Outline of physiology of sympathetic nervous system and its effect on the cerebral blood-vessels. Other factors controlling cerebral blood-vessels, such as local intra-arterial pressure and gas tension. The action of adrenalin-like and cholin-like substances on the cerebral blood-vessels. Alteration in cerebral blood flow during a convulsion, and the accompanying changes in cerebro-spinal fluid pressure. Evidence for systemic sympathetic disturbance during a convulsion. Discussion of “vaso-vagal” attacks and “diencephalitic” epilepsy.