PLEURISY. 87 



out by Dr. Stokes ; a copious effusion on one side will displace the 

 sternal mediastinum, and render the whole sternum dull on percus- 

 sion. A hepatized lung, on the other hand, will not encroach on 

 the mediastinum, but, lying under one half of the sternum, will 

 render that half dull, whilst the other half will remain resonant as 

 usual. 



The absorption of the fluid is indicated by the gradual return of 

 the respiratory murmur : first, in those points where it had persisted 

 latest; afterwards in others; and last of all in the parts where the 

 accumulation had begun. It is very faint at first, and becomes 

 stronger in time; but, generally, a very long period is required to 

 bring it on a par with that of the healthy side. In other instances, 

 however, the absorption is nearly as rapid as the effusion, and in 

 these cases a returning asgophony {agophonia reclux) also announces 

 the diminution. As the absorption proceeds, there is sometimes 

 heard a sound of friction, like that which accompanies the dry stage 

 of pleurisy. This is produced by the approximation and habitual 

 friction of the pleurae, the surfaces of which are covered with false 

 membranes. 



In double pleuritis, where both sides are simultaneously affected, 

 the indications given by percussion are less certain ; for both sides 

 sounding equally bad, the standard of comparison is lost. The upper 

 parts of the chest, however, remaining sonorous, with the exact de- 

 marcation between these and the line of effusion, will still charac- 

 terize the disease. 



CojnpUcations. — Acute pleurisy may be complicated with pneu- 

 monia, bronchitis, pericarditis, pneumo-thorax, or peritonitis. 



When pleuritis is not very acute, and the effusion is not extensive, 

 it may be mistaken for phthisis, debility, remittent fever, liver 

 disease, &c. 



Morbid appearances. — The pleura, when attacked, presents — 1st, 

 alterations of tissue ; 2d, alterations of secretion. 



1st. Alterations of tissue. — When a person labouring unde^ a 

 slight pleuritis, dies of another disease, the pleura will be found to 

 be red to a greater or less extent ; but a careful examination soon 

 shows that this redness is solely owing to the greater or less injec- 

 tion of the vessels which pass through the sub-serous cellular tissue ; 

 the membrane itself has retained its transparence, and no red vessel 

 ramifies through it. Should the inflammation be more intense, the 

 serous membrane itself then presents vessels, in greater or less 

 number, filled with blood ; sometimes these vessels, not being very 

 numerous, leave large intervals between them, and they scarcely 

 disturb the transparency of the membrane ; sometimes their number 

 is greater, they become agglomerated, and anastomose in various 

 ways, so as to produce mere points, long streaks, large patches, and 

 finally, a uniform red tint, to a greater or lesser extent ; this last 



