62 MANAGEMENT AND FEEDING OF SHEEP 



Each wool fiber is made up of three layers or por- 

 tions. These are known respectively as the epidermis, 

 the cortical substance and the medullary substance. The 

 epidermis or outer layer, which is very thin, embraces 

 a vast number of imbricated scales, lying on one another. 

 These are formed by the growth of cells, which, as they 

 grow, assume the form of scales, and in a healthy sheep 

 they have a high luster. The new portion pushes out the 

 old. The scales overlap and thus constitute the felting 

 properties of the wool. They also tend to keep dirt from 

 entering the fleece. The cortical substance, or intermedi- 

 ate layer, is fibrous in character and forms two-thirds 

 of the substance of each fiber, and also contains the mat- 

 ter which gives color to the wool. The medullary sub- 

 stance, or inner layer, is sometimes spoken of as the marrow 

 of the fiber. A majority of the fibers have the marrow hol- 

 low through much of their length. 



Discussion of yolk in wool — Yolk (see page 74) is an 

 alkaline soapy substance secreted from the glands of the 

 skin. The yolk follicle empties into the wool follicle near 

 the mouth of the latter, and extending therefrom it lubri- 

 cates the fibers to their outer extremities. It also lubri- 

 cates the skin. 



The chief function of yolk in wool is to prevent the 

 fibers from felting together and to prevent them from 

 wearing by friction ; but it also tends to protect the fleece 

 from the accumulation of foreign substances within it. 

 The less wear in the fibers that are well supplied with 

 yolk accounts in part at least for the greater strength 

 of fiber in wools well supplied with the same. The pro- 

 tection thus furnished from rain acts similarly. The 

 wool is protected from foreign substances, in part at least, 

 by the outward movement of the yolk. The edges of the 

 scales on the fiber-like little barbs point toward the tip of 

 the fiber, and, therefore, carry the yolk outward along 

 with more or less substances that may have found their 

 way into the fleece. Those wools which possess the 



