No. 



,589] 



THE EVOLUTION OF THE CELL 



33 



investigations into the structure, physiology and behavior 

 of cells on the one hand, and of the various types of or- 

 ganisms grouped under the Protista, on the other hand — 

 the combined results, that is to say, of cytology and pro- 

 tistology — appear to me to indicate that the chromatin- 

 elements represent the primary and original living units 

 or individuals, and that the cytoplasm represents a sec- 

 ondary product. I will summarize briefly the grounds 

 that have led me to this conviction, and will attempt to 

 justify the faith that I hold ; but first I wish to discuss 

 briefly certain preliminary considerations which seem to 

 me of great importance in this connection. 



It is common amongst biologists to speak of 1 * living 

 substance," this phrase being preceded by either the defi- 

 nite or the indefinite article— by either "the" or "a." 

 If we pause to consider the meaning of the phrase, it is 

 to be presumed that those who make use of it employ the 

 term "substance" in the usual sense to denote a form of 

 matter to which some specific chemical significance can be 

 attached, which could conceivably be defined more or less 

 strictly by a chemist, perhaps even reduced to a chemical 

 formula of some type. But the addition of the adjective 

 "living" negatives any such interpretation of the term 

 "substance," since it is the fundamental and essential 

 property of any living being that the material of which it is 

 composed is in a state of continual molecular change and 

 that its component substance or substances are inconstant 

 in molecular constitution from moment to moment. When 

 the body of a living organism has passed into a state of 

 fixity of substance, it has ceased, temporarily or perma- 



it can not be a "substance," and if it is a "substance" it 

 can not be "living." 



As a matter of fact, the biologist, when dealing with 

 purely biological problems, knows nothing of a living sub- 

 stance or substances; he is confronted solely by living in- 



