EXAMINATION OF TEXTILE FIBRES. 93 
thread at first sight appears like 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 gummy 
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, 6) with 
Fic. 38.—Smx. (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 » would be a fair average. Ends, except 
