THE SKIN AND KIDNEYS IO5 



easily. It can be pinched up and stretched, but lies flat 

 and smooth again as soon as it is set free. 



197. The epidermis. Upon the outside of the derma 

 is a thin layer of scalelike cells called the epidermis. The 

 cells are called epithelium. They resemble those which 

 cover a mucous membrane (see p. 18). The epidermis has 

 no blood tubes or nerves, and so can be cut or pricked 

 without bleeding or giving pain. Its cells are formed upon 

 the top of the derma and are soft at first, but as new ones 

 grow, the older ones become hard and are finally shed or 

 rubbed off. These hard scales protect the nerves and 

 soft parts of the skin. Where the epidermis is gone and 

 the nerves are touched directly, the part is very sore 

 and tender. The papillae reach into the epidermis so as 

 to feel more easily. 



Upon parts of the body which are rubbed, the epidermis 

 grows thicker and harder, so as to protect the deeper parts 

 better. This is called a calhts. Rubbing the skin too hard 

 hurts the deeper scales of the epidermis, and then water or 

 blood collects under them and raises the epidermis into a 

 little bag of fluid called a blister. In the deepest parts of 

 the epidermis there are colored cells which give the skin 

 its color. A negro is black only in a very thin layer of 

 the deepest part of the epidermis, and his color is not even 

 " skin deep." 



198. Nails. The cells of the epidermis at the end of 

 each finger and toe are matted together to form a single 

 thick and hard scale called a nail. The nails protect the 

 flesh and form a kind of knife with which we can cut 

 and make marks. They also can form a pair of pincers 

 with which we pick up and hold small things. The cells 

 of the nail are formed nearly as far back as the joint of 

 the finger or toe. As new ones are formed the nail is 



