606 IODINE AND THE THYROID. Ill 



as the writer previously found thyroidless tadpoles did. Tissues and 

 cells, other than those of the thyroid, assimilate and use the iodine 

 taken into the organism. The need for iodine is great, hence the feed- 

 ing of iodine should result in no marked deposition of colloid in the 

 imperfect thyroids of pituitaryless animals. 



In the second place, the iodine mixture used by Professor Allen 

 in his experiment (starch iodide) was obtained from the writer and 

 represented a 1 : 100 mixture of iodine and flour. The pituitaryless 

 animals probably had long passed their normal period of meta- 

 morphosis and hence required a smaller amount of iodine and flour 

 to enable them to undergo metamorphosis. 



The writer feels certain that prolonged iodine feeding increases the 

 colloid content of the thyroid, both in amount and consistency of the 

 colloid, and that the results with pituitaryless animals are due to the 

 reasons stated. 



CONCLUSIONS. 



1. Amphibian metamorphosis depends upon the amt>unt of iodine 

 secured by the larvae; the greater the quantity the more rapid the 

 differentiation. 



2. Bromine is physiologically inert when fed even in large quanti- 

 ties to frog larvse, hence it cannot be substituted for iodine. Bromine 

 feeding has no effect on the thyroid. 



3. Iodine is the active constituent of the thyroid gland, in the 

 Anura at any rate, and functions within the body by stimulating 

 intracellular oxidations; it is apparently specific in its action. 



4. The basal metabolism of patients suffering from> athyreosis, 

 whose metabolism is 40 per cent below normal, is very likely held at 

 this figure and prevented from sinking lower to the death point by 

 the introduction of iodine into the body through food and water. 



5. The thyroid gland is an organ the function of which is the ex- 

 traction from the circulation, storage, and supplying to the organism, 

 under the pressure of its needs, the small quantities of iodine taken 

 into the body. The chief function of this gland then is the utiliza- 

 tion of iodine in small quantities. 



