454 ELEMENTARY CHEMICAL MICROSCOPY 



more properly applies to the bast fibers from various species of large stingless 

 nettle of the genus Urticacea. 



Ramie fibers are long, somewhat tapering cells of uneven diameter with thick 

 rounded ends. In cross-section the cells are more or less irregularly elliptical but 

 are often flattened and show very characteristic prominent cross-lines or fissures. 

 The flattened cells when seen edgewise appear to have very thick walls and a cen- 

 tral fine lumen tapering toward the ends of the cells to fine, almost invisible lines; 

 but such cells lying flat are seen to have large, coarse lumens of very irregular 

 diameter. These central canals or medullary spaces are filled with granular 

 matter and occupy from one-third to one-half the diameter of the cells. The cell 

 walls are coarse, thickened irregularly at intervals, and exhibit well-marked nodes, 

 joints and dislocations: they are further characterized by many prominent rather 

 deep longitudinal striations crossed at irregular intervals by transverse lines and 

 fissures. The broad flattened fibers are never twisted, but many have the appear- 

 of having their edges folded over. 



The fibers of true China Grass are not readily distinguished from those of 

 Ramie. 



Both Ramie and China Grass polarize strongly and show brilliant polarization 

 colors; this is especially true of the cooked and purified fibers. 



GROUP C. ANIMAL HAIRS 1 



Wool. Hair from many varieties of sheep. After removal of fat, under proper 

 illumination and focusing, wool shows an outer scaly layer or cuticle, an inner 

 fibrous layer or cortex which may or may not be pigmented and a central canal 

 or medulla, usually filled with more or less interrupted granular-appearing matter. 

 Wool hairs in which the medullary canals are well developed are usually quite 

 smooth and free from " scales," and are commercially known as " kemps." The 

 better the grade of the wool the freer it is from " kemps." Fine grades of wool 

 polarize feebly without colors; coarse wools strongly with colors. 



Mohair. (Angora wool). Hair from the Angora goat. Scales closely adherent; 

 outline of the hair in profile smooth. Scales broad, flat, ve-ry thin, quite regular in 

 outline, with very fine serrations; serrations finer than in wool. Longitudinal 

 striations more marked than in wool. Mohair is usually much finer than wool 

 and that of high grade contains but few hairs in which the medulla is prominent. 

 Most fibers polarize strongly with high colors, very fine hairs being thinner, polarize 

 feebly. 



GROUP D. NATURAL SILKS. 



Silk. This term is generally restricted in commerce to the filaments obtained 

 from cocoons of the silk worm (Siricaria (Bombyx) mori] reared on mulberry leaves 

 in captivity. The silk worm has two glands secreting a viscous liquid which hardens 

 into silk when in contact with the air. The filament as spun is therefore double, 



1 For the technique to be followed in the identification of mammalian hairs, see 

 Hausman, L. A.: The Microscopic Identification of Commercial Fur Hairs; Sci. 

 Monthly, 1920, 70. Mammal Fur under the Microscope; Natural Hist. 20 (1920) 

 434. Structural Characteristics of the Hair of Mammals; Amer. Nat. 64 (1920) 496. 



