Under these conditions inflammation of the omasum develops slowly, and from the clinical point of view is identical with what was formerly known as obstruction of the omasum. Obstruction or impaction is probably much rarer than has been stated, in so far at least as it constitutes a primary condition, for in the great majority of cases it is consecutive to impaction, inflammation of the rumen, or inflammation of the abomasum. Obstruction of the omasum, which was formerly invoked in all doubtful and ill-defined cases of digestive disturbance, seldom occurs as an isolated disease. It has been suggested that the omasum, being supplied with nerves solely by the sympathetic system, and provided with a relatively weak muscular coat, was more susceptible than the other reservoirs to the reaction of abdominal reflexes, and therefore more subject to inflammation, indigestion and obstruction. We do not hold that view, because, as a result of its general situation and the position of its orifices of communication, this compartment is easily able to expel its contents so long as they are liquid. Its function appears chiefly to be to complete the trituration of food after rumination. We do not consider that inflammation of the omasum never occurs, for we are well aware of the contrary, and that the inflammation assumes a subacute course and is accompanied by stasis of the semi-digested food between the mucous leaves which partly fill the cavity. We simply wish to emphasise the view that the condition is not a primary and isolated inflammation. =Symptoms.= The symptoms are always vague and very difficult clearly to define. Inflammation of the omasum is indicated by relative loss of appetite, marked thirst, general atony, and diffuse and vague sensitiveness in the inferior half of the right hypochondrium (zone of the asternal ribs). There are no pathognomonic symptoms. Obstruction has also been described as accompanied by loss of appetite, constipation, the passage of black, coated, fœtid and sometimes blood-streaked fæces, symptoms of chronic tympanites with fœtid eructations and sometimes vomiting. These sometimes accompany hydrochloric acid dyspepsia, a form of chronic gastritis, and, from our standpoint, the stagnation of food in the omasum is only secondary. We therefore interpret the facts in quite a different manner, and believe that only by a rational and physiological interpretation of the symptoms observed can one diagnose the condition. =Diagnosis.= The diagnosis of inflammation of the omasum can only be made by a process of exclusion; and although we are admittedly dealing with a condition secondary to disturbance of the rumen and reticulum, or on the other hand consecutive to inflammatory states or to modifications in the secretion of the abomasum (dyspepsia), the diagnosis does not present insuperable difficulties. =The prognosis= is only grave when the primary acute or chronic conditions of the other gastric compartments are serious.