502 



BENNET M. ALLEN 



The first lot of tadpoles were operated upon April 2, 1916 and 

 the last lot on April 20 as follows: 



The earlier experiments were not maintained for long, many of 

 the tadpoles being preserved for study in early stages. Lots 15, 

 16 and 20 however, were kept for a long time and from them were 

 reared those later stages which truly form a basis for this work. 



It was quite impossible to foresee what the results of this ex- 

 periment might be. Early results were expected and eagerly 

 searched for but no peculiarities attributable to thyroid removal 

 were observed until about June 20 eleven weeks after the 

 operation had been performed. 



In lot 15 eight died inside of 2 hours after the operation, but 

 this was the only case where any appreciable mortality resulted 

 from the operation. No others died for over a month. Lots 

 15, 16, and 20 were the most carefully kept. In lot 16 the first 

 mortality occurred on May 20, 37 days after the operation. In 

 lot 20 the first mortality occurred on May 20, 26 days after the 

 operation, from this time on a few died from time to time until 

 June 10, when there was a rapid acceleration of mortality. This 

 affected the controls in slightly greater degree than the thyroid- 

 less tadpoles and was not in any degree whatever to be accounted 

 as a result of the operation. This mortality of thyroidless tad- 

 poles and controls was probably due to the fact that they had in- 

 creased in size so that they had outgrown their quarters. They 

 were kept in aquaria consisting of a series of kitchen sinks each 

 with about 5 inches of water replenished with fresh water drip- 



