THE SKIN AND BATHING 



257 



456. The epidermis. The derma is covered with a layer 

 of epithelial cells, called the epidermis or cuticle. New 

 cells are continually being produced in the deeper layers 

 of the epidermis, while the older cells become matted in a 

 firm mass which is continually being worn away. These 

 cells are directly continuous with the epithelial cells of the 

 mucous membrane and are of the same nature. The epi- 

 dermis has no nerves and no blood tubes. 



A corn. 



457. Upon the palms of the hands and soles of the feet the epi- 

 dermis forms a very thick layer for the better protection of these much- 

 used parts. When hard labor is performed with the hands, nature 

 causes the protecting epidermis in the exposed parts to form a thick 

 and horny spot called a callus. Sometimes pressure and rubbing cause 

 a small area to become thickened so that a point of hardened cells is 

 formed which presses into the deeper parts of the skin. This is a corn. 



When the skin is vigorously rubbed, or certain drugs are applied, 

 the deeper layers of the epidermis are killed, and water accumulating 

 between them and the outer layers raises a blister. 



458. Color of the skin. The deeper layers of the epidermis 

 contain colored granules which give the peculiar color to different races 

 of men. Exposure to the sun's rays produces a darker coloring matter. 

 In some people the coloring matter is deposited in small spots called 

 freckles. 



ov. PHYSIOL. 17 



