EDUARD UHLENHUTH 313 



factors; these attempts in the case of von Chauvin doubtless were 

 successful, though the actual relation between the factors employed 

 and the result obtained cannot well be understood at present. 



SUMMARY. 



1. Though thymus-fed salamander larvae often metamorphose 

 normally, thymus feeding sometimes retards and in rare cases in- 

 hibits metamorphosis completely. 



2. The addition of normal food to a thymus diet abolishes the in- 

 hibitory effect of the thymus. 



3. Addition of a small quantity of iodothyrin leads rapidly to 

 precocious metamorphosis of th3niius-fed larvae. 



4. The inhibitory effect of the thymus is not due to a specific in- 

 hibiting substance in the thymus, but to the absence from the thy- 

 mus of a substance required to develop the thyroid to the secretory 

 state. 



