■ W. W. SWINGLE 605 



Microscopic Examination of the Thyroids. 



The glands of the tadpoles were preserved for study of the gross 

 and histological structure after the method previously described.^ 

 They were first studied whole, then sectioned. 



Frog larvae of equal age, reared under identical environmental 

 conditions, vary considerably in size, hence it is necessary, in order to 

 obtain a true picture of thyroid conditions in the various cultures, to 

 preserve animals as nearly equal in size as possible. The thyroids 

 increase in size as the organism grows, consequently no comparison 

 is possible between thyroids of large and small larvae, even though 

 taken from the same culture. 



Examination of the algse-fed controls and bromine-fed animals failed 

 to reveal any differences either in size of the thyroids or in the colloid 

 content between the two cultures. Bromine feeding apparently has 

 no effect on the thyroid gland. 



On the other hand, however, a comparison of the thyroids of ani- 

 mals taken from Iodine Culture 5 with those from algae-fed controls 

 of similar size showed Httle if any difference in the gross size and 

 structure, but a difference in the colloid content of the follicles of the 

 two sets of animals. Colloid is present in the thyroid follicles of the 

 algae-fed larvae but is rather scanty in amount and thin in consistency 

 compared to that found in glands from animals fed iodine over long 

 periods. 



In an abstract presented recently before the Anatomical Associa- 

 tion^^ Allen states that "iodine feeding does not cause any marked 

 increase in colloid deposition in the thyroid glands of pituitaryless 

 tadpoles. '^ This statement, though apparently contradictory to the 

 writer's results, nevertheless is in line with them. In the first place 

 extirpation of the pituitary gland, not only in Anura but in all species 

 investigated, leads apparently to imperfect development of the thyroid, 

 and it is probably because of this malformation and consequently mal- 

 functioning of the thyroid that pituitaryless frog larvas do not normally 

 metamorphose. Hence such animals will react to iodine feeding just 



^^ Allen, B. M., The relation of the pituitary and thyroid glands of BhJo and 

 Rana to iodin and metamorphosis, 35ih Session Am. Assn. Anat., Abstracts, 

 1919 



