PLEURO-PNEUMONIA. 167 



microscopically, cellular elements, partaking of the nature of 

 pus cells and white blood globules, are seen imbedded in the 

 fibrin, which is sometimes granular, but often filamentous. The 

 turbidity of the serum is caused by these globules and some 

 amount of fatty matter. 



The tissue connecting the pleura to the thoracic walls is but 

 slightly involved, and when removed after slaughter, the under- 

 lying structures seem healthy, but a careful examination of the 

 part will show the ribs to be bare, stripped of their pleural 

 covering, and to have an unnaturally clean whitish appearance, 

 and the intercostal flesh, in advanced cases, unhealthy, moist, or 

 even dropsical. The pericardium is also covered with flakes of 

 lymph, and greatly thickened by exudative materials. 



It has been considered that the primary seat of the disease 

 is situated in the pleura ; that the inflammation is of a rapidly 

 spreading character, causing the formation of what have been 

 termed by Eokitansky "the croupy exudates," both upon the 

 surface of the serous membrane and in the substance of the 

 lungs. As a rule the inflammation in pleuro-pneumonia con- 

 tagiosa is more pronounced in the parenchyma than upon the 

 pleural surface; but this is liable to exceptions, for in some 

 cases the pleural disease is more marked than the parenchy- 

 matous. Some writers think that the disease may begin in the 

 bronchi and air cells, and that the irritation extends from the 

 tubes and cells into the parenchyma and pleura. Their con- 

 clusions are based upon the fact that inflammatory products are 

 generally found, in the advanced stages of the disease, in the 

 air vesicles, blood-vessels, and bronchi, as well as in the other 

 portions of the inflamed part. 



Dr. Yeo, in an elaborate report published in the Veterinary 

 Journal and other periodicals, concludes that the disease origi- 

 nates in the bronchial tubes, and that the surrounding tissue 

 is in a state of chronic inflammation for a lengthened period 

 before any symptoms are manifested. He says — " I am con- 

 vinced that the lung disease usually exists for months without 

 being suspected, and invariably the beast is first thought to be 

 sick only when the affection has spread to the pleura, and 

 caused intense inflammation of that membrane with its accom- 

 panying well-marked symptoms." 



