THE PROBLEM 17 



are relatively stable under the ordinary physiological 

 conditions and in such physical condition that they can- 

 not escape from the organism without change. There- 

 fore they accumulate, and their accumulation constitutes 

 growth, and their differences in different parts constitute 

 the morphological structure of the organism. The less 

 stable products appear only temporarily or not at all as 

 structural features, for they are decomposed and elimi- 

 nated. These differences in stability are of course only 

 relative and between extremes numerous intermediate 

 degrees occur. Moreover, a structure which is stable 

 under certain conditions may, under altered conditions, 

 become unstable and be broken down and replaced by 

 other structures. In general, structural stability in- 

 creases both during the development of the individual 

 and the course of evolution. The evolutionary increase 

 in structural stability is in fact what makes possible 

 the structural permanency and complexity of the higher 

 as compared with the lower organisms. 



If the organic individual is a physico-chemical entity 

 of this kind the foundation of its unity and orderly 

 character must be present somewhere and somehow in 

 this metabolic-protoplasmic system. Definite relations 

 in both space and time must exist among the reactions 

 occurring in the protoplasm, and the problem of indi- 

 viduality resolves itself into the problem of the nature, 

 origin, and maintenance of these relations. It is with 

 the problem in this form that this book is chiefly con- 

 cerned. 



TERMINOLOGY 



In order to avoid confusion and for the sake of con- 

 venience and brevity it is necessary to fix upon and 



