Chapter XLIV: Introduction

To which _branch_ of animals does man belong? To which _class_ and _order_ in that branch? (Animal Biology, pages 125, 193.) There is no other animal _species in the same genus or order_ with man. This shows a wide _physical_ difference between man and other animals, but man’s _mind_ isolates him among the other animals still more.

The human species is divided into =five varieties= or races: 1. _Caucasian_ (Fig. 1). Skin fair, hair wavy, eyes oval. (Europe except Finns and Lapps, Western Asia, America.) 2. _Mongolian._ Skin yellow, hair straight and black, face flat, nose blunt, almond eyes. (Central Asia, China, Japan, Lapps and Finns of Europe, Eskimos of North America.) 3. _Americans._ Skin copper red, hair straight, nose straight or arched. (North and South America.) 4. _Malay._ Skin brown, face flat, hair black. (Australia and Islands of Pacific.) 5. _Ethiopian_ (Fig. 1). Skin dark, hair woolly, nose broad, lips thick, jaws and teeth prominent, forehead retreating, great toe shorter than next toe and separate. (Africa, America.)

There is a _struggle between the races_ for the possession of
different lands. The Caucasian is gaining in Australia, Africa, and
America. With difficulty the Mongolians are kept from the western
shores of America. The Ethiopian in America shows a lessened rate
of increase every decade; this may be due to the tendency of the
race to crowd into cities and the strain of suddenly changing from
jungle life in less than two centuries. _Civilization is a strain_
upon any race. It is destroying the American Indian. The Mongolian
and Caucasian survive civilization best, but insanity is increasing
rapidly among the latter.

=Man’s Original Environment.=--Primitive man lived without the use
of fire or weapons other than sticks or stones. His _first home
was in the tropics_, where his needs were readily supplied, and
probably in Asia. Many nations have a tradition of a home in a
garden (Greek, _paradisos_). His food was chiefly _tree fruits and
nuts_. When because of crowding he left nature’s garden, he acquired
skill in _hunting and fishing_ and the use of fire that flesh might
supplement the meager fruits of colder climates. His weapons were
of rough (chipped) stone at first--_in the old stone age_. In this
age the mammoth lived. He learned to polish implements in the _new
stone age_. The Indians were in that stage when Columbus came to
America (Figs. 2, 3). The cultivation of grain and the domestication
of animals probably began in this age. The _bronze_ and _iron ages_
followed the stone age.

=The Reaction between Man and his Environment.=--The estimates by
various geologists of the time man has existed as a species vary from
20,000 to 200,000 years. The _active life out of doors_ which man led
for _ages_ (Fig. 4) _has thoroughly adapted_ his body _only for such
a life_. Now steam and other forces work for him, and his _muscles_
dwindle; his _lungs_ are seldom fully expanded, and the unused
portions become unsound; he lives in tight houses, and the impure
air makes his _blood_ impure and his _skin_ delicate; he eats _soft
concentrated_ food, and his _teeth_ decay and his too roomy _food
tube_ becomes sluggish. His _nerves and brain_ are fully active and
they become unsound from overwork and impure blood.[3]

[3] It has been prophesied that the future man will be a brownie-like
creature with near-sighted eyes, shrunken body, slim little legs
and arms, large hairless head, toothless gums, a stomach using only
predigested food, muscles suited only to push an electric button
or pull a lever, and mind very active. But this disregards the
indispensable need of a sound mind for a sound body. There cannot even
be a play of emotion without a change in the circulation.

=Degeneration of Unused Parts.=--Several facts just stated illustrate
the biological law that _disuse causes degeneration_.

=Man’s Modification of his Environment.=--The energy of the world,
whether of coal, waterfall, oil, forest, or rich soil, has the sun
as its source. _All of these are being destroyed by man_, often
with recklessness and wantonness. The promised land which “flowed
with milk and honey” is now almost a desert. Other examples are
Italy, Carthage, Spain. The destruction of forests causes floods
which wash away the soil. _It is estimated that there are only one
fourth as many song birds in the United States as there were fifteen
years ago._ Insects and weeds or deserts replace rich soil, noble
quadrupeds, singing birds, and stately trees. Many farmers, however,
preserve the fertility of the soil.

=To the erect posture= is due man’s free use of his hands and
the _coöperation of hands and senses_. This has given man his
intellectual development. The erect position has given greater
freedom to the chest. _Man uses fewer organs of locomotion than
any other animal._ The opossum has two hands, but they are on
the hind limbs. The ape has four hands, but must use them all in
locomotion. (What is a hand?) The erect position, however, makes
_spinal deformity_ easier to acquire, and the _whole weight being
upon one hip_ at each step man is liable to hip-joint diseases.
In the horizontal trunk the organs lie one behind another; in man
they _lie one upon another_, and are more liable to _crowding_ and
_displacement_. The prone position in sickness helps to restore
them. Large blood vessels at neck, armpits, and groins, which occupy
protected positions in quadrupeds, are _held to the front and
exposed_ to danger. The _open end_ of the vermiform appendix and
of the windpipe are _upward_ in the erect trunk of man. Valves are
lacking in some vertical veins and present where little needed in
horizontal veins. But the _freedom of the hands_ more than makes up
for all the disadvantages of erectness.

=The Survival of the Fittest.=--_Those who do not work degenerate._
Those who overwork, or work with only a few organs, as the brain and
nerves, degenerate. The workers survive and _increase in numbers_,
the idle perish and _leave few descendants_.

=What rate of adjustment to new environment= is possible for man? This has not been ascertained; _it is probably much slower than has been generally imagined_. The natives of Tasmania, New Zealand, and many of the Pacific Islands became _extinct in less than a century_ after adopting clothing and copying other habits from Europeans. Life in the country in civilized lands differs less from the environment of primitive man than does life in cities. Cities have been likened to the lion’s cave in the fable, to which many tracks led, but from which none led. _The care of health in cities_ is now making rapid strides along the biological basis of purer air, more open space, less noise, simple food, and pure water. Biology, by supplying as a standard the conditions which molded man’s body for ages, furnishes a simple and sure basis for hygiene. To mention one instance among many, man blundered for centuries in attempting the cure of consumption, and well-nigh gave up in despair. Yet it has recently been shown that if the sufferer returns only in a measure to the open-air habits of his remote ancestors, tuberculosis is one of the most curable of diseases. The biological guide to health is surer and simpler than tinkering with drugs, fussing with dietetics, and avoiding exposure. _Man is of all animals least thoroughly adjusted to his environment_, because of his continual and rapid progress. _Disease_ may be defined as the _process by which the body adapts_, or attempts to adapt, _itself to_ so sudden a _change of environment_ that some organ has failed to work in harmony with the others. By disease the body comes into adjustment with the new condition, or attempts to do so.

=Protoplasm.=--The life and growth of man’s body, as the life and growth of all animals and plants, depend upon the activity of the living substance called _protoplasm_, as manifested in minute bodies called _cells_. In fact, protoplasm cannot exist outside of cells. The cells of the human body and their relation to the body as a whole will next be considered.

=The Ameba.=--Of all the animal kingdom, the _minute creatures that
can be seen only with a microscope_ are most different from man. One
of the most interesting of these is the _a-me′ba_ (Fig. 5; spelled
also _amœba_, see Animal Biology, Chap. II). _A thousand of them
placed in a row would hardly reach an inch._ Some may doubt whether
the ameba is a complete animal. Study the figures of it, and no head,
or arms, or legs, or mouth can be found. It appears, when still, to
be merely a _lump of jelly_. But the ameba can _push out any part
of its body as a foot_, and move slowly by rolling its body into
the foot. _It can put out any part of its body as an arm_, and take
in a speck of food; or, if the food happens to be near, the ameba
can _make a mouth in any part of its body_, and swallow the food by
closing around it (Animal Biology, Fig. 12). The ameba has no lungs,
but _breathes with all the surface of its body_. Any part of its body
can do anything that another part can do. When the ameba grows to a
certain size, it multiplies by squeezing together near the middle
(Animal Biology, Fig. 13) _and dividing into two parts_. Amebas have
not been observed to die of old age; starvation and accident aside,
they are immortal.

=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.

_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.

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.

=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=.

=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.

_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=.

_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?

_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.

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.

_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.

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.