SKIN. 177 



the cervical ganglia of the sympathetic, and so reach the liver. 

 Injury to the sympathetic ganglia is often followed by diabetes. 

 Peripheral stimulation of various nerves e. g., sciatic, pneumogas- 

 tric, depressor nerve, as well as the direct action of many drugs, 

 impair or depress the hepatic vaso-motor center and so give rise to 

 diabetes. 



SKIN. 



The skin, the external investment of the body, is a most complex 

 and important structure, serving 



1. As a protective covering. 



2. As an organ for tactile sensibility. 



3. As an organ for the elimination of excrementitious matters. 



The amount of skin investing the body of a man of average size 

 is about twenty feet, and varies in thickness, in different situations, 

 from 1 to yip- of an inch. 



The skin consists of two principal layers viz., a deeper portion, 

 the corium, and a superficial portion, the epidermis. 



The corium, or cutis vera, may be subdivided into a reticulated 

 and a papillary layer. The former is composed of white fibrous 

 tissue, non-striated muscle-fibers, and elastic tissue, interwoven in 

 every direction, forming an areolar network, in the meshes of which 

 are deposited masses of fat, and a structureless, amorphous matter ; 

 the latter is formed mainly of club-shaped elevations or projections 

 of the amorphous matter, constituting the papilla; they are most 

 abundant and well developed upon the palms of the hands and upon 

 the soles of the feet ; they average y 1 ^ of an inch in length, and 

 may be simple or compound ; they are well supplied with nerves, 

 blood-vessels, and lymphatics. 



The epidermis, or scarf skin, is an extravascular structure, a 

 product of the true skin, and is composed of several layers of cells. 

 It may be divided into two layers : the rete mucosum, or the Mal- 

 pighian layer, and the horny or corneous. 



The former is closely adherent to the papillary layer of the true 

 skin, and is composed of large, nucleated cells, the lowest layer of 

 which, the " prickle cells," contains pigment-granules, which give to 

 the skin its varying tints in different individuals and in different 

 races of men ; the more superficial cells are large, colorless, and 

 semi-transparent. The latter, the corneous layer, is composed of 

 13 



