300 STABLE ECONOMY. 



forty times in a minute. Every contraction drives a column 

 of blood through the arteries. At slow work the heart may 

 beat from fifty to seventy times per minute ; but at fast work 

 it sometimes makes more than one hundred and forty strokes 

 in a minute. 



Quickness of the Breathing occurs almost simultaneously 

 with the quickness of the circulation. There is a little time, 

 however, it may be only a few seconds, between them ; the 

 circulation has the start. Acceleration of the breathing fol- 

 lows, in order that the blood may be purified as fast as it is 

 circulated. At rest, the horse respires from six to eight times 

 per minute ; at slow work he may breathe twice as fast, and 

 at very fast work, he may respire more than one hundred and 

 thirty times per minute. The velocity of the blood must 

 keep pace with the exertion of the muscles, and the respira- 

 tion must quicken as the circulation quickens. The action 

 of each is, in a certain measure, influenced by that of the 

 other, but each is also limited in its individual powers. The 

 muscles can not act if the heart do not give them sufficient 

 blood ; the heart can not give the blood if the lungs do not 

 purify it ; but the muscles may tire, even though well sup- 

 plied by blood ; or the heart may tire, though the lungs con- 

 tinue vigorous. Deficiency in either deranges the others. 



Exertion may raise the pulse to one hundred and forty, and 

 the breathing to one hundred and thirty ; but at this rate, 

 neither the heart nor the lungs can work long. After a period, 

 which varies with the condition of the horse, the blood be- 

 gins to accumulate in the right side of the heart. It is diffi- 

 cult to say what part is first in fault. The heart may be ex- 

 hausted, unable to force the blood through the lungs : or the 

 lungs may be unable to purify and transmit the blood as fast 

 as the heart sends it ; or the muscles which produce breathing 

 ma^ tire, and become unable to expand the chest, sufficiently 

 to admit the blood and the air into the lungs ; or, possibly, 

 heart, lungs, and muscles, may all be at fault, some more, some 

 less : whichever way it happen, the blood begins to accumu- 

 late, first in the right side of the heart, and then in the lungs. 

 After this stagnation commences, the horse is not able to go 

 much further. The muscles do not leceive enough of blood ; 

 and that which they do receive is not good. The obstruction 

 in the lungs forbids perfect purification. The horse becomes 

 feeble, is disposed to slacken his pace, and some stand still 

 before they are very much distressed. But such is the dis- 

 position of certain horses ; one will run on till he is blind, 



