THE PROTEIN SUBSTANCES. 35 



It seems that there exist more than one keratin, and these 

 varieties form a special group of bodies. This fact, together with 

 the difficulty in isolating the keratin from the tissues in a pure 

 condition without a partial decomposition, is sufficient explanation 

 for the variation in the elementary constitution given below. As 

 examples the analyses of a few tissues rich in keratin and of kera- 

 tin itself are given as follows : 



c H N so 



Human hair .... 50.65 6.36 17.14 5.00 20.85 (v. LAAB.) 



Nail 51.00 6.94 17.51 2.80 21.75 (MULDER.) 



Neurokeratin... 56.11-58.45 7.26-8.02 11.46-14.32 1.63-2.24 .... (KUHNE.) 



Horn (average). 50.86 6.94 .... 3.30 .... (HORBACZEWSKI.) 



Tortoise-shell... 54.89 6.56 16.77 2.22 19.56 (MULDER.) 



Shell-membrane 49.78 6.64 16.43 4.25 20.90 (LINDVALL.) 



Sulphur is at least in part in loose combination, and it is partly 

 removed by the action of alkalies (as sulphides), or indeed by boil- 

 ing with water (CHEVREUL). Combs of lead after long usage 

 become black, and this is due to the action of the sulphur of the 

 hair. On heating keratin with water in sealed tubes at a tempera- 

 ture of 150 to 200 C. it dissolves, with the elimination of sulphu- 

 retted hydrogen, forming a non-gelatinizing liquid which contains 

 albumose (called keratinose by KRUKENBERG) and peptone (?). 

 The keratin may be dissolved by alkalies, especially on heating, 

 forming, besides alkali sulphides, albumoses and peptones (?). 

 That the keratin in the organism is formed from the albumin is 

 not to be denied. DRECHSEL believes that in keratin a part of the 

 oxygen of the albumins is exchanged for sulphur, and a part of the 

 xeucin or any other amido-acid is exchanged for tyrosin. The 

 products of decomposition of keratin and of albumin are similar, 

 except that the former gives proportionally a greater amount of 

 tyrosin (3-5$). 



Keratin is amorphous or takes the form of the tissues from 

 which it was prepared. On heating it decomposes and generates 

 an odor of burnt horn. It is insoluble in water, alcohol, or ether. 

 On heating with water to 150-200 C. it dissolves. It also 

 dissolves gradually in caustic alkalies, especially on heating. It is 

 not dissolved by artificial gastric juice or by trypsin solutions. 

 Keratin gives the xanthoproteic acid reaction, as well as the reac- 



