EXAMINATION OF TEXTILE FIBRES. 



93 



thread at first sight appears Uke a broad fibre with a 

 central canal (Fig. 38, a). In preparing silk for the mar- 

 ket, however, the cocoons, before unwinding, are placed 

 in hot water to kill the chrysalis and to melt the guramy 

 material which cements all the threads together. In this 

 process the single fibres become separated and each ap- 

 pears only as a semi-transparent cylinder (Fig. 38, b) with 



Fig. 38. — Silk. (After Hassack.) 200 diameters. 



no internal structure, and no external markings except very 

 fine longitudinal cracks formed as the fresh secretion 

 sets. Flecks of the ruptured cuticula and particles of 

 foreign material which come in contact with it when semi- 

 liquid sometimes adhere to the fibres. The diameter 

 varies considerably from point to point, according to the 

 rate at which the worm was producing its secretion. 

 Perhaps 10-20 jx would be a iair average. Ends, except 



