HUMAN BIOLOGY
CHAPTER I
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.
Fig. 1.—Facial Angles of Caucasian (nearly 90°) and Ethiopian (about 70°). The angle between lines crossing at front of upper jaw near base of nose, one line drawn from most prominent part of forehead, the other through hole of ear.
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.
Fig. 2.—Indian Weapons: Lance and Arrow Heads. From a bank of mussel shells (remains of savage feast) at Keyport, N.J.
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.
Fig. 3.—Indian Tomahawk. Polished Stone. Keyport, N.J.
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.
Fig. 4.—Primitive Man, showing clothing and weapons of chase and war.
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.
Fig. 5.—An Ameba, highly magnified. nu, nucleus; psd, false foot.
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.
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.
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.
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.
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.
Fig. 10.—Three Muscle Fibers from the heart (showing the nuclei of six cells).
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.
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.
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?
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.
Fig. 15.—Epithelial Tissue (epidermis of skin, magnified).
Fig. 16.—Epithelial Tissue; cells forming two glands in wall of stomach.
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.
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.
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.