88 HUMAN PHYSIOLOGY. 



nerves emanating from it in any part of their course, is followed at once by 

 dilatation of the hepatic blood vessels, slowing of the blood current, a pro- 

 found disturbance of the normal relation existing between the blood and 

 liver cells, and a production of sugar. Many of the hepatic vasomotor 

 nerves may be traced down the cord as far as the lumbar region, while 

 others leave the cord high up in the neck and enter 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. ., sciatic, pneumogastric, depressor nerve, as well as the direct action of 

 many drugs, impair or depress the hepatic vasomotor centre and so give 

 rise to diabetes. 



SKIN. 



The Skin, the external investment of the body, is a most complex and 

 important structure, serving (l) as a protective covering ; (2) an organ for 

 tactile sensibility ; (3) 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 the 

 \ to the T ^ 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 muscular fibres 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 

 \hz papilla ; they are most abundant, and well developed, upon the palms 

 of the hands and the soles of the feet; they average the ^ 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 extra-vascular structure, a product 

 of the true skin, and composed of several layers of cells. It may be 

 divided into two layers, the rete mucosum or the Malpighian layer, and 

 the horny or corneous. 



The former closely applies itself to the papillary layer of the true skin, 

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

 " prickle cells," contain pigment granules, which give to the skin its varying 



