994 VETEKINAEY HYGIENE 



itself counts for little. All animal life in the hot weather, 

 for instance, in India, does the same during the heat of the 

 day ; even the crow of the country will sit on the ground 

 under a tree with the mouth wide open gasping for breath, 

 and he certainly should be fully acclimatized. 



In seasoned animals a dry heat is borne with comparative 

 indifference ; in the case of horses their coats may be burned 

 and their muzzles sore from the rays of the sun, but there 

 is no such thing as sunstroke and no illness due to the 

 sun's rays, though they may be exposed to them the whole 

 time the sun is above the horizon. But when the air 

 becomes saturated with moisture and the heat is a damp 

 one, then the loss of heat by evaporation from the skin is 

 interfered with, and the effects on animals are enervating 

 and depressing. 



The lessened evaporation under these circumstances is 

 due to the humidity of the air which checks evaporation 

 from the skin and lungs, for the air being nearly or wholly 

 saturated has but little drying power. Hence one of the 

 chief means of keeping the blood at its proper temperature 

 is lost, while the distress and enervation which accompanies 

 a continuous vapour bath is evident. 



One of the most remarkable physiological features is the 

 perfect manner in which the body adapts itself to a rise 

 and fall of the surrounding temperature. Adaptation to a 

 gradual rise or gradual fall one can understand, but the 

 mechanism which admits of a variation of forty degrees of 

 the thermometer in a few hours is a very perfect one. 



The effect of cold is to increase tissue metabolism, and 

 in order to provide for this a larger amount of food, especially 

 carbonaceous, must be taken. The contraction of the 

 atmosphere enables more oxygen to be taken in at each 

 inspiration, so that the hurried respirations of high 

 temperatures are wanting, while the contracted state of the 

 capillaries of the skin reduces considerably the loss of heat 

 from this surface, and in consequence of there being less 

 evaporation a larger bulk of urine is secreted. 



Low temperatures are perfectly withstood provided there 



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