SILK-PRODUCING INSECTS. 13 



highly volatile, and possesses a very peculiar strong 

 smell. 



It is useful to know how to detect the presence 

 of wool in silken tissues. Lassaigne has given us 

 an easy method of effecting this by showing that a 

 dissolution of oxide of lead in potash will blacken 

 woollen threads, forming sulphide of lead, because 

 wool contains a notable proportion of sulphur. 

 This is not observed with silk threads. If the 

 suspected tissue is coloured, it is necessary to take 

 out the dye before applying the test. 



Such are the principal chemical data we possess 

 regarding silk. 



This substance is not produced by the ' silkworm 

 alone ; endless varieties of insects, or larvge of 

 insects, produce it likewise ; and we have just seen 

 that the spider's web has a similar composition. 

 Indeed, as we shall see presently, other insects 

 besides the silkworm have been roared with a 

 view of obtaining silk, but as yet only with limited 

 success. 



The common silkworm is the larva of a kind of 

 moth (Bombyx mori) belonging to the family of 

 Lepidoptera. Much uncertainty has prevailed as 

 to the country in which this Bombyx was ori- 

 ginally found and reared. It appears evident, 

 however, that the silkworm is a native of China, 

 and that the mulberry tree was cultivated in that 



