An alteration in the texture of the mem brane itself is probably immediately subsequent to this injection in the order of time, and is generally seen in connection with it. Its surface, instead of the smooth and shining appearance which it ordinarily possesses, be comes dull and dim, while it is dry and almost rough to the touch ; and atthe same time the thin and transparent expanse of its texture acquires a milky opacity, and an increased thickness, which in the more delicate serous membranes is especially well marked. The former of these appearances probably indicates some affection of the epithelium, which clothes the free surface of the membrane ; but the latter is due to the commencement of effusion. This process begins where we should natu rally expect it, viz. in the immediate neigh bourhood of the vessels, or in the subserous and neighbouring areolar tissue.in which they ramify ; and by the filling and distention of the meshes of this net-work, it gradually com municates its own appearances to the sur rounding tissue generally.
The next stage is constituted by the ap pearance of the products of inflammation on the inner or free surface of the tnembrane, or the effusion of a plastic fluid into their cavity.
This effusion is at first a clear transparent fluid, of a tolerably limpid consistence. It is true that we are rarely able to verify this transparency in the exsudation of the larger serous membranes ; but the condition of the blood plasma from which it is derived, and the similar appearance which is visible in the case of fluid effused into the inflamed anterior chamber of the eye, together leave no doubt of the fact.
In a space of time which is a very short one, this uniformly fluid state usually gives place to a greater or less opacity and solidi fication; and in this, the earliest stage in which the effusion is generally recognized, it offers the appearance of a milky semifluid substance, which either forms the whole of its mass, or is mixed with a variable quantity of serum, frotn which it has thns already begun to separate.
The composition of this effused fluid exhibits great variety in different cases. The follow ing table is an average of five analyses by Quevenne, Scherer, and Vogel, which is corn pared with the liquor sanguinis of healthy blood, as analysed by Lecanu. This im portant comparative method of regarding these fluids is due to Vogel, in whose valu able work these analyses are given at length.
A comparison of the composition of this fluid with that of the serous effusion which was previously- described, not only exhibits the addition of a new constituent, fibrine, but it shows the quantity of albumen to be in creased in an important degree ; it being, on the average, nearly trebled. Contrasting it with the normal liquor sanguinis, it is seen to possess a considerable proportion of its albu men and fibrine, although less than this fluid itself contains. And it is important to notice, that the former of these two constituents is not only present in larger quantity than the latter, as might be expected from its very different amount in the parent fluid, but in a much greater proportion of its respective quantity, i e._ that only two-sevenths of the
fibrine of the liquor sanguinis appears in the inflammatory exsudation, while five-sevenths of its albumen is present. And in all proba bility, were the diseased liquor sanguinis of the same subjects the object of comparison, its increased quantity of fibrine would render the disproportionately small transudation of this constituent a still smaller one. Although the number of analyses from which the average is taken will allow little stress to be laid upon these facts, yet they have seemed to deserve especial notice, as having some bearing upon a question which is of the greatest importance to pathology, and which cannot yet be con sidered as settled, viz. " What is the relation of fibrine to the process of organization?" The further progress of the exsudation arranges the plastic or fibrinous constituent as a more complete coagulum, which is in contact with the inner surface of the serous membrane. The colour of this portion of the exsudation is yellowish, or somethnes reddish from mixed blood ; its thickness varies from that of a scarcely perceptible deposit to one of half an inch or more in thickness. The uniformity with which it covers the interior of the membrane is also subject to great differences ; sometimes it is arranged as a stratum of tolerably equal thickness over the whole or a greater part of its extent, at others it is limited to the formation of raised points or patches which here and there stud its surface. These conditions apparently indicate a corresponding diffusion or limitation of the inflammation. In like manner, the state of surface of this stratum is liable to great dif ferences, being sometimes level and compara tively smooth, while in other instances it offers every conceivable degree of roughness, from a trifling irregularity of surface to those long, large, and shaggy processes which are so often seen in acute pericarditis, and which have been well compared to the villi of an ox's tongue. Considerable difference of opinion prevails as to the exact mode in which this curious state is produced : thus some imagine it to be the result of the mutual movements of the visceral and parietal layers of the membrane ; or that, in separating from each other, they draw out a thread of the viscid and coagulating paste, until it breaks, and thus leaves a projecting process attached to each of these surfaces. But the fact, that an elongation very similar to that of those processes is seen in solitary warty deposits on the valves of the heart, in situations where no such physical causes as this can be supposed to obtain, renders this explanation more than doubtful ; and, on the whole, the interpretation of Vogel seems much more probable, that they result from a want of uniformity of the effusion in the first instance forming small scattered patches of lymph, on and around which, as around foreign bodies, the subsequent continuous effusion tends to deposit itself.