CHEMISTRY OF Till-: THYUOin 595 



dialyzcd, tlie active suhstaiiee diffused thnnimh the membrane, indi- 

 cating that it is not a colh)idal complex, and that if derived from the 

 proteins it must be an iodized amino-acid or some related compound. 

 This observation is to be expected in view of the fact that thyroid pro- 

 duces its effects when fed and is presumably hydrolyzed before ab- 

 sorption. Lenhart ^'-"^ considers the effect of thyroid on tadpoles to be 

 merely an expression of the (>oneral stinndatio]i of metabolism, rather 

 than a specitic effect on differentiation.""^ 



liy decomposing thyreoglobulin by boiling with 30 per cent, sul- 

 phuric acid, a body is obtained containing as high as 14.5 per cent, of 

 iodin ; this is the tJnjroiodin of Baumann, which gives no biuret re- 

 action, yet is physiologically active. The stability of this active con- 

 stituent of the thyreoglobulin explains the successful administration 

 of thyroid preparations by mouth. It appears to be absorbed un- 

 changed and, unless enormous doses are given, none appears in the 

 urine (Oswald -■''). Long-continued digestion with trypsin, or auto- 

 lysis of thyroid glands, causes a complete splitting-out of the iodin. 

 One part of the iodin seems to be more firmly bound than the rest. 



Kendall ~* has isolated from the thyroid, after alkaline hydrolysis, a 

 crystalline compound containing 60 per cent, of iodin, which he sug- 

 gests may be di-iodo-di-hydroxy-indole. This is highly active, causing 

 rapid pulse, nervous irritability, and increased metabolism. It does 

 not contain all the iodin of the thyroid, but the nature of the other 

 iodin compounds is unknown beyond the observation that they have 

 no appreciable effects on normal persons but greatly improve the con- 

 dition of cretins. A small amount of the iodin may exist as inorganic 

 and lipoid compounds.-*^ When fed to tadpoles, Kendall's active 

 principle produces the characteristic thyroid effect."*'' 



The amount of iodin in the thyroid is greatest in middle age, greater 

 in females than in males, and it is decreased in acute infectious dis- 

 eases and in tuberculosis, alcoholism, and circulatory disturbances 

 (Aeschbacher).'^ 



The thyroid is very rich in lipase, catalase and peroxidase; ex- 

 tirpation is followed by a decrease in these enzymes in the blood, 

 while thyroid feeding increases them as well as the antitrypsin 

 ( Juschtschenko) .^® 



The physiological activity of thyroid preparations, according to 

 nearly all investigators, is in direct proportion to the iodin content,-'' 



19c Jour. Exp. Med., 1015 (22), 739. 



iMSee also Kahn, Arch. (jes. Physiol., 1016 (163), 384. 



23 Arch. exp. Path. u. Pharm., 1910 (63). 263. 



24 Jour. Amer. Med. Assoc, 1015 (64), 2042; Jour. Biol. Cheni., 1915 (20), 501. 

 2-ta Blum and Griitzner, Zeit. physio]. Cheni., 1914 (91), 400. 



24b Rogoff and ^Marine, Jour. Pharmacol., 1910 (9), 57. 



25 :Mit't. a. d. Grenzgeb. med. u. C'hir., 1905 (15), 209; Pellegrini, Arch. sci. 

 med., 1915 (39), 276. 



26Biochem. Zeit., 1910 (25), 49; Zeit. phvsiol. Chem., 1911 (75), 141. 



27 Fonio, Mitt. Grenz. Med. u. Chir., 1911 (24), 123; Frey, ibid., 1914 (28), 



