418 



THE SKIN. 



Functions of the Skin. The functions of the skin are 

 numerous and very important. 



(1) Protection. The tissues which lie beneath the skin are 

 delicate and sensitive, and are protected from injury by it. The 

 epidermis, by reason of its hard and tough character, especially 

 in the palms of the hands and on the soles of the feet, is peculiarly 

 adapted to this end. 



(2) Excretion. It has already been noted that by the skin a 

 liter of fluid is daily eliminated from the body. In this fluid are 



FIG. 236. A, Shaft of the hair ; B, root of the hair ; C, cuticle of the hair ; D, 

 medullary substance of the hair ; E, external layer of the hair-follicle ; F, middle 

 layer of the hair-follicle; G, internal layer of the hair-follicle; H, papilla of the 

 hair ; I, external root-sheath ; J, outer layer of the internal root-sheath ; K, internal 

 layer of the internal root-sheath (after Du bring). 



dissolved materials representing the waste of the tissues. There 

 is a reciprocal relation between the skin and the kidneys : in 

 summer, when the skin is active, the amount of fluid passed 

 off by the kidneys is reduced, while in winter, when the skin is 

 inactive, the work of the kidneys is much increased. In diseased 

 conditions of the kidneys, the retention in the blood of poisonous 

 materials which are eliminated by them in health is prevented by 

 causing the perspiratory glands of the skin to assume this function. 

 (3) Sensation. The skin, especially at the tips of the fingers, 



