KERATINS. 113 



BERG) called atmidkeratin and atmidkeralose by BAUER. 1 Keratin is 

 dissolved by alkalies, especially on warming, producing besides alkali 

 sulphides also proteose substances. 



Besides the well-known cleavage products such as leucine, tyrosine, 

 aspartic acid, glutamic acid, arginine, and lysine, FISCHER and DORPING- 

 HAUS, 2 have recently found glycocoll, alanine, a-amino valeric acid, 

 proline, serine, phenylalanine, and pyrrolidone-carboxylic acid (secondary 

 from glutamic acid) among the cleavage products of horn substances. 

 EMMERLING claims to have found cystine as a sulphurized cleavage 

 product, but K. MORNER was the first to positively prove the abundant 

 occurrence of cystine in the cleavage products. MORNER obtained from 

 ox-horn, human hair, and the shell-membrane of the hen's egg 6.8, 13.92, 

 and 7.62 per cent cystine calculated on the basis of the dry substance. 

 BUCHTALA 3 obtained the following amounts of cystine from the respec- 

 tive keratin formations, namely, 12.98-14.53 per cent from human 

 hair, 5.15 per cent from nails, 7.98 per cent from horsehair, 3.20 per cent 

 from horse hoofs, 7.27 per cent from ox hair, 5.37 per cent from ox hoofs, 

 7.22 from pig bristles and 2.17 per cent from pig hoofs. From the 

 amount of sulphur split off by alkali, MORNER concludes that, at least in 

 ox horn and human hair, all the sulphur exists as cystine. GALIMARD 4 

 was able to get only a qualitative test for cystine in the keratin of the 

 adder eggs. SUTER, MORNER, and FRIEDMANN 5 have obtained a-thio- 

 lactic acid as a hydrolytic cleavage product of the keratin substances. 

 The last-mentioned investigator was also able to detect thioglycolic 

 acid in the cleavage products of wool. 



The shell membrane of the hen's egg and the eggshells of amphibians 

 and certain fishes are, as above mentioned, ordinarily classified as kera- 

 tins. These bodies among- themselves, as well as on comparison with 

 other keratins, show a marked difference in properties, this being very 

 evident from the tabulation on page 114. 



The large quantity of cystine in the keratins is considered as espe- 

 cially characteristic, and they differ in this regard from the other proteins. 

 The shell membrane of the hen's egg behaves like a keratin in regard to the 

 large amount of cystine contained, but differs essentially by the absence 



1 Krukenberg, Untersuch. iiber d. chem. Bau d. Eiweisskorper, Sitzunsber. d. 

 Jenaischen Gesellsch. f. Med. u. Naturwissensch., 1886; Bauer, Zeitschr. f. physiol. 

 Chem., 35. 



2 Zeitschr. f. physiol. Chem., 3(>, which contains also the older literature. 



3 Morner, ibid., 34 and 42; Emmerling, Ref. in Chemiker Zeitung, 1894; Buchtala, 

 Zeitschr. f. physiol. Chem., 52. 



4 Chem. Centralbl. II, 1905. 



5 Suter, Zeitschr. f. physiol. Chem., 20; Morner, ibid., 42; Friedmann, Hofmeister's 

 Beitriige, 2. 



