Bicycle Day on April 19 honors not the two-wheeled mode of transportation, but the colorful ride taken by Swiss chemist Albert Hoffman who accidentally discovered LSD 74 years ago. In search of new medicines, Hoffman was trying to stabilize lysergic acid, a derivative of a fungal compound used in a migraine medicine. He ended up synthesizing a compound called lysergic acid diethylamine, or LSD. Later, he accidentally exposed himself to it and felt dizzy with hallucinations. On April 19, 1943, he tested it on himself again and needed a lab assistant to help him home, via bicycle, leading to a memorable ride.