532 PLEURISY. 



abates, and a partial removal of fluid takes place. In many 

 instances, with the continuance of the morbid process in 

 intensity, or even from a comparatively early stage, the same 

 result, the prevention of adhesive action, occurs by the forma- 

 tion and presence of pus, the condition known as empysema. 



The period which may be expected to intervene between the 

 first step of the morbid action and the appearance of the 

 diseased products, eflused fluid and the formation of false 

 membranes, it is important to know has to some extent been 

 de'termined by actual experiment. However, it is always good 

 to remember that a certain amount of variation may exist as 

 respects the course and completion of morbid processes induced 

 experimentally, and such as may be developed without direct 

 or mechanical interference. 



From what is learned from symj)toms exhibited during life, 

 and comparing these with appearances observed after death, it 

 would seem tolerably certain that vascular engorgement, with 

 effusion of serous fluid, may be expected within a few hours 

 after the onset of the pleuritis. While there is a certainty, 

 from experiments which have been performed by inducing 

 artificial inflammation of the pleura, that exudation of fibrinous 

 material — false membranes — are developed in a certain foi-m 

 in twenty -four hours. 



At first soft, granular, amorphous, and very friable, these 

 pleuritic exudations or membranes steadily undergo change, 

 until at the end of the first week they may show vascularity, 

 and a steady and gradual solidification or toughening of 

 their texture, and greater closeness of theu- attachment to the 

 investing serous membrane. While, as they become supphed 

 with bloodvessels — whatever way these are produced — we have 

 from these a further and fresh exudation of fibrinous material, 

 giving to the entire exudate a stratified character and appear- 

 ance. 



The liquid material found in the pleural sac, as the result 

 of the inflammatory action, is as invariably a sequence of the 

 diseased process as the existence of the solid exudate, the false 

 membrane. 



Chemicall}^ it may be said to consist of the same materials 

 as blood, although the relative proportion of these seems to 

 vary according to the age or stage of the process at which it 



