While working purely on the lines of physical science it will be admitted that all observations recorded should be described in terms connoting physical phenomena, so given as to be capable of repetition, and, if possible, of measurement. No forces and no causes can be admitted as potent except those known to physiology and other branches of physical investigation. It follows that in dealing with the mental functions of the brain—here termed psychosis—we have nothing to do with “mind as an abstract entity” or with processes of feeling and consciousness, and must confine our attention to neural acts without either admitting or denying the existence of other potencies with which, while working on the lines of physical science, we are not concerned.