Sounds of the applying the ear over the region of the heart, two distinct sounds are heard accompanying its contraction. Though the existence of such sounds seems to have been known to Harvey,* who compares them to the noise made by the passage of fluids along the oesophagus of a horse when drinking, yet, as is well known, it is to Laennec that we owe the first accurate description of the charac ter of these sounds, the order of their succes sion, and the manner in which they may here after be made available for the important pur poses of the diagnosis of the diseases of the heart.
The first of these sounds is dull and pro longed ; the second, which follows closely upon the first, is sharp and quick, and is likened by Laennec to the flapping of a valve, or the lap ping of a dog. After the second sound a pause ensues, at the end of which the sounds are again heard. These three—the first sound, the second sound, and the pause—occur in the same uniform order, and when included along with the movements of the heart, to which they owe their origin, have received the term rhythm of the heart. As the dull prolonged sound is synchronous with the impulse of the heart, and consequently with the contraction of its ventri cles, Laennec attributed this sound to the con traction of the ventricles. The second sound, which is synchronous with the diastole of the ventricles, lie supposed must depend upon the systole of the auricles ; and to this he was naturally led by the supposition that their con traction must also produce some sound. From the weight, of Laennec's authority, this opinion seems to havebeen almost implicitly adopted un til the appearance of a paper by the late Professor Turner, in 1829. Professor Turner there re called to the attention of medical men the observations of Harvey, Lancisi, Sena; and Haller, upon the order of succession in which the cavities of the heart contract, which appear to have been forgotten amidst admiration at the brilliancy of Laennec's progress. Ile also pointed out from their experiments that if the second sound was dependent upon the con traction of the auricles, it ought to precede instead of following the first sound, and that the pause ought to occur after the first sound, and not after the second. Ile also adduced, in farther proof of Laennee's error, observations drawn from the effects of disease, when, from some impediment to the passage of the blood from the right auricle into the ventricle, a dis tinct regurgitation takes place into the large veins at the root of the neck, and showed that in these cases the regurgitation marking the contraction of the auricles occurs without any accompanying sound ; that immediately after wards the impulse is felt attended by the first sound, and that the second sound takes place during the diastole of the ventricles and the passive condition of the auricles.
Ile suggested that the second sound might be accounted for by the falling back of the heart into the pericardium during its diastole, to which "the elasticity of the ventricles at the commencement of the diastole, attracting the fluid by suction from their corresponding auri cles, may perhaps contribute." Soon after the appearance of Mr. Turner's paper, Laennec's explanation of the cause of the second sound appears to have been pretty generally aban doned ; and numerous attempts, both in this country and in France, have since that time been made to solve this difficulty. Some of these explanations appear to be mere guesses, occasionally at total variance with the anato mical structure of the organ, and at times pre senting even as wide a departure from its nor mal action as that given by Laennec himself. Others, again, have entered upon an experi mental investigation of the subject with en lightened views of its anatomy and physiology, have furnished us with much additional infor mation, and lead us to indulge in the pleasing prospect that in a short time the matter will be completely set at rest.
The result of the experiments of hope and Williams, attested as they have been by various gentlemen well qualified to judge of their accuracy,—also those of Mr.Carl isle, Magendie, I3ouillaud, and the Dublin Committee, have satisfactorily determined that the account of the order of the contractions of the heart, and their isochronisin to the sounds as stated by Mr. Turner, are perfectly correct. As, how ever, so many different circumstances attend each movement of the heart, any one of which may be capable of producing these sounds, it became a much more difficult matter, and one requiring great perseverance and accuracy of investigation, to determine upon what particular one or more of these, each sound depends.