“[A] Great plague of swollen blisters consumed the people by a loathsome rot, so that their limbs were loosened and fell off before death.” From the Annales Xantenses (857 AD).
It has been blamed for the Salem witch trials and the “Great Fear” of 1789, which contributed to the French Revolution. Its reemergence in the 20th century led to a treatment for migraine headaches and to the invention of LSD.
But in the Middle Ages, what we now call ergot poisoning, or ergotism, was a terrifying mystery known as “Holy Fire” (ignis sacer) because of the terrible burning pain it caused. Ergot — the common name for Claviceps purpurea – is a fungus that affects rye and other grains. It contains ergotamine which, in moderate doses, causes the contraction of smooth muscle fibers, such as those in the small arteries.