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in three principal varieties, but in a Avork of this kind there is no 

 necessity to discriminate, and therefore the disease will be described 

 under a common head. It already lias been mentioned that pneumonia 

 may be complicated with bronchitis, and it will hereafter be pointed 

 out that it is very commonly complicated with i3lem'is3\ In this arti- 

 cle the disease will be considered mainlj^ as an independent affection, 

 and its complications will be more fully described under separate heads. 



The inflammation usually begins in the lower part of the lung and 

 extends upwards. The first stage of the disease consists of congestion 

 or engorgement of the blood- vessels, and if tliis condition continues 

 the blood exudes from the vessels into the adjacent lung tissue; if 

 rupture of small blood-vessels occurs there will be extravasations of 

 blood in the contiguous j)arts. The fluids thus escaping collect in the 

 air-cells and in the minute branches of the little bronchial tubes, and, 

 becoming coagulated there, completely block up the cells and exclude 

 the air. 



In this condition the lung is increased in volume and is much heavier, 

 and will sink in water. The pleura covering the affected x^arts is alwaj^s 

 more or less inflamed. A continuance of the foregoing phenomena Ls 

 marked by a further escape of the constituents of the blood, and a 

 change in the membrane of the cells, which become swollen. The 

 exudate that fills the air-cells and minute bronchial branches under- 

 goes disintegration, and is converted into a fatty material. The Avails 

 of the cells almost invariablj^ remain unaltered. 



It must not be imagined, that the foregoing changes take place in 

 a uniform manner. While one portion is onlj^ congested another 

 part maj' be undergoing disintegration, while still another part may 

 be involved in the exudative stage. 



The usual termination of x)iieumonia is in resolution, that is, a res- 

 toration to health. This is gradually brought about by the exuded 

 material contained in the air-cells and lung tissues becoming degen- 

 erated into fatty and a mucus-like substance Avhich are removed by 

 absorption. The blood-vessels return to their natural state and the 

 blood circulates in them as before. Much material, the result of 

 the inflammatory process, is also gotten rid of by expectoration, or 

 rather (in the horse) by discharge from the nostrils. In the cases 

 that do not terminate so happily the lung may become gangrenous 

 (or mortified), or an abscess may form, or the disease may be merged 

 into the chronic variety. 



Pneumonia may be directly induced by any of the influences named 

 as general causes for diseases of the organs of respiration, but in 

 many instances it is due to eitlier Avillful neglect or ignorance. A 

 common cold or sore throat may run into a fatal case of pneumonia 

 if neglected or improi^erly treated. An animal may be debilitated 

 by a cold, and when in this weakened state ma}'- be compelled to 

 undergo exertion beyond his strength; or he may be kept in bad 



