Significance of the Internal Secretory System 153 



This brings us back to the way internal secretions are 

 dealt with by Loeb. His failure to distinguish between the 

 two very distinct fields of theory above indicated, namely 

 theories about the phenomena of living beings, and theories 

 about knowledge of these phenomena, largely explains the 

 defects of the theoretical parts of his work. And we are 

 now in position to give our criticism greater explicitness. 

 Consider for example in the light of what has just been said 

 about confusion relative to kinds of theory, the irreconcil- 

 able statements, cited on an earlier page, that the mesen- 

 chyme cells give rise to the legs of the tadpole, and that 

 thyroid substance is organ-forming substance for the legs. 

 Stated briefly the case seems to be thus : Loeb recognizes, as 

 every one must, that internal secretions constitute a physico- 

 chemical agency for bringing about that harmonious de- 

 velopment and functioning so characteristic of the organ- 

 ism. But this harmony is one of the very things which has 

 seemed to some biologists inexplicable without the assump- 

 tion of supernatural influences of some sort ; hence Driesch's 

 attempt to modernize the ancient entelechy. But since in- 

 ternal secretions play the role that entelechies are supposed 

 to play, namely that of establishing and maintaining the 

 unity and equilibrium of the organism, the need for ente- 

 lechies no longer exists ; at least, this would be so for all 

 persons who do not contend that "ultimate explanation" is 

 the "goal of science." 



To those who hold these absolutist beliefs as to the power 

 and aims of science three favorite courses are open and are 

 followed by different representatives of the school, depend- 

 ing on the taste, training and outlook of the person. One 

 course consists in pointing out, taking an illustrative case, 

 that internal secretions, being only contributing causes, do 

 not constitute an ultimate explanation, so that entelechies 

 or something similar are as necessary as before. This would 

 be the course followed by the vitalistic wing of the absolu- 



