Here's something from the Web:

It is now fairly widely thought, based on the research of Linnda Caporael (1976) and later Mary Matossian, that the seven girls and women tried in the Salem, Massachusetts witch trials in 1692 were suffering hallucinations and other symptoms of ergotism (convulsive ergotism). Similar eruptions of ergotism also occurred in Essex County and Fairfax County, Connecticut. In that year, the weather was damp and cool, and rye plants of New England would have had much ergot, which forms sclerotia under those cool, moist conditions. Infants died from consuming contaminated mother's milk. A famous outbreak of ergotism occurred in Sologne, France in 1777, when 8000 people died of gangrenous ergotism. The last major outbreak was 1951.

http://www.botgard.ucla.edu/html/botanytextbooks/economicbotany/Claviceps/

Edit: And this, too, from the above page:

"The psychoactive ingredient in ergot is LSD, lysergic acid diethylamide. The activity of this compound was accidentally discovered in 1943 by Dr. Albert Hofmann, an organic chemist, who hallucinated when he got some of this substance on his skin. Hofmann experimented on himself to study the effects of this colorless, odorless, and tasteless substance."