438 THE CIRCULATORY SYSTEM. 



tious emboli in small vessels. There is at first necrosis of the muscle 

 fibres near the bacterial mass (Fig. 233), followed by local suppuration 

 and the formation of abscess. The contents of the abscesses consist of 

 pus, broken-down muscle tissue, and bacteria. 1 These abscesses may 

 open into the pericardial sac and set up a purulent pericarditis ; or into 

 a heart cavity, giving rise to thrombi in the heart and infective emboli in 

 different parts of the body ; or the wall of the heart is weakened by the 

 abscess so that it ruptures, or an -aneurismal sac is formed ; or an abscess 

 in the interventricular septum may establish an opening between the 

 ventricles ; or the suppurative process may extend upward and form an 

 abscess in the connective tissue at the base of the heart. Streptococcus 

 and staphylococcus pyogenes are the most common excitants. 



In rare cases the patients recover, the contents of the abscesses be- 

 come dry and hard, and enclosed by a wall of fibrous tissue, or the con- 

 tents may be absorbed and the whole replaced by fibrous tissue. 



Chronic Interstitial Myocarditis may be associated with chronic peri- 

 carditis or endocarditis ; but in a large proportion of cases it occurs in 

 connection with lesions of the coronary arteries. 



When through obliterating endarteritis, atheroma, thrombosis, or 

 embolus of a branch of the coronary arteries, 2 the blood supply is cut off 

 from a circumscribed portion of the heart wall, the tissue in the affected 

 area may undergo fatty degeneration, leading to rupture. 3 Or, instead 

 of extensive fatty degeneration, the cutting off of the blood supply from 

 a limited region may result in necrosis white infarction. These areas, 

 grayish in color, often slightly projecting from the surface, are fre- 

 quently surrounded by a red zone of hypera3mia. The nuclei of muscle 

 and fibrous tissue fail to stain, the muscle cells become necrotic, lose 

 their striation and degenerate, and may be absorbed or gradually replaced 

 by fibrous tissue. When larger areas are involved, the muscle fibres 

 may break down into a granular detritus and the connective tissue about 

 them suffer degeneration or necrosis, so that the whole affected area may 

 be soft and yellowish-white or grayish in color. If, as not infrequently 

 occurs, there is considerable extravasation of blood, the degenerated 

 area may be of a dark red color. 4 Under these conditions the heart wall 

 may rupture, or acute inflammatory processes may occur, or the de- 

 generated tissue may be gradually absorbed and replaced by granula- 

 tion tissue formed from the surrounding fibrous tissue and blood-vessels. 



1 For a detailed consideration of the formation of such embolic abscesses, see p. 113. 



2 According to Stern berg, the right coronary artery supplies the following regions 

 of the heart : most of the right auricle ; the posterior part and most of the anterior part 

 of the right ventricle ; most of the interauricular and interventricular septa ; the pos- 

 terior part of the left ventricle and the posterior papillary muscles. The remainder of 

 the heart is supplied by the left coronary artery. 



While there are superficial anastomoses between the larger trunks of the coronary 

 arteries, their branches do not communicate after they enter the heart muscle. 



3 Through the Thebesian vessels sufficient nutriment may reach the myocardium to 

 maintain the muscle for a time, even with considerable lesion of the coronary arteries. 

 See Pratt, American Journal of Physiology, vol. i., p. 86, 1898. Also Baumgarten, 

 ibid., vol. ii., p. 243, 1899. 



4 This condition of the heart is often called " myomalacia. " 



