Chapter 3
When you are running and breathing hard, and even when you are sitting still and breathing quietly, air is going into your lungs and then coming out, going in and coming out, many times every minute. How does the air get in and out of the lungs? It will not run in of itself; for it is light and floats about, you know. Here, again, Mother Nature has planned it all out. She has made us an air bellows, or air pump, to suck it into the lungs. First we'll see what shape this pump is, and then how it works.
Stiff rings of bone called _ribs_ run round your body, just like the hoops in an old hoop skirt, or like the metal rings round a barrel. Here is a picture of the bones of the chest. Perhaps your teacher can show you the skeleton of some animal. You will notice how the rings, or ribs, slant and are joined by hinges behind to the backbone and in front to the breastbone. It looks somewhat like a cage, doesn't it? Put your hands on the sides of your chest and you can feel your own ribs. Do they slant upward or downward?
This chest-cage is our breathing-machine. Before I tell you how it pumps, I want you to get a pair of bellows and see how they work. When you lift up the handle of the bellows, you make the bag of the bellows larger so that it sucks in air; and when you press the handle down again, the air puffs out through the nozzle.
Our air machine, though it is somewhat different from the bellows in shape, works in exactly the same way. You remember that you found that the ribs slant down and can be moved on hinges. Suppose, now, you place your hands against your ribs and feel the ribs lift as you draw in a long breath. The air will be sucked into your nose just as it was into the bellows when you raised the handle. By lifting your ribs, you have made the chest-cage larger; and the air has rushed into your nose, down your windpipe, and filled your lungs. If you breathe very deeply, you will find that your stomach, too, swells out. This shows that the muscular bottom of the cage, called the _diaphragm_, has been pulled down, making the cage larger still.
In this chest-cage are millions of tiny air bags that make up the lungs; and every time you take a breath, the air bags are puffed out with the fresh air that comes rushing in. By the time you let your ribs sink again, the air has given its oxygen to the blood, and the blood has poured its carbon-dioxid smoke into the air bags for you to breathe out. Nature, with the same bellows, pumps in the oxygen and pumps out the "smoke."
Now, we breathe into our lung-bellows whatever air happens to be around us. So we should take care that the air around us is fresh air.
Unless the air were kept in motion by the heat of the sun, causing breezes and winds, it would become stale and wouldn't do at all for our lung-bellows to use. The air we breathe must be kept moving and fresh if it is to make us feel bright and strong and happy. Mother Nature has given us miles upon miles and oceans upon oceans of this clear, fresh air to breathe--"all outdoors," in fact, as far as we can see around us and for miles above our heads. She sends the winds to move the air about and blow away the dust and dirt; and the sunshine, you remember, not only to warm the air and keep it moving, but to burn right through it and kill the poisons. But this brings us to something else.
You have learned that the air we breathe out would soon smother us, just as smoke would; and now we will see why. If you blow against the window pane on a cold day, the glass is no longer clear; and when you look at it closely, you see that it is covered with tiny drops of water. This is part of the breath you have just blown out. If the room is cold enough, you can see your breath in the air; that is, the steam in your breath becomes cold and appears as tiny water-drops. You have seen how in the same way, the steam, an inch or so from the spout of the teakettle, cools, making little water-drops that float in the air like clouds. Part of the breath, then, is water; but most of it is a gas, and you can't see it at all as it floats away into the air about you.
If your teacher has a glass of limewater, and will let you breathe into it through a tube, you will see that your breath soon makes the water look milky. This shows that the gas in your breath is not like the air about you; because air was all over the top of the limewater, yet did not change it at all. The milky look is caused by carbon dioxid, one of the poisons in your breath.
When some people come close to you, you want to turn away your head, because you do not like the smell of their breath. Even when one is quite well, the breath has a queer "mousey" odor, so that we never like to breathe the breath of another person. This disagreeable odor comes not only from the lungs but from the teeth.
We are always breathing out poisons into the air. One of these you can see in the milky limewater, and others you can smell when you happen to come close to anyone else.
If you blow on your fingers, you feel that your breath is much warmer than the air. If people are crowded together in rooms with doors and windows shut, their breath soon heats and poisons the air, until they begin to have headache, and to feel dull and drowsy and uncomfortable. If they should be shut in too long, without any opening to let in the fresh air, as in a prison cell, or in the hold of a ship during a storm, the air would become so poisonous as to make them ill, and would even suffocate them and kill them outright. Even the bees found this out thousands of years ago; and in their hives in hot weather they station lines of worker-bees, one just behind another from the door right down each of the main passages, whose business it is to do nothing but keep their wings whirring rapidly, so that they fan a steady current of fresh air into every part of the hive.
How does Mother Nature get rid of these poisons from our breath? Of course, you say, "She uses the wind and the sunshine." Yes, the winds can whisk up the poison and blow it away so fast, and the sunshine can burn up the horrid smell so quickly, that even the air above big cities, and in their streets, is quite clean enough for us to breathe, except where the people are very closely crowded together and very dirty. Mother Nature wants all of us to help in keeping the air clean. This we can do by keeping ourselves and our houses clean, and by being careful not to leave scraps of waste, or dirty things, in the streets and cars and parks and other public places. And you children ought to be very careful about your school yard and the halls and the classrooms, where you spend so much of your time.
IN SCHOOL
I. BRINGING THE FRESH AIR IN
The only place where air is absolutely sure to be fresh is out of doors. There, as we have seen, the sun and the winds keep it so all the time. But, unluckily, we cannot spend all our time outdoors, either when we are little or after we have grown up. So we must try in every way that we can to bring the outdoors indoors--to get plenty of fresh air and light into the houses that we live in, especially the bedrooms we sleep in and the schoolrooms we study in when we are children, and the offices or shops we work in when we are grown up.
After you have your lungs and your blood well filled with air, either by walking briskly to school or by chasing one another about the school playground, you will suddenly hear the bell ring, and you march indoors and sit down at your desks. Here, of course, the air cannot blow about freely from every direction, because the walls and doors and windows are shutting you in on every side. The room, to be sure, is full of air; but if the doors and windows are shut, this air has no way of getting outside, nor can the fresh, pure air out of doors--even though it be moving quite fast, as a wind or a breeze--get inside.
We must let the fresh air come in and the stale air go out. This is one of the things that windows are for; and this is why they are hung upon pulleys and made to slide up and down easily. Of course, even when the windows are not open, they are letting in light, which, you remember, is a deadly enemy to germs and poisons.
Bright sunlight is best for purifying the air of a room, but even ordinary daylight has a good deal of germ-killing power. Therefore, a room that is well lighted is not only much pleasanter to live in, but much healthier, than one that is dull and gloomy. You see why we need plenty of windows and doors: we must let in the breezes and the sunshine, and let out the poisons and the dirt. Then, too, we must make the air in the building move about in order to keep it fresh; for if the air is not fresh, we soon grow tired and sleepy and have headaches. That is why your teacher keeps the windows open at the top a foot or so. You can easily see that when there are twenty or thirty of you breathing out poisons, and each one of you needing about four bushels of fresh air every minute, the old air ought to be going out and the fresh air coming in all the time.
That is also why your teacher gives you a recess, so that you can run out of doors and get some fresh air. Then she can throw open all the windows and doors and have the air in the room clean and fresh when you come back again. So when recess comes, don't hang about in the hallways or on the stairs or in the basement, but run right out of doors into the playground and shout and throw your arms about and run races to fill your lungs full of fresh, sweet air and stretch all your muscles, after the confinement and sitting still. Don't saunter about and whisper secrets or tell stories, but get up some lively game that doesn't take long to play, such as tag or steal-sticks or soak-ball, or duck-on-a-rock or skipping or hopscotch. These will blow all the "smoke" out of your lungs and send the hot blood flying all over your body and make you as "fresh as a daisy" for your next lesson.
When you come back into the schoolroom after recess, the air will seem quite fresh and pure; but unless you keep the windows open, it will not be long before your head begins to be hot, and your eyes heavy, and you feel like yawning and stretching, and begin to wonder why the lessons are so long and tiresome. Then, if your teacher will throw open all the windows and have you stand up, or, better still, march around the room singing or go through some drill or calisthenic exercises, you will soon feel quite fresh and rested again.
In the mild weather of the spring or early fall, all you need to do to keep the air fresh in the schoolroom is to keep the windows well open at the top. But in the winter, the air outdoors is so cold that it has to be heated before it is brought in; and this, in any modern and properly built schoolhouse, is usually arranged for. The fresh air is drawn in through an opening in the basement and is either heated, so that it rises, or is blown by fans all over the building. This sort of fresh air, however, is never quite so good as that which comes directly from outdoors; so it is generally best to keep at least two or three windows in each room opened at the top as well, and never to depend entirely upon the air that comes through the heating system.
Sometimes this may mean a little draft, or current of uncomfortably cool air, for one or two of you who sit nearest the windows; but your teacher will always allow you to change your seat if this proves very unpleasant. If you have plenty of warmth in the room you sit in, unless the air outside is very cold, this "breeze" won't do you any harm at all; on the contrary, it will be good for you. Instead of catching cold from a draft like this, it is from foul, stuffy, poisonous air, loaded with other people's breaths and the germs contained in them, that you catch cold.
In fact, staying indoors is usually the reason why people are sick. They don't go out into the clean fresh air for fear they'll be too cold! It seems a pity we can't just live out of doors all the time. Perhaps we shall some day; for doctors are finding out that fresh outdoor air and good food are the very best medicines known, and the only "Sure Cures." They are pleasant to take, too. Many cities are providing outdoor schools for children who have weak lungs or are not strong in other ways. Perhaps some day all school children will be allowed to study in the open air at least part of every school day.
II. HEARING AND LISTENING
Now you are all ready to go to work. What are you going to work with? Books? pencils? paper? Yes, but you have something better than those and all ready for use. It is that little kit of tools that are sometimes called our "Five Senses." You remember that we have already talked about one of them, the sense of touch in the skin. Now which one are you going to use first this morning? If your teacher talks to you, I hope it will be the one we call the sense of hearing. Suppose we try to find out something about this sense of hearing, and begin with a little experiment.
Take a piece of cork in your hand and lift it up high and then let it drop into a large basin or tub of water. What happens? The cork strikes and then goes bob-bob-bobbing up and down on its own waves. Now watch the little waves all around the cork. Where do they stop? They don't stop until they touch the edge of the pan; and no matter how big the pan is, the waves go on and on until they reach the edge.
We can see these waves of water, and so we easily believe that they are there. Now there are, just as truly, waves of air all around us. We cannot see the waves, because they are too small and roll too quickly. But some of these, when they roll against our ears, make us hear. They make what we call _sound_. You have heard about sending messages through the air, without telegraph wires. Wireless messages are often sent to ships out in the middle of the ocean. This is done by starting tiny electric waves, which travel through the air much as the waves of water are traveling across the ocean beneath. Of course there must be a machine, called a _receiver_, to catch the waves and "hear" the message.
Mother Nature has given each of you two very delicate little receivers to catch the sound waves and carry them to your brain. You know what they are--you can name them. But how are these wonderful little machines made?
You have never seen the whole of your ear. The part on the outside of the head, of course, you can easily see and feel. Sometimes you notice a deaf person put his hand behind his ear and press it forward so as to catch the sound waves better. These waves roll in at the little hole you can see, and travel along a short passage till they come to a round _drum_, a piece of very thin skin stretched tight like a drumhead.
Have you ever beaten a drum with a stick? You felt the drumhead quiver under the blow, did you not? Well, when the sound waves beat against the drum in the ear, it quivers and starts little waves inside the ear. Each little wave in turn beats against a little bone called the _hammer_; the hammer beats against another called the _anvil_, and this against a third called the _stirrup_; and the quiver of the stirrup is passed on to a little window, opening into a little room with a spiral key-board; and from this, the wave travels along a nerve to the brain. As the waves reach the brain, the brain hears. In this way we hear all sorts of sounds, from the tick of a watch to the whistle of a train.
There is a sensible old saying, "Never put anything smaller than your elbow into the inner part of your ear." Now, of course, you can't put your elbow into such a tiny hole! So the old saying means, never put anything in. The eardrum is very thin and can easily be broken. Even a slap on the ear, or a loud sound too close to it, might crack and spoil the drum and make one deaf.
The outside ear needs careful washing; there are so many little creases that gather dirt and dust. The deep crease behind the ear, too, will become sore if it is not kept clean.
Besides cleaning your ears, you must train them to listen. Some boys and girls hear just a word or two of what is said, and then guess at the rest and think they are listening, or else ask to have it repeated. We should try to hear exactly what is said; and if we listen carefully, it will soon be much easier to understand at once.
Of course, if you really cannot hear, the doctor can tell you what is the matter, and usually can help you very much. Sometimes people become deaf simply because the throat is swollen. Indeed, most deafness comes from colds and catarrhs and other inflammations of the nose and throat. These spread to the ear through a little tube that runs up to the drum cavity from the back of the throat. Sometimes, when you are blowing your nose, you may feel your ear go "pop"; and that means that you have blown air up into the ear through this little tube. Be sure to see a doctor if you don't hear well; and be sure, too, to tell your teacher, so that she may know why it is you do not hear what she says, and ask her to give you a seat near her, so that you can hear.
Then, too, you should learn to notice outdoor sounds--the songs of the birds, the noises that the animals make, the wind in the trees, and the patter of the rain. The old Norsemen have a story that their god Heimdall had such keen ears that he could hear the grass growing in the meadow and the wool growing on the backs of the sheep! Your ears can never be so keen as that; but there are many, many happy outdoor sounds that you should listen for. They will help to make you happy, too.
Careful listening may sometime save your life. You can hear the car or the train coming, and you can learn to tell from which direction a sound comes. You can learn to tell one sound from another in the midst of many sounds. In more ways than you can think of now, this habit of listening will protect you from danger.
The Germans have a proverb, "Hear much and say little." What does it mean?
III. SEEING AND READING
You can learn a great deal through your ears, but think how much more you can learn through your eyes. Just count over all the things that you have had to get your eyes to tell you to-day, and then shut your eyes for a minute and think what it would mean never to be able to see. Don't you think you ought to take very good care of your eyes? You are going to keep them very busy all your life, and they deserve the very best care you can give them.
Just as soon as lessons begin, you get out your books; and a good share of the day in school you have a book before you, reading it or studying it or copying from it. It makes a great difference to your eyes how you hold the book and how the light falls. In reading, you should always hold your book so that the light falls upon the page from behind you, or from over one of your shoulders. In this way, the brightest light that comes into your eyes is not from the window, but from the page of your book.
If the light comes from a window in front of you, or if you sit in the evening with your face toward the lamp when you read, the light coming straight from the lamp or the window, as well as the light coming up from the pages of the book, pours into your eyes; and this dazzles and confuses your eyes, so that you can't see plainly and comfortably and are very likely after a while to find that your head aches. At home, of course, you can seat yourself with your back to the light when you read; and usually at school your seats are so arranged that the light falls from behind you or from one side. If not, by turning a little in your seat, you can get the light from over your shoulder.
Notice how the light falls upon the blackboard. When the light comes from the windows behind you, or from one side, you can see what is written there quite plainly. But if the blackboard happens to be between two windows, and especially if this is the lightest side of the room, you will find that the light dazzles you so that you cannot see the writing clearly.
You must have noticed, too, that if, after you have been reading from the blackboard you look down again suddenly to the page of your book, for an instant you will not see the letters plainly. Then, almost before you have time to notice it, you feel a little change take place inside your eyes, and the print upon the page of your book becomes quite plain. This is because your eye has to change the shape of one of the parts inside it, called the _lens_, before you can see clearly the things that are near you. This change, which is called _accommodation_, is made by a little muscle of the eye; and if you keep your eyes working at close work, like reading or writing or fancy-work, too long at a time, or if your eyes need glasses to make them see clearly, and you haven't them on, this little muscle becomes tired. Then the print of your book, or your writing, or the stitches you have taken begin to blur before your eyes. Your eyes begin to feel tired, and your head begins to ache. This is what we call _eye strain_.
Sometimes this eye strain upsets your appetite or your digestion and makes you sleepless and worried. The trouble may be caused by your own carelessness: you may have been reading too long, or in a poor light, or with the light shining right in your face instead of coming over your shoulder. But sometimes it is caused by the fact that your eyes are not just the right shape; and then the only way to relieve it is to have proper glasses, or spectacles, fitted, which will make up for this too flat or too round shape, or too large or too small size, of your eyes.
If you cannot see clearly what is written on the blackboard when the light falls upon it from behind you, or above; or if, in a good light, you cannot read the words in your book quite easily, without straining at all, when you hold the book either at arm's length or a foot from your face; or if your head aches or your eyes begin to feel tired or uncomfortable, or the letters begin to blur, after you have read steadily--say, for half an hour,--it is a pretty sure sign that there is some trouble with your eyes. Then you had better have them examined at once by your family doctor or by the school doctor. In many schools now there are doctors to test the children's eyes, and ears, too, so that each child may have a chance to see and hear everything that the other children can see and hear.