602 IODINE AND THE THYROID. Ill 



crating effect upon metamorphosis both in normal and thyroidless 

 frog larvae might be due to constant irritation of the body epithe- 

 lium. Moreover, bromine, besides being an irritant to the epithe- 

 lium, is closely related chemically to iodine, and it has been recently 

 asserted by KendalP that the substitution of bromine for the iodine 

 molecule in his substance thyroxin isolated from the thyroid gland 

 would not alter the gross chemical nature or physiological activity of 

 this so called active thyroid principle. All this being true, interesting 

 results were anticipated when bromine was fed to frog larvae. As a 

 matter of fact, however, only negative results were obtained, even 

 when very strong concentrations were fed over a long period of time. 

 There was absolutely no observable effect upon growth or differentia- 

 tion. It seems useless to state in detail the entire experiment, so 

 only a brief summary will be given here. Some account is necessary 

 because of the theoretical importance of such negative findings. 



The bromine cultures were in all respects similar to the iodine cul- 

 tures; method of feeding, amounts fed, and dates of examinations 

 were also the same. It was soon observed that all the larvae in Cul- 

 tures 3,4, and 5 showed pronounced tail-fin atrophy. In several of the 

 animals the delicate tissues were literally eaten away, the action of the 

 bromine thus simulating in a superficial way the action of iodine and 

 thyroid extract. None of the bromine-fed animals developed legs 

 or limb buds any faster than the controls, whereas the tadpoles fed 

 equivalent amounts of iodine underwent marked metamorphic 

 changes. The cause of the pronounced tail atrophy among the 

 larvae at once became apparent when the tails of the animals were 

 exposed for 20 or 30 seconds over the mouth of the stock bromine 

 solution. The fumes attacked the delicate tissues, literally shriveling 

 them up. An animal treated in this way will generally lose within 

 3 or 4 days that portion of the tail so treated. This artificially in- 

 duced atrophy in no way resembles true physiological atrophy and 

 resorption. Iodine in strong concentration will have a slight caustic 

 effect on the tail in early stages of the experiment, though the effect 

 is slight compared with that of bromine. 



^Kendall, E. C, Thyroid hormone and its relation to the other ductless 

 glands, Endocrinology, 1918, ii, 81; Studies of the active constituent in crystal- 

 line form of the thyroid, Tr. Assn. Am. Phys., 1916, xxxi, 134. 



