THE BIOCHEMISTKY OF THE THYKOID GLAND 253 



lar conclusion. Wheeler and Clapp adduced some evidence that p-iodo- 

 phenylalanin may be present in sponges. 



All attempts to isolate these or similar amino-acids from the thyroid 

 have failed. 



Most, if not all, of the iodin in the gland is in organic combination. 

 Blum and Griitzner consider that there is a small amount of iodid present. 



Baumann (1895), having detected iodin in the thyroid, endeavored to 

 isolate the iodin compound. He boiled fat-free tissue with about four 

 times its weight of 10 per cent sulphuric acid until only a slight brown 

 residue was left; this was extracted several times with boiling 85 per 

 cent alcohol; the extract evaporated to dryness constituted Baumann's 

 "thyroidin" (iodothyrin) . A pepsin digest, of the fresh gland gave the 

 same residue. It contained about 10 per cent of iodin which was scarcely 

 at all split off by alkalis. Iodothyrin was considered to be united to pro- 

 tein in the gland. It was amorphous, gave no biuret reaction, was almost 

 insoluble in acids and water, easily soluble in alkalis and precipitated by 

 acids without decomposition. It amounted to about four per cent of the 

 total weight of the dried gland (Baumann and Eoos). Eoos (1896, 1898) 

 obtained the preparation by digestion with acids, removing fat with ether, 

 and twice precipitating with acids from alkaline solution. The final prod- 

 uct contained 9.3 per cent of iodin. His elementary analyses for prepara- 

 tions from sheep and human thyroids show only moderate agreement and 

 great variation in iodin content (respectively, I, 1.31, 4-31 per cent; S, 

 1.40; N, 8.91, 10.41; C, 57.04, 61.41; H, 7.28, 7.43; Ash, 0.4, 0.47; 01, 

 0.4, 0.5). Iodising iodothyrin gave in two preparations 10.89 and 10.3 

 per cent iodin. According to Blum (1898) iodothyrin is an inconstant 

 decomposition product of thyroid tissue, different successive extracts con- 

 taining different percentages of iodin; the maximum he obtained was 8.9. 

 Niirnberg (1907) considered that the iodin compound present was iodo- 

 tryptophan. 



Other preparations obtained from thyroid are S. Frankl's "thyreo- 

 antitoxin," considered to be C 6 H U N3O 5 , JSTotkin's "thyroprotein" (1896), 

 and those of Drechsel (a) (1895). With the exception of Baumann's, none 

 of these can any longer be considered to have any physiological significance. 

 Critical consideration of these preparations and of earlier similar work, 

 is given by Oswald (b) (1899), who succeeded in removing all the iodin 

 from thyroid tissue by repeated extraction with physiological saline 

 solution. The extract contained two proteins, one salted out by half 

 saturation with ammonium sulphate, the other by complete saturation. The 

 first, iodotliyroglobulin, contained iodin and no phosphorus, the second, a 

 nucleoprotein, phosphorus and no iodin. His iodothyroglobulin had the 

 elementary composition C, 52.2; H, 6.7-6.96; N, 16.51-16.67; I, 1.57- 

 1.75; S, 1.77-1.95; O, 20.85, and a molecular weight of about 8,000.^ It 

 was difficultly soluble in water, soluble in neutral salts and very dilute 



