THE activity of the cerebral centres which is independent of their common exciting causes, and which is termed “discharge,” presents indications of the character and loss of their function which can be obtained from no other source. Foremost in interest and also in importance are the sensations of sight which occur without stimulation of the retina. Of these the most important are two. (1) Those which occur at the onset of epileptic fits, from the “discharge” in the brain influencing consciousness, through the visual centre, before loss takes place. (2) Those which occur as the precursory symptoms of the paroxysmal headaches which, from their one-sided distribution, have been called “hemicrania,” “megraine” or “megrim,” from the frequent vomiting, “sick headaches,” and, from the inhibitory loss of sight, “blind headaches.” These two classes form the subject of the lecture.