STRUCTURE OF THE TRUE SKIN. 35 



From all that is known regarding the mucous coat, 

 it may be viewed generally as merely a thin soft 

 covering, placed between the outer and the inner 

 skin, to protect the nerves and vessels of the latter 

 and give them their requisite softness and pliancy. 

 Being of a dark colour in the Negro, it has been 

 supposed to diminish the heating influence of the 

 sun's rays in tropical climates by the higher radia- 

 ting power which is possessed by a black than by a 

 light surface ; but there is reason to doubt the 

 soundness of the theory at least, for black is well 

 known to excel in absorbing, as well as in radiating, 

 heat ; and late experiments on the coast of Africa 

 seem to show, that the temperature of the Negro 

 is actually about two degrees higher than that of 

 the European under the same circumstances. 



The mucous coat is the seat of the beautiful and 

 variegated colouring observed in the skins of many 

 fishes and other animals, in which it has often a high 

 and almost metallic splendour. 



The third or inmost layer, called the true skin, der- 

 mis, or corion, constitutes the chief thickness of the 

 skin, and is by far the most important of the three, 

 both in structure and functions. Unlike the cuticle 

 and mucous coat, which are homogeneous in their 

 whole extent, and apparently without organization, 

 the true skin, or simply, as we shall call it for 

 brevity's sake, the skin, is very delicately organized, 

 and endowed with the principle of life in a very high 

 degree. Not only is it the beautiful and efficacious 

 protector of the subjacent structures, but it is the 

 seat of sensation and of touch, and the instrument 

 of a very important exhalation, viz. perspiration, the 

 right condition or disturbance of which is a most 

 powerful agent in the preservation or subversion of 

 the general health. The dermis is a dense, firm, and 

 resistant tissue, possessed of great extensibility and 

 elasticity, and of a colour more or less red in pro- 

 portion to the quantity of blood it receives and con- 



