For the nervous system to receive information from the body and send out instructions, it must rely on finding a way of passing its electrical impulses from one nerve cell to another. By revealing the mode through which impulses communicate their signal across the miniscule gaps, or synapses, that separate nerve cells from each other and from their target destinations, Sir Henry Dale and Otto Loewi received the 1936 Nobel Prize in Physiology or Medicine.

Opinions as to how neurons communicate their signals across synapses were divided between those scientists who believed that the message was electrical, like the nerve impulse itself, and those who believed that chemicals must be involved, because extracts from plants and animals provoked a similar response to nerve stimulation. Otto Loewi’s demonstration that chemicals act as the messenger was beautifully simple. He showed that if the vagus nerve fibres connected to an isolated heart of a frog were stimulated by electricity, it dampened the strength and rate of its heartbeat and a fluid was released. When he collected the fluid and added it to a second frog heart, its heartbeat was affected in exactly the same manner as the first heart without any nerve being fired.

Loewi’s discovery of the nerve-stimulating fluid (he called it vagusstoff) came seven years after Sir Henry Dale had identified a chemical extracted from the fungus ergot, which appeared to stimulate organs in a similar manner. Dale speculated that this chemical, acetylcholine, and Loewi’s vagusstoff were one and the same, and while looking for another chemical in mammals, he discovered that acetylcholine is produced naturally in the body. Developing methods for extracting acetylcholine from animal tissues allowed Dale and his colleagues to carry out a series of experiments that revealed how the chemical works. Among their many findings they showed that acetylcholine acts on many tissues and organs other than the heart, that it is released from nerve endings, and that it is almost immediately destroyed by another chemical once it has carried out its task.