124 LECTITEE V. 



ence in tlie tissue elements of the skin of the dog and the ape, 

 and if this be found impossible, will anyone maintain that 

 these creatures belong to the same species ? We even go fur- 

 ther, and maintain that the skin of two known species of 

 animals, which belong to the same genus and family, would, 

 in the special arrangement of the tissue elements, not exhibit 

 such great differences as are found in the white man and the 

 negro. 



The human skin consists of two layers, — the dermis and the 

 epidermis; the latter is ag'ain composed of two layers, — the 

 mucous layer (rete mucosum), and the horny or scarf-skin. 

 The cells in the mucous layer are round and nucleated, which, 

 by development from beneath, become flattened, forming a 

 layer lying close upon the papillary layer of the dermis. The 

 horny, or scarf-skin, is the product of the cells of the mucous 

 layer, which, by evaporation of their fluid contents and by 

 attrition, become flattened, and finally form a membranous 

 scale. 



The COLOUR of the skin is mainly due to the deeper cells of 

 the rete mucosum, the nuclei of which are brown at first, 

 owing to the deposition of pigment corpuscles. These cor- 

 puscles increase, so that in some spots the whole cells seem to 

 be filled with a black pigment. In the white races, there are 

 only certain parts, the mammary gland and the scrotum, which 

 present such a dark tint, which evidently is not caused by 

 sunlight. We find a similar coloration in freckles, and in some 

 morbid states the whole body may become nearly black. Some 

 years ago, there was observed in Switzerland, during a very 

 severe winter, a peculiar form of disease in vagrants and 

 trampers, characterised by a negro-like colouration of the skin, 

 not in such exposed parts as the face and the hands, but upon 

 the abdomen and the chest. 



As regards the steuctuee of the skin in the various races, I 

 may quote the words of that competent observer, KoUiker, 

 " In the negro, and other coloured races, only the epidermis is 

 coloured, the true skin being the same as in the European ; 

 the pigment is, however, much darker and more abundant. 

 In the negro, in whom the epidermis, as regards the arrange- 



