The pleura and the subjacent lung, being so closely connected, are very often simultaneously attacked by inflammation ; perhaps the exposure to cold, which causes the pleurisy, at the same time gives rise to pneumonia, or to bronchitis. In the latter case the superadded sounds due to bronchial secretion accompany the changes in breath-sound more properly belonging to pleurisy : in other respects the physical signs are the same. But it is different with pneumonia : here the consolidation of the lung prevents its yielding so much to compression, and the fluid rises all around the upper lobe, which is not inflamed, yields to compression, and the evidences of pneumonia are confined to the central re gions of the chest; necessarily modified by a stratum of fluid being interposed and giving rise to unusual dulness. While this dulness indicates pretty plainly the presence of fluid, the observer is sur prised by the sound of breathing extending so far down, and for a moment doubts whether there can be effusion after all. In others of these complicated cases the signs of pneumonia may have been detected early, but the consolidation may not have proceeded far, or may have been limited to the outer part of the lung, which is then pushed so far away from the side of the chest by effusion, that the crepitation and blowing-sound cannot reach the ear, and the conclusion may be arrived at that very severe pneumonia exists when, in truth, it is very slight. In all of these cases we derive some instruction from the characters of the expectoration. Simple pleurisy shows nothing more than the ordinary secretion of mucus, which is brought up with difficulty or not at all ; more abundant expectoration indicates pretty surely the existence of some degree of bronchitis; rusty expectoration most certainly that of pneumonia.
It is well to limit the term hydrothorax to those cases of passive effusion in which the existence of fluid in the pleura is only one form of local dropsy; not fometting, however, that a low form of inflammation of serous membranes generally, is one of the most common occurrences in dropsy connected with Bright's disease. Such cases, besides presenting the ordinary evidence of fluid in the pleura, are marked by the comparative rarity of true legophony, and the constant presence of the moist sounds of bronchitis, or rather bron chorrcea, as the necessary result of an (edematous state of the lung. The amount of fluid is never extreme when there is no inflammation, and very commonly it is found in both pleura;, which is very uncommon in pleurisy.
By the general statement that dulness extends in greater or less intensity throughout the whole side of the chest in which pleurisy with effusion is pre sent, it is not meant to deny the existence of a sort of tympanitic sound at the apex, to which attention has been called by some auscultators. To my mind the name seems misapplied, and is apt to convey to students a wrong notion of what they are likely to hear. It somewhat approaches to the "cracked-pot" sound ; and it is important to remember that this kind of wooden hollow resonance may be heard when the only change in structure in the lung is condensation from the pressure of fluid below; it has been mis taken for the resonance of a cavity.
It may sometimes be of use to the student to observe whether the relations of dulness and want of breathing to the rest of the chest be at all altered by change of posture; the gravitation of the fluid, and floating of the lung upon its surface, bringing the breath-sound to a locality where before it was absent, would be strong confirmatory evidence of pleuritic effusion.
In the early stage obscurity is chiefly owing to the circumstances that there • is no change of structure, and that the only evidence which a physical exami nation can afford is suppression of breathing, from imperfect action of the lung : but this stage cannot last long; and pain of some days' standing, with out effusion of lymph or serum, cannot be pleurisy. In the more advanced stages, the difficulties are caused either by consolidation of lungatructure, preventing its being floated up by the liquid, or old adhesions fixing it firmly in its place. It is impossible to point out all the variations in auscultatory 'phenomena which the latter may produce; but the fact of a previous attack ought to have been ascertained in obtaining the history of the case, and the observer is thus prepared to look for unusual effects in making his examina tion. When the adhesions are very extensive, there is a permanent deficiency of resonance, which, though of no great amount in the majority of cases, may yet be perplexing, especially in children, where the panetes are thin, and changes of resonance consequently great.
The most important feature of passive effusion is that it has occurred dur ing the continuance of a disease which tends to cause dropsical accumula tions; and the that such is its true explanation, may be shown by the presence of anasarca in the lower limbs, or of disease of the heart or kid neys, even when there is no dropsy elsewhere. On the other hand, if hydro thorax be the first fact that is brought to our notice, its insidious progress, and the absence of pain or fever in the commencement, ought to lead us to look further into the case, in order to ascertain if there be any other condi tion of disease with which it may be associated. There is still greater reason for such a suspicion, if the effusion be on both sides. We also meet with other rarer causes of effusion, in pressure on, or occlusion of vessels; but in them hydrothorax is very subordinate.
Still more constant is the association of all other forms of disease of the chest with pleurisy; pneumonia is perhaps the most constant; then phthisis, which especially develops a local and asthenic pleurisy, without serious exuda tion; less frequently, bronchitis, which seems to be more distinct and inde- ' pendent, only acknowledging the same cause, and developed simultaneously.