RESPIRATION. The conception of life is so closely bound up with that of respiration that the very word "expiration" has come to connote the extinction of life, and "inspiration" its eleva tion to a super-human level. Respiration is a process common to all forms of animal life, the reason for which is that the chemical basis of life is essentially an oxidation of tissue. Rightly, we speak of the "flame" of life, for in the body, as in the fire, ma terial is all the while being consumed, with concurrent consump tion of oxygen, and the production of carbon dioxide. Respiration consists essentially in the transport of oxygen from the air to the place where the oxygen is used up by the body, and the trans port of carbon dioxide from the place where it is produced to the external air. Many animals, of course, live in water; indeed, life presumably began in that medium. But even for them the ultimate source of oxygen is the atmosphere; from it the water acquires fresh stocks of oxygen as the animals which inhabit it use up the gas. The oxygen in water is for the most part in solu tion, not in bubbles; but in the sea the constant breaking of the waves has a most potent effect in oxygenating the surface layers of the water.
In the most primitive forms of life respiration is very simple. In the amoeba, which is little more than a minute particle of jelly, the respiratory process is carried on in this way : The amoeba lives in water, from the water oxygen soaks into the body of this animalcule, where it is always being used up, and because it is always being so used the potential of oxygen inside the amoeba is always less than the potential of oxygen in the water outside. The oxygen, therefore, by a simple process of diffusion, is ever tending to migrate from the place of higher to that of lower potential, i.e., from the water to the interior of the amoeba, so a constant stream of gas is maintained. So also with the carbon dioxide; it is produced in the amoeba, from the interior of which it diffuses out, through the surface into the surrounding water. In the higher forms of life, there is no different principle in volved, so far as is known, from that of the amoeba. The appar atus for effecting respiration becomes more complicated, but the actual process is the same, namely, the diffusion of gas, oxygen or carbon dioxide from the place of higher to the place of lower potential.