As you know, the “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.
The Breathed-out 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.
How and Why our Breathing Varies
When you run or wrestle, you breathe faster in order to draw more Air into the Lungs. At the same time, your Heart beats faster in order to drive a larger amount of blood through the Lungs. If you run too far, or wrestle too hard, your Heart and your Lungs both go faster and faster, until finally they reach a point when they cannot go any quicker, and the Poisonous Waste substances are formed in your Muscles faster than they can possibly be burned up, even by the quickest breathing and the hardest pumping of your Heart. Then you begin to get “out of breath“; and if you were compelled – in order to save your life, for instance – to keep on running, or fighting, you would at last be suffocated by your own waste and dirt, and fall exhausted, or unconscious.
The Principle Waste Gas – Carbon Dioxide
But what of the principal waste gas that the blood gives off in the lungs – The carbon “smoke,” or carbon dioxide? 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.
From Where the “Heat” in Breath Come
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.
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