ergot (ûr´gət), disease of rye and other cereals caused by the fungus Claviceps purpurea. The cottony, matlike body, or mycelium, of the fungus develops in the ovaries of the host plant; it eventually turns into a hard pink or purple body, the sclerotium, or ergot, that resembles a grain of rye in shape. The sclerotium contains alkaloids (many of which are biologically active) that are toxic to humans and livestock. Ergot poisoning, or ergotism, epidemic in the Middle Ages, results from eating bread made of rye contaminated with ergot. Ergot poisoning is characterized by constriction of blood vessels, resulting in numbness and the development of gangrene in extremities; it may also affect the nervous system. Some of the alkaloids in ergot, e.g., ergotamine and ergonovine, are used as medicines; these alkaloids are chemical derivatives of lysergic acid, which is used in the synthesis of the hallucinogen LSD. Ergotamine alleviates migraine headaches. Ergonovine is used medicinally to stop hemorrhage and cause contraction of the uterus; during the 17th cent. midwives used ergot to stop postpartum uterine bleeding.