THEORIES OF INDIVIDUALITY 43 



and controlled experimentally by metabolic changes 

 which are primarily quantitative. The morphology of 

 the channel of a rapidly flowing stream is very different 

 from that of a stream which flows slowly, and there can 

 be little doubt that in the organism substances which are 

 decomposed and transformed or eliminated with a high 

 rate of reaction remain and accumulate in the protoplasm 

 and may form characteristic morphological features when 

 the rate of reaction is low. 



In this connection the question must be raised 

 whether the transmitted change is always of the same 

 sort and produces the same effect in a protoplasm of 

 given constitution. It is impossible at present to give a 

 definite answer to this question, but there seems to be 

 no positive evidence to show that the qualitative char- 

 acter of the effect is determined by the character of the 

 transmitted change, although it has often been assumed 

 that this is the case. It is very probable that the 

 chemical or physico-chemical character of the trans- 

 mitted change differs more or less widely in plants and 

 animals, and in embryonic protoplasm as compared with 

 the fully developed medullated nerve, but the effect in 

 each case seems to be primarily excitatory and quanti- 

 tative. It seems even possible that in passing through 

 different tissues the character of the transmitted change 

 may differ more or less according to the constitution 

 of the tissues, but its effect may still remain essentially 

 quantitative. 



If it should be demonstrated that the same proto- 

 plasm may transmit different kinds of excitations, then 

 of course different processes of morphogenesis and 

 differentiation might be determined by the specific 



