Causes: mobility of dog’s stomach when empty, leaping, running down stairs. Lesions: viscus doubled forward, pylorus in front of cardia, duodenum compresses cardia, liver, spleen and omentum displaced, stomach tympanitic, lungs and heart compressed, latter gorged with dark blood. Symptoms: tympanitic abdomen, and half thorax, no rumbling, murmur in front of thorax, abdomen tender, patient stands, dyspnœa, emesis impossible. Course: violent symptoms in twelve hours, death in thirty-six. Diagnosis: sudden, severe seizure, complete anorexia, tympany, tenderness, dyspnœa, no vomiting, arrest of peristalsis. Obstruction. Peritonitis. Choking. Treatment: tapping, laparotomy, replacing the viscus. This has been demonstrated by Kitt and Cadeac who believe that it is quite a common occurrence. _Causes._ The predisposing cause is the extreme mobility of the canine stomach which hangs from the œsophagus like a pear from its stalk, the remainder of the viscus being only attached to the loose omentum, spleen, and commencement of the duodenum all of which it can carry with it easily when it rolls on itself. Its mobility is, however, very restricted when full, the liver on the one side and the spleen and intestines on the other proving almost insuperable obstacles to rotation. But when empty it moves with great freedom and by a sudden shock in leaping, gamboling or running rapidly down stairs the pylorus is carried forward and to the left until it and the commencement of the duodenum are jammed in front of the cardia. The result is the obstruction of the cardia and duodenum by their mutual pressure in crossing each other, and the interruption of the gastric circulation and functions. _Lesions._ As just stated the stomach which would normally extend from the cardia downward and to the right is bent forward and doubled upon itself, the pylorus lying in front of the cardia, the duodenum extending from before backward above the cardia and tightly compressing it, the liver drawn to the left by the hepato-duodenal peritoneum, and the spleen displaced to the right by the traction on the omentum. The stomach enveloped in its omentum is distended by gas to perhaps ten times its normal dimensions and appears to fill the entire abdominal cavity while the intestines are pushed aside and concealed. The chest is compressed by the strong pressure on the diaphragm, and the lungs are congested of a deep blue and the right heart distended with dark blood. The animal appears to have perished of apnœa.