ioo HISTORY OF THE HUMAN BODY 



single layer of epidermic cells covers the cortex externally. 

 Differences in color and luster are due to the amount of pig- 

 ment in the cortex, the sculpture of the epidermic covering and 

 the presence or absence of air in the medulla. 



The cells of the epidermic covering may fit smoothly upon 

 one another or may project like scales. A typical illustration 

 of this latter case is that found in wool, and by virtue of this 

 peculiarity the separate hairs may be made to cling together 

 by causing the minute teeth to interlock, a result effected 

 throught the act of spinning. To this peculiarity the possi- 

 bility of wool as a textile fabric is due. 



In Man there is much racial variation in the hair of the 

 head, a character of considerable value in ethnology. The 

 degree of waviness or curliness is due to the shape of the 

 single hairs; if they are cylindrical, that is, circular in cross- 

 section, they are perfectly straight, as in the typical Mongo- 

 lian ; a slight degree of flatness with an elliptical cross-section, 

 allows the hairs to become wavy, as in many Europeans; 

 if more flat, they are curly, and if very flat, the hairs are 

 woolly, as in the Negroes. In this last class there are two 

 subdivisions, the Eriocomi, where the hair is evenly dis- 

 tributed, making a solid mat, and the Lophocomi, the " che- 

 veux en grains de poivre," in which the hair is collected 

 into little tufts with partings between them. This latter pe- 

 culiarity is seen in adult Bushmen and Hottentots and in the 

 children of most other negro races. 



The degree of flatness of the cross-section is expressed by 

 an index in which the longer diameter is considered unity 

 and the shorter is compared with it in the form of a decimal 

 fraction. Thus, in a perfectly cylindrical hair, the index 

 would be ioo, in one in which the breadth of the oval is half 

 the length the index would be 50. As a matter of fact there 

 is no index so high as ioo, but it ranges between 85, that of 

 the Japanese, and 40-50, that of the Hottentots. In Euro- 

 peans it varies between 62 and 72. In length the hair varies 

 greatly, straight hair being the longest and woolly hair the 

 shortest. In races with either extreme (straight or woolly) 



