RESULTS OF ANALYSIS 77 



Scleroproteins. 



The scleroproteins, which in their physical properties comprise a 

 heterogeneous collection of proteins, give on hydrolysis, as would be 

 expected, results which support their classification. 



Silk. 



Of the proteins in this group those of silk have been most 

 thoroughly investigated. Silk is a mixture of two proteins silk- 

 fibroin and silk-gelatin ; the latter is extracted from raw silk by boiling 

 out with water under pressure when it loses 15-20 per cent, in weight ; 

 the insoluble portion which has the structure of the original silk forms 

 the silk-fibroin. 



Both silk-fibroin and silk-gelatin were analysed by Fischer and 

 Skita [1901, 1902] when the ester method was first introduced. Silk- 

 fibroin is composed of practically only three amino acids, glycine, 

 alanine and tyrosine, and is probably the simplest protein known. It 

 contains more tyrosine than any other protein except that of the cara- 

 pace of the tortoise and is the best source of tyrosine. Silk-fibroin 

 differs very markedly in composition from silk-gelatin ; this substance 

 contains more serine than any other protein. 



The composition of silk-fibroin and silk-gelatin from different 

 sources is under investigation by Abderhalden and his pupils. The 

 present data show that the composition of the various silk-fibroins 

 is fairly similar, although many differences can be noted. The New 

 Chwang, Schantung and Chefoo varieties are rather peculiar in 

 leaving a somewhat large residue after hydrolysis, which seems to be 

 connected with the food-stuff of the silk-worms. The New Chwang 

 and Schantung worms are fed on oak leaves. The Canton and Bengal 

 silks are most like the Italian ; Indian Tussore silk contains a 

 considerably smaller amount of glycine. African Tussore silk is like 

 other Tussore silks and the silk of Bombyx mori from Africa resembled 

 that of Bombyx mori from other countries. The silk of Anaphe had 

 also a similar composition. In fact, the silk of caterpillars, spiders, 

 and of Pinna nobilis have an almost identical composition, with 

 tyrosine, glycine and alanine as the chief constituents [Abderhalden, 

 1911]. 



No striking differences are to be noted in the various silk-gelatins. 



The silk of other arthropods has also been examined. The silk- 

 fibroin from spider's silk, except for its high content in glutamic acid, 



