92 IRRITABILITY 



either especially those operative in the activity of the animal 

 organism or any of the physiological nerve impulses which regu- 

 late the actions of the different organs and tissues, bring about 

 primarily an assimilative excitation, which leads to an increase 

 of new formation of living substance. The much-discussed 

 teaching of the existence of the trophic nerves has not given us 

 a single case in which there was positive proof that a nerve 

 impulse brought about a primarily assimilative excitation. I have 

 endeavored for nearly fifteen years to discover such a case. 

 My efforts have been, however, without avail. In the most recent 

 critical review by Jensen 1 on the subject of the trophic nerves, the 

 same conclusion is reached although certain facts, as, for instance, 

 the excitation of assimilative processes in the green plant cell, 

 produced by light, seems at the first glance to clearly demonstrate 

 a primary excitation of the building up processes resulting from 

 a stimulation. Nevertheless closer observation invariably shows 

 that these conditions are much more complicated and that pri- 

 marily assimilative excitating reaction of the stimulus cannot be 

 conclusively shown. There remains, therefore, as a primary 

 assimilative excitating stimulus only the increased introduction 

 of nutrition in a living organism. This excitating effect on the 

 assimilative portion of metabolism is, as we shall see later, a 

 simple manifestation of the law of mass action. 



As a result manifold effects of excitating stimulation, which 

 seemed possible at a first glance, are already considerably re- 

 stricted. The great mass of excitating stimuli produce an accel- 

 eration of the dissimilative processes of the metabolic chain. But 

 here our former observations have already shown that certain 

 constituent processes are especially responsive and very readily 

 increase as a result of the most varied adequate and inadequate 

 stimuli. These are the "functional" members of metabolism. 

 These members are particularly labile, so that they are always 

 affected by every influence to which the system is subjected in 

 the form of a stimulus. The functional portion of metabolism 

 of the muscle, which is particularly labile and is always primarily 



1 Paul Jensen: "Das Problem der trophischen Nerven." Medicinisch-naturwissen- 

 schaftliches Archiv. Bd. II, 1910. 



