The food you put into your body must be made soft and pulpy before it can burn in your muscles. Now you can guess what your teeth are for.

They chop, crush, and grind the food; and the tongue rolls it over and over and mixes it with the moisture in your mouth, until it is almost like very thick soup. Then you make a little motion with your tongue and throat, and down it goes.

[Ill.u.s.tration: THE FOOD TUBE

Note the arrows. This is the trip made by every mouthful of food.]

Where does it go? It is pa.s.sed down a tube that we call the _food tube_. While I tell you about it, you can look at the picture and then try to draw it yourself.

The food goes quickly down the first part of the tube until it comes to a part much larger than the rest, which we call the _stomach_. Here it is churned about for a long time, and the meat you have eaten is melted, or dissolved. Then the food goes on into the next part of the tube, which has become narrow again. This lower part, which is about twenty-five feet long, is coiled up just below the waist, between the large bones that you can feel on each side of your body. These coils of the food tube, we call the _bowels_.

Winding all around the stomach and bowels are tiny branching pipes full of blood. They look somewhat like the creepers on ivy, or the tendrils on grapevines. These suck out the melted food from the bowels. They take what the body can use, and carry it away in the blood to all parts of the body. This is the fuel that keeps the "body fires" going. The tougher parts of the food, which the body cannot use, are carried down to the lower end of the bowels and pushed out by strong muscles.

This waste should be pa.s.sed out from the body once every day and at the same time each day. In the morning after breakfast is perhaps the best time. If you do not get rid of it every day, it makes poisons, which go into your blood and soon make you very sick indeed. You must keep clean inside as well as outside.

GOING TO SCHOOL

I. GETTING READY

As soon as you have finished breakfast, and brushed your teeth and gone to the toilet, you are ready to run out of doors to play, if you have plenty of time, or, if not, to start for school.

Doesn't it seem a nuisance, in winter time, to have to put on a coat and overshoes and a cap or a hood, and sometimes leggings and mittens, too? But your mothers know what is best for you; and when you are young and growing fast, you have so much more surface in proportion to your weight than when you are grown up, that you lose heat from the blood in your skin very fast; and unless you are warmly dressed, you become chilled.

When you are chilled, you are using up, in merely trying to keep yourself warm, some of the energy that ought to be used for growing and for working. It has been found out by careful tests that children who are not warmly dressed, and particularly whose arms and legs are not warmly covered, do not grow so fast as they ought to, and more easily catch colds and other infections. So take time to put on your cap and your coat, if the weather is cold; and, if it is snowy, to b.u.t.ton on leggings over your stockings; and then you can play as hard as you like, and run through the snow, and keep warm and rosy and comfortable.

Wool is one of the best stuffs for coats and dresses and stockings and gloves and caps, not only because it is warm, but also because it is lighter in weight than anything else you could wear that would be equally warm, and because it is _porous_; that is, it will let the air pa.s.s through it, and the perspiration from the body escape through it.

Don't wear any clothes so tight that you cannot run and jump and play and fling your arms and legs about freely, or so fine and stylish that you are afraid of getting them soiled by romping and tumbling.

It is best to wear fairly heavy, comfortable shoes with good thick soles; then you will not have to wear rubbers, except when it is actually pouring rain, or when there is melting snow or slush upon the ground. Felt, or buckskin, or heavy cloth makes very good "uppers" for children's shoes; but only leather makes good soles.

It is best not to wear rubbers too much, because the same waterproofness, which keeps the rain and the snow out, keeps the perspiration of your feet in, and is likely to make them damp. When they are damp, they are as easily chilled as if they had been wet through with rain or puddle water. Always take off your rubbers in the house or in school, because they are holding in not only the water of perspiration, but the poisons as well; and these will poison your entire blood, so that you soon have a headache and feel generally uncomfortable.

II. AN EARLY ROMP

The minute you are outside the door, the fresh morning air strikes your face, and you draw four or five big breaths, as if you would like to fill yourself as full as you could hold. If you have had a good night's sleep and a good breakfast, the very feel of the outdoor air will make you want to run and jump and shout and throw your arms about. This warms you up finely and gives you a good color; but if you keep it up long, you will notice that two things are happening: one, that you are breathing faster than you were before; the other, that your heart is beating harder and faster, so that you can almost feel it throbbing without putting your hand on your chest.

If you run too hard, or too far, you begin to be out of breath, and your heart thumps so hard that it almost hurts. What is your heart doing? It is pumping; it is trying to pump the blood fast out to your muscles to give them the strength to run with.

[Ill.u.s.tration: AN EARLY RUN IS A GOOD PREPARATION FOR THE DAY'S WORK]

Of course you have seen a pump? Perhaps some of you have to pump water every day at home. You take the handle in your hands, lift it up, then press it down, and out pours the water through the spout; and, as you keep pumping, the water spurts out every time you press the handle down. It is hard work, and your arms are soon tired; but, as you cannot drink the water while it is down in the well, you must pump to bring it up where you can reach it.

[Ill.u.s.tration: THE HEART-PUMP

The big tubes are the arteries and veins.]

Just so the heart pumps to keep the blood flowing round and round, through the muscles and all over the body. If you put your finger on your wrist, or on the side of your neck, you can feel a little throb, or _pulse_, for every spurt from your heart-pump; and that means for every heart-beat.

This heart-pump is made of muscle, and is about the size of your clenched fist. And just as you can squeeze water from a sponge or out of a bulb-syringe, by opening and shutting your hand around it, so the big heart muscle squeezes the blood out of the heart. It squeezes it out from one side of the heart; and then, when it lets go, the blood comes rushing in from the other side to fill the heart again. So the heart goes on squeezing out and sucking in the blood, all day and all night as long as we live.

When the blood comes to the muscles, it is a beautiful bright red; but after the muscles have taken what they want of it for food to burn, and warm you up, the "ashes" and the "smoke" go back into the blood and dirty its color from red to purple. Then the blood is carried to the lungs, where the fresh air you breathe in blows away the "smoke"

and makes the blood red again.

The blood is pumped all over the body through tubes or pipes, called _blood vessels_. Those that carry the red blood out from the heart, we call _arteries_. They are deep down under the skin, and we cannot see them. The pipes that carry the purple blood from the muscles and other parts back to the heart again, we call _veins_; and some of these are so close to the surface that we can easily see them through the skin.

Let your hand hang down a minute or two, then you can see the veins on the inside of your wrist, or on the back of your hand, if it is not too fat.

[Ill.u.s.tration: IT IS GOOD TO PLAY OUT OF DOORS TILL THE BELL RINGS--EVEN IN WINTER]

The muscles, the brain, the skin, and other parts of the body get liquid food from the blood by "sucking" it through the walls of the smallest of the blood vessels, for these walls are very thin. In the same way, when waste pa.s.ses from the muscles or the skin into the blood, it, too, soaks through the thin walls of the tiniest blood tubes, called _capillaries_.

Your heart beats or throbs about seventy-five times in a minute when you are well. Look at the second hand of a watch, while you count the beats in your wrist or in your neck.

Does your heart ever become tired? Not while you keep well, unless you over-drive it by running or wrestling too hard. It can rest between the beats. But the heart muscle, like any other muscle, must have plenty of good red blood to feed on. You put food into the blood by eating good breakfasts and dinners. The more you run and jump and play, the more work the heart has to do and the stronger it grows; and a good morning romp before school will send the blood flowing so merrily round from top to toe that you will feel fresher and brighter all the day.

III. FRESH AIR--WHY WE NEED IT

The heart is not the only thing that goes faster and harder when you run about in the morning and play hard. You are breathing faster and deeper as well, as if there were something in the air outside that you needed in your body as much as food.

But, of course, you know that air is not good to eat. It has no strength in it, as food has; it isn't even a liquid like milk or coffee or tea. It is so thin and light that we call it a _gas_.

Indeed, I suppose it is pretty hard for you to believe that air is a real thing at all. But all outdoors is full of the gas called air, and everything that seems to be empty, like a room or an empty box, is full of it.

You cannot even smell it, as you can that other gas which comes through pipes into our houses and burns at the gas jets; nor can you see it like the gas that comes out of a boiling kettle or from the whistle of a locomotive, and which we call _steam_. This is simply because air is so pure that it has no smell, and is so perfectly clear that we can see right through it. Almost the only way that we can recognize it is by feeling it when it is moving. But it is a very real thing for all that; and, like sunshine and food, is one of the most important things in the world for us.

What is it that air does in the body? We must need it very much, for we die quickly when we cannot get it: it takes us only about three minutes to suffocate, or choke to death, if we can't get it.

You remember that the blood is pumped out from the heart, all through the body. Everywhere it goes,--to the feet and the hands and the head,--it is carrying two things: food that it has sucked up from the food tube, and hundreds and hundreds of tiny red sponges called red _corpuscles_. These little sponges are full of air which they sucked up as the blood pa.s.sed through the lungs. When we stop breathing,--that is, taking in air,--the little red sponges of course can't get any air to carry to the different parts of the body.

The body is made up of millions of tiny, tiny animals, called _cells_,--so tiny that they can be seen only under a microscope. Each of these cells must have food and air, just like any other animal.

They eat the food the blood brings to them, and they take the air from the red corpuscles in the blood. With the air as a "draft," they burn up the waste sc.r.a.ps, as we burn sc.r.a.ps from the kitchen, in the back of the stove.

Suppose you light a candle and place it under a gla.s.s jar and watch what will happen. The flame will become weaker and weaker, and at last it will quite go out. You might think at first that the wind blew it out; but how could the wind get through or under the jar? No, the gla.s.s keeps all the outside air away from the flame; and that is just the reason why it does go out. Unless it has fresh air, it cannot burn. There is something--a gas--in the air that makes the flame burn, and when it has used up all this gas inside the gla.s.s, and can't get any more, it stops burning.

Now you will want to know what this gas in the air is. When we write about it, we use its nickname, the large capital letter _O_; but its whole name is _Oxygen_.

Just as the candle flame must have oxygen to keep it burning, so our cells must have oxygen to burn their impurities, or waste; and if they don't get the oxygen, and can't burn their impurities, they are poisoned by them and "go out," or die.

You can see the flame when the candle is burning, but you can't see the fires that burn in our bodies; there are no real flames at all. I know it is hard for you to believe that there can be any burning when our bodies are so wet and damp. But if you can't see it, you can easily feel it. Blow on your hand. How warm your breath is! Touch your hand to your cheek. It is quite warm, too. If you run or play hard, you sometimes become so hot that you want to take off your coat. That is because your fires are burning faster. The muscles are using more food and making more sc.r.a.ps to be burned. You breathe faster and faster till at last you are "out of breath" and feel as if you would smother or choke. The blood has hard work to bring oxygen enough to keep the fires going.

After the cells have burned the food sc.r.a.ps, they turn the "ashes" and "smoke" back into the blood-stream that is always flowing past them.

If the cells did not do this, they would soon smother to death, just as you could not possibly live in a house without chimneys to carry off the smoke. And, of course, the blood wants to get rid of this waste just as quickly as possible.

Part of the waste in the body is liquid, like water, and can flow away through the blood pipes without needing to be burned. Some of this watery waste comes out through the skin and stands in beads or drops upon it. That is the part we call perspiration, or sweat. The rest of it goes in the blood to another strainer called the _kidneys_, pa.s.ses through this as _urine_, and is carried away from the body as the waste water from the bathtub and the sink is carried away from a house.