128 Surgical Diseases and Surgery of the Dog 



with pleural and pulmonary lesions. Trasbot and Rousseau have 

 observed it to occur primarily as the result of a chill, such as an 

 animal may receive on entering water during the heat of the chase. 

 Such instances are probably due to the attack of microorganisms 

 already present in the blood, under a condition of lowered vitality 

 of the animal. The investigations of Porcher and Desoubry have 

 demonstrated that bacteria are constantly entering the circulation 

 by way of the alimentary canal under normal conditions. 



In the acute form the sac is filled with a sero-fibrinous liquid, 

 which is often blood-stained. At times a profuse hemorrhage 

 takes place, causing extreme distension, which may lead to rupture. 

 Both parietal and visceral layers are beset with villosities and false 

 membranes, and the presence of tubercle bacilli may usually be 

 demonstrated. 



The slowly developing chronic form is commoner, but it fre- 

 quently succeeds the acute. Most tuberculous dogs affected with 

 pleural lesions also suffer from chronic pericarditis. The effusion 

 is liquid, serous, more or less profuse, clear or yellowish, trans- 

 parent, and often free from microorganisms. The surface of the 

 visceral membrane is studded with bacilli-containing neoplasms, 

 varying in size from a grain of millet to a pea. In the vicinity 

 of the base of the heart, where there is least mobility, it is usually 

 consolidated with the parietal layer, and sometimes there is com- 

 plete fusion of the two membranes. When the latter condition is 

 present the heart sustains compression and atrophies, so that its 

 chambers can no longer contain the normal quantity of blood. 

 When there is considerable effusion present the lungs freqifently 

 suffer fron^atelectasis owing to compression. 



Pyemic pericarditis is characterized by miliary whitish foci of 

 suppuration. Both conditions usually lead to more or less myocar- 

 ditis, softening of the muscle, and dilation of the chambers, or 

 there may develop a diffuse fibrosis, particularly in narrow-chested 

 animals. 



The chief secondary complications to which pericardial effusion 

 may give rise, are: venous stasis owing to partial collapse of the 

 veins entering the heart through pressure of the fluid in the peri- 

 cardium; impairment of cardiac action; mechanical valvular in- 

 sufficiency ; one or all of which may give rise to hydrothorax, ascites, 

 and anasarca, the latter sometimes limited to the posterior ex- 



