504 PNEUMONIA. 



and feel when touched, rather firm, although on section they 

 evidently want cohesion, breaking down easily under pressure, 

 and are in their early stages surroimded with a more or less 

 marked area of congestion. 



In influenza, where pneumonic complications occur, we almost 

 invariably find that if these do not terminate in gangrene we 

 have purulent infiltration of an extensive character, accom- 

 panied with much tissue-disintegration ; the same results often 

 accompany pneumonia associated with or following common 

 catarrh, when the animals are acted upon by certain septic or 

 depressing influences. 



Interstitial Pneumonia. — There is a condition sometimes en- 

 countered in the pulmonary structure, recognised as fibroid 

 induration, which in all animals occasionally follows as the 

 result of ordinary pneumonia. The horse is certainly as little 

 liable to this as any animal, but even with him it may occur. 



In this condition of interstitial or interlobular fibroid indura- 

 tion there is a thickening of the walls of the pulmonary alveoli 

 and intervening connective-tissue, with structures resembling 

 that developed in ordinary connective-tissue which has been 

 the seat of inflammatory action, the so-called cicatricial tissue. 

 By the development of this fibro-nucleated growth, and its 

 deposition in the walls of the pulmonary alveoli and in the in- 

 terlobular structure, together with the products of endothehal 

 cell proliferation Avhicli have accumulated in the air-sacs, the 

 vesicular structures become gradually obliterated, the entire 

 lung-structure affected becomes less in volume, while the 

 feeling imparted on manipulation is one of hardness and 

 density. This progressive consolidation of pulmonary tissue, 

 the result of inflammatory action of a rather slow or chronic 

 character, with a development of fibroid and fibro-nucleated 

 elements in the walls of the pulmonary spaces, and amongst 

 the interlobular connective-tissue, is probably more frequently 

 observed in the ox than the horse ; and is in that animal 

 more prone to take on a form of caseation, and other retro- 

 gressive changes frequently comprehended under and associated 

 with the condition s})oken of as pulmonary phthisis. 



In the pneumonia of glanders in the horse wc may often 

 observe these changes, particularly in slowly progressive cases ; 

 in these Ave will find the alveolar walls thickened, and the 



