250 THE SOLIDS. 



EPIDERMIS OF THE WHITE AND COLOURED RACES. 



Between the epidermis of the white and the coloured 

 races there is a perfect identity of structure ; the only 

 difference is, that the young epidermic cells of whites con- 

 tain little or no colouring matter, or pigment granules, 

 except in certain situations, while those of blacks are filled 

 with them; this difference can scarcely be regarded as 

 permanent or structural; it is one rather of degree than 

 kind, and over which, moreover, climate exerts an all- 

 powerful influence. 



We have continual opportunities of witnessing the effect 

 of climate in increasing the amount of pigmentary matter 

 in the skin. All have noticed that after a few years' resi- 

 dence in a hot country, the skin of many individuals becomes 

 several shades darker than it was previously, and that even 

 the inhabitants of the same country are darker during the 

 summer than in winter. 



It would appear, therefore, to be very possible, that 

 climate alone, operating through many ages, would be suf- 

 ficient to change the colour of the skin from white to all the 

 varying shades of red, olive, and black, met with amongst 

 the different families of the human race. 



DESTRUCTION AND RENEWAL OF EPIDERMIS. 



The epidermis, like the epithelium, is constantly under- 

 going destruction and renewal ; the evidences of this are, 

 however, more obvious and striking in the case of the epi- 

 dermis, than were those adduced in proof of the destruction 

 of the epithelium. 



Thus the destruction of the epidermis is proved by a 

 variety of facts : 



By the gradual disappearance from the skin of indelible 

 stains, such as those produced by nitrate of silver or nitric 

 acid. 



