4.2 EQUINE PLEURO-PNEUMONIA 



which are distinctly defined from the neighboring tissues are 

 scattered through the hepatized areas and appear on the sur- 

 face of sections of the hepatized parts. Usually, several of these 

 foci are present. They vary in size from a millimeter to 20 or 

 more centimeters in diameter. In recent lesions, these areas 

 are very small, of a greyish- red color and surrounded by a 

 grayish zone consisting of leucocytes (limited reactionary in- 

 flammation). In more advanced lesions, they become yellow- 

 ish, necrotic and finally cavities varying from the size of a pea 

 to that of a hen's egg. These cavities are surrounded by a 

 smooth capsule. There are other foci which contain greasy, 

 foetid, watery pus (gangrene of the lungs), by reason of the 

 necrotic parts of the lung undergoing liquefaction in conse- 

 quence, it is stated, of the admittance of air. The lungs often 

 contain suppurating foci composed of a whitish pus mixed 

 with necrotic lung tissue. It sometimes happens that the foci 

 just described are absent in the lungs, although during life 

 distinct symptoms of such a localized affection may have been 

 present. In these cases, it is assumed that absorption of the 

 necrotic tissue has taken place. The remaining tissue of the 

 lungs is, more or less, hyperaemic and oedematous. 



The pleurae show signs of a diffuse, exudative pleuritis, 

 the starting point of which in the large majority of cases, is 

 from necrotic deposits which are situated in the periphery of 

 the lungs. Pleuritis may occur, however, apparently as a 

 primary lesion without the necrotic foci being present. The 

 contents of a necrotic deposit in the lungs rarely breaks 

 through into the pleural cavity. In some cases, the visceral 

 and costal layers of the pleura are congested, diffusely or in 

 spots, and are sprinkled with haemorrhages. Frequentl}' the 

 pleurae are covered with soft red granulations covered with 

 soft, yellowish layers of exudate which are partly membranous 

 and partly coagulated in a reticular manner, and which can usu- 

 ally be easily removed. The pleural cavities generally contain 

 a considerable quantity of fluid. Dieckerholf states that from 

 30-40 liters of a serous fluid are occasionally present. The 

 exudate is usually turbid and of an orange, greyish-red, brown- 

 ish-red, or dirty-greyish color. It is generally mixed with nu- 



