PHYSIOLOGY OF MUSCULAR EXERTION. 301 



staggering, and stumbling ; at last he falls, and rises no more. 

 He dies suffocated. Upon dissection, the lungs are found so 

 gorged with blood that almost no air could enter them. 



At the first indications of distress the horse should be pulled 

 up, or his pace should be slackened ; half a minute may be 

 sufficient to restore strength to the heart, the lungs, or the 

 muscles, whichever be in fault ; the stagnation or accumula- 

 tion ceases, and the blood passes on free and pure. 



An increased formation of Heat is the third effect of muscular 

 exertion. The surface of the body becomes warm or hot ; 

 more than the usual quantity of heat is evolved. It has never 

 been supposed that this is a necessary or useful consequence 

 of exertion. Acceleration of the blood and of the breathing 

 must take place in order that the muscles may produce pro- 

 gression. But it is not believed that an extra quantity of heat 

 is useful either as an assistant or as a principal. It is well 

 known that fast work does least mischief in cool or cold 

 weather ; and it appears that there is a contrivance almost 

 for the express purpose of removing the superfluous heat. 

 Most probably the evolution of heat is' an unavoidable result 

 of increased velocity in the circulation. 



Perspiration is the fourth effect of exertion. By this pro- 

 cess the body is relieved from superfluous heat, and super- 

 fluous fluid. It is always refreshing. It enables the horse 

 to perform his work with less distress ; but when he has 

 little superfluous fluid in him it always produces subsequent 

 exhaustion. A fat or plump horse may be all the better of a 

 good sweat ; he may be fitter for his work next day than if he 

 had not perspired. A very poor horse can not so well afford 

 such a loss of fluid ; the more he sweats to-day, the less spirit 

 and strength he has to-morrow. Both, however, are refreshed, 

 though not perhaps in equal degrees, by perspiring at their 

 work. In both, the perspiration combines with the super- 

 fluous heat, and carries it off in vapor. The evaporation 

 regulates the heat of the surface. If it were possible to con- 

 fine the heat which rapid exertion produces, it is probable the 

 horse would soon be fevered. But it is not possible to do this, 

 for whenever the skin becomes very warm, perspiration follows 

 almost immediately. 



Some horsemen, and especially, I believe, post-boys and 

 stage-coachmen, are in the habit of throwing a pailful of cold 

 water over the horse's body in the middle of a long stage on 

 a hot day. Most people would regard this as a very violent 

 and thoughtless proceeding. To deluge a horse with cold 



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