CONCLUSIONS AND SUGGESTIONS 177 



preted and harmonized. If the metabolic rate in the 

 organ or part in question is sufficiently high, it is ca- 

 pable of undergoing its characteristic development and 

 differentiation without nervous stimulation, assuming 

 of course that its other relations as a part of the indi- 

 vidual are not fundamentally altered; but when its 

 intrinsic metabolic rate falls below a certain level its 

 development does not occur, or is incomplete, or it 

 undergoes atrophy unless its rate is further increased 

 by nervous stimulation. In the case of striated muscle 

 during the earlier stages of development the intrinsic 

 metabolic rate is high enough to permit without nervous 

 stimulation the accumulation of structural material 

 and the characteristic course of differentiation deter- 

 mined by other correlative conditions, but as differ- 

 entiation and senescence progress the metabolic rate 

 falls, and finally the muscle is not even able to maintain 

 itself in the absence of the accelerating influence of 

 nervous stimulation upon its metabolic rate, because 

 when its rate falls below a certain level it does not replace 

 its losses by new muscle substance. In the regenera- 

 tion of the amphibian leg and other cases where the 

 influence of the nervous system is in dispute, the relations 

 are without doubt essentially the same. 



There is no reason to believe that the nerve impulse 

 is anything more than an acceleration of metabolism. 

 The appearance of the nervous system does not consti- 

 tute the addition of something new to the organism; it 

 is merely the visible expression of relations already 

 existing and, as the facts indicate, of the relations 

 which constitute the foundation and starting-point of 

 individuation. 



