Y. Chronic Inflammation

Chronic Inflammation may extend from the serous membrane to the pseudo-membranous structure which lines it, and lead to a deposition of its products both within the substance, and on the internal free surface of the new structure; that is to say, the exudation deposited by one inflammatory process may itself become the site of a new inflammation during the time that it is becoming, but is not yet completely, organized. This explains the otherwise unintelligible occurrence of exudations upon the inner surface of serous membranes, which have already been converted into thick fibroid rinds, while effusions, to all appearance quite recent, have taken place into the cavity.

This secondary inflammatory process, occurring during the progress of organization in the plastic product of a previous acute, or even of a chronic, inflammation, deposits exudation both upon the free surface of that product, and also within its tissue or parenchyma: the former constitutes a second free exudation, the latter an infiltration. The infiltered product, during its organization, becomes an integral part of the original exudation, and renders it thick and very dense, compact in its parenchyma, and of fibroid or fibro-cartiliginiform structure: the stratum thus formed becomes identified with the serous membrane.

The free exudation may be, and usually is, a plastic one, with more or less also of an aplastic portion; it may, however, present any of the qualities, and undergo any of the metamorphoses, already detailed: indeed, the inflammation within the parenchyma of the exudation may even have a suppurative tendency, and abscesses may be formed in it, analogous to those which occur in the subserous cellular tissue. The new plastic exudation becomes organized into a cellular tissue, and unites with the older layer of exudation beneath it; and it again may be attacked by inflammation, and become callous and indurated.

In this manner tough, fibroid laminae are formed upon serous membranes, which, if the process be repeated often enough, may measure three or six lines, and even an inch and more in thickness; they are united externally with the serous membrane, to which they become firmly and immovably fixed, or even with adjoining fibrous expansions, aponeuroses, periosteum, etc.

If no further inflammatory process take place in the last exuded layer, that layer becomes organized to cellular tissue; and if none of the effused fluid remain at the termination of the process, and the opposed layers come into contact with each other, they unite into a single layer, and the serous cavity is obliterated in whole or in part, according to the extent of the process. But if any of the earlier, or of the more recent, fluid effusion be still left, it is either kept encysted by the impermeability of the fibroid stratum, and the slight power of absorption which it possesses, or else it is slowly diminished in quantity by absorption. Whilst the serum is gradually being absorbed, the plastic (albuminous and gelatinous) matters which it contains are precipitated upon the walls of the fibroid exudation, and form a loose villous lining for it; or else they accumulate in one shapeless mass, and become enfcysted in some part, generally the most dependent part of the cavity. If under such circumstances, the walls of the serous cavity approximate and fall together, the layers of the exudation will be agglutinated to one another by means of a stratum of grayish jelly-like substance, into which the precipitate just described changes, and which Laennec, from his observations of it in pleuritic exudations compares to the central part of the intervertebral substances. In the end it becomes converted into a dense compact cellular tissue.

This process is mostly observed upon the pleura, and will be more particularly referred to amongst the diseases of that membrane.

An exudation of a peculiar nature is very frequently found upon serous membranes, and requires particular notice. Its true character was first discovered by Laennec, who named it the hemorrhagic exudation. It is usually large in quantity, and consists of fibrin, blood-corpuscles, coloring matter of the blood, and serum mixed in different proportions, and it is chiefly distinguished by its more or less intense red color.

The conditions out of which it arises are general and local. Those of the former kind include diseased states of the blood, particularly tuberculosis; the anomaly in the composition of the blood, which results from cirrhosis of the liver; the scorbutic constitution; and, that which is allied to the last two, the dyscrasia of drunkards. Besides these, there are, of course, red and variously discolored exudations, which proceed from decompositions of the blood, such as succeed exanthemata (variola and scar-tina), typhus, etc.

The following are the local conditions of its occurrence: The hemorrhagic exudation, though it sometimes, no doubt, results from primary inflammation of a serous membrane, yet it is far more frequently the product of the third mentioned form of chronic inflammation, i. e. of a secondary inflammatory process occurring in a plastic exudation; and this is, in fact, the cardinal local condition under which it takes place. For the structure in which the inflammation occurs is in course of organization; its vessels are only just forming, and have as yet no actual coats, or, at any rate, but very delicate and permeable ones; and they have not yet united into a freely inosculating circulatory system; from such a structure the exudation occurs, without question, repeatedly and at intervals, and probably also prematurely before the congestion has reached the degree of intensity which would, in any other structure, be necessary to produce it. The whole process bears throughout it the stamp of an inflammation which has not arrived at maturity: and its product is blood, altered by congestion in the composition, and mutual relation and intermixture of its elements. The fibrin, blood-corpuscles, and coloring matter contained in it vary with the state of the constitution, and with the composition, but more particularly with the stage of organization, of the substratum itself. It is remarkable, that it coexists very frequently with tubercle in the same substratum. (Vide Tubercle in Serous Membranes).

Where the hemorrhagic exudation-process borders upon actual hemorrhage it is manifest, and so is also the mode in which they are to be distinguished. The process is seen upon all serous and synovial membranes, but especially on the pleura and peritoneum; it is met with also in the pericardium, and in the tunica vaginalis testis; and, amongst synovial membranes, principally in the knee-joint.