The pericardium appears distended with a considerable quantity of liquid of a special character—sometimes sero-sanguinolent, sometimes almost or entirely purulent; sometimes yellowish, or greenish-grey; sometimes frothy, inodorous, or very fœtid.
These characters depend on the nature and number of the germs which have invaded the pericardial cavity. They also vary with the gravity and number of the hæmorrhages produced by the action of the foreign body on the myocardium.
The quantity of liquid also varies within very wide limits. There may be scarcely any exudation. In that case the pericarditis is of a partially adhesive character, with abundant false membranes. As a rule the quantity of fluid exudation varies between seven and eight quarts, but sometimes the quantity is much greater. Trasbot described an instance in which the united weights of the heart and pericardium exceeded 36 lbs. Hamon mentioned a case of pericarditis in which the liquid exudate exceeded twenty quarts.
“When inflammation is first set up the liquid is serous, yellowish, or reddish yellow. It contains fibrinous flocculi in suspension. Little by little this exudate becomes purulent, whilst the internal layers of the pericardial serous membrane undergo desquamation. These are next covered with false membranes of varying appearance; the fibro-albuminous exudation is wrinkled, villous and tufted. The two layers of serous membrane are connected at certain points by this exudation, the adhesions being sometimes very extensive. The pericardial sac properly so called becomes the seat of marked lardaceous thickening, due to inflammation. The heart appears entirely covered with a layer of greyish or earthy-coloured granulation tissue, which appears as though baked, and was compared by Hamon to the back of a toad. It is atrophied as a consequence of prolonged compression.
Under the influence of the eccentric pressure of the liquid the pericardial sac is distended and comes in contact with the walls of the chest, to which it may adhere. The foreign body, especially if small, is not always easy to find.
The myocardium often displays interesting lesions. At first there is thickening, or more commonly sclerous degeneration, of the superficial layers covering the ventricles, and then appears a crop of little miliary abscesses. Abscesses of considerable size have several times been detected in the walls of the ventricles and in the interventricular septum.
The foreign body, moreover, may not only injure the myocardium, but may even perforate it completely and produce ulcerative endocarditis (Cadéac). In this case infectious germs very rapidly invade the circulation and all the tissues, and the animal dies of pyæmia.
These essential lesions are accompanied by others of varying importance. Thus the lung is congested throughout, and by contiguity of tissue inflammation may extend from the pericardium to the lower part of the pulmonary lobes and to the pleura.
Interference with the return circulation induces lesions due to venous stasis: dropsy of the chief serous membranes, œdema of the connective tissue, pleural and peritoneal exudations, etc. If the hind limbs never become swollen it is because the skin covering them is very resistant and does not readily yield. The liver becomes hypertrophied, congested and engorged with blood, and when the animals live for some weeks, shows the appearances known as cardiac or nutmeg liver.
Treatment. The treatment of pericarditis due to the presence of foreign bodies is at present merely palliative. Often the only thing to be done is to slaughter the animal.