SOMETHING ABOUT WOOL 



323 



glands in the skin also give off wool fat. The wool fiber is 

 made up of three distinct parts, an outer layer, or epidermis, 

 consisting of flattened cells or scales which lap over each 

 other much like the shingles on a roof; the cortex, which con- 

 sists of cells more or less long from which the fiber gets its 

 form and strength; and the medulla, or pith, at the center. 

 The epidermis of wool differs from that of common hair, 

 because the scales project outward, giving a serrated ap- 

 pearance, while on hair the scales more nearly butt together 

 and give a much smoother surface to the fiber. In the case 

 of wool, the projecting edges of a mass of fibers, when brought 

 together under certain condi- 

 tions, lock or felt. It is this 

 quality of felting which gives 

 wool its special value for cloth 

 making, a property not pos- 

 sessed by ordinary hair. These 

 scales differ in size on different 

 breeds of sheep ; but, while very 

 small, may be seen under a 

 common microscope, especially 

 if the fiber is first exposed a 

 moment to boiling water, or to 

 acid or alkali, which will cause 

 the overlapping edges to open 

 up still more. These scales 

 have a very hard, smooth surface, and are more or less trans- 

 lucent, so that the cortex below may be seen through them. 

 The finer wools, such as Merino, have scales that are often 

 smooth and straight. along their edges, while the scales on 

 the larger, coarser wools have serrated, more irregular edges. 

 From the scales of the epidermal layer comes a quality known 

 as lustre in the wool trade, which is highly valued. This is 

 due to the unbroken reflection of light from the scales. 

 ^Vhen the scales are regular and uniform in their arrange- 



Figure 138. — Comparison of varieties 

 of wool fibres. M — Merino. T — 

 territory, C — coarse. Reproduced 

 from "Textile Fibers," by Dr. J. M. 

 Alatthews. 



