Ulcerative processes are very frequent upon mucous membranes; and withal very various in their forms, in regard both to the anomaly of texture which gives rise to them, the mode in which the ulcerative solution takes place, and the form which they derive from the stratum in which they occur, and from the fact of its having been the first diseased part or not, etc. However, therefore, I may think to have increased our knowledge of several of the processes connected with these ulcerations, and to have established the diagnosis of several forms of ulcer, especially upon the mucous membrane of the alimentary tube, yet not more than a few foundation-stones have been laid for a comprehensive knowledge of the ulcers of mucous membranes.

They are sometimes the result of the softening of mucous membrane which is induced by the processes just described, the catarrhal, the exudative, and the exanthematous. Sometimes they commence upon the surface, sometimes deep in the parenchyma of the membrane: they may attack the whole of a certain circumscribed space at once, or advance from a definite starting-point, as in the case, for instance, when those processes are situated in the follicles. Moreover, though sometimes the immediate result of the process, they are at other times a secondary consequence of it, being brought about by the action of matter exuded upon the free surface, as well as in the tissue, of the mucous membrane, after that matter has undergone some solution, - some change of its nature, - some metamorphosis; as is the case, for instance, with aphthae, and with the matter of typhus.

Or again, they may be produced by the metamorphosis of some new growth which has been infiltrated into the tissue of the membrane, or of some tumor which has encroached upon it, and by the reaction consequent on that metamorphosis: of this kind are the tubercular, and the cancerous ulcer, etc.

The various ulcerative processes upon mucous membranes sometimes run an acute course, sometimes a chronic. They sometimes extend readily from the mucous to the submucous tissues; sometimes their tendency is rather to spread superficially, that is, to abrade the mucous membrane, and merely expose the tissues beneath it; sometimes like the fundamental processes by which they are occasioned, as for instance, the typhous process, their progress is limited by the adjoining submucous tissues.

This subject will be found to be pursued further where the ulcerative processes of the parts of the mucous system are separately adverted to.