2 THE AMERICAN JOURNAL OF SOCIOLOGY
his death his life is on-going. The psychologist beholds in him a stream of consciousness ; the physiologist, a constant suc- cession of bodily changes. There seems to be an unvarying relation between these two aspects of his make-up, so that, as is well known, there are two roads open to anyone who would go the way of the psychologist in the examination of any problem : the first, a spiritualistic highway which finds the energy of con- sciousness to be of a nature of its own, and of such a peculiar kind that one can treat it only by figures in our common speech ; the other, a physiological path in which it is a sufficient explana- tion to adhere to the law of material equivalents, and to treat consciousness as the result of brain conditions. It is conceived that these two ways are not divergent in so far as they must be trodden in the treatment of this question ; that the results which appear from following one are just as truly furnished by the other, with perhaps but slight change of phrase ; that the activity is fundamental, and behaves in much the same way no matter whence derived. We shall for purposes of illustration follow the physiological path.
The human being is a complex activity inside of whose cir- cumference a ceaseless change is ever striving to go on. The fuel for this process the energy of the human machine is furnished us in food and air. At first it has forms of its own- is reduced to solution is taken into circulation, disappears from our sight ; but seems to reappear in the heat of the body, in the friction of its processes, and in muscular and mental energy. The two ends of this chain of energy are plain to view. The connecting links between them are as yet unseen. If, as physi- ologists believe, there are no hidden sources of energy, no inflow- ings of subtle and as yet undiscovered forms of power ; if air and food are all the outer forms of this process, they can be measured, and the amount of fuel which the machine consumes exactly determined. But it is admittedly impossible as yet to trace its many redistributions to their final outcome with exactitude. One knows how much goes in ; he knows that it is changed and, after many metamorphoses, restored again ; but the details of this change he cannot state. Yet it is known that there results
