Commentary on the Effect of Electricity on Muscular Motion

...held completing "tenerem" from the previous page with one hand, and Rialpus's hand with the other, and I asked him to either touch or strike the small box original: "capsulam"; likely referring to the housing of the experimental apparatus with his other hand, so that a kind of electric chain original: "electricæ catenæ"; what we would now call an electrical circuit might be formed. Immediately, the same phenomenon of contractions occurred, to our great delight and wonder. This effect ceased if we separated our hands and reappeared as soon as we joined them again.

Although these results seemed sufficient to demonstrate an electric-like flow of the nerve fluid original: "fluidi nervei"; Galvani's term for the vital force he believed moved through nerves through a chain of humans, we wanted to confirm this great and startlingly new discovery even further. We arranged for Rialpus and myself to form a chain, not by grasping hands, but through an intermediate object—sometimes an insulating original: "cohibens"; a material that stops the flow of electricity glass cylinder, and sometimes a conducting original: "deferens"; a material that allows electricity to pass metallic cylinder. When the test was performed, we were pleased to see the phenomenon occur with the metallic cylinder, but stop entirely with the glass one, even if the box were touched or struck firmly with it. Thus, we felt we had proven that electricity was the cause of these contractions, regardless of the specific way it acted.

To make the matter even more obvious, I found it most useful to place a frog on an insulating surface, such as glass or resin. Then, I used an arc a curved conductor used to connect two points in the circuit, sometimes entirely conducting and sometimes at least partly insulating, and applied one end to the hook fixed in the spine and the other to either the leg muscles or the feet. In the experiment, we saw contractions occur when using the conducting arc (Fig. 9. Tab. 3.), but they were entirely absent when using the arc that was part-conducting and part-insulating, as shown in Fig. 10. The conducting arc was made of iron wire, while the hook was made of brass wire.

Having discovered these facts, it seemed to us that the contractions we observed when frogs were placed on a metallic surface (caused by pressing the spinal hook against that same surface) were due to a similar arc-like effect. The metallic surface itself was acting as the arc. This explains why the contractions were not triggered when frogs were placed on an insulating surface, even if the same techniques were used.

This opinion of ours was clearly confirmed by a pleasant phenomenon observed by chance: if a frog is held by the fingers, suspended by one leg, so that the hook in the spinal cord...