148 DISEASES OF THE RESPIRATORY ORGANS 



cular origin. Tumors of the pleura, chronic nephritis, and acute articuhir 

 rheumatism may also develop pleurisy. Piana found bacilli and 

 Hutyra and Marek found it caused by streptothrix (actinomyces) canis. 



Pathological Anatomy. — The exudation which collects rapidly 

 crowds the lung of the affected side and finally presses it against the spinal 

 column and mediastinum, pressing the lung into an inert mass (lung 

 atelectasis). The opposite lung is the seat of considerable collateral 

 hyperaemia, which ma}^ lead to oedema, according to the severity of the 

 condition. When compression of a lung is continued for any length of 

 time, the alveoli lose their functional activity, their walls collapse and 

 become adherent even if the fluid exuded finally becomes absorbed. 

 After this has occurred, it can readily be recognized by the depressed 

 appearance of the ribs. In cases of primary pleuritis which have been 

 seen by the writer, the inflammatory process was always restricted to one 

 side, and that, as a rule, was the left side. The cases of secondary pleuritis 

 were generally double-sided, but the inflammatory conditions are never 

 of equal intensity on both sides, one side being always a little worse than 

 the other. Besides having the results of pressure shown on the lungs, we 

 also find the heart is pushed toward the healthy side of the mediastinum 

 or the diaphragm. 



The conclusion of pleuritic inflammation depends on the intensity 

 and duration of the disease and the character of the exudate. In favor- 

 able cases the latter is reabsorbed and good results follow. In serious 

 cases, only part of the liquid portion of the exudate is absorbed, while a 

 fibrinous exudate covers the pleura; this becomes converted into a granu- 

 lar tissue containing numerous vessels and later into a stringy cicatricial 

 tissue, called a pleuritic sward, with more or less adhesions of the pleura 

 between the lungs and inner wall of the thorax and between the lungs and 

 diaphragm. Although the sward formations may be very extensive, it 

 is possible for the lung to regain its normal extension, but this takes a 

 long time. Thin adhesions sometimes tear; and extended adhesions offer 

 a constant hindrance to the unrestricted use of the affected part of the 

 lung. Purulent exudates are sometimes reabsorbed; but, as a rule, if the 

 pus is not removed at the proper time by surgical interference it breaks 

 out, either through the pleura into the lungs and then through the bron- 

 chia, or it forms an abscess somewhere in the cavity of the chest, generally 

 in the region of the sternum, by undermining the pleura and muscles of 

 the chest. 



Clinical Symptoms. — In the primary form of pleuritis, when its 

 origin is from cold, etc., it is ushered in with a rapid rise in temperature, 

 the pulse increases in frequency, and at the onset the animal generally 

 has a chill; the temperature remains high, and the pulse is small, weak, 

 and thready. Primary pleuritis with purulent or putrid effusions is rare, 



