Vagusstoff

By the time Loewi began his experiments there was much discussion among scientists whether communication between nerves and muscles was chemical or electrical by nature.

Experiments by Luigi Galvani in the 18th century had demonstrated that electrical stimulation of the frog sciatic nerve resulted in twitching of the leg muscles, and from this he developed the concept of bioelectricity.

This led to the idea that direct electrical contact between nerves and muscles mediated transmission of excitation.

However, work by John Newport Langley had suggested that in the autonomic nervous system communication in the ciliary ganglion was chemical.

Additionally, acetylcholinesterase activity (the enzyme that degrades acetylcholine) is low, particularly in an unheated laboratory, allowing the neurotransmitter to remain long enough to be collected and applied to a second heart.

Figure 1. Diagram of the frog heart preparation used by Loewi. Vagus nerve stimulation slows heart rate while accelerator (sympathetic) nerve stimulation speeds up heart rate.
Figure 2. Loewi's experiment proving that neurotransmision was chemical, rather than electrical.
Original records from Loewi's experiment in 1921. Saline from the stimulated heart was added to the unstimulated heart whenever the number "2" is indicated in the graph.