34 FIRST PRINCIPLES. 



Thus we find that when a horse is placed in a cold atmosphere 

 he will lose heat faster when the air is in motion than when it 

 is still ; because, instead of one layer of air remaining close to 

 the skin, and becoming gradually raised in temperature with 

 comparatively little loss of heat by the animal, there will be 

 presented to his skin a more or less rapid succession of layers 

 of cold air. We have this effect heightened in the animal 

 body by the stimulus given to the evaporation of moisture 

 from the skin. Agreeably to these facts, we find that a 

 temperature of 20 F. during a Russian winter, for instance, 

 is easier to bear when the atmosphere is still, than one of, say, 

 10 F. (30 higher), when a strong wind is blowing. Under 

 the former condition, one experiences no inconvenience from 

 walking about in ordinary clothes and without an overcoat, 

 provided one's hands and ears are well covered ; for the 

 circulation of blood is comparatively torpid in these parts of 

 the system. When the temperature in the shade is higher 

 than that of the body (normal temperature of man being about 

 98.5 F., and that of the horse about 99.5 F.), the substitution 

 in question is that of air which is hotter, but also is drier than 

 the removed air. The cooling effect of the stimulus to evapora- 

 tion of perspiration given by the comparatively dry air is, 

 however, so great, that when the temperature in the shade is 

 even at 120 F., the effect of a current of air is very refreshing 

 to man and beast. 



PROTECTION BY THE COAT AGAINST COLD AND CHILL. 



The coat of the horse being composed of a material (hair) 

 which is a bad conductor of heat, and being capable of 

 holding between the hairs a large amount of air, which is a 

 still worse conductor of heat, it affords an admirable protection 

 to the body against external cold, when it is sufficiently long 

 and thick, and when it is dry. As the presence of dandruff 

 aids in this form of protection, and as grooming tends to 



