86 ELASTIN. KERATIN. 



analogous to those of the digestive products of proteids. 1 It is 

 however as yet uncertain whether a true elastinpeptone can be 

 obtained ; it is more probable that during the digestion only some 

 of the primary substances (elastoses) make their appearance, since 

 they are completely precipitated by saturation with neutral am- 

 monium sulphate. 2 Elastin is also rapidly corroded and dissolved 

 by the action of papai'n. (Gamgee.) 



Hilger 3 has obtained a somewhat similar substance from the 

 shell and yolk of certain snakes' eggs. 



Keratin. 



Hair, nails, feathers, horn, and the epidermal structures in gen- 

 eral 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 con- 

 venient source which readily yields a pure product, owing to the 

 comparatively simple composition of the mother substance, is 

 found in the shell-membrane of ordinary eggs. 4 The percentage 

 composition of keratin is in general allied to that of the true pro- 

 teids, but varies within somewhat wide limits according to the 

 source from which it has been prepared and particularly with re- 

 gard 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 sul- 

 phides 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 pro- 

 ducts which are in general identical with those obtained by the 

 similar treatment of proteids. 5 It is soluble in strong alkalis when 

 heated, and is further stated to be dissolved by prolonged treat- 

 ment with superheated water ; in the latter case a product is ob- 

 tained to which, since it somewhat resembles an albumose, the 

 name keratinose has been given, and which may now be digested 

 by means of pepsin. 6 Further investigation in this direction is 

 however needed before any positive statements can be made re- 

 specting any truly digestive products derivable from keratin, or 

 indeed as to the characteristic differences of the keratins from 

 different sources. 



1 Horbaczewski, loc. cit. 



2 Chittenden and Hart, loc. cit. 



3 Ber. d. deutscli. chem. Gesell. 1873, S. 166. See also Krukenberg, Vergl.-physiol. 

 Stud. ii R. 1. Abth. S. 68. 



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



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

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



' ; Krukenberg, Sitzb. d. Jena, Gesell. f. Med. u. Xat.-wtss. 1886, S. 22. 



