MYOCARDITIS. 



143 



of the ventricular wall. The pericardium and endocardium are hardly 

 affected. On macroscopic examination the valves show no appreci- 

 able lesion, but microscopic examination reveals lesions of acute diffuse 

 myocarditis. Even where the myocardium appears least altered its 

 fibres prove to have undergone granular degeneration. 



In the other specimen we see advanced lesions of chronic myocar- 

 ditis. This heart is moderately hypertrophied, and exhibits scattered, 

 whitish, irregular, more or less depressed areas, some isolated, others 

 united by narrow bands of the same colour ; the largest are seen on the 

 left ventricle, principally about the auriculo-ventricular furrow. Sec- 

 tions through the wall of this \entricle reveal similar whitish areas, 

 fibrous in appearance, star-shaped, isolated or united. At these points 

 the myocardium has undergone a fibrous change and the muscular 

 fibres have disappeared, having become atrophied or affected with 

 granular degeneration under the compression exercised by the fibrous 

 tissue. In addition the aortic semilunar valves show old-standing 

 change. 



Acute or chronic infiammation of the myocardium is usually diffuse, 

 extends to the greater part of the muscle, and is in most cases 

 unequally marked in the left and right hearts, the former being com- 

 monly the most markedly affected. This inflammation sometimes 

 occurs as an isolated affection, without co-existent changes in the endo- 

 cardium or pericardium ; more frequently myocarditis is accompanied 

 by endocarditis or endopericarditis, facts explained by the general 

 pathogeny of heart disease, the muscle and serous membranes covering 

 it being simultaneously attacked by the same infectious or toxic agent. 



Acute myocarditis has been divided into primary and secondary. 

 The first is stated to be produced by cold, over-exertion, or mechanical 

 injury. Apart from infection or rheumatism, myocarditis a frigore 

 cannot be said to occur. Deepl}' placed in the thorax, the heart is one 

 of the organs least susceptible to the action of cold, which, at the most, 

 only favours other agents capable of injuring the myocardium. Some 

 cases in man seemed to prove the occurrence of lesions of the myo- 

 cardium and endocardium after excessive and prolonged efforts. Similar 

 cases have also been observed in creatures used for draught, the horse 

 particularly ; but although the horse is probably the hardest worked of 

 all animals, it is very doubtful if it ever suffers from myocarditis due 

 exclusively to excessive work. Recent investigations have explained 

 the pathogenv of that form of myocarditis which follows excessive 

 exertion of the cardiac muscle. Contrary to the views formerly held, 

 we now believe that excessive exertion does not directly produce 



