Dysentery indicates an inflammatory condition of the colon and rectum characterized by ulcerations of the mucosa and the passage of numerous small, mucous, and bloody stools. It is a term that is applied to disturbances brought about by several causes. It is most common in tropic and semi-tropic, but occurs in the temperate zones as well.

It may be due to the presence of the Entamoeba histolytica, to the Shiga bacillus, or to various ferments and toxins of decomposing meat; sometimes it may follow the ingestion of poisons, particularly mercury.

In the mild or catarrhal forms there is congestion and edema of the mucosa with some petechiae. There is a slight increase in the secretion, and ulcerations may be found involving the solitary follicles.

The ulcerative or amebic variety is much more severe. There is at first a marked nodular swelling of the mucosa. The organisms pass between the epithelial cells of the mucosa, undermine the membrane, and by increasing in numbers separate it from the blood-supply. The mucous membrane at these points becomes necrotic and is cast off, exposing the infiltrated submucosa, which eventually sloughs off. The resulting ulcers vary greatly in size and shape, but are all characterized by having a decidedly undermined edge. Several ulcers may have communications beneath the mucosa and the ulcerations may extend to the serous covering. The amebae will be found in the lesions. The process tends to become chronic, and for a long time the amebae may be found in the stools, which also contain large amounts of pus.

As the inflammation subsides the ulcerations begin to cicatrize and recovery takes place. There is usually quite extensive atrophy of the mucosa and sometimes distortions due to contraction of the healed ulcers. At times a chronic thickening of the intestinal walls may follow.

The most common complication is abscess of the liver, due to the passage of micro-organisms through the veins, lymph channels, peritoneum or gall ducts from the intestinal ulcers. In amebic dysentery there is usually a single abscess. Perforation may occur; also thromboses of the veins of the colon and mesentery and of the portal vein.

Fig. 152.-Dysentery of Large Intestine. X 50 (Dürck).

The superficial layers of the mucosa are necrotic. In the deeper layers between the glands many leukocytes have accumulated (1); 2, fibrinous thrombus in a small artery; 3, muscularis mucosae ruptured in many places by leukocytic accumulations; 4, submucosa with greatly dilated blood-vessels.

There may secondarily result a diphtheritic dysentery; a variety in which there is formed a pseudo-membrane which occurs in varying extent. There may be numerous small areas so covered, or the entire colon and rectum may be involved. If the process is mild, the mucous membrane is alone affected; but if severe, the submucosa may be destroyed.

In the bacillary form the mucous membrane is swollen, congested, and hemorrhagic, with the surface covered by blood-stained mucus. The lymphatic tissue of the colon becomes swollen, the solitary follicles undergoing necrosis with superficial ulceration. The mucosa rapidly regenerates, with a practically complete recovery to normal.