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Right side of Heart. A. Superior Vena Cava. B. Aorta. C. Musculi pectinati. D. Orifice and Sigmoid Valves of Pulmonary Artery. E. Right Auricle. F. Orifice of Superior Vena Cava. G. Annulus of Vieussens. H. Fossa Ovalis. I. Eustachian Valve. K. Inferior Vena Cava. L. Orifice of Coronary Vein. M. Thebesian Valve. N. Carnece Columna. 0. Wall of Ventricle. P. Musculi Papillares.

supported underneath by the ventricular wall. The annexed figure exhibits the four great valves closed, and the relative positions of the orifices from left to right. The auricular systole is sudden, being but

as long

[graphic]

The Orifices and Valves of the Heart-Mitral, Pulmonary, Aortic, Tricuspid. as the diastole; the ventricular gradual, as more resistance has to be overcome. The diastole of both is gradual, and is believed by many to be passive, or produced by the force of the cavity behind contracting; and by others to be active, or dependent on the dilating power of the cavity itself. This view Cruveilhier supports, for he found that if the empty heart of an animal just dead were grasped in the hand, considerable dilating force was perceived during diastole.

Two sounds accompany the heart's action, and are audible to the observer, or, in some cases, perceptible to the individual. Thus Müller, when lying on his left side, could distinguish those of his own heart. The following occurrences take place during

1st Sound Ventricles contract Auricles dilate

and

2nd Sound Ventricles dilate Auricles dilate,

and an interval of repose succeeds during which the auricles contract. Cruveilhier is of opinion that no pause is appreciable; and on the contrary others believe there is one after each sound.

The First Sound is systolic, and is best heard over the apex of the heart, as there no lung muffles it, and the heart comes near the surface by the impulse which occurs at the same time. It is a dull, rumbling sound, and so prolonged as to occupy as much time as the 2nd sound and the pause. Thus, if the heart be beating 60 times per minute, the 1st sound occupies a second, the 2nd sound rather less than, and the pause rather more than. The time occupied by the action and repose of the ventricles is thus calculated by Walshe in tenths of a second-systole, 4; post-systolic silence, 1; diastole, 2; and post-diastolic silence, 3. As regards its cause, it is but the "bruit musculaire," or noise, which the heart, in common with other muscles, produces in contracting. Dr. Halford, Professor of Physiology in Melbourne University, states that this noise is in part produced by the vibration of the air in the stethoscope or auditory meatus, placed on the chest. A similar sound may be heard during contraction of the biceps, masticating muscles, or, as Wollaston suggested, by placing the little finger in the ear and rapidly moving the thumb. It has been objected to this theory, which was maintained first by Williams, that it is not proportionally increased in hypertrophy of the heart, but in such cases the superficial fibres-muscle being a bad conductor of soundmuffle the bruit produced by the deep. The weak heart in typhus produces scarcely any sound. Tension and vibration of the auriculo-ventricular valves, as suggested by Billing and ingeniously supported by Halford, the impinging of the heart's apex against the chest, the collision of the particles of the blood against each other and against the rough columnar surface of the ventricle, and the rush through the narrowed arterial openings, have

each been assigned as the cause of the first sound, and they may all in some degree contribute.

The Second Sound is diastolic, or corresponds with the filling of the ventricles, and is most audible at the base of the heart. It is a sudden, flapping sound, somewhat like the lapping of a dog. It is certainly due, as suggested by Sir R. Carswell, to the flapping together of the semilunar valves at the aortic and pulmonary apertures. This is proved by Hope's experiment, repeated by a committee of the British Association which met in this city in 1834, and included Drs. Adams, Law, E. M'Dowel, Evory Kennedy, Carlile, &c. They hooked up one of the aortic valves with an awl, in an animal whose heart was kept acting by artificial respiration, and found a hissing sound took the place of the second sound, which again occurred if the valve was let back. Disease often presents, as it were, an experiment by nature, and in that affection termed "permanent patency of aortic valves," of which Dr. Corrigan, has given an original and exhaustive account, no second sound occurs, as the valves do not act. Williams compares the sounds of the first and second sounds respectively to the syllables. "lubb," "dup." It might be expected that the sounds would be heard more distinctly on opening the thorax of a living animal; but, on the contrary, they become almost inaudible. The same fact was illustrated in the remarkable case of M. Groux, who exhibited himself before the medical societies in 1857-8. His sternum was congenitally cleft, and, as if that bone played the part of a sounding-board, his cardiac sounds were very low. Many other points were investigated in this individual, and the systole and diastole of the cavities were demonstrated by the sphygmascope, which consists of a tube containing water, and closed by a soft piece of indiarubber at one end, dilated into a bell-shape. He was able to increase the width of the cleft to 3 inches by the action of the pectorals. Several important observations

were made by a committee in this city, and are recorded in the report drawn up for the Royal Irish Academy by Prof. Lyons of the Catholic University.

The Impulse is the stroke which the hand perceives if placed over the precordial region, between the fifth and sixth ribs, about 1 inches below the nipple. It is synchronous with first sound, and just precedes the pulse. It was caused, according to Hunter, by the rush of blood straightening the aortic curve; but it will occur if the aorta be empty, and Dr. Corrigan remarks that the heart would be thrown to the right side by the direction of the aortic curve, and not to the left, as it is. That great physician and able physiologist believes the impulse due to the simple swelling forward of the muscular substance of the heart. In the cat, rabbit, or other narrow-chested animal, the impulse can be felt on both sides of the chest. Others state it is due to the heart elongating and pressing its apex against the wall of the chest, producing, according to some, a friction sound. Harvey suggested this when he says, during contraction, "the heart is erected and rises upward to a point, so that at this time it strikes against the breast, and the pulse is felt externally;" but the heart really shortens during systole. It has been also suggested that the reactionary force produced by the discharge of the blood into the aorta may give rise to the impulse. The late Prof. Carlile, of Queen's College, Belfast, suggested that the anterior fibres, which are longer than the posterior, would tilt the apex forwards. Dr. Bellingham described a second impulse synchronous with the second sound, which occurs in the healthy heart when beating vigorously, or in the hypertrophied condition.

The Rhythm, or the regular succession of the actions of the heart, is one of its most remarkable properties. It has been stated to be due to the stimulus of the oxygen in the arterial blood and Goodwin regarded the absence of this stimulus to be the cause of asphyxia;

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