HEART. 



605 



its dlMtoltt, and not during its systole. This 

 is in reality what we would a priori expect, 

 for it certainly does at first appear somewhat 

 paradoxical that the heart should strike the 

 purifies of the chest when the apex is ap- 

 proximated to the base. The concurrent tes- 

 timony of the most accurate observers has, 

 however, fully established the correctness of 

 the fact. Harvey observed it in the human 

 body when the heart had been exposed from 

 tin- Hlects of disease.* One of the principal 

 arguments adduced in support of this opinion 

 by these authors was drawn from the fact that 

 the pulse at the wrist is not synchronous with 

 the impulse against the chest, an opinion 

 which had been pretty generally maintained 

 since the time of Aristotle. It is difficult to 

 be convinced of this when the pulse is quick ; 

 but when it is slow, and in certain cases of 

 disease of the heart, it can generally be satis- 

 factorily ascertained. So far then they are right, 

 but in the next and most important step of the 

 argument they fall into a decided error; for 

 they proceed upon the supposition that the 

 pulse is synchronous in all the arteries of the 

 body at the same time, and consequently the 

 impulse of the heart at the chest cannot be 

 synchronous with the flow of blood along the 

 arteries, or, in other words, with the systole 

 of the heart. In opposition to this opinion, 

 Dr. Youngf had previously shown upon the 

 principles of hydraulics that the pulse along 

 the arteries must be progressive, yet in general 

 so rapid as to appear to arrive at the extremities 

 of the body without the intervention of any 

 perceptible interval of time. And when the 

 attention of medical men was turned to this 

 subject, various observers soon ascertained by 

 repeated experiments that the pulse could 

 be felt in favourable cases to pass along the 

 arteries in a progressive manner, that the 

 pulse in the large arteries at the root of the 

 neck and impulse at the chest are synchronous 

 or nearly so, that both precede that at the wrist, 

 and more distinctly still that of the dorsal 

 artery of the foot.J 



Various attempts have been made to expiate 



* " Siniul cordis ipsius motum observavimus, 

 nempe iilml in diastole introrsum subduci ct 

 trlnihi ; in systoh vero emcrjjere denuo et protrudi 

 lichi|uc in conic systolem quo tempore diastole in 

 carpo iirrcipiebatuv : ntque proprium cordis motum 

 et fiiiH'tioncm csse systolcm : denique cor tune 

 pcclus ficriquc ct prominulum esse cum erigitur 

 sursum.'' As quoted by Shebeare, Pract. of Phy- 

 sic, vol. i. p. 195. 



t Phil. Trans. 1809. 



$ It is interesting and curious, as shewing the 

 revolution of opinions, to compare the strict simi- 

 larity of the arguments adduced by the modern 

 supporters of this doctrine with those maintained 

 hy Shcbeare in 1755. (Practice of Physic, vol. i. 

 p. 1!CJ. ) *' This, however plausible it may ap- 

 pear, cannot be the true cause of it (impulse of 

 the heart), because then this stroke must be during 

 the systole of the ventricles, which would he syn- 

 ihrunous with the diastole of the arteries ; whereas 

 the hcalin" t the heart precedes the dilatation of 

 the arteries, and thence this stroke must be made 

 duiiiii! the diastole of the ventricles: thus the 

 diastole or distrution of the heart is the cause of 

 the beating against the ribs." 



in what manner the apex of the heart is made 

 to impinge against the parietes of the chest by 

 those who maintain that it occurs during the 

 systole' ol tin; \cntricles. Senac supposed that 

 this was principally effected by the curvature 

 of the two large arteries, but principally of the 

 aorta, which arise from the ventricles ; for at 

 each stroke of the ventricles when an addi- 

 tional quantity of blood is driven into the lar^c 

 arteries, as they are curved tliey make an at- 

 tempt to straighten themselves; and as this 

 takes place to a slight extent, the heart, which 

 is attached to their extremities, ought to be 

 displaced, and its apex, which describes the 

 arc of a circle greater than the other parts of 

 the heart, is thus made to impinge against the 

 walls of the chest. He also believed that the 

 distention of the left auricle with blood during 

 its diastole has also, from its position between 

 the spine and base of the heart, the effect of 

 pushing the heart forwards ; and this occurring 

 at the same time with the attempt which the 

 curved arteries make to straighten themselves, 

 it thus acts as a second or subsidiary cause in 

 tilting the heart forwards.* Though this sup- 

 posed effect of the curvature of the large 

 arteries has been a favourite explanation with 

 many of the impulse of the heart against the 

 chest, yet it really appears to have little, if any, 

 influence in producing this. Shebeare,t and, 

 more lately, Dr. Corrigan,J have shown that 

 the direction of the curvature of the large ar- 

 teries is such, that if any effect of this kind is 

 produced, the heart would not be carried to 

 the left sid, but in the direction of the curve, 

 which is exactly in the opposite direction. 

 Besides the tilting forwards of the heart has 

 been observed though no blood was passing 

 along the large vessels at the time, and the 

 same thing takes place after the large vessels 

 have been cut through and the heart removed 

 from the body. Haller and others have sup- 

 posed that the secondary cause assigned by 

 Senac, viz. the sudden distention with blood 

 of the left sinus venosus which lies impacted 

 between the spine and left ventricle, is the 

 principal if not the sole cause by which the 

 heart is pushed forwards against the ribs. In 

 confirmation of this opinion Haller states || 

 that if we inflate the left auricle after having 

 opened the chest, we see the point of the heart 

 approach with vivacity the region of the mam- 

 ma. As we cannot, however, under these cir- 

 cumstances distend the auricle without also 

 distending the corresponding ventricle, this 

 movement of the heart depends more upon the 

 sudden inflation of the ventricle than upon any 



* Op. cit. torn. i. p. 356. The ausc of the tilt- 

 ing motion of the heart was also, at a later pnioil, 

 attributed to the curvature of the aorta and to this 

 exclusively by Dr. W. Hunter. Note in John Hun- 

 ter's Treatise on Inflammation, p. 146, 1794. 



t Op. cit. p. 195. 



; Dublin Mcd. Trans, vol. i. p. 154. 



Dr. Carson (Inquiry into the Causes of the 

 Motion of the blood, p. 183.) maintains that no 

 proof can be adduced that the curvature of the 

 aorta is rendered more straight during the systole 

 of the heart. 



|| Sur Ic Mouvcmcnt du Sang, p. 124. 



