178 Report on the Pathological Anatomy of Pleuro-pneumonia. 
Pleural Lesion. — The changes in the pleura show the ordinary 
signs of pleurisy of rather acute type, in some one or other of 
its many phases. There is nothing definitively characteristic 
in the anatomical changes in the pleural cavity to distinguish 
this from the other forms of pleural inflammation, from what- 
ever cause they may arise. The only point of peculiarity Avhich 
seems constant in this disease of the pleura is its tendency to 
remain localised, although the inflammation is intense. In acute 
pleuritis, the inflammation is usually diffused very evenly over 
the entire organ, but here are found very different degrees of 
pathological change in different parts of the same pleura, the 
inflammatory action being always more intensely marked in 
some one part than over the general surface of the lung. This 
focus of greatest intensity is usually well seen even in old cases, 
for at this point the pleura is found to be covered with dense 
fibrinous exudation, the deeper layers of which are often stained 
with blood. This is invariably found to cover the point where 
the lung lesion is most advanced in its development. As the 
disease spreads, the contiguous lobes become firmly cemented 
together by the adhesion of their pleural surfaces. Adhesions 
may also occur between the visceral and parietal layers of the 
pleura, but it is more common to find them widely separated by 
a quantity of fluid effusion. The amount of disease found on 
the parietal pleura is, commonly, strikingly slight, when com- 
pared to that of the pleura covering the lung. 
Every variety of exudation may occur, and often a number of 
different kinds are met with in the same pleural cavity. Most 
commonly the surface of some one part is coated over with soft, 
spongy, friable, or semi-gelatinous material, while in other parts 
the pleura may only be thickened or opaque. Now and then 
dense fibrinous masses may cause firm adhesions ; but the animals 
are seldom allowed to live long enough for that to take place. 
The effusion contained in the cavity of the pleura is generally 
a thin yellowish, or greenish, whey-like fluid, containing floc- 
culent masses or shreds of fibrinous material. It forms a soft 
coagulum soon after removal. Sometimes it is quite clear, but 
more commonly it is turbid or opalescent. I have not met with 
a case where the pleural cavity contained pus. The amount of 
the fluid is sometimes very great, filling the greater part of the 
chest, compressing the lung and displacing the neighbouring 
viscera. I have seen quarts escape when the breast-bone was 
split, and on looking into the chest it still appeared to be quite 
full of fluid. 
When the anterior lobes are the seat of the disease and the 
pleura covering them is intensely affected, the neighbouring 
pericardium is often inflamed, its fibrous layer thickened, and 
