The entelechies of the inert units of inorganic nature turn the forces of these units in an _outward direction_, so that they are incapable of operating upon themselves, of modifying themselves, or of regulating themselves. They are only capable of operating upon other units outside themselves, and in so doing they irreparably externalize their energy-contents. All physicochemical action is _transitive_ or _communicable_ in character, whereas vital action is of the _reflexive_ or _immanent_ type. Mechanical action, for example, is intermolar (_i.e._ an exchange between large masses of inorganic matter); physical action is intermolecular; chemical action is interatomic; while in radioactive and electrical phenomena we have intercorpuscular action. Hence all the forms of activity native to the inorganic world are reducible to _interaction_ between discontinuous and unequally energized masses or particles. Always it is a case of one mass or particle operating upon another mass or particle distinct from, and spatially external to, itself. The effect or positive change produced by the action is received into another unit distinct from the agent or active unit, which can never become the receptive subject of the effect generated by its own activity. The living being, on the contrary, is capable of operating upon itself, so that what is modified by the action is not outside the agent but within it. The reader does not modify the book, but modifies himself by his reading. The blade of grass can nourish not only a horse, but its very self, whereas a molecule of sodium nitrate is impotent to nourish itself, and can only nourish a subject other than itself, such as the blade of grass. Here the active source and receptive subject of the action is one and the same unit, namely, the living organism, which can operate upon itself in the interest of its own perfection. In chemical synthesis two substances interact to produce a third, but in vital assimilation one substance is incorporated into another without the production of a third. Thus hydrogen unites with oxygen to produce water. But in the case of assimilation the reaction may be expressed thus: Living protoplasm plus external nutriment equals living protoplasm increased in quantity but unchanged in specificity. Addition or subtraction alters the nature of the inorganic unit, but does not change the nature of the living unit. In chemical change, entelechy is the variant and matter is the constant, but in metabolic change, matter is the variant and entelechy the constant. “Living beings,” says Henderson, “preserve, or tend to preserve, an ideal form, while through them flows a steady stream of energy and matter which is ever changing, yet momentarily molded by life; organized, in short.” (“Fitness of the Environment,” 1913, pp. 23, 24.) The living unit maintains its own specific type amid a constant flux of matter and flow of energy. It subjugates the