For accompanying, and synchronous with the first sound, we have the contraction of the ven tricles, the collision of the different currents of blood contained there thus set in motion, the approximating of the auriculo-ventricular valves, the impulse of the heart against the chest, and the propulsion of the blood along the large arteries; while attending the second sound, we have the diastole of the ventricles, and the rush of a certain quantity of blood from the auricles into the ventricles, the sudden separation of the auriculo-ventricular valves towards the walls of the ventricles, and the regurgitation of part of the blood in the arteries upon the semi lunar valves, throwing them inwards towards the axes of the vessels ; so we will find that each of these in its turn has been thought ca pable of producing the sound which it accompa nies, and still has,or until lately had, its advocates and supporters. As the subject is one surrounded with numerous and unusual difficulties, and is of comparatively recent investigation, it has fol lowed, as was to be anticipated, that as new facts and observations are collected, many of the opinions first promulgated on this question have required to be modified or changed ; and the scientific candour displayed by several of these authors in renouncing former published opinions is deserving of the highest praise.
Several of the explanations of the cause of the sounds of the heart proceed, however, upon the supposition that the relation of these sounds to the movements of the organ is different from what has been here represented. We shall merely state these without alluding to the arguments adduced in support of them, as we believe that they are founded upon inaccurate observation. Sir D. Barry believed that the first sound was synchronous with the diastole of the auricles, and the second sound with the diastole of the ventricles. Mr. Pigeaux, Dr. Corrigan also until lately, Dr. Stokes, Mr. Ilart, and Mr. Beau, have maintained that the first sound is synchronous with the diastole, and not with the systole of the ventricles. Ac cording to Mr. Pigeaux, when the auricles contract they project the blood against the walls of the ventricle, and a dull sound (first sound) is produced ; on the other hand, whilst the ventricles contract, they project the blood against the thin walls of the great vessels which spring from them, and a clear sound (second sound) is the result. Dr. Corrigan supposed that the first sound was produced by the rush of blood from the auricles into the dilating ventricles, and that the second sound owed its origin to the striking together of the internal sin faces of the ventricles during their contrac tion, after they had expelled all their blood. Mr. Beau believes with M. Magendie that the first sound arises from the impulse of the heart against the inner surface of the chest. but differs from him in maintaining that this occurs during its diastole, and not during its systole. The second sound he believes to depend upon the dilatation of the auricles. M. Piorry has revived the obsolete and perfectly untenable opinion of Nicholl, that the two ventricles contract at different times, and attributes the dull sound to the contraction of the left ventricle, mid the clear sound to the contraction of the right ventricle. Dr. David Williams, while he believes that the first sound depends upon the rush of blood into the large arteries during the systole of the ventricles, attributes the second sound to the inusculi papillares, which he considers as forming part of the val vular apparatus, causing the valves to strike against the wells of the ventricles. These mus culi do not, in his opinion, contract during the systole of the ventricles, but imme diately afterwards, for the purpose of throwing open the nurieulo-ventricular valves. in n firmer part of this article seventh circum stances are stated adverse to this opinion.
We shall now proceed to the explanation of the cause of these sounds given by those who maintain the views of the rhythm of the heart which we have here adopted, as resting upon the concurrent testimony of numerous accurate observers. These may be divided into those who attribute both sounds to causes intrinsic to the organ, or, in other words, to circumstances occurring within the organ itself, and into those who place them external to the organ, null depending upon extraneous objects. the only supporters of the latter opinion are INlagendie and his followers. blagendie maintains that
"in contract ing,and for anises long since known, the ventricles throw the apex of the heart against the lefl lateral part of the thorax, and thus produce the first sound, i. e., the dull sound. In dilating, in n great measure under the influence of the rapid influx of the blood, the heart gives it shock to the anterior panics on the right of the thorax, and thus produces the second sound, the clear sound." In proof of this, lie states that on removing the sternum of a swan (an animal selected expressly for the experiment, as it interfered less with the natural action of the heart than in the Mam mal:a), he found that the movements of the heart produced no sound, while, on replacing the sternum, and allowing the heart to impinge upon its posterior surface as in the natural state, both sounds were again distinctly heard. Ile adduces seveml arguments drawn from the action of the heart both in its healthy and dis eased state in favour of his opinion ; and he ingeniously attempts to get rid of the objection which must instantly suggest itself, that in many eases, such ns frequently occur in hyper trophy of the organ, the loudness of the sounds is diminished, while the force of the impulse is increased, by arguing that in these eases this increased impulse depends rather upon a heaving of the chest produced by the heart, which from its increased size is brought close to its inner surface, than upon a distinct im pingement upon it, such as takes place in the healdiv state. Dr. Dope, N. Itouillaud, Dr. C. J. 11. Williams, mid the Dublin and London Heart Connnitees have, however, distinctly hearth both sounds of the heart, after that por tion of the chest against which it impinges had been removed. h t may, nevertheless, be objected to these experiments, dint as the stethoscope was used m many of them, the impulse of the heart against the extremity may have produced an effect similar to its impulse against the parietcs of the thorax. AI. Itouillaud, having appa rently this objection in view, states that the rubbing of the heart during its movements against the extremity of the stethoscope, is easily distinguished from the sounds of the heart; mud that he has distinctly heard both sounds, though feelder than through a stetho scope, as was to be expeete(l when nothing but n cloth was interposed between his naked car and the surface of the heart. Dr, C..I. Williams, in his experiments, heard both sounds when the stethoscope wasplaced over the origin of the large arteries, and where no external impulse could take place ; mid this observation was repeated by the Dublin Committee. The Dublin Committee heard both sounds through the stethoscope, though feebler after the peri cardium had been injected with tepid water ; and in another experiment they were also heard when the ear was simply approximated to the organ. From all these experiments, 1 think there can bo little doubt that the move ments of the heart, independent of all extra neous circumstances, arc attended by a double sound. As the impulse of the heart against the chest must produce some sound, as nay one may convince himself by making the ex periment in the dead body, and as this occurs during the systole of the heart, or, in other words, during the first sound, it may increase the intensity of that sound. Dr. It. Spinal,* after relating several experiments in which a sound similar to that of the first sound of the heart was licanl by tapping gently with the apex of the heart or the point of the finger against the chest, both when empty and when filled with water, and after pointing out several sources of fidlacy which he supposes were not sufficiently guarded against in the experiments which we have adduced above as subversive or this view, and which deserve the nttention of future experimenters, comes to the conclusion that " it Is highly probable that the percussion of the heart against the thoracic parietes during the contraction of the ventricles assists mate rally in the production of the first sound." lie is also inclined to believe "that the act of the separation of the heart from the thorax after its approach, which was found in his experiment to produce a sharp, short sound, somewhat resembling the ordinary soma], may in certain circumstances be an assistant cause to the second sound."t Alagendie's explanation of the second sound is completely untenable.