Ergotism: a condition that develops from ergotamines, substances produced due to fungal contamination of grains. A fungus (Claviceps purpurea) that contaminates rye and wheat produces substances (alkaloids) termed ergotamines.
Ergotamines constrict blood vessels and cause the muscle of the uterus to contract. They have been much used and been very useful for the treatment of migraine. They have also been used and misused as abortifacients (agents of abortion).
In excess, however, ergotamines can cause symptoms such as hallucinations, severe gastrointestinal upset, a type of dry gangrene, and a painful burning sensation in the limbs and extremities.
Chronic ergot poisoning (ergotism) was rife during the Middle Ages due to the consumption of contaminated rye. Because of the burning pain, it was known as "ignis sacer" (holy fire), "ignis infernalis" (hell's fire) and St. Anthony's fire.