Acute Pleurisy in the Horse. Pleuritis. 247 



probably fifteen or twenty, the dark red hue must not be held to 

 imply a recent date for the attack. A relapse in the course of con- 

 valescence may easily and quickly stain anew a liquid that was 

 already limpid, or had advanced far toward this condition. 



The appearance of the lung tissue in a case of confirmed pleu- 

 risy is characteristic. The lung is of a dull red color, shrunken, 

 slightly collapsed, flabby, scarcely crepitant under pressure and 

 heavier than water or floating in water. It is tough, not friable 

 like hepatized lung, and its cut surface is dry, smooth, and pre- 

 sents the interlobular septa very well marked. This is due to the 

 compression by effused liquid, and by the organizing and contract- 

 ing false membranes covering the lung and implies nothing more 

 than simple condensation. The air cell may be collapsed, but 

 contains no new product and has not parted with its epithelium 

 and the lung can be inflated through the bronchia. 



Differentiation according to the nature of the effusion. Pathol- 

 ogists have divided acute pleurisy into the dry, sero-ffbrinous , and 

 sero-fibro-purulent. 



1. Dryer fibrinous pleurisy has usually a more acute type 

 and the exudate containing an excess of the fibrinogenous elements 

 forms a coagulum or false membrane on the affected surface tend- 

 ing to bind that to the part adjacent — the lungs to the costal 

 pleura. The serum, small in quantity, is in the main retained in 

 the exudate or if set free is actively reabsorbed by the healthy 

 pleura. 



2. Sero-fibrinous pleurisy. This form is usually less acute 

 and more extended involving perhaps an entire pleural sac, or 

 even both sides of the chest. This is the common form of pleurisy 

 and is that referred to in the experiments of St. Cyr and others 

 above. The earliest lesions in experimental cases (with chloride 

 of zinc solution) in dogs are an uniform bright red congestion, 

 with a bright, shining surface as yet perfectly dry. There is al- 

 ready shedding of patches of the endothelial cells, swelling and 

 proliferation of the superficial connective tissue cells and the for- 

 mation of a few pus globules. This is seen in from half an hour 

 to six hours after the application of the irritant. 



Next follows the exudation of fibrine and serum, which respec- 

 tively coagulate as false membrane on the inflamed membrane, or 

 drop to the bottom of the sac as liquid. The fibrine appears as 



