250 W. W. SWINGLE. 



fed iodotyrosine and iodoserumglobulin had no vestige of thyroid 

 tissue present, consequently had no mechanism for iodine utiliza- 

 tion. 



No one has ever shown that in the absence of thyroid glands, 

 other tissues of the organisms have the power of functioning 

 vicariously for the thyroid, and synthesizing its active hormone. 

 If this possibility were true then why is it that mammals with 

 atrophied or degenerate thyroids are quite unable to utilize 

 iodine or iodized proteins and amino-acids. If other tissues of 

 vertebrates besides the thyroid glands possess the power to 

 manufacture the thyroid hormone it is strange that this power 

 should be present in amphibia yet lacking in mammals. The 

 truth of the matter is that amphibian metamorphosis depends 

 upon a peculiar property inherent in the iodine, atom when 

 combined in certain ways. 



Some investigators have claimed that the pituitary can func- 

 tion vicariously for the thyroid when the latter is absent, hence 

 it might be said that in thyroidless amphibians the pituitary 

 gland may synthesize the iodine into the chemical complex 

 characteristic of the thyroid hormone. Aside from the total 

 lack of evidence that the pituitary can function vicariously for 

 the thyroid in thyroidless forms, the experiments of Allen ('19) 

 are of interest in this connection. Allen extirpated both the thy- 

 roid and the pituitary gland of frog embryos and later fed the 

 tadpoles with starch iodide. The animals underwent a precoci- 

 ous and nearly complete metamorphosis before death ensued, 

 clearly demonstrating that iodine is as effective in inducing trans- 

 formation in tadpoles lacking both thyroid and pituitary as in 

 larvae with only the thyroid missing. 



SUMMARY OF CONCLUSIONS 



1. Thyroidectomized, partially thyroidectomized, and normal 

 axolotls are readily metamorphosed by intraperitoneal injections 

 of iodotyrosine and iodoserumglobulin and iodocasein. 



2. Thyroidectomized, partially thyroidectomized and normal 

 axolotls do not metamorphose when injected with large quantities 

 of pure tyrosine, 3-5 dibromtyrosine (two atoms of bromine in 

 the molecule) and non-iodized serumglobulin. 



