Megrim (Migeaine, Hemiceania) is a form of headache, which usually recurs at tolerably definite intervals, and which sometimes is limited to one half of the head. This disease is eminently hereditary, and usually occurs in families which have a history of nervous complaints. It commences, as u rule, in early childhood, and the attacks diminish in intensity after middle life. In addition to the pain in the head, there is sometimes vomiting and dimness of sight. A peculiar symptom which is occasionally present is hemiopia - that is to say, there is a temporary dimness of vision as far as one half of the visual field is concerned. The outer boundary of the dim area is sometimes limited by an outline, which has been described as resembling that of a fortification. An attack of megrim usually lasts for eight or ten hours; it may be brought on by errors in diet, over-fatigue, or by breathing a polluted atmosphere. As regards treatment, careful attention to diet and the use of tonics are indicated.