CLIMATE AND COMPLEXION. 3 



reason that those members of a race whose skins vary in the direction 

 of this type will in each generation have the best chance of surviving 

 and begetting children, and that, by the continued increment of suc- 

 cessive variations in the same direction, the skin and the climate will 

 ultimately be brought into accord. 



The skin consists of two layers : the inner, dense and fibrous, fur- 

 nished with blood-vessels and nerves, called the dermis, or true skin ; 

 the outer, horny, nerveless, and bloodless, called the epidermis, cuticle, 

 or scarf-skin. The cells which compose the latter originate in the rete 

 Malpighli, its lowest part, are gradually forced outward by new cells, 

 and finally exfoliate. In some of these epidermic cells a pigment is 

 found which varies in different races, but always contains a yellow 

 element. The hue of the skin does not depend on this coloring matter 

 alone, but is a compound effect, resulting from the white of the dermis, 

 the red of the blood in the minute vessels near the surface, the color 

 and quantity of the pigment, and the thickness of the cuticle. Where 

 the cuticle is thick, the color of the pigment will predominate over the 

 other elements on account of the greater depth of pigment-cells. "Where 

 it is thin, and the coloring matter light, the tint of the skin will be 

 much affected by any change in the supply of blood to the capillaries 

 at the surface of the body. This is the reason why the whites alone 

 can turn pale and blush. 



Closely related to the pigment of the skin are the coloring matters 

 of the eye and hair. Dark-skinned people usually have black eyes and 

 hair ; fair hair and blue eyes are seldom found except in conjunction 

 with a fair skin ; and the eyes and hair of albinoes, in whom the pig- 

 ment of the skin is wanting, are likewise destitute of coloring matter. 

 The pink hue of their eyes is due to minute blood-vessels, whose color 

 is masked in ordinary organs by the pigment of the iris. 



It is noteworthy that the coloring matters of the epidermis and iris 

 serve a very important purpose : they protect the tender underlying 

 parts from the injurious effects of too much heat and light. Albinoes 

 everywhere find it necessary to protect their skins and eyes from the 

 effects of the sun's rays. In warm countries they seldom go out ex- 

 cept at night. There is this difference between them and other men, 

 that long-continued exposure to the sun, which ordinarily develops a 

 condition of the skin capable of resisting its rays, does not do so in 

 their case. It may here be remarked that the deeper the shade of the 

 pigment, the more rays will it reflect, and the more effective will it be 

 as a protective agency. On the contrary, the lighter the shade, the 

 more light and heat will it permit to enter the body. 



As an excretory organ, it is the function of the skin to discharge 

 water, carbonic acid, and urea the first in large, the others in small 

 quantities. Perspiration, or the excreting of water, with some saline 

 matter in solution, is effected in two ways : In the first place, sudorip- 

 arous glands, imbedded in the true skin, secrete sweat from the blood. 



