RELATION BETWEEN THYROID GLAND, METAMOR- 

 PHOSIS, AND GROWTH. 



By EDUARD UHLENHUTH. 

 {From the Laboratories of The Rockefeller Institute for Medical Research) 



(Received for publication, February 1, 1919.) 



It has been demonstrated by a number of workers that the active 

 principle of the thyroid gland in the causation of amphibian meta- 

 morphosis is iodine. Recently Swingle^ has obtained definite proof 

 that inorganic iodine when fed to larvae of Salientia induces metamor- 

 phosis in a short time after the beginning of the feeding. On the 

 other hand, it has been shown by the writer^ that the retarding in- 

 fluence of the feeding of thymus upon amphibian metamorphosis is 

 due to the absence from the thymus gland of a substance required for 

 metamorphosis, and it is possible that this lacking substance is iodine. 

 Although minute amounts of iodothyrin have been found in some 

 thymus glands, it is Ukely that the amounts found are insufficient to 

 produce metamorphosis and that some thymus glands may not contain 

 the iodine at all. This would account for the variability of the re- 

 sults obtained with thymus feeding. 



Swingle^ also subjected tadpoles deprived of their thyroid to an 

 iodine diet; although such larvai when kept on a normal diet never 

 metamorphose, they very soon metamorphosed when fed on iodine 

 crystals. 



Hence it is manifest that iodine is one of the substances involved 

 in the causation of amphibian metamorphosis. The quantities con- 

 tained in normal food are, however, so small as to have no immediate 

 effect upon the organism. If the larvae have no thyroid glands, the 

 small quantities of iodine taken up with the food apparently cannot 

 be retained by the organism and the iodine leaves the body without 



^ Swingle, W. W., /. Exp. Zool., 1919, xxvii, 397. 

 2 Uhlenliuth, E., /. Gen. Physiol., 1918-19, i, 305. 



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