xi THE ALBUMINOIDS : KERATIN 567 



' Ossein,' i.e. decalcified bone, is as readily dissolved by pepsin as are 

 other kinds of gelatine. 



Collagen of Invertebrates. Silk Glue. Hoppe-Seyler * lias found 

 gelatine-yielding tissues amongst the invertebrates in the cephalopods : 

 Octopus and Sepiola. Silk-glue is discussed on p. 571. 



Glutolin. Under this name Faust 2 has described an albuminous 

 substance which he found in blood-serum, and which he considers to 

 be the mother substance of gelatine because of its low sulphur content 

 and the feeble Millon's reaction it gives. The possibility of this sub- 

 stance being a transformation-product of one of the serum-albumins is 

 not excluded. 



2. Keratin 



Keratin is the chief constituent of the horny substances found in 

 mammals and birds. It occurs in the stratum corneum of the 

 epidermis, in hairs, nails, hoofs, horns, and in feathers. It is also 

 found, in the egg-shells of birds, 3 and of the Echidna aculeata 4 (a 

 mammal), of crocodiles 4 and snails, 5 in the cocoons of leeches, 6 and 

 probably in many other tissues amongst invertebrates. (Compare the 

 articles by Neumeister 4 and Sukatschoff 6 ). Neurokeratin is met with 

 in the medullary sheath of medullated nerves. 



Keratin is the most insoluble of all the albuminoids, being quite 

 insoluble in water, dilute acids, and alkalies ; according to Smith 7 

 even 10 per cent KOH dissolves it only with the help of heat; in 

 the cold a 20 per cent caustic soda solution is required to render it 

 soluble, and this procedure of course decomposes keratin. The 

 digestive enzymes have also the greatest difficulty in rendering it 

 soluble. 



An exact study of keratin, for the reasons just given, is impossible ; 

 on the other hand, its insolubility in acids, alkalies, pepsin, and trysin, 

 makes it possible to prepare keratin in a fairly pure state, as all other 

 albuminous substances may be removed by treatment with the reagents 

 just mentioned. 8 



Notwithstanding this the analyses given by Kuhne and Chittenden, 8 



1 Hoppe-Seyler, Med.-chem. Untersuch. p. 586 (1871). 



' 2 E. S. Faust, Arch. f. exper. Path. u. Pharm. 41. 309 (1898). 



3 V. Lindwall, Hammarsten's abstract of the Swedish original in Moly's Jahresber. 

 f. Tierchem. 11. 38 (1881). 



4 R. Neumeister, Zeitschr. f. Biol. 31. 413 (1895). 



5 W. Engel, ibid. 27. 374 (1890) ; 28. 345 (1891). 



B B. Sukatschoff, Zeitschr. f. wissensch. Zool. 56. 377 (1899). 



7 H. Smith, ibid. 19. 469 (1883). 



8 W. Kiihne and R. H. Chittenden, ibid. 26. 291 (1890). 



