Comp. Anat. and Phys. Biol. XXIII. ON THE PROXIMATE CAUSE OF FUNCTIONAL ACTION. 1856. THE actions which take place in the animal body naturally divide themselves into two classes-the nutritive and the functional; or those which are concerned respectively in the formation of the organs and their use. In some instances it may be difficult to draw the exact line at which nutrition ends and function begins, but for the most part the distinction is clearly defined, and theoretically the separation of the two forms of action is always easy. There are three forms of function-nervous action, muscular contraction, and secretion. Taken in a large sense, these divisions appear to include all the active functions known to exist in the human body. In the following remarks, no explanation will be attempted of the phenomena of nutrition: accepted for the present as ultimate facts, they form rather the basis upon which it will be sought to found a consistent theory of the cause of functional activity. Little doubt can be entertained that the force which is operative in the vital processes is but a peculiar manifestation of the same force (or forces, if there be more than one), with which we are familiar under other names, as regulating the phenomena of inorganic nature. although thus, in its origin, one with the other physical But forces, the peculiarity of the conditions under which it exists in the living bodies imparts to it specific properties, to designate which the term vital is employed. One of the most characteristic of these peculiar modes of action of the vital force is the opposition which it presents to the operation of those forms of force which are termed chemical-an opposition not of essential nature, but of special direction. The vital force (or, as from this point of view it might be called, the vital affinity, for the sake of bringing out more clearly at once the relation and the contrast) controls and holds in abeyance the chemical tendencies of the matter in which it subsists.1 From the state of chemical tension thus arising, it results that there exists in all living matter a constant tendency to change. No sooner are the conditions requisite for the manifestation of vital properties withdrawn, than chemical affinity resumes its sway and decay commences. Even during life the same process is continually going on. The tissues waste, and are renewed, and waste again. A certain connection between this waste or disintegration of the tissues and the functional activity of the body in which it takes place, is universally admitted. Yet the relation which subsists between them is by no means satisfactorily established. For the most part, the activity is held to precede and cause the waste. "Discharge of function, consequent degeneration, absorption, and replacement by new structures." "In the history of a cell there are three stages-that of its 1 There can be no difficulty in conceiving forces essentially the same acting thus circumstantially in opposition. Innumerable instances will occur to the mind in which heat, for example, opposes chemical affinity, or gravitation itself raises or suspends a weight. |