Go and watch the baby when he is asleep. See how his chest rises and falls, then rises and falls again.
He does not know what he is doing, but he breathes as perfectly as the oldest and the wisest man in the world. He began to breathe when he was born, and he will not stop until he dies; still he does it without thinking about it.
There is a special kind of machinery in each of us that takes care of our breathing even when we are asleep. Nobody has to be clever or old or good to know how to breathe, though each of us can stop our breathing if we care to try.
See how long you can hold your breath and be comfortable.
In some places men dive in the ocean for pearls. They pick up the shells that hold the pearls, and the longer they stay under water the more pearls they can find. For this reason they hold their breath as long as they possibly can. Yet even these pearl divers cannot go without breathing for over four minutes at a time.
In fact, there is no way for any of us really to stop breathing for a long time and keep alive. It is the same with animals.
If you should hold a bird in your hand, and if he were perfectly quiet and did not even breathe, you would know that he was dead, for breathing is as important for birds and animals as for children and men.
No one needs to tell us that what we breathe every minute of every day is air. It is around us everywhere, like a wonderful ocean that we cannot see. It also stretches so far above us and above the clouds that, try as we may, we cannot get outside of it.
Now this ocean of air is made up of several kinds of gases mixed together. Each is different from all the others, though not one of them is the gas that lights our houses. Indeed, the gas we use for lighting is different from the gases of the air in three ways:
- It will kill us if we breathe much of it.
- It has a smell.
- It will burn.
Still we find that air gases are like this deadly gas in two ways:
- We cannot see them.
- We can feel them when they blow against us, or when we run through them.
If you blow on your hand, you feel the air even though you cannot see it. So, too, when the wind blows, you do not see it, but you feel it rushing past.
There are men who can take a bottle full of air, separate it into its different gases, and study each gas by itself. Just now, however, you and I need to pay attention to only two of them,—oxygen and carbon dioxide.
If I should put a mouse into a jar with a good deal of oxygen in it, he would act so merry that you would think he had never before in his life felt so happy. If I should then fill another jar with carbon dioxide and put the same small mouse into it, he would surely die in a minute unless I pulled him out again as promptly as possible.
This shows the difference between oxygen and carbon dioxide: one is our friend, the other our enemy. Fortunately, in fresh, outdoor air there is always much oxygen and little carbon dioxide.
A change comes, however, in the rooms where people live and breathe, for when you take a deep breath of sweet, pure air the lungs use up a part of the oxygen at once and when you expel the air from your lungs, carbon dioxide is there in place of the oxygen. The exchange is made inside the lungs.
It is plain, then, that breathing takes oxygen out of the air and puts carbon dioxide in its place.
If a man is in a very small room, and if no fresh air can get in from anywhere, his breathing will change the air in the room so much that if he stays there long enough he will die. One of the saddest cases of this kind was in India when the British and Hindoo soldiers were fighting each other. Finally the Hindoos captured one hundred and forty-six British prisoners and put them into a room that was about twenty feet square. It had two small windows, so that a little air did manage to get in; but there was not enough of it for so many people. Fresh air could not enter fast enough to give the men the oxygen they needed, and the air that was in the room grew worse and worse until everybody suffered and gasped for breath, and when morning came only twenty-three of the men were alive. The rest had died for lack of oxygen. Ever afterwards, in memory of that terrible night, the room itself was called the Black Hole of Calcutta.
It is fortunate for us that air does not often get so bad as that in any room.