THE MICROSCOPE IN PHYSIOLOGY. 



93 



rera, and you know it is impossible to prick any part 

 of your finger with the fine point of a needle without 

 piercing some of these capillaries and drawing blood. 

 The cuticle, or outer covering, is destitute of blood- 

 vessels and nerves ; it consists of a series of layers of 



.a 



cells " that are continually wearing off at their outer 

 surface, and renewed at the surface of the true skin, 

 so that the newest and deeper layers gradually become 

 the oldest and most superficial, and are at last thrown 

 off by desquamation. In their progress from the 

 internal to the external surface of the epidermis, the 

 cells undergo a series of well-marked changes. When 



