Tuberculosis rarely manifests itself in the pericardium in any other form than as a product of inflammation. Pericarditis gives rise to an exudation, whose peripheral coagula, after passing, wholly or in part, through various metamorphoses, merge into tubercle. It frequently happens in chronic inflammations of the exudation-deposits that the deeper or older strata have become tuberculous, while the more recent coagulum, which is becoming tuberculous, is covered by a secondary, villous, and shaggy deposit from the fluid effusion.

This form of tuberculosis of the pericardium, in accordance with what has been already stated regarding tuberculosis of the serous membranes generally, is not of a primary character, being usually associated with and dependent upon an earlier tuberculous condition, which has formed as it were the focus or starting-point of the disease, and has been manifested as tuberculosis of the lungs and bronchial glands, or as a chronic tuberculosis of some of the great serous membranes, especially of the peritoneum.

In this form of pericarditis there is always much serous effusion, which is undoubtedly increased by the inflammation being paroxysmally developed in the tuberculizing coagulum. This effusion frequently becomes hemorrhagic, in consequence of such secondary exudations.

The tubercles, which are often of considerable size, and fused together into one aggregate mass, are occasionally seated close to the muscular tissue, into whose fibres they occasionally penetrate so far as to lead to much doubt regarding their original position.

This form of tubercle very rarely passes into the metamorphosis of complete softening, since death, when it ensues, is generally occasioned by the pericarditis, or the subsequent tuberculous secretions, or even by general cachexia. Occasionally one or more tubercles, or tuberculous masses, may certainly be observed to become disintegrated, but the process is seldom sufficiently prolonged to produce an abscess, or a corrosion, - tuberculous suppuration of the pseudo-membrane and of the pericardium itself. As we have already observed, the tuberculous exudation soon manifests its influence on the tissue of the heart, which, however rapidly the disease may prove fatal, is always found to be strikingly discolored, having generally acquired a dirty-brown color, and is moreover flabby and easily torn.

5. Cancer only affects the pericardium in a secondary manner; and, in most cases, only where secondary cancerous formations have been developed in the mediastinum. This secondary mass either spreads itself in the form of an infiltration of the fibrous layer of the pericardium over a large portion of its surface, or presses upon and into the tissue itself, where it becomes developed into roundish or flattened, teat-like nodules.

In the very rare cases in which cancer occurs in the pericardium, independently of the above conditions, it presents itself in the form of numerous, flattened, and roundish nodules. It then always occurs in combination with cancer of other serous membranes, especially of the contiguous pleurae, and depends upon an excessive dyscrasia, developed by previous cancerous degeneration of different parenchymatous structures, and frequently exasperated by the eradication of large carcinomatous masses.

We have never met with any other form of cancer of the pericardium but the medullary.