THE CIRCULATORY SYSTEM. 



421 



exudate so as to displace the heart and compress the larger air passages, 

 the cesophagus, or the aorta. 



PURULENT PERICARDITIS. In this form of exudative pericarditis 

 there are usually more or less serum and fibrin mingled with pus cells and 

 often red blood cells. The process may start as a sero-fibrinous inflam- 

 mation. It is apt to occur as an extension of an infectious process in the 

 neighborhood or as a part of a general pysemic process. Streptococcus 

 pyogenes, micrococcus lanceolatus, staphylococcus pyogeues aureus, and 

 the tubercle bacillus are the bacteria most commonly found in exudative 

 pericarditis. 



Chronic Pericarditis. In exudative pericarditis the mesothelium 1 (en- 

 dothelium) in the early stages, and later this with the underlying connec- 

 tive-tissue cells, contribute to the cellular elements in the exudate. In 

 recovery the exudates degenerate and are gradually absorbed, while from 

 the blood-vessels and the connective-tissue cells of the pericardium more 

 or less new fibrous tissue is formed, at first very cellular and vascular, 

 later dense in character. There may finally be local or general thicken- 



FIG. 219. OBLITERATION OF THE PERICARDIAL SAC IN A CHILD, FOLLOWING PERICARDITIS. 



Showing blood-vessels growing from the visceral pericardium into the blood clot filling the sac. Trans- 

 verse section. A, Heart ; B, pericardium ; C, new-formed vascular tissue extending above to the unorgan- 

 ized clot. A similar layer of new vascular tissue was present over the parietal pericardium, and in places 

 the two layers had coalesced, obliterating the sac. 



ings of the pericardium or adhesions between the visceral and parietal 

 layers. The new fibrous tissue may extend between the subpericardial 

 muscle fibres of the heart. Calcification of this new-formed fibrous tissue 

 may occur. 



OBLITERATION OF THE PERICARDIAL SAC. As the result of the for- 

 mation of vascular new connective tissue between the pericardial walls, 

 the sac may be partially or wholly obliterated (Fig. 219). 



This may be the conclusion of an acute inflammatory process or it 

 1 See reference to Minot, p. 325. 



