Ergot (Claviceps purpurea) is a parasitic fungus grown in 
certain cereals particularly rye. Before the use of modern 
method to remove it, mass poisoning was common. It causes 
vasoconstriction and uterine constriction. The former effect 
can lead to gangrene of the feet and arms. The affected tissue
become mummified and drop off without bleeding. The limbs
often turn black and the sufferers experience a burning 
sensation. In Medieval time, the disease was also called 
St. Antony's fire after the shrine where the sufferers sought
relief. The uterine (oxytonic) effect made it popular for inducing 
labour, this is not longer used for normal labour as it can cause 
death to the foetus. The ocular effects of ergot include marked 
retinal vasoconstriction with oedema and cataract.