338 SKIN, COLOUR, AND HAIR. 



it faster than those of a Hghter hue, as we may prove 

 by the two following experiments. If we fill with boiling 

 water two crockery teapots of the same form — one being 

 white, the other black — we shall find that if they are 

 both placed in a cool spot, the latter will lose its heat 

 quicker than the former. If, however, they are filled 

 with icy cold water, and are then exposed under similar 

 conditions to the effect of the sun on a hot day, the black 

 one will get warm in a shorter time than its fellow. The 

 skin of natives of tropical climates is darker than that of 

 inhabitants of temperate or cold countries ; and in the 

 Arctic regions, the coats of various animals turn white on 

 the approach of winter. In their case, white also acts 

 as protective coloration, by rendering them less conspicuous. 

 As the temperature of the body of the polar bear, for 

 instance, is much higher than that of the atmosphere in 

 which he lives, he can lose nothing on account of his white 

 coat being a bad absorber of heat ; while the fact of its 

 parting with (radiating) heat slowly, helps the body to 

 maintain its normal degree of warmth. The skin of the 

 negro, for example, although it absorbs heat quickly, 

 radiates it still faster ; and the vapour given off by the skin 

 cools the surface, and tends to prevent the absorption 

 of heat from the atmosphere by the mechanical protec- 

 tion it affords. Also, the pigment which is present in 

 dark skins and is absent in white skins, acts as a pro- 

 tection against the rays of the sun. At first glance, 

 we might, possibly, imagine that if the surrounding 

 air was warmer than the internal temperature (about 

 100° F. for the horse), no cooling effect could be 

 produced by radiation. When, however, the skin is in 

 healthy and untrammelled action, its temperature, on 

 account of the free evaporation of perspiration, is 

 considerably lower than that of the deeper structures, 

 even when the thermometer stands at, say, 115° F. in 

 the shade. If, under such circumstances, clothing be 

 worn, the garments will soon become almost, if not 



