COLOUR. 



245 



negro, for example, although it absorbs heat quickly, radiates 

 it still faster ; for the vapour given off by the skin cools the 

 surface, and also, by the mechanical protection it affords, 

 tends to prevent the absorption of heat from the atmosphere. 

 At first glance, we might, possibly, imagine that if the 

 surrounding air was warmer than the internal temperature 

 (about ioo*5° Fahrenheit 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 consider- 

 ably under that of the deeper structures, even when the 

 thermometer stands, say, 115° Fahrenheit in the shade. If, 

 under such circumstances, clothing be worn, the garments will 

 soon become almost, if not quite, as hot as the surrounding 

 air, evaporation will be checked, except from the exposed 

 parts, the temperature of the skin will rise, and the cooling 

 process of radiation will be more or less stopped. In this 

 case, any gain which may be obtained in lessening the 

 absorption of heat, as persons do in hot countries, by wearing 

 white will be a direct gain. During the summer months in 

 tropical latitudes, the hair on a horse's body will, usually, be 

 so short and thin, that its presence will offer no impedi- 

 ment to the action of the skin. Agreeably to the foregoing 

 observations, we find that black and brown horses stand heat 

 best ; and that white — especially if they have pink skins — and 

 grey animals sustain it comparatively badly. I have fre- 

 quently observed on hot days in tropical climates that, other 

 things being equal, horses of light hues sweated far more 

 readily and profusely than those of darker shades. 



Hair. — The possession of a fine glossy coat will naturally 



