438 J. F. GUDERNATSCH 



mals had fed for sometime on various other tissues. The tadpoles 

 were about 10 weeks old, when the th^Toid was given. They 

 were fed only four times. This feeding caused the same accel- 

 eration in differentiation that was noticed in former experiments. 

 Within 3 to 7 days the reaction to the treatment became evident. 



There were differences in the rapidity of this reaction among 

 Jbhe different sets of tadpoles, as may be seen from the diary, but 

 whether or not these differences are significant as to the value 

 of the food given before the thyroid treatment, remains an open 

 question. 



The liver-thyroid-fed tadpoles (fig. 1 k) were the first ones to 

 develop hind and fore legs. This fact might easily be explained 

 on the ground that the liver-fed group was the most advanced 

 in the entire series (May 8, June 1, June 12, and June 23, in 

 the diary). Yet why those fed, for instance, on spleen, the slow- 

 est lot in the series, having no legs even on July 19, and those fed 

 on adrenal medulla which were at the start of the thyroid treat- 

 ment smaller than the liver-fed ones, should react to the thyroid 

 stimulus as fast as the liver group, cannot be explained on the 

 above basis suggested for the liver-fed group. 



On the other hand, the adrenal cortex group though of about 

 the same size are 10 days ahead of the adrenal medulla group 

 in differentiation. Yet after thyroid application they do not 

 react with as great speed as the latter, and fall behind in the series. 



Throughout the experiment it was observed that muscle-liver- 

 and spleen-fed tadpoles belonged to one class as far as their 

 growth was concerned, while those fed on adrenal cortex, adrenal 

 medulla and ovary formed another class. As soon, however, as 

 the thyroid factor was introduced this classification was dis- 

 turbed. Thus the previous feeding may influence to some de- 

 gree the mode of reaction to the thyroid stimulus. No variety 

 of previous feeding can, however, completely prevent this reac- 

 tion for any length of time. After a shorter or longer interval 

 (in this experiment the difference was only from 3 to 7 days) 

 every tadpole, as far as macroscopic features are concerned, will 

 respond to the thyroid stimulus, no matter what kind of food had 

 been previously given. 



