VIII.—Turning from the living mechanism and its energies, to the energies derived from without that move it—the “strings of the puppet”—to use the mechanical phraseology, we come upon another class of words and phrases which are ambiguously used in the “old metaphysics,” but which have a definite and wholly different meaning in studying the organic bases of mental life. These are such words as impression, irritation, suggestion, and the like. I may be permitted to state, somewhat dogmatically, what is now admitted generally, that all changes in the constituent matter of living things result from the operation of physical or molecular energies therein. This being so, the cerebral series of changes involved in mental states of the individual, and constituting the process termed cerebral reflex action, are due to as purely physical causes as those on which spinal reflex action depends. And this is true, not less as regards feelings like corporeal pain, and sensations, than as regards the highest work of the intellectual faculties. This operation of physical energies, however, was not recognised by Marshall Hall and Dr. Carpenter in 1838, nor, indeed, by physiologists in general. One source of the difficulty experienced in doing this is in the imperfect appreciation of what is physically included under the word impression. Thus, an anonymous defender of the views of the eminent physiologists named observes, in 1846, in opposition to my views—