Hygienic Physiology : with Special Reference to the Use of Alcoholic Drinks and Narcotics

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Title: Hygienic Physiology : with Special Reference to the Use of Alcoholic Drinks and Narcotics

Author: Joel Dorman Steele

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Most recently updated: December 30, 2020

Language: English

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*** START OF THE PROJECT GUTENBERG EBOOK HYGIENIC PHYSIOLOGY : WITH SPECIAL REFERENCE TO THE USE OF ALCOHOLIC DRINKS AND NARCOTICS ***

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[Illustration]

PATHFINDER PHYSIOLOGY No. 3

HYGIENIC PHYSIOLOGY

WITH SPECIAL REFERENCE TO THE USE OF

ALCOHOLIC DRINKS AND NARCOTICS

BEING A REVISED EDITION OF THE

FOURTEEN WEEKS IN HUMAN PHYSIOLOGY

BY JOEL DORMAN STEELE, PH.D.

ENLARGED EDITION WITH SELECTED READINGS

_Edited for the use of Schools, in accordance with the recent
Legislation upon Temperance Instruction_

INDORSEMENT.

BOSTON, _June_ 20, 1889.

The Pathfinder Series of Text-books on Anatomy, Physiology, and Hygiene
consists of the following volumes:

I. Child's Health Primer (for Primary Grades).

II. Hygiene for Young People or, Young People's Physiology. (for
Intermediate Classes)

III. Hygienic Physiology (for Advanced Pupils).

The above are the series originally prepared (as their general title
indicates) to supply the demand created by the laws for temperance
instruction in public schools in the United States. They were written by
experts under the supervision of the Scientific Department of the National
Woman's Christian Temperance Union, published by the instigation of the
same, and have been carefully revised from time to time, under the same
supervision, to keep them abreast with the latest teachings of science.

Being both teachable and well adapted to grade, their educational value,
as proven by schoolroom tests, is of the highest order. We therefore
cordially indorse and highly recommend the Pathfinder Series for use in
schools.

MARY H. HUNT,

_National and International Superintendent of the Scientific Dep't of
the Woman's Christian Temperance Union; Life Director of the National
Educational Association._

ADVISORY BOARD:

JOSEPH COOK, WILLIAM E. SHELDON, ALBERT H. PLUMB, D.D., DANIEL DORCHESTER,
D.D.

PREFACE

The term Physiology, or the science of the functions of the body, has come
to include Anatomy, or the science of its structure, and Hygiene, or the
laws of health; the one being essential to the proper understanding of
physiology, and the other being its practical application to life. The
three are intimately blended, and in treating of the different subjects
the author has drawn no line of distinction where nature has made none.
This work is not prepared for the use of medical students, but for the
instruction of youth in the principles which underlie the preservation of
health and the formation of correct physical habits. All else is made
subservient to this practical knowledge. A simple scientific dress is used
which, while conducing to clearness, also gratifies that general desire of
children to know something of the nomenclature of any study they pursue.

To the description of each organ is appended an account of its most common
diseases, accidents, etc., and, when practicable, their mode of treatment.
A pupil may thus learn, for example, the cause and cure of "a cold," the
management of a wound, or the nature of an inflammation.

The Practical Questions, which have been a prominent feature in other
books of the series, will be found, it is hoped, equally useful in this
work. Directions for preparing simple microscopic objects, and
illustrations of the different organs, are given under each subject.

The Readings, which represent the ideas but not always the exact
phraseology of the author quoted, have, in general, been selected with
direct reference to Practical Hygiene, a subject which now largely
occupies the public mind. The dangers that lurk in foul air and
contaminated water, in bad drainage, leaky gas pipes, and defective
plumbing, in reckless appetites, and in careless dissemination of
contagious diseases, are here portrayed in such a manner as, it is
trusted, will assist the pupil to avoid these treacherous quicksands, and
to provide for himself a solid path of health.

Under the heading of Health and Disease will be found Hints about the sick
room, Directions for the use of Disinfectants, Suggestions as to what to
do "Till the Doctor comes," and a list of antidotes for Poisons. Questions
for Class Use, a full Glossary, and an ample Index complete the book.

Believing in a Divine Architect of the human form, the author can not
refrain from occasionally pointing out His inimitable workmanship, and
impressing the lesson of a Great Final Cause.

The author has gleaned from every field, at home and abroad, to secure
that which would interest and profit his pupils. In general, Flint's great
work on the "Physiology of Man," an undisputed authority on both sides of
the Atlantic, has been adopted as the standard in digestion, respiration,
circulation, and the nervous system. Leidy's "Human Anatomy," and Sappey's
"Traité d'Anatomie" have been followed on all anatomical questions, and
have furnished many beautiful drawings. Huxley's "Physiology" has afforded
exceedingly valuable aid. Foster's "Text-Book of Physiology," Hinton's
"Health and its Conditions," Black's "Ten Laws of Health," Williams's
practical essay on "Our Eyes and How to Use them," Le Pileur's charming
treatise on "The Wonders of the Human Body," and that quaint volume, "Odd
Hours of a Physician," have aided the author with facts and fancies. The
writings of Draper, Dalton, Carpenter, Yalentin, Mapother, Watson,
Lankester, Letheby, Hall, Hamilton, Bell, Wilson, Bower, Cutter,
Hutchison, Wood, Bigelow, Stille, Holmes, Beigel, and others have been
freely consulted.

PUBLISHERS' NOTE.

An ABRIDGED EDITION of this work is published, to afford a cheaper manual
--adapted to Junior Classes and Common Schools. The abridgment contains
the essence of this text, nearly all its illustrations, and the whole of
the Temperance matter as here presented.

ORDER "HYGIENIC PHYSIOLOGY, ABRIDGED."

READING REFERENCES.

Foster's "Text-Book of Physiology"; Leidy's "Human Anatomy"; Draper's
"Human Physiology"; Dalton's "Physiology and Hygiene"; Cutter's
"Physiology"; Johnston and Church's "Chemistry of Common Life"; Letheby's
"Food"; Tyndall "On Light," and "On Sound"; Mint's "Physiology of Man ";
Rosenthal's "Physiology of the Muscles and Nerves"; Bernstein's "Five
Senses of Man"; Huxley and Youmans's "Physiology and Hygiene"; Sappey's
"Traité d'Anatomie "; Luys's "Brain and its Functions"; Smith's "Foods";
Bain's "Mind and Body"; Pettigrew's "Animal Locomotion"; Carpenter's
"Human Physiology," and "Mental Physiology"; Wilder and Gage's "Anatomy";
Jarvis's "Physiology and Laws of Health."

Hargreaves's "Alcohol and Science"; Richardson's "Ten Lectures on
Alcohol," and "Diseases of Modern Life"; Brown's "Alcohol"; Davis's
"Intemperance and Crime"; Pitman's "Alcohol and the State"; "Anti-
Tobacco"; Howie's "Stimulants and Narcotics"; Hunt's "Alcohol as Food or
Medicine"; Schützenberger's "Fermentation"; Hubbard's "Opium Habit and
Alcoholism"; Trouessart's "Microbes, Ferments, and Molds."

CONTENTS

INTRODUCTION

I.--THE SKELETON

THE HEAD

THE TRUNK

THE LIMBS

II.--THE MUSCLES

III.--THE SKIN

THE HAIR AND THE NAILS

THE TEETH

IV.--RESPIRATION AND THE VOICE

V.--THE CIRCULATION

THE BLOOD

THE HEART

THE ARTERIES

THE VEINS

VI.--DIGESTION AND FOOD

VII.--THE NERVOUS SYSTEM

THE BRAIN

THE SPINAL CORD AND THE NERVES

THE SYMPATHETIC SYSTEM

VIII.--THE SPECIAL SENSES

TOUCH

TASTE

SMELL

HEARING

SIGHT

IX.--HEALTH AND DISEASE.--DEATH AND DECAY

1. HINTS ABOUT THE SICK ROOM

2. DISINFECTANTS

3. WHAT TO DO "TILL THE DOCTOR COMES"

4. ANTIDOTES TO POISONS

X.--SELECTED READINGS

XI.--APPENDIX

QUESTIONS FOR CLASS USE

GLOSSARY

INDEX

SUGGESTIONS To Teachers

Seeing is believing--more than that, it is often knowing and remembering.
The mere reading of a statement is of little value compared with the
observation of a fact. Every opportunity should therefore be taken of
exhibiting to the pupil the phenomena described, and thus making them
real. A microscope is so essential to the understanding of many subjects,
that it is indispensable to the proper teaching of Physiology. A suitable
instrument and carefully prepared specimens, showing the structure of the
bones, the skin, and the blood of various animals, the pigment cells of
the eye, etc., may be obtained at a small cost from any good optician.

On naming the subject of a paragraph, the pupil should be prepared to tell
all he knows about it. No failure should discourage the teacher in
establishing this mode of study and recitation. A little practice will
produce the most satisfactory results. The unexpected question and the apt
reply develop a certain sharpness and readiness which are worthy of
cultivation. The questions for review, or any others that the wit of the
teacher may suggest, can be effectively used to break the monotony of a
topical recitation, thereby securing the benefits of both systems.

The pupil should expect to be questioned each day upon any subject passed
over during the term, and thus the entire knowledge gained will be within
his grasp for instant use. While some are reciting to the teacher, let
others write on slates or on the blackboard. At the close of the
recitation, let all criticise the ideas, the spelling, the use of
capitals, the pronunciation, the grammar, and the mode of expression.
Greater accuracy and much collateral drill may thus be secured at little
expense of valuable school time.

The Introduction is designed merely to furnish suggestive material for the
first lesson, preparatory to beginning the study. Other subjects for
consideration may be found in the section on Health and Disease, in the
Selected Readings, and among the questions given in the Appendix. Where
time will allow, the Selected Readings may profitably be used in
connection with the topics to which they relate. Questions upon them are
so incorporated with those upon the text proper that they may be employed
or not, according to the judgment of the teacher.

NOTE.--Interest in the study of Physiology will be much increased by the
use of the microscope and prepared slides. These may be obtained from any
good optician.

INTRODUCTION.

Physiological study in youth is of inestimable value. Precious lives are
frequently lost through ignorance. Thousands squander in early years the
strength which should have been kept for the work of real life. Habits are
often formed in youth which entail weakness and poverty upon manhood, and
are a cause of lifelong regret. The use of a strained limb may permanently
damage it. Some silly feat of strength may produce an irreparable injury.
A thoughtless hour of reading by twilight may impair the sight for life. A
terrible accident may happen, and a dear friend perish before our eyes,
while we stand by powerless to render the assistance we could so easily
give did we "only know what to do." The thousand little hints which may
save or lengthen life, may repel or abate disease, and the simple laws
which regulate our bodily vigor, should be so familiar that we may be
quick to apply them in an emergency. The preservation of health is easier
than the cure of disease. Childhood can not afford to wait for the lesson
of experience which is learned only when the penalty of violated law has
been already incurred, and health irrevocably lost.

NATURE'S LAWS INVIOLABLE.--In infancy, we learn how terribly Nature
punishes a violation of certain laws, and how promptly she applies the
penalty. We soon find out the peril of fire, falls, edged tools, and the
like. We fail, however, to notice the equally sharp and certain
punishments which bad habits entail. We are quick to feel the need of
food, but not so ready to perceive the danger of an excess. A lack of air
drives us at once to secure a supply; foul air is as fatal, but it gives
us no warning.

Nature provides a little training for us at the outset of life, but leaves
the most for us to learn by bitter experience. So in youth we throw away
our strength as if it were a burden of which we desire to be rid. We eat
anything, and at any time; do anything we please, and sit up any number of
nights with little or no sleep. Because we feel only a momentary
discomfort from these physical sins, we fondly imagine when that is gone
we are all right again. Our drafts upon our constitution are promptly
paid, and we expect this will always be the case; but some day they will
come back to us, protested; Nature will refuse to meet our demands, and we
shall find ourselves physical bankrupts.

We are furnished in the beginning with a certain vital force upon which we
may draw. We can be spendthrifts and waste it in youth, or be wise and so
husband it till manhood. Our shortcomings are all charged against this
stock. Nature's memory never fails; she keeps her account with perfect
exactness. Every physical sin subtracts from the sum and strength of our
years. We may cure a disease, but it never leaves us as it found us. We
may heal a wound, but the scar still shows. We reap as we sow, and we may
either gather in the thorns, one by one, to torment and destroy, or we may
rejoice in the happy harvest of a hale old age.

THE SKELETON.

"Not in the World of Light alone,
Where God has built His blazing throne,
Nor yet alone on earth below,
With belted seas that come and go,
And endless isles of sunlit green
Is all thy Maker's glory seen--
Look in upon thy wondrous frame,
Eternal wisdom still the same!"

HOLMES.

ANALYSIS OF THE SKELETON.

NOTE.--The following Table of 206 bones is exclusive of the 8 sesamoid
bones which occur in pairs at the roots of the thumb and great toe, making
214 as given by Leidy and Draper. Gray omits the bones of the ear, and
names 200 as the total number.

I. FORM, STRUCTURE, ETC., OF THE BONES.

(_See page 269_.)

THE SKELETON, or framework of the "House we live in," is composed of about
200 bones. [Footnote: The precise number varies in different periods of
life. Several which are separated in youth become united in old age. Thus
five of the "false vertebræ" at the base of the spine early join in one
great bone--the sacrum; while four tiny ones below it often run into a
bony mass--the coccyx (Fig. 6); in the child, the sternum is composed of
eight pieces, while in the adult it consists of only three. While,
however, the number of the bones is uncertain, their relative length is so
exact that the length of the entire skeleton, and thence the height of the
man, can be obtained by measuring a single one of the principal bones.
Fossil bones and those found at Pompeii have the same proportion as our
own.]

USES AND FORMS OF THE BONES.--They have three principal uses: 1. To
protect the delicate organs; [Footnote: An organ is a portion of the body
designed for a particular use, called its _function_. Thus the heart
circulates the blood; the liver produces the bile.] 2. To serve as levers
on which the muscles may act to produce motion; and 3. To preserve the
shape of the body.

Bones differ in form according to the uses they subserve. For convenience
in walking, some are long; for strength and compactness, some are short
and thick; for covering a cavity, some are flat; and for special purposes,
some are irregular. The general form is such as to combine strength and
lightness. For example, all the long bones of the limbs are round and
hollow, thus giving with the same weight a greater strength, [Footnote:
Cut a sheet of foolscap in two pieces. Roll one half into a compact
cylinder, and fold the other into a close, flat strip; support the ends of
each and hang weights in the middle until they bend. The superior strength
of the roll will astonish one unfamiliar with this mechanical principle.
In a rod, the particles break in succession, first those on the outside,
and later those in the center. In a tube, the particles are all arranged
where they resist the first strain. Iron pillars are therefore cast
hollow. Stalks of grass and grain are so light as to bend before a breath
of wind, yet are stiff enough to sustain their load of seed. Bone has been
found by experiment to possess twice the resisting property of solid oak.]
and also a larger surface for the attachment of the muscles.

The Composition of the Bones at maturity is about one part animal to two
parts mineral matter. The proportion varies with the age. In youth it is
nearly half and half, while in old age the mineral is greatly in excess.
By soaking a bone in weak muriatic acid, and thus dissolving the mineral
matter, its shape will not change, but its stiffness will disappear,
leaving a tough, gristly substance [Footnote: Mix a wineglass of muriatic
acid with a pint of water, and place in it a sheep's rib. In a day or two,
the bone will become so soft that it can be tied into a knot. In the same
way, an egg may be made so pliable that it can be crowded into a narrow-
necked bottle, within which it will expand, and become an object of great
curiosity to the uninitiated. By boiling bones at a high temperature, the
animal matter separates in the form of gelatine. Dogs and cats extract the
animal matter from the bones they eat. Fossil bones deposited in the
ground during the Geologic period, were found by Cuvier to contain
considerable animal matter. Gelatine was actually extracted from the
Cambridge mastodon, and made into glue. A tolerably nutritious food might
thus be manufactured from bones older than man himself.] (cartilage) which
can be bent like rubber.

If the bone be burned in the fire, thus consuming the animal matter, the
shape will still be the same, but it will have lost its tenacity, and the
beautiful, pure-white residue [Footnote: From bones thus calcined, the
phosphorus of the chemist is made. See Steele's "Popular Chemistry," page
114. If the animal matter be not consumed, but only charred, the bone will
be black and brittle. In this way, the "boneblack" of commerce is
manufactured.] may be crumbled into powder with the fingers.

FIG. 2.

[Illustration: _The Thigh Bone, or Femur, sawed lengthwise._]

We thus see that a bone receives hardness and rigidity from its mineral,
and tenacity and elasticity from its animal matter.

The entire bone is at first composed of cartilage, which gradually
_ossifies_ or turns to bone. [Footnote: The ossification of the bones
on the sides and upper part of the skull, for example, begins by a rounded
spot in the middle of each one. From this spot the ossification extends
outward in every direction, thus gradually approaching the edges of the
bone. When two adjacent bones meet, there will be a line where their edges
are in contact with each other, but have not yet united; but when more
than two bones meet in this way, there will be an empty space between them
at their point of junction. Thus, if you lay down three coins upon the
table with their edges touching one another, there will be a three-sided
space in the middle between them; if you lay down four coins in the same
manner, the space between them will be four-sided. Now at the back part of
the head there is a spot where three bones come together in this way,
leaving a small, three-sided opening between them: this is called the
"posterior fontanelle." On the top of the head, four bones come together,
leaving between them a large, four-sided opening: this is called the
"anterior fontanelle." These openings are termed the _fontanelles_,
because we can feel the pulsations of the brain through them, like the
bubbling of water in a fountain. They gradually diminish in size, owing to
the growth of the bony parts around them, and are completely closed at the
age of four years after birth.--DALTON.] Certain portions near the joints
are long delayed in this process, and by their elasticity assist in
breaking the shock of a fall. [Footnote: Frogs and toads, which move by
jumping, and consequently receive so many jars, retain these unossified
portions (epiphyses) nearly through, life, while alligators and turtles
whose position is sprawling, and whose motions are measured do not have
them at all--LEIDY] Hence the bones of children are tough, are not readily
fractured, and when broken easily heal again; [Footnote: This is only one
of the many illustrations of the Infinite care that watches over helpless
infancy, until knowledge and ability are acquired to meet the perils of
life.] while those of elderly people are liable to fracture, and do not
quickly unite.

FIG. 3.

[Illustration: _A thin slice of Bone, highly magnified showing the
lacunæ, the tiny tubes (canaliculi) radiating from them, and four
Haversian canals, three seen crosswise and one lengthwise._]

THE STRUCTURE OF THE BONES--When a bone is sawed lengthwise, it is found
to be a compact shell filled with a spongy substance This filling
increases in quantity, and becomes more porous at the ends of the bone,
thus giving greater size to form a strong joint, while the solid portion
increases near the middle, where strength alone is needed. Each fiber of
this bulky material diminishes the shock of a sudden blow, and also acts
as a beam to brace the exterior wall. The recumbent position of the
alligator protects him from falls, and therefore his bones contain very
little spongy substance.

In the body, bones are not the dry, dead, blanched things they commonly
seem to be, but are moist, living, pinkish structures, covered with a
tough membrane, called the per-i-os'-te-um [Footnote: The relations of the
periosteum to the bone are very interesting. Instances are on record where
the bone has been removed, leaving the periosteum, from which the entire
bone was afterward renewed.] (_peri_, around, and _osteon_, a
bone), while the hollow is filled with marrow, rich in fat, and full of
blood vessels. If we examine a thin slice with the microscope, we shall
see black spots with lines running in all directions, and looking very
like minute insects. These are really little cavities, called la-cu'-næ
[Footnote: When the bone is dry, the lacunæ are filled with air, which
refracts the light, so that none of it reaches the eye, and hence the
cavities appear black.] from which radiate tiny tubes. The lacunæ are
arranged in circles around larger tubes, termed from their discoverer,
_Haversian canals_, which serve as passages for the blood vessels
that nourish the bone.

GROWTH OF THE BONES.--By means of this system of canals, the blood
circulates as freely through the bones as through any part of the body,
The whole structure is constantly but slowly changing, [Footnote: Bone is
sometimes produced with surprising rapidity. The great Irish Elk is
calculated by Prof. Owen to have cast off and renewed, annually in its
antlers eighty pounds of bone.] old material being taken out and new put
in. A curious illustration is seen in the fact that if madder be mixed
with the food of pigs, it will tinge their bones red.

REPAIR OF THE BONES.--When a bone is broken, the blood at once oozes out
of the fractured ends. This soon gives place to a watery fluid, which in a
fortnight thickens to a gristly substance, strong enough to hold them in
place. Bone matter is then slowly deposited, which in five or six weeks
will unite the broken parts. Nature, at first, apparently endeavors to
remedy the weakness of the material by excess in the quantity, and so the
new portion is larger than the old. But the extra matter will be gradually
absorbed, sometimes so perfectly as to leave no trace of the injury. (See
p. 271.)

A broken limb should be held in place by splints, or a plaster cast, to
enable this process to go on uninterruptedly, and also lest a sudden jar
might rupture the partially mended break. For a long time, the new portion
consists largely of animal matter, and so is tender and pliable. The
utmost care is therefore necessary to prevent a malformation.

THE JOINTS are packed with a soft, smooth cartilage, or gristle, which
fits so perfectly as to be airtight. Upon convex surfaces, it is thickest
at the middle, and upon concave surfaces, it is thickest at the edge, or
where the wear is greatest. In addition, the ends of the bones are covered
with a thin membrane, the _synovial_ (_sun_, with; _ovum_,
an egg), which secretes a viscid fluid, not unlike the white of an egg.
This lubricates the joints, and prevents the noise and wear of friction.
The body is the only machine that oils itself.

The bones which form the joint are tied with stout ligaments (_ligo_,
I bind), or bands, of a smooth, silvery white tissue, [Footnote: The
general term _tissue_ is applied to the various textures of which the
organs are composed. For example, the osseous tissue forms the bones; the
fibrous tissue, the skin, tendons, and ligaments.] so strong that the
bones are sometimes broken without injuring the fastenings.

II. CLASSIFICATION OF THE BONES.

For convenience, the bones of the skeleton are considered in three
divisions: the _head_, the _trunk_, and the _limbs_.

1. THE HEAD.

THE BONES OF THE SKULL AND THE FACE form a cavity for the protection of
the brain and the four organs of sense, viz.: sight, smell, taste, and
hearing. All these bones are immovable except the lower jaw, which is
hinged [Footnote: A ring of cartilage is inserted in its joints, something
after the manner of a washer in machinery. This follows the movements of
the jaw, and admits of freer motion, while it guards against dislocation.]
at the back so as to allow for the opening and shutting of the mouth.

THE SKULL is composed, in general, of two compact plates, with a spongy
layer between. These are in several pieces, the outer ones being joined by
notched edges, sutures (su'tyurs,), in the way carpenters term
dovetailing. (See Fig. 4.)

FIG. 4.

[Illustration: _The Skull._--1. _frontal bone;_ 2, _parietal bone;_
3, _temporal bone;_ 4, _the sphenoid bone;_ 5, _ethmoid bone;_ 6,
_superior maxillary (upper jaw) bone;_ 7, _malar bone;_ 8, _lachrymal
bone;_ 9, _nasal bone;_ 10, _inferior maxillary (lower jaw) bone._]

The peculiar structure and form of the skull afford a perfect shelter for
the brain--an organ so delicate that, if unprotected, an ordinary blow
would destroy it. Its oval or egg shape adapts it to resist pressure. The
smaller and stronger end is in front, where the danger is greatest.
Projections before and behind shield the less protected parts. The hard
plates are not easy to penetrate. [Footnote: Instances have been known
where bullets, striking against the skull, have glanced off, been
flattened, or even split into halves. In the Peninsular Campaign, the
author saw a man who had been struck in the forehead by a bullet which,
instead of penetrating the brain, had followed the skull around to the
back of the head, and there passed out.] The spongy packing deadens every
blow. [Footnote: An experiment resembling the familiar one of the balls in
Natural Philosophy ("Steele's Popular Physics," Fig. 6, p. 26),
beautifully illustrates this point. Several balls of ivory are suspended
by cords, as in Fig. 5. If A be raised and then let fall, it will transmit
the force to B, and that to C, and so on until F is reached, which will
fly off with the impulse. If now a ball of spongy bone be substituted for
an ivory one anywhere in the line, the force will be checked, and the last
ball will not stir.] The separate pieces with their curious joinings
disperse any jar which one may receive, and also prevent fractures from
spreading.

FIG. 5.

[Illustration]

The frequent openings in this strong bone box afford safe avenues for the
passage of numerous nerves and vessels which communicate between the brain
and the rest of the body.

FIG. 6.

[Illustration: _The Spine; the seven vertebræ of the neck, cervical; the
twelve of the back, dorsal; the five of the loins, lumbar;_ a, _the
sacrum, and_ b, _the coccyx, coming the nine "false vertebræ."_
(p. 3).]

2 THE TRUNK.

THE TRUNK has two important cavities. The upper part, or _chest_,
contains the heart and the lungs, and the lower part, or _abdomen_,
holds the stomach, liver, kidneys, and other organs (Fig. 31). The
principal bones are those of the _spine_, the _ribs_, and the
_hips_.

THE SPINE consists of twenty-four bones, between which are placed pads of
cartilage. [Footnote: These pads vary in thickness from one fourth to one
half an inch. They become condensed by the weight they bear during the
day, so that we are somewhat shorter at evening than in the morning.
Their elasticity causes them to resume their usual size during the night,
or when we lie down for a time.] A canal is hollowed out of the column
for the safe passage of the spinal cord. (See Fig. 50.) Projections
(processes) at the back and on either side are abundant for the attachment
of the muscles. The packing acts as a cushion to prevent any jar from
reaching the brain when we jump or run, while the double curve of the
spine also tends to disperse the force of a fall. Thus on every side the
utmost caution is taken to guard that precious gem in its casket.

THE PERFECTION OF THE SPINE surpasses all human contrivances. Its various
uses seem a bundle of contradictions. A chain of twenty-four bones is made
so stiff that it will bear a heavy burden, and so flexible that it will
bend like rubber; yet, all the while, it transmits no shock, and even
hides a delicate nerve within that would thrill with the slightest touch.
Resting upon it, the brain is borne without a tremor; and, clinging to it,
the vital organs are carried without fear of harm.

FIG. 7.

[Illustration: B, _the first cervical vertebra, the atlas;_ A, _the
atlas, and the second cervical vertebra, the axis;_ e, _the odontoid
process;_ c, _the foramen._]

THE SKULL ARTICULATES with (is jointed to) the spine in a peculiar manner.
On the top of the upper vertebra (atlas [Footnote: Thus called because,
as, in ancient fable, the god Atlas supported the world on his shoulders,
so in the body this bone bears the head.]) are two little hollows
(_a_, _b_, Fig. 7), nicely packed and lined with the synovial
membrane, into which fit the corresponding projections on the lower part
of the skull, and thus the head can rock to and fro. The second vertebra
(axis) has a peg, _e_, which projects through a hole, _c_, in
the first.

FIG. 8.

[Illustration: _The Thorax or Chest._ a, _the sternum;_ b _to_ c, _the
true ribs;_ d _to_ h, _the false ribs;_ g, h, _the floating ribs;_ i, k,
_the dorsal vertebræ._]

The surfaces of both vertebræ are so smooth that they easily glide on each
other, and thus, when we move the head side wise, the atlas turns around
the peg, _e_, of the axis.

THE RIBS, also twenty-four in number, are arranged in pairs on each side
of the chest. At the back, they are all attached to the spine. In front,
the upper seven pairs are tied by cartilages to the breastbone (sternum);
three are fastened to each other and to the cartilage above, and two, the
floating ribs, are loose.

The natural form of the chest is that of a cone diminishing upward. But,
owing to the tightness of the clothing commonly worn, the reverse is often
the case. The long, slender ribs give lightness, [Footnote: If the chest
wall were in one bone thick enough to resist a blow, it would be unwieldy
and heavy As it is, the separate bones bound by cartilages yield
gradually, and diffuse the force among them all, and so are rarely
broken.] the arched form confers strength, and the cartilages impart
elasticity,--properties essential to the protection of the delicate organs
within, and to freedom of motion in respiration. (See note, p. 80.)

FIG. 9.

[Illustration: _The Pelvis._ a, _the sacrum;_ b, b, _the right
and the left innominatum._]

THE HIP BONES, called by anatomists the innominata, or nameless bones,
form an irregular basin styled the _pelvis_ (_pelvis_, a basin).
In the upper part, is the foot of the spinal column--a wedge-shaped bone
termed the _sacrum_ [Footnote: So called because it was anciently
offered in sacrifice.] (sacred), firmly planted here between the
widespreading and solid bones of the pelvis, like the keystone to an arch,
and giving a steady support to the heavy burden above.

3. THE LIMBS.

TWO SETS OF LIMBS branch from the trunk, viz.: the upper, and the lower.
They closely resemble each other. The arm corresponds to the thigh; the
forearm, to the leg; the wrist, to the ankle; the fingers, to the toes.
The fingers and the toes are so much alike that they receive the same
name, _digits_, while the several bones of both have also the common
appellation, _phalanges_. The differences which exist grow out of
their varying uses. The foot is characterized by strength; the hand, by
mobility.

FIG. 10.

[Illustration: _The Shoulder Joint._ a, _the clavicle;_ b,
_the scapula._]

1. THE UPPER LIMBS.--THE SHOULDER.--The bones of the shoulder are the
collar bone (clavicle), and the shoulder blade (scapula). The
_clavicle_ (_clavis_, a key) is a long, slender bone, shaped
like the Italic _f_. It is fastened at one end to the breastbone and
the first rib, and, at the other, to the shoulder blade. (See Fig. 1.) It
thus holds the shoulder joint out from the chest, and gives the arm
greater play. If it be removed or broken, the head of the arm bone will
fall, and the motions of the arm be greatly restricted. [Footnote: Animals
which use the forelegs only for support (as the horse, ox, etc.), do not
possess this bone. "It is found in those that dig, fly, climb and seize."]

THE SHOULDER BLADE is a thin, flat, triangular bone, fitted to the top and
back of the chest, and designed to give a foundation for the muscles of
the shoulder.

THE SHOULDER JOINT.--The arm bone, or _humerus_, articulates with the
shoulder blade by a ball-and-socket joint. This consists of a cup-like
cavity in the latter bone, and a rounded head in the former, to fit it,--
thus affording a free rotary motion. The shallowness of the socket
accounts for the frequent dislocation of this joint, but a deeper one
would diminish the easy swing of the arm.

FIG. 11.

[Illustration: _Bones of the right Forearm._ H, _the humerus;_
R, _the radius; and_ U, _the ulna._]

THE ELBOW.--At the elbow, the humerus articulates with the _ulna_--a
slender bone on the inner side of the forearm--by a hinge joint which
admits of motion in only two directions, _i. e._, backward and
forward. The ulna is small at its lower end; the _radius_, or large
bone of the forearm, on the contrary, is small at its upper end, while it
is large at its lower end, where it forms the wrist joint. At the elbow,
the head of the radius is convex and fits into a shallow cavity in the
ulna, while at the wrist the ulna plays in a similar socket in the radius.
Thus the radius may roll over and even cross the ulna.

THE WRIST, or _carpus_, consists of two rows of very irregular bones,
one of which articulates with the forearm; the other, with the hand. They
are placed side to side, and so firmly fastened as to admit of only a
gliding motion. This gives little play, but great strength, elasticity,
and power of resisting shocks.

THE HAND.--The _metacarpal_ (_meta_, beyond; _karpos_,
wrist), or bones of the palm, support each a thumb or a finger. Each
finger has three bones, while the thumb has only two. The first bone of
the thumb, standing apart from the rest, enjoys a special freedom of
motion, and adds greatly to the usefulness of the hand.

FIG. 12.

[Illustration: _Bones of the Hand and the Wrist._]

The first bone (Figs. 11, 12) of each finger is so attached to the
corresponding metacarpal bone as to move in several directions upon it,
but the other phalanges form hinge joints.

The fingers are named in order: the thumb, the index, the middle, the
ring, and the little finger. Their different lengths cause them to fit the
hollow of the hand when it is closed, and probably enable us more easily
to grasp objects of varying size. If the hand clasps a ball, the tips of
the fingers will be in a straight line.

The hand in its perfection belongs only to man. Its elegance of outline,
delicacy of mold, and beauty of color have made it the study of artists;
while its exquisite mobility and adaptation as a perfect instrument have
led many philosophers to attribute man's superiority even more to the hand
than to the mind. [Footnote: How constantly the hand aids us in explaining
or enforcing a thought! We affirm a fact by placing the hand as if we
would rest it firmly on a body; we deny by a gesture putting the false or
erroneous proposition away from us; we express doubt by holding the hand
suspended, as if hesitating whether to take or reject. When we part from
dear friends, or greet them again after long absence, the hand extends
toward them as if to retain, or to bring them sooner to us. If a recital
or a proposition is revolting, we reject it energetically in gesture as in
thought. In a friendly adieu we wave our good wishes to him who is their
object; but when it expresses enmity, by a brusque movement we sever every
tie. The open hand is carried backward to express fear or horror, as well
as to avoid contact; it goes forward to meet the hand of friendship; it is
raised suppliantly in prayer toward Him from whom we hope for help; it
caresses lovingly the downy cheek of the infant, and rests on its head
invoking the blessing of Heaven,--_Wonders of the Human Body_.]

FIG. 13.

[Illustration: _The Mechanism of the Hip Joint._]

2. THE LOWER LIMBS.--THE HIP--The thigh bone, or _femur_, is the
largest and necessarily the strongest in the skeleton, since at every step
it has to bear the weight of the whole body. It articulates with the hip
bone by a ball-and-socket joint. Unlike the shoulder joint, the cup here
is deep, thus affording less play, but greater strength. It fits so
tightly that the pressure of the air largely aids in keeping the bones in
place. [Footnote: In order to test this, a hole was bored through a hip
bone, so as to admit air into the socket, the thigh bone at once fell out
as far as the ligaments would permit. An experiment was also devised
whereby a suitably prepared hip joint was placed under the receiver of an
air pump. On exhausting the air, the weight of the femur caused it to drop
out of the socket, while the readmission of the air raised it to its
place. Without this arrangement, the adjacent muscles would have been
compelled to bear the additional weight of the thighbone every time it was
raised. Now the pressure of the air rids them of this unnecessary burden,
and hence they are less easily fatigued--WEBER] Indeed, when the muscles
are cut away, great force is required to detach the limbs.

THE KNEE is strengthened by the patella_, or kneepan (_patella_,
little dish), a chestnut-shaped bone firmly fastened over the joint.

The shin bone, or _tibia_, the large, triangular bone on the inner
side of the leg, articulates both with the femur and the foot by hinge
joints. The kneejoint is so made, however, as to admit of a slight rotary
motion when the limb is not extended.

The _fibula_ (_fibula_, a clasp), the small, outside bone of the
leg, is firmly bound at each end to the tibia. (See Fig. 1.) It is
immovable, and, as the tibia bears the principal weight of the body, the
chief use of this second bone seems to be to give more surface to which
the muscles may be attached. [Footnote: A young man in the hospital at
Limoges had lost the middle part of his tibia. The lost bone was not
reproduced, but the fibula, the naturally weak and slender part of the
leg, became thick and strong enough to support the whole body.--STANLEY'S
_Lectures_.]

THE FOOT.--The general arrangement of the foot is strikingly like that of
the hand (Fig. 1). The several parts are the _tarsus_, the
_metatarsus_, and the _phalanges_. The graceful arch of the
foot, and the numerous bones joined by cartilages, give an elasticity to
the step that could never be attained by a single, flat bone. [Footnote:
The foot consists of an arch, the base of which is more extended in front
than behind, and the whole weight of the body is made to fall on this arch
by means of a variety of joints. These joints further enable the foot to
be applied, without inconvenience, to rough and uneven surfaces.--HINTON.]
The toes naturally lie straight forward in the line of the foot. Few
persons in civilized nations, however, have naturally formed feet. The big
toe is crowded upon the others, while crossed toes, nails grown-in,
enormous joints, corns, and bunions abound.

THE CAUSE OF THESE DEFORMITIES is found in the shape and size of
fashionable boots and shoes. The sole ought to be large enough for full
play of motion, the uppers should not crowd the toes, and the heels should
be low, flat, and broad. As it is, there is a constant warfare between
Nature and our shoemakers, [Footnote: When we are measured for boots or
shoes, we should stand on a sheet of paper, and have the shoemaker mark
with a pencil the exact outline of our feet as they bear our whole weight.
When the shoe is made, the sole should exactly cover this outline.] and we
are the victims. The narrow point in front pinches our toes, and compels
them to override one another; the narrow sole compresses the arch; while
the high heel, by throwing all the weight forward on the toes, strains the
ankle, and, by sending the pressure where Nature did not design it to
fall, causes that joint to become enlarged. The body bends forward to meet
the demand of this new motion, and thus loses its uprightness and beauty,
making our gait stiff and ungraceful. (See p. 271.)

DISEASES, ETC.--l. _Rickets_, a disease of early life, is caused by a
lack of mineral matter in the bones, rendering them soft and pliable, so
that they bend under the weight of the body. They thus become permanently
distorted, and of course are weaker than if they were straight, [Footnote:
Just here appears an exceedingly beautiful provision. As soon as the
disproportion of animal matter ceases, a larger supply of mineral is sent
to the weak points, and the bones actually become thicker, denser, harder,
and consequently stronger at the very concave part where the stress of
pressure is greatest.--WATSON'S _Lectures_. We shall often have
occasion to refer to similar wise and providential arrangements whereby
the body is enabled to remedy defects, and to prepare for accidents.]
Rickets is most common among children who have inherited a feeble
constitution and who are ill fed, or who live in damp, ill-ventilated
houses. "Rickety" children should have plenty of fresh air and sunlight,
nourishing food, comfortable clothing, and, in short, the best of hygienic
care.

2. _A Felon_ is a swelling of the finger or thumb, usually of the
last joint. It is marked by an accumulation beneath the periosteum and
next the bone. The physician will merely cut through the periosteum, and
let out the effete matter.

3. _Bowlegs_ are caused by children standing on their feet before the
bones of the lower limbs are strong enough to bear their weight. The
custom of encouraging young children to stand by means of a chair or the
support of the hand, while the bones are yet soft and pliable, is a cruel
one, and liable to produce permanent deformity. Nature will set the child
on its feet when the proper time comes.

4. _Curvature of the Spine_.--When the spine is bent, the packing
between the vertebræ becomes compressed on one side into a wedge-like
shape. After a time, it will lose its elasticity, and the spine will
become distorted. This often occurs in the case of students who bend
forward to bring their eyes nearer their books, instead of lifting their
books nearer their eyes, or who raise their right shoulder above their
left when writing at a desk which is too high. Round shoulders, small,
weak lungs, and, frequently, diseases of the spine are the consequences.
An erect posture in reading or writing conduces not alone to beauty of
form, but also to health of body. We shall learn hereafter that the action
of the muscles bears an important part in preserving the symmetry of the
spine. Muscular strength comes from bodily activity; hence, one of the
best preventives of spinal curvature is daily exercise in the open air.

5. _Sprains_ are produced when the ligaments which bind the bones of
a joint are strained, twisted, or torn from their attachments. They are
quite as serious as a broken bone, and require careful attention lest they
lead to a crippling for life. By premature use a sprained limb may be
permanently impaired. Hence, the joint should be kept quiet, even after
the immediate pain is gone.

6. _A Dislocation_ is the forcible displacement of a bone from its
socket. It is, generally, the result of a fall or a violent blow. The
tissues of the joint are often ruptured, while the contraction of the
muscles prevents the easy return of the bone to its place. A dislocation
should be reduced as soon as possible after the injury, before
inflammation supervenes.

PRACTICAL QUESTIONS.

1. Why does not a fall hurt a child as much as it does a grown person?

2. Should a young child ever be urged to stand or walk?

3. What is meant by "breaking one's neck"?

4. Should chairs or benches have straight backs?

5. Should a child's feet be allowed to dangle from a high seat?

6. Why can we tell whether a fowl is young by pressing on the point of the
breastbone?

7. What is the use of the marrow in the bones?

8. Why is the shoulder so often put out of joint?

9. How can you tie a knot in a bone?

10. Why are high pillows injurious?

11. Is a stooping posture a healthful position?

12. Should a boot have a heel piece?

13. Why should one always sit and walk erect?

14. Why does a young child creep rather than walk?

15. What is the natural direction of the big toe?

16. What is the difference between a sprain and a fracture? A dislocation?

17. Does the general health of the system affect the strength of the
bones?

18. Is living bone sensitive? _Ans_.--Scrape a bone, and its vessels
bleed; cut or bore a bone, and its granulations sprout up; break a bone,
and it will heal; cut a piece away, and more bone will readily be
produced; hurt it in any way, and it inflames; burn it, and it dies. Take
any proof of sensibility but the mere feeling of pain, and it will answer
to the proof.--BELL'S _Anatomy_. Animal sensibility would be
inconvenient; it is therefore not to be found except in diseased bone,
where it sometimes exhibits itself too acutely.--TODD'S _Cyclopedia of
Anatomy_.

19. Is the constitution of bone the same in animals as in man?
_Ans_.--The bones of quadrupeds do not differ much from those of man.
In general they are of a coarser texture, and in some, as in those of the
elephant's head, we find extensive air cells.--TODD'S _Anatomy_.

II.

THE MUSCLES.

"Behold the outward moving frame,
Its living marbles jointed strong
With glistening band and silvery thong,
And link'd to reason's guiding reins
By myriad rings in trembling chains,
Each graven with the threaded zone
Which claims it as the Master's own."

HOLMES.

ANALYSIS OF THE MUSCLES.

FIG. 14.

[Illustration]

THE MUSCLES.

THE USE OF THE MUSCLES.--The skeleton is the image of death. Its unsightly
appearance instinctively repels us. We have seen, however, what uses it
subserves in the body, and how the ugly-looking bones abound in nice
contrivances and ingenious workmanship. In life, the framework is hidden
by the flesh. This covering is a mass of muscles, which by their
arrangement and their properties not only give form and symmetry to the
body, but also produce its varied movements.

In Fig. 14, we see the large exterior muscles. Beneath these are many
others; while deeply hidden within are tiny, delicate ones, too small to
be seen with the naked eye. There are, in all, about five hundred, each
having its special use, and all working in exquisite harmony and
perfection.

CONTRACTILITY.--The peculiar property of the muscles is their power of
contraction, whereby they decrease in length and increase in thickness.
[Footnote: The maximum force of this contraction has been estimated as
high as from eighty-five to one hundred and fourteen pounds per square
inch.] This may be caused by an effort of the will, by cold, by a sharp
blow, etc. It does not cease at death, but, in certain cold-blooded
animals, a contraction of the muscles is often noticed long after the head
has been cut off.

ARRANGEMENT OF THE MUSCLES. [Footnote: "Could we behold properly the
muscular fibers in operation, nothing, as a mere mechanical exhibition,
can be conceived more superb than the intricate and combined actions that
must take place during our most common movements. Look at a person running
or leaping, or watch the motions of the eye. How rapid, how delicate, how
complicated, and yet how accurate, are the motions required! Think of the
endurance of such a muscle as the heart, that can contract, with a force
equal to sixty pounds, seventy-five times every minute, for eighty years
together, without being weary."]--The muscles are nearly all arranged in
pairs, each with its antagonist, so that, as they contract and expand
alternately, the bone to which they are attached is moved to and fro. (See
p. 275.)

If you grasp the arm tightly with your hand just above the elbow joint,
and bend the forearm, you will feel the muscle on the inside (biceps,
_a_, Fig. 14) swell, and become hard and prominent, while the outside
muscle (triceps, _f_) will be relaxed. Now straighten the arm, and
the swelling and hardness of the inside muscle will vanish, while the
outside one will, in turn, become rigid. So, also, if you clasp the arm
just below the elbow, and then open and shut the fingers, you can feel the
alternate expanding and relaxing of the muscles on opposite sides of the
arms.

If the muscles on one side of the face become palsied, those on the other
side will draw the mouth that way. Squinting is caused by one of the
straight muscles of the eye (Fig. 17) contracting more strongly than its
antagonist.

KINDS OF MUSCLES.--There are two kinds of muscles, the _voluntary_,
which are under the control of our will, and the _involuntary_,
which are not. Thus our limbs stiffen or relax as we please, but the
heart beats on by day and by night. The eyelid, however, is both
voluntary and involuntary, so that while we wink constantly without
effort, we can, to a certain extent, restrain or control the motion.

STRUCTURE OF THE MUSCLES.--If we take a piece of lean beef and wash out
the red color, we can easily detect the fine fibers of which the meat is
composed. In boiling corned beef for the table, the fibers often separate,
owing to the dissolving of the delicate tissue which bound them together.
By means of the microscope, we find that these fibers are made up of
minute filaments (_fibrils_), and that each fibril is composed of a
row of small cells arranged like a string of beads. This gives the muscles
a peculiar striped (striated) appearance. [Footnote: The involuntary
muscles consist generally of smooth, fibrous tissue, and form sheets or
membranes in the walls of hollow organs. By their contraction they change
the size of cavities which they inclose. Some functions, however, like the
action of the heart, or the movements of deglutition (swallowing), require
the rapid, vigorous contraction, characteristic of the voluntary muscular
tissue--FLINT.] (See p. 276.) The cells are filled with a fluid or
semifluid mass of living (protoplasmic) matter.

FIG. 15.

[Illustration: _Microscopic view of a Muscle, showing, at one end, the
fibrillæ; and, at the other, the disks, or cells, of the fiber._]

The binding of so many threads into one bundle [Footnote: We shall learn
hereafter how these fibers are firmly tied together by a mesh of fine
connective tissue which dissolves in boiling, as just described] confers
great strength, according to a mechanical principle that we see
exemplified in suspension bridges, where the weight is sustained, not by
bars of iron, but by small wires twisted into massive ropes.

FIG. 16.

[Illustration: _Tendons of the Hand._]

THE TENDONS.--The ends of the muscles are generally attached to the bone
by strong, flexible, but inelastic tendons. [Footnote: The tendons may be
easily seen in the leg of a turkey as it comes on our table; so we may
study Physiology while we pick the bones.] The muscular fibers spring from
the sides of the tendon, so that more of them can act upon the bone than
if they went directly to it. Besides, the small, insensible tendon can
better bear the exposure of passing over a joint, and be more easily
lodged in some protecting groove, than the broad, sensitive muscle. This
mode of attachment gives to the limbs strength, and elegance of form.
Thus, for example, if the large muscles of the arm extended to the hand,
they would make it bulky and clumsy. The tendons, however, reach only to
the wrist, whence fine cords pass to the fingers (Fig. 16).

Here we notice two other admirable arrangements. 1. If the long tendons at
the wrist on contracting should rise, projections would be made and thus
the beauty of the slender joint be marred. To prevent this, a stout band
or bracelet of ligament holds them down to their place. 2. In order to
allow the tendon which moves the last joint of the finger to pass through,
the tendon which moves the second joint divides at its attachment to the
bone (Fig. 16). This is the most economical mode of packing the muscles,
as any other practicable arrangement would increase the bulk of the
slender finger.

FIG. 17.

[Illustration: _Muscles of the Right Eye:_ A, _superior
straight,_ B, _superior oblique passing through a pulley,_ D; G,
_inferior oblique,_ H, _external straight, and, back of it, the
internal straight muscle._]

Since the tendon can not always pull in the direction of the desired
motion, some contrivance is necessary to meet the want. The tendon (B)
belonging to one of the muscles of the eye, for example, passes through a
ring of cartilage, and thus a rotary motion is secured.

FIG. 18.

[Illustration: _The three classes of Levers, and also the foot as a
Lever._]

THE LEVERS OF THE BODY. [Footnote: A _lever_ is a stiff bar resting
on a point of support, called the _fulcrum_ (_F_), and having connected
with it a _weight_ (_W_) to be lifted, and a _power_ (_P_) to move it.
There are three classes of levers according to the arrangement of the
power, weight, and fulcrum. In the first class, the _F_ is between the
_P_ and _W_; in the second, the _W_ is between the _P_ and _F_; and in
the third, the _P_ is between the _W_ and _F_ (Fig. 18). A pump handle
is an example of the first; a lemon squeezer, of the second; and a
pair of fire tongs, of the third. See "Popular Physics," pp. 81-83, for a
full description of this subject, and for many illustrations.]--In
producing the motions of the body, the muscles use the bones as levers. We
see an illustration of the _first class_ of levers in the movements
of the head. The back or front of the head is the weight to be lifted, the
backbone is the fulcrum on which the lever turns, and the muscles at the
back or front of the neck exert the power by which we toss or bow the
head.

FIG. 19.

[Illustration: _The hand as a Lever of the third class._]

When we raise the body on tiptoe, we have an instance of the _second
class_. Here, our toes resting on the ground form the fulcrum the
muscles of the calf (gas-troc-ne'-mi-us, _j_ and so-le'-us, Fig. 14),
acting through the tendon of the heel, [Footnote: This is called the
Tendon of Achilles (_k_, Fig. 14) and is so named because, as the
fable runs, when Achilles was an infant his mother held him by the heel
while she dipped him in the River Styx, whose water had the power of
rendering one invulnerable to any weapon. His heel, not being wet, was his
weak point, to which Paris directed the fatal arrow--"This tendon," says
Mapother, "will bear one thousand pounds weight before it will break." The
horse is said to be "hamstrung," and is rendered useless, when the Tendon
of Achilles is cut. (see p. 284.)] are the power and the weight is borne
by the ankle joint.

An illustration of the _third class_ is found in lifting the hand
from the elbow. The hand is the weight, the elbow the fulcrum, and the
power is applied by the biceps muscle at its attachment to the radius (A,
Fig. 19.) In this form of the lever there is great loss of force, because
it is applied at such a distance from the weight, but there is a gain of
velocity, since the hand moves so far by such a slight contraction of the
muscle. The hand is required to perform quick motions, and therefore this
mode of attachment is desirable.

The nearer the power is applied to the resistance, the more easily the
work is done. In the lower jaw, for example, the jaw is the weight, the
fulcrum is the hinge joint at the back, and the muscles (temporal,
_d_, and the mas'-se'ter, _e_, Fig. 14) on each side are the
power. [Footnote: We may feel the contraction of the masseter by placing
our hand on the face when we work the jaw, while the temporal can be
readily detected by putting the fingers on the temple while we are
chewing. The tendon of the muscle (digastric)--one of those which open the
jaw--passes through a pulley (_c_, Fig. 14) somewhat like the one in
the eye.] They act much closer to the resistance than those in the hand,
since here we desire force, and there, speed.

FIG. 20.

[Illustration: _The Kneejoint;_ k, _the patella;_ f, _the
tendon._]

THE ENLARGEMENT OF THE BONES AT THE JOINTS not only affords greater
surface for the attachment of the muscles, as we have seen, but also
enables them to work to better advantage. Thus, in Fig. 20 it is evident
that a muscle acting in the line _f b_ would not bend the lower limb
so easily as if it were acting in the line _f k_, since in the former
case its force would be about all spent in drawing the bones more closely
together, while in the latter it would pull more nearly at a right angle.
Thus the tendon _f_, by passing over the patella, which is itself
pushed out by the protuberance _b_ of the thigh bone, pulls at a
larger angle, [Footnote: The chief use of the processes of the spine (Fig.
6) and other bones is, in the same way, to throw out the point on which
the power acts as far from the fulcrum as possible. The projections of the
ulna ("funny bone") behind the elbow, and that of the heel bone to which
the Tendon of Achilles is attached, are excellent illustrations (Fig. 1).]
and so the leg is thrown forward with ease in walking and with great force
in kicking.

HOW WE STAND ERECT.--The joints play so easily, and the center of gravity
in the body is so far above the foot, that the skeleton can not of itself
hold our bodies upright. Thus it requires the action of many muscles to
maintain this position. The head so rests upon the spine as to tend to
fall in front, but the muscles of the neck steady it in its place.
[Footnote: In animals the jaws are so heavy, and the place where the head
and spine join is so far back, that there can be no balance as there is in
man. There are therefore large muscles in their necks. We readily find
that we have none if we get on "all fours" and try to hold up the head. On
the other hand, gorillas and apes can not stand erect like man, for the
reason that their head, trunk, legs, etc., are not balanced by muscles, so
as to be in line with one another.] The hips incline forward, but are held
erect by the strong muscles of the back. The trunk is nicely balanced on
the head of the thigh bones. The great muscles of the thigh acting over
the kneepan tend to bend the body forward, but the muscles of the calf
neutralize this action. The ankle, the knee, and the hip lie in nearly the
same line, and thus the weight of the body rests directly on the keystone
of the arch of the foot. So perfectly do these muscles act that we never
think of them until science calls our attention to the subject, and yet to
acquire the necessary skill to use them in our infancy needed patient
lessons, much time, and many hard knocks.

FIG. 21.

[Illustration: _Action of the Muscles which keep the body erect._]

HOW WE WALK.--Walking is as complex an act as standing. It is really a
perilous performance, which has become safe only because of constant
practice. We see how violent it is when we run against a post in the dark,
and find with what headlong force we were hurling ourselves forward.
Holmes has well defined walking as a perpetual falling with a constant
self-recovery. Standing on one foot, we let the body fall forward, while
we swing the other leg ahead like a pendulum. Planting that foot on the
ground, to save the body from falling farther, we then swing the first
foot forward again to repeat the same operation. [Footnote: It is a
curious fact that one side of the body tends to outwalk the other; and so,
when a man is lost in the woods, he often goes in a circle, and at last
comes round to the spot whence he started.]

The shorter the pendulum, the more rapidly it vibrates; and so short-
legged people take quicker and shorter steps than long-legged ones.
[Footnote: In this respect, Tom Thumb was to Magrath, whose skeleton,
eight and one half feet high, is now in the Dublin Museum, what a little
fast-ticking, French mantel clock is to a big, old-fashioned, upright,
corner timepiece.] We are shorter when walking than when standing still,
because of this falling forward to take a step in advance. [Footnote:
Women find that a gown that will swing clear of the ground when they are
standing still, will drag the street when they are walking. The length of
the step may be increased by muscular effort, as when a line of soldiers
keep step in spite of their having legs of different lengths. Such a mode
of walking is necessarily fatiguing. (See p. 280.)]

In running, we incline the body more, and so, as it were, fall faster.
When we walk, one foot is on the ground all the time, and there is an
instant when both feet are planted upon it; but in running there is an
interval of time in each step when both feet are off the ground, and the
body is wholly unsupported. As we step alternately with the feet, we are
inclined to turn the body first to one side and then to the other. This
movement is sometimes counterbalanced by swinging the hand on the opposite
side. [Footnote: In ordinary walking the speed is nearly four miles an
hour, and can be kept up for a long period. But exercise and a special
aptitude for it enable some men to walk great distances in a relatively
short space of time. Trained walkers have gone seventy-five miles in
twenty hours, and walked the distance of thirty-seven miles at the rate of
five miles an hour. The mountaineers of the Alps are generally good
walkers, and some of them are not less remarkable for endurance than for
speed. Jacques Balmat, who was the first to reach the summit of Mont
Blanc, at sixteen years of age could walk from the hamlet of the Pélerins
to the mountain of La Côte in two hours,--a distance which the best-
trained travelers required from five to six hours to get over. At the time
of his last attempt to reach the top of Mont Blanc, this same guide, then
twenty years old, passed six days and four nights without sleeping or
reposing a single moment. One of his sons, Édouard Balmat, left Paris to
join his regiment at Genoa; he reached Chamouni the fifth day at evening,
having walked three hundred and forty miles. After resting two days, he
set off again for Genoa, where he arrived in two days. Several years
afterward, this same man left the baths at Louèche at two o'clock in the
morning, and reached Chamouni at nine in the evening, having walked a
distance equal to about seventy-five miles in nineteen hours. In 1844, an
old guide of De Saussure, eighty years old, left the hamlet of Prats, in
the valley of Chamouni, in the afternoon, and reached the Grand-Mulets at
ten in the evening; then, after resting some hours, he climbed the glacier
to the vicinity of the Grand Plateau, which has an altitude of about
thirteen thousand feet, and then returned to his village without
stopping.--_Wonders of the Body_.]

THE MUSCULAR SENSE.--When we lift an object, we feel a sensation of
weight, which we can compare with that experienced in lifting another
body. [Footnote: If a small ivory ball be allowed to roll down the cheek
toward the lips, it will appear to increase in weight. In general, the
more sensitive parts of the body recognize smaller differences in weight,
and the right hand is more accurate than the left. We are very apt,
however, to judge of the weight of a body from previous conceptions. Thus,
shortly after Sir Humphrey Davy discovered the metal potassium, he placed
a piece of it in the hand of Dr. Pierson, who exclaimed: "Bless me! How
heavy it is!" Really, however, potassium is so light that it will float on
water like cork.] By balancing it in the hand. The muscular sense is
useful to us in many ways. It guides us in standing or moving. We gratify
it when we walk erect and with an elastic step, and by dancing, jumping,
skating, and gymnastic exercises.

NECESSITY OF EXERCISE.--The effect of exercise upon a muscle is very
marked. [Footnote: The greater size of the breast (pectoral muscle) of a
pigeon, as compared with that of a duck, shows how muscle increases with
use. The breast of a chicken is white because it is not used for flight,
and therefore gets little blood.] By use it grows larger, and becomes
hard, compact, and darker-colored; by disuse it decreases in size, and
becomes soft, flabby, and pale.

Violent exercise, however, is injurious, since we then tear down faster
than nature can build up. Feats of strength are not only hurtful, but
dangerous. Often the muscles are strained or ruptured, and blood vessels
burst in the effort to outdo one's companions. [Footnote: Instances have
been known of children falling dead from having carried to excess so
pleasant and healthful an amusement as jumping the rope, and of persons
rupturing the Tendon of Achilles in dancing. The competitive lifting of
heavy weights is unwise, sometimes fatal.] (See p. 278.)

Two thousand years ago, Isocrates, the Greek rhetorician, said: "Exercise
for health, not for strength." The cultivation of muscle for its own sake
is a return to barbarism, while it enfeebles the mind, and ultimately the
body. The ancient gymnasts are said to have become prematurely old, and
the trained performers of our own day soon suffer from the strain they put
upon their muscular system. Few men have sufficient vigor to become both
athletes and scholars. Exercise should, therefore, merely supplement the
deficiency of our usual employment. _A sedentary life needs daily,
moderate exercise, which always stops short of fatigue_. This is a law
of health. (See p. 280.)

No education is complete which fails to provide for the development of the
muscles. Recesses should be as strictly devoted to play as study hours are
to work. Were gymnastics or calisthenics as regular an exercise as grammar
or arithmetic, fewer pupils would be compelled to leave school on account
of ill health; while spinal curvatures, weak backs, and ungraceful gaits
would no longer characterize so many of our best institutions.

TIME FOR EXERCISE.--We should not exercise after long abstinence from
food, nor immediately after a meal, unless the meal or the exercise be
very light. There is an old-fashioned prejudice in favor of exercise
before breakfast--an hour suited to the strong and healthy, but entirely
unfitted to the weak and delicate. On first rising in the morning, the
pulse is low, the skin relaxed, and the system susceptible to cold. Feeble
persons, therefore, need to be braced with food before they brave the
outdoor air.

WHAT KIND OF EXCERCISE TO TAKE.--For children, games are unequaled.
Walking, the universal exercise, [Footnote: The custom of walking, so
prevalent in England, has doubtless much to do with the superior physique
of its people. It is considered nothing for a woman to take a walk of
eight or ten miles, and long pedestrian excursions are made to all parts
of the country. The benefits which accrue from such an open-air life are
sadly needed by the women of our own land. A walk of half a dozen miles
should be a pleasant recreation for any healthy person.] is beneficial, as
it takes one into the open air and sunlight. Running is better, since it
employs more muscles, but it must not be pushed to excess, as it taxes the
heart, and may lead to disease of that organ. Rowing is more effectual in
its general development of the system. Swimming employs the muscles of the
whole body, and is a valuable acquirement, as it may be the means of
saving life. Horseback riding is a fine accomplishment, and refreshes both
mind and body. Gymnastic or calisthenic exercises bring into play all the
muscles of the body, and when carefully selected, and not immoderately
employed, are preferable to any other mode of indoor exercise. [Footnote:
The employment of the muscles in exercise not only benefits their especial
structure, but it acts on the whole system. When the muscles are put in
action, the capillary blood vessels with which they are supplied become
more rapidly charged with blood, and active changes take place, not only
in the muscles, but in all the surrounding tissues. The heart is required
to supply more blood, and accordingly beats more rapidly in order to meet
the demand. A larger quantity of blood is sent through the lungs, and
larger supplies of oxygen are taken in and carried to the various tissues.
The oxygen, by combining with the carbon of the blood and the tissues,
engenders a larger quantity of heat, which produces an action on the skin,
in order that the superfluous warmth may be disposed of. The skin is thus
exercised, as it were, and the sudoriparous and sebaceous glands are set
at work. The lungs and skin are brought into operation, and the lungs
throw off large quantities of carbonic acid, and the skin large quantities
of water, containing in solution matters which, if retained, would produce
disease in the body. Wherever the blood is sent, changes of a healthful
character occur. The brain and the rest of the nervous system are
invigorated, the stomach has its powers of digestion improved, and the
liver, pancreas, and other organs perform their functions with more vigor.
By want of exercise, the constituents of the food which pass into the
blood are not oxidized, and products which produce disease are engendered.
The introduction of fresh supplies of oxygen induced by exercise oxidizes
these products, and renders them harmless. As a rule, those who exercise
most in the open air will live the longest.--LANKESTER.] (See p. 280.)

THE WONDERS OF THE MUSCLES.--The grace, ease, and rapidity with which the
muscles contract are astonishing. By practice, they acquire a facility
which we call mechanical. The voice may utter one thousand five hundred
letters in a minute, yet each requires a distinct position of the vocal
organs. We train the muscles of the fingers till they glide over the keys
of the piano, executing the most exquisite and difficult harmony. In
writing, each letter is formed by its peculiar motions, yet we make them
so unconsciously that a skillful penman will describe beautiful curves
while thinking only of the idea that the sentence is to express. The mind
of the violinist is upon the music which his right hand is executing,
while his left determines the length of the string and the character of
each note so carefully that not a false sound is heard, although the
variation of a hair's breadth would cause a discord. In the arm of a
blacksmith, the biceps muscle may grow into the solidity almost of a club;
the hand of a prize fighter will strike a blow like a sledge hammer; while
the engraver traces lines invisible to the naked eye, and the fingers of
the blind acquire a delicacy that almost supplies the place of the missing
sense.

DISEASES, ETC.--l. _St. Vitus's Dance_ is a disease of the voluntary
muscles, whereby they are in frequent, irregular, and spasmodic motion
beyond the control of the will. All causes of excitement, and especially
of fear, should be avoided, and the general health of the patient
invigorated, as this disease is closely connected with a derangement of
the nervous system.

2. _Convulsions_ are an involuntary contraction of the muscles.
Consciousness is wanting, while the limbs may be stiff or in spasmodic
action. (See p. 261.)

3. _Locked-jaw_ is a disease in which there are spasms and a
contraction of the muscles, usually beginning in the lower jaw. It is
serious, often fatal, yet it sometimes follows as trivial an injury as the
stroke of a whip lash, the lodgment of a bone in the throat, a fishhook in
the finger, or a tack in the sole of the foot.

4. _Gout_ is characterized by an acute pain located chiefly in the
small joints of the foot, especially those of the great toe, which become
swollen and extremely sensitive. It is generally accompanied by an excess
of uric acid in the blood, and a deposit of urate of soda about the
affected joint. Gout is often the result of high living, and of too much
animal food. It is frequently inherited.

5. _Rheumatism_ affects mainly the connective, white, fibrous tissue
of the larger joints. While gout is the punishment of the rich who live
luxuriously, rheumatism afflicts alike the poor and the rich. There are
two common forms of rheumatism--the inflammatory or acute, and the
chronic. The latter is of long continuance; the former terminates more
speedily. The acute form is probably a disease of the blood, which carries
with it some poisonous matter that is deposited where the fibrous tissue
is most abundant. The disease flies capriciously from one joint to
another, and the pain caused by even the slightest motion deprives the
sufferer of the use of the disabled part and its muscles. Its chief danger
lies in the possibility of its affecting the vital organs. Chronic
rheumatism--the result of repeated attacks of the acute--leads to great
suffering, and oftentimes to disorganization of the joints and an
interference with the movements of the heart.

6. _Lumbago_ is an inflammation of the lumbar muscles and fascia.
[Footnote: Lumbago is really a form of myalgia, a disease which, has its
seat in the muscles, and may thus affect any part of the body. Doubtless
much of what is commonly called "liver" or "kidney complaint" is only, in
one case, myalgia of the chest or abdominal walls near the liver, or, in
the other, of the back and loins near the kidneys. Chronic liver disease
is comparatively rare in the Northern States, and pain in the side is not
a prominent symptom; while certain diseases of the kidneys, which are as
surely fatal as pulmonary consumption, are not attended by pain in the
back opposite these organs.--WEY.] It may be so moderate as to produce
only a "lame back," or so severe as to disable, as in the case of what is
popularly termed a "crick in the back." Strong swimmers who sometimes
drown without apparent cause are supposed to be seized in this way.

7. _A Ganglion_, or what is vulgarly called a "weak" or "weeping"
sinew, is the swelling of a bursa. [Footnote: A bursa is a small sack
containing a lubricating fluid to prevent friction where tendons play over
hard surfaces. There is one shaped like an hourglass on the wrist, just at
the edge of the palm. By pressing back the liquid it contains, this bursa
may be clearly seen.] It sometimes becomes so distended by fluid as to be
mistaken for bone. If on binding something hard upon it for a few days it
does not disappear, a physician will remove the liquid by means of a
hypodermic syringe, or perhaps cause it to be absorbed by an external
application of iodine.

PRACTICAL QUESTIONS.

1. What class of lever is the foot when we lift a weight on the toes?

2. Explain the movement of the body backward and forward, when resting
upon the thigh bone as a fulcrum.

3. What class of lever do we use when we lift the foot while sitting down?

4. Explain the swing of the arm from the shoulder.

5. What class of lever is used in bending our fingers?

6. What class of lever is our foot when we tap the ground with our toes?

7. What class of lever do we use when we raise ourselves from a stooping
position?

8. What class of lever is the foot when we walk?

9. Why can we raise a heavier weight with our hand when lifting from the
elbow than from the shoulder?

10. What class of lever do we employ when we are hopping, the thigh bone
being bent up toward the body and not used?

11. Describe the motions of the bones when we are using a gimlet.

12. Why do we tire when we stand erect?

13. Why does it rest us to change our work?

14. Why and when is dancing a beneficial exercise?

15. Why can we exert greater force with the back teeth than with the front
ones?

16. Why do we lean forward when we wish to rise from a chair?

17. Why does the projection of the heel bone make walking easier?

18. Does a horse travel with less fatigue over a flat than a hilly
country?

19. Can you move your upper jaw?

20. Are people naturally right or left-handed?

21. Why can so few persons move their ears by the muscles?

22. Is the blacksmith's right arm healthier than the left?

23. Boys often, though foolishly, thrust a pin into the flesh just above
the knee. Why is it not painful?

24. Will ten minutes' practice in a gymnasium answer for a day's exercise?

25. Why would an elastic tendon be unfitted to transmit the motion of a
muscle?

26. When one is struck violently on the head, why does he instantly fall?

27. What is the cause of the difference between light and dark meat in a
fowl?

III.

THE SKIN.

A protection from the outer world, it is our only means of communicating
with it. Insensible itself, it is the organ of touch. It feels the
pressure of a hair, yet bears the weight of the body. It yields to every
motion of that which it wraps and holds in place. It hides from view the
delicate organs within, yet the faintest tint of a thought shines through,
while the soul paints upon it, as on a canvas, the richest and rarest of
colors.

ANALYSIS OF THE SKIN.

THE SKIN.

THE SKIN is a tough, thin, close-fitting garment for the protection of the
tender flesh. Its perfect elasticity beautifully adapts it to every motion
of the body. We shall learn hereafter that it is more than a mere
covering, being an active organ, which does its part in the work of
keeping in order the house in which we live. It oils itself to preserve
its smoothness and delicacy, replaces itself as fast as it wears out, and
is at once the perfection of use and beauty.

1. STRUCTURE OF THE SKIN.

CUTIS AND CUTICLE.--What we commonly call the skin--viz., the part raised
by a blister--is only the cuticle [Footnote: _Cuticula_, little skin.
It is often styled the scarfskin, and also the epidermis (_epi_,
upon; and _derma_, skin).] or covering of the cutis or true skin. The
latter is full of nerves and blood vessels, while the former neither
bleeds [Footnote: We notice this in shaving; for if a razor goes below the
cuticle, it is followed by pain and blood. So insensible is this outer
layer that we can run a pin through the thick mass at the roots of the
nails without discomfort.] nor gives rise to pain, neither suffers from
heat nor feels the cold.

The cuticle is composed of small, flat cells or scales. These are
constantly shed from the surface in the form of scurf, dandruff, etc., but
are as constantly renewed from the cutis [Footnote: We see how rapidly
this change goes on by noticing how soon a stain of any kind disappears
from the skin. A snake throws off its cuticle entire, and at regular
intervals.] below.

Under the microscope, we can see the round cells of the cuticle, and how
they are flattened and hardened as they are forced to the surface. The
immense number of these cells surpasses comprehension. In one square inch
of the cuticle, counting only those in a single layer, there are over a
billion horny scales, each complete in itself.--HARTING.

FIG. 22.

[Illustration: A _represents a vertical section of the Cuticle._ B,
_lateral view of the cells._ C, _flat side of scales like_ d,
_magnified 250 diameters, showing the nucleated cells transformed into
broad scales._]

VALUE OF THE CUTICLE.--In the palm of the hand, the sole of the foot, and
other parts especially liable to injury, the cuticle is very thick. This
is a most admirable provision for their protection. [Footnote: We can hold
the hand in strong brine with impunity, but the smart will quickly tell us
when there is even a scratch in the skin. Vaccine matter must be inserted
beneath the cuticle to take effect. This membrane doubtless prevents many
poisonous substances from entering the system.] By use, it becomes callous
and horny. The boy who goes out barefoot for the first time, "treading as
if on eggs," can soon run where he pleases among thistles and over stones.
The blacksmith handles hot iron without pain, while the mason lays stones
and works in lime, without scratching or corroding his flesh.

THE COMPLEXION.--In the freshly made cells on the lower side of the
cuticle, is a pigment composed of tiny grains. [Footnote: These grains are
about 1/2000 of an inch in diameter, and, curiously enough, do not appear
opaque, but transparent and nearly colorless.--MARSHALL.] In the varying
tint of this coloring matter, lies the difference of hue between the
blonde and the brunette, the European and the African. In the purest
complexion, there is some of this pigment, which, however, disappears as
the fresh, round, soft cells next the cutis change into the old, flat,
horny scales at the surface.

Scars are white, because this part of the cuticle is not restored. The sun
has a powerful effect upon the coloring matter, and so we readily "tan" on
exposure to its rays. If the color gathers in spots, it forms freckles.
[Footnote: This action of the sun on the pigment of the skin is very
marked. Even among the Africans, the skin is observed to lose its intense
black color in those who live for many months in the shades of the forest.
It is said that Asiatic and African women confined within the walls of the
harem, and thus secluded from the sun, are as fair as Europeans. Among the
Jews who have settled in Northern Europe, are many of light complexion,
while those who live in India are as dark as the Hindoos. Intense heat
also increases this coloring matter, and thus a furnace-man's skin, even
where protected by clothing, becomes completely bronzed. The black pigment
has been known to disappear during severe illness, and a lighter color to
be developed in its place. Among the negroes, are sometimes found people
who have no complexion, _i. e._, there is no coloring matter in their
skin, hair, or the iris of their eyes. These persons are called Albinos.]

II. HAIR AND NAILS.

The Hair and the Nails are modified forms of the cuticle.

FIG. 23.

[Illustration: A _Hair, magnified 600 diameters._ S, _the sac
(follicle);_ P, _the papilla, showing the cells and the blood
vessels:_ V.]

THE HAIR is a protection from heat and cold, and shields the head from
blows. It is found on nearly all parts of the body, except the palms of
the hands and the soles of the feet. The outside of a hair is hard and
compact, and consists of a layer of colorless scales, which overlie one
another like the shingles of a house; the interior is porous, [Footnote:
In order to examine a hair, it should be put on the slide of the
microscope, and covered with a thin glass, while a few drops of alcohol
are allowed to flow between the cover and the slide. This causes the air,
which fills the hair and prevents our seeing its structure, to escape.]
and probably conveys the liquids by which it is nourished.

Each hair grows from a tiny bulb (papilla), which is an elevation of the
cutis at the bottom of a little hollow in the skin. From the surface of
this bulb, the hair is produced, like the cuticle, by the constant
formation of new cells at the bottom. When the hair is pulled out, this
bulb, if uninjured, will produce a new one; but, when once destroyed, it
will never grow again. [Footnote: Hair grows at the rate of about five to
seven inches in a year. It is said to grow after death. This appearance is
due to the fact that by the shrinking of the skin the part below the
surface is caused to project, which is especially noticeable in the
beard.] The hair has been known to whiten in a single night by fear,
fright, or nervous excitement. When the color has once changed, it can not
be restored. [Footnote: Hair dyes, or so-called "hair restorers," are
almost invariably deleterious substances, depending for their coloring
properties upon the action of lead or lunar caustic. Frequent instances of
hair poisoning have occurred, owing to the common use of such dangerous
articles. If the growth of the hair be impaired, the general constitution
or the skin needs treatment. This is the work of a skillful physician, and
not of a patent remedy. Dame Fashion has her repentant freaks as well as
her ruinous follies, and it is a healthful sign that the era of universal
hair dyeing has been blotted out from her present calendar, and the gray
hairs of age are now honored with the highest place in "style" as well as
in good sense and cleanliness.] (See p. 285.)

Wherever hair exists, tiny muscles are found, interlaced among the fibers
of the skin. These, when contracting under the influence of cold or
electricity, pucker up the skin, and cause the hair to stand on end.
[Footnote: In horses and other animals which are able to shake the whole
skin, this muscular tissue is much more fully developed than in man.] The
hairs themselves are destitute of feeling. Nerves, however, are found in
the hollows in which the hair is rooted, and so one feels pain when it is
pulled. [Footnote: These nerves are especially abundant in the whiskers of
the cat, which are used as feelers.] Thus the insensible hairs become
wonderfully delicate instruments to convey an impression of even the
slightest touch.

FIG. 24.

[Illustration: A, _a perspiratory tube with its gland;_ B, _a hair
with a muscle and two oil glands;_ C, _cuticle;_ D, _the
papillæ;_ and E, _fat cells._]

Next to the teeth and bones, the hair is the least destructible part of
the body, and its color is often preserved for many years after the other
portions have gone to decay. [Footnote: Fine downy hairs, such as are
general upon the body, have been detected in the little fragments of skin
found beneath the heads of the nails by which, centuries ago, certain
robbers were fastened to the church doors, as a punishment for their
sacrilege.]

THE NAILS protect the ends of the tender finger, and toe, and give us
power more firmly to grasp and easily to pick up any object we may desire.
They enable us to perform a hundred little, mechanical acts which else
were impossible. At the same time, their delicate color and beautiful
outline give a finish of ornament to that exquisite instrument, the hand.
The nail is firmly set in a groove (matrix) in the cuticle, from which it
grows at the root in length [Footnote: By making a little mark on the nail
near the root we can see, week by week, how rapidly this process goes on,
and so form some idea of what a multitude of cells must be transformed
into the horny matter of the nail.] and from beneath in thickness. So long
as the matrix at the root is uninjured, the nail will be replaced after
any accident. (See p. 288.)

III. THE MUCOUS MEMBRANE.

STRUCTURE.--At the edges of the openings into the body, the skin seems to
stop and give place to a tissue which is redder, more sensitive, more
liable to bleed, and is moistened by a fluid, or mucus, as it is called.
Really, however, the skin does not cease, but passes into a more delicate
covering of the same general structure, viz., an outer, hard, bloodless,
insensible layer, and an inner, soft, sanguine, nervous one. [Footnote:
With a dull knife, we can scrape from the mucous membrane which lines the
mouth some of the cuticle for examination under the microscope. In a
similar way, we can obtain cuticle from the surface of the body for study
and comparison.] Thus every part of the body is wrapped in a kind of
double bag, made of tough skin on the outside, and tender mucous membrane
on the inside.

CONNECTIVE TISSUE.--The cutis and the corresponding layer of the mucous
membrane consist chiefly of a fibrous substance interlaced, like felt. It
is called connective tissue, because it connects all the different parts
of the body. It spreads from the cutis, invests muscles, bones, and
cartilages, and thence passes into the mucous membrane. So thoroughly does
it permeate the body, that, if the other tissues were destroyed, it would
give a perfect model of every organ. [Footnote: It is curious to notice
how our body is wrapped in membrane. On the outside, is the skin
protecting from exterior injury, and, on the inside, is the mucous
membrane reaching from the lips to the innermost air cell of the lungs.
Every organ is enveloped in its membrane. Every bone has its sheath. Every
socket is lined. Even the separate fibers of muscles have their covering
tissue. The brain and the spinal cord are triply wrapped, while the eye is
only a membranous globe filled with fluid. These membranes protect and
support the organs they enfold, but, with that wise economy so
characteristic of nature everywhere, they have also an important function
to perform. They are the _filters_ of the body. Through their pores
pass alike the elements of growth, and the returning products of waste. On
one side, bathed by the blood, they choose from it suitable food for the
organ they envelop, and many of them in their tiny cells, by some
mysterious process, form new products,--put the finishing touches, as it
were, upon the material ere it is deposited in the body.] It can be seen
in a piece of meat as a delicate substance lying between the layers of
muscle, where it serves to bind together the numerous fibers of which they
are composed.

Connective tissue yields gelatine on boiling, and is the part which tans
when hides are manufactured into leather. It is very elastic, so that when
you remove your finger after pressing upon the skin, no indentation is
left. [Footnote: In dropsy, this elasticity is lost by distension, and
there is a kind of "pitting," as it is called, produced by pressure.] It
varies greatly in character,--from the mucous membrane, where it is soft
and tender, to the ligaments and tendons which it largely composes, where
it is strong and dense. [Footnote: The leather made from this tissue
varies as greatly, from the tough, thick oxhide, to the soft, pliable kid
and chamois skin.]

FAT is deposited as an oil in the cells [Footnote: So tiny are these
cells, that there are over sixty-five million in a cubic inch of fat. As
they are kept moist, the liquid does not ooze out, but, on drying, it
comes to the surface, and thus a piece of fat feels oily when exposed to
the air. The quantity of fat varies with the state of nutrition. In
corpulent persons, the masses of fat beneath the skin, in the mesentery,
on the surface of the heart and great vessels, between the muscles, and in
the neighborhood of the nerves, are considerably increased. Conversely, in
the emaciated we sometimes find beneath the skin nucleated cells, which
contain only one oil drop. Many masses of fat which have an important
relation to muscular actions--such as the fat of the orbit or the cheek--
do not disappear in the most emaciated object. Even in starvation, the
fatty substances of the brain and spinal cord are retained.--VALENTIN.] of
this tissue, just beneath the skin (Fig. 24), giving roundness and
plumpness to the body, and acting as an excellent nonconductor for the
retention of heat. It collects as pads in the hollows of the bones, around
the joints, and between the muscles, causing them to glide more easily
upon each other. As marrow, it nourishes the skeleton, and also
distributes the shock of any jar the limb may sustain.

It is noticeable, however, that fat does not gather within the cranium,
the lungs, or the eyelids, where its accumulation would clog the organs.

IV. THE TEETH.

THE TEETH [Footnote: Although the teeth are always found in connection
with the skeleton, and are, therefore, figured as a part of it (Fig. 1),
yet they do not properly belong to the bones of the body, and are merely
set in the solid jaw to insure solidity. They are hard, and resemble bony
matter, yet they are neither true bone nor are they formed in the same
manner. "They are properly appendages of the mucous membrane, and are
developed from it."--LEIDY. "They belong to the Tegumentary System, which,
speaking generally of animals, includes teeth, nails, horns, scales, and
hairs."--MARSHALL. They are therefore classed with the mucous membrane, as
are the nails and hair with the skin.] are thirty-two in all,--there being
eight in each half jaw, similarly shaped and arranged. In each set of
eight, the two nearest the middle of the jaw have wide, sharp, chisel-like
edges, fit for cutting, and hence are called _incisors_. The next one
corresponds to the great tearing or holding tooth of the dog, and is
styled the _canine_, or eye-tooth. The next two have broader crowns,
with two points, or cusps, and are hence termed the _bicuspids_. The
remaining three are much broader, and, as they are used to crush the food,
are called the _grinders_, or _molars_. The incisors and
eyeteeth have one fang, or root; the others have two or three fangs.

THE MILK TEETH.--We are provided with two sets of teeth. The first, or
milk teeth, are small and only twenty in number. In each half jaw there
are two incisors, one canine, and two molars. The middle incisors are
usually cut about the age of seven months, the others at nine months, the
first molars at twelve months, the canines at eighteen months, and the
remaining molars at two or three years of age. The lower teeth precede the
corresponding upper ones. The time often varies, but the order seldom.

THE PERMANENT TEETH.--At six years, when the first set is usually still
perfect, the jaws contain the crowns of all the second, except the wisdom
teeth. About this age, to meet the wants of the growing body, the crowns
of the permanent set begin to press against the roots of the milk teeth,
which, becoming absorbed, leave the loosened teeth to drop out, while the
new ones rise and occupy their places. [Footnote: If the milk teeth, do
not promptly loosen on the appearance of the second set, the former should
be at once removed to permit the permanent teeth to assume their natural
places. If any fail to come in regularly, or if they crowd the others, a
competent dentist should be consulted.]

FIG. 25.

[Illustration: _The teeth at the age of six and one half years._ I,
_the incisors;_ O, _the canine;_ M, _the molars; the last
molar is the first of the permanent teeth;_ F, _sacs of the permanent
incisors;_ C, _of the canine;_ B, _of the bicuspids;_ N,
_of the second molar; the sac of the third molar is empty._--
MARSHALL.]

The central incisors appear at about seven years of age; the others at
eight; the first bicuspids at nine, the second at ten; the canines at
eleven or twelve; the second [Footnote: The first molar appears much
earlier. (See Fig. 25.)] molars at twelve or thirteen, and the last, or
wisdom teeth, are sometimes delayed until the twenty-second year, or even
later.

STRUCTURE OF THE TEETH.--The interior of the tooth consists principally of
_dentine_, a dense substance resembling bone. [Footnote: In the tusk
of the elephant this is known as ivory.] The crown of the tooth, which is
exposed to wear, is protected by a sheath of _enamel_. This is a
hard, glistening, white substance, containing only two and a half per cent
of animal matter. The fang is covered by a thin layer of true bone
(cement).

FIG. 26.

[Illustration: _Vertical section of a Molar Tooth, moderately
magnified._ a, _enamel of the crown, the lines of which indicate the
arrangement of its columns;_ b, _dentine;_ c, _cement;_ d,
_pulp cavity._]

At the center of the tooth is a cavity filled with a soft, reddish-white,
pulpy substance full of blood vessels and nerves. This pulp is very
sensitive, and toothache is caused by its irritation.

THE FITTING OF THE TOOTH INTO THE JAW is a most admirable contrivance. It
is not set like a nail in wood, having the fang in contact with the bone;
but the socket is lined with a membrane which forms a soft cushion. While
this is in a healthy state, it deadens the force of any shock, but, when
inflamed, it becomes the seat of excruciating pain.

THE DECAY OF THE TEETH [Footnote: Unlike the other portions of the body,
there is no provision made for any change in the permanent teeth. That
part, however, which is thus during life most liable to change, after
death resists it the longest. In deep-sea dredgings teeth are found when
all traces of the frame to which they belonged have disappeared. Yet hard
and incorruptible as they seem, their permanence is only relative. Exposed
to injury and disease, they break or decay. Even if they escape accident,
they yet wear at the crown, are absorbed at the fang, and, in time, drop
out, thus affording another of the many signs of the limitations
Providence has fixed to the endurance of our bodies and the length of our
lives.] is commonly caused (1) by portions of the food which become
entangled between them, and, on account of the heat and moisture, quickly
decompose; and (2) by the saliva, as it evaporates, leaving on the teeth a
sediment, which we call tartar. This collects organic matter that rapidly
changes, and also affords a soil in which a sort of fungus speedily
springs up. From both these causes, the breath becomes offensive, and the
teeth are injured.

PRESERVATION OF THE TEETH.--Children should early be taught to brush their
teeth at least every morning with tepid water, and twice a week with white
castile soap and powdered orris root, or with some dentifrice recommended
by a responsible dentist. They should also be instructed to remove the
particles of food from between the teeth, after each meal, by means of a
quill or wooden toothpick.

The enamel once injured is never restored, and the whole interior of the
tooth is exposed to decay. We should not, therefore, crack hard nuts, bite
thread, or use metal toothpicks, gritty tooth powders, or any acid which
"sets the teeth on edge," _i. e._. that acts upon the enamel. It is
well also to have the teeth examined yearly by a dentist, that any small
orifice may be filled, and further decay prevented.

V. THE GLANDS OF THE SKIN.

1. THE OIL GLANDS are clusters of tiny sacs which secrete an oil that
flows along the duct to the root of the hair, and thence oozes out on the
cuticle (Fig. 24). [Footnote: This secretion is said to vary in different
persons, and on that account the dog is enabled to trace his master by the
scent.] This is nature's efficient hair-dressing, and also keeps the skin
soft and flexible. These glands are not usually found where there is no
hair, as on the palm of the hand, and hence at those points only can water
readily soak through the skin into the body. They are of considerable size
on the face, especially about the nose. When obstructed, their contents
become hard and dark-colored, and are vulgarly called "worms." [Footnote:
Though they are not alive, yet, under the microscope, they are sometimes
found to contain a curious parasite, called the pimple mite, which is
supposed to consume the superabundant secretion.]

II. THE PERSPIRATORY GLANDS are fine tubes about 1/300 of an inch in
diameter, and a quarter of an inch in length, which run through the cutis,
and then coil up in little balls (Fig. 24). They are found in all parts of
the body, and in almost incredible numbers. In the palm of the hand, there
are about two thousand eight hundred in a single square inch. On the back
of the neck and trunk, where they are fewest, there are yet four hundred
to the square inch. The total number on the body of an adult is estimated
at about two and a half million. If they were laid end to end, they would
extend nearly ten miles. [Footnote: The current statement, that they would
extend twenty-eight miles, is undoubtedly an exaggeration. Krause
estimates the total number at 2,381,248, and the length of each coil, when
unraveled, at 1/10 of an inch, which would make the total length much less
than even the statement in the text. Seguin states that the proportion of
impurities thrown off by the skin and the lungs, is eleven to seven.] The
mouths of these glands--"pores," as we commonly call them--may be seen
with a pocket lens along the fine ridges which cover the palm of the hand.

THE PERSPIRATION.--From these openings, there constantly passes a vapor,
forming what we call the insensible perspiration. Exercise or heat causes
it to flow more freely, when it condenses on the surface in drops. The
perspiration consists of about ninety-nine parts water, and one part solid
matter. The amount varies greatly, but on the average is, for an adult,
not far from two pounds per day. Any suppression of this constant drainage
will lead to disagreeable and even dangerous results. If it be entirely
and permanently checked, death will inevitably ensue. [Footnote: Once, on
an occasion of great solemnity at Rome, a child was, it is said,
completely covered with gold leaf, closely applied to the skin, so as to
represent, according to the idea of that age, the golden glory of an angel
or seraph. In a few hours, after contributing to this pageant, the child
died; the cause being suffocation, from stopping the exhalation of the
skin; although, in the ignorance of the common people of those days, the
death was attributed to the anger of the Deity, and looked upon as a
circumstance of evil omen.]

THE ABSORBING POWER OF THE SKIN.--We have already described two uses of
the skin: (1) Its _protective_, (2) its _exhaling_, and now we
come to (3) its _absorbing_ power. This is not so noticeable as the
others, and yet it can be illustrated. Persons frequently poison their
hands with the common wood ivy. Contagious diseases are taken by touching
a patient, or even his clothing, especially if there be a crack in the
cuticle. [Footnote: If one is called upon to handle a dead body, it is
well, especially if the person has died of a contagious disease, to rub
the hand with lard or olive oil. Poisonous matter has been fatally
absorbed through the breaking of the cuticle by a hangnail, or a simple
scratch. There is a story that Bonaparte, when a lieutenant of artillery,
in the heat of battle, seized the rammer and worked the gun of an
artilleryman who had fallen. From the wood which the soldier had used,
Bonaparte absorbed a poison that gave him a skin disease, by which he was
annoyed the remainder of his life.] Painters absorb so much lead through
the pores of their hands that they are attacked with colic. [Footnote:
Cosmetics, hair dyes, etc., are exceedingly injurious, not only because
they tend to fill the pores of the skin, but because they often contain
poisonous matters that may be absorbed into the system, especially if they
are in a solution.] Snuff and lard are frequently rubbed on the chest of a
child suffering with the croup, to produce vomiting. It is said that
seamen in want of water drench their clothing in salt spray, when the skin
will absorb enough moisture to quench thirst (see Lymphatic System).

By carefully conducted experiments, it has been found that the skin acts
in the same way as the lungs (see Respiration) in absorbing oxygen from
the air, and giving off carbonic acid to a small but appreciable amount.
Indeed, the skin has not inaptly been styled the third lung. Hence, the
importance of absolute cleanliness and a frequent ablution of the entire
body.

VI. HYGIENE.

HINTS ABOUT WASHING AND BATHING.--The moment of rising from bed is the
proper time for the full wash or bath with which one should commence the
day. The body is then warm, and can endure moderately cold water better
than at any other time; it is relaxed, and needs bracing; and the nerves,
deadened by the night's repose, require a gentle stimulus. If the system
be strong enough to resist the shock, cold water is the most invigorating;
if not, a tepid bath will answer. [Footnote: Many persons have not the
conveniences for a bath. To them, the following plan, which the author has
daily employed for years, is commended. The necessities are: a basin full
of soft water, a mild soap, a large sponge or a piece of flannel, and two
towels--one soft, the other rough. The temperature of the water should
vary with the season of the year--cold in summer and tepid in winter. Rub
quickly the entire body with the wet sponge or flannel. (If more
agreeable, wash and wipe only a part at a time, protecting the rest in
cold weather with portions of clothing.) Dry the skin gently with a soft
towel, and when quite dry, with the rough towel or flesh brush rub the
body briskly four or five minutes till the skin is all aglow. The chest
and abdomen need the principal rubbing. The roughness of the towel should
be accommodated to the condition of the skin. Enough friction, however,
must be given to produce at least a gentle warmth, indicative of the
reaction necessary to prevent subsequent chill or languor. An invalid will
find it exceedingly beneficial if a stout, vigorous person produce the
reaction by rubbing with the hands.]

Before dressing, the whole body should be thoroughly rubbed with a coarse
towel or flesh brush. At first, the friction may be unpleasant, but this
sensitiveness will soon be overcome, and the keenest pleasure be felt in
the lively glow which follows. A bath should not be taken just before nor
immediately after a meal, as it will interfere with the digestion of the
food. Soap should be employed occasionally, but its frequent use tends to
make the skin dry and hard.

REACTION.--After taking a cold bath, there should be a prompt reaction.
When the surface is chilled by cold water, the blood sets to the heart and
other vital organs, exciting them to more vigorous action, and then, being
thrown back to the surface, it reddens, warms, and stimulates the skin to
an unwonted degree. This is called the reaction, and in it lies the
invigorating influence of the cold bath. When, on the contrary, the skin
is heated by a hot bath, the blood is drawn to the surface, less blood
goes to the heart, the circulation decreases, and languor ensues. A dash
of cold water is both necessary and refreshing at the close of a hot bath.
[Footnote: The Russians are very fond of vapor baths, taken in the
following manner. A large room is heated by stoves. Red-hot stones being
brought in, water is thrown upon them, filling the room with steam. The
bathers sit on benches until they perspire profusely, when they are rubbed
with soapsuds and dashed with cold water. Sometimes, while in this state
of excessive perspiration, they run out of doors and leap into snow
banks.]

If, after a cold bath, there be felt no glow of warmth, but only a
chilliness and depression, we are thereby warned that either proper means
were not taken to bring on this reaction, or that the circulation is not
vigorous enough to make such a bath beneficial. The general effect of a
cool bath is exhilarating, and that of a warm one depressing. [Footnote:
The sudden plunge into a cold bath is good for the strong and healthy, but
too severe for the delicate. One should always wet first the face, neck,
and chest. It is extremely injurious to stand in a bath with only the feet
and the lower limbs covered by the water, for the blood is thus sent from
the extremities to the heart and internal organs, and they become so
burdened that reaction may be out of their power. A brisk walk, or a
thorough rubbing of the skin, before a cold bath or swim, adds greatly to
its value and pleasure.] Hence the latter should not ordinarily be taken
oftener than once a week, while the former may be enjoyed daily. (See p.
289.)

SEA BATHING is exceedingly stimulating, on account of the action of the
salt and the exciting surroundings. Twenty minutes is the utmost limit for
bathing or swimming in salt or fresh water. A chilly sensation should be
the signal for instant removal. It is better to leave while the glow and
buoyancy which follow the first plunge are still felt. Gentle exercise
after a bath is beneficial.

CLOTHING in winter, to keep us warm, should repel the external cold and
retain the heat of the body. In summer, to keep us cool, it should not
absorb the rays of the sun, and should permit the passage of the heat of
the body. At all seasons, it should be porous, to give ready escape to the
perspiration, and a free admission of air to the skin. We can readily
apply these essential conditions to the different kinds of clothing.

_Linen_ is soft to the touch, and is a good conductor of heat. Hence
it is pleasant for summer wear, but, being apt to chill the surface too
rapidly, it should not be worn next the skin.

_Cotton_ is a poorer conductor of heat and absorber of moisture, and
is therefore warmer than linen. It is sufficiently cool for summer wear,
and affords better protection against sudden changes.

_Woolen_ absorbs moisture slowly, and contains much air in its pores.
It is therefore a poor conductor of heat, and guards the wearer against
the vicissitudes of our climate.

The outer clothing may be adapted largely to ornament, and may be varied
to suit our fancy and the requirements of society. The underclothing
should always be sufficient to keep us warm. Woolen should be worn next
the skin at all times; light gossamer garments in the heat of summer, and
warm, porous flannels in midwinter.

Light-colored clothing is not only cooler in summer, but warmer in winter.
As the warmth of clothing depends greatly on the amount of air contained
in its fibers, fine, loose, porous cloth with a plenty of nap is best for
winter wear. Firm and heavy goods are not necessarily the warmest. Furs
are the perfection of winter clothing, since they combine warmth with
lightness. Two light woolen garments are warmer than one heavy one, as
there is between them a layer of nonconducting air.

All the body except the head should be equally protected by clothing.
Whatever fashion may dictate, no part covered to-day can be uncovered
tonight or to-morrow, except at the peril of health. It is a most
barbarous and cruel custom to leave the limbs of little children
unprotected, when adults would shiver at the very thought of exposure.
Equally so is it for children to be thinly clad for the purpose of
hardening them. To go shivering with cold is not the way to increase one's
power of endurance. The system is made more vigorous by exercise and food;
not by exposure. In winter, we should wear warm shoes with thick soles,
and rubbers when it is damp. At night, and after exercise, we require
extra clothing. (See p. 295.)

DISEASES, ETC.--l. _Erysipelas_ is an inflammation (see Inflammation)
of the skin, and often begins in a spot not larger than a pin head, which
spreads with great rapidity. It is very commonly checked by the
application of a solution of iodine. The burning and contracting sensation
may be relieved by cloths wrung out of hot water.

2. _Eczema_ (Salt Rheum, etc.) is of constitutional origin. It is
characterized by an itching, burning, reddened eruption, in which a serous
discharge exudes and dries into crusts or scales. The skin thickens in
patches, and painful fissures are formed, which are irritated by exposure
to air or water. Eczema denotes debility. It occurs in various forms, and,
like erysipelas, should be treated by a physician.

3. _Corns_ are thickened cuticle, caused by pressure or friction.
They most frequently occur on the feet; but are produced on the
shoemaker's knee by constant hammering, and on the soldier's shoulder by
the rubbing of his musket. This hard portion irritates the sensitive cutis
beneath, and so causes pain. A corn will soften in hot water, when it may
be pared with a sharp knife. If the cause be removed, the corn will not
return.

4. _Ingrowing Nails_ are caused by pressure, which forces the edge of
the toe nail into the flesh. They may be cured by carefully cutting away
the part which has mal-grown, and then scraping the back of the nail till
it is thin, making a small incision in the center, at the top. The two
portions, uniting, will draw away the nail from the flesh at the edge.
Ingrowing nails may be prevented by wearing broad-toed shoes.

5. _Warts_ are overgrown papillæ (Fig. 24). They may generally be
removed by the application of glacial acetic acid, or a drop of nitric
acid, repeated until the entire structure is softened. Care must be taken
to keep the acid from touching the neighboring skin. The capricious
character of warts has given rise to the popular delusion concerning the
influence of charms upon them.

6. _Chilblain_ is a local inflammation affecting generally the feet,
the hands, or the lobes of the ear. Liability to it usually passes away
with manhood. It is not caused by "freezing the feet," as many suppose,
though attacks are brought on, or aggravated, by exposure to cold,
followed by sudden warming. Chilblain is subject to daily congestion (see
Congestion), manifested by itching, soreness, etc., commonly occurring at
night. The best preventive is a uniform temperature, and careful
protection against the cold by warm clothing, especially for the feet.

PRACTICAL QUESTIONS.

1. If a hair be plucked out, will another grow in its place?

2. What causes the hair to "stand on end" when we are frightened?

3. Why is the skin roughened by riding in the cold?

4. Why is the back of a washerwoman's hand less water-soaked than the
palm?

5. What would be the length of the perspiratory tubes in a single square
inch of the palm, if placed end to end?

6. What colored clothing is best adapted to all seasons?

7. What is the effect of paint and powder on the skin?

8. Is waterproof clothing healthful for constant wear?

9. Why are rubbers cold to the feet?

10. Why does the heat seem oppressive when the air is moist?

11. Why is friction of the skin invigorating after a cold bath?

12. Why does the hair of domestic animals become roughened in winter?

13. Why do fowls spread their feathers before they perch for the night?

14. How can an extensive burn produce congestion of the lungs?

15. Why do we perspire so profusely after drinking cold water?

16. How can we best prevent skin diseases, colds, and rheumatism?

17. What causes the difference between the hard hand of a blacksmith and
the soft hand of a woman?

18. Why should a painter avoid getting paint on the palm of his hand?

19. Why should we not use the soap or the soiled towel at a hotel?

20. Which teeth cut like a pair of scissors?

21. Which teeth cut like a chisel?

22. Which should be clothed the warmer, a merchant or a farmer? 23. Why
should we not crack nuts with our teeth?

24. Do the edges of the upper and the lower teeth meet?

25. When fatigued, would you take a cold bath?

26. Why is the outer surface of a kid glove finer than the inner?

27. Why will a brunette endure the sun's rays better than a blonde?

28. Does patent leather form a healthful covering for the feet?

29. Why are men more frequently bald than women?

30. On what part of the head does baldness commonly occur? Why?

31. What does the combination in our teeth of canines and grinders suggest
as to the character of our food?

32. Is a staid, formal promenade suitable exercise?

33. Is there any danger in changing the warm clothing of our daily wear
for the thin one of a party?

34. Should we retain our overcoat, shawl, or furs when we come into a warm
room?

35. Which should bathe the oftener, students or outdoor laborers?

36. Is abundant perspiration injurious?

37. How often should the ablution of the entire body be performed?

38. Why is cold water better than warm, for our daily ablution?

39. Why should our clothing always fit loosely?

40. Why should we take special pains to avoid clothing that is colored by
poisonous dyestuffs? (See p. 296.)

41. What general principles should guide us as to the length and frequency
of baths In salt or fresh water?

42. What is the beneficial effect of exercise upon the functions of the
skin?

43. How can we best show our admiration and respect for the human body?

44. Why is the scar of a severe wound upon a negro sometimes white?

IV.

RESPIRATION AND THE VOICE.

"The smooth soft air with pulse-like waves
Flows murmuring through its hidden caves,
Whose streams of brightening purple rush,
Fired with a new and livelier blush;
While all their burden of decay
The ebbing current steals away."

ANALYSIS OF RESPIRATION AND THE VOICE.

RESPIRATION AND THE VOICE.

The Organs of Respiration and the Voice are the _larynx_, the
_trachea_, and the _lungs_.

DESCRIPTION OF THE ORGANS OF THE VOICE.--l. _The Larynx_.--In the
neck, is a prominence sometimes called Adam's apple. It is the front of
the _larynx_. This is a small triangular, cartilaginous box, placed
just below the root of the tongue, and at the top of the windpipe. The
opening into it from the throat is called the _glottis_; and the
cover, the _epiglottis_ (_epi_, upon; _glotta_, the tongue). The
latter is a spoon-shaped lid, which opens when we breathe, but, by
a nice arrangement, shuts when we try to swallow, and so lets our
food slip over it into the _sophagus_ (e-sof'-a-gus), the tube leading
from the pharynx to the stomach (Fig. 27).

If we laugh or talk when we swallow, our food is apt to "go the wrong
way," _i. e._, little particles pass into the larynx, and the
tickling sensation which they produce forces us to cough in order to expel
the intruders.

2. _The Vocal Cords_.--On each side of the _glottis_ are the so-
called _vocal cords_. They are not really cords, but merely elastic
membranes projecting from the sides of the box across the opening.
[Footnote: The cartilages and vocal cords may be readily seen in the
larynx of an ox or sheep. If the flesh be cut off, the cartilages will
dry, and will keep for years.] When not in use, they spread apart and
leave a V-shaped orifice (Fig. 28), through which the air passes to and
from the lungs. If the cords are tightened, the edges approach sometimes
within 1/100 of an inch of each other, and, being thrown into vibration,
cause corresponding vibrations in the current of air. Thus sound is
produced in the same manner as by the vibrations of the tongues of an
accordion, or the strings of a violin, only in this case the strings are
scarcely an inch long.

FIG. 27.

[Illustration: _Passage to the sophagus and Windpipe._ c, _the
tongue;_ d, _the soft palate, ending in_ g, _the uvula;_ h,
_the epiglottis;_ i, _the glottis;_ I, _the sophagus;_ f,
_the pharynx._]

DIFFERENT TONES OF THE VOICE.--The higher tones of the voice are produced
when the cords are short, tight, and closely in contact; the lower, by the
opposite conditions. Loudness is regulated by the quantity of air and
force of expulsion. A falsetto voice is thought to be the result of a
peculiarity in the pharynx (Fig. 27) at the back part of the nose; it is
more probably produced by some muscular maneuver not yet fully understood.
When boys are about fourteen years of age, the larynx enlarges, and the
cords grow proportionately longer and coarser; hence, the voice becomes
deeper, or, as we say, "changes." The peculiar harshness of the voice at
this time seems to be due to a congestion of the mucous membrane of the
cords. The change may occur very suddenly, the voice breaking in a single
night.

FIG. 28.

[Illustration: e, e, _the vocal cords;_ d, _the epiglottis._]

Speech is voice modulated by the lips, tongue, [Footnote: The tongue is
styled the "unruly member," and held responsible for all the tattling of
the world; but when the tongue is removed, the adjacent organs in some way
largely supply the deficiency, so that speech is still possible. Huxley
describes the conversation of a man who had two and one half inches of his
tongue preserved in spirits, and yet could converse intelligibly. Only the
two letters _t_ and _d_ were beyond his power; the articulation
of these involves the employment of the tip of the tongue; hence, "tin" he
converted into "fin," and "dog" into "thog."] palate, and teeth.
[Footnote: An artificial larynx may be made by using elastic bands to
represent the vocal cords, and by placing above them chambers which by
their resonance will produce the same effect as the cavities lying above
the larynx. An artificial speaking machine was constructed by Kempelen,
which could pronounce such sentences as, "I love you with all my heart,"
in different languages, by simply touching the proper keys.] Speech and
voice are commonly associated, but speech may exist without the voice, for
when we whisper we articulate the words, although there is no
vocalization, _i. e._, no action of the larynx. [Footnote: We can
observe this by placing the hand on the throat, and noticing the absence
of vibrations when we whisper, and their presence when we talk. The
difference between vocalization and non-vocalization is seen in a sigh and
a groan, the latter being the former vocalized. Whistling is a pure mouth
sound, and does not depend on the voice. Laughter is vocal, being the
aspirated vowels, a, e, or o, convulsively repeated.] (See p. 297.)

FIG. 29.

[Illustration: _The Lungs, showing the Larynx._ A, _the
windpipe;_ B, _the bronchial tubes._]

FORMATION OF VOCAL SOUNDS.--The method of modulating voice into speech may
be seen by producing the pure vowel sounds _a, e_, etc., from one
expiration, the mouth being kept open while the form of the aperture is
changed for each vowel by the tongue and the lips. _H_ is only an
explosion, or forcible throwing of a vowel sound from the mouth.
[Footnote: When, in sounding a vowel, the sound coincides with a sudden
change in the position of the vocal cords from one of divergence to one of
approximation, the vowel is pronounced with the _spiritus asper_.
When the vocal cords are brought together before the blast of air begins,
the vowel is pronounced with the _spiritus lenis._--FOSTER.]

The consonants, or short sounds, may also be made without interrupting the
current of air, by various modifications of the vocal organs. In sounding
singly any one of the letters, we can detect its peculiar requirements.
Thus _m_ and _n_ can be made only by blocking the air in the
mouth and sending it through the nose; _l_ lets the air escape at the
sides of the tongue; _r_ needs a vibratory movement of the tongue;
_b_ and _p_ stop the breath at the lips; _k_ and _g_ (hard), at the
back of the palate. Consonants like _b_ and _d_ are abrupt, or, like
_l_ and _s_, continuous. Those made by the lips are termed _labials_;
those by pressing the tongue against the teeth, _dentals_; those by the
tongue, _linguals_.

The child gains speech slowly, first learning to pronounce the vowel
_a_, the consonants _b, m_, and _p_, and then their unions --_ba, ma, pa_.

DESCRIPTION OF THE ORGANS OF RESPIRATION.--Beneath the larynx is the
windpipe, or _trachea_ (see Fig. 29), so called because of its
roughness. It is strengthened by C-shaped cartilages with the openings
behind, where they are attached to the sophagus. At the lower end, the
trachea divides into two branches, called the right and left
_bronchi_. These subdivide in the small bronchial tubes, which ramify
through the lungs like the branches of a tree, the tiny twigs of which at
last end in clusters of cells so small that there are six hundred million
in all. This cellular structure renders the lungs exceedingly soft,
elastic, and sponge-like. [Footnote: The lungs of slaughtered animals are
vulgarly called "lights," probably on account of their lightness. They are
similar in structure to those of man. They will float on water, and if a
small piece be forcibly squeezed between the fingers (notice the creaking
sound it gives), it will retain sufficient air to make it buoyant.]

FIG. 30.

[Illustration: _Bronchial Tubes, with clusters of cells._]

The stiff, cartilaginous rings, so noticeable in the rough surface of the
trachea and the bronchi, disappear as we reach the smaller bronchial
tubes, so that while the former are kept constantly open for the free
admission of air, the latter are provided with elastic fibers by which
they may be almost closed.

WRAPPING OF THE LUNGS.--The lungs are invested with a double covering--the
_pleura_--one layer being attached to the lungs and the other to the
walls of the chest. It secretes a fluid which lubricates it, so that the
layers glide upon each other with perfect ease. [Footnote: These pleural
sacs are distinct and closed; hence, when the ribs are raised, a partial
vacuum being formed in the sacs, air rushes in, and distends the pulmonary
lobules.] The lungs are lined with mucous membrane, exceedingly delicate
and sensitive to the presence of anything except pure air. We have all
noticed this when we have breathed any thing offensive.

FIG. 31.

[Illustration: A, _the heart;_ B, _the lungs drawn aside to show
the internal organs;_ C, _the diaphragm;_ D, _the liver;_ E,
_the gall cyst;_ F, _the stomach;_ G,_ the small intestines;_ H,
_the transverse colon._]

THE CILIA.--Along the air passages are minute filaments (_cilia_,
Fig. 32), which are in constant motion, like a field of grain stirred by a
gentle breeze. They serve to fan the air in the lungs, and produce an
outward current, which is useful in catching dust and fine particles swept
inward with the breath.

HOW WE BREATHE.--Respiration consists of two acts--taking in the air, or
_inspiration_, and expelling the air, or _expiration_.

FIG. 32.

[Illustration: B, _a section of the mucous membrane, showing the cilia
rising from the peculiar epithelial cells on the outside of the mucous
membrane lining the tubes;_ A, _a single cell more highly
magnified._]

1. _Inspiration_.--When we draw in a full breath, we straighten the
spine and throw the head and shoulders back, so as to give the greatest
advantage to the muscles. [Footnote: If we examine the bony cage of the
thorax or chest in Fig. 8, we shall see that the position of the ribs may
alter its capacity in two ways.

1. As they run obliquely downward from the spine, if the sternum or
breastbone be lifted in front, the diameter of the chest will be
increased.

2. The ribs are fastened by elastic cartilages, which stretch as the
muscles that lift the ribs contract, and so increase the breadth of the
chest.]

At the same time, the diaphragm [Footnote: The diaphragm is the muscular
partition between the chest and the abdomen. It is always convex toward
the former, and concave toward the latter (Fig. 31). Long muscular fibers
extend from its center toward the ribs in front and the spine at the back.
When these contract, they depress and flatten the diaphragm; when they
relax, it becomes convex again. In the former case, the bowels are pressed
downward and the abdomen pushed outward; in the latter, the bowels spring
upward, and the abdomen is drawn inward.] descends and presses the walls
of the abdomen outward. Both these processes increase the size of the
chest. Thereupon, the elastic lungs expand to occupy the extra space,
while the air, rushing in through the windpipe, pours along the bronchial
tubes and crowds into every cell. [Footnote: It is said that in drawing a
full breath, the muscles exert a force equal to raising a weight of seven
hundred and fifty pounds. When we are about to make a great effort, as in
striking a heavy blow, we naturally take a deep inspiration, and shut the
glottis. The confined air makes the chest tense and firm, and enables us
to exert a greater force. As we let slip the blow, the glottis opens and
the air escapes, often with a curious aspirated sound as is noticeable in
workmen. To make a good shot with a rifle, we should take aim with a full
chest and tight breath, since then the arms will have a steadier support.]

2. _Expiration_.--When we forcibly expel the air from our lungs, the
operation is reversed. We bend forward, draw in the walls of the abdomen,
and press the diaphragm upward, while the ribs are pulled downward,--all
together diminishing the size of the chest, and forcing the air outward.

Ordinary, quiet breathing is performed mainly by the diaphragm,--one
breath to every four beats of the heart, or eighteen per minute. (See p.
299.)

MODIFICATIONS OF THE BREATH.--_Sighing_ is merely a prolonged
inspiration followed by an audible expiration. _Coughing_ is a
violent expiration in which the air is driven through the mouth.
_Sneezing_ differs from coughing, the air being forced through the
nose. _Snoring_ is produced by the passage of the breath through the
pharynx when the tongue and soft palate are in certain positions.
[Footnote: The soft palate must have fallen back in such a manner as
nearly or quite to close the entrance to the nasal cavity from the throat,
and the tongue must also be thrown back so far as to leave only a narrow
opening between it and the soft palate. The noise is produced by the air
being forced either inward or outward through this opening. A snore
results also when, with a closed mouth, the air is forced between the soft
palate and the back wall of the pharynx into the nasal cavity. With deep
breathing, perhaps accompanied by a variation in the position of the soft
palate, a rattling noise may be heard in addition to the snoring, which is
due to a vibration of the soft palate.--F. A. FERNALD, in "How we Sneeze,
Laugh, Stammer, and Sigh."--_Popular Science Monthly_, Feb., 1884.]
_Laughing_ and _crying_ are very much alike. The expression of
the face is necessary to distinguish between them. The sounds are produced
by short, rapid contractions of the diaphragm. _Hiccough_ is confined
to inspiration. It is caused by a contraction of the diaphragm and a
constriction of the glottis; the current of air just entering, as it
strikes the closed glottis, gives rise to the well-known sound.
_Yawning_, or _gaping_, is like sighing. [Footnote: The
usefulness of a yawn lies in bringing up the arrears, as it were, of
respiration, when it has fallen behindhand, either through fatigue or
close attention to other occupation. The stretching of the jaws and limbs
may also serve to equalize the nervous influence, certain muscles having
become uneasy on account of being stretched or contracted for a long
time.] It is distinguished by a wide opening of the mouth and a deep,
profound inspiration. Both processes furnish additional air, and therefore
probably meet a demand of the system for more oxygen. Frequently, however,
they are like laughing, sobbing, etc., merely a sort of contagion, which
runs through an audience, and seems almost irresistible.

THE CAPACITY OF THE LUNGS.--If we take a deep inspiration, and then
forcibly exhale all the air we can expel from the lungs, this amount,
which is termed the _breathing capacity_, will bear a very close
correspondence to our stature. For a man of medium height (five feet eight
inches) it will be about two hundred and thirty cubic inches, [Footnote:
Of this amount, one hundred cubic inches can be forced in only by an extra
effort, and is available for emergencies, or for purposes of training, as
in singing, climbing, etc. It is of great importance, since, if the
capacity of the lungs only equaled our daily wants, the least obstruction
would prove fatal.] or a gallon, and for each inch of height between five
and six feet there will be an increase of eight cubic inches. In addition,
it is found that the lungs contain about one hundred cubic inches which
can not be expelled, thus making their entire contents about three hundred
and thirty cubic inches, or eleven pints. The extra amount always on hand
in the lungs is of great value, since thereby the action of the air goes
on continuously, even during a violent expiration. In ordinary breathing,
only about twenty or thirty cubic inches (less than a pint) of air pass in
and out.

THE NEED OF AIR.--The body needs food, clothing, sunshine, bathing, and.
drink; but none of these wants is so pressing as that for air. The other
demands may be met by occasional supplies, but air must be furnished every
moment or we die. Now the vital element of the atmosphere is oxygen gas.
[Footnote: See "Steele's Popular Chemistry," p. 30. The atmosphere
consists of one fifth oxygen and four fifths nitrogen. The former is the
active element; and the latter, the passive. Oxygen alone would be too
stimulating, and must be restrained by the neutral nitrogen. Separately,
either element of the air would kill us.] This is a stimulating, life-
giving principle. No tonic will so invigorate as a few full, deep breaths
of cold, pure air. Every organ will glow with the energy of the fiery
oxygen.

ACTION OF THE AIR IN THE LUNGS.--In the delicate cells of the lungs, the
air gives up its oxygen to the blood, and receives in turn carbonic-acid
[Footnote: More properly _Carbon dioxide_.] gas and water, foul with
waste matter which the blood has picked up in its circulation through the
body. The blood, thus purified and laden with the inspiring oxygen, goes
bounding through the system, while the air we exhale carries off the
impurities. In this process, the blood changes from purple to red. If we
examine our breath, we can readily see what it has removed from the blood.

TESTS OF THE BREATH.--1. Breathe into a jar, and on lowering into it a
lighted candle, the flame will be instantly extinguished; thus indicating
the presence of carbonic-acid gas. 2. Breathe upon a mirror, and a film of
moisture will show the vapor. [Footnote: There is a close relation between
the functions of the skin, the lungs, and the kidneys--the scavengers of
the body. They all carry off water from the blood, and when the function
of one of the three is, in this respect, interfered with, the others are
called upon to perform its functions. When the function of perspiration is
deranged, the lungs and kidneys are required to perform heavier duty, and
this may lead to disease (see p. 62).] 3. If breath be confined in a
bottle, the animal matter will decompose and give off an offensive odor.

ANALYSIS OF THE EXPIRED AIR shows that it has lost about twenty-five per
cent of its oxygen, and gained an equal amount of carbonic-acid gas,
besides moisture, and organic impurities. Our breath, then, is air robbed
of its vitality, and containing in its place a gas as fatal to life
[Footnote: Carbonic-acid gas can not be breathed when undiluted, as the
glottis closes and forbids its passage into the lungs. Air containing only
three or four per cent acts as a narcotic poison (MILLER), and a much
smaller proportion will have an injurious effect. The great danger,
however, lies in the organic particles constantly exhaled from the lungs
and the skin, which, it is believed, are often direct and active poisons.]
as it is to a flame, and effete matter which is disagreeable to the smell,
injurious to the health, and which may contain the germs of serious
disease.

THE EVIL EFFECT OF REBREATHING the air can not be overestimated. We take
back into our bodies that which has just been rejected. The blood
thereupon leaves the lungs, bearing, not the invigorating oxygen, but
refuse matter to obstruct the whole system. We soon feel the effect. The
muscles become inactive. The blood stagnates. The heart acts slowly. The
food is undigested. The brain is clogged. The head aches. Instances of
fatal results are only too frequent. [Footnote: During the English war in
India, in the eighteenth century, one hundred and forty-six prisoners were
shut up in a room scarcely large enough to hold them. The air could enter
only by two narrow windows. At the end of eight hours, but twenty-three
persons remained alive, and these were in a most deplorable condition.
This prison is well called "The Black Hole of Calcutta."--Percy relates
that after the battle of Austerlitz, three hundred Russian prisoners were
confined in a cavern, where two hundred and sixty of them perished in a
few hours.--The stupid captain of the ship _Londonderry_, during a
storm at sea, shut the hatches. There were only seven cubic feet of space
left for each person, and in six hours ninety of the passengers were
dead.] The constant breathing of even the slightly impure air of our
houses can not but tend to undermine the health. The blood is not
purified, and is thus in a condition to receive the seeds of disease at
any time. The system uninspired by the energizing oxygen is sensitive to
cold. The pale cheek, the lusterless eye, the languid step, speak but too
plainly of oxygen starvation. In such a soil, catarrh, scrofula, and
kindred diseases run riot. [Footnote: One not very strong, or unable
powerfully to resist conditions unfavorable to health, and with a
predisposition to lung disease, will be sure, sooner or later, by partial
lung starvation and blood poisoning, to develop pulmonary consumption.
_The lack of what is so abundant and so cheap--good, pure air--is
unquestionably the one great cause of this terrible disease_.--BLACK'S
_Ten Laws of Health_.]

CONCERNING THE NEED FOR VENTILATION.--The foul air which passes off from
the lungs and through the pores of the skin does not fall to the floor,
but diffuses itself through the surrounding atmosphere. A single breath
will to a trifling but certain extent taint the air of a whole room.
[Footnote: This grows out of a well-known philosophical principle called
the Diffusion of Gases, whereby two gases tend to mix in exact
proportions, no matter what may be the quantity of each.--STEELE'S
_Popular Chemistry,_ p. 86, and _Popular Physics,_ p. 52.] A
light will vitiate as much air as a dozen persons. Many breaths and lights
therefore rapidly unfit the air for our use.

The perfection of ventilation is reached when the air of a room is as pure
as that out of doors. To accomplish this result, it is necessary to allow
for each person six hundred cubic feet of space, while ventilation is
still going on in the best manner known.

In spite of these well-known facts, scarcely any pains are taken to supply
fresh air, while the doors and windows where the life-giving oxygen might
creep in are hermetically stopped.

How often is this true of the sick room. Yet here the danger of bad air is
intensified. The expired breath of the patient is peculiarly threatening
to himself as well as to others. Nature is seeking to throw off the poison
of the disease. The scavengers of the body are all at work. The breath and
the insensible perspiration are loaded with impurities. [Footnote: The
floating dust in the air, revealed to us by the sunbeam shining through a
crack in the blinds, shows the abundance of these impurities, and also the
presence of germs which, lodging in the lungs, may implant disease, unless
thrown off by a vigorous constitution. "On uncovering a scarlet fever
patient, a cloud of fine dust is seen to rise from the body--contagious
dust, that for days will retain its poisonous properties."--YOUMANS. (See
p. 300.)] The odor is oftentimes exceedingly offensive. Sick and well
alike need an abundance of fresh air. But, too often, it is the only want
not supplied.

Our sitting rooms, heated by furnaces or red-hot stoves, generally have no
means of ventilation, or, if provided, they are seldom used. A window is
occasionally dropped to give a little relief, as if pure air were a
rarity, and must be doled out to the suffering lungs in morsels, instead
of full and constant draughts. The inmates are starved by scanty lung
food, and stupefied by foul air. The process goes on year by year. The
weakened and poisoned body at last succumbs to disease, while we, in our
blindness and ignorance, talk of the mysterious Providence which thus
untimely cuts down the brightest intellects. The truth is, death is often
simply the penalty for violating nature's laws. Bad air begets disease;
disease begets death.

In our churches, the foul air left by the congregation on Sunday is shut
up during the week, and heated for the next Lord's day, when the people
assemble to rebreathe the polluted atmosphere. They are thus forced, with
every breath they take, to violate the physical laws of Him whom they meet
to worship,--laws written not three thousand years ago upon Mount Sinai on
tables of stone, but to-day engraved in the constitution of their own
living, breathing bodies. On brains benumbed and starving for oxygen, the
purest truth and the highest eloquence fall with little force.

We sleep in a small bedroom from which every breath of fresh air is
excluded, because we believe night air to be unhealthy, [Footnote: There
is a singular prejudice against the night air. Yet, as Florence
Nightingale aptly says, what other air can we breathe at night? We then
have the choice between foul air within and pure air without. For, in
large cities especially, the night air is far more wholesome than that of
the daytime. To secure fresh air at night, we must open the windows of our
bedroom.] and so we breathe its dozen hogsheads of air over and over
again, and then wonder why we awaken in the morning so dull and
unrefreshed! Return to our room after inhaling the fresh, morning air, and
the fetid odor we meet on opening the door, is convincing proof how we
have poisoned our lungs during the night.

Each room should be supplied with two thousand feet of fresh air per hour
for every person it contains. Our ingenuity ought to find some way of
doing this advantageously and pleasantly. A moiety of the care we devote
to delicate articles of food, drink, and dress would abundantly meet this
prime necessity of our bodies.

Open the windows a little at the top and the bottom. Put on plenty of
clothing to keep warm by day and by night, and then let the inspiring
oxygen come in as freely as God has given it. Pure air is the cheapest
necessity and luxury of life. Let it not be the rarest!

SCHOOLROOM VENTILATION.--Who, on going from the open air of a clear,
bracing winter's day, into a crowded schoolroom, late in the session, has
not noticed the disagreeable odor, and been for a moment nauseated and
half stifled by the oppressive atmosphere! It is not strange. See how many
causes here combine to pollute the air. If the room is heated by a stove,
quantities of carbonic-oxide and carbonic-acid gases, as well as other
products of combustion, driven by downward drafts in the flue, escape
through seams and cracks and the occasionally opened door of the stove. In
the case of a furnace, the same effect is too often experienced, and the
odor of coal gas is a common one, especially when the fire is replenished.
The insensible perspiration is more active in children than in adults;
they, moreover, rush in with their clothing saturated with the
perspiration induced by their sports; so that, on the average, each pupil,
during school hours, loads the air with about half a pint of aqueous
vapor. The children come, oftentimes, from homes that are close, ill-
ventilated, and uncleanly; and frequently from sick rooms, bringing in
their clothing the germs of disease. (See p. 304.) Some of the pupils may
even bear traces of illness, or have unsound organs, and so their breath
and exhalations be poisonous.

In addition to all this, the air is filled with dust brought in and kept
astir by many busy feet; with ashes floating from the stove or furnace;
and especially with chalk dust. The modern method of teaching requires a
large amount of blackboard work, and the air of the schoolroom is thus
loaded with chalk particles. These collect in the nasal passages, and the
upper part of the larynx, and irritate the membrane, perhaps laying the
foundation of catarrh.

The usual schoolroom atmosphere bears in the pupils the natural fruit of
frequent headaches, inattention, weariness, and stupor; but in the teacher
its frightful influence is most apparent. His labor is severe, his worry
of mind is constant, and, when he finishes his day's work, he is generally
too tired to take proper physical exercise. He consequently labors on with
impaired health, or is forced to abandon his profession.

Instead of six hundred feet of space being allowed for each pupil, as
perfect ventilation demands--the lowest estimate being two hundred and
fifty feet--often not over one hundred feet are afforded. Instead of two
thousand cubic feet of fresh air being supplied every hour for each
person, and as much foul air removed, which, all physiologists assert, is
needed for perfect health, perhaps no means of ventilation at all are
provided, and none is secured except what an occasionally opened door, or
the benevolent cracks and chinks in the building furnish the suffering
lungs. [Footnote: Imagine fifty pupils put into a class room thirty feet
long, twenty-five feet wide, and ten feet high. This would generally be
considered a very liberal provision. Such a room contains seven thousand
five hundred cubic feet of air. But it furnishes only one hundred and
fifty feet of space for each pupil. Allowing ten cubic feet of air per
pupil each minute, in fifteen minutes after assembling, the entire
atmosphere of the room is tainted, and unfit to be rebreathed. The demand
of health is that at least one thousand five hundred cubic feet of pure
air should be admitted into this room every minute, and as much be
removed.]

HOW SHALL WE VENTILATE?--The usual method of ventilation depends upon the
fact that hot air is lighter than cold air, and so the cold air tends, by
the force of gravity, to fall and compel the warm air to rise. Thus, if we
open the door of a heated room, and hold a lighted candle first at the
top, and then at the bottom, we can see, by the deflection of the flame,
that there is a current of air setting outward at the top, and another
setting inward at the bottom of the opening. A handkerchief held loosely,
or the smoke of a smoldering match, in front of a fireplace will show a
current of air passing up the chimney; this is caused by the difference of
temperature between the air in the room and the outside atmosphere.
_Upon this difference of temperature, all ordinary ventilation is
based_. [Footnote: Public buildings are sometimes ventilated by
mechanical means, _i. e._, immense fans which are turned by
machinery, and thus set the air in motion. Such methods are, however,
expensive, and rarely adopted, except where power is also used for other
purposes.] A proper treatment of this subject and its practical
applications, would require a book by itself. There is room here for only
a few general statements and suggestions.

1. Two openings are always necessary to produce a thorough change of air.
(See "Popular Chemistry," p. 70.) Put a lighted candle in a bottle. The
flame will soon be extinguished. The oxygen of the little air in the
bottle is burned out, and carbonic acid has taken its place. Now place
over the mouth of the bottle a lamp chimney, and insert in the chimney a
strip of cardboard, thus dividing the passage. On relighting the candle,
it will burn freely. The smoke of a bit of smoldering paper will show that
two opposite currents of air are established, one setting into the bottle,
the other outward.

2. In the winter, when our schoolrooms, churches, public halls, etc., are
heated artificially, ventilation is comparatively easy if properly
arranged. [Footnote: For the escape of bad air, Dr. Bell suggests that an
efficient foul-air shaft may be fitted to the commonest of stoves by
simply inclosing the stovepipe in a jacket--that is, in a pipe two or
three inches greater in diameter. This should be braced round the
stovepipe and left open at the end next the stove. At its entrance into
the chimney, a perforated collar should separate it from the stovepipe.]
The required difference of temperature is kept up with little difficulty.
The fresh air admitted to the room should then be heated [Footnote:
Ventilation is change of air, and, unless scientifically arranged, and
especially unless the incoming volume of air be warmed in cold weather,
such change of atmosphere means cold currents, with their attendant train
of catarrhs, bronchitis, neuralgia, rheumatism, and all the evils that
spring from these diseases. The raw, damp, frosty air of our ever-changing
winter temperature ought not to have uncontrolled and constant ingress to
our dwellings. Air out of doors is suited to out of door habits. It is
healthy and bracing when the body is coated and wrapped, and prepared to
meet it, and when exercise can be taken to keep up the circulation; but to
live under cover is to live artificially, and such essential conditions
must be observed as suit an abnormal state. All the evils attaching to
ventilation, as it is generally effected, spring from the neglect of this
consistency.--_Westminster Review_.] either by a furnace, or by
passing over a stove, or through a coil of steam pipes. This cold air
should always be taken directly from out of doors, and not from a cellar,
or from under a piazza, where contamination is possible.

3. In order to remove the impure air, there should be ventilators provided
at or near the floor, opening into air shafts, or pipes leading upward
through the roof, with proper orifices at the top. These ventilating pipes
should be heated artificially so as to produce a draught. They may form
one of the flues of a chimney in which there is a constant fire; or be
carried upward in a large flue through the center of which runs the smoke
pipe of the furnace or stove; [Footnote: This plan has been adopted in the
newer school buildings of Elmira, N. Y. The older buildings were provided
with ventilating pipes, not heated artificially, and hence of no service.
These pipes are rendered effective, however, by conducting them into a
small room in the garret, heated by a coal stove. From this room, a large
exit pipe leads to the roof, where it terminates in an Emerson's
ventilator. So strong a draught is thus established that throughout the
building air is taken from the floors, and consequently the cooler portion
of the rooms, at a velocity of three to five feet per second or one
hundred and eighty to three hundred cubic feet per minute for each square
foot of flue opening. In perpendicular flues, heated throughout with a
smoke flue from the furnace, ten feet per second is attained.] or the
ventilating pipe be itself conveyed through the center of the larger
chimney flue. If the register for hot air be on the floor at one side of
the room, two or more ventilators may be placed near the floor on the
opposite side. The warm air will thus make the complete circuit of the
room, and thoroughly warm it before passing out.

If the ventilating shaft be not heated artificially; the ventilator must
be placed at the top of the room in order that the hot air may escape
through it, thus producing an upward draught. But the objection to this
method is that it allows the warmer air to escape, while economy requires
that the cooler air at the bottom of the room should be removed and the
warm air be made to descend, thus securing uniformity of temperature.

4. In the summer, ventilation may be commonly provided for by opening
windows _at the top and the bottom_, on the sheltered side of the
building, so as to avoid draughts of air injurious to the occupants. On a
dull, still, hot day, when there is little difference of temperature
between the inner and the outer air, ventilation can be secured only by
having a fire provided in the ventilating shaft; this, by exhausting the
air from the room, will cause a fresh current to pour in through the open
windows. At recess, all the children should, if the weather permit, be
sent out of doors, to allow their clothing to be exposed to the purifying
influence of the open air; meantime, the windows should be thrown wide
open, that the room may be thoroughly ventilated during their absence. In
bad weather, rapid marching or calisthenic exercises will furnish
exercise, and also permit the airing of the room.

5. The school and the church are the centers for spreading contagious
diseases. The former offers especially dangerous facilities for scattering
disease germs. Great pains, therefore, should be taken to exclude pupils
attacked by or recovering from diphtheria, scarlet fever, whooping cough,
etc., and even those who live in houses where such sickness exists.

6. In our houses [Footnote: The air of our homes is often contaminated by
decaying vegetables and other filth in the cellar; by bad air drawn up
from the soil into the cellar, by the powerful draughts that our fires
create; by defective gas and waste pipes that let the foul air from
cesspool or sewer spread through the house; and by piles of refuse, or
puddles of slops emptied at the back door. Too often, also, the water in
our wells, or in the streams that supply our towns and cities, receives
the drainage from outhouses and barnyards, and so introduces into our
systems, in the liquid--and thus easily assimilated--form, the most
dangerous poisons. The question of sanitary precautions is one that
presses upon every observant mind, and demands constant and thoughtful
attention. (See p. 305.)] open fireplaces are efficient ventilators, and
they should never be closed for any cause. Fresh air admitted by a hot-air
register and impure air passed out by a chimney, form a simple and
thorough system. Our sleeping apartments demand especial care. As soon as
the occupants leave the room, the bedclothes should be removed, and laid
on the backs of chairs to air; the bed be shaken up; and the windows
thrown open. In the summer, the windows may be closed before the sun is
high; the house is then left filled with the cool morning air. In damp and
cold weather, a fire should be lighted in sleeping apartments,
particularly if used by children [Footnote: In winter, children should
always be given a moderately warm, well-ventilated bedroom, with light,
fleecy bed coverings. Says a recent English writer: "The loving care which
prescribes for children a cold bedroom and a hot, sweltering bed is of the
nature that kills. Buried in blankets, their delicate skins become
overheated and relaxed, while they are irritated by perspiration; at the
same time, the most delicate tissues of all, in the lungs, are dealing
with air abnormally frigid. The poor little victims of combined ignorance
and kindness thus toss and dream, feverish and troubled, under a mass of
bedclothes, while the well-meaning mother, soothed by a bedroom fire,
slumbers peacefully through this working out of the sad process of the
'survival of the fittest.'"] or delicate persons, to dry the bedclothing,
and also to prevent a chill on the part of the occupants. It is not
necessary to go shivering to bed in order to harden one's constitution.

WONDERS OF RESPIRATION.--The perfection of the organs of respiration
challenges our admiration. So delicate are they that the least pressure
would cause exquisite pain, yet tons of air surge to and fro through their
intricate passages, and bathe their innermost cells. We yearly perform at
least seven million acts of breathing, inhaling one hundred thousand cubic
feet of air, and purifying over three thousand five hundred tons of blood.
This gigantic process goes on constantly, never wearies or worries us, and
we wonder at it only when science reveals to us its magnitude. In
addition, by a wise economy, the process of respiration is made to
subserve a second use no less important, and the air we exhale, passing
through the organs of voice, is transformed into prayers of faith, songs
of hope, and words of social cheer.

FIG. 33.

[Illustration: A, _the natural position of the internal organs._ B
_when deformed by tight lacing Marshall says that the liver and the
stomach have, in this way, been forced downward almost as low as the
pelvis._]

DISEASES, ETC.--1. _Constriction of the Lungs_ is produced by tight
clothing. The ribs are thus forced inward, the size of the chest is
diminished, and the amount of inhaled air decreased. Stiff clothing, and
especially a garment that will not admit of a full breath without
inconvenience, will prevent that free movement of the ribs so essential to
health. Any infraction of the laws of respiration, even though it be
fashionable, will result in diminished vitality and vigor, and will be
fearfully punished by sickness and weakness through the whole life.

2. _Bronchitis_ (bron-ki'-tis) is an inflammation (see Inflammation)
of the mucous membrane of the bronchial tubes. It is accompanied by an
increased secretion of mucus, and consequent coughing.

3. _Pleurisy_ is an inflammation of the pleura. It is sometimes
caused by an injury to the ribs, and results in a secretion of water
within the membrane.

4. _Pneumonia_ (_pneuma_, breath) is an inflammation of the
lungs, affecting chiefly the air cells.

5. _Consumption_ is a disease which destroys the substance of the
lungs. Like other lung difficulties, it is caused largely by a want of
pure air, a liberal supply of which is the best treatment that can be
prescribed for it. [Footnote: If I were seriously ill of consumption, I
would live outdoors day and night, except in rainy weather or midwinter;
then I would sleep in an unplastered log house. Physic has no nutriment,
gaspings for air can not cure you, monkey capers in a gymnasium can not
cure you, stimulants can not cure you. What consumptives want is pure air,
not physic, plenty of meat and plenty of bread.--DR. MARSHALL HALL.]

6. _Asphyxia_ (as-fix'-i-a).--When a person is drowned, strangled, or
choked in any way, what is called asphyxia occurs. The face turns black;
the veins become turgid; insensibility and often convulsions ensue. If
relief is not secured within a few minutes, death will be inevitable.
[Footnote: The lack of oxygen, and the presence of carbonic-acid gas, are
the combined causes. Oxygen starvation and carbonic-acid poisoning, each
fatal in itself, work together to destroy life.] (See p. 264.)

7. _Diphtheria_ (_diphthera_, a membrane) is characterized by
fever, debility, and a peculiar sore throat, in which exuding fibrinous
matter forms a grayish white membrane, which afterward decomposes with a
fetid odor. Its sudden and insidious approach, contagious character, and
frequent fatality, render it an exceedingly dreaded disease. A
diphtheritic patient should be quarantined, and everything connected with
the sick room thoroughly disinfected.

8. _Croup_, which often attacks young children, is an inflammation of
the mucous membrane of the larynx and trachea. It is commonly preceded by
a cold. The child sneezes, coughs, and is hoarse, but the attack
frequently comes on suddenly, and usually in the night. It is accompanied
by a peculiar "brassy," ringing cough, which, once heard, can never be
mistaken. It may prove fatal within a few hours. (See p. 260.)

9. _Stammering_ depends, not on defects of the muscles, but on a want
of due control of the mind. When a stammerer is not too conscious of his
lack, and tries to form his words slowly, he speaks plainly, and may sing
well, for then his words must follow one another in rhythmic time. Many
persons who stammer in common conversation can talk with fluency when
making a speech. The stammerer should seek to discover the cause of his
difficulty, and to overcome it by vocal and respiratory exercise,
especially by speaking only after a full inspiration, and during a long,
slow expiration.

PRACTICAL QUESTIONS.

1. What is the philosophy of "the change of voice" in a boy?

2. Why can we see our breath on a frosty morning?

3. When a law of health and a law of fashion conflict, which should we
obey?

4. If we use a "bunk" bed, should we pack away the clothes when we first
rise in the morning?

5. Why should a clothespress be well ventilated?

6. Should the weight of our clothing hang from the waist, or the shoulder?

7. Describe the effects of living in an overheated room.

8. What habits impair the power of the lungs?

9. For full, easy breathing in singing, should we use the diaphragm and
lower ribs, or the upper ribs alone?

10. Why is it better to breathe through the nose than the mouth?

11. Why should not a speaker talk while returning home on a cold night
after a lecture?

12. What part of the body needs the loosest clothing?

13. What part needs the warmest?

14. Why is a "spare bed" generally unhealthful?

15. Is there any good in sighing?

16. Should a hat be thoroughly ventilated? How?

17. Why do the lungs of people who live in cities become of a gray color?

18. How would you convince a person that a bedroom should be aired?
[Footnote: "If the condensed breath collected on the cool windowpanes of a
room where a number of persons have been assembled, be burned, a smell as
of singed hair will show the presence of organic matter; and if the
condensed breath be allowed to remain on the windows for a few days, it
will be found, on examination by the microscope, that it is alive with
animalculæ."]

19. What persons are most liable to catarrhs, consumption, etc.?

20. If a person is plunged under water, will it enter his lungs?

21. Are bed curtains healthful?

22. Why do some people take "short breaths" after a meal?

23 What is the special value of public parks?

24. Can a person become used to bad air, so that it will not injure him?

25. Why do we gape when we are sleepy?

26. Is a fashionable waist a model of art in sculpture or painting?

27. Should a fireplace be closed? [Footnote: Thousands of lives would be
saved if all fireplaces were kept open. If you are so fortunate as to have
a fireplace in your room, paint it when not in use, put a bouquet of fresh
flowers in it every morning, if you please, or do anything to make it
attractive, but never _close it_; better use the fireboards for
kindling wood. It would be scarcely more absurd to take a piece of
elegantly-tinted court-plaster and stop up the nose, trusting to the
accidental opening and shutting of the mouth for fresh air, because you
thought it spoiled the looks of your face to have two such great, ugly
holes in it, than to stop your fireplace with elegantly-tinted paper, or a
Japanese fan, because it looks better.--Leeds.]

28. Why does embarrassment or fright cause a stammerer to stutter still
more painfully?

29. In the organs of voice, what parts have somewhat the same effect as
the case of a violin and the sounding-board of a piano?

30. Why should we be careful not to "take the breath of a sick person"?

31. What special care should be taken with regard to keeping a cellar
clean?

32. How is the air strained as it passes into the lungs?

33. Can one really "draw the air into his lungs"?

34. How often do we breathe?

35. Describe some approved method of ventilation.

36. What is at once the floor of the chest and the roof of the abdomen?

37. What would you do in a case of apparent death by drowning, or by coal
gas? (See p. 264.)

38. What would you do in a case of croup, while the doctor was coming?
(See p. 260.)

39. How would you treat a severe burn? (See p. 257.)

40. Describe the various ways in which the water in a well is liable to
become unwholesome.

FIG. 34.

[Illustration]

THE CIRCULATION.

"No rest this throbbing slave may ask,
Forever quivering o'er his task,
While far and wide a crimson jet
Leaps forth to fill the woven net,
Which in unnumber'd crossing tides
The flood of burning life divides,
Then, kindling each decaying part,
Creeps back to find the throbbing heart."

HOLMES.

ANALYSIS OF THE CIRCULATION

THE CIRCULATION.

THE ORGANS OF THE CIRCULATION are the _heart_, the _arteries_,
the _veins_, and the _capillaries_.

FIG. 35.

[Illustration: A, _corpuscles of human blood, highly magnified;_ B,
_corpuscles in the blood of an animal (a non mammal)._]

THE BLOOD is the liquid by means of which the circulation is effected. It
permeates every part of the body, except the cuticle, nails, hair, etc.
The average quantity in each person is about eighteen pounds. [Footnote:
It is difficult to estimate the exact amount, and therefore authorities
disagree. Foster places it at about one thirteenth of the body weight.] It
is composed of a thin, colorless liquid, the _plasma_, filled with
red disks or cells, [Footnote: There is also one white globular cell to
every three or four hundred red ones. The blood is no more red than the
water of a stream would be if you were to fill it with little red fishes.
Suppose the fishes to be very, very small--as small as a grain of sand--
and closely crowded together through the whole depth of the stream; the
water would look quite red, would it not? And this is the way in which,
blood looks red--only observe one thing; a grain of sand is a mountain in
comparison with the little red fishes in the blood. If I were to tell you
they measured about 1/3500 of an inch in diameter, you would not be much
wiser; so I prefer saying (by way of giving you a more perfect idea of
their minuteness) that there would be about a million in such a drop of
blood as would hang on the point of a needle. I say so on the authority of
a scientific microscopist--M. Bouillet. Not that he has ever counted
them, as you may suppose, any more than I have done; but this is as near
an approach as can be made by calculation to the size of 1/3500 part of an
inch in diameter.--JEAN MACE.] so small that about three thousand five
hundred placed side by side would measure only an inch, and it would take
sixteen thousand laid flatwise upon one another to make a column of that
height. Under the microscope, they are found to be rounded at the edge and
concave on both sides. [Footnote: By pricking the end of the finger with a
needle, we can obtain a drop for examination. Place it on the slide, cover
with a glass, and put it at once under the microscope. The red disks will
be seen to group themselves in rows, while the white disks will seem to
draw apart, and to be constantly changing their form. After a gradual
evaporation, the crystals (Fig. 36) may be seen. In animals, they have
various, though distinctive forms.] They have a tendency to collect in
piles like rolls of coin. The size and shape vary in the blood of
different animals. [Footnote: Authorities differ greatly in their estimate
of the size of the disks (corpuscles) in human blood. The fact is that the
size varies in different persons, probably also in the same individual.
Many of the best microscopists therefore hesitate to state whether a
particular specimen of blood belonged to a human being or to an animal.
Others claim that they can distinguish with accuracy. Evidently, the
question is one of great uncertainty. The following statement of the size
of the cells in different animals is taken from Gulliver's tables: Cat,
1/4404 of an inch in diameter; whale, 1/3100; mouse, 1/3614; hog, 1/4230;
camel, 1/3123; sheep, 1/3352; horse, 1/4800; Virginia deer, 1/5038; dog-
faced baboon, 1/4861; brown baboon, 1/3493; red monkey, 1/3396; black
monkey, 1/3530.] Disks are continually forming in the blood, and are
constantly dying--twenty million at every breath.--DRAPER.

The plasma also contains fibrin, [Footnote: it is usual to say that fibrin
is contained in the blood. It probably does not exist as such, but there
are present in the blood certain substances known as _paraglobulin_
and _fibrinogen_, which by the action of a third substance, _fibrin
ferment_ under certain circumstances, form fibrin and so cause
coagulation. The exact nature of the process by which fibrin is produced
by these three factors is not understood--See Foster's _Text Book of
Physiology_, p 22.] albumin--which is found nearly pure in the white of
an egg--and various mineral substances, as iron, [Footnote: Enough iron
has been found in the ashes of a burned body to form a mourning ring.]
lime, magnesia, phosphorus, potash, etc.

FIG. 36.

[Illustration: _Blood Crystals_]

USES OF THE BLOOD.--The blood has been called "liquid flesh"; but it is
more than that, since it contains the materials for making every organ.
The plasma is rich in mineral matter for the bones, and in albumen for the
muscles. The red disks are the air cells of the blood. They contain the
oxygen so essential to every operation of life. Wherever there is work to
be done or repairs to be made, there the oxygen is needed. It stimulates
to action, and tears down all that is worn out. In this process, it
combines with and actually burns out parts of the muscles and other
tissues, as wood is burned in the stove. [Footnote: For the sake of
simplicity, perhaps to conceal our own ignorance, we call this process
"burning." The simile of a fire is good so far as it goes. But as to the
real nature of the change which the physiologist briefly terms
"oxidation," we know nothing. This much only can be asserted positively. A
stream of oxygen is carried by the blood to the muscles (in fact to every
tissue in the body), while, from the muscles the blood carries away a
stream of carbonic acid and water. But what takes place in the muscles,
when and what chemical change occurs, no one can tell. We see the first
and the last stage. We know that contraction of the muscles somehow comes
about, oxygen disappears, carbonic acid appears, energy is released, and
force is exhibited as motion, heat, and electricity. But the intermediate
step is hidden.

There are certain theories advanced, however, that are worth considering.
Some physiologists hold that the muscle has the power of taking up the
oxygen from the _hemoglobin_ (a body that comprises ninety per cent
of the red corpuscles when dried, and is the oxygen carrier of the blood),
and fixing it, as well as the raw material (food) furnished by the blood,
thus forming a true contractile substance. The breaking down or
decomposition of this contractile substance in the muscle, sets free its
potential energy. The process is gentle so long as the muscle is at rest,
but becomes excessive and violent when contraction occurs. (See "Foster's
Physiology," p. 118.) It is also believed by some that the chemical change
in the muscle partakes of a fermentive character; that, under the
influence of the proper ferments, the substances break up into other and
simpler products, thus setting free heat and force; and that this chemical
change is followed by a secondary oxidation by the oxygen in the arterial
blood, thereby forming carbonic acid and water, as in all putrefactive
processes. But these and other views are not as yet fully understood;
while they utterly fail to tell us how a collection of simple cells,
filled merely with a semifluid mass of matter, can contract and set free
muscular power. The commonness of this act hides from us its wonderful
nature. But here, hidden in the cell--Nature's tiny laboratory--lies the
mystery of life. Before its closed door we ponder in vain, confessing the
unskillfulness of our labor, and fearing all the while lest the _Secret
of the Cell_ will always elude our search.] The blood, now foul with
the burned matter, the refuse of this fire, is caught up by the
circulation, and whirled back to the lungs, where it is purified, and
again sent bounding on its way.

There are then two different kinds of the blood in the body: the red or
arterial, and the dark or venous.

TRANSFUSION.--As the blood is really the "vital fluid" it would seem that
feeble persons might be restored to vigor by infusing healthy blood into
their veins. This hypothesis, so valuable in its possible results in
prolonging human life, has been carefully tested. Animals which have
ceased to breathe have thus had their vitality recalled. In the
seventeenth century the theory became a subject of special investigation.
A maniac was restored to reason by the blood of a calf, and the most
extravagant hopes were entertained. But many fatal accidents occurring,
experiments upon human beings were forbidden by law, and transfusion soon
fell into disuse. It has, however, been successfully practiced in several
cases within the last few years, and is a method still in repute for
saving lives.

COAGULATION.--When blood is exposed to the air, it coagulates. This is
caused by the solidifying of the fibrin, which entangling the disks, forms
the "clot." The remaining clear, yellow liquid is the _serum_. The
value of this peculiar property of the blood can hardly be overestimated.
The coagulation soon checks all ordinary cases of bleeding. [Footnote: In
the case of the lower animals, which have no means of stopping hemorrhages
as we have, the coagulation is generally still more rapid. In some species
of birds it takes place almost instantaneously.] When a wound is made, and
bleeding commences, the fibrin forms a temporary plug, as it were, which
is absorbed when the healing process is finished. Thus we see how a Divine
foresight has provided not only for the ordinary wants of the body, but
also for the accidents to which it is liable. [Footnote: The fibrin is not
an essential ingredient of the blood. All the functions of life are
regularly performed in people whose blood lacks fibrin; and, in cases of
transfusion, where blood deprived of its fibrin was used, the vivifying
influence seemed to be the same. Its office, therefore, must mainly be to
stanch any hemorrhage which may occur.--FLINT.]

FIG. 37.

[Illustration: _The Heart._ A, _the right ventricle;_ B, _the
left ventricle;_ C, _the right auricle;_ D, _the left auricle._]

THE HEART is the engine which propels the blood. It is a hollow, pear-
shaped muscle, about the size of the fist. It hangs, point downward, just
to the left of the center of the chest. (See Fig. 31.) It is inclosed in a
loose sac of serous membrane, [Footnote: The mucous membrane lines the
open cavities of the body; the serous, the closed. The pericardium is a
sac composed of two layers--a fibrous membrane on the outside, and a
serous one on the inside. The latter covers the external surface of the
heart, and is reflected back upon itself in order to form, like all the
membranes of this nature, a sac without an opening. The heart is thus
covered by the pericardial sac, but not contained inside its cavity. A
correct idea may be formed of the disposition of the pericardium around
the heart by recalling a very common and very convenient, though now
discarded headdress, the cotton nightcap. The pericardium incloses the
heart exactly as this cap covered the heads of our forefathers.--
_Wonders of the Human Body_.] called the pericardium (_peri_,
about; and _kardia_, the heart). This secretes a lubricating fluid,
and is smooth as satin.

THE MOVEMENTS OF THE HEART consist of an alternate contraction and
expansion. The former is called the _sys'-to-le_, and the latter the
_di-as'-to-le_. During the diastole, the blood flows into the heart,
to be expelled by the systole. The alternation of these movements
constitutes the beating of the heart which we hear so distinctly between
the fifth and sixth ribs. [Footnote: Two sounds are heard if we put our
ear over the heart,--the first and longer as the blood is leading the
organ, the second as it falls into the pockets of the two arteries, and
the valves then striking together cause it. The first sound is mainly the
noise made by the muscular tissue. During the first, the two ventricles
contract; during the second the two auricles do so. The hand may feel the
heart striking the ribs as it contracts,--a feeling called the impulse,
or, if quicker and stronger than usual, palpitation. This is not always a
sign of disease, but in hypochondriacs is often an effect of the mind on
the nerves of the heart.--MAPOTHER]

FIG. 38.

[Illustration: _Chambers of the Heart_ A, _right ventricle;_ B,
_left ventricle,_ C, _right auricle,_ D, _left auricle,_ E,
_tricuspid valve,_ F, _bicuspid valve;_ G, _semilunar valves,_ H,
_valve of the aorta;_ I, _inferior vena cava,_ K, _superior vena
cava,_ L, L, _pulmonary veins._]

THE AURICLES AND VENTRICLES--The heart is divided into four chambers. In
an adult, each holds about a wineglassful. The upper ones, from appendages
on the outside resembling the ears of a dog, are called _auricles
(aures_, ears). are termed _ventricles_. The auricle and ventricle
on each side communicate with each other, but the right and left halves of
the heart are entirely distinct, and perform different offices. The left
side propels the red blood; and the right, the dark. The auricles are
merely reservoirs to receive the blood (the left auricle, as it filters in
bright and pure from the lungs; the right, as it returns dark and foul
from the tour of the body), and to furnish it to the ventricles as they
need. Their work being so light, their walls are comparatively thin and
weak. On the other hand, the ventricles force the blood (the left, to all
parts of the body; the right, to the lungs), and are, therefore, made very
strong. As the left ventricle drives the blood so much farther than the
right, it is correspondingly thicker and stronger.

NEED OF VALVES IN THE HEART.--As the auricles do not need to contract with
much force simply to empty their contents into the ventricles below them,
there is no demand for any special contrivance to prevent the blood from
setting back the wrong way. Indeed, it would naturally run down into the
ventricle, which is at that moment open to receive it. But, when the
strong ventricles contract, especially the left one, which must drive the
blood to the extremities, some arrangement is necessary to prevent it from
returning into the auricle. Besides, when they expand, the "suction power"
would tend to draw back again from the arteries all the blood just forced
out. This difficulty is obviated by means of little doors, or valves,
which will not let it go the wrong way. [Footnote: The heart of an ox or a
sheep may be used to show the chambers and valves. The aorta should be cut
as far as possible from the heart, and then by pumping in water the
perfection of these valves will be finely exhibited. Cutting the heart
across near the middle will show the greater thickness of the left
ventricle.]

THE TRICUSPID AND BICUSPID VALVES.--At the opening into the right
ventricle, is a valve consisting of three folds or flaps of membrane,
whence it is called the _tricuspid_ valve (_tri_, three; and
_cuspides_, points), and in the left ventricle, one containing two
flaps, and named the _bicuspid_ valve. These hang so loosely as to
oppose no resistance to the passage of the blood into the ventricles; but,
if any attempts to go the other way, it gets between the flaps and the
walls of the heart, and, driving them outward, closes the orifice.

FIG. 39.

[Illustration: _Diagram showing the peculiar Fibrous Structure of the
Heart and the Shape of the Valves._ A, _tricuspid valve,_ B,
_bicuspid valve;_ C, _semilunar valves of the aorta;_ D,
_semilunar valves of the pulmonary artery._]

THESE FLAPS ARE STRENGTHENED like sails by slender cords, which prevent
their being pressed back through the opening. If the cords were attached
directly to the walls of the heart, they would be loosened in the systole,
and so become useless when most needed. They are, therefore, fastened to
little muscular pillars projecting from the sides of the ventricle; when
that contracts, the pillars contract also, and thus the cords are held
tight.

THE SEMILUNAR VALVES.--In the passages outward from the ventricles, are
valves, called from their peculiar half-moon shape _semilunar_ valves
(_semi_, half; _Luna_, Moon). Each consists of three little
pocket-shaped folds of membrane, with their openings in the direction
which the blood is to take. When it sets back, they fill, and, swelling
out, close the passage (Fig. 40).

THE ARTERIES [Footnote: _Aer,_ air; and _tereo,_ I contain--so
named because after death they contain air only, and hence the ancients
supposed them to be air tubes leading through the body.] are the tube-like
canals which convey the blood _from_ the heart. They carry the red
blood (see note, p. 119). They are composed of an elastic tissue, which
yields at every throb of the heart, and then slowly contracting again,
keeps up the motion of the blood until the next systole. The elasticity of
the arteries acts like the air chamber of a fire engine, which converts
the intermittent jerks of the brakes or pump into the steady stream of the
hose nozzle.

The arteries sometimes communicate by means of branches or by meshes of
loops, so that if the blood be blocked in one, it can pass round through
another, and so get by the obstacle. [Footnote: This occurs especially
about the joints, where it serves to maintain the circulation during the
bending of a limb, or when the main artery is obstructed by disease or
injury, or has been tied by the surgeon. In the last case, the small
adjacent arteries gradually enlarge, and form what is called a collateral
circulation.] When an artery penetrates a muscle, it is often protected by
a sheath or by fibrous rings, which prevent its being pulled out of place
or compressed by the play of the muscles.

The arteries are generally located as far as possible beneath the surface,
out of harm's way, and hence are found closely hugging the bones or
creeping through safe passages provided for them. They are generally
nearly straight, and take the shortest routes to the parts which they are
to supply with blood.

THE ARTERIAL SYSTEM starts from the left ventricle by a single trunk--the
_aorta_--which, after giving off branches to the head, sweeps back of
the chest with a bold curve--the _arch of the aorta_ (_c_, Fig.
34)--and thence runs downward (_f_), dividing and subdividing, like a
tree, into numberless branches, which, at last, penetrate every nook and
corner of the body.

THE PULSE.--At the wrist (_k_, radial artery) and on the temple
(temporal artery) we can feel the expansion of the artery by each little
wave of blood set in motion by the contraction of the heart. In health,
there are about seventy-two [Footnote: This number varies much with age,
sex, and individuals. Napoleon's pulse is said to have been only forty,
while it is not infrequent to find a healthy pulse at one hundred or over.
In general, the pulse is quicker in children and in old people than in the
middle-aged; in short persons than in tall; in women than in men. Shame
makes the heart send more blood to the blushing cheek, and fear almost
stops it. The will can not check the heart. There is said, however, to
have been a notable exception to this in the case of one Colonel Townsend,
of Dublin, who, after having succeeded several times in stopping the
pulsation, at last lost his life in the act.] pulsations per minute. They
increase with excitement or inflammation, weaken with loss of vigor, and
are modified by nearly every disease. The physician, therefore, finds the
pulse a good index of the state of the system and the character of the
disorder. (See p. 314.)

THE VEINS are the tube-like canals which convey the blood _to_ the
heart. [Footnote: There is one exception to the general course of the
veins. The _portal_ vein carries the blood from the digestive organs
to the liver, where it is acted upon, thence poured into the ascending
vena cava, and goes back to the heart.] They carry the dark or venous
blood (note, p. 119). As they do not receive the direct impulse of the
heart, their walls are made much thinner and less elastic than those of
the arteries. At first small, they increase in size and diminish in number
as they gradually pour into one another, like tiny rills collecting to
form two rivers, the vena cava ascending and the vena cava descending
(_l, m_, Fig. 34), which empty into the right auricle.

Some of the veins creep along under the skin, where they can be seen, as
in the back of the hand; while others accompany the arteries, some of
which have two or more of these companions.

VALVES similar in construction to those already described (the semilunar
valves of the heart, page 114) are placed at convenient intervals, in
order to guide the blood in its course, and prevent its setting backward.
[Footnote: Too much standing, or tight elastics, often cause the veins in
the leg to swell, so that the valves can not work; the veins then become
_varicose_, or permanently enlarged, and, if they burst, the bleeding
may be profuse and even dangerous. Raising the leg and pressing the finger
on the bleeding spot will stay it. Walking does not encourage this
disease, for the active muscles force on the venous blood. Clerks who are
subject to varicose veins should have seats behind the counters where they
may rest when not actually employed. A deep breath helps the flow in the
veins, and a wound may suck in air with fatal effect. A maimed horse is
most mercifully killed by blowing a bubble of air into the veins of his
neck. As the deep-sea pressure would burst valves, the whale has none;
hence a small wound by the harpoon causes him to bleed to death.--
MAPOTHER.] We can easily examine the working of these valves. On baring
the arm, blue veins may be seen running along the arm toward the hand.
Their diameter is tolerably even, and they gradually decrease in size. If
now the finger be pressed on the upper part of one of these veins, and
then passed downward so as to drive its blood backward, swellings like
little knots will make their appearance. Each of these marks the location
of a valve, which is closed by the blood we push before our finger. Remove
the pressure, and the valve will swing open, the blood set forward, and
the vein collapse to its former size.

FIG. 40.

[Illustration: _Valves of the Veins._]

THE CAPILLARIES (_capillus,_ a hair) form a fine network of tubes,
connecting the ends of the arteries with the veins. They blend, however,
with the extremities of these two systems, so that it is not easy to tell
just where an artery ends and a vein begins. So closely are they placed,
that we can not prick the flesh with a needle without injuring, perhaps,
hundreds of them. The air cells of the blood deposit there their oxygen,
and receive carbonic acid, while in the delicate capillaries of the lungs
[Footnote: The capillary tubes are there so fine that the disks of the
blood have to go one by one, and are sadly squeezed at that. However,
their elasticity enables them to resume their old shape as soon as they
have escaped from this labyrinth.] they give up their load of carbonic
acid in exchange for oxygen.

FIG. 41.

[Illustration: _Circulation of the Blood in the Web of a Frog's Foot,
highly magnified._ A, _an artery;_ B, _capillaries crowded with
disks, owing to a rupture just above, where the disks are jammed into an
adjacent mesh;_ C, _a deeper vein; the black spots are pigment
cells._]

If, by means of a microscope, we examine the transparent web of a frog's
foot, we can trace the route of the blood. [Footnote: With small spli

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