[Illustration: FIG. 6.--A WHITE BLOOD CELL, magnified; forms noticed at

intervals of one minute.]

=The Ameba and Man Compared.=--The microscope shows us that the skin,

the muscles, the blood,--in fact, _all parts of the body_,--_contain

numberless small parts called cells_. These cells are continually

changing with the activities of the body. One of the most interesting

kinds of cells we shall find to be the _white blood cells_, or

corpuscles. One is shown in Fig. 6, with the changes that it had

undergone at intervals of one minute. The thought readily occurs that

_these cells, although part of man’s body, resemble the ameba_ that

lives an independent life. A man or a horse or a fish--in fact any

animal not a protozoan--has something of the nature of a colony, or

collection, of one-celled animals. We are now prepared to understand

a little as to how the body grows, and how a cut in the skin is

repaired. _The cells take the nourishment brought by the blood, use

it, and grow and multiply like the ameba._ Thus new tissue is formed.

All animals and vegetables--that is to say, all living things--are

made of cells.

[Illustration: FIG. 7.--DIAGRAM OF A CELL.

_p_, protoplasm; _n_, nucleus; _n′_, nucleolus.]

=A living cell= _always contains a still smaller body called a_

=nucleus= (Fig. 7). There is sometimes a small dot in the nucleus,

called the _nucleolus_. _The main body of the cell consists of the

living substance called_ =protoplasm=, _containing nitrogen_. Usually,

but not always, there is a wall surrounding the cell, called the _cell

wall_. Workers with the microscope found long ago that animals and

plants are constructed of little chambers which they called cells.

It was found later that the soft contents in the little chambers is

of more importance than the walls which the protoplasm builds around

itself. A living cell is not like a cell in a honeycomb or a prison. In

biology we define a cell as _a bit of protoplasm containing a nucleus_.

No smaller part of living matter can live alone. The protoplasm of the

nucleus is called nucleoplasm; the rest of the protoplasm is called

cytoplasm.

[Illustration: FIG. 8.--A CELL (from involuntary muscle), so slender

that it is called a _fiber_.]

A _fiber_ is threadlike, and is either a slender cell (Fig. 8), a

slender row of cells (Fig. 10), or a branch of a cell. A =tissue= is

defined as _a network of fibers or a mass of similar cells serving the

same purpose_, or doing the same work. A _membrane_ is a thin sheetlike

tissue.

=The Nature of the Human Body.=--The human body is _a community of

cells_, and may be compared to a community of people. It is a crowded

community, for all the citizens live side by side as they work. They

are so small that it takes several hundred of them to make a line an

inch long. We should never have suspected the existence of cells had it

not been for the microscope; but now we know that they eat and breathe

and work and divide into young cells which take the place of the old

ones.

A child that is born in a =community of people= may become a railroad

man and carry food and other freight from place to place; so, in

the great =community of cells= (see Fig. 9) making up the human

body, _the red blood cells, like the railroad man_, are employed

in carrying material from place to place. But the community is

old-fashioned, for the citizens build canals instead of railroads

for their commerce (see Fig. 84). Just as a child may grow up to

be a _farmer_ and aid in the conversion of crude soil into things

suitable for the use of man, so _the digestive cells_ take the food

we eat and change it into material with which the cells can build

tissue. Some of the citizens of a community must, at times, take _the

part of soldiers_ and policemen, and protect the community against

the attacks of enemies. _The white blood cells_, already referred

to, may be called the soldiers; for they go to any part attacked by

injurious germs, a particle of poison, or other enemy, and try to

destroy the enemies by devouring or digesting them. At other times

they help to repair a break in the skin. If a splinter gets into the

skin, the white blood cells form a white pus around the splinter

and remove it. In fact, the white blood cell has been referred to

as a kind of _Jack-at-all-trades_. In the human community there are

certain persons who reach the positions of _teachers, lawmakers,

and governors_; they instruct and direct the other members of the

community. Just so, in the community of cells, there are certain

cells called _nerve cells_ (see Fig. 11) that have the duty of

governing and directing the other cells. The nerve cells are most

abundant in the brain. Large cities must have _scavengers_. Likewise

in the human body, a community composed of millions of cells, there

are certain _cells in the skin and the kidneys_ which have this duty.

They are continually removing impurities from the body.[4]

[4] From Coleman’s “Hygienic Physiology,” The Macmillan Co., N.Y.

[Illustration: FIG. 9.--VARIOUS CELLS of the body. (Jegi.) Tiny

citizens of the bodily community.]

=Division of Labor.=--There is a great advantage in each cell of

the human body _having its special work_, instead of having to do

_everything for itself_, as each ameba cell must do. _Under this system

each cell can do its own work better than a cell of any other kind

can do it._ Among wild tribes there is very little division of labor.

Each man makes his own weapons, each knows how to weave coarse cloth,

how to cook, how to farm, etc. Savages do not have as good weapons

as do people who leave the making of weapons to certain men whose

special business it is. What kind of pocketknives or pencils do you

think the boys of this country would have if each boy had to make his

own pocketknife or pencil? What kind of scissors and thread would the

girls have if each girl had to make them herself? Our muscle cells

can contract better than the ameba; the cells in the lungs can absorb

oxygen better than the ameba. We have just as great an advantage in

digestion, feeling, and other processes; for the ameba eats without

a mouth, digests without a stomach, feels without nerves, breathes

without lungs, and moves without muscles. Division of labor between the

sexes also occurs among the higher animals. Those who desire that man

and woman should have the same education and work would violate the

biological law of “progress by specialization,” which could only cause

race degeneration.

A part of the body which is somewhat distinct from surrounding parts,

and has special work to do, is called an =organ=; the special work

which the organ does is called its =function=. The eye is the organ of

sight. The skin is an organ; its function is to protect the body. This

book will treat of (1) the structure, appearance, and position of each

organ, or =anatomy=; (2) the function of each organ, or =physiology=;

(3) the conditions of health for each organ, or =hygiene=; (4) the

conditions under which each organ worked in the primitive life of the

race; (5) the effects of change of environment; (6) the anatomy of

man compared with the lower animals. (5) belongs to the science of

=Ecology=. These sciences are parts of the science of =Biology=.

[Illustration: FIG. 10.--THREE MUSCLE FIBERS from the heart (showing

the nuclei of six cells).]

[Illustration: FIG. 11.--NERVE CELLS, showing their branches

interlacing.]

=The Tissues.=--_As the organs have different functions, they must have

different structures that they may be adapted to their work._ Just as a

house must have brick for the chimney, shingles for the roof, and nails

to hold the timbers and other parts together, so the body has various

tissues to serve different purposes. The bones must not be constructed

like the muscles, and the muscles cannot be like the skin. The chief

work of the cells is to construct the tissues and repair them. During

life changes are constantly going on. Careful little workmen are

keeping watch over every part of the body; thrifty little builders are

busy in repairing and restoring. No sooner is one particle removed

than another takes its place. In one direction the cells, acting as

undertakers, are hurrying away matter which is dead; in the other

direction the unseen builders are filling the vacant places with matter

that is living.

=The Seven Tissues.=--There are seven kinds of tissues. Two of them,

the muscular and nervous tissues, are called the _master tissues_,

since they control and expend the energies of the body. The other

five tissues are called the _supporting tissues_, since they supply

the energy to the master tissues, support them in place, nourish and

protect them.

=The Master Tissues.=--The =muscular tissue= consists chiefly of rows

of cells placed end to end (Fig. 10). These cells have the remarkable

property of becoming broader and shorter when stimulated by impulses

from nerve cells.

[Illustration: FIG. 12.--CONNECTIVE TISSUE CELLS, removed from among

the fibers of Fig. 13.

_n_, _c_, nucleus; _p_, branches.]

The =nerve tissue= consists of cells with long, spiderlike branches

(Fig. 11). Some nerve cells have branches several feet long, so long

that they go from the backbone to the foot. The branches are called

_nerve fibers_ (Fig. 142). Nerve fibers which carry impulses _to_ the

nerve cells are called _sensory fibers_. The nerve fibers which carry

impulses _from_ the nerve cells are called _motor fibers_. The organs

are set to work by impulses through the motor fibers. Besides these two

master tissues there are five =supporting tissues=.

[Illustration: FIG. 13.--CONNECTIVE TISSUE FIBERS.

_a_, _b_, bundles of white fibers; _c_, a yellow fiber.]

=Connective tissue=, like all other tissues, _contains cells_ (see

Fig. 12), but it consists chiefly of fine fibers. These fibers are of

two kinds,--very fine _white fibers which are inelastic_, and larger

_yellow fibers which are very elastic_ (see Fig. 13). Connective tissue

is found in every organ, binding together the other tissues and cells.

It is interwoven among the muscle cells, and the tendons at the ends

of the muscles are composed almost wholly of it. If every other tissue

were removed, the connective tissue would still give a perfect model of

all the organs. How abundant this tissue is in the skin may be known

from the fact that leather consists entirely of it.

=Fatty (Adipose) Tissue.=--Fatty tissue is formed by _the deposit of

oil in connective tissue cells_ (see Fig. 14). Fat is held in meshes

of connective tissue fibers. That fatty tissue consists not alone

of fat, but of fibers also, is shown when hog fat is rendered into

lard, certain tough parts called “cracklings” being left. What is the

difference between beef fat and tallow?

[Illustration: FIG. 14.--FATTY TISSUE. Five fat cells, held in bundles

of connective tissue fibers.

_a_ is a large oil drop; _m_, cell wall; nucleus (_n_) and protoplasm

(_p_) have been pushed aside by oil drop (_a_).]

=Epithelial tissue= consists of one or more _layers of distinct cells

packed close together_ (see Fig. 15). It contains no connective tissue

or other fibers, and is the simplest of the tissues. Epithelial

tissue forms the outer layer of the skin, called the _epidermis_, and

the mucous membrane lining the interior of the body. It contains no

blood vessels, the _epithelial cells obtaining their nourishment from

the watery portion_ of the blood which soaks through the underlying

tissues. Epithelial cells are usually transparent; for instance, the

blood is visible beneath the mucous membrane of the lips. The finger

nails are made of epithelial cells, and they are nearly transparent.

[Illustration: FIG. 15.--EPITHELIAL TISSUE (epidermis of skin,

magnified).]

[Illustration: FIG. 16.--EPITHELIAL TISSUE; cells forming two glands in

wall of stomach.]

[Illustration: FIG. 17.--SIX GLAND CELLS: at left, shrunken after

activity; at right, rested, full of granules.]

There are _two classes_ of epithelial cells; one class forms

_protective coverings_ (Fig. 15); the _other class_ forms the lining

of =glands= (Fig. 16). Glands are cavities whose lining of epithelial

cells (Fig. 17) form either useful fluids called _secretions_ to aid

the body in its work, or harmful fluids called _excretions_ to be cast

out, or excreted. Most glands empty their fluids through tubes called

_ducts_.

=Cartilag′inous tissue= is tough, yet elastic. Cartilage or gristle

may be readily felt in the ears, the windpipe, and the lower half of

the nose. This tissue consists of _cartilage cells embedded in an

intercellular substance through which run connective tissue fibers_

(see Fig. 18). If yellow fibers predominate, the cartilage is yellow

and very elastic, as in the ear; if white fibers predominate, it is

white and less elastic, as in the pads of gristle between the bones

of the spinal column. Cartilage is to prevent jars, and, in movable

joints, to lessen friction.

=Bony (Osseous) Tissue.=--Solid bone is seen under the microscope to

contain many minute cavities (Fig. 19). _In these cavities the bone

cells lie_ self-imprisoned in walls of stone; for these cells have

formed the bone by depositing limestone and phosphate of lime around

themselves. There are _minute canals_ (3, Fig. 19), however, through

which nourishment comes to the cells. The watery portion of the blood

passes through these small canals from the blood vessels that flow

through _the larger canals_ (1, Fig. 19). Bone cells may live for

years, although some of the other cells of the body live only a few

hours.

[Illustration: FIG. 18.--CARTILAGINOUS TISSUE. A thin slice highly

magnified.

_a_, _b_, _c_, groups of cells; _m_, intercellular substance.]

New cells to repair the tissues are formed by subdivision of the

cells, as with the ameba. Unlike protozoans, many-celled animals

are mortal because the outer cells prevent the deeper cells from

purifying themselves perfectly and obtaining pure food and oxygen.

Even the arteries of an old man become hardened by the deposit of

mineral matter which the body has been unable to excrete.

[Illustration: FIG. 19.--BONY TISSUE. Thin slice across bone, as viewed

through microscope.

Larger blood tubes pass through the large holes (1); the cavities

containing bone cells lie in circles, and are connected by fine tubes

(3) with the larger tubes.]

=The body is kept alive and warm= by burning, or oxidation. One fifth

of the air is oxygen gas. We breathe it during every minute of our

existence. It is carried by the blood to all the tissues. Not one of

the cells could work without oxygen. Without it the body would soon be

cold and dead, for oxygen keeps the body alive and warm by uniting in

the cells with sugar, fat, and all other substances in the body except

water and salt. Oxygen burns or consumes the substances with which it

unites, and the process is called _oxidation_. Hence the cells have to

be continually growing and multiplying to repair the tissue and replace

the material used up by oxidation. Sugar and flour and fat oxidize,

or burn, outside of the body, as well as in it, as can be proved by

throwing them into a fire. Water and salt are two foods that do not

burn. Hence they can furnish no heat or energy to the body. Water puts

out a fire instead of helping it, and so does salt. Throw salt into a

fire or on a stove; it will pop like sand, but will not burn.

The cells need the oxygen of fresh air; they need food for the oxygen

to unite with, but _they are injured by many substances called

poisons_. Arsenic destroys the red blood cells. Strychnine attacks the

nerve cells in the spinal cord. Alcohol attacks the epithelial cells

lining the stomach and, when it is absorbed, attacks the nerve cells

and other cells. Morphine attacks the nerve cells.

WRITTEN EXERCISES.--Draw a series of seven pictures to show the seven

tissues (Figs. 10, 14, 15, 18, 19). Write the “Autobiography” of a

White Blood Cell (see also pages 59 and 68). The Rewards of Caring

for the Health. Health and the Disposition. Which is more important,

a Thorough Knowledge of Geography or of Physiology? Five Things which

people Value above Health (and lose health to obtain). The Blessings

that follow Good Health. The Tissues Compared (function, proportion

of cells, intercellular material and fibers, activity, rate of

change).

See also pages 50, 116. Pupils should choose their own subjects.

CHAPTER II

THE SKIN

NOTE TO TEACHER.--The experiments should be assigned in turn to the

pupils as each chapter is reached: _e.g._ this set of 13 will leave

3 pupils in a class of 39 to stand responsible for each experiment.

Each pupil should do the work separately and credit may be given for

the best results. Encourage (or require) each pupil to try every

experiment and record them in a note book.

_Experiment 1._ (At home or in class.) =Albinism.=--Study a white

rabbit as an example of albinism. Does albinism affect only the skin?

What evidence that its blood is of normal color?

_Experiment 2._ =Use of Hairs on the Skin.=--Let one pupil rest his

hand upon the desk behind him while another touches a hair on his

hand with a pencil. He should speak at the moment, if it is felt.

Do the hairs increase the sensitiveness of the skin? What was their

use with primitive man? Are the hands of all your acquaintances

equally hairy? Are the hairs to be classed as rudimentary? Will they

disappear? Will the race become baldheaded?

_Experiment 3._ (Home or school.) =Invisible Perspiration.=--Hold

a piece of cold glass near the hand or place the cheek near a cold

window pane and notice for evidence of moisture. Its source?

_Experiment 4._--=Effect of Evaporation on Temperature.=--Read a

thermometer and cover its bulb with a moist cloth. Read again after

twenty minutes. Repeat experiment in breeze.

_Experiment 5._ Moisten one hand and allow it to dry. Touch the other

hand with it. Explain result.

_Experiment 6._ =Absorbing Power of Fabrics.=--Wet the hands and dry

them upon a piece of cotton cloth. Repeat with woolen, linen, and

silk. Arrange in list according to readiness in absorbing water.

_Experiment 7._ =Rates of Drying.=--Immerse the cloths in water and

hang them up to dry. Test their rates of drying with dry powder or by

touch.

_Experiment 8._ =Test Looseness of Weave= of above cloths by

measuring the distance pieces of equal length will stretch.

[Illustration: COLORED FIGURE 1.--SECTION OF SKIN (diagram, enlarged 25

times). On the left the connective tissue fibers of the true skin are

shown.

In cutis (_c_), or dermis, find capillaries, nerve fibers, fat cells,

_two_ sweat glands and ducts, _four_ oil glands (two in section), _two_

hairs, _three_ nerve papillæ, _five_ papillae containing capillaries,

_two_ muscles for erecting hairs. In epidermis find flat cells, round

cells, and pigment cells.

FIG. 2.--WHERE THE FOOD IS ABSORBED (villus of intestine).

FIG. 3.--WHERE THE FOOD IS USED (cells with lymph spaces).

FIG. 4.--IDEAL SECTION OF MAMMAL.

Compare with organs of man (colored Fig. 6).

_j_, _j_, jaws; _ol_, nerve of smell; _op_, nerve of sight; _b_, brain;

_t_, tongue; _ep_, epiglottis; _oe_, gullet; _th_, thymus gland; _lg_,

lung; _h_, heart; _l_, liver; _g_, stomach; _s_, spleen; _p_, pancreas;

_k_, kidney; _d_, diaphragm; _m_, muscle; _u_, bladder; _ch_, spinal

cord; _v_, vertebræ.]

_Experiment 9._ =Does Cotton or Wool protect better from Radiant

Heat?=--Lay a thermometer in the sun for ten minutes, first covering

it with a woolen cloth. Note change in reading. After it regains

first reading, repeat, covering it with a cotton cloth of same weight

and texture. Conclusion? Expose wrists or arms to sun for five

minutes, one protected by the cotton, the other by the wool. Result?

Conclusion?

_Experiment 10._ =Rates of Heat Absorption and Radiation by Different

Colors.=--Expose thermometer to sunlight, covered successively by

pieces of cloth of same thickness, material, and texture. Use black,

blue, red, yellow, and white cloth. Note rise of temperature for

equal times in each case; also the fall of temperature for equal

times after removal to shade.

_Experiment 11._ =Effects of Dry Powders.=--Prepare two squares from

the same piece of leather (_e.g._ an old shoe). Moisten them both,

and apply face powder to one. Which dries more quickly? Repeat after

oiling them. Powder a portion of the face or arm daily for a week and

compare with the clean portion.

_Experiment 12._ =Dissect the kidney= of an ox or sheep, making out

the parts mentioned in the text, p. 26.

_Experiment 13._ (In class.) =Emergency Drill.=--Have one pupil wet

an imaginary burn on the arm of another, treat it with flour or soda,

and bandage. (See text.)

=The Skin has Two Layers.=--The outer layer is called the _epidermis_;

it is _thinner, more transparent, and less elastic_ than the inner

layer, or _dermis_. The epidermis is composed of epithelial cells

packed close together (see colored Fig. 1).

=The dermis=, or inner layer, is a closely woven sheet of _connective

tissue_ (colored Fig. 1) containing a great number of _sweat_ and

_oil glands_, _roots of hairs_, _blood vessels_, _absorbent vessels_

(lymphatics), and _nerves_ (colored Fig. 1). The dermis is sometimes

called the true skin because it is of greater importance than the

epidermis. It is united loosely to the underlying organs by a layer

of connective tissue. It is in this layer that fat is stored. The

upper surface of the dermis rises into a multitude of projections (see

colored Fig. 1) called _papil′læ_ (singular, papilla). The epidermis

fits closely over them and completely levels up the spaces between them

except on the palms and the soles. Here the papillæ are in rows, and

there is a fine ridge in the skin above each row of papillæ (Fig. 24).

In the papillæ are small loops of blood vessels and sometimes a nerve

fiber (colored Fig. 1).

[Illustration: FIG. 20.--EPIDERMIS OF ETHIOPIAN.]

[Illustration: FIG. 21.--EPIDERMIS OF CAUCASIAN.]

=The epidermis= _is composed of a mass of cells_ held together by a

cement resembling the white of an egg. The cells near the surface are

hard and flattened; those deeper down near the dermis are round and

soft (see Fig. 21). These cells are living cells. They are kept alive

by the nourishment in the watery portion of the blood which soaks

through from the blood tubes in the neighboring papillæ. Hence these

cells are growing cells; they subdivide when they reach a certain

size, and replace those wearing away at the surface, thus constantly

repairing the epidermis. The dry outer cells wear away rapidly. They

have no nuclei and are dead cells. The new cells forming beneath push

them so far away from the dermis that nourishment no longer reaches

them, and they die.

=Pigment.=--The cells in the lower layers of the epidermis contain

grains of coloring matter, or pigment. All other cells of the

epidermis are transparent; the pigment has the function of absorbing

and arresting light. Albinos or animals entirely without pigment have

pallid skins and pink eyes (Exp. 1).

=Immigrants from a Cloudy to a Sunny Climate. Adaptation.=--The cells

of the deeper tissues can readily be exhausted by the stimulation

of too much light. The sunnier the climate, the greater the need of

pigment; hence the dark skin of the negro and the blonde skin and

hair of the Norwegian. European immigrants to sunny America will

grow darker. The Indian’s skin is better suited to our climate than

is a fair skin. Brunettes have a better chance for adaptation than

blondes. The American type when developed will doubtless be brunette.

=The hair= grows from a pit or follicle (Fig. 22). _Blood vessels and a

nerve fiber go to the root_ or bulb from which a hair grows. The hair

will grow until this papilla, or bulb, is destroyed (Exp. 2).

[Illustration: FIG. 22.--DEVELOPMENT OF A HAIR AND TWO OIL GLANDS.]

=Adaptation of the scalp to a tight warm covering= is accomplished

through the shedding of the hair rendered useless by the covering.

It is impossible to stop the growth of superfluous hair unless the

hair papillæ are destroyed with an electric needle, such is the

vitality of hair; yet many men, by overheating the head and cutting

off the circulation with tight hats, destroy much of the hair before

reaching middle age. The health of the hair can be restored and its

loss be stopped by going bareheaded except in the hot sun or in

extremely cold weather. This frees the circulation; cold air and

light stimulate the cells of the scalp. Some men wear hats, even at

night in summer. The brain needs the protection of the hair. Beard

protects the larynx or voice box, which is large and exposed in man.

It was also a protection in hunting wild beasts and in war. Compare

mane of lion, not possessed by lioness. “Goose-flesh” after a cold

bath is caused by the contraction of small muscles (colored Fig. 1),

raising the now tiny hairs in an absurdly useless effort to keep the

body warm.

=The nails= are dense, thick plates of epidermis growing from a number

of papillæ situated in a groove, or fold, of the skin; there are many

fine papillæ along the bed from which the nail grows. Since it grows

from its under side as well as from the little fold of skin at its

root, the nail is thicker at the end than near the root.

[Illustration: FIG. 23.--_A_, DEVELOPMENT OF SWEAT GLAND; _B_, SWEAT

TUBE DEVELOPED.]

The =oil glands= empty into the hair follicles (colored Fig. 1). They

form an oil from the blood that _keeps the hair glossy and the surface

of the skin soft and flexible_ by preventing excessive drying. Hair oil

should never be used upon the hair, as the oil soon becomes rancid, and

besides causes dust and dirt to stick to the hair.

=The sweat glands= (Fig. 23), like the hair bulbs, are deep in the

lowest part of the dermis. _A sweat gland has the form, of a tube

coiled into a ball_ (colored Fig. 1). This tube continues as a duct

through the two layers of skin, and its opening at the surface is

called a _pore_ (Fig. 24). The perspiration evaporates as fast as it

flows out through the pores, if the secretion is slow; but if poured

out rapidly, it gathers into drops (Exp. 3). The perspiration is

chiefly water, containing in solution several salts, including common

salt and a trace of a white, crystalline substance called _urea_. The

material for the perspiration is furnished by the blood flowing around

the gland in a network of fine tubes. The amount of the perspiration is

controlled in two ways: by _nerves that regulate the activity of the

epithelial_ cells lining the gland, and by nerves that _regulate the

size of the blood vessels_ supplying the gland (Fig. 25).

[Illustration: FIG. 24.--PORES on ridges in palm of hand.]

THOUGHT QUESTIONS.--=Freckles, Warts, Moles, Scars, Proud Flesh,

Pimples, Blackheads.= Use these names in the proper places below:--

A rough prominence formed by several papillæ growing through the

epidermis at a weak spot and enlarging is called a ____. Small

patches of pigment developing on the hands and face from much

exposure to the sun are called ____. The growth of exposed dermis

sprouting through an opening in the epidermis due to accident is

called ____. (This should be scraped off and cauterized to aid the

epidermis to grow over it again.) Sometimes a cut heals in such a way

that no epidermis and therefore no pigment cells cover the place of

injury, which is occupied only by white fibrous tissue (cicatricial

tissue) of the true skin. In this case the mark left is called a

cicatrice or ____. If pores or the openings of oil glands become

clogged, but not enlarged, little swellings called ____ may result.

An enlarged pore filled with oil and dirt is called a ____. A spot

present since birth, dark with pigment, and often containing hairs

and blood vessels, is called a ____.

=Regulation of Temperature.=--As is well known, rapid running or

violent exercise of any kind causes profuse perspiration. The sweat

glands are connected with the brain by means of nerves, and when the

body has too much heat, a _nerve impulse from the lowest part of the

brain causes the sweat glands to form sweat more rapidly_. Heat and

exercise may cause the activity of the sweat glands to increase to

forty times the usual rate. The evaporation of the sweat cools the

body, for a large amount of heat is required to evaporate a small

amount of water (Exp. 4 and 5). This is shown by the cooling effect of

sprinkling water on the floor on a warm day. By fanning we hasten the

cooling of the body (Exp. 4).

Exercise tends to heat the body, but it also _causes us to breathe

faster and causes much blood to flow through the skin_. Both of these

effects aid in cooling the body, for the cool air is drawn into the

lungs, becomes warm, and takes away heat when it leaves; and the warm

blood flowing in the skin loses some of its heat to the cool air in

contact with the skin.

=Effects of Alcohol upon the Skin.=--The more blood goes to the skin,

the more blood is cooled. The body as a whole may be cooler, but _we

feel warmer when there is more blood in the skin because of the effect

of the warm blood upon the nerves_ of temperature. There are no nerves

for perceiving temperature except in the skin and mucous membrane,

and the body has practically no sensation of heat or cold except from

the skin or mucous membrane. That alcoholic drinks make the skin

red is commonly noticed. Often _the skin is flushed_ by one drink;

the bloodshot eyes and purple nose of the toper are the results of

habitual use. Can you explain why alcohol brings a _deceptive feeling_

of warmth? Why does alcohol increase the danger of freezing during

exposure in very cold weather? During the chill which precedes a fever,

the body (except the skin) is really warmer than usual.

Exercise will relieve internal congestion and send the blood to the

skin better than alcohol. This is the effect sought by sedentary people

who use it to replace exercise. The long and sad experience of the

race with alcohol proves that the attempt to adapt the body to its use

should be given up.

THOUGHT QUESTIONS. =The Functions of the Skin.=--=1.= State a fact

which shows that the skin is a protection; gives off offensive

substances; regulates the temperature. =2.= What is lacking in the

skin when it cracks or chaps? Why does this occur more often in cold

weather? When the hands are bathed with great frequency?

=Effects of Indoor and Outdoor Life.=--_Those who live much out

of doors, exposed to sunlight and pure, cold air, are robust and

hardy_; while those whose occupations keep them constantly indoors,

especially if no physical labor is necessary, show by their pale

skins, their fat and flabby, or their thin and emaciated bodies, the

weakening effect of such a life. We are descended from ancestors who

lived in the open air, and it is impossible for a human being to live

much indoors without degeneration of the body and shortening of life.

=A Well-trained Skin.=--We hear a great deal about training the

muscles, the brain, the eye, the hand; yet we may fail to realize

that the skin also can be trained and its powers developed, or it

can be allowed to become weak and powerless. Soundness of the skin

is as essential to health as soundness of any other organ. A rosy

color indicates good health because of a well-balanced circulation.

Paleness often means internal congestion and great liability to

indigestion, colds, etc. Hence we think a rosy skin beautiful and a

pale skin ugly. With the skin in a healthy condition, the danger of

taking most diseases is removed.

=Characteristics of a Vigorous Skin.=--A person who readily takes

cold, who is fearful of drafts of air at all times, has a weak skin.

To one who has a healthy skin drafts are dangerous only when the

skin is moist with perspiration, and the body is inactive; cold

drafts may then do harm. Cold air and cold water are the best means

of toughening a tender skin. _A bath is to the skin what gymnastic

exercises are to the muscles._ The muscle fibers in the walls of the

blood vessels and the nerves controlling them need exercise as well

as the rest of the body (Fig. 25).

[Illustration: FIG. 25.--BLOOD VESSELS, with the VASO-MOTOR NERVES

which accompany and control them.]

=Importance of Bathing.=--_If we followed the outdoor life and wore

the scanty clothing of savage races, the rains, the cool air, and the

sunlight would keep our skins vigorous and sound._ But want of exercise

to induce perspiration allows the sweat glands to become stopped up.

The wearing of _clothes_ is a very uncleanly custom. Clothes make the

skin inactive, yet confine the impurities which the weakened skin may

still be able to excrete. Thick and heavy clothing and overheated rooms

prevent the nerves from being stimulated by cold air and sunlight. _The

best way to counteract these weakening conditions is by frequent cool

or cold baths._ An _air bath_, which consists of exposing the bare skin

to the air for half an hour or more before dressing in the morning, may

take the place of a cold bath. Even the lower animals bathe: birds,

dogs, and many lower animals bathe in the rivers. An elephant sometimes

takes a bath by showering water over his back with his trunk.

=Treatment of Burns.=--_Wet_ the burn with a little water and sprinkle

common _baking soda_ or flour thickly on it. Bind with a narrow

_bandage_. For deeper burns soak a small square of cloth in a strong

solution of baking soda, bandage it on wound, and keep it wet with the

solution. Olive, cotton seed, and linseed _oils_ are excellent for

burns (Exp. 13).

=Hygiene of Bathing.=--A bath should not be taken within an hour after

a meal. _Cold baths_ (1) should never be taken in a cold room nor

when the skin is cold; (2) are more beneficial in summer and in warm

climates, but are necessary in winter for those who live in overheated

houses or dress very warmly; (3) should be followed in winter by

vigorous rubbing and a glowing reaction; (4) should usually not last

longer than one minute in winter. _Warm baths_ (1) are more cleansing

than cold baths; (2) should not be used alone but should always be

followed by a dash of cold water; (3) are better than cold baths if the

body is greatly fatigued; (4) are more beneficial when going to bed

than upon rising.

Cold baths and very hot baths are both _stimulants_ to the nervous

system and cause an expenditure of nervous energy. For one whose

nervous energy is at a very low ebb cold baths may be weakening if

prolonged beyond a few seconds. For one with skin relaxed and body

sluggish from indoor life, cool baths arouse activity, tone up the

body, and may be as beneficial as outdoor exercise in restoring

vigorous health. As with every hygienic measure, each person must find

out by experience what suits him best.

=Clothing= was first employed for ornament. In cold climates it

aids in maintaining the uniform temperature of the body; to it man

owes his distinction of being the most widely distributed of animal

species. Clothing prevents rapid escape of bodily heat by confining

air, a non-conductor of heat, in its meshes. Hence, the effect of

clothing varies with the _weave_; likewise with the tendency of its

fibers _to keep dry_, for if water replaces air in the meshes, the

body loses heat rapidly. For cool clothing the weave should be hard

and tight, for warm clothing it should be soft and loose. The warmth

of clothing is affected more by its weave than by its weight. The

weave may be tested by stretching; the fabric with softest weave

will stretch the most (Exp. 8). _Linen_ makes the coolest of all

clothing because it weaves hard with small meshes; _silk_ ranks next

in coolness. When warmth is desired, linen or _cotton_ garments

should be made of fabrics woven like stockings. Linen and cotton both

absorb water rapidly and dry rapidly (Exp. 6); if _woolen_ did also,

it would make the warmest of all clothing, but it dries so slowly

(Exp. 7) that it cools the body after the activity is over instead

of drying rapidly and, as with linen and cotton, keeping the body

cool during the exertion (Exp. 5). Woolen weaves with the largest air

meshes of all materials; hence its warmth increases perspiration, but

woolen removes perspiration most slowly and tends to relax the skin

if the wearer has an active skin or makes active exertion. Woolen

is best for underclothing during extreme cold only or for persons

who never make such vigorous muscular exertion as to perspire. In

general, cotton or linen is best for underwear. They possess the

added advantages of less cost and of not shrinking out of size and

shape when washed. A mixture of cotton and silk or of cotton and wool

is more durable than either alone. Cotton and linen, unlike woolen,

are not attacked by insect pests.

It is better to depend more upon outer clothing than underclothing

for warmth. In the Gulf states the wearing of woolen outer clothing

indoors during warm weather (which lasts eight months) is unhealthful

and uncleanly because of the perspiration absorbed; this is as absurd

as to wear cotton outer clothing in Northern states during the eight

cold months.

Black clothing absorbs twice, blue almost twice, red and yellow

almost one and a half times, as much heat as white clothing (Exp.

10). Which material protects best from radiant heat? (Exp. 9.)

Because large blood vessels are near the surface at the _neck,

wrists, and ankles_ very thin or no covering at those points aids

greatly in keeping the body cool. High collars, long sleeves, and

high shoes are unhealthful in warm climates and in summer. What

objection to black shoes in summer? Patent leather? Show how women

dress more sensibly in hot weather than men.

The =kidneys= are located on each side of the spinal column in the

“small of the back” and extend slightly above the level of the waist.

They are _bean-shaped organs about four inches long_ (Fig. 26). The

kidneys of a sheep or ox closely resemble those of man. They are

outside of the peritoneum (Fig. 99) and attached to the rear wall of

the abdomen. A large artery (12, colored Fig. 5) goes to each kidney

and divides into many capillaries which surround _tubules_ in the

kidneys (Fig. 27). The secretion, containing nitrogenous impurities of

the blood, is continually being deposited in the tubules, which take

it to a _funnel-shaped cavity_ at the inner edge of the kidney (Fig.

26). From this cavity a white tube called the _ureter_ leads down to a

storage organ in the pelvis called the bladder.

[Illustration: FIG. 26.--SECTION OF KIDNEY.

_RA_, renal artery; _Py_, pyramids surrounding hollow space from which

the ureter (_U_) leads the secretion to the bladder.]

=Changes in Blood in the Kidneys.=--The water holding the nitrogenous

waste varies in amount with the amount of water drunk and with the

activity of the skin, being less in summer when the perspiration is

great. The lungs aid the skin and kidneys in disposing of superfluous

moisture. The kidneys have almost the entire responsibility of

relieving the body of certain _mineral salts_ and a white crystalline

solid called _urea_. This is very injurious if retained, causing

headaches, rheumatism, and other troubles.

[Illustration: FIG. 27.--PLAN OF A URINARY TUBULE, _Tb_, with artery

_A_, and _V_ in _pV_.]

THOUGHT QUESTIONS. =Hygiene of the Skin.=--=1.= What kind of a scar

is not affected by freckles or tan? =2.= Can a scar on a negro

be white? =3.= Does a scar on a child grow in size? =4.= Why is

heat most oppressive in moist weather? =5.= How do you account for

the shape and location of the usual bald spot? =6.= How does the

wearing away of the outer cells of the epidermis contribute to the

cleanliness of the body? =7.= Why does the palm of the hand absorb

water more rapidly than the back of the hand? =8.= Is it more

necessary for mental workers to bathe often or change their clothes

often? For physical workers? =9.= Is cotton or woolen clothing more

liable to stretch or shrink out of shape or size? To catch fire? To

make the skin clammy with moisture? To cost more? To be eaten by

moths?

[Illustration: FIG. 28.--THE SKELETON.]

CHAPTER III

THE SKELETON

_Experiment 1._ (At home.) =Is the Arch of the Foot Elastic?=--Wet

the foot in a basin of water and, while sitting, place the foot flat

upon a piece of paper. Draw the outline of the track. Repeat, but

stand with your whole weight upon the foot. Draw track. Conclusion?

(Take sketches to school. Which sketch shows the flattest foot?)

Devise a method for measuring the length of the foot with and without

the weight of the body upon it. What difference? Conclusion?

_Experiment 2._ =Composition of Bone.=--Place a bone in a hot fire

and let it remain for three or four hours. It will keep its shape

however long you burn it; but unless you handle it carefully when you

take it out, it will crumble to pieces. If not thoroughly burned, the

bone will be black from the carbon of the animal matter still left in

it. _Experiment 3._ Obtain a slender bone like the rib of a hog or

the leg bone of a fowl, and put the raw bone into a vessel containing

strong vinegar or two ounces of muriatic acid and a pint of water.

Leave it there for four days. When the bone is taken out, it can be

tied into a knot. The acid may be washed off, and the bone preserved

in a bottle of alcohol or glycerine.

_Experiment 4._ =The Forms of Joints.=--Obtain the disjointed bones

of a fowl or small mammal and place them one at a time in their

sockets and study the fit and motion of the joints.

_Experiment 5._ =Pivot Joints.=--Through what fraction of a circle do

the pivot joints in the forearm and neck allow the hand and head to

rotate?

=Review Questions.=--Where are the bone cells? How does nourishment

reach them? How has the mineral part of the bones been deposited? How

long may bone cells live? Name animals with outside skeletons. Inside

skeletons. No skeleton.

=Forms and Uses of Bones.=--The three chief _uses of bones are

protection, motion, and support_. In order to fulfill these purposes,

the bones must have different sizes, shapes, and positions. The bones

are classed by _shape_, as _long, flat, and irregular_. Those whose

chief use is _to protect are broad and flat_. The bones which _furnish

support are thick and solid_; those designed to _aid in motion are long

and straight_. Including six small bones in the ear, there are two

hundred and six bones in the adult skeleton.

=Gross Structure of Bones.=--The structure of a long bone is shown

in Fig. 29. It has a long, _hollow shaft_ of hard, compact bone, and

_enlarged ends_ composed of spongy bone. The hollow in the shaft is

_filled with yellow marrow_, which is composed of blood vessels and

fat, and aids in nourishing the bone. The long bones are found in the

limbs (Fig. 28). The ribs and other flat bones and the irregular bones

contain no yellow marrow; they are spongy inside, and hard and compact

near the surface. There is a _red marrow_ in the cavities in the spongy

parts of bones (Fig. 29). _New red blood cells are formed in this

marrow._ The bones have a close-clinging, fibrous covering composed of

connective tissue and blood vessels. It is called _periosteum_.

[Illustration: FIG. 29.--FEMUR, sawed lengthwise. The red blood cells

are formed in the red marrow of the spongy part.]

[Illustration: FIG. 30.--FRONT VIEW OF RIGHT FEMUR.]

=Chemical Composition of Bone.=--Experiments (2 and 3) show that the

bones contain a _mineral or earthy substance_, which makes them hard

and stiff, and a certain amount of _animal matter, called gelatine_,

which binds the mineral matter together and makes the bones tough and

somewhat elastic. The fire burned out the animal matter of the first

bone, and the acid dissolved out the mineral matter of the second bone.

_The mineral matter is chiefly lime, and makes up about two thirds

of the weight of the bone._ (Why is more mineral than animal matter

needed?) The animal gelatine is a gristly substance. As the body grows

old, the animal matter of the bones decreases, and they become lighter.

They are more easily broken and do not heal so readily as the bones of

young persons.

=The skeleton is subdivided= into the bones of the _head, trunk, and

limbs_. The bones of the trunk are those of the spine, the chest, the

shoulder blades, collar bone, and hip bones.

[Illustration: FIG. 31.--VERTEBRAL COLUMN. Side view.]

=The spinal or vertebral column= is made up of twenty-six bones (Fig.

31). It is the axis of the human skeleton, to which all other bones are

directly or indirectly attached. Animals with inside skeletons have

this column, and are called vertebrates. Fish, reptiles, birds, beasts,

apes, and man are vertebrates. The spine, as this column is sometimes

called, is not only the main connecting structure and support of the

body, but it forms a channel through which passes the spinal cord.

Fig. 32 shows a =vertebra=, or one of the bones that compose the

column. The three _projecting points or processes_ are for the

attachment of ligaments and muscles. The _main body_ of each vertebra

is for supporting the weight transmitted by the column above. Just

behind this thick body is a _half ring_ (Fig. 32), which with the

half rings on the other vertebrae form the channel for the spinal

cord. Between the vertebrae are thick pads of gristle, or cartilage,

which act as cushions to prevent jars, and by compression allow

bending of the spinal column in all directions.

[Illustration: FIG. 32.--SIDE AND UNDER VIEW OF A VERTEBRA.]

=The Chest= (see Fig. 75).--The twelve pairs of ribs are attached to

the spinal column behind, and extend around toward the front of the

body, somewhat like hoops. The first seven pairs, called _true ribs_,

are attached directly to the flat breastbone, or _sternum_. Each of the

next three pairs, called _false ribs_, is attached to the pair above

it. The last two pairs, called _floating ribs_, are free in front.

=The Shoulder Girdle.=--_The collar bones_ (Fig. 28) can be traced from

the shoulders until they nearly meet on the breastbone at the top of

the chest. The collar bone is shaped like the italic letter _f_; it

helps to form the shoulder joint and holds the shoulder blade out from

the chest that the motions of the arm may be free.

The flat, triangular _shoulder blade_ (Fig. 75) can be felt by reaching

with the right hand over the left shoulder. It spreads over the ribs

like a fan. Its edges can be made out, especially if the shoulder is

moved while it is being felt. The high ridge which runs across the bone

can be felt extending to the top of the shoulder.

=The Pelvic Girdle.=--The edges of the _hip bones_ can be felt at the

sides of the hips (Fig. 28). The hip bones, with the base of the spine,

form a kind of basin called the _pelvis_.

The =skull= (Fig. 33) rocks, or nods, on the top vertebra. It consists

of the cranium, or brain case, and the bones of the face. The shapes

and names of the bones of the skull are shown in Fig. 33.

[Illustration: FIG. 33.--HUMAN SKULL, disjointed.]

=Adaptations of the Skull for Protection.=--Its arched form is best

for resisting pressure and turning aside blows. Like all flat bones,

the skull has a spongy layer of bone between the layers of compact

bone forming the outer and inner surfaces; hence it is elastic and not

easily cracked. The nose, brow, and cheek bones project around the eye

for its protection. The delicate portions of the ear are embedded in

the strongest portion of the skull. The branches of the nerves of smell

end in the lining of the bony nasal chambers. The spinal cord rests

securely in the spinal canal.

The =arms and legs= have bones that closely correspond to each other.

The Latin names of these bones, as well as of all the other bones, are

given in Fig. 28. There are 30 bones in each arm and 30 in each leg

(Fig. 34). Here is a list of the bones of the arm, followed by the

names in brackets of the corresponding leg bones: upper arm bone [thigh

bone], 2 forearm bones [shin bone and splint bone], 8 wrist bones [7

ankle bones], 5 palm bones [5 bones of instep], 14 finger bones [14 toe

bones]. The shin bone is the larger bone between knee and ankle. The

long, slender splint bone and the shin bone are bound side by side.

[Illustration: FIG. 34.--BONES OF ARM AND LEG.]

[Illustration: FIG. 35.--SUTURES OF SKULL.]

=Differences between Arm and Leg.=--There is a saucer-like bone, called

the _kneecap_, embedded in the large ligament which passes over each

knee. There is no such bone in the elbow. There is one less bone in the

ankle than in the wrist, hence there are the same number of bones in

the arm and leg. The shoulder joint is more freely movable than the hip

joint. The fingers are longer and more movable than the toes; the thumb

moves far more freely than the big toe. The instep is much stronger

than the palm; for each instep must support, unaided, the weight of the

whole body at each step, with any other weight that the person may be

carrying. The palm is nearly flat, but the instep is arched to prevent

jars. When the weight of the body is thrown on the foot at each step,

the top of the arch is pressed downward, making the foot longer than

before. The arch springs up when the weight is removed (Exp. 1).

ILLUSTRATED STUDY. =The Shapes of Bones.=--Write _L_, _F_, or _I_

after these names (see Fig. 28, etc.), according as the bones

are long, flat, or irregular: face, cranium, vertebra, hip, rib,

breastbone, collar bone, shoulder blade, upper arm bone, lower arm

bones, wrist, palm, fingers, thigh bone, shin bone, splint bone,

ankle, instep, toes, kneecap.

=Structure of Joints.=--The meeting of two bones forms a joint

(Exp. 4). Some of the joints are immovable. The skull bones join in

zigzag lines called _sutures_, formed by the interlocking of sawlike

projections (Fig. 35). These _immovable_ joints are necessary for the

protection of the brain, which is the most delicate of the organs.

The brain attains almost its full size by the seventh year of life;

its bony case needs to grow very little after that. The joints of the

pelvis are also immovable. All _movable joints have two cartilages_,

and as the bones turn, one cartilage slips over the other. There is an

intermediate class of joints found between the vertebræ and where the

ribs join the breastbone. These joints depend for their motion upon the

flexibility and compressibility of their cartilages. They are called

mixed, or _elastic_, joints, and allow slight motion. _Such a joint has

only one cartilage._

=Kinds of Movable Joints.=--The movable joints are found chiefly

in the limbs. When one end of the bone is rounded and fits into a

cuplike hollow, the joint allows motion in all directions, and is

known as a _ball-and-socket_ joint. The hip joints and shoulder joints

are examples. A _hinge joint_ allows motion in only two (opposite)

directions; for example, the to-and-fro motion of the elbow. A _pivot_

joint allows a rotary motion; examples, the first vertebra on the

second, one bone of forearm upon the other. A gliding joint consists of

several bones that slide upon one another, as at the wrists and ankles.

=The Four Features presented by a Movable Joint= (Fig. 36).--If not

held in place, the bones would slip out of their sockets, hence there

are _ligaments_, or tough bands, to bind the bones together. Sudden

jolts would jar the bones and injure them; shocks are prevented by a

layer of elastic _cartilage_ over the end of each bone. The moving

of one bone over another in bending a joint would wear the bone

with friction unless the cartilages were very smooth and lubricated

with a fluid called the _synovial fluid_. The synovial fluid would

be constantly escaping into the surrounding tissues except for the

collarlike ligament called the _capsule_, which surrounds the joint and

is attached to each bone entirely around the joint (Fig. 36).

[Illustration: FIG. 36.--DIAGRAM OF A JOINT.]

THOUGHT QUESTIONS. =The Kinds of Joints.=--Write _B_, _H_, _G_,

_E_, _P_, or _I_ after these names according to the kind of joint

(ball-and-socket, hinge, gliding, elastic, pivot, immovable): between

bones of skull, head nodding, head turning, vertebræ, lower jaw, ribs

to breastbone (Fig. 75), shoulder, elbow, wrist, fingers, hip, knee,

ankle, toes.

=Growth of Bones.=--The blood vessels pass into the bones from the

periosteum. _If the periosteum is removed, the larger blood vessels

are taken away and the bone beneath it perishes._ If the underlying

bone is removed and the periosteum left, the bone will be replaced.

A curious proof of the active circulation in the bone is furnished

when madder is mixed with the food of pigs. In a few hours the bones

become a darker pink than usual; and if the madder is fed to the

pigs for a few days, their bones become red. A child grows in height

chiefly during three or four months in spring and summer; but its

body broadens and becomes heavier during autumn.

=Health of the Bones.=--It is plain that _a strong and free

circulation of pure blood contributes to the health and strength of

the bones_; good food and pure air make pure blood. Cases of “delayed

union,” or slow mending of broken bones, occur more often with

intemperate than with sober people. This is because the vitality of

the bone cells has been weakened by the use of alcohol. Many surgeons

dislike to operate on an old drunkard.

=Posterior Curvature of the Spine.=--The spine (see Figs. 28, 31)

has two backward curves (opposite chest and hips) and two forward

curves (at loins and neck). The deformity called posterior curvature

is chiefly an exaggeration of the upper posterior curve. Round

shoulders is the slightest, and hunchback the most marked, degree

of this deformity. Causes: 1, _bending over the work_ while either

standing or sitting; 2, _slipping down in the seat_, as in Figure 51;

3, working habitually with the _work low in front_, as reading and

writing at too low a desk (Fig. 49), or bending over while hoeing,

sitting on the floor (Japanese and Chinese); 4, _weak muscles_

in the back; 5, wearing shoes with _high heels_; 6, binding the

ribs down with _tight clothing_; 7, walking with the _head drooped

forward_ or the chest flat; 8, wearing suspenders without a pulley,

or lever, at the back; 9, carrying the hands in the pockets. (Swing

the arms to keep the hands out of the pockets and break the habit);

10, wearing a coat or vest that is tight at the back of the neck.

This deformity is brought about by _stretching the ligaments_ at the

back side of the spine, and by _compressing the cartilages until

they become wedge-shaped_, with the thin part of the wedge in front.

The flexibility of the spine is a great advantage, but it increases

the risk of deformity. One of the most serious evils of posterior

curvature is a flat chest and restricted breathing.

[Illustration: FIG. 37.--INCORRECT POSTURE.]

[Illustration: FIG. 38.--CORRECT POSTURE, but strained and stiff.]

=Lateral Curvature of the Spine.=--A perfect spine curves to neither

side (Fig. 47), but is perfectly erect. The least habitual lateral

curvature is deformity. Causes: 1, writing at a _desk that is too

high_; 2, habitually carrying a book, satchel, or other _weight in

the same hand_; 3, carrying the _head on one side_ (Fig. 46); 4,

habitually standing with the weight on the same foot; 5, a certain

defect of vision (astigmatism, Chap. IX).

=To overcome Spinal Deformities.=--The work, or the manner of doing

the work, should be so changed as _to give extra labor to the

neglected muscles_. Avoid the habits mentioned above as causing

deformity. Sit and stand in the manner described in the next

paragraph. Sleeping on the back upon a hard mattress without a pillow

tends to cure posterior curvature and flat chest.

=The correct position= in standing is: _chest forward, chin in, hips

back_ (Figs. 38, 39). To sit correctly, _sit far back in the chair_

(Figs. 49, 50, 51) with the body erect and balanced. In youth the

bones are soft and growing; they will readily grow into perfect

shape, and will almost as readily grow deformed.

=Sprains.=--_Immerse the part in hot water_ for half an hour, then

_bandage_ to keep the part at rest. _Use the limb as little as

possible._ It may be necessary for a physician to apply a plaster

dressing to a very bad sprain where the ligament is torn from the

bone.

=Broken Bones.=--To prevent bone from cutting flesh and skin, do not

move the person until a temporary splint has been provided by tying

sticks or umbrellas around the limb with handkerchiefs.

PRACTICAL QUESTIONS. =The Skeleton.=--=1.= What kind of a chair back

causes one to slide forward in the seat? =2.= What fault in sitting

is made necessary by using a chair with so large a seat that the

front edge strikes the occupant behind the knee? =3.= Why is the

shoulder more often dislocated than the hip? =4.= High pillows may

cause what deformity? =5.= Find three bones in the body not attached

to other bones. Find twenty-five bones attached to other bones by

one end only (Figs. 28 and 39). =6.= What deformities may result

from urging a young child to stand or walk? =7.= Which bone is most

often broken by falling upon the shoulder? =8.= Where in bones is

fat stored for future use? =9.= Ligaments grow very slowly. Why is

recovery from a sprain often tedious?

[Illustration: FIG. 39.--THE HUMAN SKELETON IN ACTION.]

CHAPTER IV

THE MUSCLES

It has already been stated that there are at least two muscles attached

to a bone to move it in opposite directions. Since there are two

hundred and six bones, you are not surprised to learn that to move the

bones and accomplish the various purposes just stated, there are five

hundred and twenty-six (526) skeletal muscles.

=Two Kinds of Muscles.=--All muscles are controlled by means of the

nervous system. Some of them are directed by parts of the brain that

work consciously; others are controlled by the spinal cord and the

parts of the brain that work unconsciously. Those of the first kind are

_usually controlled by the will_, but they sometimes act involuntarily.

_They are called voluntary muscles._ They move the bones and are

located in the limbs and near the surface of the trunk (Fig. 44). The

other kind of muscles are _never controlled by the will, and are called

involuntary muscles_. We cannot cause them to act, nor can we prevent

them from acting. They contract more slowly than the voluntary muscles.

Most of them are tubular and found in the cavity of the trunk. The

involuntary muscles _belong to the internal organs_, and relieve the

will of the responsibility and trouble of the activity of these organs;

otherwise, the mind would have no time for voluntary actions.

=Gross Structure of Voluntary Muscles.=--A beefsteak is seen to be

chiefly red, although parts of it are white or yellowish. The white or

yellowish flesh is fat; the red, lean flesh is voluntary muscle. If a

piece of beef is thoroughly boiled, it may be easily separated into

_bundles the size of large cords_. These bundles may, by the use of

needles, be picked apart and separated into _threadlike fibers_ (Fig.

40).

[Illustration: FIG. 40.--MUSCLE BUNDLES bound together by connective

tissue sheaths.]

=Microscopic Structure of Muscles.=--These threadlike fibers may, under

a magnifying glass, be separated into _fine strands called fibrils.

These last are the true muscle cells_; they are shown by the microscope

to be crossed by many dark lines (Fig. 48). Hence _voluntary muscles

are called striated or striped muscles_. Prolonged boiling and patient

picking with a needle are needed to dissect muscle, because the bundles

are held together by thin, glistening sheets of connective tissue by

which they are surrounded. This connective tissue surrounds and holds

in place the separate fibers of each bundle (Fig. 40).

[Illustration: FIG. 41.--TWO MUSCLE FIBERS OF HEART.]

[Illustration: FIG. 42.--INVOLUNTARY MUSCLE CELLS (or fibers).]

The fibrils of involuntary muscles are _spindle-shaped_ (see Fig. 42).

There are no cross lines on the fibrils; hence involuntary muscles are

called _smooth or unstriped muscles_. The heart fibers are exceptional;

they are the only involuntary muscle fibers that are striped (Fig. 41).

THOUGHT QUESTIONS. =Classification of Some of the Muscles.=--Copy the

following list and mark _I_ for involuntary and _V_ for voluntary

after the appropriate muscles.

Muscles for chewing. Muscles of gullet. Muscles of the heart. Muscles

that move arms. Muscles for breathing. Muscles in the skin that cause

the hair to stand on end. Muscles that move eyelids. Muscles that

contract pupil of eye. Muscles for talking. Muscles that contract and

expand the arteries (in blushing and turning pale). Muscles that move

eyeball. Muscles that give expression to the face.

=Tendons.=--_The connective tissue which binds the fibers of muscles

into bundles, and forms sheaths for the bundles, extends beyond the

ends of the muscles and unites to form tough, inelastic white cords

called tendons._ Some muscles are without tendons, and are attached

directly to bones. Study the figures and find examples of this (see

Figs. 44, 75). To realize the toughness of tendons, feel the tendons

under the bent knee or elbow, where they feel almost as hard as wires.

_The tendons save space_ in places where there is not room enough for

the muscles, and permit the bulky muscles to be located where they are

out of the way. Wherever the tendons would rise out of position when

a joint is bent, as at the wrist and ankle, they are bound down by a

ligament.

[Illustration: FIG. 43.--(For blackboard.) BICEPS relaxed and

contracted.]

=Arrangement of Voluntary Muscles.=--_Circular_ muscles, called

_sphincter muscles_, are found around the mouth and eyes. Muscles that

extend straight along the limb either bend it and are called _flexors_,

or straighten it and are called _extensors_. Most of the voluntary

muscles are arranged in pairs and cause motion in opposite directions;

they are said to be _antagonists_. The biceps (Fig. 43) bends the arm.

Its antagonist is the triceps on the back of the arm. By feeling them

swell and harden as they shorten, locate on your own body the muscles

mentioned in Fig. 44.

=How a Muscle grows Stronger; its Blood Supply.=--Nature has provided

that any part of the body shall receive more blood when it is working

than when it is resting. _When it works the hardest, the blood tubes

expand the most and its blood supply is greatest._ So whenever a muscle

is used a great deal, an unusual amount of material is carried to it

by the blood, the cells enlarge and multiply, and the muscle grows.

The walls of the capillaries are so thin that the food which is in the

blood readily passes from them to the muscle. Because of the oxidation

taking place, a working muscle is warmer than one at rest. _By use a

muscle grows large, firm, and of a darker red_; by disuse, it becomes

small, flabby, and pale. But if muscles are worked too constantly,

especially in youth, their cells do not have time to assimilate food

and oxygen, and their growth is stunted.

Unless the meal has been a very light one, vigorous exercise should

not be taken after eating, as the blood will be drawn from the food

tube to the muscles and the secretion of the digestive fluids will be

hindered. Persons whose entire circulation is weak may find that light

exercise after a meal, such as walking slowly, may help circulation and

digestion.

=Why the Muscles work in Harmony.=--_When a boy throws a stone, almost

every part of the body is concerned in the action._ His arms, his legs,

his eyes, the breathing, the beating of the heart, are all modified

to assist in the effort. As the boy wills to throw the stone, nerve

impulses are sent to all the organs that can assist, and they are

excited to just the amount of action needed.

[Illustration: Illustrated Study of Muscular Function

Draw a dotted line from each function mentioned on margin to the muscle

or muscles having that function.

Bows the head?

Straightens the elbow?

Straightens the fingers?

Swings leg outward?

Bends the knee?

Straightens the knee?

Crosses the leg?

Straightens toes?

Draws shoulder back?

Lifts the whole arm outward and upward?

Draws whole arm downward and forward?

Bends the elbow?

Bends the fingers?

Raises the body on the toes?

Raises toes?

FIG. 44.--SUPERFICIAL MUSCLES AFTER THE STATUE OF “THE DIGGER” (Lami).]

=The Nerve Impulse and the Contraction.=--Each nerve that goes to a

muscle is composed of many fibers; the fibers soon separate and go to

all parts of the muscle, _and each muscle fiber receives its nerve

fiber_ (see Fig. 45). In the brain each fiber is stimulated at once,

and all the fibers shorten and thicken together. This change is spoken

of as contraction; but since the muscle does not become smaller, the

word may be misleading. When the muscle shortens, it thickens in

proportion and occupies as much space as it did when relaxed.

=Where does Muscular Energy come from?=--_The nerve does not furnish

the energy which the muscle uses when contracting. The muscle cells

have already stored up energy from the food and oxygen brought to them

by the blood_, and the process called oxidation sets free the energy.

Activity of muscle may increase the carbon dioxid output fivefold.

Mental work has practically no effect upon it.

[Illustration: FIG. 45.--MOTOR NERVE FIBERS, ending among fibrils of

voluntary muscle. Compare with Fig. 48.]

=How a Muscle stays Contracted.=--The muscle relaxes at once after

contraction; and in order to keep it contracted, nerve impulses must be

sent in quick succession, causing in fact many contractions; the effect

of this is sometimes visible, as the trembling of the muscle. Figure 47

shows an easy standing posture.

=What causes Fatigue.=--Fatigue or exhaustion is due to the using up of

the living material in the nerve cells and muscle cells by oxidation.

Rest is necessary to give cells opportunity to repair themselves. Why

is it less fatiguing to walk for an hour than to stand perfectly still

for ten minutes?

[Illustration: FIG. 46.--IMPROPER POSITION; causes spine to curve to

side; raises one hip and shoulder above the other.]

[Illustration: FIG. 47.--BEST POSITION; chest is free to expand, and

weight is easily shifted from one foot to other.]

=Degeneration of Muscles= begins with habitual disuse. We dare not

furnish a substitute for the work of a muscle, if we wish the muscle to

remain sound. A belt or a stay at the waist will cause the muscles of

the trunk to become flabby and the abdomen to relax and protrude.

=How Muscular Activity helps the Health.=--Life is change, stagnation

is death. _Muscular activity uses up the food, gives a good appetite,

and sets the digestive organs to work; it uses up the oxygen and sets

the lungs to work; but most of all, every contraction of a muscle helps

the blood to flow._ As a muscle contracts, it presses upon the veins

and lymphatics, and, by this pressure, forces the blood and lymph along

(Fig. 48). In any ordinary activity, dozens of muscles are being used.

That the effect upon the circulation is very powerful, is shown by the

rosy skin, deep breathing, and rapid heart beat. The many benefits of

an active circulation of the blood and lymph will be discussed in the

next chapter. See page 67.

[Illustration: FIG. 48.--CAPILLARIES among fibers of voluntary (cross

striped) muscle. (Peabody.)]

A grave danger from athletics is that of developing the muscles,

including the heart, to an enormous extent by training; then _when

training ceases the muscles undergo fatty degeneration from disuse_.

Heart disease and other diseases may follow. Many athletes die young,

killed by trying to turn their bodies into mere machines for running,

boxing, or rowing, instead of living complete lives. _The athletic

ideal is not the highest ideal of health_; general activity, resembling

the occupations of hunting and farming by which the early race

supported itself, is best for health. Many kinds of factory work use

only one set of muscles. The savage did not lead a monotonous life, and

monotony is bad for both muscles and nerves.

=Advantages of Work and Play over Gymnastic Exercises.=--The interest

that comes from doing something useful, makes muscular exertion

doubly beneficial to the health. The lifting of dumbbells, Indian

clubs, and pulley weights, and letting them down again, tends to

become very irksome, even though done with the knowledge that the

exercise will benefit the health. _Useful labor and games place

definite objects in view and do not require so great an effort of the

will nor exhaust the nerves so much as mere exercise._ The interest

in the work or the game serves to arouse all the nerves and muscles

to work in harmony.

[Illustration: FIG. 49.--DESK TOO LOW. (Jegi.)]

[Illustration: FIG. 50.--CORRECT POSITION.]

[Illustration: FIG. 51.--SLIPPING DOWN IN SEAT.]

=An Advantage of Gymnastics over Work and Play.=--Gymnastics can

furnish any required variety of exercises and _can develop exactly

the muscles that need development and leave those idle that have

become overdeveloped_ by doing constantly one kind of work or playing

continually the same game. The _deformity of a flat chest_ (and round

shoulders which always accompany it) does not so often indicate a

weak chest or small lungs as it indicates weak or relaxed muscles

of the back and the habit of sitting in a relaxed position at work

(Figs. 49, 50, 51). _Gymnastic exercise is not wholly an artificial

custom._ Cats stretch themselves, stretching each leg in succession;

many animals gambol and play. A gymnastic drill, taken to music and

with large numbers of pupils in the drill, is interesting as work or

play, and should not be neglected for any study, however important.

=Environment of Early Man and Modern Man.=--A well-developed man

of one hundred and fifty pounds weight should have sixty pounds of

muscles. The proportion is often different in the puny bodies of the

average civilized men, such as clerks, merchants, lawyers, and other

men with sedentary occupations; their bodies are as likely to be

lean and scrawny or fat and flabby as to be correctly proportioned.

Why does a normal man have sixty pounds of muscles instead of twenty

pounds of puny strings such as would have sufficed for a clerk,

student, or a writer? This is because, in his native condition, he

had to seek his food by roaming through the forest, contending with

wild beasts or with other savage men, often traveling many miles a

day, climbing trees, etc.

=Too Rapid Change of Environment; Destructive Tendencies of

Civilization.=--_It is impossible for the human body to change

greatly in a few hundred years._ The body of man served him for many

ages for the manner of life outlined above. It was suited for these

conditions, and the muscles and the organs that support them cannot

accommodate themselves to changed conditions in a few generations. It

has only been a few hundred years since the ancestors of the Britons

and Germans, for instance, were running wild in the German forests,

clad in the skins of wild beasts. Yet _civilized man lets his muscles

fall into disuse_, he takes a trolley car or horse vehicle to go

half a mile, an elevator to climb to the height of thirty feet. He

neglects all his muscles except those that move the tongue and the

fingers of the right hand. He never makes enough exertion to cause

him to draw a deep breath, and his lungs contract and shrivel. He

seldom looks at anything farther than a few inches from his nose, and

his eyes become weak. At the same time that he neglects his muscles

and his lungs, he overworks his brain and his stomach; yet he expects

his body to undergo the rapid changes to suit the demands of his

life. Such rapid changes in the human race are impossible. A man that

does not see that _sound health is the most valuable thing in the

world, except a clear conscience_, is in danger both of wrecking his

own happiness _and of failing in his duty to others_.

THOUGHT QUESTIONS. =Shoes.=--=1.= What the faults of shoes may be

in size; shape; sole; heel; toe; instep. =2.= Name deformities

resulting to skin of foot; nails; joints; arch; ankle; spine. =3.=

State effects of uncomfortable shoes on muscular activity; mind and

disposition. =4.= State effect of aversion to walking on muscles;

circulation. =5.= If a shoe is too loose, it slips up and down at

the heel and chafes the skin there; if too tight, there is pressure

on the toes, which causes a corn or ingrowing nail. Have your shoes

been correct, or have they been too loose or too tight? According to

this test, what proportion of people wear shoes that are too tight?

=6.= How many sprained ankles have you known among boys; girls? =7.=

Why is it that people who grow up in warm climates have high, arched

insteps, and short, broad, elastic feet, but people of the same race

who pass their childhood in cold climates often have long narrow feet

with low arches and sometimes have the deformity called “flat foot”?

[Illustration: FIG. 52.--ARCH OF FOOT. It forms an elastic spring.]

=Instinct as a Guide for using the Muscles.=--The instinctive feeling

called _fatigue tells us when to rest_. There is also a _restless,

uneasy feeling that comes over a normal human being when confinement

and restraint of the muscles have reached an unhealthy limit. This

feeling should not be repressed_ for long at a time. Many, ruled by

avarice, ambition, interest in sedentary work, a silly notion of

respectability, or a false conception of duty, have repressed this

feeling and have lost it. There is then a feeling of languor, and a

disinclination to the very activity which health demands. An unheeded

instinct is as useless as an alarm clock that has been habitually

disregarded.

=Exercise and Climate.=--In our warmest states and in the tropics,

one hour’s vigorous physical labor a day, combined with the ordinary

activities of life, will keep a person in good condition. In the

colder states, muscular exertion for several hours is needed daily.

=Complete Living.=--Numberless people have devoted themselves to

an intellectual occupation, and planned to keep their bodies sound

by gymnastics and special exercises. Because of the monotony of

exercises, they are soon given up in nearly every instance. _The

safest way is never to allow all the energies to be devoted to a

one-sided occupation, but so to plan one’s life and work that a

part of the time is devoted to some physical work_, whether it be

in a garden, workshop, or orchard; in walking a long distance to

the office; at bookbinding, cooking, wood carving, or any one of

various other useful occupations. The result of manual training shows

_that not only strength of body, but strength of mind, is promoted

by physical labor_. Problems of war and of the chase kept active

both the body and mind of the savage. Hence he led a more nearly

complete life than his civilized descendants, and his body was strong

accordingly. We should admit the hopelessness of having permanent

good health without muscular activity and should determine that

muscular exertion shall be as much a habit and pleasure as eating and

sleeping.

=Alcohol and Muscular Strength.=--Benjamin Franklin, one of the

wisest and greatest of Americans, was a printer when he was a young

man. In his autobiography he gives an account of his experience as a

printer in London. He says: “I drank only water; the other workmen,

fifteen in number, were great drinkers of beer. On occasion I carried

up and down stairs a large form of types in each hand, when others

carried but one in both hands. They wondered to see, from this and

several instances, that the Water-American, as they called me, was

stronger than themselves, who drank strong beer. My companion at the

press drank every day a pint before breakfast, a pint at breakfast

with his bread and cheese, a pint between breakfast and dinner, a

pint at dinner, a pint in the afternoon about 6 o’clock, and another

when he had done his day’s work. I thought it a detestable custom,

but it was necessary, he supposed, to drink strong beer that he might

be strong to labor.”

EXERCISES IN WRITING.--The Right and the Wrong Way to ride a Bicycle.

Pay Day at a Factory. A Graceful Form: how Acquired; how Lost. A

Drinking Engineer and a Railway Wreck.

PRACTICAL QUESTIONS.--=1.= Can we always control the voluntary

muscles? Do we shiver with the voluntary or involuntary muscles?

=2.= If a man had absolute control over his muscles of respiration,

what might he do that he cannot now do? =3.= Why is one who uses

alcoholic drinks not likely to be a good marksman? =4.= Why should a

youth who wishes to excel in athletic contests abstain from the use

of tobacco? =5.= Is there any relation between the amount of bodily

exertion necessary for a person’s health and the amount of wealth

or the amount of intelligence he possesses? =6.= Can you relax the

chewing muscles so that the lower jaw will swing loosely when the

head is shaken? Can you relax your arm so that it falls like a rope

if another person raises it and lets it fall? =7.= The average man

has sixty pounds of muscle and two pounds of brain; one half of the

blood goes through the muscles and less than one fifth goes through

the brain. What inference may you draw as to the kind of life we

should lead? =8.= Why is a slow walk of little value as exercise?

=9.= How can we best prove that we have admiration and respect for

our wonderful bodies? =10.= Why is the ability to relax the muscles

thoroughly of great benefit to the health? How is this ability

tested? (Question 6.) =11.= Why is it as correct to say that the

muscles support the skeleton as the reverse?

[Illustration: COLORED FIGURE 5. DIAGRAM OF CIRCULATION.

1. Head arteries (carotid).

2. Nameless arteries (innominate).

3. Collar bone (subclavian) artery.

4. Great bend of the aorta.

5. Pulmonary arteries.

6. Thoracic aorta.

7, 10. Abdominal aorta.

8. Artery to liver (hepatic).

9. Artery to spleen (splenic).

11. Artery to intestine (mesenteric).

12. Artery to kidney (renal).

13. Descending vena cava.

14. Nameless vein (innominate, 15 and 16 before branching).

15. Collar bone vein (subclavian).

16. Jugular vein.

17. Pulmonary vein.

18. Ascending vena cava.

19. Vein from liver (hepatic).

20. Vein from stomach (gastric).

21. Vein from spleen.

22. Vein from intestine.

23. Vein to liver (portal).

24. Vein from kidney.

25. Right auricle.

26. Left auricle.

27. Right ventricle.

28. Left ventricle.

29. Thoracic duct.

30. Stomach.

31. Spleen.

32. Liver.

33. Kidneys.

34. Duodenum.

35. Ascending colon.

36. Descending colon.

37. Lymphatic glands of mesentery.]

CHAPTER V

THE CIRCULATION

_Experiment 1._ =Anatomy of Mammalian Heart.=--Get a sheep’s or

beef’s heart from the butcher. Get the whole heart, not simply the

ventricles (as usually sold). Note the blood vessels, four chambers,

thickness of different walls, valves, cords, openings.

_Experiment 2._ =Does Gravity affect the Blood Flow?=--Hold the right

hand above the head for a few minutes. At the same time let the left

hand hang straight down. Then bring the hands together and see which

is of a darker red because of containing more blood. Now reverse the

position of the hands for a few minutes, and find whether the effect

is reversed. (Entire class.)

_Experiment 3._ =Study of Human Blood.=--Examine a drop of blood

under the microscope, first diluting it with a little saliva. See

Fig. 60.

_Experiment 4._ =The Circulation in a Frog.=--Wrap a small frog in a

moist cloth, lay on a slip of glass, place under the microscope, and

study the circulation in the web of its foot.

_Experiment 5._ (Entire class.) =Effect of Exercise upon the

Pulse.=--Tap a bell as the second hand of a watch begins a minute

and let the pupils count the pulse at the radial artery on the wrist

above base of thumb. Repeat standing, or after gymnastics or recess.

Result?

_Experiment 6._ =The Action of the Valves in the Veins.=--Place the

tip of the middle finger on one of the large veins of the wrist;

with the forefinger then stroke the vein toward the elbow so as to

push the blood from a portion of it, keeping both fingers in place.

The vein remains empty between the fingers. _Lift the finger nearer

the heart and no blood enters the vein; there is a valve above which

holds it back. Lift the other finger and the vein fills instantly._

Stroke a vein toward the hand, and notice that the veins swell

up into little knots where the valves are. Stroke in the reverse

direction. Result?

_Experiment 7._ =Finding the Capillary Pressure.= This is found by

pressing a glass plate or tumbler upon a red part of the skin. When

the skin becomes pale the capillary pressure is counterbalanced.

_Experiment 8._ =Emergency Drill.=--Let one pupil come forward, mark

with blue chalk or pencil the position on his arm of a supposedly cut

vein. Let another pupil use means to stop the imagined blood flow.

_Experiment 9._ Let another pupil stop the flow from an imaginary

cut artery marked red. See text. _Experiment 10._ In a case of nose

bleed do not let pupil lean over a bowl. (Why?) Cause him to stand

rather than lie. (Why? See Exp. 2.) Apply cold water to contract

arteries to nose, also have pupil hold a small roll of paper or a

coin under upper lip (to make muscular pressure on arteries to nose).

_Experiment 11._ Let one pupil treat another for a bruise (see p.

62). _Experiment 12._ Emergency drill, restoration from fainting (see

p. 57).

=The Cells have a Liquid Home.=--The cells in the body of man, like

the ameba, live in a watery liquid. This liquid is called _lymph_.

The cells cannot move about as the ameba does to obtain food, so the

_blood_ brings the food near them and it soaks through the blood

tubes into the lymph spaces next to the cells (see colored Fig. 3).

The ameba gives off waste material into the water; the cells of the

body give it off into the lymph to be carried off by the circulation.

The blood, then, has _two functions_: (1) to take nourishment to the

tissues; (2) to take away waste material from them.

=The Organs of Circulation.=--These are the _heart_, which propels

the blood; the _arteries_, which take blood away from the heart; the

_veins_, which take the blood back to the heart; and the _capillaries_

(Fig. 53), which take the blood from the arteries to the veins.

[Illustration: FIG. 53.--CAPILLARIES, connecting artery (_b_) with vein

(_a_).]

=The heart= is a cone-shaped organ about the size of its owner’s fist.

It lies in a diagonal position behind the breastbone, with the small

end of the cone extending toward the left. The smaller end (Exp. 1)

taps or beats against the chest wall at a point between the fifth and

sixth ribs on the left side. The breastbone and ribs protect it from

blows. An inclosing membrane called the _pericardium_ secretes a serous

fluid and lessens the friction from its beating.

=Why the Heart is Double.=--_There must be a pump to move the impure

blood from the body to the lungs_ to get oxygen from the air, and there

must be _another pump to send the pure blood from the lungs back to the

body_. Hence there are two pumps bound together into one heart, beating

at the same time like two men keeping step, or like two carpenters

keeping time with their hammers. There are valves in the heart, as in

other pumps. These valves are so arranged that when any part of the

heart contracts and forces the blood onward, the blood cannot return

after that part of the heart relaxes. Are the pumps placed one behind

the other? Or is one above the other? Neither; they are side by side,

with a fleshy partition between them (Fig. 54). The pump on the right

moves the impure blood from the body to the lungs, and the one on the

left moves the pure blood from the lungs to the body. There is no

direct connection between the right and left sides of the heart.

[Illustration: FIG. 54.--DIAGRAM OF HEART.

Notice the two dark spots in the right auricle, and four dark spots in

left auricle, where the veins enter. Does the aorta pass in front of,

or behind, the pulmonary artery?]

=To trace one complete circuit of the blood= (Fig. 54), let us begin

with the blood in the _capillaries_ of the outer tissues, such as the

skin or muscles. The blood goes through small veins which unite into

_two large veins_, through which it enters the receiving chamber, or

_right auricle_, goes through the _tricuspid valve_ into the expelling

chamber, or _right ventricle_, then through a _semilunar valve_ into

the _pulmonary artery_ leading to the _lungs_. Becoming purified while

passing through the _capillaries of the lungs_, the blood goes _through

the pulmonary veins_ to the _left auricle_ (Fig. 54), then through

the _bicuspid_ or mitral valve, to the _left ventricle_, whence it is

forced through a _semilunar valve_ into the largest artery of the body,

called the _great aorta_ (Fig. 54). Thence it goes to the _smaller

arteries_, and then to the _capillaries_ of the tissues in general,

thus completing the circuit.

[Illustration: FIG. 55.--THE LEFT SIDE OF HEART (plan), showing the

left ventricle at the moment when relaxing and receiving the blood from

the auricle; and the same at the beginning of contraction to send blood

into aorta. Notice action of the valve.]

=Structure of Veins and Arteries.=--Seen under the microscope the

arteries and veins show that they are made of _three kinds of tissues_

arranged in _three coats_ (Fig. 56): a tissue resembling epithelial

tissue (Chap. 1), as a lining to lessen friction; an outer connective

tissue (Chap. 1), to give elasticity; and a middle coat of muscular

tissue to enable the vessels to change in size. Let us see why blood

vessels must have these three properties.

=Why the Blood Vessels must be Elastic.=--The aorta and its branches

are always full of blood. When the left ventricle with its strong,

muscular walls contracts, the blood in the aorta and small blood

tubes _cannot move forward fast enough to make room for the new

supply so suddenly sent out of the ventricle_. Where can this blood

go? If a cup is full, it cannot become more full; not so with an

artery. The elastic connective tissue allows it to expand as a rubber

hose does under pressure. The first part of the aorta having expanded

to receive the incoming blood, _the stretched walls contract_ because

of the elasticity of the outer connective tissue coat _and force

blood into the portion of the aorta just ahead_, forcing it to expand

in turn. Thus _a wave of expansion_ travels along the arteries. This

wave is called the _pulse_.

=The Pulse= may be most easily felt in the wrists and neck. As the

artery stretches and springs back, one beat of the pulse is felt. In

men there are about _seventy heart beats or pulse beats a minute_.

In women the rate is about eighty a minute. It is slowest when one

is lying down, faster while sitting, still faster when standing,

and fastest of all during running or violent exercise. (Exp. 5.) It

should not be thought that the muscular or middle layer of the artery

actively contracts and helps to send along the pulse wave; for this

wave is simply the passive stretching and contracting of the outer

connective coat, and travels like a wave crossing a pond when a stone

is dropped into the water. The force of the pulse is furnished, not

by the muscle fibers in the artery, but by the beat of the heart; the

outer, or connective tissue, coat enables the pulse to travel. Why

must there be a middle, or muscular, coat for variation in size?

[Illustration: FIG. 56.--SECTION OF ARTERY, _A_, AND VEIN, _V_, showing

inner coat, _e_ (endothelial); middle coat, _m_ (muscular); and third

coat, _a_ (connective tissue).]

=Use of the Middle Coat; Quantity of Blood and its

Distribution.=--The body of an adult contains about five quarts of

blood. The blood furnishes the nourishment needed for the activity of

each organ. The more vigorous the work of any organ, the greater is

the amount of blood needed. _The whole amount of blood in the body

cannot be suddenly increased, but the muscular coat of the arteries

going to the working organ relaxes, and allows the arteries to become

enlarged by the pressure from the heart._ Consequently, more blood

goes to the active organ, and the other organs get along with less

blood for the time. When we are studying, our brains get more blood;

when running, the leg muscles get more; after a hearty dinner, the

stomach and intestines get more than any other part of the body. Why

is it difficult to do the best studying and digest a meal at the same

time? We see that the muscular coat of the arteries is a very useful

coat, for _it enables the supply of blood to be increased in any

organ which is in temporary need of it_.

=Why the Blood Vessels must be Smooth.=--The inner coat of the heart

and other blood vessels is made of tissue like the epithelial tissue

which forms the epidermis and the smooth lining of the mouth and

other organs. _The purpose of this lining is to lessen friction_,

and thus save the work of the heart. The friction is greatest in the

capillaries because of their small size. The inner coat of smooth

cells is the only coat that is prolonged to form the capillaries (see

Fig. 57).

[Illustration: FIG. 57.--CAPILLARIES MAGNIFIED, SHOWING CELLS forming

their walls. Notice that each cell has a nucleus and three branches.]

=The capillaries= are small, thin, short, and very numerous. _They are

very small_ so that they may go in between the cells of the tissues.

_The capillaries are very thin_ so that the nourishment from the blood

may pass readily into the tissues, and the waste material pass readily

into the blood. _They are very short_ so that the friction may be less;

and _they are very numerous_ so that all parts of the tissues may be

supplied with blood, and that the blood may flow very slowly through

them. Because of the number of the capillaries, their total volume is

several hundred times larger than the volume of the arteries that empty

into them, or of the veins that flow from them. Hence the blood flows

slowly through the capillaries, as water flows slowly through a lake

along the course of a river. All the changes between the blood and

the lungs, and between the blood and the tissues, take place in the

capillaries, and the object of the other parts of the circulation is

merely to move the blood continually through the capillaries.

=The effect of gravity= is to retard the flow in certain parts of the

body and aid the flow in other parts, according to the position of

the body (Exp. 2).

=Fainting= is usually due to _lack of blood in the brain_, which

in turn results from a weakening of the heart beat. Since the

brain cannot work without fresh blood, fainting is accompanied by

unconsciousness. Recovery from fainting is aided by loosening the

clothing at the neck and by placing the head of the patient a little

lower than the body so that the weight of the blood may aid the flow

to the brain. Dashing a little cold water in the face shocks the

nerves and arouses the heart to stronger beats.

=The veins have valves= placed frequently along their course (Fig.

58). These valves are pockets made by a fold in the inner coat of the

wall of the vein. When a boy places his hand in his pocket, the pocket

swells out; but if he rubs his hand on the outside of the pocket from

the bottom toward the top, it flattens down. So with the action of the

blood upon the valves in the veins. (Repeat Exp. 6 in class.)

[Illustration: FIG. 58.--VALVES IN VEINS. (Jegi.)]

=How Muscular Exercise aids the Heart.=--_When a muscle contracts_,

it hardens and presses upon a vein which goes through the muscle,

and _the blood is pressed out of the vein_ (see Fig. 58). The blood

cannot go toward the capillaries, for the valves fill and close when

it starts that way; so it must all go out toward the heart. _When

the muscle relaxes_, the blood that has been pressed forward cannot

go back because of the valves, but the valves nearer the capillaries

open, and _the veins are filled from the capillaries_ (Fig. 53). When

the muscle contracts again, the same effect on the blood movement is

repeated. We see, therefore, that every contracting muscle converts

into a pump the vein running through it, and when a person works or

exercises, many little pumps are working all over the body, aiding

the heart in its function. This aid makes the blood flow faster and

relieves the heart of part of its work, so that it beats faster, just

as a horse might trot faster if another horse helped to draw the load

(Exp. 3). The pressure of a contracting muscle upon an artery does

not aid the blood flow in the artery because the latter is destitute

of valves.

=How Breathing aids the Heart.=--Breathing is a blood-pumping process

as well as an air-renewing process. When the chest expands, blood is

drawn into it. When the chest contracts, the flow of blood away from

it is aided. As the chest expands, the downward pressure of a great,

broad muscle, the diaphragm (Fig. 74) compresses the liver, stomach,

and other abdominal organs, and forces the venous blood upward into

the expanding chest, thus helping it on its way to the heart. But if

the abdominal wall is weakened by tight lacing or by the pressure of

belts and bands which support the clothing, the weak abdominal wall

yields to the downward pressure of the diaphragm, and no compression

of the liver or aid to the circulation will result.

[Illustration: FIG. 59.--THE VENTRICLES OF A DOG’S HEART relaxed

(above), and contracted (below).]

=How the Blood Vessels are Controlled.=--Evidently the blood vessels

are not regulated by the will. We cannot voluntarily increase the

beating of the heart, or cause it to slacken its action. Even an

actor cannot cause his face to turn pale or to blush at will. This

is because the tiny muscles in the walls of the blood vessels are

involuntary muscles. They are controlled by nerves of the sympathetic

system called vaso-motors. They are not subject to the will (see Fig.

25). The nerve center which controls the blood vessels is located

in the top of the spinal cord at the base of the brain. When cold

air strikes the skin the nerves near the arteries are stimulated,

the arteries in the skin contract, and the skin turns white. When

the heat from a hot fire strikes the skin, the nerves are soothed,

the arteries relax, and the face becomes red. When the stomach is

filled with food, the heart beats faster and sends more blood to aid

in digestion. When we run fast, the heart beats fast to supply more

blood to the muscles, but it slows down as sleep comes on, that the

body and brain may rest.

=Parts of the Blood.=--The blood which flows from a cut finger seems

to be a bright red throughout. When a drop of it is looked at through

a microscope, however, the liquid itself is seen to be almost as clear

as water. This liquid is called the _plasma_. Floating in it are

millions of biconcave disks containing a pigment (hemoglobin) which

gives the red color to the blood. The disks are called _red corpuscles_

(Fig. 60). A few irregularly shaped bodies, nucleated and almost

transparent, and called _white corpuscles_, are also found in the

blood. The red corpuscles go only where the plasma carries them (Exps.

3, 4). The white corpuscles sometimes leave the blood vessels entirely.

At times one may be seen shaped like a dumb-bell, half of it through

the wall of the blood vessel and half still in the blood vessel.

After the corpuscle is out, no hole can be found to account for its

mysterious passage. _The white corpuscles consist of protoplasm. The

red corpuscles contain no protoplasm. Hence the latter are not really

alive._

[Illustration: FIG. 60.--HUMAN BLOOD CELLS (magnified 40,000 areas),

showing many red cells and a single white blood cell on left, larger

than red cells. (Peabody.)]

[Illustration: FIG. 61.--SIDE AND FRONT VIEWS OF FROG’S AND MAN’S RED

CORPUSCLES, drawn to same scale. Compare outline, concavity, diameters.]

=The Use of Each Part of the Blood.=--The _plasma_ keeps the blood in a

liquid state, so that it may flow readily; the plasma also transports

the food that has been eaten and digested, and carries carbon dioxid to

the lungs and other waste material to the kidneys. The _red corpuscles_

transport the oxygen from the lungs to the tissues. The _white

corpuscles_ devour and destroy irritating particles, such as drugs,

poisons, and germs. They are of great importance in purifying the blood

and as a protection against disease. One is shown in Fig. 60.

=The sounds of the heart beat= may be heard by applying the ear to the

chest. They are two, a _long, dull_ sound and a _short, clear_ one. The

first comes from the vibration of the bicuspid valve together with an

unexplained tone arising from large contracting muscles, in this case

the walls of the ventricles. The second, or short, clear sound, is

produced by the sudden closing and vibration of the semilunar valves.

=Changes in the Composition of the Blood as it passes through the

Various Organs.=--When the blood is forced out by the heart, part of

it goes to the stomach and intestines through arteries which divide

into capillaries. These capillaries _absorb all kinds of food_ from

the alimentary canal except the fats (see p. 64), and unite to form

the portal vein, which takes the absorbed food to the liver. In the

liver some of the _impurities of the blood are burned up_ and changed

into bile. The blood, purified and laden with food, is carried from

the liver to the heart, where it reënters the general blood stream.

The blood flow from the food tube through portal vein and liver to the

heart, as just described, is called the _Portal circulation_.

_Renal circulation._ Two branches from the aorta carry blood to the

_kidneys_. There the _urea_ and _a large amount of water_ are taken

out, and the purified blood is emptied into the large vein that leads

up to the heart.

_Pulmonary circulation_ (Fig. 67). This is the circulation through the

lungs. During this circulation _carbon dioxid gas is removed_ from the

blood and _oxygen is added_ to it.

[Illustration: FIG. 62.--BLOOD CLOT separated from serum.]

Some impurities and a large amount of water escape from the blood as it

passes through the skin.

=Coagulation.=--So long as blood is in an uninjured blood vessel it

remains a liquid. In a few minutes after it flows from a blood vessel,

it forms into a stiff, _jellylike mass called a clot_ (Fig. 62). The

process of forming the clot is called coagulation, and it is brought

about by the albuminous substance called fibrin, which is always in

the plasma of healthy blood. On exposure to air the _fibrin forms

into a network of fine threads throughout the mass_ (Fig. 63) and the

corpuscles become entangled in the meshes. The clot consists of the

fibrin of the plasma and corpuscles; the watery portion of the plasma,

called the _serum_, separates from the clot (Fig. 62). The property of

coagulating is a great safeguard, as a clot often plugs up a cut blood

vessel. What is the difference between serum and plasma?

[Illustration: FIG. 63.--NETWORK OF FIBRIN IN HUMAN BLOOD (enlarged).]

=Veins and Arteries compared.=--The veins have _thin, soft walls_ and

the arteries have _thick, tough, elastic walls_. When a vein is cut,

it may usually be closed by pinching the walls of the end together.

If an artery is cut, the _walls will not readily stick together_, but

often stand open until the end of the artery is tied. For this reason,

and because an artery is subject to the direct pressure of the heart,

a cut artery is more dangerous to life than a cut vein. Because of the

toughness of the arteries, and because they are _located close to the

bones_, they are less likely to be cut than the veins, which are softer

and nearer the surface. The veins begin in capillaries and _empty into

the auricles_; the arteries begin at _the ventricles_ and empty into

capillaries; and there is a semi-lunar valve at the origin of each

artery.

=Cuts and Bruises.=--1. _Wash_ a cut under _running_ water. 2. _Stop

the bleeding._ The washing in cold water may do this. Elevating an

injured arm or leg will aid the blood greatly in forming a clot at

the opening. 3. _Bandage_ firmly with a strip of cloth and sew the

end. Keep wet the part of the bandage where the cut is; this lowers

the temperature of the wound. It may be necessary to hold a gaping

wound closed with strips of surgeon’s plaster placed across the cut.

A handkerchief folded first into a triangle and then into a narrow

bandage is often useful. A cut artery may be known from a cut vein by

the brighter _color of the blood_, and by the flow being _stronger at

each heart beat_, while the flow from a vein is uniform. Pressure to

stop the flow of blood from an artery should be applied _between the

cut and the heart_; but when the blood comes from a vein, the pressure

should be applied _to the side of the cut farthest from the heart._

Apply hot water immediately for several minutes to a =bruise=. Either a

bruise or a cut may be washed with a weak solution of some antiseptic

such as carbolic acid. After washing a bruise it may be bound with a

cloth soaked in witch hazel or arnica.

THE LYMPHATIC SYSTEM

This system contains and conveys a liquid called the lymph. It consists

of lymph spaces, lymph tubes, (lymphatics), and lymphatic glands.

_Lymph corresponds nearly to the blood without the red corpuscles._ It

is the familiar liquid seen in a blister, or oozing out where the skin

has been grazed without breaking a blood vessel.

=Necessity for Lymph and Lymph Spaces.=--The body cannot be nourished

with the albumin, sugar, oxygen, and other digested food in the blood,

until this food passes out of the blood vessels. The food leaves the

blood through the thin walls of the capillaries. Many of the cells do

not touch the capillaries, and the _lymph penetrates the spaces between

the cells to reach them_ (see colored Fig. 3). If there were no lymph

spaces, these cells could not get any food. The lymph bathes the cells,

and the cells absorb what they want from the nourishing fluid. The red

corpuscles bearing the oxygen cannot pass through the capillary walls.

Oxygen, being a gas, readily passes through the walls and reaches the

cells through the lymph in the lymph spaces. The waste materials must

go back into the blood; carbon dioxid passes back through the capillary

walls and is taken to the lungs; how the other waste materials formed

in the cells pass back will soon be explained.

=Need of Lymphatics.=--_The plasma continually passes into the tissues,

but it cannot return directly into the blood._ The lymph contains waste

material which must be removed, and also much unused food which nature,

like an economical housekeeper, will offer to the tissues again. _There

are vessels called lymphatics that take the lymph back into the blood_

(see Fig. 64).

=The Lymphatic Circulation= (Fig. 64).--The blood flow does not begin

nor end, but makes a never ending circle. The countless _lymphatics

begin, with open ends, in the lymph spaces_ between the cells

(colored Fig. 3). The smaller lymphatics unite into larger ones until

finally they all unite into two large ones that empty into the large

veins under the collar bones, near the neck. The one that empties

under the left collar bone (3, Fig. 66) is called the _thoracic duct_

because it goes up through the thorax just in front of the spinal

column (1, Fig. 66). The other at the right side of the neck is

called the _right lymphatic duct_ (see Figs. 64, 65).

[Illustration: FIG. 64.--SURFACE LYMPHATICS OF HAND.]

In persons with the _dropsy_, the lymph accumulates in the lymph

spaces and is not drained away by the lymph flow. Dropsy usually

shows itself first by swelling of the feet and the leg below the

knee. (Why? See Exp. 2.)

There is a set of lymphatics called _lacteals_, situated in the

abdomen, which have the function of absorbing digested fats from the

intestine (Figs. 66, 100, and colored figure 2).

[Illustration: FIG. 65.--DIAGRAM TO SHOW THE TWO PARTS OF THE BODY

DRAINED BY THE TWO LYMPH DUCTS.]

=What makes the Lymph Flow?=--The heart does not, for its pressure

is not transmitted beyond the blood tubes. _The successive pressures

of a working muscle_ move the lymph forward in the lymphatics in

the same way that the blood is moved forward in the veins, and the

valves keep it from moving back. When riding a trotting horse, or

in a jolting vehicle, the lymph is moved beyond the valves at every

jolt (Fig. 64). Without exercise the lymph stagnates, and the body

becomes poisoned by its own wastes. At every expansion of the lungs

lymph is drawn into the chest; and it is forced out of the chest at

every contraction. Deep breathing is as great a benefit to the body

in moving stagnant lymph as it is in purifying the blood.

[Illustration: FIG. 66.--CHIEF LYMPHATIC VESSELS AND GLANDS of trunk.

1, 3, Thoracic duct (emptying at 3); 2, receptacle for chyle (lacteals

below it).]

=The lymphatic glands= are kernel-like enlargements along the

lymphatics, and they contain a great many lymph cells which _purify the

lymph as it passes through them_. The lymphatic glands are numerous in

the armpits and the groins. The cells in the lymph glands multiply, and

some of them are carried by the lymph into the blood _to become those

remarkable little bodies, the white corpuscles_.

HYGIENE OF THE CIRCULATION

=Effects of Work, Fresh Air, and Rest on Corpuscles and Plasma.=--_Work_

uses up the nutritious elements in the blood. A few hours after food is

eaten the nutritious materials in the blood are found to be increased.

By the breathing of _fresh air_ the carbon dioxid in the plasma is

diminished and the oxygen in the colored corpuscles is increased,

changing the blood to a brighter red. _Sleep_ gives time for the

exhausted cells and depleted blood to be replenished. _Loss of sleep_

means longer hours of activity and greater consumption of nutriment

with shorter hours for replacing the nutriment. The pale skin of one

who has lost sleep tells of the exhausted condition of the blood.

=How the Muscles help the Circulation.=--The imperative need of

muscular exercise to keep the body sound exists because of the lack of

other means to cause movement in the veins and lymphatics. Good food,

pure air, and plenty of exercise are necessary for healthy blood. Many

so-called “blood purifiers” are advertised to entrap the ignorant.

It is impossible to imagine how “blood purifiers” can aid the blood.

_The blood is purified, not by putting anything into the blood, but

by something going out of it as it passes through the skin, kidneys,

liver, and lungs._ These organs all send out impurities brought to them

by the blood.

=The one great hygienic effect of muscular exercise= is an _active

circulation_, and from an active circulation _nine chief effects_ may

be traced. The effects upon the body will be given in order, beginning

with the surface--skin, fat, muscles, bones; and the effects upon the

internal organs are given in order of position, beginning with the

highest--brain, lungs, heart, digestive organs.

=Effects of Exercise and Improved Circulation.=--1. _The skin_ is

made fresh, pink, and smooth from the flushing of the capillaries; it

is purified by the perspiration and the renewal of cells. 2. If _the

fat_ is too great in amount, it is burned up; if it is too small in

amount, the better nourishment brought by the blood increases it. 3.

_The muscles_ are better fed (see Fig. 48) and grow firm, strong, and

large. 4. _The skeleton_ is held in proper position by the stronger

muscles, and deformity is prevented. 5. _The brain._ The pure, fresh

blood, loaded with oxygen from expanded lungs, flushes every capillary

of the brain, clears the mind, and doubles or trebles its power to

work. 6. _The lungs_ are expanded by deep breathing if the exercise be

rapid and vigorous. A slow stroll or saunter is not of value. 7. _The

circulation._ Every contracting muscle aids the heart in its work. The

deep breathing moves stagnant lymph. 8. _The stomach._ Exercise burns

up the food and increases the appetite. 9. _General effects._ Exercise

promotes good humor, decreases loafing, cigarette smoking, gossiping,

and other vices.

=The effect of tobacco on the heart=, if cigarettes or cigars are used,

is sometimes to cause attacks of irregular beating; the heart flutters

faintly for a while, then palpitates strongly, then flutters again.

This condition is called _tobacco heart_, or _trotting heart_.

=Effect of Alcohol upon the Circulation.=--After a person has taken

an alcoholic drink his face and skin are likely to become flushed,

and perhaps his heart beats faster. Most investigators have found

that the _alcohol itself does not directly increase or strengthen the

action of the heart_. Hence it is probably wrong to call alcohol a

heart stimulant. The flushing of the skin is believed to be due to the

relaxing effect of alcohol. It relaxes, it paralyzes, the vasomotor

nerves which control the little muscle fibers in the walls of the blood

vessels. The relaxing and enlarging of the blood vessels decreases the

resistance to the blood flow, and the heart beats faster under its

lighter load. The narcotic effect of alcohol is much more powerful than

its irritating or stimulating effect. The effect of alcohol in causing

fatty degeneration of the muscles often weakens the heart and other

blood vessels.

=Climate and Brain Work.=--_In going to sleep_ the vessels in the

skin dilate and _blood is drawn from the brain to the skin_. It is

difficult to go to sleep when cold, for cold sends the blood to

the brain and keeps the mind active. On the same principle, mental

work is difficult in very warm weather _because of the enlarged

capillaries in the skin_ and the withdrawal of blood from the

brain to the skin. This increases the perspiration and keeps the

temperature of the body down to normal, but it deprives the brain of

blood needed for good mental work. Mental workers in warm weather and

in warm climates _should seek every condition favoring coolness_.

Benjamin Franklin was accustomed to strip himself almost entirely

of clothing when he was writing and wanted his brain to work at its

best. The wearing of _barefoot sandals_ and the _thinnest cotton

clothing, light in color_, helps to prevent mental inertia in hot

weather. In the Gulf states in summer and in our tropical islands the

best mental work can be done by _rising at dawn and working before

the hot part of the day begins_. Some of the greatest thinkers in the

world have lived in warm climates (Greece and India), but they _wore

very few clothes_ and _ate moderately_ of the simplest food (see p.

44).

=Congestion= is a swelling of the blood vessels of some part, with

the accumulation of blood therein. Congestion is _active_ when a

_rapid_ flow of blood distends the capillaries. Example, flushing of

face when running. Congestion is _passive_ when there is a narrowing

of the outlet of the capillaries, the blood moves slowly and partly

stagnates in the swollen vessels. Example, when the nose feels

stopped up during a cold. If a syringe is worked so fast that the

rubber tube swells, this is like active congestion; if the end of the

tube is pinched together so that moderate pumping causes it to swell,

this is like passive congestion.

=Inflammation= is congestion where the vessels of any part are

strained and injured. _White corpuscles collect_ there to repair

the vessels and devour the blood that escapes and stagnates there.

They also _destroy germs_ that have usually found lodgment and begun

to multiply. The serum of the blood also destroys the germs by the

antitoxins in it. Inflammatory troubles are: colds, rheumatism,

diarrhœa, and all diseases with name ending “_itis_.” An inflamed

part is red, swollen, hot, and painful.

=Prevention and Care of Colds.=--_A cold is an inflammation of a

mucous membrane._ Colds are prevented by so living as to encourage

a _free, vigorous circulation_, and especially by not coddling the

body so tenderly that the circulation becomes deranged by the least

exposure. The circulation may be _deranged by overheating_ as well

as by chilling the body; usually it would be more appropriate to say

that the person caught “a hot” than “a cold.” At the _first sign of

a cold_ vigorous exercise, a cold bath, or going outdoors into cold

air may aid in sending fresh blood to remove the stagnation and stop

the inflammation. A warm foot bath and hot drinks may relieve by

drawing blood from the congested mucous membrane. _After the cold

has become fixed_ such measures will not help, but the cure is aided

by helping the skin to keep its full share of blood. The cold must

run its course. The cells will be given every chance to repair the

injury and destroy the germs (if any) by avoiding hard work, eating

moderately of digestible food, avoiding drugs, especially infallible

drugs advertised in newspapers, even if recommended by otherwise

intelligent people. Repeated colds tend to become a disgusting

disease called _chronic catarrh_. Constricting the blood vessels of

the skin causes congestion of the (internal) mucous membranes. _A

skin tenderly protected_ constricts more readily than one accustomed

to cold. _Cold is the best preventive of cold._ Cold baths, pure air,

light clothing, free breathing, moderate eating, ward off colds.

Fussing with sprays, gargles, and drugs will not; for the main factor

in bringing on a cold is not germs, nor temperature, but _the state

of the system itself_. Persons who have suffered much with colds have

found that after substituting _cotton underwear_ for woolen, colds

became very rare. Linen will have a similar effect, but it is not as

durable, soft, or heat-retaining as cotton (see p. 16).

PRACTICAL QUESTIONS.--=1.= Through what kind of skin do the

blue veins in the wrist show most plainly? =2.= Which is more

compressible, a vein or an artery? =3.= Why are those who take little

exercise likely to have cold feet? (p. 57.) =4.= Where does the

so-called venous blood flow through an artery? =5.= What vein begins

and ends in capillaries? (The portal vein, colored Fig. 5.) =6.= To

what purifying organ, after leaving the lungs, does the heart send

part of the blood for further purification? (Colored Fig. 5.) =7.=

What keeps the blood moving between the beats of the heart?

CHAPTER VI

THE RESPIRATION

_Experiment 1._ (Home.) =Study of the Throat.=--Sit with the back to

the light. Study the open mouth and throat with a mirror and make out

the uvula, tonsils, and other parts shown in Fig. 68.

_Experiment 2._ =Anatomy of Lungs.=--Study fresh lungs of sheep, hog,

fowl, or frog. Will they float? Will they contract when expanded by

air blown in through a quill or other tube? What is the structure of

the windpipe? Can you distinguish the arteries from the veins by the

stiffness of their walls? Which contain pure blood? Study branching

of air tubes. Make a sketch.

_Experiment 3._ =Tests of Expired Air.=--Breathe upon a mirror,

bright knife blade, or cold window pane. Result? State your

conclusion. _Experiment 4._--Carbon dioxid added to limewater will

cause a white cloud consisting of particles of limestone. Breathe

through a tube or straw or the hollow stem of a reed into clear

limewater. Result? Conclusion? (Limewater may be had at druggist’s

or made by pouring water upon a lump of unslackened lime and

draining it off when lime has settled.) _Experiment 5._ Breathe for

several minutes upon the bulb of a thermometer. Result? Conclusion?

_Experiment 6._ Breathe a few times into a large, carefully cleaned

pickle jar, or a bottle. Cork it tightly, and set it in a warm place

for several days. Then uncork and smell the air in it. Result?

Conclusion? _Experiment 7._ Pierce a small hole in a card, place card

over a wide-mouthed bottle, and breathe into bottle through a tube,

lemonade straw, or hollow reed. Pull out straw. Place bottle, mouth

downward, on table, and slip out card. Slide bottle to edge of table

and lift lighted candle into bottle. Result? _Experiment 8._ Place

bottle of fresh air over lighted candle. Result? Conclusion? (See

Animal Biology, p. 4.)

_Experiment 9._ (School.) =Testing the Air of a Room.=--Fill a fruit

jar or large bottle with water, and take it into a room containing

many people. Pour out the water. (This insures that all the air now

in the jar is air obtained in the room to be tested.) Seal the jar if

test is not to be made at once. Test by pouring in two tablespoonfuls

of clear limewater and shake. If the limewater turns milky, the

ventilation is bad.

_Experiment 10._ (Home and school.) =Homemade Current

Detector.=--Dangle a bit of paper by means of a spider web or thread

from the end of a walking stick or ruler. (Or test with the flame of

a candle.) Hold it near cracks of window, above and below doors, and

especially before openings intended for entry and exit of air, and

test if air moves as desired.

_Experiment 11._ =Ventilation of the Schoolroom.=--Let the whole

class rise, and with the fingers test cracks around doors and

windows. Wherever the air feels cold to the hand the air is entering.

_Experiment 12._ =Dust.=--With a mirror cause a sunbeam to play like

a search light into a closed room several hours after it has been

swept. Result? Do the same in a room where every window and door were

open during sweeping and left open afterwards. Result? Conclusion?

Note also the amount of dust on the furniture of each room.

_Experiment 13._ =Study of Habitual Quiet Breathing.=--Without any

more disturbance of the breathing than can be helped, direct your

attention to your breathing while sitting quietly. Record motions of

any parts of chest and abdominal walls that may be noticeable. If

necessary, lay the hands successively against different parts of the

wall to test for motion. Think of another subject, and later repeat

observations.

_Experiment 14._ =Study of Deep Breathing.=--Place your hands

successively upon the front and sides of your chest, waist, and

abdomen, while drawing in and sending out deep breaths. What motions

of the several parts are observed at each stage?

_Experiment 15._ =Study of Elasticity as a Factor in Breathing.=--(1)

Notice whether in quiet breathing there is an elastic rebound as the

breath goes either in or out. If so, it is due to the elasticity

of the cartilages or air cells of lungs, or both. (2) Breathe by

inflating the lungs strongly at each breath. Is the air then forced

out without effort? (3) Breathe by flattening the chest and abdomen

as much as possible at each breath. Does the air then rush in without

effort?

_Experiment 16._ =Chest Breathing.=--Try to breathe wholly by deep

expansions and contractions of chest wall. What motions, if any, are

noticed in abdominal wall as breath goes in? As it goes out? (Test

motions with hand.)

_Experiment 17._ =Abdominal Breathing.=--Try to hold the chest walls

still and breathe by strong contraction and expansion of abdomen. Do

the chest walls move at all? Neither “chest breathing” nor “abdominal

breathing” is the normal way. See text.

_Experiment 18._ =Full Breathing.=--Try breathing by outward and

inward movement of walls of chest, _waist_, and abdomen. Do you

succeed? This is normal breathing. Is the motion greater at the front

or the sides of the waist? Put a belt around the waist tight enough

to stay in place and repeat. Is the waist motion interfered with?

_Experiment 19._ =How the Ribs are Lifted.=--Make a model-like sketch

to represent backbone, breastbone, and two ribs, using pins to make

joints loose at corners. Use cords for diagonals. What happens when

cord _ac_ is pulled? When cord _bd_ is pulled? The cords correspond

to the two sets of muscles between the ribs.

[Illustration]

_Experiment 20._ =Study of Laughing.=--Place the hands upon the waist

and abdomen when laughing. What motion occurs at each sound of laugh?

Draw in the abdominal wall with a jerk. What is the effect upon the

breath?

_Experiment 21._ =Modifications of the Breath.=--Write I, E, or IE

after each word in this list, according as inspiration, expiration,

or both, are involved in the action. (Test with sham acts if

possible.) Sighing, sobbing, crying (of a child), coughing, laughing,

yawning, sneezing, hiccoughing, snoring.

_Experiment 22._ =Effects of Exercise.=--Count and record the rates

of breathing before and after vigorous exercise.

_Experiment 23._ =Comparative Study.=--Observe and record the rate

and manner of breathing of cow, horse, dog, cat, etc. Is the air

drawn in or sent out more quickly? Is there a pause? If so, after

which stage of breathing?

_Experiment 24._ =Emergency Drill.=--Resuscitation from drowning,

etc. See Coleman’s “Elements of Physiology,” page 356.

=Necessity for Breathing and for Specialized Organs of Breathing.=--The

body is a self-regulating machine which possesses energy. This

energy, like that of steam engines, arises from oxidation which takes

place continually, but at a varying rate. Food for fuel is taken at

intervals, but oxygen must be taken in continually. Man breathes about

eighteen times per minute. The blood in the tissues soon becomes

dark because of loss of oxygen and absorption of carbon dioxid. It

is then pumped through the heart to the organ which has the function

of absorbing oxygen and giving off carbon dioxid (Fig. 67). In some

animals, as the ameba and the earthworm, the surface of the body

suffices for breathing. This cell breathing is the true essential

respiration; it is universal among living things, both plants and

animals. _To supply the deeper cells large animals require a breathing

surface greater than the area of the skin. This is supplied by having

the oxygen-absorbing surface folded inward to form folds, tubes, and

cavities_ of great complexity. If the lungs of a man were unfolded and

all their tubes and cavities spread upon one surface, an area of more

than one hundred square feet (or ten feet square) would be covered.

Each =respiration=, or breath, consists of the passing in of the air,

or _inspiration_, sending it out, or _expiration_, and a _pause_ after

one but not after both of the other stages.

[Illustration: FIG. 67.--CIRCULATION THROUGH LUNGS (schematic):

“venous” blood (in pulmonary artery) black; “arterial” blood (in

pulmonary veins) white.]

[Illustration: FIG. 68.--OPEN MOUTH, showing palate and tonsils.]

[Illustration: FIG. 69.--LUNGS, _P_; with trachea, _TA_; thyroid gland,

_th_; larynx, _L_; and hyoid bone, _H_.]

=The Air Passages.=--The air usually passes in at the nose and

returns by the same way, except during talking or singing. Observe

your mouth with a mirror (Fig. 68); at the back part, an arch is seen

which is the rear boundary line of the mouth (Exp. 1). Just above

the arch is likewise the rear boundary line of the nasal passages.

The funnel-shaped cavity beyond, into which both the mouth and nasal

passages open, is called the _pharynx_ (far′inks), or throat (see Fig.

68, also Fig. 83). Below, two tubes open from the pharynx. One is

the _trachea_ (trā′kea) or windpipe, the other is the _esophagus_ or

_gullet_. At the top of the trachea is the cartilaginous _larynx_, or

voice box. If the finger is placed upon the larynx or Adam’s apple,

it is plainly felt to move up and down when swallowing. The opening

into the larynx is provided with a lid of cartilage, the epiglottis.

Inside the larynx, the vocal cords are stretched from front to back.

Just below the larynx comes the _trachea_ proper, which is a tube about

three fourths of an inch in diameter and about four inches long (Fig.

69). It consists of hoops of cartilage (Fig. 69) which are not complete

circles, but are shaped somewhat like the letter C, being completed at

the rear by involuntary muscular tissue, whose function is to draw the

ends together at times (for instance, during coughing) and reduce the

size of the tube. The function of the hoops of cartilage is to keep the

windpipe open at all times. If it should be closed by pressure, life

might be lost. These rings of cartilage may be felt in the neck.

[Illustration: FIG. 70.--LOBULE OF LUNG.]

The lower end of the trachea is just behind the upper end of the

breastbone; there it divides into two large tubes. These subdivide

into a great number of smaller branches called _bronchial tubes_.

Cartilage is found in the walls of all but the smallest of the tubes.

The subdivision continues, somewhat like the branching of a tree, until

the whole lung is penetrated by bronchial tubes. Each tiny tube finally

ends in a wider funnel-shaped chamber called a _lobule_ (Fig. 70), into

which so many dilated sacs, called _air cells_, open, that the walls of

the terminal chamber or lobule may be said to consist of tiny cups, or

air cells, placed side by side. The lobules, or clusters of air cells,

are chiefly near the surface of the lung. (The word “cell” is here used

in its original sense to denote a cavity or chamber, and not in the

sense of a protoplasmic cell.)

[Illustration: FIG. 71.--CAPILLARIES AROUND AIR SACS OF LUNGS (enlarged

30 diameters). Air sacs in white spaces. Dark lines are capillaries.

(Peabody.)]

The _air cells are elastic_ and enlarge by stretching as the chest

expands; hence, the cells must have many of the _yellow_ elastic fibers

of connective tissue in their walls. They are lined with an exceedingly

thin membrane of epithelial cells through which _oxygen and carbon

dioxid are exchanged_. In the walls of the air cells there is _a

network of capillaries_ (Fig. 71). The dark red blood comes into these

capillaries from the pulmonary arteries, and is changed to a bright red

by the time it leaves them to enter the pulmonary veins. The air leaves

the lungs warmer, moister, and containing more carbon dioxid than when

it entered.

Most of the =mucous membrane lining the air passages= has a surface

layer of ciliated cells. _Cilia are tiny thread-like projections_ (Fig.

72) which continually wave to and fro, the quicker stroke always being

outward; for their function is to remove particles of dust and germs

that may find entrance to the air passages. When the mucus containing

the dust is raised nearly to the larynx, it may be thrown out by

coughing. _Near the opening of the nostrils are placed many hairs_,

hundreds of times larger than cilia, through which the air is strained

as it enters the nose. Hairs are multicellular; cilia are parts of

cells. See Animal Biology, Fig. 14.

[Illustration: FIG. 72.--CILIATED CELLS, lining the air passages.]

=The Lungs.=--The entire _chest cavity_ is occupied by the lungs except

the space occupied by the heart, the larger blood vessels, and the

gullet. The right lung has three lobes, or divisions, and the left

lung has two lobes. The lungs are light pink in early life, but become

grayish and darker as age advances. This change is more marked in those

who dwell in cities, or wherever the atmosphere is smoky and dusty.

The lungs are covered and inclosed by a smooth membrane called the

_pleura_. This membrane turns back and lines the chest wall, so that

when the chest expands, the two sleek membranes glide over each other

with far less friction than would be the case if the lungs and chest

wall were touching (Exp. 2).

[Illustration: FIG. 73.--VERTICAL SECTION OF TRUNK, showing diaphragm,

cavities of thorax and abdomen.]

=The Respiratory Muscles.=--(Repeat Exps. 13, 14, 15.) The chief

breathing muscles are the _diaphragm_ (see Figs. 73 and 74), the

muscles _forming the abdominal walls_ (see Fig. 44), and _two sets of

short muscles_ (an internal and an external set), _between the ribs_.

They are called _intercostals_. (They are the flesh eaten when eating

pork ribs.) The _diaphragm_, which is shaped like a bowl turned upside

down, rounds up under the base of the lungs somewhat like a dome and

separates the chest from the abdomen. Its hollow side is toward the

abdomen and its edges are attached to the lowest ribs and the vertebra

of the loins. Inspiration is brought about by the rising of the ribs

and the descent of the diaphragm. Expiration takes place when the ribs

descend, the abdominal walls draw in, and the transmitted pressure

lifts the relaxed diaphragm.

[Illustration: FIG. 74.--DIAPHRAGM (or midriff), seen from below.

(Cunningham.)

The central portion (light) is tendinous. As the diaphragm descends, it

acts like the piston of a great pump and the blood is forced up through

the vena cava, and the lymph through the thoracic duct (Fig. 66).]

=Inspiration.=--To cause inspiration the diaphragm contracts, it

flattens and descends, since its edges are attached lower than its

middle (Fig. 73); the lungs descend with it, thus lengthening the

chest from top to bottom; at the same time the ribs are raised upward

and outward (Fig. 76) by the contraction of the outer set of muscles

between the ribs. Thus the _chest is made longer, broader, and deeper

from front to back_. The lungs expand when the chest expands, and the

air rushes in. Why is this? The lungs contain no muscles and cannot

expand themselves; the air cannot be pulled in, for its parts do

not stick together. The true reason is that the air has weight. The

atmosphere has a height of many miles, and the air above is pressing

on that below. When the chest walls are raised there would be an empty

space or vacuum between these walls and the lungs, did not the pressure

of _the outside air push air through the windpipe into the lungs and

expand them_ (Exp. 19).

[Illustration: FIG. 75.--FRAMEWORK OF CHEST.]

=Expiration.=--In very active breathing the abdominal walls actively

contract so that they press strongly upon the digestive organs, which

in turn _press the diaphragm up. The ribs are also drawn down and in_.

Thus the chest becomes smaller and forces the air to flow out through

the windpipe (Exps. 20 and 21).

[Illustration: FIG. 76.--BLACKBOARD SKETCH, to show how the chest is

expanded when the ribs move upward and outward.]

THOUGHT QUESTIONS.--_Why breathing with the waist is easier than

breathing with the upper chest. Effects of confining the waist_.

1. There are two pairs of ____ ribs below, while there are none

above. 2. There are three pairs of ____ ribs below, while there

are none above, but all ribs of the upper chest are ____ ribs. 3.

The lower of the joints between the seven pairs of true ribs and

the sternum are more flexible than the upper joints because ____.

(Observe the joints in Fig. 75.) 4. The walls of the waist swing ____

and ____, while the walls of the upper chest must move ____ and ____.

5. The bones of the ____ rest upon the upper chest. In upper chest

breathing their weight, and the weight of both of the ____ must,

therefore, be lifted. (Fig. 28.) Test by trying it.

[Illustration: FIG. 77.

FIG. 78.

FIG. 79.

FIG. 77.--FEMALE FIGURE ENCASED IN CORSET. Expansion at the waist is

here impossible and the breathing is called “collar-bone breathing.”

FIG. 78.--MALE FIGURE. Here, owing to pressure of clothing and faulty

position, expansion of chest is hindered and breath is taken by the

“abdominal method.”

FIG. 79.--FIGURE PROPERLY POISED AND FREE. Here the entire thorax can

move freely, and natural breathing is the result. (For blackboard.)

From Latson.]

=Hygienic Habits of Breathing.=--Chest breathing uses chest chiefly,

abdominal breathing uses abdomen chiefly, full breathing uses both.

These three forms depend upon whether the breathing is carried on

by using the muscles of (1) the chest, (2) the abdomen, or (3) both

(see Figs. 77, 78, 79). There has been much debate among physicians,

surgeons, and singers as to which of these methods is best. Probably

this question would not have been raised but for the confining and

deforming effect of clothing upon the waist. _Full breathing is used by

children of all races, by both men and women of wild tribes, and by men

of civilized countries._ It is undoubtedly the natural way, as well as

the easiest and most effective way (Exps. 16, 17, 18).

Breathing with the upper chest is exhausting because of the stiffness

of the upper part of the bony cage (see Fig. 75); for it is inclosed

by true ribs fixed to the breastbone by short cartilages. The ribs

in the waist (Fig. 75) are either floating in front or fixed by

long cartilages to the ribs above. In pure abdominal breathing

the diaphragm must contract more than in full breathing in order

to descend, because its edges have been drawn together and fixed

by binding the ribs at the waist. In full breathing the floating

and false ribs at the waist (five pairs in all) float in and out

as nature provided. As they move out, this broadens and deepens

the chest, and aids the flattening of the diaphragm by moving its

edges farther apart. Those persons, perhaps one in a thousand, who

voluntarily deform the body with tight clothing are beneath contempt.

But so uniform is the pressure of tight clothes and shoes that the

wearer soon becomes unconscious of them, and so powerful are the

effects that not one person in a thousand escapes deformity and

injury. Children’s clothing should be supported by the shoulders, and

adults’ clothing by both shoulders and hips, but by the waist, never.

=Cellular Respiration.=--The chemical activities within the cells and

their need of oxygen, not the amount of oxygen in the lungs or blood,

determine how much oxygen the cells absorb from the blood. Oxygen

cannot be forced even into the blood beyond the required amount. Deep

breathing movements, however, help the flow of the blood and lymph.

Carried to excess, they tire the will and exhaust the nerves.

=Changes in Blood while in the Lungs.=--The coloring matter

(or hemoglobin) of the corpuscles absorbs oxygen (and becomes

oxy-hemoglobin). Carbon dioxid is given off from the plasma. The blood

becomes a brighter red.