1 62 WITHROW MORSE. 



aspect, Allen (27) have examined the relations of the thyroid and 

 thyroid components upon metamorphosis. The writer found that 

 an iodized amino-acid (3-5-di-iodo-tyrosin, C 6 H 5 OHI 2 CH 2 .CH. 

 NHs.COOH), induces metamorphosis in the frog's larvae, this 

 amino-acid being derived from the thyroid tissue by means of 

 acid hydrolysis and hence being a normal component of the 

 thyroid. These observations taken in connection with the 

 interesting morphological studies of Allen give us a rationale of 

 the role of the thyroid in inducing metamorphosis. When thy- 

 roid tissue or its components is fed to an organism, the general 

 metabolism is increased as evidenced by the increased output of 

 the end products of protein, carbohydrate and fat metabolism. 

 When thyroid is removed from the economy of the organism, as in 

 Allen's thyroidectomy experiments, metabolism is decreased ; 

 this is indicated by his further observations that reduced nourish- 

 ment obtains the same results, that is, in both cases metamor- 

 phosis is suppressed or delayed. We may conclude, then, that 

 metamorphosis involves, as one of its principal factors, heightened 

 metabolism. 



It is necessary to distinguish between heightened metabolism, 

 which involves only catabolism, in Gudernatsch's experiments and 

 the accelerated anabolism present in Allen's cases. In both 

 instances, metabolism is heightened, but the current is down 

 stream in the one case, leading to loss of storage materials and a 

 piling up of materials in the form of fat, etc., in the second case. 

 Now it is of interest to recall that according to Voegtlin and 

 Strouse, the iodized amino-acid which was found to operate as 

 whole thyroid tissue in inducing precocious metamorphosis, 

 fails to replace the function of thyroid in those pathological cases 

 where there is a deficiency in thyroid function. It would be of 

 considerable interest to determine whether 3-5-di-iodo-tyrosin, 

 thyreoglobulin or any of the chemical components of the intact 

 thyroid tissue replaces the absent thyroid in cases of thyroid- 

 ectomy in inducing metamorphosis, for wrapped up with the 

 question is the important and fundamental one as to what rela- 

 tion the iodine has in the thryoid. If the iodized amino-acid 

 should in itself, in the absence of the thyroid, induce metamor- 

 phosis, it would show that the theory that iodine stimulates an 



