268 COORDINATION AND SENSATION 



corpuscles and their connecting nerve fibers. This pro- 

 tection is of at least three kinds, as follows : 



1. From mechanical injuries such as might result from 

 contact with hard, rough, or sharp objects. The main 

 quality needed for resisting mechanical injuries is tough- 

 ness, and this is supplied both by the epidermis and by the 

 connective tissue of the dermis. 



2. From chemical injuries caused by contact" with various 

 chemical agents, as acids, alkalies, and the oxygen of the 

 air. The epidermis, being of such a nature as to resist to 

 a considerable extent the action of chemical agents, affords 

 protection from these substances. 1 



3. From disease germs which are everywhere present. 

 The epidermis is the main protective agent against attacks 

 of germs, but should the epidermis be broken, they meet 

 with further resistance from the fluids of the dermis and 

 the white corpuscles of the blood. 



4. From an excessive evaporation of liquid from the 

 surface of the body. In the performance of this func- 

 tion, the skin is an important means of keeping the 

 tissues soft and the blood and lymph from becoming too 

 concentrated. 



Other Functions of the Skin. Through the perspiratory 

 glands the skin is an organ of excretion. While the secre- 

 tion from a single gland is small, the waste that leaves the 

 body through all of the perspiratory glands is considerable 2 

 (page 206). By means of the nerves terminating in the 

 touch corpuscles, the skin serves as the organ of touch, or 

 feeling (Chapter XX). To a slight extent also the skin 



1 The epidermis does not afford complete protection against chemicals, many 

 of them being able to destroy it quickly. The rule of washing the skin immediately 

 after contact with strong chemical agents should always be followed. 



2 " Rough calculations have placed the number of sweat glands on the entire 

 body at about 2,000,000." Rettger, Studies in Advanced Physiology. 



