a. Inflammation is the most common form of disease of the pericardium, and is of the greatest importance, not only in itself, but also from the subsequent results to which it may give rise.

Inflammation may either be primary or secondary, being in the latter case metastatic or derived from the inflammation of neighboring structures. It may be either general or partial. It may be acute in its course, or, and such is more frequently the case, of a chronic form. The greatest variety is found to exist both in the quantity and the character of the exudation. The following remarks on the inflammation of the pericardium will be found to be in accordance with what has been already stated regarding inflammation of serous membranes in general.

1. From the importance of the subject, we will, in the first place, consider primary inflammation of the pericardium; next, its general and partial forms, the character of the peripheral coagula of the exudation, with the mode of their organization generally; acute and chronic inflammation with purulent exudation; chronic inflammation recurring in the false membranes; inflammation with hemorrhagic effusion; and lastly, and specially, inflammation with an exudation of a tuberculous nature.

Primary general inflammation of the pericardium, in accordance with what has been already stated, affects the parietal as well as the visceral surface, that is to say, the external serous investment of the heart and vascular trunks; it is more developed on the former than the latter, excepting in a few cases, and its peripheral coagula are more copious and abundant. Among the anatomical indications of inflammation most worthy of notice, we may especially mention injection, because it may here often be distinctly observed and investigated. The serous surface of the pericardium assumes in that case the appearance of soft, red velvet, having obliquely erect piles, and looking pale and turbid, as if infiltrated.

Partial Inflammation may affect any part of the pericardium, as will be seen when we have occasion to refer to the circumscribed organized inflammatory products, - the so-called milk-spots.

The periipheral coagula appear very fully developed and distinct upon the pericardium, in the forms that have already been generally described. Their free surface commonly appears as if covered with villous threads, which are either soft and lax, or stiff, and vary in character. Laennec has compared them to the inequalities remaining on two plates, which, after having been covered with a layer of butter, and laid against one another, have been quickly separated, and it is probable that this appearance gave rise to the terms made use of by the ancients, when they described the heart as cor villosum, tomentosum, hirsutum, hispidum, etc. Sometimes these shaggy masses are more or less accumulated at different spots, or ranged side by side, which is doubtlessly owing to the direction of the undulations produced in the serous effusion by the heart's motion. In many cases they may be aptly compared to the appearance presented by the dorsal surface of a bullock's tongue, whilst in others, the coagulum exhibits an areolar free surface, similar to that of the mucous membrane of the gall-bladder.

When the coagulable matter occurs in larger quantities in the serous portion of the effusion, it is found in some few cases in the form of roundish and somewhat flattened free bodies, about the size of a bean or hazelnut, and generally constituting a network between the heart and pericardium, to both of which it adheres.

The plastic coagula become converted into a cellular or cellulo-fibrous dense tissue, with a permanent thickening of the pericardium, corresponding to the intensity of the process; and the different loose filamentous adhesions, or close fusions of the heart and pericardium, which are so frequently observed, either partially or totally (according to the extension of the process) are formed by this tissue. Amongst the partial adhesions, we may specially draw attention to those of a circumscribed nature occurring at the apex of the heart, those occurring at different parts along the sulcus transversalis, and the adhesions of the pericardium in the vicinity of the arterial trunks. In the first of these spots, the connecting medium is often drawn into long threads or strings by the movement of the heart's apex, and the adhesion is thus at length broken through, in consequence of which we usually find an accumulation of long, shaggy, cellular tissue at that part, and on the opposite portion of the pericardium; the second class of adhesions derive importance from their ordinary combination with diseases of the valves, especially towards their margin of insertion; and the last from the evidence which their common occurrence affords of the frequency of pericarditis, which may prove of serious moment at the origin of the large vessels, as we shall subsequently have occasion to consider.