On opening the cavity of the abdomen all the viscera contained in it appear, in general, more vascular than natural, and invariably of a darker colour than in the state of health. Several of the organs are affected in a uniform and peculiar manner, but that which is by far the most constantly diseased is the mucous membrane of the small intestines; and especially that portion of it which lines the ileum and the cæcum. The varieties of disease exhibited by this membrane may be comprehended under three, namely, vascularity, thickening and ulceration. In all cases increased vascularity is the first stage of disease: in a great proportion of cases this increased vascularity is confined to the inferior extremity of the small intestines, which is often distinctly inflamed when not the slightest deviation from healthy structure is traceable in any other part of the canal. The second stage of disease consists in thickening of the membrane, or in deposition of matter beneath it, or in both. Preternatural thickening of the membrane is often of very considerable extent: deposition of matter beneath it appears to be confined to the situations of the mucous glands. These glands are found in all states and stages of disease from the least to the greatest enlargement, and from the mere abrasion of their surface to the entire ulceration of their substance. Perhaps one of the glandulæ solitariæ enlarged and covered with inflamed mucous membrane may constitute the only morbid appearance discernible in the intestine; or this deposition may take place in so many of these glands as to present a most extensive surface of disease. The third stage is that of ulceration, which may supervene when the membrane is affected in either of the modes just described; but the ulcer will not be the same in both cases: in each it will have a different and a distinctive character. If ulceration take place while the mucous coat is in a state of simple vascularity, the ulcer will in general be extensive but superficial; its surface will present a smooth appearance, and its margin will be regular and defined: if, on the contrary, it occur after thickening of the membrane or enlargement of its glands, its characters will be just the reverse: it will be less extensive, but more deep, because it must penetrate a mass of adventitious matter before it can reach the other coats; and, for the same reason, its margin will be more elevated and its surface more ragged. It is in this form of ulcer that perforation of the intestine generally occurs; in which case the mucous and muscular coats alone are ulcerated: the peritoneal gives way from gangrene. Whenever the mucous membrane is ulcerated, whatever be the form of the ulcer, the corresponding portion of the peritoneal coat is more vascular than natural; and perforation must be attended with inevitable death, on account of the extensive and intense peritonitis excited by the escape of fæces into the peritoneal cavity.