54 STRUCTURE OF THE SHEEP 



Structure of Wool. The structure of wool is similar in many 

 respects to that of hair. Both grow from hair follicles in the skin ; 

 both are nourished in the same way ; both consist of epithelial cells 

 arranged in three layers, but the medullary layer may be absent in 

 wool. The striking and essential difference between them is in the 

 cells forming the outer layer or cuticle. In hair these cells are 

 rather rounded in form and smooth along the edges, while in wpol 

 they tend to be pointed and irregular along the edges. In the hair, 

 the overlapping cells are attached to the under layer up to the very 



25 26 



FIG. 25. Coarse hairs, showing regular scales unsuitable for interlocking or felting. 



FIG. 26. Typical wool fiber, showing irregular scales. Such fibers felt easily. (From 



"Structure of the Wool Fibre," Bowman. Courtesy of The Macmillan Co.) 



margin of the cell, while in wool they are free for about two-thirds 

 of their length and they turn slightly outwards. Because of their 

 shape, position and manner of attachment to the cells beneath, the 

 cuticle cell of wool fibers will interlock, but those of hairs will not 

 to any marked degree. It is this property of interlocking, called 

 felting, that makes wool so much more valuable than hair in the 

 manufacture of fabrics (Figs. 25 and 26). 



As a rule wool is smaller in diameter than hair, and in white 

 wool, as in white hair, there is little if any pigment or coloring 

 matter in the cortex layer. Wool is also more wavy than hair, 

 the waves in the finer wools being so short and distinct as to be 

 called crimps. 



Function of Wool. Wool is a protective covering for the 



animal. The cuticle cells point outward from the skin and serve 



to keep out foreign substances such as dirt and chaff. Sheep with 



fairly dense, oily fleeces are less subject to colds than those having 



6 Bowman, "Structure of the Wool Fibre," 1908. 



