What did Luigi Galvani argue in his 1794 book about the conductive arch?

In his 1794 book, Dell’uso e dell’attività dell’arco conduttore nella contrazione dei muscoli ("On the Use and Activity of the Conductive Arch in the Contraction of Muscles"), Luigi Galvani defended his theory of animal electricity against the criticisms of Alessandro Volta.

While Volta argued that muscular contraction was caused by the contact of dissimilar metals, Galvani used this work to further his position. Crucially, the book included a supplement describing experiments where he achieved muscular contraction without the use of any metal at all. By touching the exposed muscle of one frog with the nerve of another, he demonstrated that bioelectric forces exist inherently within living tissue, thereby providing evidence for his theory that an innate "animal electricity" activates nerves and muscles.1