PLEURITIS— PLEURISY 61 



(/) Pleuritis is very often found during the course of infec- 

 tious diseases. In the dog it occurs frequently as a secondary 

 disease following distemper, septicemia and pyemia, the 

 infection being carried by the blood and lymph. It is also 

 seen during the course of rheumatic conditions. 



(g) Other predisposing causes are extreme exertion (hunt- 

 ing dogs, greyhounds), or living under adverse conditions 

 (bench shows, during transportation, etc.) which reduce the 

 natural resistance. 



Pathology.— The involvement in pleuritis may be acute 

 or chronic, local or general, and according to the variety of 

 exudate, serous, serofibrinous, hemorrhagic or purulent. A 

 single case of pleuritis may pass through all of the above 

 stages. In all cases the pleura becomes hyperemic, rough 

 and dull. The roughness interferes with the free movement 

 of the gliding surface producing pain and the characteristic 

 frictional sounds. Later exudation takes place into the 

 pleural cavity. In the fibrinous form there is soon an exudate 

 of fibrin, forming a thin, yellowish layer on the surface, and 

 as this increases it causes the pleural surfaces to adhere 

 together slightly. The exudate is composed of flakes and 

 masses of fibrin containing leukocytes. The exudate may 

 be absorbed completely, but if there has been much fibrin 

 formation adhesions of varying density result. These 

 adhesions later are organized into connective tissue which is 

 at first delicate but soon becomes very dense, and in some 

 cases so extensive as to obliterate almost completely the 

 pleural cavity; or they may be in scattered areas only. 



In serofibrinous pleuritis there is a large amount of serous 

 as well as fibrinous exudate. It may originate as the fibrinous 

 form, but usually begins with a serous outpouring. This 

 exudate is denser than the transudate seen in hydrothorax, 

 and contains the usual inflammatory products. The amount 

 of fluid will vary with individual cases and in the different 

 small animals from 100 c.c. to 5000 c.c. When present 

 in large quantities the lung is pushed backward and the 

 neighboring organs pressed upon. This pressure on the 

 lungs of the dog and cat is often sufficient to completely 

 occlude the passage of air into the right posterior lobes. 



