242 W. W. SWINGLE. 



difference was observed between the iodotyrosine-fed animals and 

 those of the other cultures. The tyrosine and dibromtyrosine-fed 

 tadpoles showed no changes either in regard to growth or meta- 

 morphosis from the algae-fed controls, whereas the iodotyrosine- 

 fed animals appeared thin and emaciated; the hind legs had 

 increased in length also the skin of the pectoral region where 

 later the fore-legs appear, was undergoing autolysis. 



October 3, four of the iodotyrosine-fed tadpoles had fore legs 

 and frog mouths. The hind legs of all of the animals had markedly 

 increased in length, and the tail was undergoing resorption. In 

 several individuals large patches of skin over the region of the 

 fore-limbs was totally destroyed by autolysis. The animals of the 

 remaining cultures showed no change. 



October 6, the animals of the iodotyrosine culture were all in 

 advanced stages of metamorphosis and many were dying; only 

 one animal remained alive on October 8. Table I. gives the 

 measurements of the tadpoles of the various cultures at the close 

 of the diiodotyrosine experiment, twenty-three days after the 

 date of first feeding. 



The remaining cultures were continued until October 30. The 

 tyrosine and dibromtyrosine-fed tadpoles were then taken off the 

 tyrosine diet and fed alga?. The larvae were measured November 

 13 two months after the beginning of the experiment but no 

 indications of metamorphic change was observed. It is quite 

 evident that insofar as the metamorphosis of the green frog is con- 

 cerned, tyrosine and dibrom tyrosine are ineffective, even when 

 administered in large quantities. These results are in agreement 

 with those obtained in similar experiments on thyroidless axolotls 

 and thyroidless and pituitaryless anuran tadpoles (Swingle, '22). 



DISCUSSION. 



The experiments described in this paper and elsewhere on the 

 administration of iodine, iodized amino-acids and proteins to 

 thyroidless and pituitaryless anuran larvae and to thyroidless 

 axolotls demonstrate that other forms of iodine than that peculiar 

 to the thyroid hormone (thyroid iodine) possess the power of 

 inducing amphibian transformation. This property of iodine is 

 apparently unique, since so far as known at present it is not shared 

 by other substances, and is inherent in the iodine atom when 



