OF VETERINARY MEDICINE. 81 



PLEURISY. 



Definition. — Pleurisy is an inflammation of the pleura, a 

 serous covering to the inside of the chest cavity (parietal) and 

 to the outside of the lung (pulmonary). Between the two sides 

 is a partition called the mediastinum. In the horse cribriform 

 openings are in it making a communication between the right and 

 left pleural cavities. The pleura normally secretes serum, 

 which, however, is different from the serum of inflammation. 



In the horse pleurisy frequently exists as a separate and un- 

 complicated disease, but in man and cattle, it often exists in 

 combination with pnemonia. Pleurisy may affect either side 

 fright or left lateral) and it may be on both sides (general). It 

 may originate on either the costal or pulmonary pleura and ex- 

 tend to the other parts by contiguity. In most cases in the 

 horse the costal pleura is the one most usually affected. 



Etiology.— ThevQ are several causes which come into play: 



1. Extension of inflammation to the 



pleura from contiguous tissues. 



2. Direct irritation from local injury or 



from adventitious growths. 



3. Exposure to cold and dampness. 



4. Blood contamination. Pleurisy in 



this case is the localization of a spe- 

 cific disease, e. g., the contagious 

 pleuro-pneumonia of cattle. In horses 

 we find an equally typical case in 

 this localization of influenza. 

 Extension.— The pulmonary pleura can easily be affected by 

 an inflammation in the adjacent lung tissue, such a? we find in 



pneumonia. 



Direct Irritation. —Suppose a broken rib juts into the costal 

 pleura, though not puncturing it. This irritation will set up an 

 inflammation. A shaft thrust into the chest of a horse will 

 always cause pleurisy; grapy tumors so common in cattle and 



hogs will cause it. 



Exposure.— ^leteovologkaX conditions will cause pleurisy. If 



