RELATION OF lODIN TO THYROID 399 



Kendall ('14) has reported the separation of the physiologi- 

 cally important thyroid constituents into two fractions : an A or 

 alpha fraction, containing ten times the percentage of iodin of 

 the original thyroid. This alpha fraction is toxic and its ad- 

 ministration produces typical symptoms of excess thyroid 

 feeding. The B fraction contains less iodin and is non-toxic. 



The relation of- iodin to the physiological activity of the 

 thyroid is very close; in fact, the activity of the gland appears 

 to depend upon its iodin content. 



One investigator, Roos ('99), working with dogs, found that 

 more nitrogen was excreted after the administration of thyroid 

 rich in iodin than after that of thyroid containing little iodin. 



Marine and Williams ('08) observed that thyroid containing a 

 larger percentage of iodin caused a greater loss of weight in dogs 

 than did a preparation containing a smaller percentage. 



Hunt and Hunt and Seidell ('07 and '08), in an extended 

 series of experiments in which the effects of thyroid upon the 

 resistance of animals to certain poisons was determined, found 

 that the physiological activity of the thyroid depended upon 

 its iodin content. 



JMorse ('14) fed the larvae of Rana pipiens on various iodin 

 compounds, but obtained negative results with all inorganic 

 iodin. He was able to accelerate metamorphosis in these 

 animals by feeding iodized amino-acids (3-5-di-iodo-thyrosin, 

 Cg HsOHIoCHo.CHo.CHNHoCOOH). This amino-acid was de- 

 rived from the thyroid tissue by acid hydrolysis. 



Lenhart ('15) fed thyroid tissue to tadpoles and observed that 

 the higher the iodin content of the gland fed, the more rapid the 

 body metabolism. 



This review is by no means exhaustive. Besides the investi- 

 gators quoted, there are equally as many, if not more, who claim 

 that iodin has no relation to thyroid activity and that it does 

 not function within the organism. 



