PERICARDIUM, DISEASES OF THE. (For anatomy, see COELOM AND SEROUS MEMBRANES.) The serous sac in which the heart is contained may be the seat of inflammation (peri carditis) along with the cardiac valves and heart muscle in the course of acute rheumatism or other acute diseases. The normal shiny appearance is then lost, the membrane becomes congested and inflammatory serum exudes into the cavity. In this stage the visceral and parietal layers grate upon one another with the heart's beat and give rise to a "friction rub" over the front of the chest which can be heard with the stethoscope and may be perceptible to the hand. As more inflammatory exudation is poured out the surfaces are separated and friction disappears. From this point the course of the disease varies according as the inflam mation advances or recedes. If it advances fluid may accumulate in the sac to an extent that seriously impedes cardiac action, while if the pericarditis accompanies or follows pneumonia the fluid may become purulent. In either event exit must be given to
the fluid surgically. If the disease recedes the roughened pericar dial surfaces again come into contact through absorption of the ex uded fluid, and friction reappears. Later, fibrous adhesions are formed between the two layers of pericardium over a greater or smaller area; sometimes they become universally adherent and the cavity is obliterated. Exudation of fluid into the pericardial cavity, apart from inflammation, occurs in certain diseases of the kidney and is then often unaccompanied by symptoms though it is a very grave omen. In rupture of the heart or of certain vari eties of aneurism the pericardial sac is suddenly filled with blood. Distress is extreme and death occurs after a few seconds from mechanical interference with the action of the heart. Other con ditions affecting the pericardium either act by inducing inflam mation or are so rare that they cannot be considered here.