ACTION OF THE HEART. 37 



hape that, by patient investigation, we may at least find out the means of alle- 

 viating their evil tendency. These considerations should excite particular 

 alttMition to the subject in hand, being that to which all other functions are 

 but subservient or conducive; respiration and digestion being more closely 

 connected with it than any other, and requiring a corresponding degree of at- 

 tention. The heart, jointly with the lungs, occupies the cavity of the chest, 

 rather incliniag towards the left side, against which its point maybe feltbea* 

 ing, whenever the animal is agitated by exercise, or internally affected by in- 

 flammatory complaints. Its figure is too well known to render description 

 necessary : in size it approaches that of an ox, and, like it, is enclosed in a 

 membraneous sac, but very thin, not unlike a tight purse. Another sac, 

 called the heart-bag, less tight, surrounds the former, but is never so large, 

 nor encumbered with fat like that of the bullock. On opening this sac there 

 issues forth a fluid which turns to water, if it were not so already ; in the ox 

 It is confessedly water, and rather more in quantity than in the horse; — the 

 reason for which diflference I will show presently. So great is the stimulus 

 of this organ, that its contractile power often exists long after the animal is 

 dead, and the arteries cease to flow : a phenomenon that occurs when the 

 horse is killed in full health, by an accident, or otherwise, while in full pos- 

 session of its functions. In animals of much mettle or courage the heart at- 

 tains to a great size, that of the famous horse EcUpse weighing 181bs. In 

 some horses, the vessels that nourish this muscular organ lie exposed on the 

 surface ; with others, they lie wholly concealed ; a fact from which I have yet 

 found no opportunity of making any sure deduction, but apprehend it may 

 arise from the breed, and conclude it must have considerable effects on his 

 disposition. 



As the heart is the principal organ employed in converting into blood what 

 is drawn from the finer particles of food sent into the system for that purpose, 

 as well as iu renovating that which has been exhausted of its vital prin- 

 ci[)le in the circulation, it may well be supposed full of small blood- 

 vessels. Four large ones meet at its thick end, and suspend it, by being at- 

 tached to the bones of the back and ribs : two of them, bringing the dark vi- 

 tiated blood from the extremities of the fore-part and of the hind-part, are 

 veins ; the other two large vessels are arteries, which, receiving the blood from 

 the heart, just now refined by the process of nature, convey it with rapid con- 

 tractions to every part of the system, there to give fresh vigour, and to impart 

 health to the whole. These contractions constitute the pulsation, or pulse ; 

 a criterion of health as of disease, which we investigate with primal anxiety, 

 »s from it may be deduced the best prognostic of the state of disease, espe- 

 cially of inflammatory ones, to which this noble animal is more than any other 

 eubject, from causes to be explained hereafter. 



38, Two large chambers (as I call them') and two small ones, each of the 

 latter appended to one of the former, mainly contribute to the process of cir- 

 culation ; these by their co-action, aid the contractile power of the heart, com- 

 pelling the contents of the larger chambers to issue with much force into the 

 arteries. But, before the blood can be thus again fit for circulation, nature 

 has provided the means of rendering it so, by the action and re-action of • 

 Ihexi four chambers (or cavities) in the heart, contributing to refine it for 

 Lhat purpose; one large chamber, with its small one, being placed on the right 

 side of the heart, and the like pair on the left side thereof. The blood from 

 the veins flowing into the small chamber on the right side, irritates its inner 

 coats, and they each contract upon its contents with nearly as much strength' 

 and quickness as we can open and shut the hand ; — but certainly not so much- 

 open, although there is a flap on the entrance of each small chamber, which 

 thpv liken to "a dog's ear," and call by the Greek word auricley that being 

 5* 



