THE MECHANISM OF LIFE 491 



or, vice versa, depression of assimilation and excitation of dissimi- 

 lation. There would thus be added to the above six cases of 

 reactions the last conceivable ones as follows : 



7. Excitation of assimilation + depression of dissimi- 



lation. 



8. Depression of assimilation + excitation of dissimi- 



lation. 



These various possible effects of stimulation, which Hering 

 ('88) has fully treated in his short dissertation upon the events 

 occurring in living substance, give us an idea of the manifold ways 

 in which biotonus can change under the influence of different 

 stimuli. But in reality the relations are much more complex. 



When we remember that the numerator as well as the denominator 



^ 

 of the fraction - represents a whole series of single members, 



and that these members are able to change in a certain degree in- 

 dependently of one another, we obtain an approximate picture of 

 the extraordinary variety of effects which stimuli are able to pro- 

 duce in living substance. 



In a previous chapter it was found possible to arrange the re- 

 actions to stimuli in the living cell according to their external 

 appearances in a few groups. It was found that the changes under- 

 gone by spontaneous vital phenomena as the result of stimulation 

 are either quantitative or qualitative. The quantitative changes 

 were termed excitation when they consisted of an augmentation of 

 the vital phenomena, and depression when characterised by a diminu- 

 tion of the latter. In accordance with the foregoing considerations, 

 we now obtain an approximate idea of the great complexity of the 

 events the external expression of which was termed briefly 

 excitation and depression. But the acme of the complexity is to 

 be seen in those reactions that are at the basis of the qualitative 

 changes of the normal vital phenomena. The metamorphic pro- 

 cesses of necrobiosis, typified by amyloid metamorphosis, show 

 clearly that here individual members of series A and series D must 

 slowly and gradually change independently of one another, other- 

 wise accumulations of individual substances that normally do not 

 occur in the cell can not take place. Metamorphic processes 

 constitute a stimulation-phenomenon that is conditioned by changes 

 of biotonus analogous to those conditioning the phenomena that 

 occur spontaneously in development. The differentiation of gland- 

 cells, muscle-cells, nerve-cells, etc., from the ovum must depend upon 

 changes in the individual members of series A and I) that are 

 independent of one another ; but these changes occur spontaneously 

 in the course of development, while in amyloid metamorphosis 

 and analogous phenomena they are produced by external in- 

 fluences. 



Because of our very faulty knowledge of the special members of 



