Fred C. Koch 103 



of hydrolysis where also the greater part of the organically com- 

 bined iodine is found. What relation the activity bears to the 

 iodine content therein has however not been determined. As 

 stated above we have evidence that some of the iodine is split 

 off as iodide, but we have no direct evidence that all the organ- 

 ically combined iodine found in the products of hydrolysis is still 

 in the same complex or in the same structural relationship as in the 

 original thyreoglobulin. A number of iodized amino-acids have 

 been studied qualitatively as to physiological activity. In no 

 case has thyroid activity been detected. The most conclusive 

 results as to the inactivity of 3,5-iodo-laevo-tyrosine are those 

 reported by Strouse and Voegtlin. 11 Other observations on the 

 inactivity of various iodized proteins, which on hydrolysis yield 

 3,5-iodo-tyrosine, also bear out these conclusions. The studies 

 on other iodized amino-acids do not lead to definite conclusions. 

 Thus von Fiirth and Schwarz 12 prepared and studied what they con- 

 sidered iodized phenylalanine, histidine and tryptophane. They 

 reported all these substances as physiologically inactive, but gave 

 no data indicating that they had really separated iodo-deriva- 

 tives of these substances. Pauly 13 however actually separated 

 pure tetra-iodohistidine anhydride and tri-iodo-imidazol and re- 

 ported that these substances increased the respiratory and pulse 

 frequencies, although uniodized imidazol had no such action. 

 These considerations lead us to conclude that for the present the 

 validity of the third and fourth assumptions is unknown to us and 

 that the true answers thereto are part of the problem in hand. 



EXPERIMENTAL PART. 



The mode of attack has already been outlined above. The 

 details as to the methods employed and the preparation of the 

 substances studied are given below. 



A. Preparations. 



Dried hog thyroids. Hog thyroids 14 were freed mechanically from fat 

 as much as possible and dried on glass plates in a current of air at 30-35 C. 



11 Journ. ofPharm. andExp. Ther., i, p. 123, 1909. 



12 Pfliiger's Archiv, cxxxiv, p. 113, 1908. 



13 Ber. d. deutsch. chem. Gesellsch., xliii, p. 2243, 1910. 



14 The raw material for this research was supplied by the Armour Labora- 

 tory Department. 



