CHAPTER V. 

 DISEASES OF THE PLEURA. 



PLEURITIS. 



Definition. — An inflammation of the pleura. Pleuritis is 

 nearly always a secondary condition in animals. 



Occurrence. — Affects all animals but principally the horse. 

 In the horse pleuritis is usually a symptom of infectious 

 fibrinous pneumonia; in the ox of tuberculosis, contagious 

 pleuropneumonia and hemorrhagic septicemia, and in swine 

 most frequently of so-called swine plague. Pleuritis, 'how- 

 ever, may occur unattended by pneumonia, as is frequently 

 observed in horses. 



Etiology. — Pleuritis in animals is always due to infection. 

 Cold, which was believed to be the most potent etiological 

 factor, is now considered merely predisposing (pleuritis in 

 sheep following shearing; exposure of horses to cold wind 

 , and rain). The microorganisms which produce pleuritis are 

 many. Rarely is pleuritis a primary disease — it is most 

 commonly seen in practice accompanying diseases of the 

 lungs (pleuropneumonia). The microorganisms causing 

 pleuritis may enter as follows: (a) through penetrating 

 thoracic wounds; (6) through deep contusions on the chest 

 wall, especially if rib fractures be present (kicks, blows, 

 falls) ; (c) from disease foci in the lung, which are in contact 

 with the pleura; (d) via blood and lymph microorganisms 

 of certain specific diseases, notably those which affect 

 principally the respiratory tract, may also invade the 

 pleura and cause inflammation thereof (influenza, fibrinous 

 pneumonia, swine plague, hemorrhagic septicemia, acute 

 rheumatism). It may happen that the dominant lesions 

 are in the pleura, in which case primary pleuritis is spoken of 

 (pleurisy of the horse without pneumonia). 



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