Introduction

The alimentary canal is lined throughout by a mucous membrane, which consists of loose connective tissue covered with epithelium in one or several layers. In the mucous membrane, and to some extent beneath it, are glands which in different parts have different structures, but everywhere secrete materials that pass into the canal. In addition to these there are in many parts closed follicles of a lymphatic structure which usually lie near the surface and frequently take part in changes going on there. Beneath the mucous membrane is the submucous tissue which, for the most part, is loose, and so allows the mucous membrane to go into folds or be stretched out flat according to the state of dilatation or contraction of the canal. Outside this there is a muscrtlar coat, generally in two layers, by means of which movements and variations in calibre are effected. In most parts of the intestinal canal there is a limiting serous coat.

In the diseases of the alimentary canal it is chiefly the mucous membrane that we have to deal with, the subjacent structures being usually subordinate and affected secondarily. The serous coat, it is true, is often affected independently its diseases, however, do not belong specially to the alimentary canal, but to the peritoneum as a whole. The mucous membrane, on account of its exposure to a variety of influences derived from the varying contents of the canal, is specially liable to inflammation, and the great majority of the diseases to be considered here are inflammatory.