CHAPTER XVIII 

 THE SKIN 



The skin, a prfctection. Besides aiding in the excre- 

 tion of certain waste products from the body, the skin 

 serves to enclose the body and thus to protect its more 

 delicate tissues from harmful contact with surrounding 

 objects. For this purpose, it is tough and elastic, and 

 ^has the power of becoming still thicker and tougher 

 when habitually exposed to hard contact, as in the soles 

 of the feet and the palms of the hands. 



The skin, a sense organ. The skin is richly supplied 

 with nerves, by means of which information is given of 

 the objects with which contact is made, so that the indi- 

 vidual knows not only when an object is touched but 

 also whether it is warm or cold, large or small, rough 

 or smooth. He is thus able to recognize in general 

 whether the objects touched are harmful or not and to 

 act accordingly. 1 



Structure. The skin is built up of several layers, of 

 which the outermost, the epidermis, is solely protective. 

 The epidermis consists of numerous layers of cells, the 

 surface layers of which are flat and scalelike, while the 

 deeper ones are more spherical. The layers of cells 

 on the surface are constantly being worn away and are 

 as constantly being replaced by new cells from the lower 

 layers, which on approaching the surface become flat- 

 tened and scale-like. 



1 For a further discussion of the skin as a sense organ, see p. 247. 



200 



