In the early stage, excited action, altered rhythm, and creaking noise before friction is established, should prepare us for ita ap pearance, especially if pain occur in the course of rheumatism, pleurisy, or albummuria. In the latter disease, the plastic exuda tion is generally much less, the tendency to pour out fluid much greater.
In the course of pericarditis we must be prepared for the occur rence of pleurisy, and in inflammation of the pleura for its attack ing the pericardium. When the friction occurs in the immediate vicinity of the heart, it may be difficult to say by which mem brane the sound is produced ; because even when the breath is held, the impulse of the heart may cause pleuritic friction. Gene rally the diagnosis is not difficult, and, besides, it is not of very great importance.
The student must refer to the last chapter for the distinguishing characters of friction. His attention must, however, be especially called to two points in regard to the diagnosis of pericarditis. a. All double bruits are not friction. b. Friction may exist as a single sound. Independently of such considerations aa its loudness, distinctness, rubbing character, superficial position, &c., which can only be learnt by the habit of constant observation, and are never tho-. roughly trustworthy, the best and safest indication is to be obtained from comparing the rhythm of the sounds heard over the arch of the aorta, beyond the pericardial sac, with that of the bruit wherever heard most distinctly. An endocardial murmur when double, corresponds in time to the 1st and 2d sounds beard over the arch. while friction does not : a single murmur when anomalous in time is most likely to be rricardial ; if endocardial, it would correspond either to the systole or the diastole.
§ 2. Endocarditis.—The presence of an endocardial murmur is cot decisive of endocarditis ; for it may be of long standing, or it may be merely functional. Excitement of the heart's action, per sistent and not arising from some temporary cause, as well as febrile disturbance and cardiac anxiety, must be present to render the diagnosis certain ; indeed, in affection of the mitral valve, these symptoms may for some days precede the development of the murmur. And in old standing disease, where a murmur already exists, their occurrence may lead to a well-grounded suspicion of fresh inflammatory action and exudation, especially during the existence of rheumatism. Of murmurs developed
under observation, the most important is that indicative of mitral disease, and next, that already described as found at the base of the heart, of local character, and inclining towards the right side of the sternum. When general symptoms are wanting, and the heart is quiet, a systolic murmur at the base, diffuse in character or one heard best above the third rib, may be generally disre garded : in cases of doubt it is, however, safer to act on the suspi cion of endocarditis. Its incursion has been most frequently recognized whild watching the heart in cases of rheumatic fever, but its existence must not be supposed to be limited to that dis ease, and in a large number of instances I doubt not endocarditia has been assumed when, in fact, the valvular disease had been developed in a previous attack.
The murmur at the base, at first developed by the presence of a few adher ing vegetations, is of course very local, and indeed amounts to little more than a roughness of the let sound at the third interspace. The murmur at the apex, again, cannot be produced until the deposit is of considerable amount; for, as we have already seen, the contraction of the auricle has not sufficient force to develop a murmur during the ventricular diastole except in rare instances, while a systolic mitral murmur necessarily implies mitral insufficiency: it is consequently preceded by no changes, but appears suddenly, as soon as the lymph on the valves prevents their perfect adapts,. tion. In neither case, therefore, does the stethoscope afford us very sure means of diagnosis in the early stage of endocarditis : the modification of sound at the base is the earliest when the aortic valves suffer; but it is in some measure obscure and uncertain, from the possibility of blood-change in rheumatism, and practically the aortic valves are not involved so soon as the mitral. Hence it is important to view general symptoms, and to anticipate the appearanre of the physical signs, which come too late to be of much service.