410 DISEASES LOCALIZED IN CERTAIN ORGANS 



rapid spread among cattle on pasture has been frequently 

 noted. 



Very commonly a supposedly recovered ox with an encap- 

 suled lung focus is the infecting agent. So long as the 

 sequestered center in the lung is completely encysted, no 

 virus will be thrown off, but once a communication is estab- 

 lished with a bronchus giving the virus exit the patient becomes 

 a source of danger to healthy cattle. The virus may. remain- 

 virulent for two or three years in a lung sequestrum of an 

 apparently healthy ox. 



The disease is more prevalent in stable-fed than among 

 pastured animals. It affects all breeds, although some indi- 

 viduals possess natural immunity. 



Necropsy. — As a rule only one lung (left) is involved. 

 Usually a large area is hepatized. On cross-section a clear, 

 yellow fluid, which quickly coagulates, flows over the cut 

 surface. The interlobular connective tissue is greatly thick- 

 ened, forming yellow, gelatinous strands one-half an inch or 

 more in thickness, which divide the lung tissue into islands 

 of varied color. Characteristic of the lung lesions are the 

 different degrees of inflammation which appear at the same 

 time, fresh areas of congestion lying beside those showing red 

 or gray hepatization or even necrosis. As a result the cut 

 sm-face presents a distinctly variegated, marbled appearance 

 very characteristic of the disease. The bloodvessels are dis- 

 tended and thrombosed. The corresponding lymph glands 

 are swollen and edematous. 



In chronic cases the proliferated interlobular connective 

 tissue is almost white in color and very firm. The portions of 

 the lung they surround are necrotic and sometimes calcified. 

 In such cases a thick, connective-tissue capsule may inclose 

 areas from the size of a walnut to a grape fruit — so-called 

 sequesters. A zone of reactive inflammation surrounds the 

 capsule. The pleura shows serofibrinous pleuritis which can 

 involve the pericardium. Rarely there is serofibrinous peri- 

 tonitis especially in the region of the diaphragm and liver. 

 In calves arthritis of individual joints and a gelatinous infil- 

 tration of the subcutis (dewlap, chest) may exist. 



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