The dream that proved nerve cells talk to each other with chemicals

In 1921, physiologist Otto Loewi jolted awake from a dream, ran to his lab, and tested it on two frog hearts joined only by shared fluid. Stimulating the vagus nerve on one heart slowed it - and when he transferred its fluid to the second heart, that heart slowed too. The messenger was acetylcholine, the first neurotransmitter ever identified, and Loewi shared the 1936 Nobel Prize for finding it.

— Otto Loewi, Otto Loewi — Pflügers Archiv, 1921; Nobel Prize in Physiology or Medicine, 1936