Acute cerebral vascular insufficiency may be defined physiologically as a deficiency of cerebral arterial blood flow resulting from an inadequate systemic arterial blood pressure or impairment of the cardiac output.1This condition is often transient and correctible, although the resulting deleterious effect upon the brain may or may not be permanent. The deficit in cerebral blood flow may involve the whole brain, or it may be localized. When it is generalized, the well-known symptoms of syncope, generalized grand mal seizures, etc. may occur. It has not been clearly recognized, however, that focal cerebral manifestations, such as hemiplegia, hemisensory disturbances, and Jacksonian seizures, are not uncommonly the result of localized cerebral vascular insufficiency. In the past, such disorders when permanent have been attributed to cerebral hemorrhage, thrombosis, or embolism. When focal cerebral signs have been transient, they have usually been considered a result of localized cerebral vascular spasm. It is