THE PARS BUCCALIS OF THE HYPOPHYSIS 67 



substance normally furnished by the tadpole's own gland. It ie 

 significant of the stability of this substance that its efficacy 

 or physiological nature has not been seriously impaired by the 

 severe treatment accorded it in the prolonged extraction with 

 boihng water or absolute alcohol. It would seem certain that 

 the retardation in the growth rate of the albinos receiving liver, 

 hypophysial extracts, and colloid is due to the absence of the 

 morphogenic principle normally furnished by the anterior lobe 

 of the pituitary. 



The growth rate of thyroidedomized larvae 



It has been noted by previous workers (Allen, Hoskins) that 

 thyroidectomized larvae attained a size much in excess of the 

 normal and that the pituitary glands of these specimens were 

 relatively increased in size. Since the larval condition persists 

 in the thyroidless larvae and since the hypophysis is hyper- 

 trophied, it might be expected that these specimens would ex- 

 hibit a more prolonged, and a more rapid rate of growth than 

 even the anterior-lobe-fed albinous tadpole. By thyroidectomy, 

 then, there would be obtained tadpoles which would simulate the 

 rapid growth exhibited at times by the acromegalous human 

 subject. 



Observations, however, made on two groups of thyroidec- 

 tomized frog larvae, one group (seventy-two specimens) fed on 

 anterior lobe, the other (fifty-nine specimens) fed on liver, show 

 that their growth is identical in rate with that of their normal 

 brothers or with the albinos supplied with a continuous diet 

 of the fresh anterior lobe (fig. 5). Their large size is never 

 attained by a more rapid growth rate, but rather, as in the 

 anterior-lobe-fed albinos, by a prolongation of the growth period. 

 No variation in growth rate was caused by feeding the fresh 

 anterior lobe of the pituitary, a non-effect already reported upon 

 by Allen ('18). The enlarged pituitary which these animals 

 possess does not appear to have supplied any growth stimulus 

 in excess of the normal. 



Nevertheless, a different condition obtains with the thyroidec- 

 tomized toad larvae, at least when supplied with a liver diet. 



