172 



THE SKIN AND KIDNEYS 



.apia^trmi's 



-nerve 



Structure of the skin. The skin is a smooth, moist, flexible 

 organ varying from one one hundredth to one tenth of an inch in 



# - -» 4. ^1 -» '^ I— thickness. It consists 



— of an outer layer called 



the eindermis, and an 

 inner layer called the 

 dermis. As the cells 

 grow out in the deep- 

 est part of the epider- 

 mis layer, they are 

 gradually transformed 

 into flat scales. The 

 outermost layers are 

 dead and are being 

 constantly rubbed off 

 the surface of the skin. 

 The deepest layer of 

 the epidermis contains 

 pigment cells, and is 

 called the jNIalpighian 

 layer after the scien- 

 tist who first observed 

 it. There are normal pigments in this layer, which are the basis 

 for white, yellow, red, or black skin colors of various people. In this 

 layer may develop deposits of pigment, which are known as freckles. 

 The dermis is the true skin. It is composed largely of connec- 

 tive tissue. Tiny muscles may run through the dermis. These, 

 by contracting, will cause the tiny hairs in the epidermis to stand 

 erect. They also cause the " goose flesh " when a person is cold. 

 The contraction of millions of tiny muscles give a little heat and, 

 at the same time, a warning that the body is cold. The dermis is 

 richly supplied with blood vessels, lymph vessels, nerves, and hair 

 follicles. The blood vessels carry water in which urea and carbon 



The surface cells of the skin are constantly wearing or 

 washing off and are replaced by cells underneath. Blood 

 vessels nourish the skin; and the various nerve endings re- 

 ceive different stimuli from the environment. 



