78 THE CHEMICAL CONSTITUTION OF THE PROTEINS 



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

 Suzuki, Yoshimura and Inouye [1909] 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. 



Origin of the Amino Acids in Silk. 



Abderhalden and Dean [1909] and Abderhalden and Weichardt 

 [1909] have tried to ascertain whether the amino acids composing the 

 silk are elaborated at the moment of spinning or whether they are 

 selected out of the protein material by the spinning gland. Since the 

 composition of the moth and cocoon together is about the same as the 

 silk-worm, it seems most likely that the spinning gland selects the 

 constituents in making the silk and does not synthesise them from 

 other products. 



Pigorini's experiments [1915] with Bombyx mori indicate that 

 glycine is assimilated if it be added to the food in small quantities ; 

 in large quantities it had a toxic action, probably due to the formation 

 of ammonia and other decomposition products. This fact supports the 

 hypothesis that silk-formation is mainly a protective measure of the 

 silk-worms, the object being to remove free amino acids from the 

 organism. 



Inouye [1912] showed that a great change in chemical composition 

 of the animal takes place in the preparation of the cocoon by the 

 caterpillar, but there is very little change between the pupa and the 

 moth. No nitrogen is given off in the gaseous state, but fat is stored 

 up in the pupa stage and consumed by the pupa and moth. In all 

 stages the amount of mono-amino acids present is greater than that 

 of di-amino acids ; mono-amino acids are found almost entirely in the 

 cocoon. Protein is hydrolysed by a proteoclastic enzyme and its loss 

 is balanced by the increase in amino acids, which are partially con- 

 verted into ammonia. Inouye [1910] determined the amount of food 

 (mulberry leaves) consumed by the silk-worm. 1000 silk-worms ate 

 12579-6 grams of fresh leaves whose dry matter was 4056*6 grams ; 

 1324 grams or nearly 33 per cent, of the mulberry leaves were assimi- 

 lated. The silk-worms were hatched on July 1 2th, attained maturity, 



