These circumstances have been gone into with some minuteness because the cases are very apt to be misunderstood ; the moist sounds passing from fine to coarse, as we descend, is just what we expect to meet with in bronchitis, and the mind is very readily satisfied with the explanation of all the constitu tional symptoms which this disease in its chronic form affords, when it is very apt to simulate phthisis; the important point is overlooked that phthisis may simulate bronchitis: to guard against such an error demands close scrutiny and careful reasoning, for it must be remembered that the prognosis in the two disorders is widely different.
D. The difference on percussion may be unobserved because of the thickness of the walls of the chest.
a. Commencing pneumonia in one lung may be indicated by fine crepitation with'exaggeration of voice, or there may be only a few moist sounds from irritation of the bronchial tubes, or even this may be wanting, and nothing but exaggeration of the voice be found; these differences merely depending upon the distance from the surface at which the fibrinous effusion is taking place, the overlying lung tissue being resonant and but little implicated in the disease. Vocal resonance, therefore, taken along with general symptoms, occasionally becomes a valuable distinguishing sign between pneumonia, and bronchitis of one lung, which no doubt has been often mistaken for it. Friction in the very early stage of pleurisy, before dulness can be detected, sometimes indi cates the form which the inflammation is about to take, for un doubtedly the constitutional symptoms are very often pronounced before the physical signs give us any very definite information.
b. Dulness at the apex posteriorly is very apt to be overlooked. The restriction of moist sounds to the apex is a very important sign, because of the natural tendency of the fluid in the bronchial tubes to gravitate to the base of the lungs. All the superadded sounds mentioned, as occasionally heard in the clavicular region, when dulness is only slightly marked (Div. I., § 3), may be found over the scapula when no difference on percussion can be detected there; and in the supra-spinal fossa the crumpling sound is more frequently met with than anywhere else.
c. When the ordinary signs of bronchitis prevail throughout one lung, and are limited to the upper part of the other, we have great reason to suspect that the disease has a tubercular origin, even when we cannot make out any sign of consolidation at all.
In proportion as the thickness of the walls of the chest interferes with the evidences of change of structure derived from alterations in breath and voice sounds and percussion resonance, so do the superadded sounds acquire import ance. The cases included under 1 are therefore less dependent for their
diagnosis on the latter characteristics than those in which the percussion sound is less distinct; but they may be of some use, as when, for example, with disease of the kidney, we are anxious to know whether effusion into the pleura be merely passive, or the result of intercurrent pleurisy ; the existence of friction would prove the presence of lymph. Still the right discrimination of all the cases mentioned in this section depends more upon the correct in terpretation of other signs : whiffing breath-sound, for instance, is much more valuable tharf crepitation.
In 2 we meet with two very important sounds—succession and metallic tinkling. The first of these cannot exist under any other circumstances than when air and fluid are present together in the pleura ; the second, although liable to be mistaken for other sounds, is also, when pure, very distinct evi dence of the same fact. But we must be able to assert the existence of pneumothorax when neither are heard, and we know that the effusion of fluid is a necessary consequence of the presence of air. It is unnecessary to ex plain why these sounds are sometimes absent ; it is enough to be prepared for such an occurrence. It has happened to careless observers to mistake the gurgling sounds in the stomach for succession; and by the best authorities the name of metallic tinkling is used when there is no pneumothorax : it is well to remember that the sound is merely that of fluid dropping in a par tially filled cavity of some size, whether that be in the lung or in the pleura. There is not any chance of a careful observer • mistaking emphysema for pneumothorax.
The coincidence of fine crepitation with the other signs of pneumonia, as mentioned in 3, gives great certainty to the diagnosis; but this sign has been more than once alluded to as a very common source of fallacy. Cases of tuberculosis in which crepitation at the back of the chest is very distinct are rare; but they are to be borne in mind, especially when the history does not correspond with the suggestion which this sound gives of the existence of pneumonia. Tubercular deposit limited to the base, or more advanced there than at the apex, is that condition which causes the greatest difficulty in diagnosis with reference t,o the posterior region : such cases may be mis taken for pneumonia, but are more commonly confounded with bronchitis, se explained in 4.