172' THE HORSE. 



supposed resemblance to a dog's ear, and two ventricles or little bellies, 

 occupying the substance of the heart. The blood which has circulated 

 through "the frame, and nourished it, returns to the heart through the 

 veins. It enters the auricle on the right side, where it accumulates 

 as in a reservoir, until there is enough to fill the ventricle below. The 

 auricle then contracts, and throws the blood into the ventricle. That 

 contracts in its turn, and drives the blood, not back again into the auricle, 

 for there is as complete a valve as that in the sucker of a pump to prevent 

 this, but through an aperture that leads to the lungs. The blood tra- 

 verses, as we shall presently see, all the little vessels and cells of the lungs, 

 and undergoes an important change there, and is carried to the left auricle ; 

 thence it descends to the left ventricle, and by the powerful closing of the 

 ventricle, is propelled into the arteries. The first artery, the aorta, rises 

 from the left ventricle, and the blood, by the force communicated to it, by 

 the sudden contraction of the ventricle and assisted by the elastic power 

 of the arteries which keeps them open and free from obstruction, and also 

 by the pressure of the muscular and elastic coats, endeavouring to return to 

 their former dimensions, pursues its course through every part of the frame. 

 The heart is subject to disease. It powerfully sympathises with the ma- 

 ladies of every part. An injury of the foot will speedily double the quick- 

 ness of the beatings or pulsations of the heart. It sometimes is inflamed, 

 without previous affection of any other part. This is not a frequent, but a 

 most dangerous disease, and is characterised by a pulse quick and strong, 

 and a bounding action of the heart that may occasionally be seen at the 

 side, and even heard at the distance of several yards. There is also a 

 peculiar alertness and quickness in every motion of the animal ; and an 

 energy of expression in the countenance exceedingly remarkable. Speedy 

 and copious blood-letting will alone avail to save the horse ; for the heart, 

 over excited and called on to perform this double work, must soon be 

 exhausted. 



THE ARTERIES. 



The vessels which carry the blood from the heart are called arteries {keep- 

 ing air, the ancients thought that they contained air). They are composed 

 of three coats ; the outer or elastic is that by which they are enabled to 

 yield to the gush of blood, and enlarge their dimensions as it is forced 

 along them, and by which also they contract again as soon as the gush of 

 blood has passed ; the middle coat is the muscular, by which this contrac- 

 tion is more powerfully performed, and the blood urged on in its course ; 

 the inner or membranous coat is the mere hning of the tube. 



This yielding of the artery to the gush of blood, forced into it by the 

 contraction of the heart, constitutes 



THE PULSE. 



The pulse is a very useful assistant to the practitioner of human medicine, 

 and much more so to the veterinary surgeon, whose patients cannot de- 

 scribe either the seat or degree of ailment or pain. The number of pulsa- 

 tions in any artery will give the number of the beatings of the heart, and 

 so express the irritation of that organ, and of the frame generally. In a 

 state of health, the heart beats in the farmer's horse about thirty-six times 

 in a minute. In the smaller, and in the thorough-bred horse, the pulsations 

 are 40 or 42. This is said to be the standard pulse, — the pu^se cf health. 

 It varies singularly little in horses of the same size and breed, and 



