188 INDIVIDUALITY IN ORGANISMS 



order, of "organization," specialization, and differentia- 

 tion in the organic individual, not only presents no 

 fundamental difficulties, but is supported by a great 

 body of experimental and observational evidence from 

 various biological fields. 



THE FUNDAMENTAL REACTION SYSTEM 



If the dynamic conception of the organic individual 

 is correct, the starting-point lies, not in a certain organi- 

 zation, but in a certain reaction system. This is a 

 protoplasm of specific constitution with a corresponding 

 metabolic specificity, or one may say that this specificity 

 is the expression of a specific constellation of conditions 

 and that this in turn has been determined by the specific 

 constellation of factors external to itself to which each 

 organism, individual, or part has been subjected in the 

 past. It is this reaction system, not an organization, 

 which constitutes the basis of inheritance, and it is 

 in this system that differences in metabolic rate initiate 

 the process of organization. We may for convenience 

 regard the embryonic or undifferentiated cell of the 

 species as representing this fundamental reaction system, 

 although even there the system is doubtless not reduced 

 to its lowest terms. The developmental changes in this 

 system fall into two groups, the self-determined 1 changes 



'It is perhaps desirable to indicate just what is meant by self- 

 determination in this connection. All that the word is intended to 

 imply here is that the region of highest metabolic rate may undergo 

 certain progressive changes, which are determined by its own 

 constitution and by continued metabolism in it. These changes may 

 in time make this region different structurally and physiologically 

 from what it was originally, even though it is independent of other 

 parts. 



