In human medicine at the present day there is a tendency to refer the development of round ulcer and ulcerative gastritis to the secretion of an excess of hydrochloric acid. Probably the same cause may be at work in domestic animals, but the proof has not yet been given. With regard to the pathogeny, the theories of embolism or of thrombosis of capillary vessels find favour with few authorities at the present day. Yet these explanations are logical enough, for if we prevent physiological irrigation of any given part, it is possible to conceive that ulcer formation may follow from auto-digestion, _i.e._, from the simple action of the gastric juice on a surface which is no longer protected. The theory of microbic origin has been advanced; but although it may be accepted in relation to the intestine, where the most varied organisms abound, it is scarcely so applicable to the stomach, in which acidity is always very marked and must exercise a very energetic antiseptic action. In sucking calves, however, this theory appears the most plausible. It is quite certain that ulceration may result from the unwise use of drugs, like tartar emetic or arsenious acid, especially if these be administered for long periods; but such ulceration always occurs at the same points, viz., at the deepest portion of the rumen, reticulum, or abomasum. On the other hand, ulceration due to secretory disturbance occurs at different points, and the figure opposite shows that the mucous folds themselves may be injured and perforated. =Lesions.= Ulceration of the abomasum varies in severity. The case referred to showed excavated ulcers from the site of which a portion or the whole of the epithelium and glandular layer had been shed; true round ulcers, which had destroyed the entire depth of the mucous membrane and had produced chronic inflammation and sclerosis of the muscular layer; and finally perforations resembling cleanly punched-out holes. =The Symptoms= are those of a mild form of ordinary acute gastritis, without marked fever, and without special injection of the conjunctiva. The appetite is diminished and irregular, but more as a consequence of excessive reflex sensibility of the injured organ than from absence of hunger. This excessive reflex sensibility of the abomasum causes relative or absolute gastric intolerance, so that only a small amount of the food ingested passes towards the intestine. Absolute intolerance on the part of the abomasum may even occur, as in a case described by Moussu in 1895, which produced a very special form of impaction of the rumen, absolutely different from primary impaction.