494 PNEUMONIA. 



perfected, to bo succeeded, during the same period of moderate 

 fever, by liquefaction of the inflammatory-action products and 

 their removal, chiefly by absorption, and maybe by expectora- 

 tion. 



Of the influences Avhich appear to be in operation for the pro- 

 duction of 2^neumonia, some may be regarded as predisposing 

 and others as immediate or exciting. Of the former the most 

 obvious are — 1. Season and locality. It is more prevalent 

 during spring and autumn, when temperature is liable to 

 sudden variations, particularly with moisture ; also in districts 

 where north and north-easterly winds prevail at the periods 

 when horses are changing their coats. 2. Previous attacks 

 of inflammatory and other weakening affections of the pul- 

 monary structures. 3. Particular states of the general health , 

 it being more liable to attack animals weakened by some 

 previous general disease, and where the vital powers are some- 

 what depressed. 



Of the latter the chief are — 1. All agencies ivhich ive observe 

 operating in the production of the allied affections laryngitis, 

 bronchitis, and common catarrh, (a) Exposing animals in 

 a state of inaction to cold and damp after having undergone 

 severe exertion or fatigue, (b) Confinement in close, badly- 

 ventilated stables, with foul emanations operating in addition 

 to deficiency of respirable air. 



2. As the residt of pmlmonary engorgement. This, we are 

 satisfied, is more apt to be the case than is generally supposed; 

 nor do the chances of such an untoward result seem to be 

 confined to a few hours immediately succeeding the congestive 

 attack ; they arc in operation for some days. In such cases 

 very trivial disturbances, either from irregularities of diet or 

 changes in location, are exceedingly apt to be followed by in- 

 flammation in the lung-substance. 



8. Direct irritation is not an unfrequent cause of pneu- 

 monia, and may occur («) through medicinal agents in the 

 liquid form — when attempted to be administered to animals 

 of violent temper, or where, from physical impediments, deglu- 

 tition is difticult — finding their way into the trachea and 

 minute ramifications of the air-passages. (?>) From wounds or 

 portions of fractured ribs penetrating the thoracic Avails and 

 injuring the contained structures. 



