86 KERATIN. 



Keratin. 



Hair, nails, feathers, horn and the epidermal structures in general 

 are composed chiefly of keratin, admixed however with small quantities 

 of proteids and other substances, from which it may be freed by 

 thorough extraction with water, alcohol, ether and dilute acids in 

 succession, followed by digestion with pepsin and trypsin (Kiihne) 

 and a renewed washing with the above reagents. A convenient 

 source which readily yields a pure product, owing to the compara- 

 tively simple composition of the mother substance, is found in the 

 shell-membrane of ordinary eggs 1 . The percentage composition of 

 keratin is in general allied to that of the true proteids, but varies 

 within somewhat wide limits according to the source from which it has 

 been prepared and particularly with regard to the sulphur which it 

 contains. This latter element varies in amount from *5 to 5*0 p.c. and 

 leads to the formation of sulphides of the metal when keratin is 

 dissolved in alkalis. Unlike the proteids, gelatin and elastin, keratin 

 is quite unaffected by the most prolonged and active digestion with 

 either pepsin or trypsin. On the other hand, when decomposed at high 

 temperatures by either caustic baryta or strong hydrochloric acid, it 

 yields large quantities of leucin (15 p.c.), tyrosin (3 4 p.c.) and other 

 products which are in general identical with those obtained by the 

 similar treatment of proteids 2 . It is soluble in strong alkalis when 

 heated, and is further stated to be dissolved by prolonged treatment 

 with superheated water ; in the latter case a product is obtained to 

 which, since it somewhat resembles an albumose, the name keratinose 

 has been given, and which may now be digested by means of pepsin 3 . 

 Further investigation in this direction is however needed before any 

 positive statements can be made respecting any truly digestive products 

 derivable from keratin, or indeed as to the characteristic differences of 

 the keratins from different sources. 



Lindwall (loc. cit.) described the formation of an albuminate and a peptone-like 

 (? albumose) substance during the treatment of keratin with dilute (1 2 p.c.) 

 caustic soda at digestion temperatures. 



Neurokeratin 4 . 



When the substance of the brain or any mass of medullated 

 nerves is thoroughly extracted with water, alcohol and ether, and 



1 Lindwall (Swedish). See abst. in Maly's Jahresber. 1881, S. 38. 



2 Horbaczewski, Sitzb. d. k. Akad. d. Wiss. Wien. Bd. LXXX. (1879), 2 Abth. 

 Juni-Hft. Bleunard, Compt. Eend. T. LXXXIX. (1879), p. 953, T. xc. (1880), p. 612. 



3 Krukenberg, Sitzb. d. Jena, Gesell. f. Med. u. Nat.-wiss. 1886, S. 22. 



4 Kiihne u. Ewald, Verhand. naturhist.-med. Ver. Heidelbg. Bd. 1, 1877, S. 457. 

 Kiihne u. Chittenden, Zt.f. Biol. Bd. xxvi. (1890), S. 291. 



