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Serum or lymph effused into the pericardium have the effect of obscuring the intensity of the sounds, by rendering the source of their production more distant from the surface and interposing an indifferent conducting medium.

The quality and pitch of the sounds are also prone to undergo alteration. Cæteris paribus, the first sound becomes duller, and its pitch is lowered in proportion to the thickness of the ventricles and the rigidity or imperfect elasticity of the auriculo-ventricular valves ; whilst, on the other hand, it becomes clearer, and its pitch is raised in proportion to the thinness of the ventricles and the elasticity of the auriculo-ventricular valves. The quality of the sound, however, undergoes innumerable variations, according to the precise texture of the heart, the condition of its valves, and the state of the blood and the nervous influence, and it is impossible to connect many of these slight gradations of sound with the structural and functional changes from which they originate. The most remarkable changes are those already alluded to, viz., the dull, muffled, low-pitched sound which results from extreme hypertrophy of the heart; the clear and often high-pitched sound which is produced by dilatation of the heart; and the knocking character which is imparted by nervous excitement. To these, perhaps, should be added a peculiar clanging character which is sometimes observed when the heart is irritable and the free edges of the valves are indurated.

The second sound becomes dull and has its pitch lowered by want of contractility in the arteries, and also by thickening and impaired elasticity of the semilunar valves. In certain instances in which the elasticity of the arteries is great, and thickening or rigidity affects the free edges of the valves, the sound assumes a clanging character.

The duration of the sounds also varies in strict conformity with the physical changes which occur in the condition of the heart and great vessels. Hypertrophy of the walls of the heart increases the duration of the first sound by lengthening the period which the ventricle occupies in contracting; and an undue accumulation of blood in the heart, whether caused by general plethora or by obstruction at the aortic orifice, produces a similar result, . by rendering it a slow and difficult operation for the heart to expel its contents. On the contrary, simple dilatation or atrophy, or any other circumstance which weakens the heart, renders the first sound short, by impairing the contractile powers of the ventricles, and so lessening the vibrations caused by tension of the valves. The duration of the second sound is lengthened by anything which impairs the contractility of the arteries, and also by thickening of the semilunar valves ; it is shortened by extreme irritability of the arteries, and by an attenuated condition of the valves.

The duration of the first interval of silence is increased by whatever disproportionately shortens the first sound of the heart, and also by whatever impairs the elasticity of the arteries, and thus leads to delay in the recoil of the blood on the semilunar valves, or, in other words, in the commencement of the second sound; the duration of the second interval of silence, by whatever obstructs the auriculoventricular orifices, and thus, by causing delay in the filling of the ventricles, necessitates a longer delay than usual before the ventricles are again ready to contract. In most instances in which the pulsations of the heart are greatly reduced in frequency, the second interval of silence is disproportionately prolonged, and constitutes the principal auscultatory feature of the case.

But the rhythm of the heart's sounds may be even more seriously disturbed. Not only may one or other of the sounds or intervals of silence be inordinately prolonged or shortened, but there may be even a pause in the action of the heart, so that both sounds may cease during the period occupied by one entire action of the heart. When this occurs the sounds are said to intermit. In many instances this intermission of the sounds appears to follow some definite law; for it takes place at regular intervals,—as, for example, every fourth, fifth, or sixth beat. In other cases the intermission is irregular in its occur. rence, taking place, perhaps, after two or three pulsations, then after six or seven, and then, again, perhaps, after nine or ten. Sometimes the sounds of the heart are regular, both in rhythm and intensity, during the interval which occurs between the intermission; at others they are regular in succession, but irregular in intensity, one or more weak sounds being succeeded by others comparatively loud; but more commonly they are irregular both in rhythm and intensity, each contraction of the ventricles differing from the preceding one in force and duration.

Another form of abnormal rhythm is connected with an alteration in the number as well as in the duration of the sounds of the heart. Sometimes one sound is altogether absent either at the base or the apex- 80 that a single sound only is heard in one of those situations. If the first sound is at fault, its absence is due to one or more of the causes already specified, as contributing to weakness of that sound. If the second sound is inaudible at the base, the fact is explicable by the existence of one or more of the conditions which have been already pointed out as occasioning weakness of that sound, or else by its being masked by a prolonged systolic sound or murmur. In the first case, mental excitement or active exercise, by stimulating the action of the heart, will usually render the sound audible; and, in the second, the sound, if inaudible at the base, will be heard at the right apex. In some instances a triple sound, due to the reduplication of the systolic or the diastolic sound is heard, instead of the ordinary double sound; and in others four sounds, consequent on the reduplication of the first and second sounds, are heard within the period of one entire action of the heart. Indeed, reduplication, as it is termed, of the sounds of the heart, may exist in every possible variety. It may be audible at one spot, inaudible at another; it may exist at one moment, and may disappear the next; it may affect the first sound at one time, and the second shortly afterwards. In all cases its essential cause is the absence of synchronous action in the valves of either or of both sides of the heart. Thus, if one ventricle contracts before the other, the auriculo-ventricular valves on the two sides of the heart will not close simultaneously, and the first sound will be reduplicated; if the elasticity and irritability of the pulmonary artery and the aorta be unequal, the one vessel will probably contract before the other, and thus cause a want of synchronism in the closure of the semilunar valves on the two sides of the heart.

But in some instances the reduplication appears to be confined to one side of the heart; for a double first sound may be audible at the left apex and not at the right, or a double second may be audible at the aortic cartilage, and not at the pulmonary, or vice versá. In these cases there is a want of synchronous action between the different segments of each set of valves—of the mitral or of the tricuspid, as the case may be, in the first instance; and of the aortic or of the pulmonary semilunar valves in the second instance.

Thickening and want of elasticity in one set of valves has been thought capable of occasioning reduplication of the sounds ; but, although theoretically, the explanation seems probable, I very much doubt it being founded on fact. Certain it is, that reduplication of the sounds is at least a rare attendant on valvular mischief; whereas, it is of constant occurrence in cases which are unaccompanied by valvular disease, whilst its frequent intermission, and its appearance and disappearance under different conditions of excitement, seem to point to perverted irritability of certain portions of the heart as its essential cause.

It might be supposed that the altered rhythm of the heart would be indicated by the state of the arterial pulse, inasmuch as in a normal state, each systole of the ventricles is followed by a corresponding pulse at the wrist. And such in most instances is found to be the case. Each systole of the left ventricle, however irregular in point of time and force, is ordinarily followed by a precisely similar irregularity in the arterial pulse. But cases are met with occasionally in which this correspondence between the ventricular systole and the arterial pulse altogether fails ; two complete actions of the heart, two ventricular systoles, giving rise to only one radial pulse.* This occurs as well when the rhythm of the heart is regular as well as when it is irregular, and is due to the fact that one of the two systoles of the ventricles is too feeble to cause pulsation in the radial artery.

Extreme irregularity both in the rhythm and intensity of the sounds of the heart is observed in many forms of cardiac disease, and also in persons who are in apparently good health, and in whom physical examination of the heart during life, and inspection of its structure after death fails to discover organic disease. Nay more, there are so many persons who have had an extremely irregular or intermittent pulse for years without perceiving the slightest indications of ill health, that experience compels us to doubt whether much practical significance can be attached to it. My own impression is that in many instances it is more closely connected with perverted innervation of the heart than with organic disease of its valves or muscular structure, and that in such cases life is not seriously compromised by its existence. When it does occur in a marked degree in connection with disease of the heart, the conditions which are ordinarily found to be present, are, fatty degeneration and softening of the tissue of the heart, constriction of the mitral orifice, and mitral regurgitation, rupture, or acute ulceration of a valve, or of the chordæ tendineæ, or the presence of fibrinous coagula in the cavities of the heart. It may occur, however, in any form of cardiac disease, just as it may, apparently, in cases unconnected with structural alteration.

* A case of this kind, in the person of a young woman named Cross, aged thirtysix, is at present (December 11th, 1861,) under my care in the Roseberry Ward of St. George's Hospital. The least exertion or mental excitement will rouse her heart's action sufficiently to make each systole felt at the wrist. The most remarkable instance I ever met with was one which I saw in consultation with Dr. C. J. B. Wil. liams and Mr. Gardner, of Gloucester Terrace. In that case probably one of fatty degeneration of the muscles, though we were not permitted to verify the fact after death-the pulse for nearly three weeks varied between 28 and 34, whilst the heart was heard contracting between 60 and 70 times in the minute. Occasionally there was only one pulse of the radial artery to three contractions of the ventricle.

But auscultation informs us of other changes in the sounds accompanying the action of the heart, besides those connected with their intensity, pitch, duration, and rhythm ; it makes us aware of adventitious sounds, which are superadded to, or entirely replace the ordinary sounds. These sounds are termed murmurs, and may arise either within the heart and great vessels, or external to them.

Those which arise within the heart are termed endocardial murmurs, the seat of their production being the cavities of the heart, or the commencement of the great vessels, whilst those which originate from mischief external to the heart itself, are termed exocardial or pericardial murmurs, the seat of their production being the pericardium, the external covering of the heart. The former invariably result from an eddy in the current of the blood capable of producing sonorous vibrations ; the latter from the attrition of the two roughened surfaces of the pericardial membrane.

Endocardial murmurs are always of a more or less “ blowing ” character; but their quality may be simply blowing, or it may be rasping, grating, purring, whistling, or cooing, and in some instances distinctly musical. Practically, however, the precise quality of the murmur is of little importance, for the same cardiac lesion may give rise to murmurs of different qualities, according to the condition of the blood, the force of the heart's action and other modifying influences. A murmur which is loud and rasping when the heart is acting violently, may be soft and simply blowing, or may even disappear when the heart acts gently. Their pitch varies greatly, for whilst, as pointed out by Dr. Hope, the lowest pitch murmurs may be aptly represented by the word “who,” pronounced in a whisper, the highest may be more nearly imitated by the letters S S pronounced in the same manner. They also vary much in their apparent distance from the surface, and likewise in their force and duration, being at one time loud and prolonged, at another weak, and of shorter duration. They vary also in the period at which they occur in relation to the sounds of the heart. Thus a murmur may be synchronous with one of the sounds of the heart, and

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