THE HEART 61 



tricles, sudden death ensues ; when it occurs in the auricles, death 

 does not follow, for fibrillation cannot pass along the bundle con- 

 necting the auricles with the ventricles. The degree of heart 

 failure which follows auricular fibrillation depends upon the extent 

 to which changes have occurred in the structure of the heart muscle 

 of both auricle and ventricle. 



In severe inflammatory chest invasions of the horse, the heart, 

 but especially its sac, may become acutely affected. There are few 

 attacks of severe pleurisy in the horse which are not associated with 

 pericarditis, followed not only by great thickening of the heart sac, 

 but by more or less extensive effusion into it. The heart then 

 becomes enveloped in a water jacket, which greatly adds to the 

 gravity of the case. In the above acute cases the heart muscle 

 suffers, and haemorrhages into it are common and widespread. 



In the dog the heart's action is normally intermittent. 



Foreign bodies in the heart of cattle, especially cows, are well 

 known, and give rise to a peculiar train of symptoms. Vegetations 

 on the valves of both the dog and pig are recognised in connection 

 with certain infectious diseases. 



