ABSTRACT
The two great classes of vital phenomena which Physiology and Psychology respectively embrace, are broadly distinguished in this; that while the one class includes both simultaneous and successive changes, the other includes successive changes only. While the phenomena forming the subject-matter of Physiology, exhibit themselves as an immense number of different series bound up together; those forming the subject-matter of Psychology, exhibit themselves as but a single series. The briefest consideration of the many continuous actions constituting the life of the body at large, suffices to show that they are synchronous—that digestion, circulation, respiration, excretion, secretion, in all their many subdivisions, are going on at one time, in mutual dependence. Throughout the homogeneous tissue of which the lowest creatures consist, there is complete community of actions. The first great differentiation established, is that between the inner and outer tissues—the mass, and its limiting membrane—the substance of the body, and its skin.
