2(i2 THEORY AND PRACTICE 



Nature. — It is an auto-intoxication with fatigue toxines and 

 toxic decomposition products due to overwork in hot weather. 



The heat of warm blooded animals is produced by chemic 

 metabolism, and is regulated by the thermal center in the medulla 

 oblongata. The natural channels through which heat is lost 

 are, according to Helmholtz, 21/2% by the solid and fluid egesta, 

 5/4% by warming inspired air, 1434% by evaporation of the 

 water carried out by the expired air, and 771/2% by radiation. 



Alexander Lambert gives the normal loss of animal heat as 

 follows : 2.6% by warming food and drink, 2.6% by warming in- 

 spired air, 14.7% by evaporation and 80.1% by radiation. These 

 losses are affected by meteorological conditions. In very hot 

 weather the loss caused by warming the food, drink and inspired 

 air is almost nil, and in hot, humid weather, with low baromet- 

 ric pressure, especially if there is no breeze, evaporation and 

 radiation are reduced to a minimum. When the barometer is 

 high the neve tonus is good, the animal feels well and evapora- 

 tion keeps pace with the perspiration. Then there are no sun- 

 strokes, but when the barometer is low, the weather hot and 

 humid, the animal feels languid, perspiration is profuse, and 

 evaporation is nil sunstrokes are common. Consequently sun- 

 strokes are common on the Atlantic coast, in the region of the 

 great lakes and in tropical climates, but in the Northwestern 

 States they are rare. 



Etiology. — A condition of cerebral hyperaemia may come on 

 from excessively active exercise in hot weather, attended by 

 convulsions, syncope, coma and death. This is most often seen 

 in dogs. 



In the horse the predisposing causes are old age, overwork 

 or indigestion. The exciting causes are hard work in hot, humid 

 weather with low barometer, insufficient water supply over- 

 heating in horses working between other horses in three horse 

 teams or gangs. 



Symptonvatology. — At first there is profuse perspiration, then 

 the horse begins to pant and the sweat dries up ; he now b^ins 

 to stagger, becomes insensible, goes down, is unable to rise, soon 

 becomes comatose, the surface of the body is dry and hot, the 



