568 CHEMISTRY OF THE PROTEIDS CHAP. 



Lindwall, 1 van Laer, 2 Horbaczewski, 3 Bibra, 4 Suter, 5 and Mohr 6 differ 

 greatly from one another on all points except as regards the high 

 sulphur content, which has already been alluded to on p. 73. 



Its dissociation -products are enumerated on p. 73, under Nos. 

 25 to 27. Keratins are remarkable for the high percentage of tyrosin, 

 and in particular of cystin, a compound which was prepared for the 

 first time in a pure state from keratin by Morner ; 7 from human hair 

 he obtained 14 per cent. 8 Other sulphur-containing dissociation-pro- 

 ducts have also been found in keratin, for on dissociating keratin, 

 sulphuretted hydrogen and methyl mercaptane are obtained 9 (see 

 index). 



Ammonia is as a rule also obtained in large amounts ; 10 amongst the 

 bases, arginin has been observed, while the others have not yet been 

 looked for. A carbohydrate was neither found by Kiihne and Ewald n 

 nor by Neumeister. 12 When keratin is treated with alkalies or with 

 superheated water, albuminates, albumoses, and peptones are formed, 

 according to Lindwall l and Bauer. 9 



As can be judged by its composition, keratin gives the following 

 reactions typical of albumin : an intense Millon's reaction and equally 

 intense xanthoproteic and lead-sulphide tests. Whenever, therefore, a 

 substance gives the just-mentioned tests very strongly, and is at the 

 same time insoluble in acids and alkalies and resists trypsin and pepsin, 

 we know we are dealing with keratin. Very finely divided, i.e. very 

 young, keratin is digested, however, by pepsin, according to Kiihne 13 

 and Neumeister 12 (Cohnheim) ; young keratin differs chemically from 

 adult keratin (the author). 



Neuro-keratin was discovered by Kiihne and Ewald, and more 

 carefully investigated by Kiihne and Chittenden ; it is even more 

 resistant to the action of alkalies than is the keratin of the skin, and 



1 V. Lindwall, Hammarsten's abstract of the Swedish original in Malys Jahresber. 

 f. Tierchem. 11. 38 (1881). 



2 J. F. J. van Laer, Liebig's Annalen, 45. 147 (1843). 



3 J. Horbaczewski, Sitzungsber. d. Wiener Akad. 80. math.-nat. Kl. II. (1879). 

 (Reprint). 4 v. Bibra, Liebig's Annalen, 96. 289 (1855). 



5 F. Suter, Zeitschr. f. physiol. Chem. 20. 564 (1895). 



6 P. Mohr, ibid. 20. 400 (1894). 



7 K. A. H. Morner, ibid. 28. 595 (1899). 



8 K. A. H. Morner, ibid. 34. 207 (1901). 



9 R. Bauer, ibid. 35. 343 (1902). 



10 J. Horbaczewski, Wiener Akad. 80. math.-nat. Kl. II. (1879). 



11 A. Ewald and W. Kiihne, Verhandl. d. naturh.-med. Vereins Heidelberg, New 

 Series I. p. 457 (1876). 



12 K. Neumeister, Zeitschr. f. Biol. 31. 413 (1895). 



13 W. Kiihne, Untersuch. an dem Heidelberg, physiol. Institut, I. p. 219 (1877). 



