St Anthony’s fire is the historical name for ergotism, the poisoning caused by eating grain contaminated with ergot, the dark fungal sclerotia of Claviceps purpurea that replace kernels on rye and other cereals. The alkaloids in ergot constrict blood vessels and disturb the nervous system, producing two dreaded forms: gangrenous ergotism, in which fingers, toes, and limbs blacken and die from lost circulation, and convulsive ergotism, with hallucinations, spasms, and seizures. Medieval epidemics swept Europe, and sufferers sought the shrine of St Anthony, patron of the afflicted, giving the disease its name. Modern grain cleaning has made ergotism rare, but it remains a textbook lesson in mycotoxin danger and the origin of important drugs, including ergometrine.