298 HORNY MATTER. [BOOK I. 



in sealed glass tubes heated to 150 200 C.), yielding a turbid 

 solution which furnishes on evaporation a dry mixture insoluble in 

 water. Keratin swells, and subsequently is dissolved by boiling in 

 alkalies, and on the addition of acids to the alkaline solutions 

 sulphuretted hydrogen is given off. 



Horny substances swell when immersed in dilute acetic acid, and 

 are in great part dissolved by boiling glacial acetic acid. 



When boiled with dilute sulphuric acid, Keratin yields aspartic 

 acid, volatile fatty acids, leucine, and tyrosine. Nitric acid dissolves 

 it, and oxalic acid is formed as an ultimate product. 



When strongly heated, horny substances burn, evolving the charac- 

 teristic smell of burned feathers. 



Results of Though we cannot obtain by any known process a 



ultimate ana- definite substance Keratin, which can be considered as 

 lyses of Horny pure, yet the horny tissues present a very close resem- 

 Tissues. blance in the proportion in which their elements are 



contained, as will be seen by perusing the analyses here appended 1 . 



Hair, Nails, Cow's horn, Horse's hoof, 



(v. Laer). (Mulder). (Tilanus). (Mulder). 



50-60 51-00 51-03 51'41 



H 6-36 6-94 6'80 6'96 



N 1714 17-51 16-24 17'46 



O 20-85 2175 22-51 19'49 



S 5-00 2-80 3-42 4'23 



The sulphur which is contained in these horny substances is very 

 loosely combined; it varies also remarkably in quantity in various 

 samples of the same tissue, as for example in human hair between 

 3 and 8" 23 per cent. When heated with barium hydrate and water 

 in sealed glass tubes, nearly the whole of the sulphur is obtained in 

 the form of Ba(SH) 2 (Hoppe-Seyler 2 ). 



Inorganic Matters contained in the Horny Tissues. 



All these tissues contain inorganic matters. In the nails the ash 

 is said to be specially rich in calcium phosphate. Hair contains from 

 0'5 to 7 per cent, of mineral constituents, and the latter contain 

 alkaline sulphates, iron and silica (40 per cent, of the ash). The pro- 

 portion of iron in the hair varies, and it has been stated that it is 

 larger in dark than fair hair; but this statement must be received 

 with some doubt. 



The composition of the mineral matters of feathers varies, accord- 

 ing to von Bibra, with the nature of the food upon which birds feed; 

 thus, the silica may vary between 27 and 40 per cent, of the total 

 mineral matters. 



1 Hoppe-Seyler, Physiologische Chsmie, 1 Theil, p. 90. 



2 Hoppe-Seyler, Op. cit., p. 91. 



