Why our Bodies Need Air-Oxidation. The body is made up of millions of tiny living animals called cells, which eat the food that is brought to them from the blood and pour their waste and dirt back again into the same current. Now, what would happen if we were to throw all the garbage from the kitchen, and the wash water from the kitchen sink, and the dirty water from the bathroom right into the well out of which we pumped our drinking water? We should simply be poisoned within two or three days, if indeed we could manage to drink the disgusting mixture at all. That is exactly what would happen to our body cells if they were not provided with some way of getting rid of their waste and dirt. [Illustration: THE GREAT ESSENTIAL TO LIFE--AIR If the air, supplied to the diver through the tube, is cut off for three minutes, or even less, the diver cannot live.] Part of the waste that comes from our body cells is either watery, or easily dissolved in water; and this is carried in the blood to a special set of filter organs--the liver and the kidneys--and poured out of the body as the _urine_. Another part of it, when circulating through the skin, is passed off in the form of that watery vapor which we call perspiration, or sweat. But part of the waste can be got rid of only by burning, and what we call burning is another name for combining with oxygen, or to use one word--_oxidation_; and this is precisely the purpose of the carrying of oxygen by the little red blood cells from the lungs to the deeper parts of the body--to burn up, or oxidize, these waste materials which would otherwise poison our cells. When they are burnt, or oxidized, they become almost harmless. Why the Red Cells Carry only Oxygen to the Body. But why do not the red cells carry air instead of just oxygen? This is simply a clever little economy of space on nature's part. As a chemist will tell you the air which we breathe is a mixture of two gases--one called nitrogen and the other oxygen; just as syrup, for instance, is a mixture of sugar and water. Then too, as in syrup, there are different amounts of the two substances in the mixture: as syrup is made up of about one-quarter sugar and three-quarters water, so air is made up of one-fifth oxygen and four-fifths nitrogen. Now the interesting thing about this mixture, which we call air, is that the only really "live" and vital part of it for breathing purposes is the one-fifth of oxygen, the four-fifths of nitrogen being of no use to our lungs. In fact, if you split up the air with an electric current, or by some other means, and thus divide it into a small portion of pure oxygen (one-fifth), and a very much larger portion (four-fifths) of nitrogen, the latter would as promptly suffocate the animal that tried to breathe it as if he were plunged under water.[18]