The question here follows: Is there a _constancy of this interruption of the equilibrium of rest produced by the stimulus_ which can be formulated into a general law? To begin with, the number of possible responses are greater than the variety of forms of living substance, for every living organism with its specific properties can undergo alteration in its metabolism in various directions. Thereby results an infinite number of manifold reactions to stimuli. However, in answer to the question, in which direction the change in the specific metabolism of rest in response to a stimulus takes place, we find a comparatively simple scheme of general reaction. All phenomena can change in their rapidity as well as in their nature. That is quantitatively and qualitatively. In this way the specific vital process of an organism can be altered by the stimulus, on the one hand, in its rapidity; on the other, in the manner of its action. The majority of all temporary responses to stimuli consist in _alterations of rapidity of the vital process_, and form either a quickening or retardation of its course. The former is manifested in a strengthening or an increase, the latter in a decrease or repression of the specific action of the living organism. The stimuli have the same effect as in the case of the catalysers in chemical processes. According to _Ostwald’s_[43] well-known definition of catalysis a catalyser is a substance which, without appearing in the final product of a chemical reaction, alters its rapidity. This group of reactions can, therefore, be referred to as “_catalytic stimulation and response_.” When the response consists in _increase_, we speak, in a physiological sense, of an excitation, and when there is decrease in the vital processes, we speak of a depression. [43] _Ostwald_: “Ueber Katalyse.” Verhandl. d. Ges. Deutscher Naturf. und Aerzte zu Hamburg 1901.