To continue the investigation of the modifying action of Environment into the moral and spiritual spheres, would be to open a fascinating and suggestive inquiry. One might show how the moral man is acted upon and changed continuously by the influences, secret and open, of his surroundings, by the tone of society, by the company he keeps, by his occupation, by the books he reads, by Nature, by all, in short, that constitutes the habitual atmosphere of his thoughts and the little world of his daily choice. Or one might go deeper still and prove how the spiritual life also is modified from outside sources--its health or disease, its growth or decay, all its changes for better or for worse being determined by the varying and successive circumstances in which the religious habits are cultivated. But we must rather transfer our attention to a second aspect of Environment, not perhaps so fascinating but yet more important.
So much of the modern discussion of Environment revolves round the mere question of Variation that one is apt to overlook a previous question. Environment as a factor in life is not exhausted when we have realized its modifying influence. Its significance is scarcely touched. The great function of Environment is not to modify but to _sustain_. In sustaining life, it is true, it modifies. But the latter influence is incidental, the former essential. Our Environment is that in which we live and move and have our being. Without it we should neither live or move nor have any being. In the organism lies the principle of life; in the Environment are the conditions of life. Without the fulfillment of these conditions, which are wholly supplied by Environment, there can be no life. An organism in itself is but a part; Nature is its complement. Alone, cut off from its surroundings, it is not. Alone, cut off from my surroundings, I am not--physically I am not. I am, only as I am sustained. I continue only as I receive. My Environment may modify me, but it has first to keep me. And all the time its secret transforming power is indirectly moulding body and mind it is directly active in the more open task of ministering to my myriad wants and from hour to hour sustaining life itself.
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.