Mucous membranes are sometimes actively congested, either in consequence of some direct irritation, or from a special relation of the constitution of the blood to a particular portion of the membrane: sometimes the congestion is passive, and occurs as a consequence of marasmus and adynamia, particularly in the tracts of membrane lining the respiratory organs and intestinal canal. Again, it may be mechanical, and extend over large areas, and even over the whole of large divisions of the mucous system: the congestions which are found in the respiratory organs and intestinal canal, in diseases of the heart, lungs, and liver, are of this kind.

It presents various degrees. In the ordinary and slight degree, it either entirely disappears after death, and the membrane, whatever may have been its state during life, is found pale; or the ramifications of veins, or perhaps the capillary vessels, are full of blood, and the membrane is red and injected. When it has been acute, it leaves the membrane swollen and relaxed, and more or less evidently succulent, while the mucous and submucous tissues are slightly oedematous; when chronic, it occasions thickening and hypertrophy of the membrane, and a permanent increase of its secretion of mucus.

In a higher degree, the congestion advances to vascular apoplexy, and apoplexy is followed by bleeding into the parenchyma, and from the surface of the membrane: the more rapidly the congestion has arisen, or been augmented, the sooner does the hemorrhage take place. These occurrences are met with chiefly in the bronchi and alimentary tube, where they may arise either from active or passive or mechanical congestion. The mucous membrane appears red and swollen, from its injected capillaries standing thick together; or dark-red and tumid, from injection that cannot be distinguished from effusions of blood into the parenchyma; or, lastly, more or less blood is found upon its surface, or collected in the cavity which it encloses, while it is itself either in one of the states just mentioned, or collapsed, pale, and bloodless.

It must, however, be remarked, that bleeding from mucous membranes in general, excepting that from the bronchial membrane, is rarely the result of mere congestion; for the most part, and in the case of the stomach and intestinal canal especially, the hemorrhage proceeds from some other part of the membrane, which is diseased in texture, though it very often appears quite trifling in extent, or may be so small as to be scarcely discoverable.

Anaemia in mucous membranes is the result of diminution of the general mass of the blood, and especially of loss of blood by hemorrhage; it is, therefore, only a local symptom of general anaemia. The pallor which ensues, under such circumstances, especially in the mucous membrane of the intestinal canal, where it proceeds chiefly from gelatinous softenings, presents a remarkable waxen hue, and a yellowish shade of color.