Suppose, as an example of the former conditions, a man living apart from his fellows and obliged to secure his own food. The trees hang their fruit at such a height that in order to reach it he must exert himself moderately, not enough to exhaust himself, but enough to insure a good digestion. In pursuit of game he must keep out of doors and be much afoot. Unpolluted mountain streams invite him to drink and to bathe. To keep within easy reach of his food supply summer and winter, he must frequently change his abode. For this reason he depends upon clothing rather than upon closely built walls for shelter, and moves away from the _débris_ which collects around him before it has endangered his bodily well-being. Thus the conditions of his life combine to give him the exercise and fresh air and sunlight and good food and good water and cleanliness that are necessary for his physical vigor. Now, suppose a man living under the other conditions--those that stimulate mental activity. A library tempts him to read, a university to study. The sight of great works of art or of other material products of human genius awakens any talents he may have. Association with thinking men and women induces currents of thought within him. Finally, contact with people who are willing and glad to climb his tree for him and pursue his game makes it possible for him to find time for brain work. But the opportunity to read and study instead of the necessity for climbing trees and chasing game means the loss of the condition that made for muscular activity, for good circulation, and good digestion. The decline in muscular activity makes his body produce heat less rapidly, and creates a demand for closely built walls and roof in addition to clothing. This means a loss of the condition that insured a plentiful supply of sunlight and fresh air. The permanent shelter makes it impossible for him to move away from the _débris_ of his food and the excretions of his body, and thus destroys the condition that in itself favored and practically compelled cleanliness. All this would make no difference, providing physical vigor were not necessary to mental activity. This, however, is a theory with which in the past we toyed to our sorrow. We conceived of a physical life and of an intellectual life, of a healthy body as necessary for the physical but not for the intellectual, and of development as coming through the putting off of the physical and the putting on of the intellectual. But we found that we were mistaken. The man from whom we were expecting beautiful poetry breathed bad air, weakened his lungs, fell a victim to tuberculosis, and we lost him and his song. The man to whom we were looking to plan for us beautiful buildings, to compensate in part for the natural beauties we had lost, weakened his body by insufficient exercise, then drank polluted water, died of typhoid fever, and we lost him and the beauties he might have created.