A Handbook of Health

The Meaning of Good Color. It is the red blood in this spongy network of tiny vessels that gives a pink coloring to our lips and the flush of health to our cheeks. Whenever for any reason the blood is less richly supplied with food or oxygen, or more loaded with "smoke" and other body dirt than it should be, we lose this good color and become pale or sallow. If we will remember that our hearts, our livers, our brains, and our stomachs, are at the same time often equally "pale" and sallow—that is, badly supplied with blood—as our complexions, we can readily understand why it is that we are likely to have poor appetites, poor memories, bad tastes in our mouths, and are easily tired whenever, as we say, our "blood is out of order." The blood is the life. Starve or poison that, and you starve or poison every bit of living stuff in the body.

THE HEART

Structure and Action of the Heart. Now what is it that keeps the blood whirling round and round the body in this wonderful way? It is done by a central pump (or more correctly, a little explosive engine), with thick muscular walls, called the heart, which every one knows how to find by putting the hand upon the left side of the chest and feeling it beat. The heart is really a bulb, or pouch, which has ballooned out from the central feed pipe of the blood supply system, somewhat in the same way that the stomach has ballooned out from the food tube.

The walls of this pouch, or bulb, are formed of a thick layer of very elastic and powerful muscles almost as thick as the palm of your hand. When the great vein trunk has poured blood into this pouch until it is swollen full and tight, these muscles in its walls shut down sharply and squirt or squeeze the blood in the heart-pouch into the great artery-pipe, the aorta. In fact, you can get a very fair, but rough, idea of the way in which the heart acts by putting your half-closed hand down into a bowl of water and then suddenly squeezing it till it is shut tight, driving the water out of the hollow of your hand in a jet, or squirt.

"But," some of you will ask at once, "what is to prevent the blood in the heart, when the muscle wall squeezes down upon it, from shooting backward into the vena cava, instead of forward into the aorta?"

Nature thought of that long ago, and ingeniously but very simply guarded against it by causing two little folds of the lining of the blood pipes to stick up both where the vena cava enters the heart and where the aorta leaves it, so as to form little flaps which act as valves. These valves allow the blood to flow forward, but snap together and close the opening as soon as it tries to flow backward. While largest and best developed in the heart, these valves are found at intervals of an inch or two all through the veins in most parts of the body, allowing the blood to flow freely toward the heart, but preventing it from flowing back.

As the heart has to pump all the blood in the body twice,—once around and through the lungs, and once around and through the whole of the body,—it has become divided into two halves, a right half, which pumps the blood through the lungs and is slightly the smaller and the thinner walled of the two; and a left half, which pumps the purified blood, after it has come back from the lungs, all over the rest of the body.

Each half, or side, of the heart has again divided itself into a receiving cavity, or pouch, known as the auricle; and a pumping or delivering pouch, known as the ventricle. And another set of valves has grown up between the auricle and the ventricle on each side of the heart. These valves have become very strong and tough, and are tied back in a curious and ingenious manner by tough little guy ropes of tendon, or fibrous tissues, such as you can see quite plainly in the heart of an ox. It is important for you to remember this much about them, because, as we shall see in the next chapter, these valves are one of the parts of the heart most likely to wear out, or become diseased.

Heart Beat and Pulse. The heart fills and empties itself about eighty times a minute, varying from one hundred and twenty times for a baby, and ninety for a child of seven, to eighty for a woman, and seventy-two for a full-grown man.

When the walls of the ventricles squeeze down to drive out their blood into the lungs and around the body, like all other muscles they harden as they contract and thump the pointed lower end, or apex, of the heart against the wall of the chest, thus making what is known as the beat of the heart, which you can readily feel by laying your hand upon the left side of your chest, especially after you have been running or going quickly upstairs. As each time the heart beats, it throws out half a teacupful of blood into the aorta, this jet sends a wave of swelling down the arteries all over the body, which can be felt clearly as far away as the small arteries of the wrist and the ankle. This wave of swelling, which, of course, occurs as often as the heart beats, is called the pulse; and we "take" it, or count and feel its force and fullness, to estimate how fast the heart is beating and how well it is doing its work. We generally use an artery in the wrist (radial) for this purpose because it is one of the largest arteries in the body which run close to the surface and can be easily reached.

Summary of the Circulation of the Blood. We will now sum up, and put together in their order, the different things we have learned about the circulation of the blood through the body.

Starting from the great vein trunk, the vena cava, it pours into the receiving chamber, or auricle, of the right side of the heart, passes between the valves of the opening into the lower chamber, the right ventricle. When this is full, the muscles in the wall of the ventricle contract, the valve flaps fly up, and the blood is squirted out through the pulmonary artery to the lungs. Here it passes through the capillaries round the air cells, loses its carbon dioxid, takes in oxygen, and is gathered up and returned through great return pipes to the receiving chamber, or auricle, of the left side of the heart. Here it collects while the ventricle below is emptying itself, then pours down between the valve flaps through the opening to the left ventricle. When this is full, it contracts; the valves fly up and close the orifice; and the blood is squirted out through another valve-guarded opening, into the great main artery, the aorta. This carries it, through its different branches, all over the body, where the tissues suck out their food and oxygen through the walls of the capillaries, and return it through the small veins into the large vein pipes, which again deliver it into the vena cava, and so to the right side of the heart from which we started to trace it.

Although the two sides of the heart are doing different work, they contract and empty themselves, and relax and fill themselves, at the same time, so that we feel only one beat of the whole heart.

One of the most wonderful things about the entire system of blood tubes is the way in which each particular part and organ of the body is supplied with exactly the amount of blood it needs. If the whole body is put to work, so that a quicker circulation of blood, with its millions of little baskets of oxygen, is needed to enable the tissues to breathe faster, the heart meets the situation by beating faster and harder. This, as you all know, you can readily cause by running, or jumping, or wrestling.

CHAPTER XII

Every kind of work, of course, done in the body throws more work upon the heart. When we run, or saw wood, our muscles contract, and need more food-fuel to burn, and pour more waste-stuff into the blood to be thrown off through the lungs; so the heart has to beat harder and faster to supply these calls. When our stomach digests food, it needs a larger supply of blood in its walls, and the heart has to pump harder to deliver this. Even when we think hard or worry over something, our brain cells need more blood, and the ever-willing heart again pumps it up to them. This is the chief reason why we cannot do more than one of these things at a time to advantage. If we try to think hard, run foot races, and digest our dinner all at one and the same time, neither head, stomach, nor muscles can get the proper amount of blood that it requires; we cannot do any one of the three properly, and are likely to develop a headache, or an attack of indigestion, or a "stitch in the side," and sometimes all three. So the circulation has a great deal to do with the intelligent planning and arranging of our work, our meals, and our play. If we are going to increase our endurance, we must increase the power of our heart and blood vessels, as well as that of our muscles. The real thing to be trained in the gymnasium and on the athletic field is the heart rather than the muscles.

Fortunately, however, the heart is itself a muscle, alive and growing, and with the same power of increasing in strength and size that any other muscle has. So that up to a proper limit, all these things which throw strain upon the heart in moderate degree, such as running, working, and thinking, are not only not harmful, but beneficial to it, increasing both its strength and its size. The heart, for instance, of a thoroughbred race-horse is nearly twice the size, in proportion to his body weight, of the heart of a dray-horse or cart-horse; and a deer has more than twice as large a heart as a sheep of the same weight.

The important thing to bear in mind in both work and play, in athletic training, and in life, is that this work must be kept easily within the powers of the heart and of the other muscles, and must be increased gradually, and never allowed to go beyond a certain point, or it becomes injurious, instead of beneficial; hurtful, instead of helpful. Over-work in the shop or factory, overtraining in the gymnasium or on the athletic field, both fall first and heaviest upon the heart.

Importance of Food, Air, and Exercise. At the same time, the system must be kept well supplied through the stomach with the raw material both for doing this work and for building up this new muscle. When anyone, in training for an event, gets "stale," or overtrained, and loses his appetite and his sleep, he had better stop at once, for that is a sign that he is using more energy than his food is able to give him through his stomach; and the stomach has consequently "gone on a strike."

How to Avoid Heart Overstrain and Heart Disease. The way, then, to avoid overstrain and diseases of the heart and blood vessels is:—

First, to take plenty of exercise, but to keep that exercise within reasonable limits, which, in childhood, ought to be determined by a school physician, and in workshops and factories by a state factory physician.

Second, to take that exercise chiefly in the open air, and as much of it as possible in the form of play, so that you can stop whenever you begin to feel tired or your heart throbs too hard—in other words, whenever nature warns you that you are approaching the danger line.

Third, to keep yourself well supplied with plenty of nutritious, wholesome, digestible food, so as to give yourself, not merely power to do the work, but something besides to grow on.

Fourth, to avoid poisonous and hurtful things like the toxins of infectious diseases; and alcohol, tobacco, and other narcotics, which have a harmful effect upon the muscles, valves, or nerves of your heart, or the walls of your blood vessels.

Fortunately, the heart is so wonderfully tough and elastic, and can repair itself so rapidly, that it usually takes at least two, and sometimes three, causes acting together, to produce serious disease or damage. For instance, while muscular overwork and overstrain alone may cause serious and even permanent damage to the heart, they most frequently do so in those who are underfed, or badly housed, or recovering from the attack of some infectious disease. While the poisons of rheumatism and alcohol will alone cause serious damage to the valves of the heart and walls of the blood vessels, yet they again are much more liable to do so in those who are overworked, or underfed, or overcrowded.

The Disease of the Stiffening of the Arteries. The points at which our pipe-line system is most likely to give way are the valves of the heart, and, more likely still, the muscles of the heart wall and of the walls of the blood vessels. These little muscles are slowly, but steadily, changing all through life, becoming stiffer and less elastic, less alive, in fact, until finally, in old age, they become stiff and rigid, turning into leathery, fibrous tissue, and may even become so soaked with lime salts as to become brittle, so that they may burst under some sudden strain. When this occurs in one of the arteries of the brain, it causes an attack of apoplexy, or a "stroke of paralysis." Overstrain, or toxins in the blood, may bring about this stiffening of the arteries too soon, and then, we say that the person is "old before his time." A man is literally "as old as his arteries."

The causes which will hasten the stiffening of the arteries are, first of all, prolonged overwork and overstrain,—due especially to long hours of steady work in unwholesome shops or surroundings; second, the presence in the blood of the poisons of the more chronic infectious diseases, like tuberculosis; third, the waste products that are formed in our own body, and are not properly got rid of through lungs, skin, and kidneys; and fourth, the use of alcohol, tobacco, and other narcotics.

The Bad Effects of Alcohol. Alcohol is particularly likely to damage the walls of the blood vessels and the heart, first, because it is a direct poison to their cells, when taken in excess, and often in what may appear to be moderate amounts, if long continued; secondly, because it is frequently taken, especially by the poorer, underfed class of workers, as a substitute for food, causing them literally to "spend their money for that which is not bread," and to leave their tissues half-starved; and thirdly, because, by its narcotic effects, it decreases respiration and clogs the kidneys and the skin, thus preventing the waste products from leaving the body.

How the Heart Valves may be Injured. The valves of the heart are likely to give way, partly because they are under such constant strain, snapping backward and forward day and night; and partly, because, in order to be thin enough and strong enough for this kind of work, they have become turned, almost entirely, into stringy, half-dead, fibrous tissue, which has neither the vitality nor the resisting power of the live body-stuffs like muscles, gland-cells, and nerves. They are so tough, however, that they seldom give way under ordinary wear and tear, as the leather of a pump valve, or of your shoes, might; but the thing which damages them, nine times out of ten, is the germs or poisons of some infectious disease.

These poisons circulating through the blood, sometimes set up a severe inflammation in the valves and the lining of the heart. Ulcers, or little wart-like growths, form on the valves; and these may either eat away and destroy entirely parts of the valves or, when they heal, leave scars which shorten and twist the valves out of shape, so that they can no longer close the openings. When this has happened, the heart is in the condition of a pump which will not hold water, because the leather valve in its bucket is broken or warped; and we say that the patient has valvular or organic heart disease.

The disease which most frequently causes this serious defect is rheumatism, or rheumatic fever; but it may also occur after pneumonia, typhoid, blood poisoning, or even after a common cold, or an attack of the grip. This is one of several reasons why we should endeavor, in every way, to avoid and stop the spread of these infectious diseases; not only are they dangerous in themselves, but although only two of them, rheumatism and pneumonia, frequently attack the heart, all of them do so occasionally, and together they cause nearly nine-tenths of all cases of organic heart disease.

Should you be unfortunate enough to catch one of these diseases, the best preventive against its attacking the heart, or causing serious damage, if it does, is a very simple one—rest in bed until the fever is all gone and your doctor says it is perfectly safe for you to get up; and avoid any severe muscular strain for several months afterward.

This is a most important thing to remember after all infections and fevers, no matter how mild. Even where the heart valves have been seriously attacked, as in rheumatism, they will often recover almost completely if you keep at rest, and your heart is not overtaxed by the strain of heavy, muscular work, before it has entirely recovered. Ten days' "taking it easy" after a severe cold, or a bad sore throat, may save you a serious strain upon the heart, from which you might be months or even years in recovering.

But even where serious damage has been done to the heart, so that one of its valves leaks badly, nature is not at the end of her resources. She simply sets to work to build up and strengthen and thicken the heart muscle until it is strong enough to overcome the defect and pump blood enough to keep the body properly supplied—just as, if you are working with a leaky pump, you will have to pump harder and faster in order to keep a good stream of water flowing. It is astonishing how completely she will make good the loss of even a considerable part of a valve.

Doctors no longer forbid patients with heart disease to take exercise, but set them at carefully planned exercise in the open air, particularly walking and hill-climbing; at the same time feeding them well, so as to assist nature in building up and strengthening the heart muscle until it can overcome the defect. In this way, they may live, with reasonable care, ten, fifteen, or twenty years—often, in fact, until they die of something else.

Don't worry about your heart if it should happen to palpitate, or take a "hop-skip-and-jump" occasionally. You will never get real heart disease until you have had some fever or serious illness, which leaves you short of breath for a long time afterward.

Danger to the Heart through the Nervous System. The other chief way in which the heart may be affected is through the nervous system. Being the great supply pump for the entire body, it is, of course, connected most thoroughly and elaborately by nerve wires with the brain and, through it, with every other organ in the body. So delicately is it geared,—set on such a hair-trigger, as it were,—that it not only beats faster when work is done anywhere in the body, but begins to hurry in anticipation of work to be done anywhere. You all know how your heart throbs and beats like a hammer and goes pit-a-pat when you are just expecting to do something important,—for instance, to speak a piece or strike a fast ball,—or even when you are greatly excited watching somebody else do something, as in the finish of a close race.

Two-thirds of the starts and jumps and throbbings that the heart makes, are due to excitement, or nervous overstrain, or the fact that your dinner is not digesting properly; and they don't indicate anything serious at all, but are simply useful danger signals to you that something is not just right.

In work and in athletics for instance, this rapid and uncomfortably vigorous action of the heart is one of nature's best checks and guides. When your heart begins to throb and plunge uncomfortably, you should slow up until it begins to quiet down again, and you will seldom get into serious trouble. The next time you try the same feat, you will probably find that you can go a little farther, or faster, without making it throb. Indeed, getting into training is very largely getting the heart built up and educated, so that you can run or play, or wrestle hard without overtaxing it. Whatever you can do within the limits of your heart is safe, wholesome, and invigorating; whatever goes beyond this, is dangerous and likely to be injurious.

Occasionally, however, some of the nerves which control the heart become disturbed or diseased so that, instead of the heart's simply beating harder and faster whenever more blood is really needed, it either throbs and beats a great deal harder and faster than is necessary, or goes racing away on its own account, and beats "for dear life," when there is no occasion for it, thus tiring itself out without doing any good, and producing a very unpleasant feeling of nervousness and discomfort. This may be due to overwork, whether with muscles or brain; or to worry or loss of sleep, in which case it means that you must put on the brakes, take plenty of rest and exercise in the open air, and get plenty of sleep. Then these danger signals, having accomplished their warning purpose, will disappear.

Other Causes of Heart Trouble. At other times, this palpitation is due to the presence of poisons in the blood, either those of infectious disease, or of certain waste products produced in the body in excess, as, for instance, when your digestion is out of order, or your skin, kidneys, and bowels are not working properly; or it is due to tea, coffee, or tobacco.

Effects of Tea and Coffee. Tea and coffee, if taken in excess, will sometimes produce very uncomfortable palpitation, or rapid over-action of the heart, with restlessness and inability to sleep. They usually act in this way only when taken in large amounts, or upon a small percentage of persons who are peculiarly affected by them; and this palpitation is seldom serious, and disappears when their excessive use is stopped.

Tobacco and its Dangers to the Heart. Tobacco has a very injurious effect upon the nerves of the heart in the young, making them so irritable that the heart will beat very rapidly on the least exertion; so that gradually one becomes less and less inclined to attempt exertion of any sort, whether bodily or mental, and falls into a stagnant, stupid sort of condition which seriously interferes with both growth and progress.

In other cases, tobacco dulls and deadens the nerves controlling the heart, as it does the rest of the nervous system and the brain, so that the smoker feels as if nothing were worth while doing very hard, and it becomes difficult for him to fix his mind upon a subject. At the same time, it dulls the appetite so that one takes less wholesome food; and it checks, or clogs up, the sewer-pipes of the skin, the liver, and the kidneys.

Of course, as you know, all trainers and coaches, even though they be habitual smokers themselves, absolutely forbid tobacco in any form to athletes who are training for a contest, on account of its effects upon the nervous system and the heart.

A certain percentage of individuals are peculiarly susceptible to tobacco, so that it has a special poisonous effect upon the nerves of the heart, causing a rapid pulse and shortness of breath, known as tobacco heart. This is not of very common occurrence; but it is exceedingly troublesome when it does occur, and it takes a long time to get over it, even after the use of tobacco has been stopped entirely. Sometimes it leads to permanent damage of the nerves and of the heart.

Give your heart plenty of vigorous exercise, but don't make it beat uncomfortably hard. Give it plenty of food, sleep, and fresh air; avoid poisoning it, either with the toxins of diseases, or with your own waste-poisons, or alcohol, or tobacco; and it will serve you faithfully till a good old age.

CHAPTER XIII

Short Storage Supply of Air. There is a difference between the kind of things that you take in when you breathe and the kind of things you take in when you eat or drink. Food and drink are solids and liquids; and the body is a great sponge of one soaked full of the other, so that large amounts of food and water can be stored up in the body. But what you take in when you breathe is, of course, air—which is neither a solid nor a liquid, but a gas, very light and bulky. Of gases the body can soak up and hold only a very small amount; so its storage supply of them will be used up completely in about three minutes, and then it dies if it cannot get more air.

Why our Bodies Need Air-Oxidation. The body is made up of millions of tiny living animals called cells, which eat the food that is brought to them from the blood and pour their waste and dirt back again into the same current. Now, what would happen if we were to throw all the garbage from the kitchen, and the wash water from the kitchen sink, and the dirty water from the bathroom right into the well out of which we pumped our drinking water? We should simply be poisoned within two or three days, if indeed we could manage to drink the disgusting mixture at all. That is exactly what would happen to our body cells if they were not provided with some way of getting rid of their waste and dirt.

Part of the waste that comes from our body cells is either watery, or easily dissolved in water; and this is carried in the blood to a special set of filter organs—the liver and the kidneys—and poured out of the body as the urine. Another part of it, when circulating through the skin, is passed off in the form of that watery vapor which we call perspiration, or sweat. But part of the waste can be got rid of only by burning, and what we call burning is another name for combining with oxygen, or to use one word—oxidation; and this is precisely the purpose of the carrying of oxygen by the little red blood cells from the lungs to the deeper parts of the body—to burn up, or oxidize, these waste materials which would otherwise poison our cells. When they are burnt, or oxidized, they become almost harmless.

Why the Red Cells Carry only Oxygen to the Body. But why do not the red cells carry air instead of just oxygen? This is simply a clever little economy of space on nature's part. As a chemist will tell you the air which we breathe is a mixture of two gases—one called nitrogen and the other oxygen; just as syrup, for instance, is a mixture of sugar and water. Then too, as in syrup, there are different amounts of the two substances in the mixture: as syrup is made up of about one-quarter sugar and three-quarters water, so air is made up of one-fifth oxygen and four-fifths nitrogen. Now the interesting thing about this mixture, which we call air, is that the only really "live" and vital part of it for breathing purposes is the one-fifth of oxygen, the four-fifths of nitrogen being of no use to our lungs. In fact, if you split up the air with an electric current, or by some other means, and thus divide it into a small portion of pure oxygen (one-fifth), and a very much larger portion (four-fifths) of nitrogen, the latter would as promptly suffocate the animal that tried to breathe it as if he were plunged under water.[18]

It may perhaps be difficult to think of anything burning inside of your bodies where everything is moist, especially as you do not see any flame; but you do find there one thing which always goes with burning, and that is warmth, or heat. This slow but steady and never-ceasing burning, or oxidation, of the waste and dirt inside your bodies is what keeps them warm. When you run fast, or wrestle, or work hard, your muscle-cells work faster, and make more waste, and you breathe faster to get in the oxygen to burn this up—in other words, you fan the body fires, and in consequence you get a great deal hotter, and perhaps perspire in order to get rid of your surplus heat.

The Ocean of Air. Where does the blood in the body go in order to get this oxygen, which is so vital to it? Naturally, somewhere upon the surface of the body, because we are surrounded by air wherever we sit, or stand, or move, just as fishes are by water. All outdoors, as we say, is full of air. We are walking, just as fishes swim, at the bottom of an ocean of air some thirty miles deep; and the nearer we get up toward the surface of that ocean, as, for instance, when we climb a high mountain, the lighter and thinner the air becomes. Above ten thousand feet we often have great difficulty in breathing properly, because the air is so thin and weak in oxygen.

How the Lungs Grew Up. In the simplest forms of life, any part of the soft and delicate surface will do for the blood to reach, in order to throw off its load of carbon "smoke" and take on its supply of oxygen. In fact, animals like jellyfish and worms are lungs all over. But as bodies begin to get bigger, and the skin begins to toughen and harden, this becomes more and more difficult, although even the highest and biggest animals like ourselves still throw off a certain amount of this carbon dioxid and other gases through the skin. Accordingly, certain parts of the surface of the body are set apart specially for this business of breathing; and as we already have an opening into the body provided by the mouth and food tube, the simplest thing to do is to use the mouth for taking in air, when it is not being used for taking in food, and to set aside some part of the food tube for breathing purposes.

The lungs sprout out from the front of the gullet, just below the root of the tongue, in the days when we are getting ready to be born. The sprout divides into two, forming the beginning of the pair of lungs. Each lung sprout again divides into two, and each of the two smaller buds again into two, until finally we have the whole chest filled up with a "lung-tree" whose trunk stems and leaves are hollow. The stem of the tree or bush becomes the windpipe (trachea). The first two branches into which it divides form the right and left lung tubes, known as bronchi. The third, fourth, fifth, sixth, etc., divisions, and so on, form what are known as the bronchial tubes. These keep on splitting into tinier and tinier twigs, until they end, like the bush, in little leaves, which in the lung, of course, are hollow and are called the air cells (alveoli). This budding off of the lungs from the gullet is the reason why the air we breathe and the food we swallow go down the same passage. Every mouthful of our food slides right across the opening of the windpipe, which has to be protected by a special flap, or trap-door of gristle, called the epiglottis. If you try to eat and talk at the same time, the epiglottis doesn't get warning of the coming of a swallow of food in time to cover the opening of the windpipe, and the food goes down the wrong way and you cough and choke.

Now, if you will just place your fingers upon the front of your neck and slide them up and down, you will, at once, feel your windpipe—a hard, rounded tube with ridges running across it,—while, no matter how carefully you feel, or how deeply you press, you cannot feel your gullet or esophagus at all. Just take a mouthful of water, however, put your fingers deeply on each side of the windpipe, and swallow, and you will feel something shoot down the esophagus, between your fingers, toward the stomach.

Both of these tubes were made of exactly the same materials to begin with. Why have they become so different? A moment's thought will tell you. One, the gullet, has only to swallow solid food or drink, so that its walls can remain soft, and indeed fall together, except when it is actually swallowing. The other tube, the air-pipe or windpipe, has to carry air, which neither will fall of its own weight, nor can readily be gulped down or belched up. It is absolutely necessary that its walls should become stiff enough to keep it open constantly and let the air flow backward and forward. So we find growing up in the walls of this air pipe, cells which turn themselves into rings of gristle, or cartilage.

What the Breath Is. As you know, your "breath," as you call it,—that is to say, the used-up air which you blow out of your lungs,—is different in several ways from pure, or unused air. In the first place, it is likely to have a slight musky or mousy odor about it. You never like to breathe any one else's breath, or have any one breathe in your face. This dislike is due to certain gases, consisting of impurities from the blood, the cells of the lungs, the throat, the nose, and, if the mouth is open, the teeth. These are not only offensive and disagreeable to smell, but poisonous to breathe.

Then your breath is much warmer than the rest of the air. In fact, on a very cold morning you may have tried to warm up your fingers by breathing on them; and you have also noticed that if a number of people are shut up in a room with doors and windows closed, it soon begins to feel hot as well as stuffy. This heat, of course, is given off from the blood in the lungs and in the walls of the throat and nose, as the air passes in and out again.

When you stand at the window on a cold day, the glass just in front of your mouth clouds over, so that you can no longer see through it; and if you rub your finger across this cloud, it comes away wet. Evidently, the air is moister than it was when you breathed it in; this moisture also has been given off from the blood in the lungs.

But what of the principal waste gas that the blood gives off in the lungs—the carbon "smoke," or carbon dioxid? Can you see any trace of this in the breath? No, you cannot, for the reason that this gas is like air, perfectly clear and transparent, and never turns to moisture at any ordinary temperature. But it has a power of combining with certain other things and forming substances which, because they are combinations of carbon, are called carbonates. The commonest substance with which it will do this is lime. If you take a glass or a bottle two-thirds full of lime water, and breathe into it through a glass tube or straw, you will see in a very few minutes that it is becoming milky or cloudy from the formation of visible carbonate of lime, which, when you get enough of it, makes ordinary limestone. So, although you cannot see, or smell, this carbon "smoke" in your breath, you can readily prove that it is present.

How and Why our Breathing Varies. When you run or wrestle, you breathe faster in order to draw more air into the lungs. At the same time, your heart beats faster in order to drive a larger amount of blood through the lungs. If you run too far, or wrestle too hard, your heart and your lungs both go faster and faster, until finally they reach a point when they cannot go any quicker, and the poisonous waste substances are formed in your muscles faster than they can possibly be burned up, even by the quickest breathing and the hardest pumping of your heart. Then you begin to get "out of breath"; and if you were compelled—in order to save your life, for instance—to keep on running, or fighting, you would at last be suffocated by your own waste and dirt, and fall exhausted, or unconscious.

On the other hand, by carefully training your muscles and your heart and your lungs by exercises of various sorts in the open air, beginning with easy ones and going on to harder and longer ones, you can "improve your wind," so that your heart will be able to pump more blood through the lungs per minute, and your lungs will be able to expand themselves more fully and more rapidly without fatigue.

If you can recall having had a fever of any sort, even a slight one, such as comes with a sore throat or a bad cold, you may remember that you breathed faster and that your heart beat faster, and yet you were not doing any work with your muscles. The cause, however, is the same; namely, the amount of waste that is being produced in the body—in this case, by the poisons (toxins) of the germs that cause the fever. The more waste that is formed in the body, the more effort the heart and lungs will make to try to get rid of it.

The Ribs. How does the air get in and out of the lung tubes? Evidently you do not and cannot swallow it as you would food or drink; and as it will not run down of its own accord when you simply open your mouth, nature has had to devise a special bit of machinery for the purpose of sucking it in and pressing it out again. This she has done in a rather ingenious manner by causing certain of the muscle-rings in the wall of the chest to turn first into gristle, or cartilage, and then later into bone, making what are known as the ribs; these run round the chest much as hoops do round a barrel, or as the whalebone rings did in the old-fashioned hoop skirt. When the muscles of the chest pull these ribs up, the chest is made larger,—like a bellows when you lift the handle,—air is sucked in, and we "breathe in" as we say; when the muscles let go, the ribs sink, the chest flattens and becomes smaller, the air is driven out, and we "breathe out."

CHAPTER XIV

Shut-in and Stagnant Air is Foul. This restless air-gas cannot be stored outside of the body, any better than it can be inside. For one thing, it is too bulky; and for another, it begins to become impure in various ways, as soon as it is shut up. It is the most unmanageable food that we "eat," for we can neither cook it nor wash it like solid food, nor filter it nor boil it like water, except on a very limited scale. We can do nothing to it except to foul it, which we do with every breath that we breathe, every fire that we make, every factory that we build. Our only chance of safety, our only hope of life, is to connect every room and every corner of those little brick and mortar boxes, those caged sections of out-of-doors, that we call houses, with nature's great system of air supply, "All Outdoors." Fortunately, the only thing needed to make the connection is to open a window—no need to send for a plumber or put in a meter, and there is no charge for the supply after connections have been made.

The Enormous Amount of Air. Air outdoors is everywhere, for practical purposes, absolutely pure, just as water is when it comes down from the clouds. And like water, its only dangerous impurities are what we put there ourselves. The purity of outdoor air is due mainly to the fact that there is such an enormous amount of it, not only the miles and miles of it that stretch away on every side of us, but nearly thirty miles of it straight up above our heads; its purity is also due to the fact that, like water, it is always in motion. When heated by the sun, it expands; and, in doing so, it rises because it is less dense and therefore lighter. As soon as the pressure of the air above is lessened, air rushes in below from all the cooler regions around. This rushing of air we call a wind. If the low pressure lies to the north of us, the air rushes northward over us to fill it, and we say the wind is from the south; if the air is flowing to the south of us, we say the wind is from the north.

How Air is Purified. In these winds certain small amounts of dust, or dirt, or leaf mould are whirled up into the air, but these are promptly washed down again whenever it rains; and the same is true of the smoke impurities in the air of our great cities. Air is also constantly being purified by the heat and light of the sunbeams, burned clean in streaks by the jagged bolt of the lightning in summer, and frozen sweet and pure by the frosts every winter. So that air in the open, or connected with the open, and free to move as it will, is always pure and wholesome. But to be sure of this, it must be "eaten alive"—that is, in motion. Stagnant air is always dead and, like all dead things, has begun to decay.

The Carbon Dioxid in the Air. Air, as you will remember (p. 132), is a mixture of oxygen and nitrogen, and its value in the body is that it gives off part of its oxygen to combine with the body wastes and burn them to carbon dioxid. Oddly enough, even pure outdoor air contains tiny traces of carbon dioxid; but the amount is so very small as to be of no practical importance, in spite of the fact that every kind of animal that lives and moves upon the earth is pouring it out from his lungs every second. The rapidity with which it disappears is due in part to the rapidity with which it rises and spreads, or is blown, in every direction; and in part to the wonderful arrangement by which, while animals throw off this poisonous gas as waste, plants eagerly suck it in through the pores in their leaves and eat it, turning it into the carbohydrates, starch and sugar, which, in turn, become valuable foods for the animals. So perfect is this system of escape, or blowing away, of carbon dioxid, combined with its being eaten up by plants, that even the air over our great cities and manufacturing towns contains only the merest trifle more of carbon dioxid than that over the open country. Its other smoke-impurities, dirts and dusts, escape, or are blown away so rapidly that they are seldom thick enough to be injurious to health, except in the narrowest and darkest streets; so that it is always safe to open your windows wide for air, wherever you may live. The principal danger from smoke is that it cuts off the sunlight.

The Necessity for Ventilation—Impurities of Indoor Air. The worst impurities in air are those that come from our own breaths and our own bodies; and, unexpectedly enough, carbon dioxid is not one of them. In spite of hundreds of experiments, we do not yet know exactly what these impurities are, though they are doubtless given off from our lungs, our skins, our mouths, and teeth, especially if the latter are not kept clean and sweet, but left dirty and decaying.

We do know, however, to a certainty that air shut up in a room, or house, with people, rapidly becomes poisonous and unwholesome. As we breathe on an average about eighteen or twenty times to the minute when we are grown up, and twenty-five to thirty times a minute when we are children, you can readily see how quickly the air in an ordinary-sized room will be used up, and how foul and unfit for further breathing it will become from being loaded with these bad-smelling lighter gases, with the carbon "smoke," with heat, and with moisture. The only way in which a room can be kept fit for human beings to breathe in is to have a draught, or current of air, pouring into it through open windows, or open doors, or ventilating shafts, at least as rapidly as it is being breathed by the persons who occupy that room. By hundreds of tests this has now been found to be on an average about four bushels a minute for each person, and any system of proper ventilation must supply this amount of air in order to make a room fit to sit in.

If a man, for instance, accidentally gets shut into a bank-vault, or other air-tight box or chamber, it will be only a few minutes before he begins to feel suffocated; and in a few hours he will be dead, unless some one opens the door. A century ago, when the voyage from Europe to America was made in sailing vessels, whenever a violent storm came up, in the smaller and poorer ships the hatches were closed and nailed down to keep the great waves which swept over the decks from pouring down the cabin-stairs and swamping the ship. If they were kept closed for more than two days, it was no uncommon thing to find two or three children or invalids among the unfortunate emigrants dead of slow suffocation; and many of those who were alive would later have pneumonia and other inflammations of the lungs. On one or two horrible occasions, when the crew had had a hard fight to save the ship and were afraid to open the hatches even for a moment, nearly one-third of the passengers were found dead when the storm subsided. So it is well to remember that we are fearfully poisonous to ourselves, unless we give nature full chance to ventilate us.

There are also other ways in which the air in houses may be made impure besides by our own bodies, but none of them is half so serious or important. All the lights that we burn in a house, except electric ones, are eating up oxygen and giving off carbon dioxid. In fact, a burning gas jet will do almost as much toward fouling the air of a room as a grown man or woman, and should be counted as a person when arranging for ventilation.

If gas pipes should leak, so that the gas escapes into a room, it is very injurious and unwholesome—indeed, in sufficient amounts, it will suffocate. Or, if the sewer pipes in the walls of the house, or in the ground under the cellar, are not properly trapped and guarded, sewer gas may escape into the house from them, and this also is most unwholesome, and even dangerous.

Cellar and Kitchen Air. Houses in which fruit and vegetables are stored in the cellar become filled with very unpleasant odors from the decay of these. Others again, where the kitchen is not properly ventilated, get the smoke of frying and the smell of cooking all through them. But such sources of impurity, while injurious and always to be strictly avoided, are neither half so dangerous when they occur, nor one-tenth so common as the great chief cause of impure air—our breaths and the other gases from our bodies, with the germs they contain.

Drafts not Dangerous. Now comes the practical question, How are we to get rid of these breath-poisons? From the carelessness of builders, and the porous materials of which buildings are made, most houses are very far from air-tight, and a considerable amount of pure air will leak in around window-casings, door-frames, knot-holes, and other cracks, and a corresponding amount of foul air leak out. But this is not more than one-fifth enough to keep the air fresh when the rooms are even partially occupied, still less when they are crowded full of people. As each individual, breathing quietly, requires about four bushels of air (one and a half cubic yards) a minute, it is easy to see that, when there are ten or more people in a room, there ought to be a steady current of air pouring into that room; and when there are twenty or even forty people, as in an average schoolroom, the current of air (provided there is one) must move so fast to keep up the supply that the people in the room begin to notice it and call it "a draft." It would be difficult to ventilate a room for even four or five persons without producing, in parts of it, a noticeable draft of air. In fact, it is pretty safe to say that, if somebody doesn't feel a draft the room is not being properly ventilated. At one time this was considered a very serious drawback—drafts were supposed to be so dangerous. But now we know that a draft is only air in motion, and that air in motion is the only air that is sure to be pure. There is nothing to be afraid of in a draft which is not too strong, if you are clean outside and in, and reasonably vigorous. If the draft is too strong, move away from the window or the door. Colds are very seldom caught from the cold, pure air of a draft, but nearly always from the germs, or dirt, in the still, foul air of a tightly closed room. This fact has swept away the chief objection to the direct, or natural, method of ventilating through open windows.

Methods of Ventilation. Fortunately, as often happens, the simplest and most natural method of ventilation is the best one. Open the windows, and let the fresh air pour in. If there be any room which hasn't windows enough in it to ventilate it properly, it is unfit for human occupation, and is seldom properly lighted. Most elaborate and ingenious systems of ventilation have been devised and put into our larger houses, and public buildings like libraries, court-houses, capitols, and schools. Some of them drive the air into each room by means of a powerful steam, or electric, fan in the basement; others suck the used-up air out of the upper part of each room, thus creating an area of low pressure, to fill which the fresh air rushes in through air-tubes or around doors and windows. They have elaborate methods of warming, filtering, and washing the air they distribute. Some work fairly well, some don't; but they all have one common defect—that what they pump into the rooms is not fresh air, though it may conform to all the chemical tests for that article. "The proof of the pudding is in the eating," and fresh air is air that will make those who breathe it feel fresh, which the cooked and strained product of these artificial ventilating systems seldom does.