ELEMENTS OF PHYSIOLOGY 



buried beneath the cells of epidermis, like a tiny moun- 

 tain range. As the epidermis fills up the valleys between 

 them, the papillae do not show plainly on the surface 

 of the skin. However, on the palm of the hand and 

 the fingers, where the papillae are especially numerous, 

 they are crowded into rows, their 

 position being shown by the paral- 

 lel ridges seen on the epidermis of 

 the palm. Within the papillae are 

 found the ends of nerves and loops 

 of small blood vessels called capil- 

 laries (Figs. 2 and 3). 



The cells of the epidermis which 

 lie next to the dermis are living cells. 

 They are kept alive by nourishment 

 brought by the watery portion of 

 the blood in the blood vessels of the 

 neighboring papillae. These cells 

 are, therefore, growing cells, and 

 when they grow to a certain size, 

 each cell subdivides into two. (The 

 way in which the cells form new cells 

 will soon be studied in another 



FIG. 3. Diagram of Epi- 

 dermis and Upper Part of 

 Dermis. 



Showing nerve, , and tactile cor- chapter.) This multiplication of the 



pu.cle, t.c t or organ of touch; jj M th epidermis tO 



also sweat tube, d. 



increase greatly in thickness, were 



not the outer cells constantly worn away by friction. This 

 more easily happens as the outer cells are dead cells. The 

 new cells forming beneath push them so far away from 

 the dermis, that nourishment from the blood no longer 

 reaches them, and they die. 



By this constant loss and renewal, the body always 

 has a comparatively new outer skin. Even on the scalp, 

 which is partly protected from friction, the flat dry cells 

 are constantly coming off. If there is much oil on the 



