THE SILKWORM ITS DISEASES AND IMPERFECTIONS. // 



and the silk industry, one of the most important occupations of 

 the peasantry of France, was rescued from ruin. 



The brief account given above of the epidemic diseases to 

 which silkworms are liable will suffice to show that the breeders 

 of these insects on a large scale need to exercise great watchful- 

 ness, and that the occupation is not by any means the mere 

 amusement it might on first thoughts be imagined to be, but that, 

 on the contrary, it is sometimes an exceedingly anxious under- 

 taking, which may result even in considerable pecuniary loss. 

 But when the insects have once mounted into the heather twigs 

 and have commenced spinning, there is very little further cause 

 for anxiety, at least so far as that year's produce is concerned. 



There are, however, certain imperfections in the cocoons which 

 occasionally occur and render a few of them unfit for commercial 

 purposes. We have already mentioned double and multiple 

 cocoons, that is, such as are produced when two or more 

 silkworms combine to form a single investment for their chrysalises. 

 These, which cannot be reeled in consequence of the interference 

 of the threads, can generally be distinguished by their rounder 

 shape, though occasionally they so closely resemble the normal 

 form as to be practically undistinguishable. It is said that when 

 the worms are allowed to spin as they please in the heather twigs, 

 the proportion of double cocoons is usually from 4 to 10 per cent, 

 of the total. 



The perfect cocoon should be hard and tough and capable of 

 resisting pressure at the ends as well as at the sides. The ends 

 should be well rounded, and the thread should become detached 

 easily, with a sort of crackling sound. Finally the colour should 

 not be too bright. In all these respects there are many variations 

 in the cocoons. Sometimes the ends are too thin and yield to 

 pressure ; sometimes, again, one end is prolonged to a point and 

 is open at the extremity ; such a cocoon would be of no use for 

 reeling, as the water of the reeling basin would gain access to the 

 inside, and thus detach the different patches of silken loops in 

 several parts at once, so that the thread would unwind in lumps. 

 Cocoons with a satiny lustre also are imperfect, the brilliant 

 appearance arising from an incomplete adhesion of the different 

 layers of silk. 



If the insect, after having formed its cocoon, should die of an 

 epidemic disease such as flacherie, its body would putrefy and 

 stain the silk black and thus render it valueless. Again, it may 

 die in the chrysalis state, or the newly- hatched moth may be 

 unable completely to extricate itself from the pupa skin. This is 

 the more likely to be the case when the pupa has been removed 



