298 STABLE ECONOMY. 



with ease, and perhaps to draw it a considerable distance 

 But next day he is sore all over, stiff, feeble, dull, almost un 

 able to c; rry his own weight. If the same work be exacted 

 day after day, the horse loses flesh, and at last becomes unfit 

 for any work. But if the work be less severe at first, and 

 gradual'y increase from week to week, the horse at last ac- 

 quires strength and endurance greater perhaps than he ever 

 before possessed. He is then able to do with ease as much 

 in a week as would have completely knocked him up at the 

 beginning. For slow moderate work this is all the prepara- 

 tion the horse needs. At first let it be very gentle ; and the 

 weight he is to carry or draw, and the distance he is to travel, 

 may be increased as he is found able to bear it. In preparing 

 the horse for work, such as hunting, racing, or coaching, the 

 treatment must be somewhat different. See the next two 

 sections. 



PHYSIOLOGY OF MUSCULAR EXERTION. 



BY this I mean an account of what is going on in different 

 parts of the body during exertion. Motion produces certain 

 changes, and it is good to know what they are, and for what 

 reason they occur. All can not be traced ; but it is satisfac- 

 tory to know all that can be known. A few preliminary re- 

 marks are necessary upon 



THE CIRCULATION OF THE BLOOD. This fluid is dis- 

 tributed over every portion of the frame. Without its agency 

 there is nothing done in any part of the body ; and, in per- 

 forming its varied duties, it suffers some alteration, which 

 renders it unfit to reproduce the same effects, or perform the 

 same functions, until it has acquired something it has lost, and 

 parted with something it has gained. The purification, or re- 

 generation, takes place chiefly in the lungs. To these organs, 

 which almost entirely fill the chest, the blood must be con- 

 ducted. It is collected from every tissue, by veins infinitely- 

 numerous and small ; too numerous to be counted, and too 

 small to be traced even with the aid of optical instruments. 

 These, as they approach the heart, concentrate, become lar- 

 ger and fewer, till they end in two main trunks of very large 

 size, which pour their contents into a cavity on the right side 

 of the heart. The heart sends this blood to the lungs, by 

 one large tube. This, running into the substance of the lungs, 

 divides and subdivides, till its branches become so numerous 

 and minute that they can not be distinguished from the tissue 



