92 ELEMENTS OF y4PPUED MICROSCOPY. 



sheep's wool with camel's hair will prove instructive, 

 showing the lesser length of the latter, its freedom from 

 twisting, the scales lying almost fiat against the surface, 

 and the granular spots in the medulla. Different grades 

 of wool may then be studied, contrasting the high-grade 

 merino wools with a diameter of 15 /i and 10 or more 

 twists in every centimeter of length with a wool of poor 

 quality having perhaps four or five times that diameter 

 and not more than one twist in a centimeter. These 

 two qualities, fineness und convolution, principally deter- 

 mine the quality of wool, although its regularity and the 

 projection of its scaly covering are also of importance. 

 A sample of wool shoddy may profitably be examined; 

 various foreign fibres, dyed fibres, and torn and broken 

 fibres will be apparent. 



II. Silk. — One other aniiftal fibre of quite a different 

 character remains to be considered, the secretion of the 

 silkworm. The larvae of many moths spin their cocoons 

 out of threads long and strong enough to be used for 

 textile purposes, but that of Bombyx mori is cultivated 

 most extensively for commercial purposes in China, 

 Japan, India, France, and Italy. 



The substance of which silk is composed is poured out 

 in a liquid condition from two glands at the anterior end 

 of the worm, and when discharged in the air at once sets 

 in the form of solid structureless rods. The pair of 

 fibres formed by the two large spinnerets are cemented 

 together by an incomplete cuticula of somewhat differ- 

 ent composition produced by another set of glands and 

 Joaown as seridn. Under the microscope such a double 



