144 The Unity of the Organism 



mammalian substance, shows at once that there is something 

 badly askew in the theory. So we are incited to examine 

 the facts, and particularly the reasonings, carefully. 



The following is taken from one of Gudernatsch's papers : 

 'The most striking and at the same time unquestionable re- 

 sults were attained by thyroid feeding. . . . The influence 

 of the thyroid food was such that it stopped any further 

 growth but on the contrary led to an abnormal diminution 

 of the size in the animals treated, while simultaneously it ac- 

 celerated the differentiation of the body immensely and 

 brought it to a premature end." 3 In other words, the effect 

 of thyroid food was to stop the increase in size of the frog's 

 larva and start, almost at once, its transformation into the 

 adult. Now this transformation does not consist merely in 

 the production of legs, but in a whole series of changes, 

 some of which, like leg transformation, are progressive, 

 while others are regressive. For example, one of the re- 

 gressive changes to which Gudernatsch gives particular 

 attention is the resorption of the tail. "Reduction of the 

 body mass (resorption of the tail, loss of water, therefore 

 an increasing compactness of the body, etc.)" 4 more than 

 in normal development, the author says, goes hand in hand 

 with the progressive changes. That is, when the entire series 

 of results of thyroid feeding are considered, and not merely 

 one result picked out arbitrarily, then in case we choose to 

 say the thyroid substance is organ-forming as regards legs, 

 we should have to say it is organ-destroying as regards 

 tail. Furthermore, if we call the thyroid substance organ- 

 forming, consistency would compel us to recognize that one 

 and the same substance is not only formative of legs but 

 of numerous other organs and parts, as of the skin, mouth, 

 respiratory and blood systems, all of which undergo, as is 

 well known, progressive changes during metamorphosis. Nor 

 is this complex series of morphological changes the while 

 story. Striking and characteristic changes in the habits 



