The most important of the modifications just enumerated is that in which the rhythm of the sounds materially deviates from that in health. The relative duration of each sound and of each pause is in the normal state so constant, that it may be assumed with great confidence that disease is present when this relation is broken through. It is therefore of very great value in leading us either to discover past changes in structure, of which the evidence is imper fect, or to prepare for impending inflammation : it may thus lead to the dis covery of an endocardial murmur which was not suspected, or may be the only proof left that pericarditis has preceded when friction is already abolished; while in cases of acute rheumatism, or inflammation in the chest, it prepares us for an attack of peri- or endocarditis : and in those cases in which it passes off without any further evidence of disease, we are left to conclude that our remedies have aided in warding off very serious mischief.
The loudness of the sounds depends so much more upon the proximity of the heart to the chest-wall than upon the intensity of the sound itself, that but little reliance is to be placed on it as an indication : and perhaps in no case is it so marked as in the palpitation of nervous excitement. The very same circumstance which most frequently serves to conceal the dulness, and increased impulse in hypertrophy, serves also to diminish the loudness of the sound ; and therefore, when much overlapped by the lung, the one source of information does not help to correct the other. Its intensity is of most ser vice in cases of nervous palpitation, and in thinning of the walls of the heart without palpitation; in the one the shrillness of the sound is opposed to the idea of hypertrophy, in the other it leads to the suspicion of change of struc ture, which is not revealed by any other sign.
Reduplication, like intermission, suggests some imperfection in the relation of nervous force and muscular contraction, in so far as one serves to regulate the other; but while we are able to draw a distinction between intermisvion and irregularity, as indications of disease, we are not able to lay down the same certain rules in reduplication. We may be very confident that when both sounds are reduplicated there is some form of disease present: redupli cation of the second sound is very often caused by imperfect closure of the anriculo-ventricular aperture on one side, which causes the systole of one ventricle to terminate more quickly than the other ; but it is also beard, like intermission, in what we call mere functional disturbance. It will be readily understood that when either sound becomes prolonged by the presence of a murmur, the reduplication is lost in the continuous bruit. It is wise in prac
tice to restrict the t,erm reduplication to cases in which no bruit is detected ; for example, when there is a slight diastolic aortic murmur, the second sound of the heart, formed at the pulmonic valves, may be heard quite distinct and separate from the aortic bruit, which replaces the second sound there; but the two do not consist of a reduplicated second sound, but of the sound and the bruit, which are heard separately, the one short and terminating at its usual time, the other prolonged.
§ 2. Friction.—The distinctive character of this sound is to be sought less in its peculiar acoustic properties than in the time of its occurrence with reference to the natural sounds of the heart. It has no further relation to them than that it is caused by the movement of the organ consequent on its alternate contraction and dilatation ; hence it forms no part of the natural sounds, does not occur at the same instant, does not follow the same rhythm, but is usually heard somewhere between and distinct from them. The natural sounds may be inaudible either because effusion renders them indistinct, or because the friction is so loud as to overpower them, but it neither takes their place nor alters their character. Though called a " to-and-fro" sound, it is not neces sarily double, but it certainly is so in a great majority of cases. Among its distinguishing features the following may be regarded as the chief:— a. It may be heard anywhere over the primordial space, and frequently only at one point distinctly : when thus circumscribed it is especially to be sought either where the membrane is reflected at the base of the heart, or where the apex impinges against the ribs.
b. The sound is usually rough and grating, and seems to be superficial and close to the ear of the listener.
c. A double friction-sound is more easily recognized than when it is single ; endocardial bruits are also sometimes double, but in the to-and-fro friction the duration of each is more equal, and shorter.
The time of its occurrence with reference to the natural sounds forms our best guide in determining its nature. It com mences distinctly after the 1st sound and impulse of the heart; the to and the frofriction bruits follow each other rapidly, with a very short interval, which corresponds with the beginning of the 2d sound of the heart; then comes a longer pause, during which the first sound is again heard, followed up by the recurrence of friction.