634 SPORADIC DISEASES. 



ETIOLOGY. 



The causes of sporadic pneumonia are similar to those of bron- 

 chitis, laryngitis, &c., namely, exposure to cold and wet, sudden 

 chills, and housing in very cold, draughty stables. Horses kept 

 in ill-ventilated stables are undoubtedly rendered susceptible to 

 many diseases, and to pneumonia amongst the rest, but they will 

 bear impure air even better than cold draughts blowing directly 

 upon them. I have repeatedly observed that the slightest cold 

 contracted by a horse kept in a draughty stable has almost in- 

 variably been succeeded by pneumonia, and that if the animal 

 were not removed to a more comfortable situation the disease 

 tended to a fatal termination. It has already been stated that 

 inflammation may succeed the congestive condition induced by 

 severe exertion ; it may also be induced by irritating gases ; 

 smoke of burning hay and straw; foreign bodies entering the 

 lungs from the bronchi, examples of which are not uncommon 

 in cows, as sequelae to parturient apoplexy, where medicine finds 

 its way into the trachea and bronchial tubes, and in horses choked 

 by irritating and powerful remedies, such as ammonia. 



Direct injuries to the lung through wounds in the thoracic 

 w^alls are not always succeeded by much inflammation, the lungs 

 appearing to have remarkable powers of recovery from direct 

 injury, provided it be not crushed, or that foreign bodies or 

 extravasated blood are not forced into the wound in its tissue. 



Pneumonia may also be induced by any material altering the 

 composition of the blood, epizootic influences, purpura, anthrax ; 

 accidental products accumulating in the blood; mechanical or 

 solid materials (thrombi) formed elsewhere, and conveyed to 

 the lungs by the blood, as in phlebitis ; infecting influences of 

 materials conveyed to the lungs, as in pypemia or glanders. It 

 may be the result of passive congestion arising from disease of 

 the heart or weakness of the circulation, induced by exhausting 

 diseases or old age ; or it may be the localization of a specifio 

 disease, as in pleuro-pneumonia contagiosa. 



SYMPTOMS. 



The symptoms of pneumonia, namely, the greatly accelerated 

 respiratory movements, oppressed pulse, and other signs of 

 excitement described by Youatt, Gamgee, and others, are not by 



