A STUDY OF THE SKIN AND THE KIDNEYS 233 



1. ANATOMY AND PHYSIOLOGY OF THE SKIN 



Layers of the Skin. The skin everywhere consists of two 

 distinct layers : an outer, called the ep-i-der'mis (Greek epi 

 upon + derma = skin), and an inner, the der'mis. When one 

 gets a blister by burning the skin, most of the epidermis is 

 lifted up by an excessive amount of lymph that comes out 

 of the bl'ood capillaries and lymph vessels. In a blister one 

 can easily distinguish the white epidermis from the pink 

 layers of the dermis lying beneath. 



Characteristics of the Epidermis. Let one wash with soap 

 and water the surface of any portion of one's body and then 

 rub it vigorously. One will 

 find that thin layers of the 

 outer skin are easily removed 

 and rolled into tiny cylinders. 

 If a needle be inserted into 

 the skin that covers a blister, 

 the touch of the needle will 

 be felt, but no pain is caused, 

 nor does the blood flow. By 

 means of these simple experi- 

 ments we learn the following facts in regard to the epidermis : 

 (1) the outermost layers are being constantly worn away, and 

 hence we infer there must be a constant growth from beneath 

 to supply this loss; (2) blood vessels are lacking in the 

 outer skin ; and (3) nerve fibers are present in the epidermis ; 

 for we are conscious when the covering of a blister is touched. 



When we examine closely the skin on the palm of the 

 hand and the tips of the fingers, we see that the surface is 

 covered by a great number of ridges that run in many cases 

 more or less parallel to each other (see Fig. 108). The pat- 

 tern formed by this succession of ridges and grooves varies 

 on different fingers. On a given finger, however, it persists 

 throughout life, and use is sometimes made of this fact in 

 identifying criminals by finger prints. 



FIG. 108. Surface of Palm, mag- 

 nified, showing Ridges and Pores 

 from Sweat Glands. 



