As the rationale of these rules, the following considerations may be sug gested. Bruits are all heard more loudly over an interspace than over the rib immediately above or below : the third interspace on the left side is that in which the sound actually produced at the valve is beat heard ; and for all practical purposes we may for the present disregard disease of the pulmonic valves altogether, and assume that the question lies between disease of the aortic valves and anemia. True valvular sound is therefore necessarily heard best, unless the heart be much enlarged upwards, in the third interspace ; and it may possibly not be propagated to any distance beyond, but heard there only : if, on the other hand, any anaemia be present as well as disease of the valve, the sound will be propagated along the aorta, not along the pulmonary artery ; and therefore it will be relatively loudest on the right side above the third rib, though not so loud there as where it is actually produced. The case of a simple anemic bruit is quite different : there is no distinct point in the course of its passage through the heart where the blood is thrown into vibration, but wherever vibration occurs, the sound is produced : practically the pulmonary artery is most superficial, and therefore, though it can be heard in the aorta, the bruit is relatively louder in the pulmonary artery, and consequently at that interspace where in very thin persons this artery may be often felt pulsating ; the second on the left side.
In consequence of the statement here made, it will be seen that proof of the actual existence of anaemia, whiffing sounds in the arteries, "bruit de diable" in the jugular veins, &c., although it throw some doubt over the probability of true valvular murmur, must not be assumed to disprove it altogether. It is probable that when a valvular brait is distinctly propagated along the artery, there is almost always some degree of menus to account for it ; and that the really valuable indication is that there is a point at which the vibra tion commences, while its propagation along one vessel or the other is of minor importance ; because, although it be true that a pulmonic valve murmur is exceedingly rare, the principles of diagnosis must recognize its possibility, and endeavor to prove its presence or absence. Such a murmur is very likely to be propagated along the pulmonary artery; and here, again, the only valu able indication would be the existence of a point somewhere below the third rib, probably very close to or under the sternum, from whence the vibration commences. If any one will take the trouble to listen to the sound heard in
the carotid arteries in a few instances of acknowledged disease of the aortic valves, he will very quickly find that thepropagation of the bruit depends on something else than the diseased valve which produces it, as the intensity of the bruit in the one situation bears no constant relation to its loudness in the other. This subject has been mentioned at some length, because the direction which the sound takes is often alluded to as the great indication in diagnosis.
An inquiry into the means of distinguishing between a blood sound and a valvular murmur is necessarily somewhat compli cated ; and yet it may become of very considerable importance when, for example, in watching a case of acute rheumatism, we have to determine whether a bruit of some sort indicate the super vention and endocarditis. The rules which may be laid down as the most valuable for the &Mance of the student in such a case are the following.: 1. To observe the point of its greatest intensity with reference to the three principal positions referred to, (a) the apex, (b) the base at the third left interspace, (c) above the base at the second left interspace. 2. To ascertain in how far at the points (a) and (b) it is capable of distinct localization. 8. If its character be, on the contrary, at all diffuse, to observe whether it can be traced towards or across the sternum or towards the shoulder. 4. To watch, from day to day, whether there be any variation in intensity at different points.
In addition to these considerations, account must be taken of the past history of the case, as it may show the possibility of pre vious disease ; as well as of the present condition of the circula tion, as it may indicate such an amount of excitement as must of necessity exist when endocardial inflammation is going on, or such a state of quiescence as is incompatible with it. Nor is it to be forgotten that bruit is produced in many cases of thoracic aneu rism, and that these have to be separated by their position before the sound is taken as an indication of disease of the valves.