38 THE PRACTICE OF VETERINARY MEDICINE. 



theless, it sometimes exists as an independent affection, as is 

 often proved by the fact of an animal dying of effusion 

 into the pleural cavity, and the lung-substance on examina- 

 tion being found to have undergone no change. Inflamma- 

 tion of a serous membrane, if extensive, constitutes a 

 dangerous condition. There is a cavity known as the 

 pleural cavity situated between, and formed by, the pleura 

 pulmonalis and the pleura costalis ; here, exuded from the 

 two membranes, is a small quantity of fluid — serum — just 

 sufficient being secreted to lubricate the parts and enable 

 them to move smoothly. When the pleura becomes involved 

 in the inflammatory process, serum ceases to be secreted, 

 and dryness of the membrane takes place, giving rise to the 

 grating or crepitating sound heard on auscultation. This 

 condition soon passes off, and effusion into the pleural 

 cavity and formation of fibrinous bands take place. The 

 fibrinous bands may be found in from two to four days after 

 the disease appears. In pleurisy a certain amount of 

 effusion invariably takes place, and treatment is always 

 directed with a view to preventing, if possible, the pouring 

 out of a large quantity of fluid. When a copious flow takes 

 place, it constitutes a condition known as hydro thorax. 



Causes. — Pleurisy is caused by alternations of tempera- 

 ture, exposure to cold and wet, and by the various conditions 

 which cause pneumonia. It may also be due to the presence 

 of some morbific poison or influence in the blood. During 

 the prevalence of east winds in the old countries people and 

 horses, as well as other animals, suffer from pleurisy. 



SiimiJtoms. — Like other chest diseases it is usually ushered 

 in with a chill, which soon passes off. The pulse is wiry, the 

 animal stands with his feet out, as in laminitis, and occasion- 

 ally lies down, but only for a very short time ; the animal 

 shows evidence of great pain : he is suffering from what are 

 known as cutting pains. On auscultation the crepitating 



