Fig. 1 A. Effect of inhalation of small amount of amyl nitrite on preheadache scotomas in migraine subject. The amount was insufficient to cause a drop in blood pressure or “light-headedness.” B. With inhalation of a large amount of amyl nitrite, a drop in pressure occurred with amblyopia and faintness. (Wolff HG: Headache and Other Head Pain, 2nd ed. New York: Oxford University Press, 1963)