314 



THE SKIN 



ever, with anywhere near the readiness with which it would be absorbed 

 by the average naked body-tissues served with an abundance of lym- 

 phatics and of capillaries. Water finds its way through the unctuous 

 scaly epidermis only in minute amounts, this waterproofing of the skin 

 being produced by the sebum, a fat poured out into the hair-follicles 

 and on the surface (see below). 



The skin is freely movable over the fatty subcutaneous tissues and is, 

 moreover, .very elastic. These two properties prevent the body's injury 

 by contact with such heavy objects as press and move at the same time. 

 In these cases the skin glides over the muscles, etc., beneath it and the 

 surface of the body is not torn or bruised. 



FIG. 174 



The lower part of the epidermis of the hand-palm, as seen in schematic section: a, layer of 

 cylinder cells; b, basal fibers; c, layer of cells whose fibers extend in all directions; d, layer of 

 cells whose fibers are parallel to the skin's surface; e, layer of cells whose fibers are beginning to 

 disappear in the cytoplasm; f, stratum granulosum; g, stratum corneum (a small part of it). 

 (Kromayer.) 



The two parts of the skin, the corium and epidermis, are both very 

 elastic, the former by virtue of its network of elastic fibers and the latter 

 because of its scaly structure, which allows of considerable stretching. It 

 is essential that the covering of the different parts of the body should be 

 extensible to a large degree, because many temporary conditions, normal 

 and abnormal, increase the size of local portions of the organism. Thus 

 when the biceps of the arm contracts vigorously the arm increases much 

 in circumference around the center of the muscle. In pregnancy, if the 

 skin were not elastic to a high degree it would be torn at times. Tumors 

 superficially placed and ascites sometimes show a like need for dermal 

 stretching. 



In several places by the thickness of its epidermis the skin constitutes 

 a pad which prevents frequent injury to the parts beneath it, for example, 



