The presumption that the transmission of excitation is due to the formation of some sort of chemical compound dates from the beginning of the 20th century. It was substantiated experimentally in 1921 in the works of O. Loewi, who showed that the vagus nerve’s effect on the heart is caused by the formation of what he called the vagus substance (later established to be acetylcholine) and that the effect of the sympathetic nerves is caused by a “sympathetic substance” (norepinephrine). Subsequent research by A. F. Samoilov and C. Sherrington showed that the transfer of excitation from motor nerve to striated muscle occurs with the participation of a mediator, acetylcholine. The next stage was the discovery of the chemical transmission of excitation from neuron to neuron in the peripheral nerve ganglia and the central nervous system.