Physiological processes are all those changes that take place in the living irritable substance of plants and animals, such as nutrition, growth, and propagation. Its characteristic features are (1) hunger or thirst, i. e. the want of certain materials (food), (2) the reception of the wanted materials by suction or other means, which in some cases are a quite mechanical or physical process, not unlike the afflux of oxygen caused by a burning candle or the suction of water by a sponge, and (3) the assimilation of food. The materials received are distributed in the places wanted, thus adding to the building up of the living substance according to the nature of its structure. This produces as a natural result (4) the phenomenon of growth with a preservation of form. (5) Propagation is a special kind of growth; it is the growth of a part that at some stage of its development becomes an independent individual. Psychical phenomena are such in which feelings and the meanings of feelings are the determinant factors. It is apparent that all these terms, mechanical, physical, chemical, physiological, and psychical, are mere abstracts. In describing a mechanical phenomenon, we limit our attention to the mechanical change. We do not mean to say that the body moved does not possess chemical, physical, perhaps physiological, or even psychical qualities. The calculation of the curve of a jump is a mechanical problem, although the jumping body may be a human being. However, the question why did the man jump, is a psychical question. The motive of the jump is an idea in that class of mental activity characterised as purpose. The man had an end in view. And this idea of an end to be realised is the combined result of special conditions and of the character of the man. The different spheres of mechanical, physical, chemical, physiological, and psychical actions being abstractions, it is obvious that science when dealing with so-called purely mechanical phenomena, has to do with a fiction. There are no purely mechanical phenomena. There are features of reality which are purely mechanical; and these we call motions. But the world does not consist of motions only. It also possesses other qualities. The mechanical philosopher assumes that the world consists of matter and motion only, and so he feels warranted in the hope that every event that takes place, the actions of man included, can be explained by the laws of motion. Yet the premiss is wrong, and we may anticipate that the conclusion also will prove erroneous. And so it is. The laws of motion are applicable to and will explain all motions; but they are not applicable to that which is not motion.