1 10 EXCRETION. 



an important function as a secretion, in connection with the 

 process of digestion. 



Physiological Anatomy of the Skin. 



The skin is one of the most complex and important 

 structures in the body, and possesses a variety of functions. 

 In the first place it forms a protective covering for the gen- 

 eral surface. It is quite thick over the parts most subject to 

 pressure and friction, is elastic over movable parts and those 

 liable to variations in size, and in many situations is covered 

 with hair, which affords an additional protection to the sub- 

 jacent structures. The skin and its appendages are bad 

 conductors of caloric, are capable of resisting very consider- 

 able variations in temperature, and thus tend to maintain 

 the normal standard of the animal heat. As an organ of 

 tactile sensibility, the skin has an important function, being 

 abundantly supplied with sensitive nerves, some of which 

 present an arrangement peculiarly adapted to the nice ap- 

 preciation of external impressions. The skin assists in pre- 

 serving the external forms of the muscles ; it relieves the 

 abrupt projections and depressions of the general surface, and 

 gives roundness and grace to the contours of the body. In 

 some parts it is very closely attached to the subjacent struc- 

 tures, while in others it is less adherent, and is provided with 

 a layer of adipose tissue. 



As an organ of excretion, the skin is very important ; and 

 although the quantity of excrementitious matter exhaled from 

 it is not very great, and probably not subject to much varia- 

 tion, the evaporation of water from the general surface is 

 always considerable, and is subject to such modifications as 

 may become necessary from the varied conditions of the ani- 

 mal temperature. Thus, while the skin protects the body 

 from external influences, its function is important in regu- 

 lating the heat produced as one of the numerous phenomena 

 attendant upon the general process of nutrition. 



