Enteritis (Gr. EVTEpov, an intestine), a medical term denoting inflammation of the mucous membrane of the small intestine. It is most frequent in young children, being a rare disease in adult life. It is marked by redness, softening, and thickening of the mucous membrane, ecchymoses in its substance and beneath it, and serous infiltration of the submucous connective tissue. The symptoms of enteritis are a moderate febrile movement, pain, tenderness, and diarrhoea, with nausea and vomiting. The pain is restricted to a small part of the abdomen, or spreads over its whole surface, according as the inflammation extends to the whole or part of the intestines; it is commonly severest about the navel, and is always increased by pressure. This pain is generally the first manifestation of the disease. The brain usually but not always remains unaffected. As occurring in adults, this is not usually a fatal disease, but generally terminates in convalescence in about a week or ten days from the commencement of the attack.

Acute enteritis is distinguished from dysentery, or inflammation of the large intestine, by the absence of tenesmus and the characteristic dysenteric discharges; from gastritis, or inflammation of the stomach, by the comparatively mild character of the general symptoms; and from colic by the presence of tenderness, diarrhoea, and fever, and the absence of severe spasmodic pain. - The treatment usually adopted is a purgative at the outset, followed by opiates in sufficiently large doses to relieve the pain and diarrhoea, with warm fomentations to the abdomen.