THE GENERAL EFFECT OF STIMULATION 73 



the resultant error is inconsiderably minute. This period of time 

 is of greatly varying length in different living organisms and this 

 fact must be taken into account in every living form. Only with 

 this restriction can we justify the use of the term "equilibrium 

 of metabolism." Then, however, its use is of great value. 



The metabolism of stimulation is then a disturbance of the 

 metabolism of rest, that is, a disturbance of the equilibrium of 

 metabohsm through the effect of stimuli. 



The question here follows: Is there a constancy of this inter- 

 ruption 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 prop- 

 erties can undergo alteration in its metabolism in various direc- 

 tions. Thereby results an infinite number of manifold reactions 

 to stimuli. However, in answer to the question, in which direc- 

 tion 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 mani- 

 fested 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^ well-known defi- 

 nition 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 



1 Ostwald: "Ueber Katalyse." Verhandl. d. Ges. Deutscher Naturf. und Aerzte zu 

 Hamburg 1901. 



