ANATOMICAL CHARACTERS. 499 



changes, there are some others which, in exceptional cases, 

 attract attention, namely : 1. The formation of one or more 

 abscesses. This is probably a rather rare condition, unless we 

 regard the extensive purulent infiltration in the light of a large 

 collection of very small abscesses. When an abscess does 

 exist, it may, by opening into some of the air-tubes, become 

 discharged, or from being perfectly encapsuled, may undergo 

 calcareous or cheesy degeneration. 2. Gangrene, this is 

 certainly not more common than the preceding. By some 

 this condition is considered more likely to follow excess of 

 inflammatory action, but from what I have observed of the 

 condition in the horse, I am disposed to credit peculiarities 

 in the type of the inflammatory action, and depressing or 

 pestilential influences operating upon the animals affected, 

 with the onus of the production of this peculiar change. 

 When occurring, I have not observed that it aftects the whole 

 lung-structure which is invaded by the pneumonia ; the extent 

 of its inroad is circumscribed, sometimes rather extensive, at 

 others limited. The a2:»pearance is that of the so-called humid 

 gangrene, the tissue being of a greenish-brown or metallic 

 hue. It is often marked off from the healthier lung-structure 

 by a distinct line of demarcation, and feels soft and doughy. 

 Accompanying this state I have observed, particularly in 

 foals suffering from specific arthritis, where the pneumonia is a 

 secondary affection, that thrombosis of pulmonary vessels is a 

 rather frequently associated feature. 8. Chronic pulmonary 

 inflammation tending to the development of a form of fibroid 

 or cicatricial tissue, apparently closely connected with the walls 

 of the alveolar cavities and the connective-tissue intervening. 

 The growth of this fibro-nucleated structure may be of such a 

 character and extent as largely to impair the cajoacity of the 

 air- vesicles, and by its firmness and tenacity give to the lung- 

 tissue the character of cirrhosis or induration. When once 

 established, this is likely to go on increasing, while the struc- 

 ture so affected seems rather decreased in bulk because less 

 dilatable and expansive, the air-vesicles gradually becoming 

 smaller from the steady thickening of the alveolar walls 

 and increase of the fibroid material in the interconnective- 

 tissue. 4. This last condition may further develop into 

 more extensive circumscribed or nodulated portions of indura- 



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