Has it ever occurred to you to ask yourself why the pleasant wind blows over hills and fields, and through lanes and streets? You know very well that the wind always is blowing, more or less. Go out when you will, you find it, if you turn the right way. It is the most uncommon thing in the world for the air to be altogether still. The fresh wind blows so constantly over hill and plain, because God sends it to sweep away and destroy the poison vapors that steam out from decaying substances. The breeze is God’s invisible antidote to the invisible poison. The pleasant wind blows in order that the air may be kept fresh and pure.
In the open air the fresh wind very soon scatters and destroys all poison vapors. But civilized men do not dwell always in the open air. The wind sometimes makes them feel cold, so they build themselves houses to shut out the wind. To-night, before you go to bed in your small sleeping room, you will close the windows and the door; and you will think, when you have done so, that you have shut out everything which could harm you, with the cold. But what will you say to me if I show you that after you have closed the windows and the door, poison vapors are bred in great quantities in the room where you are lying? and that so long as you remain in it, they keep gathering more and more strength, and becoming more and more dangerous. Just come back with me to the cottage, and let us look at the room in which you were sleeping last night. The beds, you believe, are not yet made. Never mind that. I often go into rooms under such circumstances, and perhaps upon this occasion it may be even better for the purpose I have in view, if I find the chamber in disorder. At any rate let us go upstairs and take our chance.
Sure enough you have been at great pains here to keep the cold from getting in. There is only one casement in this low small room, and that casement has not been unbarred since yesterday. I do not need to be told this. I make the discovery myself; for you have also kept something from getting out, which had better have been away. I feel at once this is not the same kind of air which we were breathing just now in the open garden. Indeed, I can not remain in the room without opening the window. There; I throw open the casement, and in a few minutes the air will be as fresh here as it is outside of the house.
Now what do you think it was that made the air of this room so unpleasant? It was the poison-vapor with which it was laden, and which had steamed out of your body mixed with your breath during the night. Poison-vapors are bred in the bodies and in the blood of all living animals, just as they are in manure-heaps. All the working organs of your frame being exhausted by use, undergo decay and are turned into vapor, and that vapor, being bred of decay, is poison-vapor, which must be got rid of out of the body as quickly as it is formed. Living bodies are worn away into vapor by working just as mill-stones are worn away into dust by grinding. You would see them waste under work, if it were not that they are repaired by food. You wonder, then, that as this vapor is poisonous, living creatures do not destroy themselves by the poison they form in their blood? Occasionally human creatures do so destroy themselves, as I shall presently show you. But the merciful Designer of the animal frame has furnished a means by which, in a general way, the poison is removed as fast as it is formed. Can you not guess what this means is?
God employs the same plan for driving away poison vapors from the inside of living animal bodies, that he uses for the purification of the air in the open country. He causes a current of air to circulate through them. Notice how, while we are talking together, our chests heave up and down. You know this is what we term breathing. Now, when we breathe, we first make the insides of our chests larger by drawing their walls and floors further asunder. Then we make them smaller by drawing their walls and floors once more nearer together. When the chest is made larger, fresh air rushes in through the mouth and wind-pipe, and through the twig-like branches of this pipe, until it fills a quantity of little round chambers which form the ends of those branches. The wind-pipe branches out into several millions of fine twig-like tubes, and then each tube ends in a blind extremity, or chamber exactly like this.
The air-chamber in the body is covered by a sort of net-work, stretched tightly over it. That net-work is formed of blood-vessels, through which the blood is constantly streaming, driven on by the action of the heart. This blood sucks air from the air-chambers into itself, and carries that air onward to all parts of the living frame. But the blood-streams in the net-work of vessels also steam out into the air-chambers poison-vapors, which are then driven out through the windpipe and the mouth. Thus the breath which goes into the mouth is fresh air; but the breath which comes out of the mouth is foul air. Air is spoiled, and, as it were, converted to poison, by being breathed; but the body is purified by the breathing, because it is its poison-vapors that are carried away, mingled with the spoiled air.
This, then, is why men breathe. Breathing is the blowing of a fresh wind through the living body for the cleansing away of its impurities. The purifying part of the air which is breathed actually circulates with the blood through all parts of the frame.
Exercise quickens and exalts the cleansing powers of the breathing—and this is why it is of such great importance to the health. When you go and take a brisk walk in the open air, you increase the force of the internal breeze. The exertion makes your chest expand to a larger size, so that it can admit more fresh air, and it also causes your blood-streams to course along more rapidly, so that a greater abundance of the air is carried on through your frame.
[To be concluded.]
