CHAP. II.] THE HEART ; ITS SHAPE— PULSATION. 123 



others whose bodily exertions and arterial functions 

 are less laboured than those of the horse (the sheep's, 

 for example) it is more round: and, indeed, the 

 heart of this last-mentioned animal is, from this 

 circumstance, usually termed, in the London dis- 

 trict, a " round heart." Out of the small chamber 

 on the left side is the blood driven through a valve, 

 as before, into the larger chamber of the same side, 

 which in its turn contracts, with much force, upon 

 its contents, expelling the same into the great artery. 

 This periodical rushing of the blood into the 

 arteries, imparts to these vessels a motion we term 

 pulsation, whereby the blood is propelled forward, 

 to the remotest parts of the body. Lessening in 

 size, and increasing in number, the branch-arteries 

 which receive this blood, become more sensitive as 

 they are farther removed from the heart, and afford 

 us, at certain places, the means of ascertaining by 

 the touch the degree of heat at which may at any 

 time be the state of the animal's blood ; the con- 

 tractions of the heart being regulated, in quickness 

 and force, by the degree of stimulation, the heat of 

 the blood may occasion it. This is termed the ir- 

 ritability of the heart, and the medical test of which 

 we speak, is called " feeling his pulse." Even in 

 the tail may this contractile power of the arteries, 

 and its effects be seen to advantage : when a colt is 

 being docked, the blood squirts forth with frequent 

 gushes, answering in a tolerably accurate manner 

 to the state of his pulse, although the artery at that 

 remote part is very small. But the blood that is so 



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