INFLAMMATION OF THE PLEURA. 277 



reach the thoracic wall under any circumstances, we lack an important 

 aid to the diagnosis of pleuritic effusion. 



Finally, palpation is of use in ascertaining the existence of the 

 displacements of the neart and liver, alluded to in speaking of inspec- 

 tion, and which result from the effusion and its subsequent reabsorp- 

 tion. In cases of copious exudation into the right pleura, the edge of 

 the liver may often be felt several fingers' breadth below the border 

 of the ribs, or even lower. 



Percussion affords no information of the presence of exudation 

 when it is scanty and lies upon the pleura in the form of a thin, coagu- 

 lated coating. On the other hand, large effusions, by which a consid- 

 erable part of the lung is separated from the diaphragm and thoracic 

 wall, furnish very characteristic signs upon percussion : 1. Over the 

 /egion where the bulk of the liquid effusion lies in contact with the 

 side of the chest, all vibration is checked, and the percussion-sound 

 is dull. 2. Over the space where the retracted lung (which, how- 

 ever, may still contain air) touches the thoracic wall, percussion is 

 hollow and tympanitic. The conditions under which the dull, hollow, 

 and tympanitic sounds arise have already been fully and repeatedly 

 explained. No disease is better adapted for the demonstration of the 

 difference between the dull and the hollow percussion-sounds than 

 pleurisy with copious effusion. The dulness proceeding from pleuritic 

 effusion generally first becomes perceptible in the region of the back 

 and below the scapulae. As it ascends it spreads toward the front. 

 The dulness scarcely ever extends as far upward in front as it does 

 behind. In many cases the dulness which reaches far up the back is 

 not found at all over the breast, but only reaches as far as the axillary 

 line. At other times, when nearly the whole pleural sac is occupied 

 by the effusion, the upper boundary of the dull sound is but little 

 lower in front than behind. Anteriorly, the dull percussion-sound 

 changes abruptly to the empty tympanitic sound ; posteriorly, as the 

 upper limit of the effusion is approached, the dulness gradually be- 

 comes fainter and less distinct. The reason for this is, that the 

 thickness of the body of effusion upon which the dull sound depends 

 gradually diminishes from below upward. The form and boundaries 

 of the dulness are not generally altered by changing the attitude of 

 the patient, as agglutination and adhesions soon form about the effu- 

 sion, which, although they still allow the pleural surfaces to slide upon 

 each other, oppose their separation by the pressure of the exudation. 8 



Upon auscultation, friction-sounds are heard whenever the sur- 

 faces of the pleura lose then- smoothness through fibrinous deposit 01 

 the growth of rugged vegetations ; but of course these sounds are 

 only audible when the roughened surfaces are in contact, and when 



