THE EFFECT OF IODINE AND lODOTHYRIN ON THE 

 LARV^ OF SALAMANDERS. 



IV. The Role of Iodine in the Inhibition of the Metamorphosis 

 OF Thymus-Fed Salamanders. 



By EDUARD UHLENHUTH. 



(From the Laboratories of The Rockefeller Institute for Medical Research.) 



Received for publication, November 2, 1921.) 



In previous papers I have shown that feeding thymus gland to the 

 larvae of salamanders retards or completely inhibits metamorphosis'"'^ 

 as well as growth. ^ It was also demonstrated^ that the inhibition of 

 both growth and metamorphosis is not caused by specific growth- 

 inhibiting substances contained in the thymus, but by a deficiency of 

 the thymus in certain substances which are necessary for growth and 

 metamorphosis. Later I suggested that these substances might be 

 identical with iodine.'* 



Recently, however, I found^ that inorganic iodine even when 

 administered in excessive quantities does not accelerate either growth 

 or metamorphosis of salamander larvae. Although this result does 

 not necessarily mean that salamander larvae can grow and metamor- 

 phose in the complete absence of iodine, the correctness of my assump- 

 tion that inhibition of growth and metamorphosis of thymus-fed 

 salamander larvae may be caused by a deficiency of the thymus in 

 iodine, became doubtful, and special experiments were carried out to 

 test this assumption. In the light of these experiments which will 

 be briefly reported below, it appears that the substances which are 

 deficient in the food of thymus-fed salamander larvae are not identical 

 with iodine. 



' Uhlenhuth, E., Proc. Soc. Exp. Biol, and Med., 1917-18, xv, 37. 

 - Uhlenhuth, E., J. Gen. Physiol., 1919, i, 305. 

 3 Uhlenhuth, E., /. Exp. Zool., 1918, xxv, 141. 

 * Uhlenhuth, E., J. Gen. Physiol., 1919, i, 473. 



5 Uhlenhuth, E., Endocrinology, 1922 (In press); Biol. Bull., 1922 (In press). 



319 



