114 THE PROTEIN SUBSTANCES. 



was the first to prove positively 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 l obtained 

 the following amounts of cystine from the respective keratin forma- 

 tions, 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, 

 2.17 per cent from pig hoofs, 6.30 per cent from goose feathers, 2.14 

 per cent from chicken spurs, 1.88 per cent from the epidermis scales of 

 chicken feet and 4.7 per cent from elephant epidermis. 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 2 

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

 adder eggs. SUTER, MORNER, and FRiEDMANN 3 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 115. 



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 

 of tyrosine. It is remarkable that the egg membrane of the Selachii, 

 which biologically is analogous with ovokeratin, differs from the typical 

 keratins by the absence of cystine, while it contains, on the contrary, 

 large amounts of tyrosine. The typical keratins differ among them- 

 selves in regard to composition, thus the keratin from the sheep hoofs 

 contains 2 per cent phenylalanine, while this amino-acid is absent in the 

 keratin of hair and feathers. It is difficult to say whether or not this 

 is due to a difference in the purity of the bodies or not. The keratins 

 investigated chemically, thus far, do not form a sufficient characteristic 

 group. 



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

 Zeitschr. f. physiol. Chem., 52, 69, and 78. 



2 Chem. Centralbl. II, 1905. 



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

 Beitrage, 2. 



