Tuberculosis is one of the most frequent, and, at the same time, most destructive diseases of mucous membranes: its frequency, however, is not the same in all of them. The devastations which it produces, too, though they vary considerably in their degree, are greater, on the whole, than those which result from any other process upon mucous membranes. The tubercle is deposited in the parenchyma, i. e. in the corium of the membrane, and in the immediately adjoining stratum of submucous cellular tissue, a. Either gradually and at intervals, for the most part without any manifest congestion and stagnation, in the form of isolated or clustered gray crude granulation;

B. Or, with evident symptoms of inflammation, as an inflammatory product, infiltered into the parenchyma of the membrane, and partly also exuded upon its free surface. The product in this case, either has from the first the character of yellow tubercle about to soften; or it becomes rapidly discolored, and soon acquires that character. Large tracts of mucous membrane degenerate into a lardaceo-caseous and firm, but friable layer, and the submucous tissues become dense, callous, and thickened. Acute tuberculosis, in the form of extremely fine, transparent, and crystalline, or of opaque, wheylike, grayish granulation, seems not to occur on mucous membranes, at least, not in the marked degree in which it prevails on serous membranes, and in certain parenchymatous organs.

Precisely the same forms of tuberculosis seem to occur in the follicles and glandular apparatus peculiar to certain mucous membranes, such as those of the mucous membrane of the bowel.

Of the several large sections of the mucous system, the most frequently diseased is the intestinal tract; next come the air-passages, and after them the lining membrane of the sexual organs of the female, the seminal ducts of the male, and the urinary passages in both sexes. And it is chiefly certain parts of these membranes that are subject to the disease, as will appear in the consideration of the diseases of the several organs; for there are some parts which rarely, and others that never become tuberculous. Those to which the former observation applies, are certain portions of several mucous membranes, which, in the abundance of their glandular apparatus, approximate to the character of so-called parenchymatous organs; but still there are remarkable exceptions to this rule. Thus, in the intestinal mucous membrane, the disease occurs chiefly in the ileum, which has an extensive follicular apparatus, and in the follicles themselves; and, in the mucous membrane of the air-passages, principally at the posterior wall of the larynx, which is so rich in glands; in the sexual organs of the female, on the other hand, the cervix and vaginal portion of the uterus, and the vagina itself, all which are richly supplied with follicles, are exempt from tuberculous disease; the glandular mucou3 membrane of the stomach is rarely the seat of it, etc Tuberculosis of mucous membranes is sometimes a primary disease, as is the case particularly when it occurs on the inner coat of the Fallopian tubes and uterus; but far more frequently it is a secondary and dependent affection, occasioned by previous, and for the most part advanced, tuberculosis of some parenchyma which stands in close relation with the diseased membrane, or of some generally important parenchymatous organ, such, for instance, and, above all, as the lungs.

This condition of tuberculoses in mucous membrane, viz. their originating from a considerable amount of constitutional disease, which is already manifested by an advanced tuberculous affection of a parenchymatous organ, is the reason why tubercle in that membrane undergoes scarcely any other metamorphosis than that of softening, and gives rise to tubercular phthisis of the membrane.

The gray granular tubercle softens in the substance of the mucous membrane, and forms a small vomica. Opening on the free surface of the membrane, the vomica becomes a small circular ulcer, the margin of which is sometimes flabby, but usually is hard and prominent: its base is composed of a stratum of mucous membrane, or of submucous cellular tissue; and it also may be soft and lax, but it is usually callous and condensed.

This primary minute tubercular ulcer enlarges superficially as well as in depth, by coalescing with neighboring ulcers, and by the softening of tubercles which have been deposited secondarily, during its progress, at its border and base. It thus exchanges its original form for a secondary and still more characteristic one; for it acquires sinuous, serrated, jagged, and gelatino-lardaceous borders, and a dense callous base, beset with islands and far-jutting promontories of mucous membrane; while the tissue of the base, as well as of the borders, appears interwoven with tubercles, for the most part yellow and softening.

The tuberculous infiltration of mucous membrane burrows in different directions, and becoming caseo-purulent, degenerates, together with the tissue which it involves, and which has lost its characteristic structure, to a tubercular sanious matter.

From the mucous membrane, and especially from the base of the tubercular ulcer, the deposition of tubercle advances into the different submucous tissues, and gives rise to a destructive ulceration that in membranous canals and cavities leads to perforation.

The tubercular ulcer of mucous membrane very rarely heals, as may be supposed from what has been said. When it does so, it always leaves at its borders, and still more in the structures that formed its base, a permanent callous condensation, corresponding to the original size of the ulcer. But for an account of this, and of several essential peculiarities which tubercle and the tubercular ulcer present on different mucous membranes, I must refer to the description of the diseases of particular mucous organs.