To understand the sustaining influence of Environment in the animal world, one has only to recall what the biologist terms the extrinsic or subsidiary conditions of vitality. Every living thing normally requires for its development an Environment containing air, light, heat, and water. In addition to these, if vitality is to be prolonged for any length of time, and if it is to be accompanied with growth and the expenditure of energy, there must be a constant supply of food. When we simply remember how indispensable food is to growth and work, and when we further bear in mind that the food-supply is solely contributed by the Environment, we shall realize at once the meaning and the truth of the proposition that without Environment there can be no life. Seventy per cent. at least of the human body is made of pure water, the rest of gases and earth. These have all come from Environment. Through the secret pores of the skin two pounds of water are exhaled daily from every healthy adult. The supply is kept up by Environment. The Environment is really an unappropriated part of ourselves. Definite portions are continuously abstracted from it and added to the organism. And so long as the organism continues to grow, act, think, speak, work, or perform any other function demanding a supply of energy, there is a constant, simultaneous, and proportionate drain upon its surroundings. This is a truth in the physical, and therefore in the spiritual, world of so great importance that we shall not mis-spend time if we follow it, for further confirmation, into another department of nature. Its significance in Biology is self-evident; let us appeal to Chemistry.