THE GENERAL EFFECT OF STIMULATION 71 



cile ourselves to dry pedantic definitions. In the case of that 

 of the equilibrium of metabolism indeed we have before us one 

 of the most important conceptions in physiology. 



The justification to speak of an equilibrium of metabolism 

 arises from investigations of metabolism in mammals. The clas- 

 sical experiments of the previous century, as is well known, have 

 shown that in the adult mammal receiving a necessary quantity 

 of nourishment and in a state of rest, the intake and outgo of 

 the constituent elements are the same. The carbon, hydrogen, 

 nitrogen, oxygen, sulphur, phosphorus, etc., taken in during 

 a lengthened period in the form of food and respired air, 

 appear again in equal quantity, in other combinations, in the 

 products of excretion of the organisms. Calorimetric experiments 

 likewise show an equilibrium of the consumption and elimination 

 of energy. If there thus exists an equilibrium of metabolism for 

 the whole cell community, it is clear that the same must also apply 

 to the individual cell, that is, for all living substance. The quan- 

 titative relations of the foodstuffs taken in, and the excreted meta- 

 bolic products given off, are, however, merely a standard of the 

 metabolism. We know that the former are used to build up new 

 living substance and that the latter represent the result of dis- 

 integration of that previously existing living substance; for we 

 find, as in the case of the plant, complicated protein combinations, 

 which are built up from comparatively simple constituents of the 

 food and are again broken down into comparatively simple sub- 

 stances. And so the building up and breaking down processes 

 form the two great processes of metabolism, which with Hering^ 

 we can briefly call "assimilation" and "dissimilation." ■ In the 

 terms assimilation and dissimilation are comprised the sum of all 

 processes of construction and disintegration in the living organ- 

 ism. It is apparent that equilibrium of metabolism occurs when 

 assimilation and dissimilation are equal. The formula A : D, that 

 is, the relation of the sum of all assimilation to the sum of that of 

 all dissimilative processes, is a factor of fundamental importance 

 in the study of the course of the vital processes, for upon its 



1 E. Hering: "Zur Theorie der Vorgange in der lebendigen Substanz." In Lotos, 

 Bd. 9, Prag. 1888. 



