Animal electricity

Animal electricity is the name that Luigi Galvani (September 9, 1737 to December 4, 1798) gave to an electrical force that he concluded was produced by animal tissue and carried by the nerves to the muscles. He announced it in 1791 in a treatise on the forces of electricity in muscular motion, De viribus electricitatis in motu musculari commentarius, after years of work on the legs of frogs.^[1] Alessandro Volta, a professor at Pavia, held that the twitching came from the contact of two different metals, and his work on that question produced the voltaic pile of 1800, the first electric battery.^[2]

Each man was partly right. Living cells do hold an electrical imbalance between the inside and the outside, a difference in potential of 0.03 to 0.1 volt across the membrane, and the signals of nerve and muscle are currents through channels in that membrane.^[3] The first currents through single channels were recorded in 1976, from frog muscle.^[4][5]

By the 1780s electrical machines and Leyden jars were common in physics demonstrations, and electricity was being applied to the body as medicine. In 1773 John Walsh showed that the shock of the torpedo ray is electrical, in a letter to Benjamin Franklin printed in the Philosophical Transactions.^[6] Galvani had been public lecturer in anatomy at the University of Bologna since 1762 and was known as a comparative anatomist for his work on the hearing and genito-urinary organs of birds.^[1]

Galvani told the story of his discovery in the first pages of the treatise, saying that he wanted to set out the discoveries in the order in which chance and luck, or diligence and effort, had brought them, so that no more would be credited to him than to his luck, or more to luck than to him.^[7][a] In the account he gave, he had dissected a frog and laid it on a table that held an electrical machine, some distance from its conductor. One of the people helping him touched the nerves of the inner thigh with the point of a scalpel, and the muscles contracted as if in a violent cramp. Another assistant, who was helping with the electrical experiments, thought it had happened when a spark was drawn from the conductor and pointed this out to Galvani, who was busy with something else entirely and lost in thought. He was then, he writes, "inflamed with an incredible zeal" to test it himself. He touched a thigh nerve with the point of the knife while someone drew a spark, and the muscles contracted every time.^[7]

The Britannica of 1911 notes that documents in Bologna show he had been working on frogs and electricity some twenty years before the treatise appeared.^[1] The treatise reports a second discovery. Prepared frogs hung by brass hooks through the spinal cord from the iron railing around the hanging garden of his house twitched during lightning and also under a calm, clear sky. Tired of waiting for weather, he pressed the hooks against the railing himself. The first of his experiments with the metallic arc is dated September 20, 1786.^[1] He took a frog indoors, laid it on an iron plate and pressed the hook against the plate, and it contracted again, more or less violently depending on the metal. Dry bodies of glass, rubber, resin, stone or wood gave nothing. He concluded that the animal itself held electricity. In the model he built in 1791, the nerve and muscle together acted as what Piccolino calls a "minute animal Leyden jar", with an electricity "in a condition of disequilibrium between the interior and the exterior of excitable animal fibers".^[7][4]

Volta attributed the contractions solely to electricity arising at the junction of the two dissimilar metals of the arc, and regarded the nerve and muscle simply as conductors.^[1] Galvani's own account had noted that the effect varied with the metal used. The dispute lasted until Galvani's death, and his nephew Giovanni Aldini became a principal defender of the theory.^[8] Galvani answered in 1794, in an anonymous paper, with experiments in which frogs' legs twitched with no metal in the circuit.^[9]

Volta's reply was the pile. In a letter dated Como, March 20, 1800, to Joseph Banks, the president of the Royal Society, he described a column of discs of two metals separated by moistened cloth or cardboard, which gave a steady current without any animal.^[2][10] The letter was read to the Society on June 26, 1800.^[10]

Galvani had refused, on religious grounds, to swear allegiance to the Cisalpine Republic and had lost his professorship. The republican government decided to reinstate him, but too late, and he died in Bologna in the house of his brother.^[1]

Aldini carried on in public. In January 1803 in London he applied a voltaic pile to the body of George Forster (the Newgate Calendar spells it Foster), who had been hanged at Newgate for murder. The Calendar's account says that "the jaws of the deceased criminal began to quiver, and the adjoining muscles were horribly contorted, and one eye was actually opened".^[11] In Frankenstein, Victor's boyhood interest in natural philosophy turns after lightning shatters an oak, when a man of research explains "a theory which he had formed on the subject of electricity and galvanism".^[12]

Carlo Matteucci's essay on the electric phenomena of animals, published in 1840, was given to Emil du Bois-Reymond by his teacher Johannes Müller as the start of an inquiry that "determined the work of Du Bois-Reymond's life". His Researches on Animal Electricity appeared in parts from 1848 to 1884, and he proposed that muscle was made of "electric molecules".^[13] In 1952 Alan Hodgkin and Andrew Huxley described the currents of the squid giant axon in equations, the Hodgkin-Huxley model.^[14] Erwin Neher and Bert Sakmann recorded the current through one ion channel in frog muscle fibers in 1976, using the technique of the patch clamp, 185 years after Galvani's treatise. Piccolino, who has written the modern defense of Galvani, argues that his work "swept away from life sciences mysterious fluids and elusive entities like 'animal spirits'", and that two centuries of research have shown "how insightful was Galvani's conception of animal electricity".^[15]

• Ion channel
• Patch clamp
• Hodgkin-Huxley model
• Single-molecule biophysics