398 W. W. SWINGLE 



criteria for judging the effect of iodin administration and 

 thyroid activity upon the organism as do frog larvae. The 

 original work of Gudernatsch (since followed by that of Morse, 

 Lenhart, and Swingle) showed that any increased stimulation of 

 thyroid activity, as for instance by feeding thyroid extract, was 

 at once indicated by metamorphic changes in the tadpoles. The 

 present problem was to utilize these somatic changes as a cri- 

 terion of hyperthyroid function and to gauge the effects of iodin 

 upon the gland by feeding it to immature larvae. 



Mr. Eitzen followed the suggestion, and, in conjunction with 

 the writer, started the work, but owing to induction into military 

 service shortly afterward gave up the problem. Consequently 

 if fell to the writer to work out his own suggestion. The results 

 obtained contribute some additional information regarding the 

 relation of iodin to the physiological activity of the thyroid, to 

 the probable role of this gland in the economy of the organism, 

 and to the more general problem of amphibian metamorphosis. 



LITERATURE 



The active principle of the thyroid gland is at present un- 

 known, or at any rate much in dispute. The relation of iodin 

 to this gland has been for many years a matter of great interest 

 to clinicians and investigators, and it has long been recognized 

 that iodin holds an important place among the constituents of 

 the thyroid. Since 1820 iodin has been used more or less in the 

 treatment of thyroid diseases, but it was not until 1895 that it 

 became known that the glands usually contain iodin. Baumann 

 ('95) contributed this important information to our knowledge 

 of the gland. 



This investigator isolated a specific iodin compound from the 

 gland which he named iodothyrin. It apparently has many of 

 the specific properties of the gland tissue itself. 



Oswald ('02) succeeded in isolating the protein with which the 

 iodin in the gland is combined. He called this protein thyro- 

 globulin; it was found to constitute one-third to one-half of the 

 weight of the dry gland. The iodin content varied from zero to 

 0.86 per cent or more. Baumann' s iodothyrin could be obtained 

 from it by hydrolysis. 



