How did Volta’s explanation of electricity differ from Galvani’s animal-electricity idea?

Luigi Galvani and Alessandro Volta held opposing views regarding the source of electricity observed in biological experiments.

Luigi Galvani proposed the existence of "animal electricity," a vital force he believed was innate to living tissue. He theorized that the brain secreted an "electric fluid" that traveled through the nerves to muscles, which acted similarly to a Leyden jar to produce motion.1

Alessandro Volta rejected this theory, arguing that the frog's leg was merely acting as an electroscope to detect electricity generated by external sources. He contended that the true source of the current was the contact between two dissimilar metals, which he termed "metallic electricity".12

Ultimately, both scientists were partially correct. Galvani was right that electrical stimuli cause muscular contractions, and he later proved the existence of bioelectric forces. Volta was correct that animal tissue is not required to generate a current, a realization that led him to invent the voltaic pile—the first true battery—which provided a constant source of current electricity independent of biological organisms.12