But not unfrequently pneumonia of the upper lobe is only en grafted on previous tubercular deposit, and then the crepitation is coarser, the breathing less whiffing, the voice not so brassy ; the special signs and the general symptoms each approximate to those of pbthisis, of which we have yet to speak (§ 9). One source of fallacy is when loud blowing breathing is heard in an empty vomica, and crepitation exists in its immediate neighbor hood: but, if carefully examined, clicking or squeaking sounds will be found mingled with the crepitation, which is always coarse; the expiration is more blowing, and less whiffing ; the voice-sound is less brassy, and more shrill ; and careful percussion will detect a hollowness or wooden resonance over one particular point, which, under certain circumstances, presents what is called the cracked-pot sound : still more, these characters are strictly local, and limited to the immediate region of the cavity ; above, below, and on either side, are heard the sounds belonging to tubercular consolidation ; and, above all, the history and symptoms are of phthisis, not of pneumonia.
Pneumonia sometimes runs on to the formation of abscess. Apart from those cases which are due to secondary suppuration, this is a very rare event, and inasmuch as in its advanced stages the exudation becomes purulent, while the physical signs of complete consolidation around large tubes differ but little from those of a cavity, mistakes have often been made in the interpre tation of abundant purulent expectoration, with loud blowing breath-sound confined to some particular spot at the base of the lung. It is true that care ful auscultation would prove this to be more diffuse than cavernous breathing ought to be ; but this fact may be overlooked : another consideration, how ever, forces itself on our attention ; when pneumonia terminates in abscess, some portion of the lung structure becomes disorganized, and pus evacuated from an abscess of this sort has always a fetid odor, and it is not safe to diagnose abscess of the lung in such circumstances where this character is wanting. This rule does not apply to secondary deposits which precede the pneumonia, gradually enlarging as the inflammation goes on. Such cases are very commonly called gangrene of the lung; but while there is undoubtedly destruction of some portion of the tissue, the primary cdndition is suppura tion, and they may be readily distinguished from true gangrene by the appear ance of the sputa: in the latter always brown or blackish, in the former chiefly purulent ; the odor in both is that of sphacelus, which impregnates the breath of the unfortunate patient, and is diffused throughout the apartment. Gan
grene is a much more fatal disease than fetid abscess, and is generally not im mediately related to pneumonia.
Chronic pneumonia seldom exists independent of tubercles ; sometimes in a ease of long standing, when the period of fever and rusty expectoration has gone by, we find evidence of consolidation, with coarse crepitation and moist sounds at the base of one lung. In the absence of the tubercular diathesis we may hope, and if the patient get thoroughly well, we may believe, that it is a case of chronic simple pneumonia ; but such are rare.
Cases sometimes present themselves in which we find evidence of a low form of pneumonia coexisting with some other disease, and we must be care ful that the diagnosis of pneumonia, however clearly made out, does not cause us to overlook the complication. Fever, for example, often presents such a combination, when it may require very nice diagnosis to say in how far the fever arises from the pneumonia, or the pneumonia from the fever. This is not merely an idle speculation, because important practical results in regard to treatment depend upon the decision. When properly considered, the tres,tment of one or other disease will not be blindly followed ; but the educated practitioner will ever bear in mind the two very opposite diseases he has to treat together, and modify his remedies to meet the exigencies of the case—especially when an acute inflammatory disease supervenes on a chronic exhausting one. The combination with pleurisy will be subsequently referred to ; its chief importance with regard to diagnosis comes from the manner in which it modifies the auscultatory phenomena ; to its presence we must no doubt ascribe the circumstance, that sometimes the Bound of crepi tation, heard early in the disease, ceases, and instead of being replaced by blowing breathing, and other phenomena of advanced consolidation, the breath sound itself becomes inaudible ; it seems impossible that fibrinous deposit beginning near the surface should of itself cause a stagnation of the air in the large tubes, which can never be closed by.such means ; neither is there any reason why the sound of its necessary movement should not be transmit ted to the ear, unless the lung be pushed aside by fluid. The condition already referred to, in which the presence of vesicular breathing at the surface prevents our hearing the blowing sound of deepaeated pneumonia is of quite a different nature.