200 The Unity of the Organism 



into the definition. 



That the structures referred to and all others of the or- 

 ganism are composed of chemical substances and nothing 

 else, is beyond question. Why, then, does the author not 

 bring into the definition this truth about the ultimate make- 

 up of the structures.^ The central aim of his researches 

 on animal activities being what they are — "a physico- 

 chemical analysis of behavior," is it not surprising that he 

 should be satisfied with even a working description or defini- 

 tion of a reflex act which takes no notice of the results of 

 such analysis.^ If the understanding of complicated life 

 phenomena consists in resolving them into their simple ele- 

 mentary components (see the first sentence of the Physi- 

 ology of the Brain) ^ then a definition of a tropism that 

 would contribute largely to an understanding of it should 

 not be content with such proximate constituents as "irri- 

 table structures," "muscles," and so on, but should go right 

 back to the ultimate physico-chemical elements. 



The typical elementalist answer to these restrictive criti- 

 cisms is well known. It is, substantially, that the understand- 

 ing and hence the definition of tropism, or for that matter 

 of any other life phenomenon, is final or ultimate only when 

 expressed in physico-chemical terms. The criticism sug- 

 gested concerning the mere proximateness and hence inade- 

 quacy of a definition that uses such terms as "structures," 

 "muscles" and "body surface" is allowed to have a large 

 measure of validity, the usage being justified mainly, it is 

 claimed, on practical grounds. The morphological concep- 

 tions involved, it is held, are so strongly intrenched in bio- 

 logical terminology, indeed are so necessary in a historic 

 and subsidiary sense, that it is very inconvenient, if indeed it 

 is not impossible, to dispense with them. In a word, the 

 contention is that while morphology and general physiology 

 are necessary, their necessity is secondary or subsidiary to 

 physics and chemistry. But what should be seen in this 



