Frogs and Animal Electricity

In the late 18th century, frogs were the talk of the Italian scientific establishment. Two prominent experimentalists, Luigi Galvani and Alessandro Volta, presented novel theories of animal and chemical electricity that they attempted to defend by reference to scientific instruments. At issue was the nature of nervous response and muscular motion in the frog. The Whipple Museum's voltaic piles, Leyden jars, and electro-galvanic machine embody distinct interpretations of the frog's ambiguous body.

In the 1780s, the Bolognese physician Luigi Galvani (1737-1798) conducted a vast range of experiments on electricity's effect on "prepared" frog specimens - that is, frog legs severed at the base of the spine, with nerves exposed. These studies culminated in his Commentary on the electrical force of muscular motion of 1791, which quickly seized the attention of the physical scientist and Galvani's eventual rival, Alessandro Volta (1745-1827).

Galvani's first crucial result in his frog experiments was the product of good fortune: while investigating the effect of atmospheric electricity on "prepared" specimens, Galvani and his assistants hung frog legs from an iron railing, with brass hooks dangling from their spinal nerves. One hook touched the railing, and the attached frog's leg kicked. Placing the legs and hooks on other metals and doing the same had a similar effect, but nothing happened when they placed the frog on non-conducting materials like wood, glass, or resin.

Instruments as Frogs: the Leyden Jar and Voltaic Pile

By the late 18th century, natural philosophers knew that electricity could stimulate muscular motion. What kind of electricity was it, though, and how was it produced? To answer this question, Galvani and Volta each pointed to an instrument used for storing or producing electric current whose operation was more convincingly understood than the frog's kick: Galvani said the frog's leg works like a Leyden jar, and Volta compared it to his own, new invention, the battery pile.

When Galvani hung a frog's leg over his iron banister and saw it kick, a familiar electrical instrument came to mind:

"These results surprised us greatly and led us to suspect that the electricity was inherent in the animal itself. An observation that a kind of circuit of a delicate nerve fluid is made from the nerves to the muscles when the phenomenon of contractions is produced, similar to the electric circuit which is completed in a Leyden jar, strengthened this suspicion and our surprise." (1)

See Catalogue Record of Wh.1142

The twitching leg reminded Galvani of the Leyden jar. The Leyden jar was one of the first and most important electrical tools to spread throughout Europe. Pieter van Musschenbroek invented it around 1745 in the Dutch town of Leiden, from which the jar derives its name. Another 'electrician' named Ewald Georg von Kleist, however, invented a jar with the same capabilities independently, and roughly simultaneously.

By filling the jar with water, then directing an electrical current into that water via a metal cap, one can store or 'condense' current within the jar. The water's charge in turn produces the opposite electrical charge in the outer metal plate. 'Electricians' would perform stunning displays of electrical power by establishing a circuit between the water and the outer plate. We now call this a 'capacitor' or 'condenser.'

In his experiments on electricity and frogs, Luigi Galvani imagined that the frog's muscle and nerve acted like the two sides of a Leyden jar. Establishing a circuit between them allows the discharge of 'animal electricity' analogous to the artificial electricity of the jar. Animal motion resulted from distributions of charges in nerves that would, when sufficiently strong, discharge relative to muscles and cause them to contract. To Galvani, the frog comprised an ensemble of capacitors. Electricity created and used by animal bodies for this purpose constituted 'animal electricity.'

Physicians later applied this idea to medicine by creating machines for administering therapeutic shocks - see The Electo-galvanic machine, below.

Volta took Galvani's brass hook experiment to demonstrate an opposing claim: the frog's body does not produce its own electrical current, which is merely conducted by the brass and iron through an imbalance of charges. Instead, the brass and iron in contact with the moist, conducting frog body produce 'artificial' electricity that makes the frog kick. This reinterpretation amounted to the entirely new theory of 'contact electricity,' which Volta mobilised in the invention of his battery pile.

Volta first created the pile in 1799 to demonstrate the capacity of moistened metals to produce electric current through contact alone. Little is known about the many voltaic piles owned by the Whipple Museum, in part because it was such a common and generic scientific tool. Many were produced in early 19th century England according to Volta's general design. This example consists of alternating copper and zinc plates separated by 'cells', or cloth pads moistened with saltwater or acid.

See Catalogue Record of Wh.2016

Electro-galvanic machine

The electrical nature of muscular motion that Galvani and Volta investigated did not only spur further physiological research, but also provided foundations for innovative medical therapies.19th century physicians and scientists applied Galvani's model of the frog's muscular motion, which he considered the product of carefully balanced and imbalanced electrical currents, to new forms of medical therapy, which they called "Galvanism." Electrical medicine gave rise to new machines and new types of treatment.

The Whipple Museum's Electro-Galvanic Machine was built in the late 19th century (likely between 1886 and 1893) by Horne, Thornwaite, and Wood at 123 Newgate Street London, where they ran an instrument company. Ironically, perhaps, given their inventors' disagreements, the Galvanometer was powered by a voltaic pile. Metal electrodes channelled current through specific contact points on the body, each selected for a precise medical purpose.

Covering the lid's inside surface is a pamphlet on "Administering Medical Galvanism". Scientific studies on the medical uses of Galvanism proliferated in the second half of the 19th century. They claimed, for its uses, the healing of paralysis and other disorders related to the nervous stimulation of muscles. Some used Galvanian stimuli to treat hoarseness, ocular distortions apparently due to anemia, asthma, and constipation. Several obstetricians tried to induce and facilitate labour by administering shocks to pregnant women, which usually met with tragic results.

See Catalogue Record of Wh.5813

References

A. Mauro, 'The Role of the Voltaic Pile in the Galvani-Volta Controversy Concerning Animal vs. Metallic Electricity', Journal of the History of Medicine and Allied Sciences (Oxford: Oxford University Press, 1969).

Henry Schmidt

Henry Schmidt, 'Frogs and Animal Electricity', Explore Whipple Collections, Whipple Museum of the History of Science, University of Cambridge.

Frogs and Animal Electricity

Instruments as Frogs: the Leyden Jar and Voltaic Pile

Electro-galvanic machine

References

Next Article: Frogs and Physiological Instruments in 20th Century Cambridge

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