Part 5

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.

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.

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.

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 passes 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 passed 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 scraps, as we burn scraps from the kitchen, in the back of the stove.

Suppose you light a candle and place it under a glass 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 glass 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 glass, 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 scraps 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 scraps, 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, passes 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.

For the "smoke" Mother Nature has still another beautiful plan. She sends the blood-stream flowing through the lungs, where it can send off its "smoke" and then get fresh air to carry to the cells in the muscles. When you breathe out, you are sending out the "smoke"; and when you breathe in, you are taking in fresh air.

Our body "smoke" is not brown or blue, like the smoke from a fire; it is a clear, odorless gas, called carbon dioxid. This is the same gas that makes the choke-damp of coal mines, which suffocates the miners if the mine is not well ventilated; and the same gas that sometimes gathers at the bottom of a well, making it dangerous for anyone to go down into the well to clean it. And this gas is poisonous in our bodies just as it is in the mine or the well.