature or putting of vinegar on its skin causes any movement.
Its muscles and nerve-trunks are intact, but the spinal reflex centre,
which in the previous experiments was excited by afferent nerves,
and then in turn stimulated efferent nerves, is destroyed. The heart
continues to beat, on account of the automatic nerve-centres in it;
but no voluntary and no reflex actions are exhibited by the animal.

7. The nerve-trunks and the muscles are, however, still active.
Turn the frog on its back and carefully expose (p. 299) the origins of
the sciatic nerves. On pinching these, the muscles of the leg will be
seen to contract. The irritation of the nerve by the pinch starts in
it a nervous impulse which travels down the nerve -branches to the
muscles.

CHAPTER XXI.

THE SENSES.

Common Sensation and Special Senses. — Changes in
many parts of our bodies are accompanied or followed by
states of consciousness which we call sensations. All
such parts (sensitive ]ja?'ts) are in connection, direct or in-
direct, with the brain by sensory nerve-fibres. Since all feel-
ing is lost in any region of the body when this connecting
path is severed, it is clear that all sensations, whatever their
primary exciting cause, are finally dependent on conditions
of the brain. Since all nerves lie within the body as circum-
scribed by the skin, one might be inclined to suppose that the
cause of all sensations would appear to be within our bodies
themselves; that the thing felt would be recognized as a
modification of some portion of the person feeling. This is
the case with regard to many sensations: a headache, tooth-
ache, or earache gives us no idea of any external object ; it
merely suggests to each one a particular state of a sensitive
portion of himself. As regards many sensations this is not
so; they suggest to us external causes, to properties of which,
and not to states of our bodies, we ascribe them ; and so they
lead us to the conception of an external universe in which we
live. A knife laid on the skin produces changes in it which

With what are all sensitive parts of the body in connection ? By
what nerve-fibres? How do we know that all sensations finally de-
pend on the brain?

Why might we suppose that the causes of all sensations would
seem to lie within the body? Name sensations merely suggesting
to us a state of the body itself. What do some other sensations sug-
gest to us? Illustrate.

COMMON SENSATIONS. 315

lead us to think not of a state of the skin, but of proper-
ties of some object outside the skin; we believe Ave feel a
cold heavy hard thing which is not the skin. We have,
however, no sensory nerves going into the knife and inform-
ing us directly of its condition; what we really feel are the
modifications of the body produced by the knife, although
we irresistibly think of them as properties of the knife — of
some object that is no part of the body. Let now the knife
cut through the skin; we feel no more knife, but ex-
perience pain, which we think of as a condition of our-
selves. "We do not say the knife is painful, but that the
finger is, and yet we have, so far as sensation goes, as much
reason to call the knife painful as cold. Applied one way
it produced local changes in the skin arousing a sensation of
cold, and in another local changes causinga sensation of pain.
Nevertheless in the one case we speak of the cold as being
in the knife, and in the other of the pain as being in the
finger.

Sensitive parts, such as the surface of the skin, through
which we get, or believe we get, information about outer
things, are of far more intellectual value to us than sensi-
tive parts, such as the subcutaneous tissue into which the
knife may cut, which only give us sensations referred to
conditions of our own bodies. The former are called Organs
of Special Sense ; the latter are parts endowed with Common
Sensation.

Common Sensations are quite numerous ; for example,
pain, hunger, nausea, thirst, satiety, and fatigue.

"What is meant by "organs of some special sense"? What by
parts endowed with common sensation?
Name some common sensations.

316 THE HUMAN BODY.

Hunger and Thirst. — These sensations regulate the tak-
ing of food. Local conditions play a part in their produc-
tion, but general states of the body are also concerned.

Hunger in its first stages is due to a condition of the
gastric mucous membrane which comes on when the stom-
ach has been empty some time; it may then be tempo-
rarily stilled by filling the stomach with indigestible sub-
stances. But soon the feeling comes back intensified and
can only be allayed by the ingestion of nutritive materials;
provided these are absorbed and reach the blood their mode
of entry is unessential; hunger may be stayed by injections
of food into the intestine as completely as by filling the
stomach with it.

Similarly, thirst maybe temporarily relieved by moisten-
ing the throat without swallowing, but then soon returns ;
while it may be permanently relieved by water injections
into the veins, without wetting the throat at all.

Both sensations depend in part on local conditions
of sensory nerves, but may be more powerfully excited
by poverty of the blood in foods or water ; this deficiency
directly stimulates the hunger and thirst centres of the
brain.

The Special Senses are commonly described as five in
number, but there are at least six; namely, sight, hearing,
touch, the temperature sense, smell, and taste.

To what is the first stage of hunger due? How may it be tempo-
rarily stayed? Need food enter the stomach in order to alleviate
hunger?

How may thirst be temporarily relieved? How permanently
without swallowing water? On what do the sensations of hunger
and thirst in part depend? How may they be more powerfully ex-
cited ? Enumerate the special seuses.

BlGiit. 317

Tho Visual Apparatus consists of nervous tissues immedi-
ately concerned in giving rise to sensations, supported,
protected, and nourished by other parts. Its essential parts
are, (1) the retina, a thin membrane lying in the eyeball and
containing microscopic elements which are so acted upon
by light as to stimulate (2) the optic nerve; this nerve ends
(3) in a part of the brain {visual centre) which when stimu-
lated arouses in our consciousness a feeling or sensation of
sight. The visual centre may be excited in very many ways,
and quite independently of the optic nerve or the retina;
as is frequently seen in delirious persons, in whom inflamma-
tion or congestion of the brain excites directly the visual
centre and gives rise to visual hallucinations.

Usually, however, the cerebral visual centre is only ex-
cited through the optic nerve, and the optic nerve only by
light acting upon the retina. The eyeball, containing the
retina, is so constructed that light can enter it, and so placed
and protected in the body that as a general thing no other
form of energy can act upon it so as to stimulate the retina.
Under exceptional circumstances we may have sight-sensa-
tions when no light reaches the eye; anything which stimu-
lates the retina, so long as it is connected by the optic nerve
with the cerebral visual centre, will cause a sight-sensation.
A severe blow on the eye, even in complete darkness, will
cause the sensation of a flash of light; the compression of the
eyeball excites the retina, the retina excites the optic nerve,

Of what does the visual apparatus consist? What are its essen-
tial parts? What happens when the visual centre is stimulated?
Is it only stimulated by the agency of light? Illustrate.

How is the visual centre usually excited? Why is light the form
of energy which most often stimulates the retina? Give an example
of the production of a sight-sensation in the absence of light. What
happens in the nervous system when a man "sees sparks" on receiv-
ing a blow in the eye?

318 THE HUMAN BODY.

the optic nerve the visual nerve-centre, and the result is a
sight-sensation.*

The Eye-Socket. — The eyeball is lodged in a bony cav-
ity, the orbit, open in front. Each orbit is a pyramidal
chamber containing connective tissue, blood-vessels, nerves,
and much fat ; the fat forms a soft cushion on which the
back of the eyeball rolls.

The Eyelids are folds of skin, strengthened by cartilage
and moved by muscles. Opening along the edge of each eye-
lid are from twenty to thirty minute glands, called the
Meibomian follicles. Their secretion is sometimes abnor-
mally abundant, and then appears as a yellowish matter
along the edges of the eyelids, which often dries in the
night and causes the lids to be glued together in the
morning. The eyelashes are curved hairs, arranged in one

In what is each eyeball lodged? What does the orbit contain?

What are the eyelids? The Meibomian glands? Why are the
eyelids sometimes stuck together in the morning? What are the uses
of the eyelashes?

* The fact that sight-sensations may be aroused quite independently of all
light acting upon the eye is paralleled by similar phenomena in regard to other
senses, and is of fundamental psychological and metaphysical importance.
That a blow on the closed eye gives rise to a vivid light-sensation, even in the
absence of all actual light, proves that our sensation of light is quite a different
thing from light itself. The visual sensory apparatus, it is true, is so con-
structed and protected that of all the forces of nature, light is the one which far
most frequently stimulates it. But as regards the peculiarity in the quality of
the sensation which leads us to classify it as " a visual sensation," that pecu-
liarity has nothing to do with any property of light. The visual nerve-centre
when stimulated causes a sight-sensation, whether it has been excited by light,
or by a blow, or by electricity. Similarly the auditory brain-centre gives us
a sound-sensation when stimulated by actual external sound-waves, or by a
blow on the ear, or by disease of the auditory organ. One kind of energy, light,
excites more often than any other the visual nerve-apparatus ; another, sound,
the auditory nerve-apparatus; a third, pressure, the touch nerve-organs.
Hence we come to associate light with visual sensations and to think of it as
something like our sight- feelings; and to imagine sound as something like our
auditor}' sensations; and so forth. As a matter of fact both light and sound are
merely movements of ether or air; it is our own stimulated nerve-centres
which produce visual and auditory sensations; the ethereal or aerial vibrations
merely act as the stimuli which arouse the nervous apparatus.

THE TEAR APPARATUS. 319

or two rows along each lid and helping to keep dust from
falling into the eye; and, when the lids are nearly closed,
to protect it from a dazzling light.

The Lachrymal Apparatus consists of the tear-gland in
each orbit, of ducts which carry its secretion to the upper
eyelid, and of canals by which this, unless when excessive,
is carried off from the front of the eye without running
down over the face. The lachrymal or tear gland, about
the size of an almond, lies in the upper and outer corner of
the orbit. It is a compound racemose gland, from which
twelve or fourteen ducts run and open at the outer corner
of the upper eyelid on its inner surface. The secretion
there poured out is spread evenly over the exposed part of
the eye by the movements of winking, and keeps it moist ;
finally it is drained off by two lachrymal canals, one of
which opens by a small pore on an elevation, or papilla,
near the inner end of the margin of each eyelid. The aper-
ture of the lower canal can be readily seen by examin-
ing its papilla in front of a looking-glass. The canals
run inwards and open into the lachrymal sac, which lies
just outside the nose, in a hollow where the lachrymal and
superior maxillary bones (L and Mx, Fig. 1G) meet. From
this sac the nasal duct proceeds to open into the nose-
chamber below the inferior turbinate bone (q, Fig. 41, p.
133).

Tears are constantly being secreted, but ordinarily in

such quantity as to be drained off into the nose, from

which they flow into the pharynx and are swallowed.

When the lachrymal duct is stopped up, however, their

Of what parts does the lachrymal apparatus consist ? Describe
the lachrymal gland. Where do its ducts open ? How is the front
of the eyeball kept moist? Describe the arrangement by which the
tears are usually carried off,

320

THE HUMAN BODY.

continual presence makes itself unpleasantly felt, and
may need the aid of a surgeon to clear the passage. In
loeeping the secretion is increased, and then not only more
of it enters the nose, but some flows down the cheeks.
The frequent swallowing movements of a crying child,
sometimes spoken of as "gulping down his passion," are
due to the need of swallowing the extra tears which reach
the pharynx.

Fig. 8S. — The left eyeball in horizontal section from before back. 1, scle-
rotic; 2. junction of sclerotic and cornea; 3, cornea; 4, 5, conjunctiva; 6, pos-
terior elastic Layer of cornea; 7, ciliary muscle; 10, choroid; 11, 13. ciliary pro-
cesses; 14, iris; 15, retina: 16, optic nerve; 17. artery entering retina in optic
nerve; 18, fovea centralis; 19, region whete sensory part of retina ends: 22,
suspensory ligament; 23 is placed in the canal of Petit, and the line from 25
points to it: 24, the anterior part of the hyaloid membrane : 20, 27, 28, are placed
on the lens; 28 points to the line of attachment around it of the suspensory liga-
ment; 29, vitreous humor: 30, anterior chamber of aqueous humor; 31, poste-
rior chamber of aqueous humor.

Why do tears run down the face during a fit of weeping?

Why does a crying child make frequent swallowing movements?

TUB EYEBALL. 321

The Globe of the Eye is on the whole spheroidal, but

consists of segments of two spheres (see Fig. 88), a portion
of a sphere of smaller radius forming its anterior transpar-
ent part, and being set on to the front of its posterior
segment, which is part of a larger sphere. In general
terms it may be described as consisting of three coats and
three refracting media.

The outer coat 1 and 3, Fig. 88, consists of the sclerotic
and the cornea, the latter being transparent and situated in
front ; the former is opaque and white and covers the back
and sides of the globe and part ot the front, where it is
seen between the eyelids as the white of the eye. Both are
tough and strong, being composed of dense connective tissue.

The second coat consists of the choroid, 9, 10, and the
iris, 14. The choroid consists mainly of blood-vessels sup-
ported by loose connective tissue, which in its inner layers
contains many darK brown or black pigment granules.*
Towards the front of the eyeball, where it begins to dimin-
ish in diameter, the choroid separates from the sclerotic
and turns in to form the iris, or that colored part of the
eye which is seen through the cornea ; in the centre of the
iris is a circular aperture, the pupil, through which light
reaches the interior of the eyeball.

The third or innermost coat of the eye, the retina, 15,
is its essential portion, being the part in which the light
produces those changes that give rise to nervous impulses
in the optic nerve. It lines the posterior half of the eyeball.

The Microscopic Structure of the Retina is very com-

What is the form of the globe of the eye? Of what does it consist?
Describe the outer coat. The second coat. What is the retina?

*In Dink-eyed rabbits and in the pink-eyed ladies of "dime museums" this
pigment is absent.

822

THE HUMAN BODY.

plex ; although but -fa inch in thickness it presents ten dis-
tinct layers.

10i

Fig. 89. — A section through the retina from its anterior or inner surface. 1
in contact with the hyaloid membrane, to its outer. 10. in contact with the chc*
roid. 1, internal limiting membrane; 2. nerve-fibre layer: 3. nerve-cell layer; 4,
inner molecular layer; 5, inner granular layer; 6, outer molecular layer; 7.
outer granular la5'er; 8, external limiting membrane; 9, rod and cone layer; 10)
pigment-cell layer.

Beginning (Fig. 89) on its front or inner side we find,

THE RETINA. 323

first, the internal limiting membrane, 1, a thin structure-
less layer. Next comes the nerve-fibre layer, 2, formed by
radiating fibres of the optic nerve ; third, the nerve-cell
layer, 3; fourth, the inner molecular layer, 4, consisting
partly of very fine nerve-fibrils, and largely of connective
tissue ; fifth, the inner granular layer, 5, composed of nu-
cleated cells, with a small amount of protoplasm at each
end, and a nucleolus. These granules, or at any rate the
majority of them, have an inner process running to the in-
ner molecular layer, and an outer running to, 6, the outer
molecular layer, which is thinner than the inner. Then
comes, seventh, the rod and cone fibre layer, 7, or outer
granular layer, composed of thick and thin fibres on each
of which is a conspicuous nucleus with a nucleolus. Xext
is the thin external limiting membrane, 8, perforated by
apertures through which the rods and cones, 9, of the
ninth layer join the fibres of the seventh. Outside of all,
next the choroid, is the pigmentary layer, 10. The nerve-
fibres are believed to be continuous with the rods and cones.
Light entering the eve passes through the transparent retina
until it reaches the rods and cones and excites these, and
they stimulate the nerves.

The action of the light is probably in the first instance
chemical. The rods are stained by a purple substance,
which is bleached by light and regenerated in the dark. In
the healthy eye the purple is reproduced nearly as fast as de-
stroyed, by the pigment-cells of the retina. Parts of the retina
which contain none of this vision purple can see, but they m ay
possess uncolored substances which are changed by light.

Describe the microscopic structure of the retina. On what con-
stituents of the retina does light first act, in producing a sensation?

With what are the rods of the retina stained? How is the pig-
ment reproduced?

324

THE HUMAN BODY.

The Blind Spot. — Where the optic nerve enters the re-
tina it forms a small elevation (Fig. 90), from which nerve-

Fig. 90. — The right retina as it would be seen if the front part of the eyeball
with the lens and vitreous humor were removed. The white disc to the right
marks the entry of the optic nerve (bliud spot); the lines radiating from this are
the retinal arteries and veins. The small central dark patch is the yellow spot,
the region of most acute vision.

fibres radiate. This elevation is quite blind, because it pos-
sesses neither rods nor cones. Its blindness may be readily
demonstrated. Close the left eye and look steadily with the
right at the cross (Fig. 91), holding the page vertically in

Fig. 91.

What is meant by the "blind spot"? Describe a method of
demonstrating its blindness

THE REFRACTING MEDIA OF THE EYE. 325

front of the face, and moving it alternately from and towards
you. The eye must all the time be kept looking fixedly at
the cross. When the book is about ten inches from the
eye the white disc entirely disappears from view: its image
then falls on the part of the retina where the optic nerve
enters, and causes no visual sensation.

Light consists of vibrations in an ether which pervades
space. An object which sets up no waves in the ether does
not excite the visual nervous apparatus, and appears black;
an object which sets up ethereal vibrations capable of
exciting the rods and cones of the retina appears white
or colored when we look at it. The ethereal vibrations
enter the eye through the cornea, pass on through the
pupil, and reach and stimulate the retina.

The Refracting Media of the Eye are three in number:
(1) the aqueous humor; (2) the crystalline lens; (3) the
vitreous humor. Their relative positions are shown in Fig.
Sb. These media act like a convex lens, such as a common

Fig. 92. — Illustrating the formation behind a convex lens of a diminished
and inverted image of an object placed in front of it.

burning-glass, and bend the rays of light which pass through
them (Fig. 92), so that all those which start from one point
of an external object meet again in a, focus on one point of

What is light? When does an ohject appear black?
Name the refracting media of the eye. State their relative posi
tion. Describe their actiou.

326 THE HUMAN BODY.

the retina. In this way a small ami inverted image of the
things at which we look is formed on the retina, and stimu-
lates its rods and cones.

Accommodation. — In the healthy eyeball the crystalline
lens is controlled by muscles which change its convexity,
making this greater when we look at near objects, and less
when we look at distant objects. When the lens is very

Fig. 93.— Section of front part of eyeball showing the change in the form
of the lens when near and distant objects are looked at. a, c, 6, cornea; A, lens
when near object is looked at; B, lens when distant object is looked at.

convex we cannot see a distant object distinctly, and when
it is less convex we only dimly see a near object. For
example, standing at a window behind a lace curtain we
can look at the curtain and see its threads plainly, but while
so doing we only see indistinctly houses on the other side
of the street; because the convexity of the lens is then such
as to focus light from the near object on the retina, and not
that from the distant. We can, however, "look at" the
houses over the way and see them plainly; but then we no
longer see the curtain distinctly, because the lens has so
changed its form as to focus light from the far object on the

When we look at an object, -what is formed on the retina?

How is the form of the crystalline lens controlled? When is its
convexity greater? Can we see near and distant objects distinctly
at the same moment? Illustrate.

SHORT SIGHT AND LONG SIGHT.

327

retina, instead of light from the near. The power of chang-
ing the form of the lens according as near or distant objects
are looked at is called "accommodation"

Short Sight and Long Sight. — In the normal eye the range
of accommodation is very great, allowing light from objects
infinitely distant up to
that proceeding from
those only about eight
inches in front of the eye
to be brought to a focus
on the retina. In the
natural healthy eve par-
allel rays of light meet on
the retina when the mus-
cles controlling the crys-
talline lens are at rest and
the lens is at its flattest
(A, Fig. 94). Snch eyes
are emmetropic. In other
eyes the eyeball is too
long from before back;
in the resting state paral-
lel rays meet in front of the retina (B). Persons with
such eyes cannot see distant objects distinctly without the
aid of diverging (concave) spectacles; they are short-sighted
or myopic. Or the eyeball may be too short from before
back; then, in its resting state, parallel rays are brought

What is meant by the "accommodation" of the eyeball?

Where do parallel rays of light which have entered a healthy eye
meet in a focus? Where do such rays meet when the eyeball is too
long from back to front? What is the result as regards vision?
What form of spectacle lenses do short-sighted persons require? Ex-
plain what is meant by a hypermetropic or long-sighted eye. What
sort of spectacles do long-sighted persons require?

Fiq. 94.— Diagram illustrating the path
of parallel rays after entering: an emme-
tropic (A), a myopic (B), and a hyperme-
tropic (C) eye.

S28 TEhl HUMAN BODY.

to a focus behind the retina (C). To see even distant ob-
jects, such persons must therefore use muscular effort to
increase the converging power of the lens; and when objects
are near they cannot, with the greatest effort, bring the
rays proceeding from them to a focns soon enough. To
get distinct retinal images of near objects, they therefore
need converging (convex) spectacles. Such eyes are called
hypermetropic, or in common language long-sighted.

Hygiene of the Eyes. — The healthy eye is so constructed
that when its muscles are at rest distinct images of distant
objects are focussed on the retina. To see near objects
muscular effort is required; hence the greater fatigue which
follows long gazing at them.

In a hypermetropic eye more effort is needed to see near
objects, and this results in muscular fatigue. Hyper-
metropic persons can often read well for a while, but then
complain that they can no longer see distinctly. This kind
of weak sight should always lead to examination of the
eyes by an oculist, to see if glasses are needed; otherwise
severe neuralgic pains about the eyes are apt to come on,
and the overstrained organ may be permanently injured.

Children sometimes have hypermetropic eyes, and in
that case should be at once provided with suitable spec-
tacles. In old age another kind of long-sightedness (pres-
byopia) is common: it is due to too great stiffness of the
crystalline lens, which does not become convex enough
during accommodation to focus on the retina the images of
near objects.

Short-sighted eyes appear to be more common
now than formerly, especially in those given to indoor

Why is the eye apt to be fatigued by the continued contempla-
tion of near objects ?

How does the hypermetropic eye differ from the normal in the
above respect? What should be done at once if a child is found to
have hypermetropic eyes? What is presbyopia?

In what classes of persons is myopia most frequent?

BEARING.

329

pursuits. Myopia is rare among those who cannot read or
who live mainly out of doors. It is not so apt to lead to
permanent injury of the eye as hypermetropia, but the
effort to see distinctly any but near objects is apt to pro-
duce headaches and other symptoms of nervous exhaus-
tion. If the myopia becomes gradually worse, the eyes
should be rested for several months.

Hearing. — The auditory organ (Fig. 95) consists of three
portions, known respectively as the external ear, the middle

Fig. 95. — Semi-diagrammatic section through the right ear. M, concha. G,
external auditory meatus. T. tympanic or drum membrane. P, Tympanum.
o, oval foramen, r. round foramen. Extending from 7'to o is seen the chain of
tympanic bones. R, Eustachian tube. V, B, 8, bony labyrinth: V, vestibule;
B, semicircular canal; 8, cochlea, b, I, I', membranous semicircular canal
and vestibule. A, auditory nerve dividing into branches for vestibule, semi-
circular canal, and cochea.

ear or tympanum, and the internal ear or labyrinth; of

these the latter is the essential one, containing the ends of

the auditory nerve-fibres.

What is apt to result from short sight?
Of what does the auditory organ consist?

330

THE HUMAN BODY.

The External Ear consists of the expansion, M, seen on
the exterior of the head, called the concha, and a passage
leading in from it, the external auditory meatus, G. This
passage is closed at its inner end by the tympanic or drum
membrane, T. It is lined by a prolongation of the skin,
through which numerous shiall glands, secreting the wax
of the ear, open.

The Tympanum, or drum chamber of the ear (Fig. 96 and

P, Fig. 95), is an
irregular cavity in
the temporal bone,
closed externally by
the drum membrane.
From its inner side
the Eustachian tube
(E, Fig. 95) pro-
ceeds and opens
into the pharynx.
This tube allows air
from the throat to
enter the tympanum,
and serves to keep
equal the atmospher-
ic pressure on each
side of the drum
membrane. Three small bones (Fig. 96) stretch across
the tympanic cavity from the drum membrane to the laby-
rinth ; they transmit the vibrations of the membrane,
produced by sound-waves in the air, to the liquid of the

Describe the external ear.

What is the tympanum? The Eustachian tube? What is the use
of the Eustachian tube? What bones lie in the tympanum? What
is their function?

Fig. 96.— The tympanic cavity and its bones, con-
siderably magnified. G, the inner end of the ex-
ternal auditory meatus, closed internally by the
conical tympanic membrane: L, the malleus, or
hammer-bone ; H, the incus, or anvil-bone ; £>', the
stapes, or stirrup-bone.

TOUCH. 331

labyrinth. The outmost bone is the malleus ; the inmost,
the stapes ; and the middle bone, the incus.

The Internal Ear, or Labyrinth, consists primarily of
chambers and tubes hollowed out in the temporal bone.
The middle chamber, called the vestibule ( V, Fig. 95), has
an opening, the oval foramen, o, in its outer side, into which
the inner end of the stapes, or stirrup-bone, fits. Behind,
the vestibule opens into three semicircular canals, one of
which is shown at B, Fig. 95; and in front into a spirally
coiled tube, S, the cochlea. In these bony chambers and
tubes lie membranous chambers and tubes, in which the
fibres ©f the auditory nerve (A, Fig. 95) end. All the
labyrinth chamber outside these membranous parts is
occupied by a watery liquid, known as perilymph; the
membranous chambers are filled with a similar liquid, the
endolymph.

When sound-waves of the air make- the tympanic mem-
brane vibrate, it shakes the tympanic bones; the stapes
then shakes the liquids in the labyrinth, and sets up vibra-
tions in them, which excite the endings of the auditory
nerve. The stimulated auditory nerve then conveys a
nervous impulse to the brain-centre of hearing and excites
it, and a sensation of sound results.

Touch, or the Pressure Sense. — Many sensory nerves end
in the skin, and through it we get several kinds of sensa-

Of what does the internal ear primarily consist? What is the
vestibule?

What is found on the outer side of the vestibule?

Into what does the vestibule open behind? In front? What lie
in the bony cavities of the labyrinth? What is the perilymph? The
endolymph?

What happens when sound-waves set the tympanic membrane in
vibration?

332 TUB HUMAN BODY.

tion; touch proper, heat and cold, and pain ; and we can
with more or less accuracy localize them on the surface of
the body. The interior of the mouth possesses also these
sensibilities. Through touch proper we recognize pressure
or traction exerted on the skin, and the force of the pres-
sure; the softness or hardness, roughness or smoothness, of
the body producing it; and the form of this, when not too
large to be felt all over.

The delicacy of the tactile sense varies on different parts
of the skin; it is greatest on the forehead and temples,
where a weight of T-f ¥ of a grain can be felt.

The Localization of Skin Sensations. — When the eyes are
closed and a point of the skin is touched we can with some
accuracy indicate the region stimulated; although tactile
feelings are alike in general characters, they differ in some-
thing (local sign) besides intensity by which we can distin-
guish them as originated on different parts of the skin.
The accuracy of the localizing power varies widely in dif-
ferent skin regions, and is measured by observing the least
distance which must separate two objects (as the blunted
points of a pair of compasses) in order that they may be
felt as two. The following table illustrates some of the
differences observed:

Tongue-tip 04 inch

Pnlm side of last phalanx of finger 08 "

Red part of lips 16 "

Tip of nose 24 "

Back of second phalanx of finger 44

Heel 88 "

What sensations do we get through the skin? Name another part
of the body -which also gives rise to these sensations. What do we
recognize by means of the sense of touch?

Where is the tactile sense most acute?

What is meant by the localization of skin sensations? Does the ac-
curacy of localization differ in different regions of the skin ? Illustrate.

SMELL. 333

Back of band 1.23 inches

Forearm 1.58 "

Sternum... 1.76 "

Back of neck 2.11 "

Middle of back 2.64 "

The Temperature Senses. — By these is meant our faculty
of perceiving cold and warmth; and, with the help of these
sensations, of perceiving temperature differences in external
objects. The organs are the skin, the mucous mem-
brane of mouth, pharynx, and gullet, and of the entry of
the nose. Burning the skin will cause pain, but not a true
temperature sensation, which is quite as different from
pain as is touch.

Smell. — The olfactory organ consists of the mucous
membrane of the upper parts of the nasal cavities; in it the
endings of the olfactory nerves are spread. It covers the
upper and lower turbinate bones (o, p, Fig. 41) (which are
expansions of the ethmoid on the outer wall of the nostril-
chamber), the opposite part of the partition between the
nares, and that part of the roof of the nose (n, Fig. 41)
which separates it from the cranial cavity.

Odorous Substances, the stimuli of the olfactory apparatus,
are always gaseous. They frequently act powerfully when
present in very small quantity. A grain or two of musk
kept in a room will give the air in it an odor for years, and
yet at the end will hardly have diminished in weight, so
infinitesimal is the quantity given off from it to the air
and able to excite the sense of smell. While some gases or

Wbat is the temperature sense? What are its organs?

Of what does the olfactory organ consist?

In wbat point do all odorous substances agree? Illustrate the
efficiency, so far as producing smell sensations is concerned, of a
very small quantity of an odorous substance. Do all gases stimulate
the olfactory apparatus?

334 TnE HUMAN BODY.

vapors have this powerful influence upon the olfactory
organ, others, as pure air, do not stimulate it at all.

Taste. — The organ of taste is the mucous membrane on
the upper side of the tongue, and possibly on other parts of
the boundary of the mouth cavity. The mucous membrane
of the tongue presents innumerable elevations or papilla3
(Fig. 46) of three kinds (p. 139). The filiform papillae are
organs of touch, for the tongue has the sense of touch as
well as of taste. The circumvallate ;md fungiform papilla?
contain the endings of brandies of the glossopharyngeal
and trigeminal nerves (pp. *92, 2'j3), which, when excited
by sapid bodies, stimulate the taste-centres in the brain.

Many so-called tastes (flavors) are really smells; odorif-
erous particles of substances which are being eaten reach
the nose through the posterior nares and arouse smell sen-
sations which, since they accompany the presence of ob-
jects in the mouth, we take for tastes. Such is the case
with most spices; Avhen the nasal chambers are blocked or
inflamed by a cold in the head, or closed by pinching the
nose, the so-called " taste" of spices is not perceived when
they are eaten; all that is felt when cinnamon, e.g., is
chewed under such circumstances is a certain pungency
due to its stimulation of nerves of common sensation in the
tongue. This fact is sometimes taken advantage of in the
practice of domestic medicine when a nauseous dose, as
rhubarb, is to be given to a child.

What is the organ of taste? What is found on the mucou3 mem-
brane of the tongue? "What papillae are concerned iu the tactile sen-
sibility of the tongue? In the gustatory? What nerves supply the
taste-papillae?

What are many so-called tastes? Illustrate

CHAPTER XXII.

VOICE AND SPEECH.

Voice consists of sounds produced by the vibrations of
two elastic bands called the vocal cords. These cords lie
in the larynx, which is situated between the pharynx and
the windpipe, and is a portion of the passage conveying air
to the lungs specially modified to form a voice-organ.

The vocal cords project into the larynx so that but a
narrow slit, called the glottis, is left between them. When
the vocal cords are put in a certain position air driven
through the glottis sets them vibrating and they give
origin to sounds. The stronger the blast the louder the
voice.

The pitch of the voice is primarily dependent on the size
of the larynx. The larger it is, or what comes to the same
thing, the longer the vocal cords are, the lower is the pitch
of the voice. In children, therefore, the voice is shrill;
and, as the female larynx is usually smaller than the male,
a woman's voice is usually higher pitched than a man's.
About sixteen or seventeen years of age a boy's larynx
grows very fast, and his voice "breaks," becoming about
an octave deeper in tone.

How is voice produced? Where do the vocal cords lie? Where
is the larynx situated?

What is the glottis? When do the vocal cords give origin to
sounds? On what does the loudness of the voice depend?

How does the size of larynx influence the pitch of the voice?
Why is a woman's voice commonly higher pitched than a man's?
Why does a youth's voice break?

336 THE HUMAN BODY.

While every one's voice has a certain natural pitch which
leads us to call it soprano, tenor, bass, and so forth, this
pitch can be modified within limits, so that we each can
sing a number of notes. This variety is due to the action
of muscles in the larynx which alter the tension of the
vocal cords; the more tightly these are stretched, other
things being equal, the higher pitched is the tone which
they emit.

Speech. — The vocal cords alone would produce but feeble
sounds. If a fiddle-string be attached to a hook on the
ceiling and stretched by hanging a heavy weight on its
lower end, we can get tones out of it when it is plucked
or bowed; but the tones are feeble and deficient in charac-
ter and fullness. In the violin the strings are attached to a
hollow wooden box, and when the string is set in move-
ment it causes the wood to vibrate, and this, in turn, the air
contained in the cavity of the instrument; in this way the
tone is intensified, and altered and much improved in
quality. The air in the pharynx, mouth, and nose an-
swers pretty much to that in the hollow of the violin; those
cavities together form a resonance-chamber, and when the
vocal cords vibrate they set this air in vibration also, and
so the sound is made louder and is altered in character.
By movements of throat, soft palate, tongue, cheeks, and
lips, the size and form of the sounding chamber are varied,
and with them the tone of voice; by movements of tongue,
lips, and palate, the air-current, and therefore the sound,
is interrupted from time to time; on other occasions the

How is it that we can sing a number of notes of different pitch?

Why is a hollow wooden box an essential part of a violin? How
do the throat and mouth cavities influence the loudness and quality
of the voice? How do tongue, lips, and cheeks cooperate in con-
verting voice into speech?

THE LARYNX.

337

air is forced through a narrow passage in the mouth, giving
rise to new sounds added on to those originated by the vocal
cords. In such manners the primitive feeble monotonous
tone due to the vocal cords is reinforced and altered in
various ways in throat and mouth, and voice is developed
into articulate speech.

The Larynx consists of a framework of nine cartilages,

I'TG. 97.— The more important cartilages of the larynx from behind, t. thy-
roid; Cs, its superior, and Ci, its inferior, horn of the right side: **. cricoid
cartilage: t, arytenoid cartilage: Pv, the corner to which the posterior end of a
vocal cord is attached : Pm , corner on which the muscles which approximate or
separate the vocal cords are inserted; co, cartilage of Santorini.

movably articulated together, and having muscles attached
to them by whose contractions their relative positions are
altered; the cartilages surround a tube, continuous below
with the windpipe, and lined by mucous membrane. At
one level in the laryngeal tube the vocal cords project and,

Of what does the laryngeal framework consist? "What do the
cartilages of the larynx surround? How is the glottis formed?

338 THE HUMAN BODY.

pushing out the mucous membrane, leave for the passage
of air only the narrow slit of the glottis, above mentioned.

The largest cartilage of the larynx (t, Fig. 97) is the
thyroid. It is placed in front and consists of right and
left halves which meet at an angle in front, but separate
behind so as to enclose a V-shaped space. The front of
l lie thyroid cartilage causes the prominence in the neck
known as Adam's apple. The epiglottis, not represented
in the figure, is attached to the top of the thyroid cartilage
and overhangs the entry from pharynx to larynx. It may
be seen, covered by mucous membrane, projecting at the
root of the tongue, if that organ be pushed down, while
the mouth is held open before a mirror. It is represented
as seen from behind at a, Fig. 98. The cricoid cartilage
(%*, Fig. 97) has the form of a signet-ring, with its broad
part turned towards the back of the throat, and placed in
the lower part of the opening between the halves of the
thyroid. The two arytenoid cartilages ( f, Fig. 97) are
placed on the top of the wide posterior part of the cricoid;
each is pyramidal in form. The remaining laryngeal car-
tilages are of less importance.

The Vocal Cords, which are rather projecting pads of
elastic tissue than cords in the ordinary sense of the word,
proceed, one from each arytenoid cartilage behind, to
the angle where the halves of the thyroid meet in front.
In quiet breathing the interval (glottis) between them (c,

Describe the position and form of the thyroid cartilage. What
causes "Adam's apple"? What is the epiglottis? How may you see
it in your own throat? Describe th« cricoid cartilage. What carti-
lages are set on top of the cricoid? What is their form?

Between what points are the vocal cords stretched? Under what
circumstances does air driven through the glottis not set them vi-
brating?

MUSCLES OF THE LARYNX.

339

Fig. 98) is narrow in front and wider behind: under such
circumstances air driven through the opening dues not set
the margins of the cords in vibration, and no sound is pro-
duced.

The Muscles of the Larynx, The laryngeal muscles

Fig. 98.— The larynx viewed from its pharyngeal opening. The back wall of
the pharynx has been divided and its edges (11 ) turned aside. 1, body of hyoid;
2. its small, and 3, its great, horns; 4, upper and lower horns of tliyroid car-
tilage; 5, mucous membrai)3 of front of pharynx, covering the back of the cri-
coid cartilage; 6, upper end of gullet; 7, windpipe, lying in front of the gullet;
8, eminence caused by cartilage of Santorini: 9, eminence caused by cartilage of
Wrisberg; both lie in, 10, the aryteno-epiglottidean fold of mucous membrane,
surrounding the opening {aditua larynqis) from pharynx to iarynx. «. project-
ing tip of epiglottis; c, the glottis, the lines leading from the letter-point to the
free vibrating edges of the vocal cords. 6', the ventricles of the larynx: their
upper edges, marking them off from the eminences 6. are the false vocal cords.

340 TUB HUMAN BODY.

are numerous, and are arranged — (1) to pull the arytenoid
cartilages towards one another and so narrow the glottis
behind; then air forced through the narrowed slit sets the
cords vibrating and produces voice. (2) To increase the
distance between the arytenoid cartilages behind and the
thyroid in front: as the vocal cords are attached to both,
this action stretches and tightens them, and so raises the
pitch of the voice. (3) To pull the front of the thyroid
cartilage nearer the arytenoids and so slacken the cords and
lower the pitch of the voice. (4) To separate the arytenoid
cartilages, and with them the vocal cords, and thus widen
the glottis and allow air to pass through it without pro-
ducing voice.

The Range of the Human Voice from the lowest note
(/ of the unaccented octave) of an ordinary bass to the
highest note (g on the thrice-accented octave) of a fairly
good soprano is about three octaves: the former note is
produced by 88 vibrations per second, the latter by 792.
Celebrated singers of course go beyond this limit in each
direction: bassos have been known to take a on the great
octa\e (55 vibrations per second), and Mozart, at Parma,
heard a soprano sing a note of the extraordinarily high pitch
c on the fifth accented octave (2114 vibrations per second).

Vowels are musical tones produced in the larynx and
modified by resonance of the air in the pharynx and mouth.
To get the broad a sounds, as ah, the mouth is widely
opened and the lips drawn back; to get such vowels as

State the uses of the muscles of the larynx.

What is the ordinary range of the human voice? What notes
have celehrated singers taken beyond the ordinary highest and lowest
limits?

What are vowels? Illustrate the influence of the shape given to
the mouth-cavity in the production of different vowels.

VOWELS AND CONSONANTS. 341

00 (moo?-) the lips are protruded and the mouth-cavity
lengthened. The change in the form of the mouth may
be noticed by pronouncing consecutively the vowel-sounds
ah, eh, ee, oh, 00. The English i (as in spire) is a diph-
thong, consisting of a (pfld) followed by e (ieet), as may be
readily found on attenrpting to sing a sustained note to the
sound 1.

Semivowels. — In uttering true vowel-sounds the soft
palate is raised so as to cut off the air in the nose, which
then does not take part in the resonance. For some other
sounds (the semivowels or resonants) the initial step is, as
in the case of the true vowels, the production of a laryngeal
tone; but the soft palate is not raised, and the mouth-exit
is more or less closed by the lips or the tongue; hence the
blast partly issues through the nose, and the air there takes
part in the vibrations and gives them a special character;
this is the case with m, n, and ng.

Consonants are sounds produced not mainly by the vocal
cords, but by modifications of the expiratory blast on its
way through the mouth. The current may be interrupted
and the sound changed by the lips (labials, as p and b);
or, at or near the teeth, by the tip of the tongue (denials,
as t and d); or, in the throat, by the root of the tongue
and the soft palate (gutturals, as k and g).

Consonants may also be classified by the kind of move-
ment which gives rise to them. In explosives an interrup-
tion to the air-current is suddenly interposed or removed
(p, b, I, d, Jc, g). Other consonants are continuous (f,
s, r) and may be divided into (1) aspirates, when the air

Is the long i of English a true vowel ?

What is meant by the semivowels ?

What are consonants ? How raav they be classified ?

342 THE HUMAN BODY.

is made to rush through a narrow aperture, as, for ex-
ample, between the lips (/) or the teeth (s) or the tongue
and the palate (sh) or the tongue and the teeth (th);
(2) resonants or semivowels; (3) vibratories, the different
forms of r, due to vibrations of parts bounding a constric-
tion put in the way of the air-current on its passage.

CHAPTER XXIII.

THE ACTION OF ALCOHOL AND OTHER STIMULANTS
AND NARCOTICS UPON THE HUMAN BODY.

Introductory. — "We have already seen (p. 121) that alcohol
is not to be regarded as either a tissue-forming or a force-
giving food.

By causing a transference of heat from internal parts to
the skin, in which the main organs of the temperature-
sense (p. 333) are located, it produces a temporary feeling
that the body is warmer; but the final result is a loss of
animal beat to the air, and a decrease of the temperature of
the body as a whole. Experiments made on men under
military regimen and discipline have proved that alcohol
does not increase the power of sustained muscular work,
though it may for a brief time stimulate to unhealthy
activity. The relative amount of energy liberated in the
body for its own use may be very fairly calculated by com-
paring the amount of oxygen absorbed by the lungs on one
day with the amount absorbed on another. We have learned
that on the days when alcohol is taken the oxygen absorbed
is not increased. Alcohol seizes some of the oxygen which
the foods and tissues would have utilized in its absence ;
and what it takes they lose. Most authorities even main-
tain that alcohol prevents oxidation, and therefore tissue

How does alcohol make one feel warmer? What is the result?
What have experiments on soldiers shown as to the effect of
alcohol on muscular work? How is the absorption of oxygen
affected on days when alcohol is taken? What does alcohol do with
some of the oxygen? Why do some authorities believe that alcohol
directly checks tissue activity?

[343]

344 TEE HUMAN BODY.

activity, indirectly as well as directly; these experimenters
find that it not only takes oxygen from the tissues, but
so influences them as to diminish their power of using
what it leaves. We may conclude that under ordinary
circumstances alcohol is of no use as an energy-yielding
food; although, since it is oxidized in the body, it would
act as a real food to a starving man; or to a very sick per-
son who might be unable for the moment to absorb and
digest other substances.

As regards tissue-formation, alcohol cannot build up
proteid material, since it contains no nitrogen; and proteid
material constitutes the essential part of muscular, gland-
ular, and nervous tissues. There is even some evidence that
alcohol leads to excessive waste of such tissues : several
competent observers have found that its use increases the
amount of nitrogen waste excreted from the body. The
only tissues whose formation alcohol seems sometimes to
increase are fatty and connective tissues; and we shall pres-
ently learn that in most cases the superabundance of these
tissues is deposited in places where it does harm.

The study of alcohol as an article of diet le ids therefore
to the result that (though a physician may find it useful as
a medicine in a crisis of disease when the system needs
urging to make a special effort) it cannot fairly be regarded
as a food when taken by persons in good health and properly
nourished.

The whip applied to a horse will arouse him to call on

"What <reneral conclusions may be reached as to the value of alco-
hol as a food?

What relation has alcohol to the formation and waste of proteid
tissues? Of fatty and connective tissues?

When may a physician find alcohol a useful medicine?

Illustrate the action of alcohol on the body by comparison with a
whip used on a horse.

ALCOHOL. 345

his reserve force, and perhaps carry himself and his rider
safely past some point of special danger; but it does not in
any way nourish the horse. As regards the healthy human
body alcohol may be compared to a whip: an amount of it
not sufficient to cause drunken sleep, temporarily excites
various organs; but the consequence is subsequent greater
exhaustion.

So far we have learned that alcohol as a regular article
of diet is, at least, useless. Were that all. we might regret
the annual waste of corn, barley, wheat, and fruits in its
production; and think the man foolish who spent his
money on it. In such case the matter would be one for
moralists and political economists to deal with, and phy-
siologists and students of hygiene might leave it alone.
Unfortunately, alcoholic drinks are not merely useless but
positively hurtful, when taken regularly, even in what is
usually called moderation. Alcohol has probably caused
in the past, and is certainly causing at present in civilized
nations, more disease and death than either bad drainage,
bad ventilation, overcrowding, deficient food, overwork, or
any other of the conditions prejudicial to health concern-
ing which Physiology and Hygiene warn us. The moral
degradation and the physical condition of the drunkard
speak for themselves; it is therefore the more insidious
consequences of alcohol-drinking that we shall mainly
describe.

Alcohol, when pure, is a transparent colorless liquid,
containing the elements carbon, hydrogen, and oxygen
(C2H60); it is lighter than water, and boils at a con-

What substances are wasted that alcohol may be produced?
Compare the injury to health resulting from bad draiuage, etc.
with that produced by alcohol.
Describe pure alcohol.

346 THE HUMAN BODY.

siderably lower temperature; is highly inflammable, burn-
ing with a bluish flame; and is the essential constituent of
all fermented liquors in common use.

Alcoholic Beverages include (1) malt liquors, as beer, ale,
stout, and porter; (2) cider and perry; (3) wines, as claret,
sherry, port, champagne, and catawba; (4) distilled spirits,
as brandy, rum, and whiskey; and their compounds, as gin,
cherry brandy, pineapple rum, and so forth; (5) liqueurs,
made by adding various flavoring essences to different kinds
of spirits. All contain alcohol in greater or less propor-
tion, varying from over 70 volumes in the 100 in some
kinds of rum to less than 2 in the 100 in "small" beer.

The Direct Physiological Action of Pure Alcohol. — Pure
alcohol is a very expensive substance, mainly employed in
chemical experiments and in the manufacture of certain
perfumes and essences. However, some clues to the ac-
tion of diluted alcohol on the body may be obtained by a
study of its action in the concentrated form.

Strong alcohol having a great tendency to combine with
water, rapidly extracts that substance from any animal organ
placed in contact with it; as is shown by the hardening
and shrivelling of museum specimens placed in it.

Added to raw white of egg it coagulates it, much as if the
egg had been boiled: added to fresh blood it acts in a simi-
lar manner, coagulating the serum albumen as heat does
(p. 183).

Pure alcohol placed on the skin evaporates very rapidly,
and in so doing abstracts heat (p. 274, note), producing a

Of what is alcohol an essential constituent?

Classify and name common alcoholic beverages. Within what
limits does the quantity of alcohol in them vary?

For what purposes is pure alcohol mainly used? What is its ac-
tion on animal organs placed in it? On fresh blood? On the skin
when evaporation is permitted?

DILUTED ALCOHOL. 347

sensation of coolness. This is succeeded by a feeling of
warmth in the part; which also becomes red from tempo-
rary paralysis of its blood-vessels, causing them to dilate.
If the evaporation be prevented, as by putting a little alco-
hol on the skin and covering it with a thimble, the alcohol
acts as an irritant; it causes smarting, and finally sets up
inflammation.

On mucous membranes alcohol acts much as on the skin,
but its irritant effect is more marked. Placed on the tongue
it causes a feeling of coolness, followed by a hot biting sen-
sation, and a red congested condition of the area with which
it came in contact. Introduced into the stomach of a
rabbit or dog, where it cannot readily evaporate, strong
alcohol causes congestion and inflammation varying in in-
tensity with its amount. If the dose is large the animal
dies almost instantly, because the powerfully irritated sen-
sory nerves of the gastric mucous membranes reflexly ex-
cite a nerve-centre which slops the heart's beat.

Diluted Alcohol does not produce the above-described
direct actions of the pure liquid: this latter taken into the
stomach acts as a powerful irritant poison, and generally
produces its main effects on the stomach itself. Alcohol in
such proportion as it exists in most alcoholic drinks exerts
much less local action on the gastric mucous membrane; but
it is absorbed and carried in the blood and lymph through
the body, and if steadily taken day after day acts upon and

When evaporation is prevented? Action on mucous membranes?
Illustrate by tongue. By stomach.

How does strong alcohol when swallowed sometimes cause sud-
den death?

How does the action of dilute alcohol differ from that of concen-
trated? What results follow its frequent absorption? What condi-
tions influence the organs soonest injured? Why are alcoholic dis-
eases often not recognized until incurable?

348 THE BUM AN BODY.

alters for the worse nearly every important organ. The
organ first or most seriously attacked varies with the form
in which the alcohol is taken, with the amount consumed
daily, and with the constitution of the individual. Prob-
ably no one individual ever suffered from all the diseased
states produced by alcohol described in the following
pages; but habitual drinkers are very apt to experience
one or more of them. The diseases produced by alco-
hol after absorption into the blood come on so grad-
ually (except in the case of obvious drunkards) that the
victim rarely perceives them until serious if not irreme-
diable damage has been done: indeed, physicians have only
recently come to clearly recognize that men who in com-
mon phrase "were never in their lives under the influence
of liquor" may nevertheless be drinking enough to do
them grave injury.

Absorption of Alcohol. — When alcohol (so diluted as not
to cause active inflammation of the stomach) is swallowed,
it is quickly absorbed by the capillary blood-vessels of the
gastric mucous membrane.* These pass it on to the portal
vein, which carries it (p. 208) direct to the liver. Collected
from the liver by the hepatic veins it is conveyed through
the inferior vena cava to the right auricle of the heart.
Thence it passes on in the general blood-flow (pp. 198, 199,

Can a man who drinks but is never drunk be injured by alcohol?

By what vessels is alcohol first absorbed? To what vessel do
they carry it? Describe its further course to the right auricle of the
heart. From there to the left auricle.

* An exception to the rapid absorption of alcohol sometimes occurs when a large
quantity of raw spirits is taken. Many cases are recorded where men have for
a wager drunk a bottle of whiskey or brandy. The result is often sudden death;
but sometimes no effect is noticed for fifteen or twenty minutes ; then there is
sudden unconsciousness, passing into stupor, which ends in death. In such cases
the large quantity of strong spirits seems temporarily to paralyze the absorbing
power of the stomach.

PRIMARY EFFECTS OF ALCOHOL. 349

209) to right ventricle, lungs, left auricle, left ventricle,
aorta, and by branches of the aorta to the body in general:
to the heart-muscle (by the coronary arteries, p. 202), to the
brain and spinal cord, to the muscles, to the kidneys, to
the skin. We have to study its action on all tbese organs.

The Primary Effects of a Moderate Dose of Diluted Alco-
hol, as a glass of whiskey and water, on one unaccustomed
to it, are to cause temporary congestion of the stomach;
dilatation of blood-vessels of the skin, indicated by the
flushed face; a more rapid and forcible beat of the heart;*
nervous excitement, exhibited by restlessness and talkative-
ness. Then some incoherence of ideas, and often giddi-
ness. Finally there is a tendency to sleep. On awaking
the- person has some feeling of depression, not much ap-
petite, and is in general a little out of sorts for a day.

If the dose be larger the stage of giddiness is accompanied
by diminution of the sensibility of the skin; and imperfect
control over the voluntary muscles, indicated by defective
articulation and a staggering gait. The muscles moving
the eyeballs cease to work in harmony. Xormally they
act unconsciously, turning the eyes so that images of
objects looked at are focussed on corresponding points
of the retinas; and objects are seen single. Soon after
the voluntary movements are affected the involuntary
regulation of the eye-muscles is impaired, and objects are
seen double; the eyeballs being no longer so turned as to
bring images on corresponding retinal points. The stora-

Name important organs to -which the alcohol is ultimately carried
in the hlood.

Describe the primary effects of a moderate dose of dilute alcohol.
Of a larger but not fatal dose.

*It is doubtful if chemically pure alcohol diluted with water quickens the
pulse; most ordinary alcoholic beverages, however, undoubtedly do.

350 THE HUMAN BODY.

ach may also be so irritated as to lead to vomiting. Then
comes deep drunken sleep; followed by headache, loss of
appetite, and prostration similar to, but more marked than,
that occurring after the smaller dose.

If the alcoholic indulgence be repeated, day after day,
some of the above-described primary consequences become
less marked; but they give way to more serious functional
and structural diseases.

The Secondary Effects of Alcohol vary much in inten-
lity with the form in which it is taken; also, no doubt,
with the constitution of the person taking it, and with
the length of time during which he has been drink-
ing. We shall consider them in three groups: I. Compa-
ratively slight and curable diseased states due to what
is commonly considered moderate drinking. II. Severe
acute alcoholic diseases. III. Chronic and usually incur-
able morbid states, due to steady prolonged drinking;
these fall into three main subdivisions: a. General tissue-
deterioration; b. Destruction, more or less complete, of cer-
tain organs; c. Deterioration of mind and character.

I. Minor Diseased Conditions produced by Moderate
Drinking. — Of these, alcoholic dyspepsia is the most
frequent. A vast number of persons suffer from it
without knowing its cause; people who were never drunk
in their lives, and consider themselves very temperate.
" The symptoms vary, but when slight are something like
these: A man (or woman) complains of slight loss of appe-
tite, especially in the morning for breakfast; feels languid
either on rising or early in the day; retches a little in the

What happens if the dose of alcohol be taken day after day?
Classify the secondary actions of alcohol upon the body.
Give an account of alcoholic dyspepsia.

ACUTE ALCOHOLIC DISEASES. 351

morning, and perhaps brings up a little phlegm only, or
may actually vomit; or may be able to take breakfast
but feels sick after it. Towards the middle of the
morning he is heavy and languid, perhaps, and does not
feel easy until he has had a glass of sherry or some spirits,
then gets on pretty well, and can eat lunch or dinner. Or
if worse, the appetite for both is defective, and there is

undue weight or discomfort after meals Now all

these symptoms may be due to other causes, but when
taken together they are by far most commonly due to al-
cohol." *

Another frequent result of regular "moderate" drinking
is tremor, orshakiness of the hands. The hand is unsteady
when the arm is folded, and is seen to tremble if it be held
out with the arm extended. This tremor is very marked
in the alcoholic disease known as delirium tremens (p. 352).
Even in its simple form it interferes with the performance
of any action calling for manual dexterity. The trembling
may, in most cases, be stopped for a time by an extra glass;
and thus often leads to the acquirement of more serious
diseases.

We class the above as minor diseased conditions, because
in most cases they occur before the will-power is seriously
impaired, and abstinence from alcohol is soon followed by
recovery.

II. Acute Alcoholic Diseases. — A single large dose of alco-

Describe alcoholic tremor. In what disease is it very marked ?
What results from even its simple form? How does it often lead to
the acquirement of more serious alcoholic disease?

Why do we class the dyspepsia and tremor as minor alcoholic dis-
eases ?

What results from a large dose or repeated small doses of alcohol ?

* Dr. Greenfield, in " Alcohol: its Use and Abuse."

352 THE HUMAN BODY.

hoi, or the repetition of small doses at short intervals, ends
in a fit of drunkenness.

The disgusting appearance of a drunken man, the loath-
ing which he excites even in those most attached to him,
the loss of control over his actions, which makes him the
prey of criminals, or, yet worse, a criminal himself, taken
together make a picture to which the physiologist need add
nothing. A man not deterred by its contemplation will
not be hindered in the indulgence of his appetite by any
argument based on injury to his health.

Delirium Tremens. — Repeated drunkenness usually ends
in an attack of delirium tremens, but this disease is more
frequently the result of prolonged drinking which has
never culminated in actual drunkenness. It is especially
apt to occur in "those who drink hard, but keep from
actual loss of consciousness, especially those engaged in
hard mental work or subjected to great moral strain or
shock ; and, too, those of certain temperaments are pecu-
liarly liable to it. It is preceded, usually, by loss of sleep,
ideas of persecution or injury, witli no foundation in fact,
and slight hallucinations, especially at night ; the man,
meanwhile, in the day looking anxious, slightly excited,
nervous and tremulous, and perhaps narrating as actual
occurrences the hallucinations of the preceding night.
Then the senses are partly lost; he sees spectres, horrible
and foul creatures about him; has all sorts of painful, terri-
fying visions (whence the common name of the 'horrors');
is extremely tremulous, and either excited or lies prostrate,
trembling violently on movement, sleepless, anxious, and a
prey to spectres and terrors of the imagination." *

Under what conditions may delirium tremens occur?
What symptoms usually precede this disease? Describe the con-
dition of a person suffering from delirium tremens.

* Dr. Greenfield, in " Alcohol: its Use and AOuse."

DELIRIUM TREMENS. 353

Few persons die in their first attack of delirium tremens,
but it is nature's unmistakable warning to the tippler; let
him not disregard it, unless he is prepared to die without
hope in maniacal imaginings so frightful that those around
his death-bed can never recall the scene without horror !

Dipsomania is often confounded with delirium tremens,
but though it may lead to that disease it is an essentially
different pathological state. The word properly means a
mental disease in which there is periodically an irresistible
passion for alcohol; in any form, no matter how distasteful,
the dipsomaniac will swallow it with avidity. The disease
is sometimes produced by indulgence in drink, but is more
often inherited, especially from parents addicted to alco-
holic excess. In the families of such, one child is often
epileptic, another idiotic, a third eccentric or perhaps quite
mad, and a fourth a dipsomaniac. When the fit seizes him
the dipsomaniac is as irresponsible as a raving madman.
His only safeguard against a frightful debauch is to place
himself under restraint as soon as he perceives the symp-
toms which he has learned to recognize as premonitory of
his fit of madness. After a time the paroxysm passes off ;
the patient regains self-control, loses his passion for drink,
is greatly ashamed of himself if he has indulged it, and
usually behaves in an irreproachable manner for some weeks
or months.

The sufferers from this frightful disease are entitled to a
sympathy to which the common drunkard has no claim.

III. Chronic and often Incurable Diseased Conditions
produced by Alcohol. — These are apt to be insidious in their

What is the proper meauing of the word dipsomania? "What dis-
eases are apt to be found in the children of parents given to alcoholic
excess? "What should a dipsomaniac do when he feels the fit coming
or ? "What happens when the paroxysm passes off?

354 tSE HUMAN BODY.

approach, and overlooked until they have firmly seated
themselves. They include, (a) deterioration of tissue; (b)
practical destruction of important organs; (c) mental and
moral enfeeblement.

(a) Deterioration of Tissue due to Alcohol. — A serious
structural change in the body produced by alcoholic excess
is fatty degeneration. The oily matter of the body exists
in two forms: first, as adipose or fatty tissue collected
under the skin, and in less amount elsewhere, as on the
surface of the heart and around the kidneys; second, as
minute fat-droplets in the interior of various cells and fibres.
Some forms of alcoholic drinks tend to increase the
adipose tissue, and may lead to undue accumulation of it
about the heart, impeding the action of that organ. A
more important and frequent result is an increase of fat-
droplets in the cells of the liver and the muscular fibres of
the heart, the oily matter replacing the natural working
substance. A heart which has undergone this change is
commonly spoken of by pathologists as a "whiskey heart;"
for although fatty degeneration of the heart may occur
from other causes, alcoholic indulgence is the most frequent
one. Fatty liver or fatty heart is rarely if ever curable;
either will ultimately cause death. It is probable that in
both cases the fatty degeneration is due to over-stimulation
of the organ. Most wines and spirits quicken the beat of
the heart, leaving it less time for repair between its strokes.

Why are chronic alcoholic diseases often unnoticed in their curable
stages? What main forms do they include?

In what forms is the oily matter of the body found? How do some
forms of alcohol affect the development of adipose tissue? What
may result? How does alcohol produce more serious changes in the
fatty matter of the body? What is meant by a " whiskey heart"?

What is the consequence of fatty liver or fatty heart? To what
is the fatty degeneration in these organs due? Explain for the heart.

ALCOHOLIC DETERIORATION OF TISSUE. 355

Alcohol also increases the breaking down of proteid matter
in the body; the liver has much to do in preparing this
broken-down proteid for removal by the kidneys, and so
gets overworked.

Another serious bodily deterioration produced by alco-
hol is fibrous degeneration: by this is meant an excessive
growth of the connective-tissue, which as we have seen
(p. 24) pervades the organs of the body as a fine sup-
porting skeleton for the more essential cells. Alcohol-
drinking causes this tissue to develop to such an extent as
to crush and destroy the cells, especially in the liver and
kidneys, which it should protect. So far as the liver is con-
cerned, the result is a shrunken, rough mass {hob-nailed
liver, or gin-drinker's liver), with hardly any liver-cells left
in it. This not only prevents the proper manufacture of
bile and glycogen (p. 151), but the contracted liver presses
on the branches of the portal vein within it (p. 208) so as to
impede the drainage of blood from the organs in the abdo-
men. As a consequence, an excess of the watery part of
the blood oozes into the peritoneal cavity and accumulates,
causing abdominal dropsy (ascites). In similar manner the
superabundant connective tissue in the kidneys crushes
and injures the essential kidney substance, and interferes
with the proper function of the organ in excreting nitrogen
waste and water. The ultimate consequence is one form of
'■' Bright's disease" — a very fatal malady, characterized by
elimination of albumen in the kidney secretion; retention
of proteid wastes in the blood, poisoning the various
organs; and accumulation of water in the loose tissue bind-

Explain for the liver.

What is fibrous degeneration? Describe the results whan it occurs
in the liver. In the kidneys.
What are the characteristics of Bright's disease?

356 THE HUMAN BODY.

ing the skin to underlying parts, producing that kind of
dropsy known as anasarca.

(p) The Organs of the Body most apt to be impaired or
destroyed by Alcohol have been in part mentioned in pre-
ceding pages. It will, however, be convenient to collect
them together, and point out the kind of change produced
in each. Probably no tippler ever suffered from all of
these diseases, and most of them may develop in persons
who are total abstainers; but the organic lesions which are
mentioned below are more frequently due to intemperance
than to any other cause.

A primary action of alcohol after absorption is to cause
dilatation of the cutaneous blood-vessels. With occasional
alcoholic indulgence this is temporary; with repeated, it be-
comes permanent. The Skin is then congested and puffy,
and on exposed parts it is seen to have a purplish or red-
dish blotched appearance; pimples appear on parts, such
as the nose, where the natural circulation is more feeble.
The result is the peculiar degraded look of the sot's face.
The congestion interferes with the nutrition of the skin;
the epidermis (p. 266) is imperfectly nourished and collects
in scaly masses, interfering with the proper action of the
sweat-glands, thus throwing undue work on the kidneys.

When constantly irritated by the direct action of strong
alcoholic drinks, the Stomach gradually undergoes lasting
changes. Its vessels remain dilated and congested, its
connective tissue becomes excessive, its power of secreting
gastric juice diminished, and its mucous secretion abnor-
mally abundant.

The Liver suffers fatty and fibrous degeneration, and is

Describe the consequences of alcoholic indulgence on the skia.
On Hie stomach.

ORGANS INJURED BY ALCOHOL. 357

one of the organs most often and earliest attacked. This
we might expect, as all the alcohol absorbed from the stom-
ach is carried direct to the liver by the portal vein (p. 208).

The Heart has its walls at first thickened (Jiypertrqphied)
and its cavities dilated by the excessive work (p. 354) which
alcoholic drinks stimulate it to perform. If, as is usually
the case, fatty degeneration ensues, the organ gradually
becomes too feeble to pump the blood around the body,
and death results.

The walls of the Arteries of drinkers frequently undergo
fatty degeneration; they lose their strength and elasticity,
and are liable to rupture, or to the disease known as aneu-
rism.

The Kidneys are excited to undue activity, in part by
the dilatation of their blood-vessels, in part, perhaps,
through direct stimulation of their cells by alcohol circu-
lating in the blood. Once the liver is attacked the nitro-
genous waste of the body is not carried to the kidneys in
proper form for excretion: some is held back, producing a
tendency to gout and rheumatism ; the rest is got rid of by
extra kidney effort. The usual result is fibrous degenera-
tion of the kidneys, causing one kind of Bright's disease.

The Lungs, from the congested state of their vessels pro-
duced by alcohol, are more subject to the influence of cold,
the result being frequent attacks of bronchitis. It has also
been recognized of late years that there is a peculiar form
of consumption of the lungs which is very rapidly fatal, and
found only in alcohol-drinkers.

On the liver? "Why is the liver especially apt to he attacked? On
the heart? On the arteries?

How does alcohol affect the kidneys directly? How through the
liver-disease produced by it? "What results?

What lung-diseases arc often produced by alcohol?

358 THE HUMAN BODY.

The Sense-organs are also affected : their acuteness of per-
ception is dulled; and many physicians believe that cata-
ract and retinal disease may be produced by drinking. The
red inflamed white of the eye of topers is well known.

The Brain and Spinal Cord are kept in a chronic state of
congestion* and over-excitement. This results at first in in-
flammatory disease (delirium tremens); later, in fibrous de-
generation, leading to certain forms of paralysis or to epi-
lepsy, of which there is one variety well recognized by phy-
sicians as due to alcohol.

(c) Moral Deterioration produced by Alcohol. — One re-
sult of a single dose of alcohol is that the control of the
Will over the actions and emotions is temporarily enfeebled;
the slightly tipsy man laughs and talks loudly, says and
does rash things, is enraged or delighted without due cause.
If the amount of alcohol be increased, further diminution
of will-power is indicated by loss of control over the mus-
cles. Excessive habitual use of alcohol results in perma-
nent over-excitement of the emotional nature and en-
feeblement of the Will; the man's highly emotional state
exposes him to special temptation to excesses of all
kinds, and his weakened Will decreases the power of
resistance: the final outcome is a degraded moral condi-
tion. He who was prompt in the performance of duty be-

Describe the action of alcohol on the sense-organs. On the brain and
spinal cord, and the resulting diseases.
Describe the moral deterioration produced by alcohol.

* " I once had the unusual though unhappy opportunity of observing the same
phenomenon in the brain-structure of a man who, in a fit of alcoholic excitement,
decapitated himself under the wheel of a railway -carriage, and whose brain was
instantaneously evolved from the skull by the crash. The brain itself, entire, was
before me within three minutes after death. It exhaled the odor of spirit most
distinctly, and its membranes and minute structures were vascular in the ex-
treme. It looked as if it had been recently injected with vejrmilliou."— Dr. B, W.
Uichardson.

THE OPIUM HABIT. 359

gins to shirk that which is irksome; energy gives place to
indifference, truthfulness to lying, integrity to dishonesty;
for even with the best intentions in making promises or
pledges there is no strength of "Will to keep them. In for-
feiting the respect of others respect for self is lost and
character is overthrown. Meanwhile the passion for drink
grows absorbing: no sacrifice is too costly which secures it.
Swift and swifter is now the downward progress. A mere
sot, the man becomes regardless of every duty, and even in-
capacitated for any which momentary shame may make
him desire to perform.

For such a one there is but one hope — confinement in
an asylum where, if not too late, the diseased craving for
drink may be gradually overcome, the prostrated Will re-
gain its ascendency, and the man at last gain the victory
over the hrute.

Opium and Morphia. — Opium is a gummy mixture con-
taining several active principles, of which the most impor-
tant is morphia. The forms in which it is most frequently
employed are (1) gum opium, the crude substance, often
put up in the form of pills; (2) laudanum, an alcoholic
extract of the gum; (3) paregoric, a liquid containing sev-
eral substances, of which opium is the most important;
(4) morphia and its compounds.

The Opium Habit. — Opium is perhaps the most valuable
drug at the disposal of the physician. On the other hand,
it is one of the most injurious substances used by mankind.
It may be that it does not do so much harm in the United
States as alcoholic drinks, but only because not so many

What is the confirmed drunkard's only hope for cure?
What is opium ? In what forms is it most often used?
Compare the damage done in the United States by indulgence in
alcohol and opium.

360 THE HUMAN BODY.

persons have acquired the craving for it. Used constantly
it is as certainly fatal and the habit is perhaps even harder to
break; for it may be indulged more secretly and its effects
are not so readily recognized. There is also this to be
said: that most inebriates are originally of weak character,
wrecking themselves on a rock in full view, through lack of
a strong hand at the helm; while many a one of highest
gifts and noblest character, who would loathe the low vice
of drunkenness, has gone under in the insidious maelstrom
spread by opium for its victims. Using the drug at first
as prescribed for the relief of suffering, he (or she, for more
women than men are addicted to opium excess) is scarcely
conscious of danger before being swept on to destruction.
Most medical men now fully recognize the danger and only
order prolonged use of opium with great caution. Never-
theless there are so many persons who habitually use opium
that it is important to point out the disastrous results.

The Diseased Conditions produced by Regular Use of Opium
are fairly uniform. The first phenomenon is deadening of
sensibility, accompanied by mental exaltation if the dose be
small. This is succeeded by unnatural sleep, disturbed by
fantastic dreams.

On awaking there is great depression of mind and body:
often associated with defective memory, and a feeling that
something terrible is about to happen. There is muscular
weakness; distaste for food, without actual nausea; and an
almost irresistible craving for another dose.

If the habit be continued further, mental and physical
changes occur. Distaste and inaptitude for any kind of

Why is opium more disastrous from one point of view?
What are the first phenomena following a dose of opium? What
is the condition of the person on awaking?
What results follow continuance of the habit?

OHLOMAL. 30 1

exertion; greatly impaired digestion; deficient secretion of
bile; sluggishness of the muscles of the intestines, causing
constipation. The muscles waste, the skin shrivels, and
the person looks prematurely aged. The pulse is quick,
the body feverish; the eye dull, except just after the drug
has been taken.

The final result is failure of the nervous system. Incom-
plete paralysis of the lower limbs is followed by a similar
state of the muscles of the back. The victim crawls along,
bent like an old man. Death finally results from starva-
tion, due to complete failure of the digestive organs.

Morphia. — When morphia is used, a solution of it is often
injected under the skin by a fine syringe. Prolonged use
of it in this way is followed by all the symptoms of chronic
opium-poisoning above described. The digestive organs
are not, however, as soon attacked; but the punctures of
the skin repeated for weeks, several times a day, cause in-
flammation and ulceration.

Danger of administering Opiates to Children. — Children
are remarkably sensitive to opium and all preparations con-
taining it. Opiates should never be administered to children
except by order of a physician. Many an infant has been
poisoned by a few drops of paregoric or of some soothing
^yrup given by parent or nurse to check diarrhoea or pro-
duce sleep.

Chloral. — The chloral habit is in this country at present

What is the final result?

In what do the consequences of injection of morphia beneath the
skin resemble and differ from those of opiates taken by the mouth?

How are children peculiar as regards opiates? Under what condi-
tions only should they be administered to children? What often re-
sults from giving opiates to infants?

Compare the frequency of the chloral and opium habits in the
United States.

362 THE HUMAN BODY.

more common than the opium habit, and, like it, more fre-
quent among women than men.

Chloral was, on its discovery a few years ago, heralded
as a wonderfully safe and certain promoter of sleep and al-
leviator of pain. Medical men have since learned that it is
by no means so harmless a drug as they once believed; but
the general public do not seem to have had their eyes
opened to its danger. A great many preparations of it
have been put on the market, and are sold in drug-stores
to all comers. The result is that many persons who would
hesitate to take opium without medical advice use chloral,
believing it harmless.

Chloral, taken habitually, is at least as mischievous as
opium. It should be forbidden by law to retail it in any
form except on the prescription of a physician.

The chloral habit is acquired with great ease, and is very
hard to break. The first phenomena of chloral disease
{chloralism) are these: The digestion is greatly impaired;
the tongue is dry and furred; there is nausea; sometimes
vomiting, and a constant feeling of oppression from wind
on the stomach.

Next, nervous and circulatory disturbances occur. The
temper becomes irritable, the Will weak; the hands and legs
tremulous; the heart-beat irregular; the face easily flushed.
Sleep becomes impossible without use of the drug: when
obtained it is troubled, and the person awakes unrested.

In later stages the blood is seriously altered. Its color-
ing matter is dissolved, and soaks through the walls of the

What have medical men lately learned about chloral? Why
do so many people take chloral without medical advice?

Describe the first symptoms of chloralism.

What are the symptoms in more advanced chloralism? What in
the latest stages?

THE LOCAL ACTION OF TOBACCO. 353

capillary vessels, causing purplish patches on the skin.
Jaundice also frequently occurs.

Tf the chloral-taking be still continued, death results
from impoverished blood, weakened heart, or paralysis of
the nervous system. Not unfrequently chloral-takers un-
intentionally commit suicide by indulging in too large a
dose.

Tobacco contains an active principle, nicotin, which
in its pure form is a powerful poison, paralyzing the
heart. When tobacco is smoked some of the nicolin is
burned, but there are developed certain acrid vapors which
have an irritant action on the mouth and throat. The
effects of smoking are thus in part general, due to absorbed
nicotin; and in part local, due to irritant matters in the
smoke. They vary much with the constitution, habits,
and age of the smoker. One general rule at least may be
laid down: tobacco is very injurious to young persons ivliose
physical development is not completed.

The Local Action of Tobacco is at first manifested by in-
creased flow of saliva. This usually passes off after some
practice in smoking; dryness of the mouth follows, and con-
sequent thirst, often leading to alcoholic indulgence; and
in this, perhaps, lies the greatest danger from tobacco.
The habitual smoker usually suffers eventually from what
is known to medical men as "smoker's sore-throat." The
inflammation often extends to the larynx, injuring the
voice and producing a hacking cough, or may spread up

How does death from chloral occur?

What is nicotin? What other injurious substances are found in
tobacco-smoke? What general rule may be stated concerning the
action of tobacco on the human body?

Describe the local actions of tobacco. How may tobacco-smoking
injure the voice? How the hearing?

364 THE HUMAN BODY.

the Eustachian tubes (p. 330) and impair the hearing.
Cigarettes are especially apt to cause these symptoms.
Cure is impossible unless smoking be given up. Those
who draw the smoke into their lungs often suffer from
chronic inflammation of the bronchial tubes in consequence.
The General Action of Tobacco. — The more commor.
effects of absorption of tobacco products are to interfere with
development of the red blood-corpuscles, leading to pallor
and feebleness; to impair the appetite and weaken digestion;
to affect the eyes, rendering the retina less sensitive; to
cause palpitation of the heart and enfeeblement of that
organ; to induce a lassitude and indisposition to exer-
tion that, in view of the heavy odds man has to contend
with in the life-struggle, may prove the handicap that
causes his failure. If success in life be an aim worth striv-
ing for, it is surely unwise to shackle one's self with a habit
which cannot promote and may seriously jeopardize it.

Describe the general action of tobacco on the body.

INDEX.

Abdominal aorta, 202

Abdominal cavity, 11

Abdominal respiration, 246

Abducentes nerves, 292

Abduction, 63

Absorbents, 107. 188; relation of
to excretion, 108

Absorption, from tbe month,
pharynx and gullet, 166; from
the stomach, 167; from the
small intestine, 167; from the
large intestine, 168; of fats,
162

Accommodation, 326

Acetabulum, 60

Acid, glycocholic, 161; hydro-
chloric, 20, 157; oleic, 21; pal-
mitic, 21; stearic, 21; tauro-
cholic, 161

Acinous glands, 129, 131

Adam's apple, 338

Adduction, 63

Afferent (sensory) nerves, 305

Air, changes produced in by
being breathed, 251; necessary
quantity of for each person,
255; quantity of breathed daily,
250; renewal of in the lungs,
240; unwholesome, 254

Air-cells, 237

Air-passages, 234; cilia of, 236

Albumen, egg, 21, 117; serum,
21, 113

Albuminoid alimentary prin-
ciples, 117

Albuminous (proteid) substances,
21; action of bile on, 161; of
gastric juice on. 157; of pan-
creatic secretion on, 159, 172;
special importance of as food,
111

Alcohol, 121, ;>43; absorption of,
348; diseases produced by, 350>
is it a food, 121. 343; mental

Alcohol (Gontinuedfy,

and moral deterioration due to,
353, 358

Alimentary canal, 9, 106; absorp-
tion from, 166; anatomy of,
169; general arrangement of,
128; sub-divisions of, 132

Alimentary principles, 116; al-
buminoid, 117: carbohydrate,
118; hydrocarbon, 117; inor-
ganic, 118; proteid, 117

Amoeba, 179

Amyloids (see Carbohydrates)

Anaemia, 185

Anatomy, human, 2. 17

Anatomy, microscopic (see His.
tology)

Anatomy, of alimentary canal,
132, 169; of circulatory organs,
192; of ear, 329; of eyeball,
321; of joints. 60; of larynx,
337; of liver, 149: of muscular
system, 67; of nervous s}'stem,
282, 299; of respiratory organs,
233; of skeleton, 23;" of skin,
266; of urinary organs, 261,
278

Animals, classification of, 8 (foot-
note)

Animal charcoal, 55

Animal heat, 96

Ankle joint, 83

Aorta, 198. 212; thoracic, 202,
abdominal, 202

Apex beat (cardiac impulse), 217

Apex of heart, 195

Appendicular skeleton, 26

Appetite, cause of, 165

Aqueous humor, 325

Arachnoid, 286

Arch of foot, 42. 45

Areolar tissue, subcutaneous, 268

Arm, skeleton of, 28

Arterial blood, 178, 211

366

INDEX.

Arterial pressure, 227

Arteries, 195, 202; action of
alcohol on, 357; aorla, 198,
212; axillary, 202; brachial,
202; coeliac axis, 202; com-
mon iliacs, 204; coronary.
199, 202, 213; femoral, 204,
hepatic, 150; left common
carotid, 202; left subclavian,
202; mesenteric, 202; peroneal,
204; popliteal, 204; pulmouary,
199, 212; radial, 202, 222;
renal, 202, 261; right common
carotid, 202; right subclavian,
202; temporal, 222; tibial, 204;
ulnar, 202

Arteries, course of the main, 201 ;
muscles of the, 228: properties
of the, 204; why placed deep,
205

Articular cartilage, 26, 48

Articular extremities of bones, 48

Articulations, 25

Arytenoid cartilages, 338

Assimilation, 108

Astragalus, 40

Atlantoaxial articulation, 32

Atlas vertebra, 32

Auditory nerve, 293

Auditory organ, 329

Auricles, 197; function of the, 220

Auricular appendages, 213

Auricular contraction, 217

Auriculo-ventiicular orifice, 197

Auriculo- ventricular valves, 201,
217; demonstration of their
action, 232

Auscultation, 245

Automatic nerve centres, 307;
use of, 309

Axial skeleton, 26

Axillary artery, 202

Axis cylinder of nerves, 296

Axis vertebra, 32

Backbone (see Vertebral column)
Ball and socket joint(enarthrosis),

62
Basement membrane, 131
Base of heart, 195
Bathing, 230, 275; proper time

for, 276

Beans, nutritive value of, 121

Beef-tea, 77

Beeswax, 118

Beverages, alcoholic, 346

Biceps muscles, definition of, 71

Biceps muscle, 69, 72

Bicuspids (premolars), 136

Bile, 150, 161; action of in fat
absorption, 162, 172; uses of,
161

Bile duct, common (ductus com-
munis choledochus), 150, 170

Bi-penniform muscles, 71

Bladder, urinary, 263, 278

Blind spot, 324

Blood, action of oxygen on, de-
monstration, 259; arterial and
venous, 178, 211; changes un-
dergone by in the lungs, 257;
circulation of, 207; coagulation
of, 179; colorless corpuscles of,
179; compared with waler,
182; experiments with, 190;
flow of in the capillaries and
veins, 224; functions of, 174,
175; gases of, 183; histology
of, 176; hygiene of, 184;
quantity of in the bod}', 185;
red corpuscles of, 177; whipped
(defibrinated), 181

Blood plasma, 176

Blood serum, 180, 191; composi-
tion of, 182

Blushing, 228

Body, centre of gravity of, 85;
chemical composition of, 19;
constructive power of, 112;
cooperation of the organs of,
279; daily need of foods by,
124; general plan of, 6; levers
in the, 80; movements of, 59;
oxidations in, 99; oxygen food
of, 103; pulleys in, 84; quan-
tity of blood in, 185; tempera-
ture of, 97; wastes of, 105

Boues, chemical composition of,
54; fractures of, 57; function
of, 23; gross structure of, 47;
histology of, 51 ; internal stru<v
ture of, 49; of cranium, 37; of
ear, 331, of face, 37; of lower
limb, 28; of pectoral arch, 27;

INDEX.

367

Bones {Continued).
of pelvic arch, 28; of upper
limb, 28; reason that they are
hollow, 50; varieties of, 51

Bone-ash, 55

Bone-black (animal charcoal), 55

Bone corpuscles, 54

Bony skeleton, 26; hygiene of, 56

Brachial artery, 202

Brain, 288; dissection of, 299;
hygiene of, 311

Bread, composition of, 116;
wheaten, superiority of, 120

Breastbone, 27, 34

Bright's disease, 266 (foot-note)

Bronchi, 235

Bronchitis, 237

Brunner, glands of, 148

Buccal cavity (See mouth cavity)

Butter, 117

Butyrin, 117

Cabbage, nutritive value of, 121

Caecum, 148, 170

Calcium carbonate, 20, 55

Calcium phosphate, 20, 55, 57

Calcaneum, (heel bone') 42

Calices of kidney, 263,' 278

Canaliculi of bone, 54

Cane sugar, 118

Canine teeth, 136

Capillaries, 195, 204; absence of
pulse in, 226; circulation in,
224, 225; demonstration of the
action of, 232; pulmonary,
199; systemic, 198

Capsular ligament, 61

Carbohydrates (amyloids), 22,
118; kinds of in the body,
22

Carbonate of lime, 20, 55

Carbon dioxide, as a waste pro
duct, 105 ; demonstration of
presence of in expired air,
259; in the blood, 184; per-
centage of in unwholesome air,
255; quantity of passed from
the lungs in a day, 252; useless
as a food, 112

Cardiac impulse (apex beat), 217

Cardiac orifice of stomach, 143,
170

Cardiac period, events occurring
in a, 217

Carotid arteries, 202

Carpal bones, 28, 51; joints be-
tween, 65

Carrots, nutritive value of, 121

Cartilage, articular, 26, 48; cells
of, 23; costal, 34; function of,
33; intervertebral, 30, 33

Casein, 21, 117; vegetable, 117

Cells, 15, 17; air, of lungs, 237:
cartilage, 23 ; ciliated, of air
passages, 236; forms of, 15;
nerve, 297; plain muscle, 76:
structure of, 15

Cellulose, 116, 164

Cement of teeth, 137

Centres, nerve (see Nerve-cen-
tres)

Centre of gravity of body, 85

Centrum of vertebra?, 30

Cerebellum, 289; functions of,
306; removal of, 313

Cerebral hemispheres, 289; re-
moval of, 312

Cerebro-spinal liquid, 286

Cerebro- spinal nerve system,
284

Cervical enlargement of spinal
cord, 287

Cervical vertebrae, 30

Cheese, nutritive value of, 120

Chemical changes in respired air,
251

Chemical composition of albu-
mens, 21 ; of bile, 161 ; of blood-
serum, 182; of body, 19; of
bone, 54; of carbohydrates. 22
of fats, 21 ; of gastric juice, 156
of lymph, 189; of muscle, 77
of pancreatic secretion, 159; of
red corpuscles, 183; of respired
air, 252

Chest (see Thorax)

Chloral, 361

Chordae teudineoe, 201, 214

Choroid, 321

Chyle, 158

Chyme, 158

Cilia, 236; demonstration of ac
tion of, 249

Circulation, 107, 207; in capilhv

368

INDEX.

Circulation {Continved).

ries and veins, 224; portal, 208;

pulmonary, 208; systemic, 208;

diagram of, 209
Circulatory organs, 192; relation

of to excretion, 108; diagram

of, 194
Circumduction, 63
Circumvallate papillae, 139, 334
Clavicle (collar bone), 27
Clotting of blood (see Coagula-
tion)
Coagulation of blood, 179; cause

of, 180; experiments unon, 190;

uses of, 181
Coccyx, 30
Cochlea, 331
Cceliac axis, 202
Coffee, 123
Cold, taking, 229
Collar-bone (clavicle), 27
Colloids, 157
Colon, 149, 170
Colorless blood corpuscles, 179,

190
Columnse carneae, 215
Comminuted fracture of bones, 57
Common bile-duct (ductus com-
munis cboledochus), 150, 170
Compact bone, 49; structure of, 51
Compound fracture of bone, 58
Concha, 330

Condiments as foods, 115
Connective tissue, 24
Conservation of energy, law of,

93; illustrations of, 94
Consonants, classification of, 341
Constructive power of tbe body,

112
Convolutions of the brain, 290
Cooking, 123

Co-ordination, 281 ; centre of, 306
Corium (cutis vera, dermis), 268;

papillae of, 270
Corn, nutritive value of, 121
Cornea, 321

Coronary arteries, 199, 202, 213
Coronary sinus, 214
Coronary veins, 200, 213
Corpus Arantii, 214
Corpuscles of blood, 176, 190
Costal cartilage, 34

Costal respiration, 246
Cranial nerves, 290; sutures, 38
Cranium, bones of, 37
Cricoid cartilage, 338
Crystalline lens, 325
Crypts of Lioberkuhn, 148
Cuticle (epidermis), 266

Death, from starvation, 98; from
alcohol, 347, 352, 353; from
chloral, 363; from opium or
morphia, 361

Death-stiffening (rigor mortis), 74

Defibrinated blood,' 181 [355

Degeneration, fatty, 354; ;ibrous,

Deglutition (see Swallowing)

Delirium tremens, 352

Dentine, 136

Dermis 'see Corium)

Dialysis (osmosic), 186

Diaphragm (midriff), 11, 242; de-
monstration of, 248

Diarrhoea, 229

Die(, advantages of a mixed, 125

Digestion, 107, 128; gastric, 157,
171 : influence of saliva in, 154;
intestinal, 163; object of, 152

Dipsomania, 353

Disassimilation, 108

Diseases due to alcohol, 350; to
chloral, 362; to morphia or opi-
um, 360; to tobacco, 363

Dislocations, 65; reduction of, 66

Division of labor, physiological,
17 '

Dorsal (neural) cavity, 7, 31 ; con-
tents of, 9, 13

Dorsal vertebrae, 30

Duct of glands, 131

Duct, common bile, 150, 170; cys-
tic, 150; hepatic, 150; of parotid
;;land, 169; of submaxillary
gland, 169

Dura mater, 285

Dyspepsia, 164

Ear, 330

Efferent (motor) nerves, 305
Eggs, nutritive value of, 120
Egg-albumen, 21, 117
Eighth pair cranial (auditory/
nerves, 293

INDEX.

3C9

Elasticity of the arteries, 226,
232; of the lungs, 238

Elastic tissue, 164

Elbow joint, 65, 70

Elements found in the body, 20
(foot-note)

Eleventh pair cranial (spinal ac-
cessory) nerves, 293

Emmetropic eye, 327

Emulsion, 160

Enamel, 136

Endolymph, 331

Endoskeleton, 23 (foot-note)

Energy, 93, 101; chief forms of
expended by the body, 101;
conservation of, 93, 101; liber-
ation of by oxidations at low
temperature, 10-1; source of in
the body, 95

Epidermis, 266

Epiglottis, 142, 333

Etbmoid bone, 37

Eustachian tube, 141, 330

Excretion and reception, inter-
mediate steps between, 106

Excretions, removal of, 108

Excretory organs, 106

Exercise, 90

Exoskeleton, 23 (foot-note)

Expiration, 242. 244

Extension at joints. 63

Extensor muscles, 80

External auditory meatus, 330

Extracts of meat, 78

Eye, action of alcohol on, 358;
accommodation :f, 326; hy-
giene of, 328

Eyeball, anatomy of, 321

Eyelashes, 318

Eyelids, 318

Eye-socket, 318

Face, bones of, 37

Facial nerve, 293

Fasciculi of muscles, 73

Fatty acids. 117

Fats (hydrocarbons), 21. 117; ab-
sorption of, 162; action of bile
on, 161, 172; of gastric juice
on, 157; of pancreatic secretion
on, 160, 172; as a reserve

Fats {Continued).

food, 98, 102: emulsifying of,
160, 163: kinds of in body, 21

Fauces, 141 ; isthmus of the," 133,
155; pillars of the, 141

Femoral artery, 204

Femur, 28

Fibres, 16 ; plain muscle, 76:
striped muscle. 74

Fibrillae, 74

Fibrin, 21, 180

Fibula (peroneal bone), 28, 51

Fifth pair cranial (trigeminal)
nerves, 292

Filiform papillae, 139, 334

Flexion at joints, 63

Flexor muscles, 80

Food, amount of required daily,
124; as a force generator, 115;
as a force regulator, 115: as
a machinery former, 114: as
a tissue former, 110; composi-
tion of, 111; cooking of, 123;
definition of, 114; inorganic,
118; is alcohol a food, 121,
343; need of, 95, 97; non oxi-
dizable, 118; nutritive value
of differenl. 119; special im-
portance of albuminous, 111;
supply of animal, 112

Food-stuffs (see Alimentary prin-
ciples)

Foot, skeleton of. 29; peculiari-
ties of human, 45

Foramen, intervertebral, 32:
magnum, 37; oval, 331

Force-generating foods, 115

Force-regulating foods, 115

Forearm, movements of, 64, 70

Fore limb (see Upper limb)

Fossa, glenoid, 63

Fourth pair cranial (pathetici)
nerves, 292

Fractures of bones, 57

Free (floating) ribs, 34

Frog's web, circulation in, 224

Frontal bone. 37

Fruits, nutritive value of, 121

Fundus of stomach, 170

Fungiform papilla, 139, 334

Furred tongue, 140

INDEX.

Gall (see Bile)

Gall bladder, 150

Games, use of, 92

Ganglia, 284; Gasserian, 292;
spinal, 287; sympathetic, 294

Gases of the blood, 183

Gasserian ganglion, 292

Gastric digestion, 157; experi-
ments illustrating, 171

Gastric glands, 144

Gastric juice, 144, 156; artificial,
171

Gelatine, 55, 117

Gelatin ization, stage of in coagu-
lation, 179

Glands, 129; forms of, 131; gas-
tric, 144; kinds of, 129; lachry-
mal, 319; mammary, 11; mei-
bomian, 318; of Brunner, 148;
of skin, 272; of small intes-
tine, 148; salivary, 140, 169

Glenoid fossa, 63

Gliding joints (arthrodia), 65

Glossopharyngeal nerves, 293

Glottis, 335

Glucose (grape sugar), 22, 118;
conversion of starch into, 153

Gluten, 117, 120

Glycerine, 21, 117

Glycocholic acid, 161

Glycogen, 22, 118. 151, 167

Grape sugar (see Glucose)

Gray nerve fibres, 296

Gullet (see ffisophagur)

Gums, 118, 134

Habits, 309

Haemal cavity (see Ventral cavity)

Haemoglobin, 178, 210, 258

Hairs, 270

Hair-follicle, 271

Hand, skeleton of, 28

Hard palate, 133

Haversian canals, 52

Haversian system, 53

Hearing, 329

Heart, 9; action of alcohol on,
349, 357; beat of, 216; cavi-
ties of, 197; dissection of,
210; experiments upon, 230;
position of, 195; how nour-
ished, 199; muscle of, 76; pal-

Heart {Continued).
pitation of, 144; sounds of,
220; vessels connected with,
198; work done by daily, 221
Heat of body, source of, 96; in-
fluence of starvation upon, 97
Hepatic artery, 150
Hepatic duct, 150
Hepatic veins, 209, 212
Hibernation, 98 (foot-note)
High heels, bad effects of, 56
Hilus of kidney, 263, 278
Hind limb (see Lower limb)
Hinge joints (gingl} mi), 63
Hip-joint, 28, 60
Histoloay, definition of, 2; of
blood^ 176; of bone, 51; of
kidneys, 265; of lungs, 237;
of lymph, 189; of muscle, 74;
of nerve cells, 297; of nerve
fibres, 296; of retina, 321; of
skin, 266
Hollow veins (see Venae cava?)
Human anatomy, definition of,

2, 17
Human physiology, definition of,

1, 2, 17
Humerus, 28, 47
Hunger, 316
Hydrocarbons (see Fats)
Hydrochloric acid, 20, 157
Hysriene, definition of, 1, 2; of
blood, 184; of bony skeleton,
56; of brain, 311; of eyes, 328;
of muscles, 89; of respiration,
245, 254; of skin, 274; of
teeth, 137
Hyoid bone, 26
Hypermetropia, 328
Hypoglossal nerves, 293

Ileo-colic valve, 149
Ileum, 145
Iliac arteries, 204
Incisors, 135
Incus (anvil bone), 331
Indigestible substances, 164
Inferior maxillarv bone (mandi-
ble), 37
Inferior maxillary nerve, 292
Inferior turbinate bone, 38, 333
Innominate artery, 202

INDEX.

371

Innominate bone (os innomina-

tum or pelvic bone), 28, 60
Inorganic constituents of the

body, 20
Inorganic foods, 118
Insertion of muscles, 70
Inspiration, 242, 244
Intercellular substance, 16, 23
Internal ear (labyrinth), 331
Intervertebral foramina, 32; discs,

30, 33
Intestinal digestion, 163
Intestinal juice (succus enteri-

cus), 163
Intestines, digestion in, 163;

large, 148 (see Large intestine):

small, 145 (see Small intestine)
Invertebrate animals, character

istics of, 8
Involuntary muscles, 75
Iris, 321
Isthmus of the fauces, 133, 155

Jejunum, 145

Joint, ankle, 83; elbow, 65, 70;
hip. 28, 60; knee, 63; shoulder,
42, 63

Joints, 25; ball and socket, 62;
general structure of, 60; glid-
ing, 65; hinge, 63; pivot, 64;
movements at, 63

Kidneys. 9, 261, 278; action of
alcohol on, 355, 357 ; gross
anatomy of, 263; histology of,
265; secretion of, 266

Knee-cap (patella), 29

Knee-joint, 63

Labor, physiological division of,
17

Labyrinth (internal ear). 331

Lachrymal apparatus, 319

Lachrymal bones, 38

Lacteals, 147, 168, 188

Lactose (milk sugar), 22, 118

Lacunae of bone, 54

Lamellae of bone, 53

Large intestine, 133, 148; absorp-
tion from. 168

Larynx, 235, 337; muscles of, 339

Leg, skeleton of, 28

Levers in the body, 80, 81, 82, 83,
84

Lieberktlhn, crypts of, 148

Liebig's extract of meat, 78

Ligaments, 24, 61; capsular, 61;
round, 61; transverse, of atlas
32, 64

Light, action of, on the retina,
323, 325

Limbs, comparison of upper and
lower, 38; general structure of,
10

Liver, 149; action of alcohol on,
357; functions of, 151

Localization of skin-sensations,
332

Local sign, 332

Locomotion, 86

Long bones, 51

Long sight (hypermetropia), 328

Lower jaw, bone of, 37; move-
ments of, 64

Lower limb, comparison of up-
per and, 38; peculiarities of, in
man, 45; skeleton of, 28

Lumbar enlargement of spinal
cord, 287

Lumbar vertebra?. 30

Lungs, 8, 106, 237; action of al-
cohol on, 357; changes under-
gone by blood in, 257; de-
monstration of the action of,
248; dissection of, 247; elas-
ticity of, 238; expansion of,
239; quantity of C03 passed out
from, in a day, 252; quantity
of O taken up by, in a day, 252;
renewal of air in, 240

Lunula of nails, 271

Lymph, 186; chemistry of. 189;
*)iistolo<ry of, 189; renewal of,
187

Lvmpliatics of small intestine,
*147

Lvmphatic vessels (absorbents),
188

Malar bone, 38
Malleus (hammer) bone, 331
Malpighi, pyramids of. 264. 278
Mammalia, definition of, 11, 13
Mammary glands, 11

372

INDEX.

Man, as a vertebrate animal, 7
13; place of, among vertebrates,
11, 13

Mandible (inferior maxillary-
bone), 37

Margarin, 117

Marrow, 49, 50; red, 50

Maxilla (superior maxillary
bone), 38

Meat extracts, 78

Meats, cooking of, 124; nutritive
value of, 119

Medulla oblongata, 289

Medullary cavity of bone, 49, 51

Medullary sheatb of nerves, 296

Meibomian follicles, 318

Membranes of the brain and
spinal cord, 285

Mesenteric arteries, 202

Mesentery, 170

Metacarpal bones, 28, 51

Metatarsal bones, 29, 51

Microscopic anatomy (see His-
tology)

Midriff (see Diaphragm)

Milk, as a food, 57; nutritive
value of, 120; sugar (lactose),
22, 118; teeth, 135

Mitral valve, 201, 215

Molar teeth, 136

Moral deterioration due to alco-
hol, 361

Morphia, 361

Motor (efferent) nerves. 305

Motores oculi t>erves, 291

Mouth-cavity, 133; absorption
from, 165

Movements, at joints, 63; of the
body, how effected, 59; in
space, 86

Mucin, 164

Mucous coat, small intestine, 146

Mucous membrane, of air-pas-
sages, 236; of alimentary
canal, 123

Mumps, 140

Muscles, 59, 67; chemical com-
positioi of, 77; contraction of,
69: gross structure of, 73; his-
tology of, 74; how controlled,
72; hygiene of, 89; of arteries,
228; of heart, 76; A larvnx,

Muscles (Continued).
339; of small intestine, 148; of
stomach, 144; origin and in-
sertion of, 70; papillary, 201.
214, 219; parts of, 67; rectus
abdominis, 72; special physi-
ology of, 80; varieties of, 71

Muscular fibres, 74

Muscular tissue, striped, 73;
plain, 74

Muscular work, influence of
starvation upon, 97; source, 93

Mustard, use of, as a food, 115

Myopia, 327

Myosin, 21, 77, 117

Nails, 271

Narcotics, 343

Nares, posterior, 38

Nasal bones, 38

Nerves, cranial, 290; kinds of,
294; spinal, 287

Nerves, inferior maxillary, 292;
ophthalmic, 292; right phrenic,
212; sciatic, 299; superior max-
illary, 292; sympathetic, 294

Nerve- eel Is, 297

Nerve centres, 282, 284; classifi-
cation of, 305; functions of,
304

Nerve- fibres, afferent and effe-
rent, 305; kinds of, 295

Nerve-ganglia, 284

Nerve-trunks, 382; functions of,
304

Nervous system, anatomy of,
282; properties of, 301, 312

Neural arch, 31

Neural cavity (see Dorsal cav-
ity)

Nicotin, 363

Ninth pair cranial (glossopha-
ryngeal) nerves, 293

Nitrogen-excreting organs, gene-
ral arrangement of, 261

Non-oxidizable foods, 113

Non-vascular tissues, 175

Nucleolus, 15

Nucleus, 15

Nutrition, 109

Nutritive value of different
foods.. 119

INDEX.

373

Occipital bones, 37; condyles,
33

Odontoid (tooth like) process of
the axis, 32, 64

Odorous substances, 333

(Esophagus (gullet), 8. 133, 142,
169; absorption from, 166

Oils (see Fats)

Oil glands (sebaceous - glands),
273

Oleic acid, 21

Oleine, 21, 117

Olfactory lobes, 289

Olfactory nerves, 290

Omentum, 13, 170

Ophthalmic nerves, 292

Opium, 359

Optic commissures, 291

Optic nerves, 290, 317

Organ, definition of. 4; circula-
tory, 107, 192, 194; digestive,
107, 128; uiirotrcii excreting,
261; of hearingr329; of sight,
317; of smell, 333; of taste, 334,
of temperature sense, 3o:5; of
touch, 331; receptive and ex-
cretory, 105; respiratory, 108,
233

Organic constituents of the body,
20

Organs diseased by alcohol,
356

Origin and insertion of muscles,
70

Osiunominatum (see Innominate
bone)

Osmosis, 186

Oval foramen, 331

Oxidations in the body, 99

Oxidations, 99, 100

Oxygen, absorption of from the
lungs, 258; in the blood, 184;
influence of on the color of
the blood, 259; quantity of
taken up by the lungs in a
day, 252

Oxygen food of the body, 103

Oxyhemoglobin, 258

Palate, 133
Palate bones, 38
Palmitic acid, 21

Palmitin.21, 117

Palpitation of the heart, 144

Pancreas, 151, 170

Pancreatic secretion, 159; action
of on foodstuffs, 160, 172

Papillae of the dermis, 270

Papillae of the tongue, 139

Papillary muscles, 201, 214; use
of the, 219

Parietal bones, 37

Parotid gland, 140, 169

Patella (kuee-cap), 29

Patlietici nerves, 292

Peas, nutritive value of, 121

Pectoral arch or girdle, 27; com-
parison of pectoral and pelvic
girdles, 38

Pedicle of velebrae, 32

Pelvic arch or girdle, 28; com-
parison of pectoral and pelvic
girdles, 38

Pelvis, 28, 45

Pelvis of kidney, 263

Penniform muscles, 71

Pericarditis, 196

Pericardium, 195, 212

Perilymph, 331

Perimysium, 73

Periosteum, 47, 51

Permanent teeth, 135

Peroneal artery, 204

Perspiration, 272

Pepper, use of as a food, 115

Pepsin, 157

Peptones, 157; absorption of. 167

Phalanges of fingers, 28, 51; of
toes, "29, 51

Pharynx, 133, 141; absorption
from, 166

Phosphate of lime, 20, 55, 57

Phrenic nerve, 212

Physiological division of labor,
17

Physiology, human, definition
of, 1, 2, 17

Physiology of muscle, special
and general, 80

Pia mater, 285

Pillars of the fauces, 141

Pivot joints, 64

Plain muscular tissue, 74

Plants, as food for animals, 112

374

INDEX.

Pleura, 238

Pleurisy, 238

Pneumogastric nerve, 293

Poison, definition of, 116

Polysrastric muscles, 72

Pons'varolii, 289

Popliteal arteiy, 204

Pork, nutritive value of, 119

Portal circulation, 208

Portal vein, 150, 170, 208

Posterior nares, 38

Potatoes, nutritive value of, 121

Premolars (bi cuspids), 136

Primitive sheath of nerves, 296

Pronation, 65

Proteid alimentary principles,
117

Proteid substances (see Albumin-
ous substances)

Psychic nerve centres, 305

Pulleys in the body, 84

Pulmonary artery, 199, 212

Pulmonary circulation, 192, 208

Pulmonary veins, 199, 212

Pulp cavity of tooth, 136

Pulse, 222; disappearance of in
capillaries and veins, 226; hard
and soft, 223; rate of, 223

Pupil, 321

Pus, 179

Pyloric orifice of stomach, 143,
170

Pyloric sphincter, 144, 157, 158

Pyramids of Malpighi, 264, 278

Racemose (acinous) glands, 129,
131

Radial arteiy, 202, 222

Radius, 28, 51

Receptive organs of the body,
105

Reception and excretion, inter-
mediate steps between, 106

Rectum, 149, 170

Rectus abdominis muscle, 72

Red blood corpuscles, composi-
tion of. 183; function of, 178,
259; of man, 177, 190; of other
animals, 177

Red -marrow, 50

Reduced haemoglobin, 210

Reducing dislocations, 66

Reflex centres, 308; experiments
showing action of, 313; use of,
309

Refracting media of the eye, 325

Renal arteries, 202, 261

Renal secretion (urine), 266

Renal veins, 261

Respiration, 108; abdominal, 246;
chemistry of. 250: costal, 246;
experiments in, 248, 259; hy-
giene of, 245, 254; object of,
233

Respirator}' organs, 108; anat-
omy of, 233

Respiratory sounds or murmurs,
245

Retina. 317; histology of, 321

Ribs, 26, 34; action of in respira-
tion, 244

Rice, nutritive value of, 121

Right phrenic nerve, 212

Potation at joints, 63

Round ligament, 61

Running, 89

Sacrum, 30, 34

Saliva, 152, chemical action of,
153, 171; influence of in diges-
tion, 154; uses of, 152

Salivary glands, 140, 169

Salt, as a constituent of the body,
20, importance of as food, 118

Sarcolemma, 74

Scapula (shoulder-blade), 27, 51

Sciatic nerve, 299

Sclerotic, 321

Sebaceous glands (oil glands), 273

Sebaceous secretion, 274

Secretion, of gastric glands, 144,
156; of glands of small intes-
tine, 163; of kidneys, 266; of
lachrymal gland, 319; of liver,
150, 161 (see bile); of meibomi-
an follicles, 318; of pancreas,
159 (see Pancreatic secretion);
of salivary glands, 152 (see
Saliva); of sebaceous glands,
274; of sweat glands, 272

Semicircular canals, 331

Semilunar valves, 201, 218; dem-
onstration of actiou of, 231

Semivowels, 341

INDEX.

375

Sensations, 314; common, 315;
localization of skin, 332

Senses, special, 316

Sensory (afferent) nerves, 305

Septum of heart, 197, 213

Serum (see Blood serum)

Serum albumen, 21, 113; coagu-
lation of, 183, 191

Seventh pair cranial (facial)
nerves, 293

Shaft of bones, 48

Short bones, 51

Short sight (myopia), 327

Shoulder girdle(see Pectoral arch)

Shoulder joint. 42, 63

Shower baths, 277

Sight, sensation of, 317; organ of,
317

Sigmoid flexure, 149

Simple fracture of bones, 57

Sinuses of Valsalva, 215

Sixth pair cranial (abducentes)
nerves, 292

Skeleton, appendicular, 27; axi-
al, 26; composition of, 23; of
cranium, 37; of face, 37; of
lower limb, 28; of upper limb,
28; peculiarities of human, 43

Skin, 266; action of alcohol on,
356; as a sense-organ, 274;
glands of, 272; histology of,
266; hygiene of, 274; Vensa.
tions, localization of, 332

Skull, 26, 35; peculiarities in the
position of, 43

Small intestine, 133, 145, 170;
absorption from, 167; glands
of, 148; lymphatics of, 147;
mucous coat of, 146: muscular
coat of, 148; villi of, 146

Smell, 333

Sounds of the heart, 220

Sounds, respiratory, 245

Sound waves, action of on the
ear, 331

Special physiology of muscles, 80

Speech, 336

Sphenoid bone, 37

Spinal accessory nerves, 293

Spinal cord, 9, 286; dissection of,
299

Spinal ganglia, 287

Spinal nerves, 287

Spine (see Vertebral column)

Spinous process of vertebrae
(neural spine), 31

Spleen, 170

Spongy (cancellated) bone, 49

Sprains, 66

Standing, 84

Stapes (stirrup bone), 331

Starch, 118; action of bile on,
161; of gastric juice on, 157; of
pancreatic secretion on, 159,
172; of saliva on, 153, 171; sol-
uble, 124

Starvation, death from, 98; in-
fluence of on muscular work
and animal heat, 97

Stearic acid, 21

Stearin, 21, 117

Sternum (breast bone). 27, 34

Stimulants, 115.122, 343

Stomach, 8 143, 170; absorption
from, 167; action of alcohol on,
350, 356; digestion in, 157,
171; glands of, 144; muscular
coat of, 144

Striped muscular tissue, 73, 74

Sub-clavian artery, 202

Sub lingual gland, 141, 169

Sub-maxillary gland, 140, 169

Succus entericus (intestinal
juice), 163

Sudoriparous glands (sweat-
glands), 131, 272

Suffocation, 104. 253

Sugar, cane, 118; grape (see
Grape-susrar)

Sugar of milk (lactose), 22. 118

Superior maxillary bone, 38

Superior maxillary nerve, 292

Supination, 64

Swallowing (deglutition), 154; as
a reflex action, 309

Sweat. 272

Sweat (sudoriparous) glands, 131,
272

Sweetbread (see Pancreas)

Sympathetic nerve centres, 9, 12,
"284; ganglia of, 293

Synovial fluid, 61

Synovial membrane, 61

Syntonin, 77, 117

376

INDEX.

Systemic circulation, 192, 208
Systole of heart-beat, 216

Tabular bones. 51

Tarsal bones, 29, 51 ; joints be-
tween, 65

Tarsus, benefits of peculiar
structure of, 45

Taste, 334

Taurocbolic acid, 161

Tea, 123

Tears, 319

Teeth, characteristics of indi-
vidual, 135; general structure
of, 134; hygiene of, 137; kinds
of, 134

Temperature changes in respired
air, 251, 259

Temperature of the body, 96;
regulation of, 97: regulation by
means of sweat glands, 274
(footnote)

Temperature sense. 333

Temporal artery, 222

Temporal bone. 37

Tendons, 24. 67, 69

Tenth pair cranial (pneumogas-
tric) nerves, 293

Thein, 115

Thigh bone (femur), 28

Third pair cranial (motores
oculi) nerves, 291

Thirst, 316

Thoracic aorta, 202

Thorax, contents of, 11; dorso-
ventral enlargement of, 244;
structure of, 242; vertical en-
largement of, 242

Thyroid cartilage, 338

Tibia. 28, 51

Tibial artery, 204

Tight lacing, evil effects of, 247

Tissues, classification of, 4 (foot-
note); connective, 24; nerve,
294; non-vascular, 175; plain
muscular, 74; striped muscular.
74; subcutaneous areolar, 268:
ultimate structure of, 15

Tobacco, 363

Tonsrue, 139; furred, 140

Tonsils, 141

Touch, 331

Trachea (windpipe), 8, 235; dis
section of, 247; structure of,
236

Transverse ligament of the atlas,
32, 64

Triceps muscle, 72

Triceps nmscles, definition of, 71

Trichina. 120

Tricuspid valve, 201, 214

Trigeminal nerves, 292

Trypsin, 160

Tubular elands, 129, 131

Turbinate bones, 38, 333

Turnips, nutritive valve of, 121

Twelfth pair cranial (hypoglos-
sal) nerves, 293

Tympanic membrane, 330

Tympanum, 330

Ulna, 28, 51

Ulnar artery, 202

Unslriped muscle cells, 76

Upper jaw bone, 38

Upper limb, comparison of upper

and lower limbs, 38; skeleton

of, 28
Urea, 105. Ill, 266; useless as

food, 112
Ureters, 263, 278
Urethra, 263

Urinarv bladder, 263. 278
Urine. '266

Uriniferous tubules, 265
Uvula, 134

Vagi. 293

Valsalva, sinuses of, 215

Valves, auriculo-ventricular, 201.
214. 217, 232; ileocolic, 149;
of the heart, demonstration of
their action, 231; of the veins,
206; semilunar, 201, 215, 218,
231

Valvulae conniventes, 146

Vascular system, function of the
different* parts of, 193

Veins, 194, 205; absence of pulse
in, 226; circulation in, 224;
valves of the, 206

Veins, coronary, 199, 213; he-
patic, 209, 212; hollow (venae
cavae), 199, 212; portal, 150,

INDEX.

377

Veins (Continued).
170,208; pulmonary, 199, 212;
renal, 261

Vegetable casein, 117

Venae cavae (hollow veins), 199,
212

Venous blood, 178, 211

Ventilation, 253; methods of, 256

Ventral (haemal) cavity, 6; con-
tents of, 8, 13

Ventricles, 197

Ventricular contraction, 218

Vermiform appendix, 148

Vertebrae, 30, 51; structure of, 30

Vertebral column, (spine, back-
bone), 7, 26, 30, 34, curvatures
of, 33; mechanism of, 33; pecu-
liarities of human, 44

"Vertebrate animals, characteris-
tics of, 7; classification of, 11
(foot-note)

Vestibule of ear, 331

Villi of small intestine, 146, 170

Visual apparatus, 317

Visual centre, 317

Visual purple, 323

Vitreous humor, 325

Vocal cords, 338

Voice, 335; range of human, 340
Voluntary muscles, 75 (see also

foot-note)
Vomer, 37
Vowels, 340

Walking, 87

"Warm baths, 277

Wastes of the body, 105; removal
of, 175

Water, as a constituent of the
body, 20; as a food, 113, 118;
as a force regulator, 115; as a
waste product, 105; quantity
of lost through the kidneys,
266; through the lungs, 251;
through the skin, 273

Wheat, nutritive valve of, 120

Whipped (defibrinated) blood,
181

White blood corpuscles. 179, 190

White nerve fibres. 295

Windpipe (see Tnu-liea)

Wisdom teeth, 135

Work, daily, of heart, 221; in-
fluence of starvation upon
muscular, 97; power of the
body to do, 93

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