80 THE CHEMICAL CONSTITUTION OF THE PROTEINS 



the cystine fraction dissolved in ammonia [Buchtala, 1907]. More 

 cystine is present in the hair than in the horn of the same animal, as 

 the following figures show : 



Human hair 13-9 per cent. (Morner) 



14-0 ,, , (Buchtala) 



14*5 



,, (white) 11*6 

 nails 5-2 



Ox hair 7-3 per cent. (Buchtala) 



(Morner) 



horn 6' 



,, hoof 5 '4 



Horse hair 8'o 



hoof 3-2 



Pig's bristles 7-2 



hoof 2*2 



(Buchtala) 



Human hair thus contains nearly double the amount of cystine 

 that is found in the hair of other animals. White hair has less 

 cystine than brown hair. 



Horn and hair differ further in respect to their content in glycine 

 and phenylalanine. Hair contains very little or no phenylalanine and 

 from 3-4 per cent, of glycine (white hair 9 per cent.) : horn contains 

 very little glycine and from 2-3 per cent, of phenylalanine. 



The keratins of sheep's wool and of goose feathers correspond in 

 most respects with the keratin of hair. 



Comparative analyses by Abderhalden and Fuchs [1908] show that 

 the horn of older animals contains slightly less glutamic acid than that 

 of younger: ox hoof one year old contained 18 per cent, four years 

 old 17; ox horn one year old 14, four years old 13. The data for 

 the horny material of the epidermis of a fish, a tortoise, a snake, an 

 armadillo and an elephant form an interesting series in comparative 

 physiological chemistry. The high tyrosine content of tortoise shell, 

 armadillo scales and snake's scales is particularly noticeable and it is 

 high also in whalebone and elephant hide. Tortoise shell has a high 

 glycine content, like gelatin and elastin, and does not appear to con- 

 tain glutamic acid. Tortoise shell has the highest tyrosine content of 

 any protein. 



The analysis of the egg-membrane of hen's eggs was made with 

 material from 25,000 eggs; only a qualitative analysis with 17 grams 

 of the egg-membrane of the eggs of Testudo graeca was possible. No 

 tyrosine is present in these proteins, but the egg-membrane of the 

 eggs of Selachians contains tyrosine and only traces of cystine. 

 Koilin, the horny material in birds' gizzards, has also a low cystine 

 content. The egg-membranes and koilin are not considered by 

 Hofmann and Pregl [1907] to belong to the sub-group of keratins. 



