A Handbook of Health

by Woods Hutchinson

DIAGRAM OF THE AIR TUBES AND LUNGS

The arrows show the direction of the incoming air.

The lungs sprout out from the front of the gullet, just below the root of the tongue, in the days when we are getting ready to be born. The sprout divides into two, forming the beginning of the pair of lungs. Each lung sprout again divides into two, and each of the two smaller buds again into two, until finally we have the whole chest filled up with a "lung-tree" whose trunk stems and leaves are hollow. The stem of the tree or bush becomes the windpipe (trachea). The first two branches into which it divides form the right and left lung tubes, known as bronchi. The third, fourth, fifth, sixth, etc., divisions, and so on, form what are known as the bronchial tubes. These keep on splitting into tinier and tinier twigs, until they end, like the bush, in little leaves, which in the lung, of course, are hollow and are called the air cells (alveoli). This budding off of the lungs from the gullet is the reason why the air we breathe and the food we swallow go down the same passage. Every mouthful of our food slides right across the opening of the windpipe, which has to be protected by a special flap, or trap-door of gristle, called the epiglottis. If you try to eat and talk at the same time, the epiglottis doesn't get warning of the coming of a swallow of food in time to cover the opening of the windpipe, and the food goes down the wrong way and you cough and choke.

Now, if you will just place your fingers upon the front of your neck and slide them up and down, you will, at once, feel your windpipe—a hard, rounded tube with ridges running across it,—while, no matter how carefully you feel, or how deeply you press, you cannot feel your gullet or esophagus at all. Just take a mouthful of water, however, put your fingers deeply on each side of the windpipe, and swallow, and you will feel something shoot down the esophagus, between your fingers, toward the stomach.

Both of these tubes were made of exactly the same materials to begin with. Why have they become so different? A moment's thought will tell you. One, the gullet, has only to swallow solid food or drink, so that its walls can remain soft, and indeed fall together, except when it is actually swallowing. The other tube, the air-pipe or windpipe, has to carry air, which neither will fall of its own weight, nor can readily be gulped down or belched up. It is absolutely necessary that its walls should become stiff enough to keep it open constantly and let the air flow backward and forward. So we find growing up in the walls of this air pipe, cells which turn themselves into rings of gristle, or cartilage.

What the Breath Is. As you know, your "breath," as you call it,—that is to say, the used-up air which you blow out of your lungs,—is different in several ways from pure, or unused air. In the first place, it is likely to have a slight musky or mousy odor about it. You never like to breathe any one else's breath, or have any one breathe in your face. This dislike is due to certain gases, consisting of impurities from the blood, the cells of the lungs, the throat, the nose, and, if the mouth is open, the teeth. These are not only offensive and disagreeable to smell, but poisonous to breathe.

Then your breath is much warmer than the rest of the air. In fact, on a very cold morning you may have tried to warm up your fingers by breathing on them; and you have also noticed that if a number of people are shut up in a room with doors and windows closed, it soon begins to feel hot as well as stuffy. This heat, of course, is given off from the blood in the lungs and in the walls of the throat and nose, as the air passes in and out again.

When you stand at the window on a cold day, the glass just in front of your mouth clouds over, so that you can no longer see through it; and if you rub your finger across this cloud, it comes away wet. Evidently, the air is moister than it was when you breathed it in; this moisture also has been given off from the blood in the lungs.

But what of the principal waste gas that the blood gives off in the lungs—the carbon "smoke," or carbon dioxid? Can you see any trace of this in the breath? No, you cannot, for the reason that this gas is like air, perfectly clear and transparent, and never turns to moisture at any ordinary temperature. But it has a power of combining with certain other things and forming substances which, because they are combinations of carbon, are called carbonates. The commonest substance with which it will do this is lime. If you take a glass or a bottle two-thirds full of lime water, and breathe into it through a glass tube or straw, you will see in a very few minutes that it is becoming milky or cloudy from the formation of visible carbonate of lime, which, when you get enough of it, makes ordinary limestone. So, although you cannot see, or smell, this carbon "smoke" in your breath, you can readily prove that it is present.