254 A. T. CAMEKCOT 



acetic acid, more easily in dilute alkali. On boiling with five per cent 

 hydrochloric acid it split off much carbohydrate, which was not a pentose. 

 The nucleoprotein contained carbohydrate radicals (not pentose), xanthin 

 bases, and 0.16 per cent of phosphorus. 



A pepsin digest of iodothyroglobulin yielded a substance resembling 

 iodothyrin, with 5.27 per cent iodin. A trypsin digest completely dis- 

 solved the compound, the solution containing no iodin nor iodid, but much 

 tyrosin, indicating that the iodin was not present originally in the tyrosin 

 group. Decomposition with acids gave an "iodothyrin" residue ; with con- 

 centrated acids iodin was liberated as iodid. 



Iodothyroglobulin from different sources (glands of sheep, pigs, oxen, 

 calves) has the same composition except for the iodin content (01.7 per 

 cent) . Iodothyroglobulin from children's thyroids has a low iodin con- 

 tent; that from a man dosed with potassium iodid was high. The com- 

 pound amounts to about 10 per cent of the fresh gland (one-half to two- 

 thirds of the dry tissue) . 



Further examination of prolonged digests with trypsin and with baryta 

 led Oswald (/) (1909) to the conclusion that the iodin is united in the 

 indolradical in the protein. 



Blum (c) (1899) considered that iodothyroglobulin cannot be a defi- 

 nite compound since its iodin percentage' varies. If, however, some one or 

 more of the radicals of this protein have the power to unite with iodin, it 

 is possible to conceive a variation in iodin content, and in iodin content 

 only. 



Wiener (1909) found from experiments on dogs that under normal 

 condition the two thyroid lobes have approximately the same weight, con- 

 tain the same amount of iodothyroglobulin, and the same iodin percentage. 

 The iodothyroglobulin varies between 14 and 60 per cent of the weight of 

 the dried gland. Feeding with sodium iodid increases the amount. Niirn- 

 berg (1909) confirmed the constant elementary composition. The hydro- 

 lysod contents include arginin, histidin, lysin, tyrosin, glutamic acid, 

 idycin, alanin, leucin, phenylalanin, aspartic acid, and a-pyrrolidin car- 

 boxylic acid. Niirnberg considered that the iodin is probably united in 

 the tyrosin or tryptophan radical. Koch (a) (~b) (1911) confirmed the 

 presence of histidin in the digest, and he subsequently (1913) tried to 

 ascertain the nature of the iodm-containing-complex, using the Keid Hunt 

 acetonitril test without success. 



Marine and Feiss (1915) consider, from experiments on iodin absorp- 

 tion, that the elaboration of iodothyroglobulin is a slow and complex 

 process. 



In 1915 E. C. Kendall (c) (i) published the results of his first four 

 years' work on the gland ; in 1919 he was able to announce the isolation of 

 a definite crystalline iodin compound, tJiyroxin (a-iodin), subsequently, 

 with A. E. Osterberg, verifying the constitution of the compound and de- 



