THE PROCESS OF EXCITATION 113 



we have a case of an inanimate system, in which the amounts of 

 the reacting substances are in constant equilibrium. The reaction 

 following the mixture of equal amounts of alcohol and acetic acid 

 is as follows: 



YZ Mol. C 2 H 5 OH + y$ Mol. CH 3 COOH 

 = 2 /3 Mol. CH 3 COOC 2 H 5 + 2/3 Mol. H 2 O. 



In this reaction there is an alteration only in the absolute 

 quantity of the individual constituents but never in the relative 

 amount. In the living system we have a completely analogous 

 instance, which apart from its course differs from the inanimate 

 example merely in the following points : In the first place, certain 

 quantities of substances reacting on each other are continually 

 introduced into and certain reaction products continually re- 

 moved from the living system. Secondly, the reacting mixture 

 of the living substance is not homogeneous, and at the same 

 time is more complicated than that of the inanimate example. 

 Thirdly, the sum total of the reaction is not reversible in its en- 

 tirety. The question arises, should any essential difference 

 between metabolic self-regulation and the maintenance of chemi- 

 cal equilibrium be assumed upon this statement? I must con- 

 fess that this does not appear to me to be the case. The fact 

 that organisms exist in a stream of substances by which their 

 nutrition is introduced and the metabolic products removed, 

 cannot have any influence on the state of equilibrium so long as 

 the conditions are again and again replaced in the same manner. 

 The equilibrium can only be influenced when the introduction of 

 foodstuffs or the output of metabolic products is changed in value. 

 Then they occur as the inanimate example, when various amounts 

 of material are brought together. A new equilibrium takes place, 

 having a higher or a lower mass level. This is also true in the 

 living substance, in growth and in atrophy. The equilibrium is 

 disturbed as happens in the inanimate reacting mixture, where 

 different quantities of reacting substances are brought together. 

 In both instances we have in principle a conformity of behavior 

 of the inanimate and the living system. Secondly, as far as the 

 greater complexity and inhomogeneity of the living reacting mix- 



