632 SPORADIC DISEASES. 



remarkable tiling that suppuration of the lungs very rarely runs 

 on to the formation of abscesses when the inflammation is not 

 due to a specific cause, such as glanders or pyaemia, I have 

 certainly seen abscesses in the lungs of both oxen and horses, 

 but the event is a very rare one, and Sir Thomas Watson 

 endeavours to account for the rarity of pulmonary abscesses in 

 a very ingenious manner. He says—" When I was speaking of 

 inflammation in general, I pointed out to you the remarkable 

 influence which the presence of air in contact with the inflamed 

 part has in accelerating or determining the event of suppuration. 

 In a recent cut through the skin the admission or the exclusion 

 of the air to the cut surface will make all the difference between 

 the adhesive and the suppurative inflammation ; and so in other 

 cases which I then mentioned, and will not now trouble you by 

 repeating. Now it seems to me that the same principle obtains 

 in inflammation of the lung. First, there is an effusion of serum 

 and blood, then of lymph and blood ; but the air, passing into the 

 surrounding sounder tissue, and penetrating for a time even the 

 inflamed portion itself, causes the suppurative process to super- 

 sede the adhesive ; and so no wall of circumvallation is formed 

 by the coagulable lymph, as is the case in areolar tissue when 

 not accessible by the air." — (Watson's Lectures, page 81.) 



Gangrene is more generally a result of congestion than of 

 inflammation of the lungs, but its occasional occurrence in pneu- 

 monia is indisputable. Sometimes it occupies a large portion 

 of the lung, and is not circumscribed, sometimes it is more 

 limited. The affected parts are dark, dirty olive or greenish- 

 brown in colour ; foetid in odour ; moist, wet, and diffluent in 

 consistence. The occurrence of mortification has been ascribed 

 to thrombosis occurring in the branches of the pulmonary artery 

 — (Huss, Carswell) — and to the destructive effect of the in- 

 flammatory process destroying the vitality of the tissue, or to 

 an arrest of the circulation by the excessive accumulation of its 

 products in the interior of the air cells. 



Pneumonia may be double (bilateral) or single (unilateral), that 

 is to say, it may affect one or both lungs ; double pneumonia is, 

 however, very uncommon. I have for many years carefully 

 noted the site of pneumonia, and have found that the inflamma- 

 tion is much more commonly situated in the right than in the 

 left lung, both in horses and in cattle, in epizootic, sporadic, 



