The Exanthematous Processes Upon Mucous Membranes are allied to the exudative. They are sometimes the manifestation of a very great degree of constitutional disease, and form a complementary addition to eruptions on the general integuments; sometimes they are vicarious with the crisis of an exanthema upon the skin, which, from various influences that we are ignorant of, is insufficiently developed; and sometimes they constitute a specific eruption, arising from a special relation between the general disease and a particular tract of mucous membrane, - mucous exanthema, as it has been lately denominated. The seat of the two former kinds is chiefly mucous membrane where it adjoins skin, but to a certain extent also it is found where mucous membrane is connected with the original "atriis morbi;" such as the lining of the mouth, pharynx, tracheal passages, conjunctiva, or urethra: the last kind, on the contrary, is confined to particular parts of the mucous system, as to the ileum in typhus, and the colon in dysentery.

The following are the forms observed: diffused or circumscribed redness or spots, - erythema which sometimes, by their various tints, betray the kind of constitutional affection that exists; vesicles of various sizes and number, separate or confluent, and filled with a fluid that is chiefly serous, but passes through sundry changes as the process goes on: and pimples and pustules of different dimensions. As belonging to this class, we may enumerate erysipelatous affections of the pharynx, especially those which take place in scarlatina, and in its anomalies; the miliary eruptions that occur upon mucous membranes affected with catarrhal inflammation, or at the commencement of dysentery; the affections of the mucous membrane of the larynx in measles; the pustules of variola on the pharynx and air-passages, and on the urethra; and herpetic pustules. In many processes, generally enumerated in this class, which assume the form of papules and nodules on the membrane, the principal seat of the affection is the follicular apparatus, as is the case in true intestinal typhus, and in several other processes allied to it.

Exanthemata upon mucous membranes pass, in favorable cases, to the same terminations as the corresponding processes upon the integuments; but in acute cases, in which, from any cause, the exanthematous process is concentrated upon one section of the mucous system, it may readily occasion softening of the membrane, and loss of substance by ulceration of its tissue. Of this kind are the ulcerations that occur, rarely indeed, on the mucous membrane of the throat and larynx during and after scarlet fever, measles, and variola; as well as the softening of the mucous membrane of the large intestine that constantly accompanies severe cases of dysentery, and the peculiar metamorphosis that almost invariably takes place in the typhous follicle of the intestinal mucous membrane.

The study of this portion of the pathological anatomy of mucous membrane is attended with great difficulties: for, with the exception of some of the processes that have been mentioned, such as typhus and dysentery, they occur so seldom, the products of the exanthema are so delicate, and there is such loss of color and collapse of the membrane after death, that very little is known about it.