Lung Plagtce of Cattle. 609 



with the rest of even the hepatized lung, it is almost as charac- 

 teristic as the marbling. The further progress of this necrosis is 

 varied. Most commonly the exudate surrounding the necrotic 

 mass becomes organized into white fibrous tissue and forms an 

 investing sac in the interior of which is the dead lung tissue, 

 showing for a time distinctly, the bronchia, blood vessels, lobu- 

 lettes, and interlobular tissue. This gradually becomes detached 

 and floating in a liquid debris, slowly undergoes solution, and is 

 absorbed, the sac meanwhile closing in on the cavity. A large 

 sequestrum may be a year or sixteen months in undergoing com- 

 plete solution. In other cases the pulmonary lobulettes undergo 

 an individual softening while the interlobular tissue becomes or- 

 ganized and when cut across, the lung presents a distinct honey- 

 combed appearance. In still other cases a considerable area of 

 both lobulettes and interlobular tissue is necrosed and liquefied, 

 while the exudate, around the bronchial tubes, that supplied it, 

 becomes organized, and on the necropsy the latter are found to 

 constitute a thick branching mass of a very characteristic appear- 

 ance. 



The newly affected lobulettes have a watery or gelatinoid or 

 dropsical appearance and if freely incised give out a large amount 

 of serum and flatten down in doing so. When hepatized the cut 

 surface is granular, and microscopic examination shows the termi- 

 nal bronchia and alveoli filled with a fibrinous exudate containing 

 great quantities of red blood globules and leucocytes. The dis- 

 tension of the lung is enormous, so that when the entire organ is 

 infiltrated it may weigh from 50 to 100 pounds. 



In recent cases the lung may be extensively affected without 

 affecting the pleura ; in other cases both are early involved. In 

 advanced cases the pleurae are always implicated. First there is 

 the subpleural infiltration over the affected part of the lung ; later 

 the pleural surface has reddened arborescent patches, with a 

 slight solid exudate, and a yellowish (sometimes blood-stained) 

 serum collects in the bottom of the cavity ; later still the affected 

 portion of the lung is covered more or less thickly with false 

 membranes, while others cover the organ or the parietal pleura 

 below this level, and hang in shreds or bind the lung to the ribs. 

 In old standing and recovered cases these may be largely repre- 

 sented by dense, white fibrous investments covering the lung or 

 39 



