Among those who maintain that these sounds depend upon causes intrinsic to the heart, the first sound is referred by llonanet, Bryan, and llouillaud to the rapid tion of the auriculo-ventrieular valves during the systole of the ventricles, to which llouillaua adds the sudden separation of the semilunar valves when the Wood is forced into the large arteries ; by Itle. Carlisle to the rushing of the blood along the inner surfiwe of the large 'merles during the systole of the ventricles." 1)r. I lope, in the appendix to the second edition of his work, describes it ns consisting, 1st, possibly of a degree of valvular sound ; 2d, of a loud smart !IOWA produced by the abstract act of a sudden jerking extension of the muscular walls, in the same manner that such n sound is produced by similar extension of the leather of a pair of bellows ; to avoid circumlocution, he calls it the sound exten sion; 3d, a prolongation and possibly an aug mentation of this sound by the sonorous vibra tions peculiar to muscular fibre." Dr. C. J.
has very justly objected to the correct ness of the second cause here adduced as aiding in the production of the first sound, as the phrase " sound of extension" is obviously contradictory when applied to a contractii.g muscle.l Dr. C. J. It. Williams maintains " that the first sound is produced by the mus cular contraction itself," the clearness of which is increased by the quantity of blood in the heart " affording an object around which the fibres effectually tighten, whilst the auricular valve, by preventing the reflux of the blood, increases its resistance, and thus adds to the tension necessary for its expulsion." Ile was first led to the adoption of this opinion by the observations of Erman and Wollaston upon the existence of a sound accompanying every rapid muscular contraction. This opinion he afterwards put to the test of experiment, the results of which we give in his own words. " Experiment 1st, observation IIth ; I pushed my linger through the mitral orifice into the lett ventricle and pressed on the right so as to prevent the influx of blood into either ventricle; the ventricles continued to contract strongly (especially when irritated by the nail of the finger on the left), and the first sound was still distinct, but not so clear as when the ventricles contracted on their blood. Observation Dth. The same phenomena were observed when both the arteries were severed from the heart." 110 also found in other observations that the first sound was louder over the surface of the ven tricles than over the origin of the large arteries, which is in direct opposition to the opinion of those who believe that this is produced by the rush of blood along the great nrtcries. That
the first sound is not dependent upon the closing of the anriculo-ventneular valves, he also ascertained from observations, in which the closure of these valves was partially or com pletely prevented, and yet the first sound was still heard. Ilesides, this sound continues during the whole of the ventricular systole, while the shutting of the valves must take place anti he completed at the commencement of the systole." 'that the collision of the particles of fluid in the ventricles Coes not produce this sound he was convinced front observations, in which it continued although there was 110 blood in the ventricles.
Though we must admit that these experi ments of Dr Williams prove that part at least of the first sound is caused by the muscular contraction of the ventricles, yet we must con sider it still problematical, until we obtain farther observations, whether it produces thu whole of that sound, for it is very possible that some of the other circumstances attending the systole of the heart may increase its intensity. M. Mare d'hIspine has maintained that both sounds depend on muscular movements; tho first sound upon the systole, and tlto account upon the diastole of the ventricles. The Dub lin Committee have in the inenntime concluded that the lirst sound is produced either by the rapid passage of the blood over the irregular internal surfitce of the ventricles on its way towards the mouths of the arteries, or by the bruit musculaire of the ventricles, or probably by both these causes. NVe must wait for further experiments before this question can be fairly settled.• Second sound.—Later experimenters appear to bo more nearly agreed about the cause of the second sound than that of the first sound. M. Itounnet apprars to have been the first who publicly maintained the opinion that the second sound was dependent upon the shock of blood against the semilumw valves at the origin of the aorta and pulmonary artery. M. lb:tunnel himself acknowledges that he owed the sug Festion to Dr. Carswell, at that time studying in Paris, who came to that conclusion by a beautiful process of reasoning upon the pheno mena which presented themselves in a case of aneurism of the aorta. The same opinion has been supported by (tilling, Bryan, Carlisle, and Douillaud4 It is, however, to Dr. C. J. 11.