70 SECRETION. 



What is the function of the epidermis ? 



The epidermis is a stratification of epithelial cells of varying 

 thickness. The epithelium is flat and horny at the surface, in the 

 deeper portions are flattened and polyhedral cells, and it is closely 

 adapted to the surface of the corium beneath it. In its deeper 

 layer is found the pigment .which characterizes the complexion of 

 individuals and of races. Its function is purely one of protection. 

 The growth to replace worn-out cells is very rapid, and in cases 

 of considerable use of a part, with interrupted pressure upon the 

 skin, the cuticle becomes very thick and horny, as is often seen 

 upon the hands and feet. The hair and nails are modifications of 

 the epidermal epithelium. 



Describe the structure of the corium. 



The true skin is a tough, elastic tissue composed of interlacing 

 bundles of connective-tissue cells containing spaces between the 

 fasciculi. These spaces are known as areolse. There are also num- 

 erous unstriped muscular fibres. This structure lies upon a more 

 or less thick layer of fatty or loose cellular tissue. In the cutis are 

 found the active organs of the skin the papillae, sweat- and seba- 

 ceous glands, and the hairs (Fig. 16). 



What are the papillae and their uses ? 



Upon the superficial surface of the cutis vera are innumerable 

 minute elevations which project into the epithelium. They are 

 very vascular, and contain the nerve-endings which give to the skin 

 its sensibility, the sense of touch. The papillae are especially abun- 

 dant upon the parts in which this sense is most acute palms, finger- 

 tips, soles. 



Describe the sweat-glands. 



Each gland lies in the subcutaneous fat, and consists of a con- 

 voluted mass of tubules which terminates in a duct leading up 

 through the derma and epidermis, discharging the secretion of the 

 gland through a minute opening. This secretion is known as per- 

 spiration or sweat. 



What is meant by the term " insensible perspiration " ? 



When the secretion of the sweat-glands forms in drops upon the 

 skin, we speak of this as sensible perspiration or sweat. However, 

 at all times the glands continue active and the fluid evaporates rap- 



