Percussion resonance and changes in the breath and voice sounds serve to point out the greater or less relative density of the contents of the chest; and it is very important for the student to learn to reason logically upon the indications thus presented to him. We have therefore kept out of view for the present all the additional information which superadded sounds necessarily convey, because the first question to be solved, before assigning a cause for any such sound, is whether there be or be not any change of structure, any increase or diminution in the solids, the fluids, or the air of that part where the abnormal sound, whatso ever it may be, is heard. We find, then, that the lung itself may be either more or less dense, and the pleura may contain either fluid or air ; or we may have, for example, in advanced phthisis, dense lung surrounding a hollow cavity ; and in hydro-pneumo thorax both air and fluid in the pleura.
§ 1. Condensation presents itself in three forms: (1) carnifica tion, when, from mere pressure, the air is excluded from the vesi cles, and only permeates those larger tubes which are kept open by their own elasticity ; the most. prominent example of this class is the leathery lung of pleurisy with no accompanying pneumonia; an analOgous condition is found in some instances where the pressure is caused by a tumor, and we may regard in the same light the atelectasis of new-born children, the pressure in this case being simply atmospheric, the inspiratory act not having sufficient power to force the air into the minute tubes. (2) Hepa tiz.ation : the parenchyma of the lung is solidified by an effusion of coagulable lymph, which occludes the vesicles, but does not fill up any of the tubes; the only real representative of this form is pneumonia ; cedema, and engorgement of the lungs, which are both passive states, although increasing to a small extent the relative density of the tissue, do not produce the same occlusion of the vesicles, and do not give rise to similar auscultatory phe nomena; the condensation from these causes is rarely such as to produce .definite dulness on percussion. (3) Tuberculization, which is seen under very different aspects, either as minute de posits separated by certain intervals, and in so far obstructing either vesicles alone, or vesicles and tubes together ; or as aggre gated into masses, some of which have been expelled and have left hollow spaces remaining; or, again, what is very rare, as a uniformly diffused deposit, closely analogous to that of coagulable lymph. Percussion resonance can only show that the condensed lung is more solid than its fellow, and may give a rough estimate of the extent to which air is excluded ; but it is quite a mistake to suppose that it can ever discriminate the cause of its exclusion: auscultation reveals more definitely the extent to which the air penetrates the lung, and also teaches us how far the tissue is changed as a medium for the formation and transmission of sound.
In each of these forms of condensation, the proper vesicular murmur is wanting. In the first, the sounds are similar to those heard over a healthy trachea, but deadened by passing through the tough inelastic tissue placed between the large tubes and the ear; the inspiration and expiration are both loud and harsh, and the voice ringing; and these sounds are diffused over the whole space where the carnified lung exists, except where the voice is so modified by the presence of fluid in the pleura, as to acquire the quality which has been denominated a3gophony. In the
second, the breathing gives rise to a peculiar whiffing sound as it enters the small tubes, the aides of which have acquired hardness and increased vibratory power from the effusion of lymph around ; and it is readily transmitted to the ear through the dense elastic structure : the voice has at the same time a very loud, sonorous, and metallic or brassy sound, from the same circumstance.s, and is diffused over the whole hepatized portion of the lung. In the third, the characters vary very much, according to the amount and the state of the deposit : in the early stage, the breathing is heard in smaller tubes than in carnification, and does not produce in them the whiffing sound of hepatization ; the voice is not ring ing as in the one, nor metallic as in the other there is, indeed, a period in tubercular deposit in which moclifie'd vesicular 'breath ing 'is heard, while no marked change has passed on the voice at all ; proceeding further, the vesicular breathing is more or less suppressed, and the lung acquires greater power of transmitting sound, so that the breathing and the voice, which properly belong to the bronchial tubes, are heard at the surface, and are, therefore, louder and harsher than in health : this gradually increases in intensity till the tubes are encroached upon, when the breath sound becomes more faint, and, their elasticity being lost, the ex• piration is prolonged ; at the same time, consolidation has pro ceeded to a greater extent, and the voice-sound is therefore louder; next, the foreign matter softens and is expelled, the air begins to vibrate in larger spaces, and the breath-sound becomes louder, harsher, and more blowing, till at length the large cavity, with unyielding walls, gives out a long, loud, blowing inspiratory and expiratory sound : at the same time the voice-sound attains such loudness a,nd distinctness that it seems as if it were produced at that very spot, and spoken up through the stethose,ope to the ear. As might be anticipated, in the rarer cases in which tubercle is deposited in the same way as lymph, the auscultatory phenomena are also analogoua In e,ach of these e,ases, diagnosis is aided by several other cir cumstances : in carnifie,ation, by evidence of the presence of fluid or air in the pleura or of some solid substance which has pressed on the lung and expelled the air from its vesicles ; in hepatization, by the lower and back parts being more commonly affected ; in tuberculization, by the upper lobe being first or most extensively diseased. The difficulties are chiefly connected with the revers ing of the ordinary rule regarding situation, and the combination of two conditions of condensation—carnification with hepatiza tion or with tubercles, tuberculization with hepatization, or even all three together. We have also to consider the condition of the opposite lung: when the breathing is much obstructed on one aide, it is usually exaggerated on the other—puerile as it is often miscalled--and if it be equable throughout, the disease is pro bably not tubercular : if the apex of the comparatively healthy side be affected, the opposite lung is almost certainly in a state of tuberculization ; if the sounds at its base be changed, the cause of disease in the other is probably inflammation.