1. Deficiency And Excess Of Development In The System Of Serous Membranes

There are various kinds of primordial defect in serous membranes. They may be entirely wanting. Sometimes the organs they should enclose are wanting too; but if these exist, the deficiency of the membrane is supplied by some adjoining serous expansion. They may be but partially developed. This is the case when serous cavities are fissured, or when, in consequence of a partial defect in the wall of separation between two serous sacs, their cavities have an unnatural communication with one another. Thus the cavity of the pericardium is sometimes continuous with that of the pleurae, the peritoneum with the latter or with the tunica vaginalis of the testicle, bursae communicate with the synovial cavities of joints, etc. Moreover, a deficiency in the development of a serous or synovial membrane may depend upon the absence of the organ usually contained within it; in which case, particular duplica-tures of the membrane do not exist.

Wasting of a serous membrane, obliteration of its cavity, degeneration of it into cellular tissue (Rückbildung), and its destruction by suppuration, constitute instances of acquired defect.

Excess of development may present itself as a congenital anomaly. It then sometimes assumes the form of unusual saccular prolongations and duplicatures of the membrane, or of folds which, though such as usually exist, are preternaturally developed, - a form of excess which may partly be traced to an arrest of development: sometimes appearing under another form, as a serous cyst, or an aggregation of serous cysts, or as a honeycombed serous tissue, it marks the site of some originally defective part, or of an organ which had been diseased and destroyed during foetal life, - the brain, for instance, in hemicephalus, or the kidneys.

It more frequently happens, that new serous tissue is formed at some period subsequent to birth; it may present the characters of true serous membrane, or may be cellulo-serous or fibro-serous. Thus, a. Bursae, which are the simplest form of the synovial system, are developed beneath the skin, where it is exposed to unusual and permanent pressure and friction, as is the case in clubfoot (Béclard), over the point of an angular curvature of the spine (Brodie), or on the stump of an amputated limb; and they are also observed in deeper parts, between muscles and tendons, as well as between them and the unusual protuberances of bone, etc. Moreover, dislocated bones are sometimes firmly fixed by a new synovial capsule; and the preternatural joints formed in cases of ununited fracture, furnish another example of the same new growth.

B. Membranous capsules are sometimes formed around foreign bodies, or around effusions of blood either in cellular tissue, or in various parenchymatous structures.

y. Cicatrices upon mucous surfaces, the lining membrane of abscesses, and the material by which they are finally consolidated and closed, are composed of plates or of capsules of serous tissue.

Acquired excess of development includes further the change of texture, and simultaneous alteration of secreting power to which, in some few instances, the skin is liable when excessively stretched; especially the skin covering broad expanses of tendon (as for instance, that on the abdomen). The fact is observed more frequently under similar circumstances in mucous membranes, particularly in the excretory ducts and reservoirs of glands, when they become distended, and in the mucous membrane of the intestinal tube, especially in the appendix vermiformis.

e. In like manner, the products of inflammation in serous membranes sometimes become organized into a cellulo-, or fibro-serous tissue, the characters of which, as to extent, intimate structure, and firmness, vary considerably, and give rise to corresponding varieties in the adhesions which they produce between the parietal and visceral layers of the membrane.

t. The serous cysts, which are found in cellular, and in various parenchymatous, tissues, belong to the same class.

2. Deviations Of Serous Sacs From Their Natural Size And Form

The principal deviations in these particulars are those in which serous sacs are enlarged; a change to which their great extensibility renders them extremely liable. In enlargements of this kind, the sac may be distended equally in all directions, and thus preserve its natural form; or being bound down in some situations by fibrous membranes, aponeuroses, muscular coverings, etc, it may yield at some other circumscribed spot, and give rise to a hernial protrusion or diverticulum, which communicates with the general cavity of the sac by a constricted neck.

3. Solutions Of Continuity

Besides being exposed to wounds from fragments of bone and various instruments, serous membranes may burst or be torn by violent concussion and compression, and such rupture may be the only injury produced. Moreover, they are sometimes opened by primary and by secondary ulcerations, but that subject will be referred to again.

4. Diseases Of Texture

1. Congestion, - Hemorrhage

Serous membranes are liable, under various circumstances, to an increased flow of blood into them, and to congestion: the cause may be active, passive, or mechanical; and the extent may be partial, or universal: the walls of hernial sacs, and the peritoneum covering the organs protruded into them, sometimes furnish an instance of partial congestion.

In proportion to their duration, or to the frequency of their recurrence, these congestions occasion more or less of a whey-like, or milky opacity, a loss of transparency, and at last thickening of the membrane. Such changes are sometimes general over the whole sac, and sometimes are confined to a portion of its visceral, or of its reflected, layer: they must be distinguished from organized exudations upon the free surface of the membrane. They give rise to the developments of growths resembling cartilage or bone beneath the serous membrane, and are often accompanied by an increased secretion of serous fluid, which may be retained and so accumulate. The quality of the fluid varies with the character of the congestion and the constitution of the blood; and may be pure serum, or may contain various coagulable matters, particularly albumen, or the coloring matter of the blood. Such cases constitute dropsies of serous membranes.

Congestion is sometimes so intense as to occasion hemorrhage into the sac; but this is a very rare occurrence in serous membranes generally, and can be called frequent only in the sac of the cerebral arachnoid. The bleeding in that case proceeds from the parenchyma, and is capillary; it must not be confounded with that which can be traced to the rupture of larger vessels, whether spontaneous or traumatic; or with that which originates with membranous or parenchymatous structures; or yet with hemorrhagic products of inflammation.