In the same way stagnant and septic water may be harmless to one animal of great vigor and good tone and pathogenic to another which lacks these qualities; or the excess of the ferment and its toxins may overcome the natural resistance of the animal. The lack of the natural antiferments of the intestine, pepsin and hydrochloric acid, on the one hand and bile on the other, will also conduce to multiplication of the microbes and their products, so that they can successfully attack the mucous membrane. Other accessory causes operate more or less, thus any impairment of the process of mastication, through diseased teeth or jaws tends to the escape of undigested food through the stomach, as a specially favorable culture media for the microbes, and irritants of the mucosa. _Lesions._ As the disease very often implicates the stomach (gastro-enteritis), the usual lesions of gastritis will be seen. Most commonly the lesions are best marked in the small intestine, and again in other cases in the colon, but usually there is more or less change in all parts of the intestinal canal. The small intestine is almost devoid of aliments and the mucosa deeply congested in patches or striæ, with at points thickening, softening so that it crushes under the finger, hemorrhagic discoloration, and even ulceration, and necrotic changes. It is covered with a layer of mucus, thin and mucilaginous or thick and glutinous, containing many granular and pus cells. The villi are swollen, the follicles of Lieberkuhn puffed up, and the agminated and solitary glands widely dilated, filled with exudate, and surrounded by an area of congestion. Proliferation of small, round cells has produced embryonic tissue in the mucosa and especially between the glands. _Symptoms._ In the _mildest form_ there is hyperthermia, thirst, insensible loins, scanty, high colored urine, costive bowels, a few small pellets only being passed at a time, hard, dry and covered with a mucous film, hot, clammy mouth, coated tongue, with redness along the edges and tip, yellowish red eyes, impaired appetite, dull, sluggish habit, a tendency to hang back on the halter, and a steady loss of flesh and increased dryness and unthriftiness of the coat. Slight, intermittent colics occurring especially after meals and attended by loud rumbling of the bowels are marked features. This may be followed by slight relaxation of the bowels and recovery in about a week, unless it should become complicated by intestinal indigestion or impaction, or should merge into the acute form.