452 J. F. GUDEENATSCH 



animals could not feed on it. The gland was placed in a small 

 glass vial closed with gauze and allowed to stand upright, the 

 open end being beneath the surface of the water. Thus no thy- 

 roid particles could get out into the water, merely an extract or 

 emulsion of thyroid constituents which diffused from the vial into 

 the dish. Animals kept in these dishes developed their hind 

 legs 8 days after the beginning of the experiment and the frog 

 shape became noticeable about the same time. Six days later 

 they all died without having grown fore legs, but their size on 

 that day J June 19, shows that they were completely under the 

 thyroid influence. Therefore the product of the thyroid which 

 caused the rapid differentiation in all the previous experiments 

 must be soluble in water. 



The control animals which were, kept starving after the 50 days 

 feeding did not grow hind legs until July 5, considerably later 

 than the thyroid treated ones. Thus the results after thyroid 

 application are different from those Barfurth reports in his ' ' Der 

 Hunger als forderndes P.rinzip in der Natur," and cannot be 

 attributed to starvation of the tadpoles. Among the ten main 

 groups of the experiment the thyroid influence manifested itself 

 in different ways. As a general result it may be stated that a 

 thyroid application of only 24 hours sufficed to show decided ef- 

 fects (fig. 2 c, 2/), and that a treatment of more than 24 hours 

 (2 to 5 days) gave the typical results described in all previous 

 experiments. 



In the five groups that received vegetable food following the 

 thyroid dose and in the five groups that were fed again on muscle, 

 a great number of individuals, 50 to 60 per cent, mainly the shorter 

 ones, died within 2 or 3 days after the first feeding. This ac- 

 cords with observations in other cases where thyroid was given 

 after previous feeding, but is in striking contrast with the hap- 

 penings in experiments where thyroid food was applied from the 

 start. In the latter experiments very few animals were lost dur- 

 ing the first days. It remains to be answered why the applica- 

 tion of thyroid should affect tadpoles that had not been previ- 

 ously fed on other diets less harmfully than those previously fed 

 on various tissues. 



