Chapter 4 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.

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.

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.

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 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.