There need be no practical difficulty in distinguishing this metallic clang from that produced by a similar cause on a much larger scale, viz., the pre once of air and fluid together in the pleura; the great and constant distinc tion is simply that in the one case, if we tarn to the back of the chest, we And the indications of lung tissue, however diseased, occupying its natural pod. Lion; in the other we have the tympanitic resonance produced by its absence; and if any breathing be heard, it is only a loud blowing sound resounding through the empty cavity, while at the base there is complete dulness, from the presence of fluid, and no breathing at all. In addition to this there are two minor sources of information ; the metallic sound'is seldom produced by dropping when heard in a cavity, but is more commonly the result of solitary bubbles of air passing through the fluid ; it therefore keeps time with the breathing—dropping does not ; the voice is less like that produced by speak ing into an empty jar, and seems rather to be spoken into the stethoscope.
The student must be reminded, too, of the possibility of a portion of air spontaneously developed, or admitted by paracentesis, rising to the apex when the lung is not shrunken as it is in true pneumothorax, and when there is no communication between the bronchi and the pleura. He has only to think of the fact that, if there be at the apex a cavity capable of causing tympanitio resonance, there must be blowing breath-sound and loud voice ; when there is air in the pleura just the opposite effect is produced, and both sounds are less loud than on the opposite aide.
Another general pathological fact may be turned to account in diagnosis—viz., that if tubercles be at all advanced in one lung, they are almost certain to exist in minor degree in the other; and when their presence is equally distinct in both lungs, they are still seldom found in exactly the same stage, or giving rise to the same modifications of sound. This is especially to be borne in mind when any one auscultatory phenomenon stands alone at either apex in a very marked degree, which would indicate an advanced stage of the disease, if it were found in conjunction with other corresponding signs and symptoms : alone, we must be content to regard it as an anomaly to be hereafter cleared up as the disease proceeds ; but we may consider the possibility of morbid growth—such, for instance, as enoephaloid disease dis seminated at the apex. (See § 10.) Tubercular disease is sometimes found solely or chiefly at the base of the lung : such cases are very apt to be misunderstood simply from the fact that they are so rare. When dulness on percussion is perceptible, and the morbid sounds are limited to one side of the chest, the phenomena may be caused either by chronic pneumonia, or by old thickening of the pleura with bron chitis confined to that lung. Gurgling or clinking sounds, showing that softening was going on and cavities were forming, would negative both of these hypotheses, because abscess without tuber cle is attended with fetor : more reliance, however, is to be placed on the history of the case; long duration, gradual progress, and the absence of any distinct acute attack, all point more directly to tubercle, and when found in conjunction with general symptoms of phthisis, must be held, if not as conclusive, yet as affording grounds for very grave suspicion. In other instances phthisis of
this particular form closely simulates bronchitis : and this is thd more common case, because the difference onnation, when both lungs are more or less affected, is not readily madeout, and these is, in truth, some amount of coincident bronchitis caused by the tubercular deposit. This subject has been already fully considered, and it is one which requires very nice discrimination. (See Chap. XIX., Div. II. § 4, D.) The existence of htemoptysis, beyond what mere straining might cause, of emaciation, quick pulse, thin skin, clubbed nails, or any of the more important symptoms of phthisis, ought to put us on our guard against pro nouncing too favorable a diagnosis in such cases.
It is a less rare occurrence to meet with tubercles equally dis seminated through the lung : such cases are almost always recent, and this fact alone tends greatly to embarrass the diagnosis. Still the history wants something of the severity of an acute attack ; it is insidious ; there is not immediate prostration but gradual decline : there is often htemoptysis ; the febrile symptoms are commonly of mild character, but the pulse is quicker than the other symptoms would lead us to expect ; emaciation cannot have proceeded far, nor can there be hectic fever till softening have commenced ; commonly there is a general blue discoloration of the face, which most nearly resembles that seen in severe bron chitis it differs from the dusky flush of pneumonia, as well as from ihe blueness of diseased heart, and the dirty hue of emphy sema; it is rather a flush or suffusion of face which, if the lungs were healthy, would be florid, and is dark-colored only because the vesicles are obstructed. The physical signs at first resemble pneumonia, but of such an extensive character that they cannot possibly be caused by acute inflammation when the general symp toms are so moderate : indeed, the sounds, when more carefully studied are not exactly those of pneumonia; the crepitation is coarser and more disseminated, the breathing and vocal resonance are both free from any brassy tone, all the phenomena are more distinct at the upper part, and, unlike pneumonia, they are not strictly confined to one lobe, but gradually decrease towards the base of the lung ; the expiration is simply harsh and prolonged, and the voice exaggerated. At a later stage the signs resemble those of bronchitis, but the 'moist sounds are fewer and more squeaking with proldnged expiration, especially at the apex, which is not the case in bronchitis. If one lung present such signs of disease, while in the other consolidation is commencing at the apex, most unquestionably the whole is due to tubercular deposit.