2 E. R. HOSKINS AND M. M. HOSKINS 



INTRODUCTION 



One of the experimental methods most frequently used in 

 the study of the thyroid gland is that of extirpation. Mammals 

 have usually been employed in this study and have usually 

 proved unsatisfactory for definite results, especially where data 

 on the relation of the thyroid to growth processes were sought 

 for. In most mammals complete thyroidectomy is followed 

 shortly by death. Moreover, in such animals the gland cannot 

 be removed until after it has functioned for a time. Still further, 

 growth processes are relatively rapid in the higher animals. 

 We thought that if use were made of a lower form wherein growth 

 processes are relatively slow and wherein a larval existence 

 would permit extirpation of the thyroid before it could possibly 

 have become functional, a new approach would be opened to 

 the problem of the relation of the thyroid to growth and to life 

 processes in general. With this in mind, we selected amphibia 

 for our material. An added interest lay in the fact that Guder- 

 natsch ('12, '14) had clearly shown that the opposite sort of 

 experiment, i.e., feeding thyroid substance to larval frogs, alters 

 remarkably their growth processes and hastens metamorphosis. 

 The forms selected were Rana sylvatica and Amblystoma puncta- 

 tum, which are very abundant about New Haven. 



The first operations were performed by one of us in April, 

 1916, and in the spring of 1917 and 1918 the experiments were 

 repeated. We learned in November, 1916, that Doctor Allen, 

 of the University of Kansas, had performed similar experiments 

 with R. pipiens at about the time when our first were made. 

 Doctor Allen's and our own work were done independently 

 of each other, neither of us at the time knowing of the other's 

 experiments. We wish to thank Prof. R. G. Harrison for the 

 kind interest he has taken in the work and for his very helpful 

 suggestions. Abstracts of different portions of this paper have 

 already been published (Hoskins and Morris, '17; Hoskins and 

 Hoskins, '18). 



