The biologic sciences are rarely able to avail themselves of the use of theory, as can so commonly be done in the physical sciences, in such a way that the theory serves as a prophecy for the future, as well as an articulation with the past. When, however, phases of biologic knowledge are securely founded on a physical basis, it becomes possible to review a subject from the point of view of theoretic interpretation. Within recent years such a procedure has become possible in several directions in physiology.
The subject of the rôle of ferment-reversions in metabolism is naturally one of great interest; and, as the barristers say of a line of interrogation in the introduction of evidence, the proper foundation has been laid for it. It must be clearly realized, however, that if such a procedure as I contemplate is to be made profitable, the scope of