The second sound is the result of the sudden tension of the semilunar valves caused by the resistance which these valves offer to the retrograde flow of the blood from the aorta and pulmonary artery respectively into the ventricles on the cessation of systole. [Sir Richard Quain, after referring to the doubt existing as to the cause of the first sound, continued :—] ] It seemed to me to be desirable, amidst sucti differences of opinion, to solve if possible a problem which has its special

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... st and its special importance. Two of the most striking events which take place during systolenamely, the closure of the auriculo-ventricular valves and the muscular contraction of the ventricular walls-are regarded by many authorities as the sources whence the first sound proceeds. The result of my investigations, on the one hand, leads me to the conclusion that neither of these explanations is satisfactory ; and, on the other hand, enables me to indicate what I believe to be the real explanation of the phenomenon. 2 A. The action of the auriculo ventricular valves is not the source of the first sound of the heart. -The mechanism of these valves (the mitral and tricuspid) and their action do mot possess the elements necessary for the production of such a sound. [Sir Richard Quain here gave an account of the action of the valves and proceeded :-] Further evidence on this point may be found in another direction—namely, in the fact that the first sound can be heard independently of the existence and action of mitral and tricuspid valves. Aware of the fact that in some of the lower animals, more especially in the reptile cla';s, the auriculo-ventricular valves exist in but a very rudimentary form, I obtained permission to examine some of these creatures in the Zoological Gardens, and spent many hours on many occasions in the investigation, assisted by my valued friend Dr. John Sibbald. [Sir Richard Quain then referred to the first sound being audible in the python and the kangaroo-which have only rudimentary aurículo.ventricular valves.] Objections will, co doubt, suggest themselves to the view above expressed. For example, the clinical physician will say, "I am in the daily habit of hearing a distinct murmur accompanying the systole in cases of diseased heart, and apparently replacing the first sound. On examining the heart after death I find the auriculo-ventricular valves diseased--a condition with which I therefore connect the murmur." It will at once be seen that we have here to deal with morbid sounds, totally difeerent in character and totally different in the seat and mode of production, from the first sound of the heart. To make the explanation more simple I will confine my observations to two principal forms of mitral disease associated with systolic murmur-namely, first, 1 A paper read before the Royal Society of London on June 3rd, 1897. 2 I have to acknowledge with thanks the assistance rendered me in arianging my notes of this memoir by my valued friend, Dr. Mitchell Bruce, during my recent severe indisposition. imperfection in structure with distinct regurgitation ; and, secondly, induration, roughness, and irregularities on the mitral valve. [Sir R. Quain described (a) the mitral regurgitant murmur, and (b) the systolic murmur without regurgitation. He continued :-] These murmurs, striking and characteristic as they are, are merely accidental complications which occur at the moment of the systole of the heart; but they are unconnected with, and have no relation except in point of time to, the healthy first sound, which may be heard apart from, and independently of, them. The weight of evidence, then, is clearly against the possibility of the structure or the functions of the auriculo-ventricular valves being the source whence proceeds the first sound of the heart. Two other phenomena occur synchronously with the systole of the heart, and consequently with the occurrence of the first sound. They are (a) the contraction of the muscular walls of the ventricles, and (b) the propulsion and movement of the blood from the ventricles into the arteries. I shall first consider the supposed share which muscular contraction has in the formation of the sound. .B. The muscular contraction of the walls of the heart during systole is not the source of the first sound of the heart.-The sound produced by muscle during its contraction was first described by Dr. Wollaston. He compared it to "a sound which resembles most nearly that of carriages at a very great distance passing rapidly over a rough pavement." 4 It is very difficult to conceive the slight, soft, rolling sound produced by muscles in action being convertible into the loud, booming first sound of the heart. Yet the theory is accepted. If muscle during contraction could produce so marked a sound, we should expect to find that the powerful muscles of the neck attached to the base of the skull and those attached to the jaw (being through the bones of the skull in direct relation with the hearing apparatus) would give us some striking evidence of the production of muscular sounds when they are thrown into strong action. But there is nothing of the kind. I have failed to hear such sounds when listening to the powerful contraction of the biceps, 3 or on listening to the contraction of the shoulder muscles of a strong cart horse struggling with a heavy load in ascending a hill. I could hear no other sound save the . soft, rolling sound described by Dr. Wollaston. Still, many observers have argued that the contraction of the walls of ' the heart differs from the action of the skeletal muscles, and . that it is this peculiar form of contraction which causes f the first sound. They have adduced so many observations . in favour of this doctrine that it will be necessary to examine them. But before doing so, for the sake of making my argument more clear, I desire to point out that there is another event which occurs simultaneously with the systole of the ventricle. This is the propulsion of the blood from the ventricles and its impact against the column of blood restiDg on the semilunar valves. With a view to showing bow large a share the sound of muscular contraction has in . producing the first sound observers have cut off altogether the supply of blood from the cavities, and on listening during the contraction of the heart have heard a systolic sound. Such were the old experiments of Ludwig and : Dogiel, represented as confirmed by Krehl 5 and by . Kasem-Beck.** The conclusions which have been drawn from these . experiments are disproved by those conducted by my friend Professor Halford, and described in his essay on" The Action , and Sounds of the Heart," published by Churchill (1860). , He writes : " Large dogs were obtained, and, as in my preceding experiments, the heart was exposed, and the circulation kept up by artificial respiration. A stethoscope beirg applied to the organ, sounds were distinctly heard. The superior and inferior venæ cavæ were now compressed with ' a bull-dog forceps, and the pulmonary veins by the finger and thumb; the heart continuing its action, a stethoscope was again applied, and neither first nor second sounds were heard. After a short space of time the veins were allowed to pour their contents into both sides of the heart,