In certain obstructive diseases of the heart the circulation in the lungs is so impeded, that effusion of blood, constituting pulinonary apoplexy, or effusion of lymph, producing general increase of density of the whole lung, inay occur.
Long continued pressure by a pleuritic effasion, has the effect of rendering the lung nearly solid and impervious to air.
In treating of alterations in the cohesion of mucous, serous, and articular membranes, it is necessary to premise that they consist of a basement membrane sustaining epithelium cells and supported by sub-basement areolar tissue in which vessels, nerves, and ents, are found.
The nutrition of the basement membrane and the proper development of the epithelium cells depend upon the amount and health of the fluid parts of the blood supplied to them by the capillaries of the sub-basement tissue. It is evident that any morbid state of this tissue will influence the integrity of the base ment membrane and the epithelium cells ; and it is known that, for the most part, physical alterations of these last depend upon such morbid states, and that these changes are most likely to happen where the cellular structure is loose and considerable in amount.
Softening has been found in all serous and fibro-serous membranes, and may be produced by inflammatory action and by a defective and perverted state of the general nutrition of the body.
The lining viembrane of the heart is fre quently softened, being at the same time redder and more vascular than usual. It is occasionally so soft as to peel very readily from the muscular structure ; a like state of the pericardium exists with effusion of pus into its cavity. Softening of the internal niembrane of the venous system is found of either a deep red or pale colour ; the tissue is very lacerable and breaks down into a pulp under the scalpel ; it may be caused by phle bitis, by the pressure of a considerable column of blood, especially when the valves have been obliterated ; and is found in cases of malignant fever, scurvy, and vvhenever the fluids are greatly altered. Post mortem softening is frequent enough to raise our sus picions, and great allowance must be made for the macerating and colouring properties of the blood.
Chronic softening of the internal membrane of arteries is occasionally found ; when so affected the serous tissue is easily lacerable, and such solutions of continuity are deter mined by causes, which ought in health to have no influence. Portions of the interior lining membrane may be found retracted and rolled up within the canal, so that with the effusion of lymph which generally occurs at the same time, and the consequent coagula tion of a small portion of blood, the artery may become completely obstructed and ob literated in a part of its course. Occa sionally, the arteries of the upper and lower extremities become thus affected in succes sion, on tbe emplopnent of the slightest exertion, indicating a very extensive affection of' the nutrition of the arterial system. 'We find, in cases of anwmia, and where athe roma is being deposited, considerable dimi nution of the general tenacity of the large vessels.
Softening of the arachnoid, peritoneum, and pleura is generally found where there is effusion of pus, or blood into the sub-base ment tissue ; it rarely occurs when lymph is thrown out into the serous cavity, but seems to be a more advanced phenomenon of in flammation, or, rather, is produced by inflam mation of a more intense and destructive character.
Dalmas ascribes nearly all serous softenings to diseased states of the subserous cellular tissue, and we find constantly that on account of the altered state of this cellular structure, the peritoneum and pleura may be stripped off large spaces of the parts they cover ; it is notorious, that in the pelvis sero-sanguineous effusion into the subserous cellular tissue, and consequent lacerability of the serous mem brane, frequently occur. Pulpy degeneration of synovial membrane is a kind of softening with a perverted state of the nutrition-of the tissue.
Softening of mucous niembranes is gene rally produced by- inflammatory causes : it is most frequently noticed, and is best studied, in the alimentary canal, part or the whole of which may be affected ; it is most frequently observed at the end of the ilium, in the de pending portion of the colon, and in the cm cum ; in the right and left hypochondriac re gions, and in the sigmoid flexure.