Around each joint has grown up a strong sheath of tough, fibrous tissue to hold the bones together; and, inside this, between the heads of the bones, is a very delicate little bag, or pouch, containing a few drops of smooth, slippery fluid (synovial fluid) to lubricate the movements of the joint. This is sometimes called the "joint oil," though it is not really oil.

Bones are covered with a tough skin, or membrane (periosteum). They are hardest and most solid on their surfaces, and hollow, or spongy, inside. The long bones of the limbs are hollow, and the cavity is filled with a delicate fat called marrow—just as an elderberry stem or willow-twig is filled with pith. This tubular shape makes them as strong as if they were solid, and much lighter.[25]

The short, square, and flattened bones of the body, such as those of the wrist, the skull, and the hips, instead of being hollow inside are spongy; and the spaces in the bone-sponge are filled with a soft tissue called the red marrow in which new red and white corpuscles for the blood are born, to take the place of those which die and go to pieces.

FOOTNOTES:

[24] You can easily prove that a bone is made up of living tissue soaked and stiffened with lime, by putting it into a jar filled with weak acid. This will gradually dissolve and melt out the lime salts, and then you will find that the bone has lost three-fourths of its weight and that what remains of it is so soft and flexible that it can be bent, or even tied into a knot.

[25] The hollow spaces in the bones of birds, however, are filled with air, which makes them lighter for flying.



CHAPTER XX

OUR TELEPHONE EXCHANGE AND ITS CABLES

The Brain. We are exceedingly proud of our brain and inclined to regard it as the most important part of our body. So it is, in a sense; for it is the part which, through its connecting wires, called the nerves, ties together all the widely separated organs and regions in our body, and helps them to work in harmony with one another. We speak of it as the master and controller of the body; but this is only partially true.

The brain is not so much the President of our Cell Republic as a great central telephone exchange, where messages from all over the body are received, sifted, and transmitted in more or less modified form, to other parts of the body. Three-fourths of the work of the brain consists in acting as "middle-man," or transmitter, of messages from one part of the body to another. In fact, the brain is far more the servant of the body than its ruler; and depends for its food supply, its protection, its health, and its very life, upon the rest of the body. The best way to keep the brain clear and vigorous is to keep the muscles of the stomach, the liver, the heart, and the entire body in good health.

What the Brain Does. The brain is the very wonderful organ with which we do what we are pleased to call our thinking, and also a number of other more important things of which we are not conscious at all. It is a large organ, weighing nearly three pounds when full grown. In shape it is like an oval loaf of bread split lengthwise by a great groove down the centre, and with a curiously wrinkled or folded surface. The two halves of the brain, called hemispheres (though more nearly the shape of a coffee-bean), are alike; and each one, by some curious twist, or freak, of nature, receives messages from, and controls, the opposite half of the body—the right half controlling the left side of the body, while the left half controls the right side of the body. Thus an injury or a hemorrhage on the left side of the brain will produce paralysis of the right side, which is the side on which a stroke of paralysis most commonly occurs.

All the nerve fibres in each half or hemisphere of the upper brain run downward and inward like the sticks of a fan, to meet in a strap-like band, or stalk, which connects it with the base of the brain and the spinal cord. A very small amount of damage at this central part, or base, of the brain will produce a very large amount of paralysis. We may have large pieces of the bones of the skull driven into the outer surface of the brain, or considerable masses of our upper brain removed, or destroyed by tumors or disease, without very serious injury. But any disease or injury which falls upon the base of the brain, where these stalks run and big nerve-knots (ganglia) lie, will cause very serious damage, and often death.

The whole upper brain is a department of superintendence, which has grown up from the lower brain to receive messages, compare them with each other, and with the records of previous messages which it has stored up, thus giving us the powers which we call memory, judgment, and thought. Unfortunately, however, long and carefully as we have studied the brain, we really know little about the way in which it carries out these most important processes of memory, of judgment, and of thought, or even of the particular parts of it in which each of these is carried out.



No part of the brain, for instance, seems to be specially devoted to, or concerned in, memory or reason or imagination, still less to any of the emotions, such as anger, joy, jealousy or fear; so all those systems which pretend to tell anything about our mental powers and our dispositions by feeling the shapes of our heads, or the bumps on them, are pure nonsense.

The most important and highest part of the brain is its surface, a thin layer of gray nerve-stuff, often spoken of as the gray matter (the cortex, or "bark"), which is thrown into curious folds, or wrinkles, called convolutions. This gray matter is found in the parts of the nervous system where the most important and delicate work is done. The rest of the nervous system is made up of what is called white matter, from its lighter color; and this is chiefly mere bundles of telephone wires carrying messages from one piece of gray matter to another, or to the muscles.

We also know that a certain rather small strip of the upper brain-surface, or cortex, about the size of two fingers, running upward and backward from just above the ear, controls the movements of the different parts of the body. One little patch of it for the hand, another for the wrist, another for the arm, another for the shoulder, another for the foot, and so on. We can even pick out the little patch which controls so small a part of the body as the thumb or the eyelids. So when we have a tumor of the brain or an injury to the skull in this region, we can tell, by noticing what groups of muscles are paralyzed, almost exactly where that injury or tumor is. Then we can drill a hole in the skull directly over it and remove the tumor, lift up the splinter of bone, or tie the ruptured blood vessel.

Three other patches, or areas, running along the side of the brain, each of them about two inches across, are known to be the centres for smell, hearing, and sight, that for sight lying furthest back. Damage to one of these areas will make the individual more or less completely blind, or deaf, or deprived of the sense of smell, as the case may be.

At the lower part of the area which controls the muscles of the different parts of the body, above and a little in front of the tip of the ear, lies a very important centre, which controls the movements of the tongue and lips, and is known as the speech centre. If this should be injured or destroyed, the power of speech is entirely lost. This, curiously enough, lies upon the left side of the brain, and is the only one-sided centre in the body. Why this is so is somewhat puzzling, except that as speech is made up both of sound and of gesture, and our gestures are usually made with the right hand, it is not unreasonable to suppose that the speech centre should have grown up on that side of the brain which controls the right hand, which is, as you remember, the left hemisphere. What makes this more probable is that in persons who are "left-handed," the speech centre lies upon the opposite or right side of the brain. So it is waste of time and does more harm than good to try to "break" any child of left-handedness.

The Spinal Cord. Running downward from the base of the brain, like the stalk of a flower, is a great bundle of nerve-fibres, the central cable of our body telephone system, the spinal cord. This, you will remember, runs through a bony tube formed by the arches of the successive vertebrae; and as it runs down the body, like every other cable it gives off and receives branches connecting it with the different parts of the body through which it passes. These branches are given off in pairs, and run out through openings between the little sections of bone, or vertebrae, of which the spinal column is made up. They are called the spinal nerves, and each pair supplies the part of the body which lies near the place where it comes out of the cord.

The spinal nerves contain nerve wires of two sorts—the inward, or sensory, and the outward, or motor, nerves. The sensory, or ingoing, nerves come from the muscles and the skin and bring messages of heat and cold, of touch and pressure, of pain and comfort, to the spinal cord and brain. The outward, or motor, nerves running in the same bundle go to the muscles and end in curious little plates on the surface of the tiny muscle fibres, and carry messages from the spinal cord and brain, telling the muscles when and how to contract.

As the spinal cord runs down the body, it becomes gradually smaller, as more and more branches are given off, until finally, just below the small of the back and opposite the hip bones, it breaks up by dividing into a number of large branches which go to supply the hips and lower limbs.

While most of the spinal cord is made up of bundles of white fibres, carrying messages from the body to the brain, its central portion, or core, is made of gray matter. The reason for this is that many of the simpler messages from the surface of the body and the movements that they require are attended to by this gray matter, or ganglia, of the spinal cord without troubling the brain at all.

For instance, if you were sound asleep, and somebody were to tickle the sole of your bare foot very gently, the nerves of the skin would carry the message to the gray matter of the spinal cord, and it would promptly order the muscles of the leg to contract, and your foot would be drawn away from the tickling finger, without your brain taking any part in the matter, though, if you had been awake, you would of course have known what was going on.

This sort of reply to a stimulus, or "stirring up," without our knowing anything about it, is known as a reflex movement. Not only are many of these reflexes carried out without any help from the will, or brain, but they are so prompt and powerful that the brain, or will, can hardly stop them if it tries, as, for instance, in the case of tickling the feet. You can, if you make up your mind to it, prevent yourself from either wriggling, pulling your foot away, or giggling, when the sole of your foot is tickled; but if you happen to be at all "ticklish," it will take all the determination you have to do it, and some children are utterly unable to resist this impulse to squirm when tickled.

This extraordinary power of your reflexes has developed because only the promptest possible response, by jerking your hand away or jumping, will be quick enough to save your life in some accidents or emergencies, when it would take entirely too long to telephone up to the brain and get its decision before jumping. When you are badly frightened, you often jump first and discover that you are frightened afterwards; and this jump, under certain circumstances, may save your life. On the other hand, like all instinctive or impulsive movements, it may get you into more trouble than if you had kept still.

As you will see by the picture, the spinal nerves, which are given off from the cord in the lower part of the neck and between the shoulder blades, are gathered together into a great loose bundle to form the long nerve-wires needed to supply the shoulders and arms. Those given off from the small of the back just above the hips also run together to form, first a network and then a big single nerve-cord, called the sciatic nerve, which many of you have probably heard of from the frightfully painful disease due to an inflammation of it, called sciatica. It is the largest nerve-cord in the body, running down the middle of the back of the thigh to supply the muscles of two-thirds of the leg.[26]

The substance of both the spinal cord and the brain is made up of millions of delicate, tiny cells, called neurons, most of which, with very long branches, are arranged in chains for carrying messages, forming the white matter; while the others lie in groups, or ganglia, for sorting and deciding upon messages, forming the gray matter.

Just at the top of the spinal cord, where it passes into the skull and joins with the brain, it swells out into a sort of knob, about the size of a queen olive or the head of a gold-headed cane, which is known as the medulla, or "pith." This is the most vital single part of the entire brain and nervous system; and the smallest direct injury to it will produce instant death, partly because all the messages which pass between the brain and the body have to go through it, and partly because in it are situated the centres which control breathing and the beat of the heart, and another quite important but less vital centre,—that for swallowing.

How Messages are Received and Sent. Now to learn how smoothly and beautifully this nerve telephone system of ours works, and how simple it really is, although it has such a large number of lines and so many telephones on each line, and such a large central exchange, let us see how it deals with a message from the outside world. Suppose you are running barefoot and step on a thorn. Instantly the tiny nerve bulbs in the skin of the sole of your foot are stimulated, or set in vibration, and they send these vibrations up the sciatic nerve, into and up the whole length of the spinal cord, through the medulla, which switches them over to the other side of the brain up through the brain stalk, and out to the part of the surface (cortex) of the brain which controls the movements of the foot. All this takes only a fraction of a second, but it is not until the message reaches the brain-surface that you feel pain. If you were to cut the sciatic nerve, or even tie a string tightly around it, you could prick or burn the sole of your foot as much as you pleased, and you would not feel any pain at all.

As soon as the surface of the brain has recognized the pain and where it comes from, it promptly sends a return message back down the same cable, though by different nerve-wires, to the muscles of the foot and leg, saying, "Jerk that foot away!" As a matter of fact, this message will arrive too late, for the centres in the spinal cord will already have attended to this part of the matter, often almost before you know that you are hurt.

However, there is plenty of other work for the brain to do; and its next step, quicker than you can think, is to wake up a dozen muscles all over the body with the order, "Sit down!" And you promptly sit down. At the same time, the brain "central" has ordered the muscles of your arms and hands to reach down and pick up the foot, partly to protect it from any further scratch, and partly to pull the thorn out of it. Next it rushes a hurry call to the muscles controlling your lungs and throat, and says, "Howl!" and you howl accordingly. Another jab at the switchboard, and the eyes are called up and ordered to weep, while at the same time the muscles of the trunk of your body are set in rhythmic movement by another message, and you rock yourself backward and forward.

This weeping and rocking yourself backward and forward and nursing your foot seem rather foolish,—indeed you have perhaps often been told that they are both foolish and babyish,—but, as you say, you "can't help it," and there is a good reason for it. The howl is a call for help; and if the hurt were due to the bite of a wolf or a bear, or the cut had gone deep enough to open an artery, this dreadfully unmusical noise might be the means of saving your life; while the rocking backward and forward and jerking yourself about would also send a message that you needed help, supposing you were so badly hurt that you couldn't call out, to anyone who happened to be within sight of you. So that it isn't entirely babyish and foolish to howl and squirm about when you are hurt—though it is manly to keep both within reasonable limits.

If the message about the thorn had been brought by your eyes,—in other words, if you had seen it before you stepped on it,—then a similar but much simpler and less painful reflex would have been carried out. The image of the thorn would fall on the retina of the eye and through its optic nerve the message would be flashed to the brain: "There is something slim and sharp in the path,—looks like a thorn." When this message reached the brain, and not till then, would you see the thorn, just as in the case of the pain message from the foot. Then the brain would take charge of the situation just as before, flashing a hasty message to the muscles of the legs, saying, "Jump!" while its message to the throat and lungs, instead of "Yell," would be merely, "Say, 'Goodness!' or 'Whew!'" and you would say it and run on.

If the thing in the grass, instead of a thorn, happened to be a snake, and you heard it rustle, then the warning message would come through your ears to the brain, and you would jump just the same; though, as it is not so easy to tell by a hearing message exactly where the sound is coming from, you might possibly jump in the wrong direction and land on top of the danger.

This is the way in which you see, hear, and form ideas of things. Your eye telegraphs to the brain the colors; your ear, the sounds; and your nose, the smells of the particular object; and then your brain puts these all together and compares them with its records of things that it has seen before, which looked, or sounded, or smelt like that, and decides what it is; and you say you see an apple, or you hear a rooster crow, or you smell pies baking. Remember that, strange as it may seem, you don't see an orange, for instance, but only a circular patch of yellowness, which, when you had seen it before, and felt of it with your hand, you found to be associated with a feeling of roundness and solidness; and when you lifted it toward your nose, with the well-known smell of orange-peel; so you called it an orange. If the yellow patch were hard, instead of elastic, to the touch, and didn't have any aromatic smell when you brought it up to your nose, you would probably say it was a gourd, or an apple, or perhaps a yellow croquet ball. This is the way in which, we say, our senses may "deceive" us, and is one of the reasons why three different people who have seen something happen will often differ so much in their accounts of it.

It is not so much that our senses deceive us, but that we draw the wrong conclusions from the sights, sounds, and smells that they report to our brains, usually from being in too great a hurry and not looking carefully enough, or not waiting to check up what we see by touching, hearing, or tasting the thing that we look at.

This message-and-answer system runs all through our body. For instance, if we run fast, then the muscle cells in our legs burn up a good deal of sugar-fuel, and throw the waste gas, or smoke, into the blood. This is pumped by the heart all over the body, in a few seconds. When this carbon dioxid reaches the breathing centre in the medulla, it stirs it up to send promptly a message to the lungs to breathe faster and deeper, while, at the same time, it calls upon the circulation centre close to it, to stir up the heart and make it beat harder and faster, so as to give the muscles more blood to work with. If some poisonous or very irritating food is swallowed, as soon as it begins to hurt the cells lining the stomach, these promptly telegraph to the vomiting centre in the brain, we begin to feel "sick at the stomach," the brain sends the necessary directions to the great muscles of the abdomen and the diaphragm, they squeeze down upon the stomach, and its contents are promptly pumped back up the gullet and out through the mouth, thus throwing up the poisons.

And so on all over the body—every tiniest region or organ in the body, every square inch of the skin, has its special wire connecting it with the great telephone exchange, enabling it to report danger, and to call for help or assistance the moment it needs it.

FOOTNOTES:

[26] To give you an idea of what real things nerve-trunks are, this sciatic nerve is as large as a small clothes-line, or, more accurately, as a carpenter's lead pencil, and so strong that when the surgeon cuts down upon it and stretches it to cure a very bad case of sciatica, he can lift the lower half of the body clear of the table by it. This strength, of course, is not due to the nerve-fibres and cells themselves but to the tough, fibrous sheath, or covering, with which all the nerves that run outside of the brain and spinal cord are covered and coated. The spinal cord, though it is between one-half and three-fourths of an inch across, or about the size of an ordinary blackboard pointer, has little or none of this fibrous tissue in it, and is very soft and delicate, easily torn when its bony case is broken; hence its old name, the spinal marrow, from its apparent resemblance to the marrow, or soft fat, in the hollow of a bone.



CHAPTER XXI

THE HYGIENE OF BONES, NERVES, AND MUSCLES

HOW TO GET AND KEEP A GOOD FIGURE

Erect Position is the Result of Vigorous Health. Naturally and properly, an erect, graceful figure and a good carriage have always been keenly desired; and much attention has been paid to the best means of acquiring them; as we say, we try to "get the habit" of carrying ourselves straight and well. But it must be remembered that an erect figure and a good carriage are the results of health and vigor, rather than the cause of them.

Stooping, round shoulders, sitting "all hunched up," or a shuffling gait, are owing partly to bad habits, or "slouchiness," but chiefly to weak muscles and a badly-fed nervous system, often due to a poor digestion and a weak circulation. If a child is not healthy and vigorous, then no amount of drilling or reminders to "sit straight" and "stand erect" will make him do so.

It is of great importance that the child should take an erect and correct position for reading and writing, and while sitting at his desk; and that the desk and the seat should fit him. But it is more important that he should not sit at his desk in a stuffy room long enough to be harmed by a cramped position.

There are few children who will "hump over" at their desks, if the muscles of their backs and necks are strong and vigorous, and their brains well ventilated. Nor will many of them bore their noses into their books, or sprawl all over their copy books when they write, unless the light is poor, or they have some defect of the eyes which has not been corrected by proper glasses. A bad position or a bad carriage in a child is a sign of ill health, and should be treated by the removal of its cause.

Curvatures—Their Cause and Cure. There are various forms of curvatures, or bendings, of the spine which are supposed to be owing to faulty positions of sitting or of carrying the body. There is wide difference of opinions as to their cause; but this all are agreed on, that they practically never occur in sturdy, well-grown, active children; and the way that they are now corrected is by careful systems of balancing, muscular exercise, open-air life, and abundant feeding, instead of using steel braces, or jackets, or schoolroom drills.



Much the same is true of other deformities and defects of the body, as, for instance, round shoulders, or "flat-foot," or even such serious ones as "club-foot" and "bow-legs." Nearly all these are caused by the weakness or wrong action of some muscle, or groups of muscles. If this be long continued or neglected, the bones—which, you will remember, were made by the muscles in the first place—will be warped out of shape. When this has occurred, it is often necessary to bring back the limb, or foot, into a nearly straight position by mechanical or surgical means; but we now largely depend upon muscular exercises combined with rubbing and massage with the hand, and on building up the general vigor of the entire body, so that the muscles will pull the limb or the backbone back into proper position. Take care of the muscles, and the bones will take care of themselves! Make the body strong, vigorous, and happy, and it will "hold" and "carry" itself.

OUR FEET

The Living Arches of the Foot. One of the most important things to look after, if we wish to have an erect carriage and a swift, graceful gait, is the shape and vigor of the feet. Each foot consists of two springy, living arches of bone and sinew, which are also used as levers, one running lengthwise from the heel to the ball of the toes, and the other crosswise at the instep. These arches are built largely of bones, but are given that springy, elastic curve on which their health and comfort depend, and are kept in proper shape and position, solely by the action of muscles—those of the lower part of the leg and calf.



The purpose of these arches is to "give," or spring, like carriage springs, and thus break the shock of each step and cause the body to "ride" easily and comfortably. In order that a spring may "give," it must expand, or spread. Far the commonest and most serious cause of a poor, easily tired gait and a bad carriage is tight shoes, which, by being too short, or too narrow, or both, prevent the arches of the foot from "giving" and expanding. Not only does this produce corns, bunions, and lame feet, but it makes both standing and walking painful and feeble, and destroys the balance of the entire body, causing the back to ache, the shoulders to droop forward, and the neck muscles to tire themselves out trying to pull the head back so as to keep the face and eyes erect. Thus one soon tires, and never really enjoys walking. If this disturbance of balance is increased by high heels, thrust forward under the middle of the foot, the result is very bad.



Our Shoes, an Important Factor in Health. Few more ingenious instruments of crippling and torture have ever been invented than fashionable tight shoes with high heels.

Kipling never said a shrewder or truer thing than when he made Mulvaney, the old Irish drill-sergeant, tell the new recruit, "Remimber, me son, a soljer on the marrch is no betther than his feet!" and this applies largely to the march of life as well.

Every shoe should be at least three-quarters of an inch longer, and from half to three-quarters of an inch wider, than the foot at rest, to allow proper expansion of these great "carriage-spring" arches. If children run free in the open air, either barefoot, or with light, loose, well-ventilated shoes, or sandals, they will have little trouble, not only with bunions, corns, "flat-foot," or lameness, but also with their backs, their gait, and their carriage. Easily half of our backaches, and inability to walk far or run fast in later life, to say nothing of over-fatness and dyspepsia, are caused by tight shoes.

SLEEP AND REST

Why We Need Rest. A most important element in a life of healthful exercise, study, and play is rest. Even when we are hard at work, we need frequent breathing spells and changes of occupation and amusement to keep one part of our muscles, or our brains, from poisoning itself. But after a time, in even the strongest and toughest of us, there comes a period when no change of occupation, no mere sitting still, will rest us; we begin to feel drowsy and want to go to sleep. This means partly that the fatigue poisons, in spite of fresh air and change, have piled up faster than we can burn them, so that we need sleep to restore the body.

All day long we are making more carbon dioxid than the oxygen we breathe in can take care of; while we sleep, the situation is reversed—the oxygen is gaining on the carbon dioxid. This is why the air in our bedrooms ought to be kept especially pure and fresh.

But the need goes deeper than this: sleeping and waking are simply parts of the great rhythm in which all life beats—a period of work followed by a period of rest. Continuous, never-ceasing activity for any living thing quickly means death. While externally the body appears to be at rest, the processes of growth and upbuilding probably go on more rapidly when we are asleep than when we are awake. The benefits of exercise are made permanent and built into the body during the sleep that follows it. The more rapidly young animals are growing, the more hours out of the twenty-four they spend in sleep. When you sleep, you are not stopping all the useful activities of your body and mind, you are simply giving some of the most useful and most important of them a chance to work. The only likeness between sleep and death is that in both the body is quiet and the eyes are closed. Really we are never more alive and growing than when asleep.

It is of the utmost importance that young children especially have all the sleep they need, and that is precisely all that they can be induced to take. The best rule for you, then, to follow, is to go to bed when you feel sleepy, and to get up when you wake rested. Every child under twelve should have at least ten hours of sleep, and every grown person eight, or better still, nine hours. Time spent in sound, refreshing sleep, is time well spent. If you cannot sleep well, it is a signal that something is wrong with your health, or your habits—a danger signal of great importance, which should be attended to at once. The best and only safe sleep-producer is exercise in the open air.

DISORDERS OF MUSCLES AND BONES

The Muscles and Bones Have Few Diseases. Considering how complex it is, and the never-ceasing strain upon it, this moving apparatus of ours, the nerve-bone-muscle-machine, is surprisingly free from disease. The muscles, though they form nearly half our bulk, have scarcely a single disease peculiar to them, or chiefly beginning in them, unless fatigue and its consequences might be so regarded. They may become weakened and wasted by either lack or excess of exercise, by under-feeding, or by loss of sleep; but most of their disturbances are due to poisons which have got into the blood pumped through them, or to paralysis or other injuries to the nerves that supply them.

The muscles of an arm, for instance, which has been lashed to a splint, or shut tightly in a cast for a long time, waste away and shrink until the arm becomes, as we say, "just skin and bone"; and the same thing will happen if the nerve supplying a muscle, or a limb, is cut or paralyzed.

The bones have more diseases than the muscles, but really comparatively few, considering their great number and size, and the constant strain to which they are subjected in supporting the body, and driving it forward and doing its work under the handling and leverage of the muscles. Most of their diseases are, like those of the muscles, the after-effects of general diseases, particularly the infections and fevers, which begin elsewhere in the body; and the best treatment of such bone diseases is the cure and removal of the disease that caused them.



Repair of Broken Bones. If bones are broken by a fall, or blow, they display a remarkable power of repair. The "skin" covering them (periosteum) pours out a quantity of living lime-cement, or animal-mortar, around the two broken ends, which solders them together, much as a plumber will make a joint between the ends of two pipes. This repair substance is called callus. The most remarkable thing about the process is that, when it has held the two broken ends together long enough for them to "knit" firmly—that is, to connect their blood vessels and marrow cavities properly—this handful of lime-cement, which has piled up around the break, gradually melts away and disappears; so that, if the ends of the bone have been brought accurately together, you can hardly tell where the break was, except by a slight ridge or thickening.

TROUBLES OF THE NERVOUS SYSTEM

The Nervous System is not easily Damaged. The nervous system is subject to a good many more diseases than are either the muscles or the bones; but, considering how complex it is, it is not nearly so easily damaged or thrown out of balance as we usually imagine, and has astonishing powers of repair. Instead of being one of the first parts of the body to be attacked by a disease, such as an infection or a fever, it is one of the very last to feel the effects of disease, except in the sense that it often gives early that invaluable danger signal, pain.

Headache. Next after fatigue the most valuable danger signal given us by our nerves is that commonest of all pains, headache. Indeed, it is not too much to say that headache is the most useful pain in the world. It has little to do with the condition of the brain, but occurs in the head chiefly because the nerves of the head and face are the most sensitive of all those in the body, and the first ones, therefore, to "cry out" when hurt.

Headache has been described as the cry of a poisoned or starved or over-worked nerve, and is simply nature's signal that something is going wrong. Toxins, or poisons, formed anywhere in the body, from any cause, get into the blood, are carried to the sensitive nerves of the head and face, and irritate them so that they ache. It is foolish to try to do anything to the head itself for the relief of headache, although cold cloths, or a hot-water bottle, may be soothing in mild cases. The thing to do is to clear the poison out of the blood, and the only way is to find what has caused it.

Nearly all the things that cause headache do so by poisoning the blood. A very common cause of headache, for instance, is getting over-tired, especially if at the same time you do not get enough sleep; and, as you already know, tiredness, or fatigue, is a form of self-poisoning. Another very common cause of headache is bad air—sitting or sleeping in hot, stuffy rooms with the windows shut tight. If you do this, not only are you not getting oxygen enough into your blood to burn up the waste poisons that your own cells are making all the time, but also you are breathing in the waste poisons from other people's lungs, and the germs that are always in bad air.

Another very common cause of headache is eye-strain. Whenever you find that, when you try to read, the letters begin to dance before your eyes, and your head soon begins to ache, it is a sign that you need to have your eyes examined and perhaps a pair of glasses fitted to enable you to see properly.

Constipation and disturbances of digestion also very often cause headache by poisoning the blood; and, as you know, the first sign of a bad cold, or the beginning of a fever, or other illness, will often be a bad headache.

In short, a headache always means that something is going wrong; and the thing to do is to set to work at once to see if you can find out what has caused it, and then to remove the cause. If you cannot find out the cause, then go to a doctor and ask him to tell you what it is, and what to do to get rid of it.

Above all things, don't swallow a dose of some kind of headache medicine, and go on with your work, or your bad habits of eating, or using your eyes; because, even though it may relieve the pain, it doesn't do anything whatever to remove the cause and leaves you just as badly off as you were before you took it. Besides, most of these headache medicines, which for a time will relieve the pain of a headache, are narcotics, or pain-deadeners; and in more than very moderate doses they are poisons, and often dangerous ones. Those in commonest use, known as the "coal tar" remedies, because the chemists make them out of coal tar,[27] are likely to have a weakening effect upon the heart; and, while not very dangerous in small doses, they are very bad things to get into the habit of using.

The Exaggerated Claims of Patent Medicines. The same thing must be said of the habit of dosing yourself every time you feel a pain or an ache, with some sort of medicine, whether obtained at some previous time from a doctor, or bought at a drug store. A large majority of the medicines that are most widely advertised to cure all sorts of pains and aches contain some form of narcotic—most commonly either alcohol or opium. The reason for this is that no one medicine can possibly be a cure for all sorts of diseases; and the only kind of medicine that will make almost every one who takes it feel a little bit better for the time being is a narcotic, because it has the power of deadening the nerves to pain or discomfort.

Careful analyses by boards of health and government chemists of a great number of advertised medicines have shown that three-fourths of the so-called tonics and "bitters" and "bracers" of all sorts contain alcohol—some of them in such large amounts as to be stronger and more intoxicating than whiskey. The same investigations have found that a large majority of the "colic cures," "pain relievers," nearly all the "soothing syrups" and "teething syrups," and most of the cough mixtures, cough cures, and consumption cures contain opium, often in quite dangerous amounts. The widely-advertised medicines and remedies guaranteed to cure all sorts of diseases in a very short time are almost certain to be one of two things: either out-and-out frauds, costing about four cents a bottle and selling for fifty cents or a dollar, or else dangerous poisons. All patent pain relievers are safe things to let entirely alone.

Another risk in taking medicines wholesale, especially those that are known as patent medicines, is that you never can be quite sure what you are taking, as their composition is usually kept a strict secret. It may happen to be something very good for your disease, it may be entirely useless, and it may be something very harmful. There is no one drug, or medicine, known to the medical profession, that will cure more than one or two diseases, or relieve more than four or five disturbed and uncomfortable conditions. As you not only do not know what you are taking, but are not always quite sure what is the matter with you, the chances of your getting the right remedy for your disease are not much more than one in a hundred. If it isn't the right thing, you are certainly wasting your money, and may be doing yourself a serious injury.

We should not pour drugs of which we know little into a body of which we know less. Doctors give scarcely a fourth as much medicine now as they did fifty years ago. The best cures are food, exercise, sleep, and fresh air.

The Effects of Disease. In the case of nearly all infectious diseases, the effects on the nervous system are among the last to appear, and may not occur until weeks, months, or even years after the main fever or attack of sickness. This is one of the reasons why, when they do occur, they are often hard to cure; the whole system has become saturated with the poisons before they reach the nerves at all. So it happens that the idea has grown up that nervous diseases are very hard to cure. When, however, we know that two-thirds of them are a late result of some of the preventable infectious diseases and fevers, we can realize that it is perfectly possible to prevent them, and that prevention is the best cure.

The poisons that attack the brain and nervous system may be formed in the body by disease germs or brought in from without, as are alcohol, tobacco, lead, or arsenic. Even such mild infections as measles, scarlet fever, and influenza may poison certain nerves supplying the muscles of an arm or a leg, causing temporary paralysis, or even permanent laming; or they may attack the nerve of sight or of hearing and produce blindness or deafness.

A great many of the cases of paralysis and insanity are caused by alcohol. Alcohol in excess may attack the nerves supplying the arms and legs, producing severe pain and partial paralysis. It may also, after long-continued use, affect the cells of the brain itself, producing the horrible condition known as delirium tremens—a form of acute insanity with distressing delusions, in which the patient imagines that he sees rats, snakes, and other reptiles and vermin crawling over him, or in his room. Even in those who never use it to such excess as this, or indeed in those who may never become intoxicated, the long-continued use of alcohol may produce a slow poisoning and general breaking-down of the whole nervous system, causing in time the hand to tremble, the eye to become bleared and dim, the gait weak and unsteady, the memory uncertain, and the judgment poor.

Are Nervous Diseases Increasing? The direct use of the brain and nervous system has much less to do with the production of its diseases or even its serious disturbances than is usually believed. Most of these, as we have seen, are due either to the poisons of disease or alcohol, or to the fatigue-poisons, or other poisons, produced in the stomach, the liver, the muscles, or other parts of the body. The worst results of brain-work are due to the extent to which it deprives us of proper exercise and fresh air. Good, vigorous mental activity,—hard brain work, in fact,—when you are in good condition, is, if not overdone, as healthful and almost as invigorating as physical exercise or hearty play. We often hear it said that the rush and hurry of our modern strenuous life is increasing the number of mental diseases and nervous breakdowns. But there is no evidence that the strain of civilization upon our brains and nervous systems is damaging them, or that either nervous diseases or insanity are more frequent now than they used to be one hundred or five hundred years ago. In fact, all the evidence that we have points in exactly the opposite direction; for, as we have seen, most of these brain and nerve diseases are due to infectious diseases, bad food, and bad living conditions generally, all of which the progress of modern civilization is rapidly lessening and preventing.

We are collecting our insane in modern hospitals and comfortable homes, instead of letting them wander in rags about the country, and this makes them live longer and seem more numerous. But the poorest and least highly civilized classes and races have much more insanity among them than those who live under more favorable conditions.

FOOTNOTES:

[27] Some of these coal-tar remedies are Acetanilid, and Antipyrin, and Phenacetin.



CHAPTER XXII

EXERCISE AND GROWTH

Fatigue as a Danger Signal. The chief use of exercise in childhood, whether of body or mind, is to make us grow; but it can do this only by being kept within limits. Within these limits it will increase the vigor of the heart, expand the lungs, clear the brain, deepen sleep, and improve the appetite. Beyond these limits it stunts the body, dulls the brain, overstrains the heart, and spoils the appetite. How are we going to tell when these limits are being reached? Nature has provided a danger signal—fatigue, or "tiredness."

Fatigue is due, not to complete exhaustion, but to poisoning of the muscle, or nerve, by its own waste substances. If the fatigue is general, or "all over," it is from these waste substances piling up in the blood faster than the lungs, skin, and kidneys can get rid of them. In other words, fatigue is a form of self-poisoning.

We can see how it is that exercise, which, up to the point of fatigue, is both healthful and improving, when carried on after we are tired, becomes just the opposite. Fatigue is nature's signal, "Enough for this time!" That is why all methods of training for building up strength and skill, both of mind and muscle, forbid exercising beyond well-marked fatigue. If you yourself stop at this point in exercising, you will find, the next time you try that particular exercise, that you can go a little further before fatigue is felt; the third time, a little further yet; and so, by degrees, you can build up both your body and brain to the fullest development of which they are capable.

In muscular training, a series of light, quick movements, none of which are fatiguing, repeated fifteen, twenty, or a hundred times, will do much more to build up muscle and increase strength, than three or four violent, heaving strains that tax all your strength. Real athletes and skilled trainers, for instance, use half-or three-quarter-pound dumb-bells and one-or two-pound Indian clubs, instead of the five-pound dumb-bells and ten-pound clubs with which would-be athletes delight to decorate their rooms. A thoroughbred race-horse is trained on the same principle: he is never allowed to gallop until tired, or to put out his full speed before he is well grown. In fact, the best methods of all forms of exercising and training always stop just short of fatigue. Education and study ought to be planned on the same principle. Exercise of either our muscles or our minds after they have begun to poison themselves through fatigue never does them any good, even if it does not do them serious harm; and, where the exercise is for the sake of building us up and developing our powers, it is best to stop for a little while, or change the task, as soon as we begin to feel distinctly tired, and then to try it again when we are rested.



This is one of the secrets of the healthfulness and value of play and games for children, and for older persons as well. When you get tired, you can stop and rest; and then start in again when you feel rested—that is to say, when your heart has washed the poisons out of your muscles and nerves. In fact, if you will notice, you will find that nearly all play and games are arranged on this plan—a period of activity followed by a period of rest. Some games have regular "innings," with alternate activity and rest for the players; or each player takes his turn at doing the hard work; or the players are constantly changing from one thing to another—for instance, throwing or striking the ball one minute; running to first base the next; and standing on base the next. Every muscle, every sense, every part of you is exercised at once, or in rapid succession, and no part has time to become seriously fatigued; so that you can play hard all the afternoon and never once be uncomfortably tired, though your muscles have done a tremendous lot of work, measured in foot-pounds or "boy-power," in that time.

The good school imitates nature in this respect. The recitation periods are short, and recesses frequent; a heavy subject is followed by a lighter one; songs, drawing, calisthenics, and marching are mixed in with the lessons, so as to give every part of the mind and body plenty to do, and yet not over-tire any part.

All-Round Training from Work and Play. Every game that is worth playing, every kind of work that accomplishes anything worth while, trains and develops not merely the muscles and the heart, but the sight, hearing, touch, and sense of balance, and the powers of judgment, memory, and reason, as well.

If you are healthy, you know that you don't need to be told to play, or even how, or what, to play; for you would rather play than eat. You have as strong and natural an appetite for play as you have for food when you are hungry, or for water when you are thirsty, or for sleep when you are tired. It is just as right to follow the one instinct as the others, though any one may be carried to extremes.

Some of the most important part of your training and fitting for life is given by plays and games. Not only do they put you in better condition to study and enjoy your work in school, but they also teach you many valuable lessons as well. Our favorite national game, base-ball, for instance, not only develops the muscles of your arms and shoulders in throwing the ball and in striking and catching it, and your lungs and heart in rushing to catch a fly or in running the bases, but also develops quickness of sight and hearing,—requires, as we say, "a good eye" for distance,—makes you learn to calculate something of the speed at which a ball is coming toward you or flying up into the air, requires you to judge correctly how far it is to the next base and how few seconds it will take to get there and whether you or the baseman can get there first.

More important yet, like all team games, it teaches you to work with others, to obey orders promptly, to give up your own way and do, not what you like best, but what will help the team most; to keep your temper, to bend every energy to win, but to play fair. It also teaches you that you must begin at the beginning, take the lowest place, and gradually work yourself up; and that only by hard work and patience and determination can you make yourself worth anything to the team, to say nothing of becoming a "star" player.

If you will just go at your studies the way you do at base-ball, you will make a success of them. Make up your mind to gain a little at a time, to learn something new every day, and you will be astonished how your knowledge will mount up at the end of the year. When you first start in a new study, it looks, as you say, "like Greek" to you. You feel quite sure that you never will be able to understand those hard words or solve those problems "clear over in the back of the book." But remember how you started in on the diamond as a "green player," with fumbling fingers that missed half the balls thrown to you, with soft hands that stung every time you tried to stop a "hot" ball; how you ducked and flinched when a fast ball came at you, and how you fumbled half your flies and, even when you fielded them, were likely to send them in six feet over the baseman's head. But by quietly sticking to it—watching how the good players did it, and playing an hour or two every day during the season—you gradually grew into the game, until, almost without knowing how it happened, you had trained your muscles, your nerve cells, and your brain and found yourself a good batsman and a sure catcher.



So it will be in your school work. Just stick quietly to it, taking your work a lesson at a time; give yourself plenty of sleep and plenty of fresh air, and eat plenty of good food three times a day, and your mind will grow in strength and skill as gradually, as naturally, and as happily as your body does.

Every season of the year has its special games suited to the weather and the condition of the ground. If you take pride in playing all of them in their turn, hard and thoroughly, and making as good a record in them as you can, you will find that it will not only keep you healthy and make you grow, but will help you in your school work as well, by keeping your wits bright and your head clear. There is a fine group of running games, for instance, such as Prisoner's Base, or Dare Base, Hide-and-Seek, or I Spy, and the different kinds of tag,—Fox-and-Geese, Duck-on-Rock,—which are not only capital exercise for leg muscles, lungs, and heart, but fine training in quickness of sight, quickness and accuracy of judgment, and quickness of ear in catching the slightest rustle on either side, or behind you, so that you can rush back to the base, or "home," first.

Then with the winter comes skating, with hockey and Prisoner's Base on the ice, and coasting and sledding and snow-balling, to say nothing of forts and snowmen. You should try to be out of doors as many hours a day in the winter-time as in the summer, so far as possible. If you play and romp hard, you will find that you don't mind the cold at all, and that, instead of taking more colds and chills, you will have fewer of these than you had when you cooped yourself up indoors beside the warm stove.



It is just as important for girls to play all these games as it is for boys; and girls enjoy them just as much and can play them almost, if not quite, as well, if they are only allowed to begin when they are small and do just as they please. There is no reason whatever why a girl should not be just as quick of eye and ear, and as fast on the run, and as well able to throw or catch or bat a ball, as a boy. Up to fifteen years of age boys and girls alike ought to be dressed in clothes that will allow them to play easily and vigorously at any good game that happens to be in season. Girls like base-ball as well as boys do, if they are only shown how to play it.

In summer, of course, the whole wide world outdoors turns into one great playground; and it is largely because we turn out into this playground that we have so much less sickness, and so many fewer cases of the serious diseases like tuberculosis, pneumonia, and rheumatism in summer than in winter.

Boys and girls ought to know how to swim and how to handle a boat before they are twelve years old; for these are not only excellent forms of exercise and most healthful and enjoyable amusements in themselves, but they may be the means of saving lives—one's own life or the lives of others.

As a form of exercise and education combined, nothing is better than walks in the country or, where this is impossible, in parks and public gardens. An acquaintance with trees, flowers, plants, birds, and wild animals, is one of the greatest sources of enjoyment and good health that any one can have all his life through.

Last, but not by any means least, comes that delightful combination of work and play known as gardening, and the lighter forms of farming. Every child naturally delights in having a little patch of ground of his own in which he can dig and rake and weed and plant seeds and watch the plants grow. In our large cities, where most of the houses have not sufficient space about them to allow children to have gardens of their own at home, land is being bought near school-houses and laid out as school gardens, and the work done in them is counted as part of the school work. Indeed, so important is this work considered as a part of school education, that some large cities are actually building their schools out in the open country, so that they can have plenty of space for playgrounds and gardens and shops, and carrying the children from the central parts of the city out to them by trolley or train in the morning and back at night.



Wherever you happen to live, you should engage in healthy happy, vigorous play in the open air at least two to four hours a day all the year round. If you live in a town, while it will not be quite so easy to reach the woods and the fields and the swimming holes and the skating ponds, yet you will have a large number of playmates of your own age, and have good opportunity to play the games calling for half a dozen or more players; and there will be plenty of vacant lots and open spaces, or little-traveled streets, in which to play base-ball and foot-ball and Prisoner's Base and tag. And although you may not be within reach of the best zoological garden ever made,—a barnyard,—yet you can make occasional trips to the city "Zoo," or the botanical gardens, or to parks.

Healthful Methods of Study. In the growth and training of the highest, most valuable, and most wonderful part of the body—the brain—the same methods followed in our outdoor games will give the best results. We do not create intelligence by study, nor manufacture a brain for ourselves, in school. We simply develop and strengthen and improve the brains and the mental power that we were born with.



Our minds grow as our bodies do, by healthful exercise—little at a time, with plenty of rest and change of occupation between the periods of work. That is why our school studies are arranged as they are: instead of one subject being studied all the morning, or all day, four or five subjects are studied for twenty or thirty minutes each, and a change is made to another before our minds become over-tired and begin poisoning themselves with fatigue toxins. A subject that is rather hard for us is followed by one that is easier; and the hardest subjects in the course are usually taken up early in the morning session, or after recess, or early in the afternoon, when we are well-rested and feeling fresh and ready for work.

We should try to keep our bodies and our brains and our sight and hearing in the very best possible condition for our work, so as to come up to each task that we have to master keen and fresh and clear-headed, rather than to take pride in spending so many hours a day studying in a half-tired, half-hearted, listless kind of way. You will find that you will be able to master a lesson and see through a problem in half the time if you get plenty of sleep in a room with the windows open, play a great deal out-of-doors, and do not hurry through your meals for either school or play.



Study just as you play ball when you are trying to make a place on the team. Bend every energy that you have to that one thing, and forget everything else, until you have finished it. You can do more work in fifteen minutes in this way than you can in forty minutes of sitting and looking out of the window and wondering how much longer the study period is to last, and what the next chapter is about in the story that you are reading at home, or what you are going to wear to the party next week.

Keep yourself in good condition, and then buckle down to your work as if that were the only thing there was in the world for the time being, and you will be surprised to find, not only how much more easily and quickly you will do your work, but how much better you will remember it afterwards. Do not set out to accomplish too much at a time; but when you undertake a task, don't let go until you have finished it. If you will train yourself in this way, you will soon find that it will seldom take you longer to master a lesson than it will to recite it. It is becoming more and more the custom in the best schools to plan to do all the school work in school hours, alternating periods of recitation and play with periods of study, so that no school-books need be taken home at night. This cannot always be done; but it is well to come as near to it as possible, in order, first, to learn to do work quickly and thoroughly and to drop it when it is finished, and, secondly, to give time to playing and resting and forming the priceless habit of reading. You will leave school some day, but you may still be a student in the great University of Books; and the pleasure of widening your knowledge and kindling your imagination will never fail you or pall on you as long as you live. An evening spent with newspapers and magazines, with books of travel and adventure, with good stories and poetry, with enjoyable and sensible parlor games such as authors, checkers, chess, charades, and with music and singing, will help you more with your lessons next day than two hours of listless yawning over text-books.



If you take your school work in this spirit, you will find that you will enjoy it quite as well as any other form of exercise—even play itself. The harder and more intelligently you play, the better you will be able to work in the schoolroom; and the harder and more intelligently you study, the more you will enjoy your play.



CHAPTER XXIII

THE LOOKOUT DEPARTMENT

Why the Eyes, Ears, and Nose are Near the Mouth. If you had no eyes, ears, or nose, you might just as well be dead; and you soon would be, if you had no one to feed you and guide you about and take care of you. Naturally, all three of these scouts and spies of the body, which warn us of danger and guide us to food and shelter, are near the mouth, at the head-end of the body. The nose by means of which we smell food, to see whether it is sweet and good or not, is directly above the mouth; the eyes are above and on each side, like the lamps of an automobile, but swinging in sockets like search-lights; while the ears are a couple of inches behind, on each side of us, for catching from the sea of air the waves that we call sound.

You could almost guess what each of these is for, just by looking at it. The nose and the ears are open and hollow because air must pass into them in order to bring us odors or sounds; while the eyes are solid, somewhat like big glass marbles, to receive light—because light can go right through anything that is transparent. Eyes, ears, and nose all began on the surface, and sank gradually into the head, so as to be surrounded and protected, leaving just opening enough at the surface to allow smells, light-rays, and sound-waves to enter; and all of them have at their bottom, or deepest part, a sensitive patch of surface, which catches the light, or the smells, or the sounds, and sends them by a special nerve to the brain.

These three sets of organs have gradually and slowly grown into the shape in which we now find them, in order to do the particular kind of smelling, seeing, and hearing that will be most useful to us. Every kind of animal has a slightly different shape and arrangement of eye, of ear, and of nose to fit his particular "business"; but in all animals they are built upon the same simple, general plan.

THE NOSE

How the Nose is Made. The nose began as a pair of little puckers, or dimples, just above the mouth, containing cells that were particularly good smellers, in order to test the food before it was eaten. All smells rise, so these cells were right on the spot for their particular "business."

The original way of breathing, before the nose-dimples or pits opened through into the throat, was through the mouth; and that is one reason why it is so easy to fall into the bad habit of mouth-breathing whenever the nose gets blocked by adenoids or catarrh. Some creatures—fishes, for instance,—breathe through their mouths entirely; if you watch one in an aquarium or a clear stream, you will easily see that it is going "gulp, gulp, gulp" constantly. The saying "to drink like a fish" is a slander upon an innocent creature; for what it is really doing is breathing, not drinking. Even a frog, which has nostrils opening into its throat, still has to swallow its air in gulps, as you can see by watching its throat when it is sitting quietly. And, strange as it may seem, if you prop its mouth open, it will suffocate, because it can no longer gulp down air.[28]

Our noses are nine-tenths for breathing, and only about one-tenth for smelling; so that by far the greater part of the nose is built on breathing lines. But the smelling part of it, though small, is very important, because it now has to decide, not merely upon the goodness or badness of the food, but also upon the purity or foulness of the air we breathe. The nostrils lie, as you can see, side by side, separated from each other by a thin, straight plate of gristle and bone known as the septum. This should be perfectly straight and flat; but very often when the nose does not grow properly in childhood, it becomes crumpled upon itself, or bulged over to one side or the other, and so blocks up one of the nostrils. This is a very common cause of catarrh, and requires, for its cure, a slight operation, a cutting away of the bulging or projecting part of the septum. The rims of the openings of the nose, known as the wings, have little muscles fastened to them which pull them upward and backward, thus widening the air openings or, as we say, dilating the nostrils. If you will watch any one who has been running fast, or a horse that has been galloping, you will see that his nostrils enlarge with every breath; and these same movements occur in sick people who are suffering from disease of the lungs or the heart, which makes it difficult for them to get breath enough.

Each nostril opens into a short and rather narrow, but high, passage, known as the nasal passage, through which the air pours into the back of the throat, or pharynx, and so down into the windpipe and lungs. Instead of having smooth walls, however, the passage is divided into three almost separate tubes, by little shelves of bone that stick out from the outer wall. These are covered with thick coils of tiny blood vessels, through which hot blood is being constantly pumped, like steam through the coils of a radiator, so that the air, as it is being drawn into the lungs, is warmed and moistened. The passage is lined with a soft, moist "skin," called mucous membrane, very much like that which lines the stomach and bowels, except that it is covered with tiny little microscopic hairs, called cilia, and that its glands pour out a thin, sticky mucus, instead of a digestive juice. This thick network of blood vessels just under the thin mucous "skin" is easily scratched into or broken, and then we have "nose-bleed."

The purpose of this mucus is to catch and hold, just as flypaper catches flies, all specks of dust, lint, or germs that may be floating in the air we breathe, and to keep them from going on into the lungs. As these are caught upon the lining of the nose, they are washed down by the flow of mucus or wafted by the movement of the tiny hairs back into the throat, and swallowed into the stomach, where they are digested. Or, if they are very irritating, they are blown out of the nostrils, or sneezed out, and in that way got rid of.

If the dust is too irritating, or the air is foul and contains disease germs, these set up an inflammation in the nose, and we "catch cold," as we say. If we keep on breathing bad or dusty air, the walls of the nasal passages become permanently thickened and swollen; the mucus, instead of being thin and clear, becomes thick and sticky and yellowish, and we have a catarrh.

Catarrh is the result of a succession of neglected "bad colds," caused, not by fresh, cold air, but by hot, stuffy, foul air containing dust and germs. The best and only sure way to avoid catarrh is by breathing nothing but fresh, pure air, day and night, keeping your skin clean and vigorous by cool bathing every day, and taking plenty of play in the open air.

So perfect is this heating, warming, and dust-cleansing apparatus in the nose, that by the time quite cold air has passed through the nostrils, and got down into the back of the throat, it has been warmed almost to the temperature of the body, or blood-heat, and has been moistened and purified of three-fourths of its dust or disease germs. When you go out of doors on a cold, frosty morning, your nose is very likely to block up, because so much hot blood is pumped into these little steam-coils of blood vessels, in order to warm the air properly, that they swell until they almost block up the nostrils.

The Sense of Smell. The lower three-fourths of the nasal passages have nothing whatever to do with the sense of smell; this is found only in the highest, or third, division of the passages, right up under the root of the nose, where odors can readily rise to it. Here can be found a little patch of mucous membrane of a deep yellowish color, which is very sensitive to smells, and from which a number of tiny little nerve twigs run up to form the nerve of smell (olfactory nerve), which goes directly to the brain. The position of the smell area at the highest and narrowest part of the nose passage explains why when you have a very bad cold, you almost lose your sense of smell; the lining of the lower part of the nose has become so inflamed and swollen as to block up the way to the highest part where the smelling is done.



Adenoids. If colds are neglected and allowed to run on, the inflammation spreads through the nose back into the upper part of the throat, or pharynx. Here it attacks a spongy group of glands, like a third tonsil, which swells up until it almost blocks up the nose and makes you breathe through your mouth. These swollen glands are called adenoids, and cause not only mouth-breathing, but deafness, loss of appetite, indigestion, headache, and a stupid, tired condition; so that children that are mouth-breathers are often two or more grades behind in school, poor students, and even stunted and undersized. You can often tell them at sight by their open mouths and vacant, stupid look. A very simple and harmless scraping operation will remove these adenoids entirely, and what a wonderful improvement the mouth-breather will make! He will often catch up two grades, and gain two inches in height and ten pounds in weight within a year.



Adenoids not only cause deafness by blocking up the tube (Eustachian) that runs from the throat to the ear,—the tube through which the air passes when your ear "goes pop,"—but are also the commonest cause of ear-ache and gatherings in the ear, which may burst the drum.

THE TONGUE

The Tongue is not Used chiefly for Tasting. If you will notice the next time that you have a bad cold, you will find that you have almost lost your sense of taste, as well as of smell, so that everything tastes "flat" to you. This illustrates what scientists have known for a long time, but which seems very hard to believe, that two-thirds of what we call taste is really smell. If you carefully block up your nostrils with cotton or wax, so that no air can possibly reach the smell region at the top of them, and blindfold your eyes, and have some one cut a raw potato, an apple, and a raw onion into little pieces of the same size and shape, and put them into your mouth one after the other, you will find that it is difficult to tell which is which.

The only tastes that are really perceived in the mouth are bitter, sweet, sour, and salty; and even these are perceived quite as much by the roof and back of the mouth, especially the soft palate, as they are by the tongue. All the delicate flavors of our food, such as those of coffee or of roast meat or of freshly baked bread, are really smells.

The tongue, which is usually described as the organ of taste, is really a sort of fingerless hand grown up from the floor of the mouth—to help suck in or lap up water or milk, push the food in between the teeth for chewing, and, when it has been chewed, roll it into a ball and push it backward down the throat. It is not even the chief organ of speech; for people who have had their tongues removed on account of cancer, or some other disease, can talk fairly well, although not so clearly as with the whole tongue.

The tongue is simply a "tongue-shaped" bundle of muscles, covered with a thick, tough skin of mucous membrane, dotted all over with little knob-like processes called papillae, which are of various shapes, but of no particular utility, except to roughen the surface of the tongue and give it a good grip on the food. If the mucous "skin" covering the tongue does not shed off properly, the dead cells on its surface become thickened and whitish, and the germs of the mouth begin to breed and grow in them, forming a sort of mat over the surface. Then we say that the tongue is badly coated. This coating is in part due to unhealthy conditions of the stomach and bowels, and in part to lack of proper cleaning of the mouth and teeth.

The Sense of Taste can usually be Trusted. Since the nose and the tongue have had about five million years' experience in picking out what is good and refusing what is bad, their judgment is pretty reliable, and their opinion entitled to the greatest respect. As a general thing, those things that taste good are wholesome and nutritious; the finest and most enjoyable flavors known are those of our commonest and most wholesome foods, such as good bread, fresh butter, roast meats, apples, cheese, sugar, fruit, etc.; while, on the other hand, those things that taste bad or bitter or salty or sour, or that we have to learn to like, like beer or pickles or strong cheese or tea or coffee, are more often unwholesome or have little nutritive value. Very few real foods taste bad when we first try them. If we used our noses to test every piece of food that went into our mouths, and refused to eat it if it "smelt bad," we should avoid many an attack of indigestion and ptomaine poisoning. It is really a great pity that it is not considered polite to "sniff" at the table.

THE EYE

How the Eye is Made. Next in importance after the smell and the taste of our food comes the appearance of it; hence, our need of eyes to help us in choosing what to eat, as well as how to avoid the dangers about us.

The eyes began as little sensitive spots on the surface of the head. Like the nose pits, as they became more sensitive, they too sank in beneath the surface; but with this difference, that, instead of remaining open, the rims or edges of the eye-pit grew together and became transparent, forming a cover, or eye-glass, which became the clear part of the eye, called the cornea. At the same time, the little sensitive spot at the bottom of the eye-pit spread out into the shape of the bottom of a cup, called the retina; and then the hollow of that cup between the retina and the cornea filled up with a clear, soft, animal jelly called the vitreous humor, and we have the eye as it is in our heads to-day.

The sensitive retina, spreading out, as it does, to form the back of the eyeball, is the nerve-coat of the eye; and from its centre a thick round bundle of nerve fibres, known as the optic nerve, runs back to the brain.



The bones of the head, grown out in a ring in order to protect the eyes, are called the orbit or socket.

To protect the delicate glass (cornea) of the eye, there are two folds of skin, one above and one below, known as the eyelids. The eyelids carry a row of extra long hairs at their edges, called the eyelashes, and a number of little glands, somewhat like those of the stomach, to pour out a fluid, which makes the lids glide smoothly over the eyeball and keeps them from sticking together. Underneath the upper lid a number of these glands become gathered together and "grow in," after the fashion of the salivary glands, to form a larger gland about the size of a small almond, which pours out large amounts of this fluid as tears. It is called the tear gland (lachrymal gland).

Whenever a cinder or a grain of sand or a tiny insect or any other irritating thing gets into the eye, this gland pours out a flood of tears, which washes the intruder down into the inner corner of the eye where it can be wiped out; or, if it be small enough, carries it down through a little tube in the edge of each eyelid, through a little passage known as the nasal, or tear, duct, into the nose. So, if you get anything into your eye, much the best and safest thing to do is to hold the lids half shut, but as loose, or relaxed, as possible, and allow the tears to wash the speck of dust down into the inner corner of the eye. If you squeeze down too hard with the lids, and particularly if you rub the eye, you will be very likely to scratch the cornea with the speck of dust or sand, or, if the speck be sharp-edged, to drive it right into the cornea and give yourself a great deal of unnecessary pain and trouble, or even seriously damage the eye. If the cinder or dust doesn't wash down quickly, pull the upper lid gently away from the eyeball by the lashes and hold it there a minute or so, when often the cinder will drop or wash out.

As the light rays cannot be bent, or drawn into the eyes as smells can into the nostrils, it is necessary that the eyes should be able to roll about so as to turn in different directions; and so nature has made them round, or globular, attaching to their outer coat or shell (the sclerotic coat) little bands of muscle, each of which pulls the eyeball in its particular direction. There are four straight bands—one for each point of the compass: one fastened to the upper surface of the eye to roll it upward; another to the lower to roll it downward; another to the outer to roll it outward; and another to the inner side to roll it inward for near vision.[29]

There is another reason for the rounded shape of the eye—that it may act as a lens in condensing the rays of light. In order that we may see things clearly, the rays of light must be brought to a focus upon or close to the retina, at the back of the eye; and our eyes are so shaped that they form a lens of proper thickness, or strength, to do this.

You can see how this is done with an ordinary magnifying glass, or burning-glass. The little sharply lighted and heated point to which the light-rays can be brought is the focus of the lens, and the distance it lies behind the lens is called the focal distance. The thicker the lens, or burning-glass, is in the middle, the shorter its focal distance, and the more strongly it will magnify.

A healthy, or normal, eye is of just such shape and "bulge" that rays of light entering the eye are brought to a focus on, or close to, the retina at the back of the eyeball. Some people, however, are unfortunately born with eyes that are too small and flat, or do not "bulge" enough; and then the rays of light are focused behind the retina instead of upon it, and the image is blurred. This is known as "long sight" (hyperopia), and can be corrected by putting in front of the eyes lenses of glass, called spectacles, which bulge sufficiently to bring the rays to focus on the retina.

An eye that is too large and round and bulging brings the rays to a focus in front of the retina, and this also blurs the image. This form of poor sight is called "short sight" (myopia), and can be relieved by putting in front of the eye a glass that is concave, or thinnest in the middle and thickest at the edges, in the right proportions to focus the image where it belongs, right on the retina. This kind of glass is sometimes called a "minifying" glass, from the fact that it makes objects seen through it look smaller. It is also called a "minus" glass, while the magnifying glass is called a "plus" glass. The shape of the glasses or spectacles prescribed for an eye is just the opposite of that of the eye. If the eye is too flat (long-sighted), you put on a bulging, or convex, glass; and if the eye is too bulging (short-sighted), a hollow, or concave, glass. Other eyes are irregularly shaped in front and bulge more in one direction than another, like an orange. This defect is called astigmatism and is very troublesome, making it hard to fit the eye with glasses, as the glasses have to be ground irregular in shape.



We have just seen how the eye deals with rays of light coming from a distance, which are practically parallel. When, however, books or other objects are brought near the eye, the rays of light coming from them do not remain parallel, but begin to spread apart, or diverge; and a stronger lens is required to bring them to a focus upon the retina. To provide for this, there is in the middle of the eyeball a firm, elastic, little globular body about the size and shape of a lemon-drop, called the crystalline lens. Around this is a ring of muscle, which is so arranged that when it contracts it causes the lens to change its shape and become more bulging, or thicker in the middle. This makes the eyeball a "stronger" lens so that the rays of light can be brought to a focus upon the retina.

This action is known as accommodation, or adjustment; and you can sometimes feel it going on in your own eye, as when you pick up a book or a piece of sewing and bring it up quickly, close to the eye, in order to see clearly.

If this little muscle is worked too hard, as when we try to read in a bad light, it becomes tired and we get what is called "eye-strain"; and if the strain be kept up too long, it will give us headache and may even make us sick at the stomach. The commonest cases of eye-strain are in eyes that are too flat (hyperopic) where this little muscle has to "bulge" the lens enough to make good the defect and bring the rays to a focus. This, however, of course keeps it on a constant strain; and the eye is continually giving out, and its owner suffering from headache, neuralgia, dyspepsia, sleeplessness, and other forms of nervous trouble, until the proper lens or spectacle is fitted.[30]

A surface as delicate and sensitive to light as the retina, would, of course, be damaged by too bright a glare; so in the front of the eye, just behind the cornea, a curtain has grown up, with an opening or "peep-hole" in its centre, which can be enlarged or made smaller by little muscles. This opening is the pupil; the curtain, which is colored so as to shut out the rays of light, is known as the iris, for the quaint, but rather picturesque, reason that Iris in Greek means "rainbow," and this part of the eye may be any one of its colors.



It is the iris which, according to the amount of coloring matter (pigment) in it, makes the eye, as we say, blue, gray, green, brown, or black. Blue eyes have the least; black, the most.[31]

The Care of the Eyes. The most dangerous diseases of the eye are caused by infectious germs, which get into them either from the outside, as in dust, or by touching them with dirty fingers; or through the blood, as in measles, smallpox, tuberculosis, and rheumatism. The more completely we can prevent these diseases, the less blindness we shall have in the nation. About one-sixth of all cases of blindness in our asylums is caused by a germ that gets into babies' eyes at birth, but can be done away with by proper washing and cleansing of the eyes.

THE EAR

Structure of the Ear. Next after sight, hearing is our most important sense; without it, speaking, and consequently reading and writing, would be impossible. Man learned to speak by hearing the sounds made by other people and things, and then by listening to his own voice and practicing until he could imitate them. Children who are unfortunate enough to be born deaf also become dumb, not because there is anything the matter with their voice organs, but simply because, as they cannot hear the sounds they make, they do not form them by practice into words and sentences. By proper training, deaf mutes can now be taught to speak, though their voices sound flat and "tinny," like a phonograph.

As in the nose and the eye, the important part of the ear is the nerve spot that can "feel" the air waves that we call sound, just as the retina "feels" light. It is from this sensitive spot that the auditory nerve carries the sound to the brain. This spot has grown into quite an elaborate structure, buried, for safety, deeply in the bones of the skull, close to the base of the brain. It is made up of a long row of tiny little nerve rods, laid side by side like the keys of a piano, only there are about three thousand of them. Each one of these is supposed to respond, or vibrate, to a particular tone, or sound. This keyboard, from the fact that, to save space, it is coiled upon itself like a sea-shell, instead of running straight, is called the cochlea (Greek for "snail-shell"); it is also called, because it is the deepest, or innermost, part of the hearing apparatus, the internal ear.

Just as the retina has a lens and a vitreous humor in front of it to act upon the light, so the internal ear has an apparatus in front of it to act upon the sound waves. This is called the drum (tympanum). It consists of a fold of thin, delicate skin stretched tightly across the bottom of the outer ear canal, as parchment is stretched across the head of a drum. If you should take a hand-mirror—best a hollow, or concave, one—and throw a bright ray of light deep into some one's ear, you would be able, after a little trying, to see this drum-skin stretched across the bottom of it and about an inch and a quarter in from the surface of the head.



When the sound waves go into the ear canal and strike upon this tiny drum, which is about two-thirds the size of a silver dime and really more like a tambourine or the disk of a telephone or phonograph than a drum, they start it thrilling, or vibrating, just as a guitar string vibrates when you thrum it. These little vibrations are carried across the hollow behind the drum by a chain of tiny bones, known as the ear-bones (called from their shapes, the hammer, the anvil, and the stirrup), and passed on to the keyboard of the cochlea.

Here comes in one of the most curious things about this ingenious hearing-apparatus. This little hollow behind the drum-skin has to be kept full of air in order to let the drum vibrate properly, and this is arranged for by a little tube (the Eustachian tube) which runs down from the bottom of it and opens into the back of the throat just behind the nasal passages, and above the soft palate. When you blow your nose very hard, you will sometimes feel one of your ears go "pop"; and that means that you have blown a bubble of air out through this tube into your drum cavity.

If your nose and throat become inflamed, then the mouth of this little tube may become blocked up; the drum can no longer thrill, or vibrate, properly; and, for the time being, you are deaf. This tube is of great importance, because nearly all the diseases that attack the ear start in at the throat and travel up the tube until they reach the drum cavity. This is why one so often has earache after an attack of the grip or after a bad cold. The drum cavity, with its chain of bones and its tube down to the throat, is called, from its position, the middle ear.

The outer, or external, ear, though far the largest of the three parts, and quite imposing in appearance, is really of little use or importance. It is simply a sort of receiving trumpet for catching sounds, with a very wide and curiously curved and crumpled mouth, or bell. The large, expanded mouth of the trumpet, called the concha ("conch shell"), was at one time capable of being "pricked up" and turned in the direction of sounds, just as horses' or dogs' ears are now; and in our own ears there are still for this purpose three pairs of tiny unused muscles running from them to the side of the head. But the concha is now motionless and almost useless, except for its beauty; and it is very troublesome to wash.

The Care of the Ear. The tube of the trumpet leading down from the surface of the ear to the drum is lined with skin; and this skin is supplied with glands, which pour out a sticky, yellowish fluid called ear wax, which catches the bits of dust or insects that get into the ear and, flowing slowly outward, carries them with it. If it is let alone, it will keep the ear canal clean and healthy; but some people imagine that, because it looks yellowish, it must be dirt; and consequently, from mistaken ideas of cleanliness, they work at it with the end of the finger, the corner of a towel, or even with a hairpin, an ear-spoon, or an ear-pick, and in this way stop the proper flow of the wax and make it dry and block up the ear.

Remember, you should not wash too deeply into your ears; (as the old German proverb puts it, "Never pick your ear with anything smaller than your elbow"). And if you don't, you will seldom have trouble with wax in the ear. Scarcely one case of deafness in a hundred is caused by wax. When your ear does become blocked up with wax, it is best to go to a doctor and let him syringe it out. Picking at it, or even syringing too hard, may do serious damage to the ear.

If an earache is neglected, the inflammation may spread into some air-cells in the bony lump behind the ear (the mastoid) and thus cause mastoid disease, which may spread to, and attack, the brain if not cured by a surgical operation.

OUR SPIRIT-LEVELS

The Sixth Sense. Though we usually speak of having five senses,—sight, smell, hearing, touch, and taste,—we really have also a sixth—the sense of direction, or of balance. The "machine" of this sense is comparatively simple, being made up of three tiny curved tubes, which, from their shape, are called the semi-circular canals. These are buried in the same bone of the skull as the internal ear, and so close to it that they were at one time described as part of it. These little canals are three in number, one for each of the dimensions—length, breadth, and thickness,—so that whichever way the head or body is moved,—backward and forward, up and down, or from side to side,—the fluid with which they are filled will change its level in one of them, just as the "bead" does in the carpenter's spirit-level that you can find in any tool shop. The delicate nerve twigs that run out into the fluid in these tiny canals are gathered together into a bundle, or nerve-cable, which runs back to the part of the brain known as the cerebellum or hind-brain, which has most to do with controlling the balance and movements of our bodies.

It is the disturbance set up in these spirit-level canals by the pitching and rolling of a ship, which makes us seasick. Neither the stomach, nor anything that we may have eaten, has anything to do with it. In the same way we sometimes become sick and dizzy from swinging too long or too high, or from riding on the cars.

FOOTNOTES:

[28] To show in how many different ways nature may carry out the same purpose, the smelling organs in insects, lobsters, and crabs are on the ends and sides of tiny feelers, which they wave about; and the eyes in lobsters, crawfish, and snails, are on the ends of stalks, which they thrust about in all directions as a burglar handles a bull's-eye lantern. Snakes "hear," or catch the sound-waves, with their flickering, forked tongues; and grasshoppers and locusts have "ear-drums" on the sides of their chests.

[29] These are called the recti or "straight" muscles, upper, lower, inner, and outer, according to their position. Then, to roll the eye round and round, there are two little muscles, one above and one below, which run "crosswise" of the orbit, called the upper and lower oblique muscles.

[30] The retina is chiefly made up of a great number of fine little nerve cells called, from their shape, the rods and cones. These are kept soaked in a colored fluid called the retinal purple, which changes under the influence of light, somewhat in the same way that the film on a photographic plate does, thus forming pictures, which are translated by the rods and cones and telegraphed along the fibres of the optic nerve to the brain. Naturally, all parts of the retina are not equally sensitive to light; its centre, which is directly opposite the pupil of the eye, is far the most so, while those around the rim of the cup are dull. This is why, when you are looking, say at some one's face across the room, only the face and a few inches around it are seen perfectly clear and sharp, while the rest of the room is seen only vaguely.

[31] As the inside of the eye is dark, or comparatively so, the pupil, or little opening in the centre of the iris, looks black, and was at one time supposed to be a solid body instead of a hole. You can easily watch the pupil changing in size, according to the brightness of the light, from a mere pin-point in very bright sunlight or gaslight, up to the size of the butt-end of a lead pencil in the dark or in a dim light.