720 



SCIENCE 



[Vol. LVI, No. 1460 



SPECIAL ARTICLES 

 IODINE AND ANURAN METAMORPHOSIS 



The following experiment shows clearly the 

 importance of iodine in indncing anuran meta- 

 morphosis and indicates that other halogens 

 such as bromine can not be su<bstituted for it. 



Thyroidectomized and hypophysectomized 

 B. sylvatica, the glands of which had been ex- 

 tirpated early in embryonic life, were kept 

 until after the normal time for metamorphosis 

 had elapsed and the normal controls had trans- 

 formed, and then divided into three sets for 

 experimental purposes. It will be recalled that 

 thyroidless and pituitaryless larvse do not meta- 

 morijhose but remain permanent tadpoles unless 

 fed thjToid derivatives or very large amounts 

 of iodine. One set of animals was fed quanti- 

 ties of pure tyrosine 'CH2CH(N"H2)COOH 

 each day and allowed to remain in weak solu- 

 tions of this substance six to eig'ht hours every 

 day. The remainder of the time they were kept 

 in large glass containers and fed large quan- 

 tities of spirogyra. 



The second lot of animals was fed equal 

 quantities of tyrosine in which two atoms of 

 iodine had been substituted for two hydrogen 

 atoms of the tyrosine — forming the well-known 

 compound, 3-5-di-iodo-tyro9ine. The iodine in 

 this compound is, of course, an integral part 

 of the molecule. 



Tyrosine 



CH2CH(NH2)COOH 



OH 



3-5-didodotyrosiiie 



CH2CH(NHo)C00H 



OH 



The third set of tadpoles was fed quantities 

 of tyrosine equal in amount to that received by 

 the other two cultures, in which two atoms of 

 bromine had been substituted for two hydrogen 

 atoms of the tyrosine molecule forming the 

 compound 3-5-di-brom-tyrosine. 



CH2CH(XH2)COOH 



OH 



The dinbrom-tyrosine was prepared according 

 to the method of C. T. Morner, 1913, Zeitschrift 

 f'dr physiologisclie Chemie, Vol. 88. 



The animals fed tyrosine and spirogyra 

 showed no changes indicative of metamorphosis 

 after sixty days of continuous feeding, though 

 the normal growth rate was not interrupted. 

 After the twenty^flfth day 'the hind legs differ- 

 entiated and grew very slowly until they 

 attained a length of 3 to 5 millimeters. There 

 were no signs of fore legs, skin autolysis in 

 the pectoral region, tail shrinkage or anything 

 su'ggesting transformation. 



The animals fed 3-5-di-brom-tyrosine be- 

 haved in identical fashion with those of the 

 tyrosine-fed culture and no metamorphosis re- 

 sulted. At the end of the second month of 

 feeding the hind legs of the animals of the 

 culture averaged five millimeters. The growth 

 rate of the animals was not interfered with by 

 the Ijrom-itjn-osine c-ompound. Insofar as 

 the acceleration of metaanoi'phosis is con- 

 cerned, the results obtained by feeding 

 tjTosine and 3-5-di-brom-tyrosine are essen- 

 tially negative. 



Conversely the administration of 3-5-di-iodo- 

 tyrosine to thyroidless and pituitaryless larva 

 brought about very striking results, and in so 

 far as metamorphosis is concerned, simulated 

 the action of thyroid extract, although the 

 effect of the latter is somewhat more rapid. 

 Within a few days after feeding iodo-tyrosine 

 the animals appear thin and emaciated; the 

 limbs grow rapidly and the other changes inci- 

 dent to metamorphosis appear. Twenty days 

 after the date of first feeding the entire culture 

 of thyroidless animals had completed metamor- 

 phosis except for the loss of the tail. The 

 pituitaryless animals developed fore and hind 

 legs, frog mouths but invariably died before 

 tail resorbtion was complete. In two pituitary- 

 less animals the right fore 'legs broke through 

 the skin eight days after the animals were 

 placed upon the iodo-tyrosine dieit. These two 



