50 THE CHEMICAL CONSTITUTION OF THE PROTEINS 



closely resembles that of the silk-worm. The silks examined by 

 Suzuki, Yoshimura, and Inouye were distinctly different. The material 

 spun by Oeceticus of the family Psychidae in order to unite the bits 

 of wood together with which it builds its house contained no tyrosine, 

 but otherwise resembled silk-fibroin. The absence of tyrosine brings 

 out a resemblance to ovokeratin. 



Gelatin contains no tryptophane, cystine, or tyrosine, but it contains 

 more glycine than any other protein, except elastin and tortoise-shell. 

 It also contains a large amount of proline. This protein appears to 

 have no similarity to silk-gelatin, which contains so much serine. The 

 protein of the carapace of the tortoise is peculiar in containing 1 3 *6 per 

 cent, of tyrosine ; silk-fibroin had, until this analysis was performed, 

 been regarded as the protein with most tyrosine in its compositioa 

 Whalebone, however, does not show any particular feature. 



Spongin resembles gelatin in its high content of glycine, but differs 

 in its content of glutamic acid. 



Elastin seems to be made up almost entirely of glycine and leucine ; 

 like gelatin, it contains no tyrosine, but it differs from gelatin in con- 

 taining more phenylalanine. 



The keratins are distinguished by containing more cystine than 

 any other protein ; in human hair cystine exists to the extent of 

 about 14 per cent, in other keratins its amount varies from 2-8 per 

 cent. (Morner, Buchtala). Tyrosine is also present in fair quantities, 

 and the amounts of leucine and of glutamic acid are high. Comparative 

 investigations by Abderhalden and Fuchs show that the glutamic acid 

 content of the keratin of ox horn is less in older animals than in 

 younger. 



Conjugated and other Proteins. 



The only analysis which we possess of a glucoprotein pseudomucm 

 was carried out before the ester method had become of general use. 

 Pregl with the small quantity of material available could only perform 

 a qualitative analysis. 



A large variety of proteins which cannot be included in any of the 

 above groups have been examined, including micro-organisms and the 

 muscle of Egyptian mummies. The qualitative data given by Abder- 

 halden and Rona for Aspergillus niger are of special interest, as this 

 mould was grown on particular nutrient solutions and in each case the 

 same amino acids were synthesised. 



