Significance of the Internal Secretory System 145 



of the tadpoles resulted. "Towards the end of metamor- 

 phosis the animals hardly moved about in the water. Tliey 

 were always lying quietly, generally on Huir hacks. When 

 disturbed they would move for a few seconds in a somewhat 

 convulsive manner and tlien drop again to the bottom of 

 the dish, while tadpoles fed on otlier material would swim 

 about for a long time." ^ So mammalian thyroid substance 

 is not only organ-forming for a whole series of frog organs 

 but it is habit-forming for a variety of frog habits ! 



But Ave must not let the ludicrousness of this veer us 

 away from the reasoning; in the case. Takin"; the facts 



.,'0 o 



actually brought out by Gudernatsch, what becomes of the 

 specificity of the substance, which according to Loeb's state- 

 ments was what Sachs hypothesized.^ "Sachs suggested that 

 there must be in each organism as many specific organ-fonn- 

 ing substances as there are organs in the body." ^' The trutli 

 appears to be that thyroid substance in tliis case is organ- 

 forming in much the same sense that water is organ-forming 

 for the leaves, flowers, and fruit in a squash vine, which could 

 not develop without water. Indeed the analogy suggested 

 goes further than appears at first sight. As everybody 

 knows, the effect on young plants of a scant water supply 

 is to stunt the plant as to size and to hasten its blossoming 

 and fruiting. That is, an under-supply of water has an 

 effect on immature plants similar to that of an over-su])ply 

 of thvroid substance on immature frogs, namelv that of re- 

 tarding growth and hastening metam()r|)hosis. The total 

 effect in each case is systemic. In other words, tiie real 

 significance of the instance used by I.oeb is just the opjiosite 

 of his interpretation of it. Thyroid substance is oryau- 

 forming only through being organism-transforming. Full 

 justification of this way of interpreting the ])art in 

 development played by thyroid substance is furnished by the 

 recent studies of 15. ^\. Allen. This investigator has, like 

 Gudernatsch, experimented with frog larva\ lie has, how- 



