Original article by Dr. Peter J Koehler, published 6 February 2012, Neurological History in World Neurology Vol 27 No. 1

The Leyden jar, discovered in1745, was of fundamental importance in the medical application of electricity.
The Leyden jar, discovered in 1745, was of fundamental importance in the medical application of electricity.

As far back as the second century AD, the Alexandrian physician Galen suggested that animal spirits drove nerve function, and that view – that the animal spirits were a volatile substance that flowed through hollow nerves and caused muscles to move – prevailed until the late 18th century. At that time, Benjamin Franklin's discoveries and theories about electricity became known and scientists began to explore whether electricity might be the key to explaining nerve function.

It had been known for a long time that several kinds of fish, such as catfish and rays, could cause numbness. In 1714, the influential French scientist René-Antoine Ferchault de Réaumur explained the numbness as the "effects of a very lively percussion, operated by a curious apparatus of muscles placed under the back of the animal." There was one fish, found in creeks of Dutch colonies in the north of South America, Surinam, and surroundings that had a very strong numbing effect. Colonists who had experienced the effect of the Leyden jar, (an early capacitor discovered by Pieter van Musschenbroek in 1745) realized that the shocking, numbing effect of the "tremble eel" felt similar that of the jar and that the numbness from the eel might have been caused by electricity.

The Leyden professor of natural history Jan Nicolas Sébastien Allamand (1713-87; of Swiss origin) published his correspondence with the colonists in Essequibo, a Dutch colony in what is now Guyana, in the Proceedings of the Dutch Society of Sciences (of Haarlem) in 1756:

Almost two years have past since I received a fish from Mr. [van] 's Gravesande, general director of the Volksplanting of Issequebo; a fish that the inhabitants of the place consider a kind a eel; although basically it is a fish, called Gymnoti.


Allamand's correspondent, Laurens Storm van 's Gravesande (1704-1775) was administrator and secretary of the Dutch West-Indies Company and informed Allamand about his observations:

The experiment was done with an eel called a tremble fish, and what I had written to you about it in my previous letter is true. It produces the same effect as the electricity that I felt with you, while holding [my] hand in a bottle [Leyden jar] that was connected to an electrified tube by an iron wire.

The effect of the fish is much stronger than that of rays: If one touches the fish, it does not give off fire or sparks, similar to the apparatus for electricity. But for everything else it is the same; yes, even much stronger, because if the fish is big and lively, the shock produced by the animal will throw anyone who touches it to the ground, without exception, and one feels it throughout the whole body.

The tremble eel
The tremble eel that Linnaeus (1766) named Gymnotus electricus is known today as Electrophorus electricus.

Images Courtesy Museum Boerhaave, Leiden, the Netherlands

At the time, electricity was gradually introduced for treatment of various afflictions, as Allamand had reported in the Proceedings several years previously. For example, Abbé Nollet in cooperation with Sauveur F. Morand and Joseph Marie F. de la Sône at the Charité Hôpital in Paris tried to get body parts that had been affected by paralysis to move on application of an electric pulse from the Leyden jar, but were not successful (1746).

A year later, the Swiss professor of experimental philosophy and mathematics, Jean Jallabert, was able to produce contractions in the arm of person with right hemiplegia and shortly thereafter of his own, healthy, arm muscles. Allamand wrote that clinical trials with electricity usually did not produce great medical benefits. Nevertheless, he found an exception with a young girl suffering from affectum paralytico-spasmodicum, who, after an intense terror, displayed hemiparesis, fits, and aphasia. Following electrical treatments, her speech improved, but she was not as fluent as she had been before her illness. She showed more recovery of her other impaired functions (Verhandelingen Hollandsche Maatschappye der Weetenschappen Haarlem 1754;1:485-497)

In another letter by a certain Van der Lott (1762) we read the following passage:

[A 9-year-old boy] suffered from obstruction of the nerves in such a way that his arms and legs were crooked. Each day, this gentleman threw the boy in a tub of water with a large Conger-eel of the black variety, which shocked the boy so powerfully that he crept out on all fours.

It was not easy to transport a live eel to Europe, although several dead eels had been taken to European cities, including Amsterdam, where specimens were collected and drawn for books.

In the 1770s at the Royal Society in London, scientists proved that the eels did indeed discharge an electrical current after they drew a spark at the time of a living eel's discharge, a fundamental criterion at the time. The finding endorsed the Italian scientist Luigi Galvani's concept of animal electricity based on his findings that the legs of dead frogs would move when touched by a spark of electricity. However, due to the opposition of Allesandro Volta, an Italian physicist who was also studying electricity, and the lack of refined measuring methods, it was several decades before the nerve action potential was measured by the German physiologist Emil du Bois-Reymond in 1843.

It is apparent that during the century that elapsed between colonists' first realization that the eel produced electricity, a great number of scientists from various countries made scientific contributions that finally led to the observation of a nerve action potential. ■


Dr Peter J Koehler

At time of print, Dr. Koehler is a neurologist in the department of neurology at the Atrium Medical Centre, Heerlen, the Netherlands. Visit his web site at www.neurohistory.nl..

Further reading

Koehler PJ, Finger S, Piccolino M. The eels of South America: Mid-eighteenth century Dutch contributions to the theory of animal electricity. Journal of the History of Biology 2009;42:235-251.