DISEASES OF THE OX AND SHEEP. 179 



deprived of their functions. This solid substance mechanically 

 alters the processes going on in the lungs, the blood-vessels and 

 lymphatics being thereby subjected to pressure. The new tissue 

 may undergo fatty, caseous, calcareous, or in rare cases gan- 

 grenous degeneration. The air-cells usually contain a little 

 serum. Sometimes, though very rarely, they contain fibrine. 

 They are sometimes, therefore, obliterated, and sometimes densely 

 packed with red and white cells, as in ordinary pneumonia (red 

 hepatisalion). The exudation may then become a whitish turbid 

 fluid, so that the lung appears greyish, and thus we have " grey 

 hepatisation " instead of the more general "red hepatisation," 

 in which the lung tissue looks bluish red or purple. 



Sometimes the tissue suppurates, and masses of lung tissue 

 may be detached and isolated in the midst of a thick purulent 

 fluid, contained within rigid walls of newly-formed connective 

 tissue. In some cases these detached portions are decomposed, 

 friable, off'ensive in smell, and produce gangrene in the adjoin- 

 ing tissues. Sometimes there may be found large or small 

 cavities filled with more or less fluid pus. Thus there are 

 abscesses in the substance of the lung, and sometimes, though 

 not frequently, they open into the chest cavity, producing what 

 is called empyema. A cavity is then left in the lung which gives 

 rise to the amphoric rale. The pus may be partially absorbed, 

 and produce purulent infection, or the abscess may discharge 

 itself through the air tubes, in which case there will probably 

 be an expectoration of fetid pus. 



Necrosis may result, too, from pressure of the bronchial 

 vessels, or from thrombosis of the bronchial arteries. The pul- 

 monary arteries are liable to thrombosis and embolism, and thus 

 gangrene may be produced. Gangrene is evidenced by the 

 brownish or nearly black hue of the lobules, the interlobular 

 bands being thin and infiltrated with bloody serum, and the 

 lung tissue being easily torn and fetid. 



Blood abstracted at an early stage of the disease is usually 

 viscid, thick, and soon coagulates. At a later stage it has 

 become dark and fluid, and has lost its coagulability. '* The 

 stomach contains dry food, and its lining membrane, as 

 well as that of the intestines, may exhibit patches of conges- 

 lion." — (Fleming.) It is said that there is more effusion into 

 the pleural cavities in some epizootics than in others. As a 



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