Vagusstoff (literally translated from German as "Vagus Substance") refers to the substance released by stimulation of the vagus nerve which causes a reduction in the heart rate. Discovered in 1921 by physiologist Otto Loewi, vagusstoff was the first confirmation of chemical synaptic transmission and the  first neurotransmitter ever discovered. It was later confirmed to be acetylcholine, which was first identified by Sir Henry Hallett Dale in 1914.  Because of his pioneering  experiments, in 1936 Loewi was awarded the Nobel Prize in Physiology or Medicine, which he shared with Dale.