A STUDY OF THE SKIN AND THE KIDNEYS 235 



and these daughter cells gradually approach the surface of 

 the skin as the outer layers are worn away. During this 

 process the cells become dryer and thinner, until finally all 

 their protoplasm dies, and they become the outer horny 

 scales to which we referred above. This layer is of special 

 use in protecting the more delicate cells beneath. 



In the layers of the epidermis are certain irregular cells 

 of very dark color known as pigment spots. They abound 

 in the skin of a negro and give to this race its dark color. 

 The skin of a brunette contains more pigment granules than 

 that of a blonde. Freckles are due to an increase in the 

 amount of this pigment, caused oftentimes by the action of 

 the sun. 



Structure of the Dermis. If a thick piece of -skin were to 

 be soaked for a time in a weak acid or alkaline solution, one 

 could easily pull off the epidermis from the dermis. It 

 would then be seen that the surface of the latter is thrown up 

 into numerous cone-shaped elevations called pa-pil'lce of the 

 dermis, which fit into corresponding depressions in the under 

 layer of the epidermis. 



These small papillae are of two sorts (see Fig. 109). One 

 kind is supplied with loops of blood capillaries, which thus 

 bring the blood near to the living cells of the epidermis. In 

 the papillae of the second class are little sense organs called 

 tactile corpuscles, from which nerve fibers run in to connect 

 with the spinal cord and the brain. 1 These highly sensitive 

 papillae are especially numerous on the palm of the hand and 

 the tips of the fingers. Here they are arranged in rows ; 

 the epidermis fills in the spaces between the little mountain 

 peaks of the same range, and thus are formed on the outer 

 skin the ridges to which we have already referred (Fig. 108). 



The dermis is, therefore, well supplied with nerves and 

 with blood vessels. The larger portion of this layer of the 

 skin, however, is composed of loosely arranged fibers of con- 



1 The consideration of the skin as a sense organ will be taken up 

 more fully in connection with the nervous system. 



