144 CLINICAL VETERIXARV MEDICINE AND SURGERY. 



inflammation of the muscular tissue of the heart, but onl}- diminishes 

 its resistance to the attacks of pathogenic organisms — a theory strongly 

 corroborated by bacteriological experiments made during the past few- 

 years, especially by those of M. Roger. Myocarditis due to " over- 

 exertion " is therefore included in the group of infectious m}-ocardites. 



Mechanical injury of the thorax over the heart only causes inflam- 

 mation of the cardiac muscle when a penetrating wound is produced, 

 or when the muscle itself is immediately injured, and the lesion be- 

 comes infected. 



I have only observed acute myocarditis in the horse as a secondary 

 affection ; nor have I seen its characteristic lesions, except in animals 

 which had died of toxic or infectious disease, and in which, conse- 

 quently, myocarditis had occurred as a complication of the original 

 disease. The various forms of pneumonia, the typhoid form of 

 influenza, strangles, hctmoglobinuria, septicaemia, p3-gemia, and other 

 microbic diseases may be accompanied b}' myocarditis, either be- 

 cause of pathogenic organisms dispersed by the blood-stream 

 arriving at the myocardium through the medium of the coronary 

 arteries, and arrested there, producing embolism of more or less 

 extensive tracts; or even more frequentl}- because of injury to the 

 myocardium by the toxins of microbes multiplying at a distant point. 

 M. Charrin produced myocarditis in animals b}- injecting filtered 

 cultures free of all li\ing organisms ; but, whether infectious or toxic, 

 these forms of myocarditis are primarily due to the life processes of 

 microbes. 



Diffuse or localised m30carditis, whether limited to the deep or 

 superficial layers of muscle, always results from the extension of inflam- 

 mation from the endocardium or epicardium. They show that Stokes's 

 law on extension of inflammatory processes from mucous membranes 

 to subjacent muscles also holds true in regard to serous membranes. 



The changes produced in the heart muscle by acute diffuse inflam- 

 mation are usually well marked, and (juite apparent on superficial 

 examination, though seldom to such an extent as in the specimen I 

 exhibit, where they are truly remarkable. Usually the heart is more 

 or less enlarged, dilated, flabby, and decolourised. Sometimes its 

 surface is almost uniforml}- pale gre}-ish, or the colour of a dead leaf; 

 sometimes it is marked with yellowish patches of varying form and 

 size, the majorit}- irregular in shape, with sharply defined margins, 

 and usually more numerous and larger in size on the ventricles. 

 Under the epicardium and endocardium little hsemorrhagic centres 

 can be seen. Sections made through the myocardium appear of a dull 



