VIII. But the experiment may be performed in a manner still more simple. Provide a glass vessel (Plate IV. fig. 10.) filled with mercury, and let the muscles of a prepared frog be laid to float on the surface of the metal; then suspend the spinal marrow by a silk thread in such a manner, that by letting down the thread the marrow can be made to touch the mercury at pleasure. As soon as the spinal marrow is brought into contact with the surface of the metal, contractions will take place in the muscles; and the same will be observed if a plate of gold or silver be substituted in the room of the mercury. This phænomenon will be exhibited not only by a whole frog, but by half a frog divided longitudinally; which, as soon as it touches the mercury, by the method above described, will be violently convulsed. Having mentioned these experiments to Galvani, to whom I often had recourse for instructions, he regretted that I had confined my researches to frogs only, and advised me to try warm-blooded animals. I therefore took the leg of a lamb or a chicken, and holding it in my hand in a vertical position, in such a manner that the bare muscles were in communication with the mercury, I then raised the crural nerve without any armature, so that, by being left to itself, it could be made to touch the mercury at pleasure. As soon as it did so, I observed a violent agitation and contraction in the whole limb, and likewise when I used the before described apparatus, Plate IV. fig. 2. IX. While I made these experiments, I was well aware that the contractions produced in the limb might by some be ascribed to the impulse of the mercury, acting on it like a kind of stimulus, or to electricity received from the surrounding bodies, rather than to the innate electricity of animals. I would advise those who entertain such an opinion to hold the hind legs of a frog in their hand, in a vertical position, and to press only the spinal marrow against the surface of the mercury. Let them immerse also the spinal marrow in salt water, or in vinegar: no contraction will take place, though in this case there is still a mechanical impulse; and though the saline or acid quality of these liquids is exceedingly proper for acting as a stimulus. To this I may add, that in the apparatus already described (Plate IV. fig. 2.) there is no impulse from the mercury, which acquires only that gentle motion necessary to enable it to put itself into a state of equilibrium. In a word, I have observed (Plate IV. fig. 1.) that when both the upper and lower vessels are filled with mercury, if the aperture be opened so that the metal which falls down shall not strike against the muscles; yet the same contractions take place: which indeed ought to serve as a proof that mechanical impulse has no share in producing the effect.