We have already seen that the mucous membrane is frequently irritated by the contents being of an obnoxious nature by reason of decomposition or otherwise. In.addition to that, inflammation may be produced by the action of specific morbid poisons, chiefly those of dysentery, typhoid fever, and cholera. We have therefore in the first place to consider the simple inflammations and afterwards these others.

1. Catarrh

Catarrhal inflammations of the intestine are very common in children and can usually be traced to the character of the ingesta, perhaps along with exposure to cold. The common autumn diarrhoea, which is so fatal to children, is generally due to improper food. Cold, by interfering with digestion and peristaltic action, may induce the intestinal contents to stagnate and decompose. The influence of the intestinal contents in producing catarrhs is shown by the localities at which inflammations are most common. The large intestine is much more frequently affected than the small, and in the large intestine the caecum, with the vermiform appendage, is the most frequent seat and next to that the rectum.

The catarrh may be Acute or Chronic. It is characterized by hyperaemia and swelling of the mucous membrane, with exudation of serous fluid and leucocytes. There is also increased secretion of mucus, which in the case of the colon may be very excessive. The exudation is usually Mucous in character, but in the more acute inflammations it may assume more or less of a Purulent character. If this be the case the mucous membrane is liable to be infiltrated with inflammatory cells, and after a time to undergo Ulceration. This occurs with peculiar frequency in the caecum, and next to it in the rectum.

Catarrhal ulcers are usually of considerable area and comparatively superficial. Neighbouring ulcers may coalesce so as to produce extensive, variously shaped losses of substance, in the midst of which the remaining mucous membrane appears as raised patches with irregular outline. Sometimes the floor of the ulcer is so smooth, and the remaining mucous membrane so irregular from inflammatory infiltration, that it looks as if the ulcer were the normal mucous membrane and the patches of persisting mucous membrane adventitious. The ulcers of ordinary catarrh are superficial, and unless exposed to continued irritation, as by the prolonged presence of hard faeces, they do not tend to perforation, and readily heal when the cause of catarrh is removed.

In the course of catarrhs, ulcers also arise from the Closed follicles. There are indeed some catarrhs in which the latter are mainly affected, appearing as rounded prominences and flat elevations, corresponding to the solitary follicles and Peyer's patches. This form is called Follicular enteritis. The follicles may be so infiltrated with inflammatory products as to form virtually small abscesses resulting in crater-shaped ulcers which may afterwards enlarge. In this way arise the so-called Follicular ulcers.

A frequent result of catarrh is Atrophy. This occurs as part of the induration of the mucous membrane which follows chronic inflammation. The atrophy affects first.the mucous membrane, its glands being specially involved, but it may extend to the submucosa and even to the muscular coat. According to Nothnagel, atrophy is of very frequent occurrence.

Another result is Hypertrophy of the mucous membrane such as we find so frequently in the case of the stomach. Here also there may be Mucous polypi and Cysts as in the stomach. They are most frequent in the large intestine, and if seated in the rectum they may project through the anus.

A condition of not infrequent occurrence is Enteritis membranacea. In this disease considerable pieces of membrane are passed at stool, sometimes in hollow cylinders as if casts of the intestine. These are composed of mucus, with epithelium entangled in them. They are generally regarded as the result of chronic catarrh of the large intestine, but Nothnagel asserts that inflammation is not necessary, and that it may be the result merely of defective peristaltic action allowing of accumulation of mucus in the folds of the large intestine. Hence Nothnagel suggests the name Colica mucosa.