Endocarditis. 469 



by the absence of tenderness on manipulation or percussion, and 

 by the presence of the valvular, blowing or purring sounds. 



From myocarditis it is distinguished by the greater force of 

 the heart impulse and the pulse, by the greater loudness and 

 clearness of the heart sounds, by the diminished tendency to 

 faintness and syncope and above all by the onset of blowing val- 

 vular murmurs and the lack of duplication of the heart sounds 

 (arhythmia, polycratic heart). 



From pleurisy it is differentiated by the absence of friction 

 sound, of the short, painful, hacking cough, the pleuritic ridge, 

 intercostal tenderness, and later of the flatness in the lower part 

 of the chest corresponding to the effusion. The forcible impulse 

 and loud sounds of the heart in endocarditis, the faintness or 

 fainting and the supervention of valvular murmurs are further 

 diagnostic signs. 



From pneumonia it is easily distinguished by its own character- 

 istic signs, as well as by the absence of definite areas of flatness 

 on percussion, with zones of crepitation around them. The 

 early rusty discharge and the later muco-purulent one are absent 

 in endocarditis. 



From influenza it is to be distinguished by its virtual sporadic 

 appearance, without any evidence of the rapidly extending qual- 

 ities of a plague ; by the marked excess of the cardiac move- 

 ments and sounds ; and above all by the valvular murmurs. 



Causes. These are in the main the same as those oi pericarditis. 

 Microbian infection is the main cause as already stated under 

 pathology. Weak health, exposure to extremes of weather, punct- 

 ures with foreign bodies, but above all, primary infected centres 

 elsewhere including the rheumatic condition are common causes. 

 Indeed rheumatism appears more prone to attack the serous 

 membrane lining the heart cavities than that enveloping it 

 externally. One reason for this is to be found in the great and 

 incessantly recurring strain on the fibrous structure of the 

 valves, and particularly in hard-worked horses and hunting dogs 

 in which the strain is often extreme. It has been argued that 

 the increased blood pressure caused by digitalis is an appreciable 

 cause. Its frequent connection with rheumatism is shown in the 

 rheumatic lesions of joints and fibrous structures seen in carcasses 

 dead of endocarditis. 



