Numerous investigations have been concerned with the effects of acute arrest of cerebral circulation in animals. The earlier workers1 studied the effects of ligation of the cerebral arteries. More recently, observations have been made on the effects of temporary occlusion of the chief cerebral arteries2 and of temporary cessation of the heart beat.3 Using the method of occlusion of the chief cerebral arteries, Sugar and Gerard4 measured the survival time for different regions of the cat brain by the persistence of spontaneous action potentials. A careful study of the changes in function and structure of the brain of the cat resulting from temporary occlusion of the pulmonary artery was reported on by Weinberger, Gibbon and Gibbon.5 These methods involved one or another of the following complications: anesthesia; surgical procedures at the time of arrest of circulation in the brain; incomplete arrest of circulation as a