Having soon after this suspended some frogs, from the iron palisades which surrounded his garden, by means of metallic hooks fixed in the spines of their backs, he observed that their muscles contracted frequently and involuntarily, as if from a shock of electricity. Not doubting that the contractions depended on the electric fluid, he at first suspected that they were connected with changes in the state of the atmosphere. He soon found, however, that this was not the case; and having varied, in many different ways, the circumstances in which the frogs were placed, he at length discovered that he could produce the movements at pleasure, by touching the animals with two different metals, which at the same time touched one another, either immediately, or by the intervention of some other substance capable of conducting electricity. CHAP. II. _Of the Animals best fitted for Galvanic Experiments, of the Metals best calculated for making these Experiments, and of Conductors._ Almost every animal can be made to produce these muscular contractions by the Galvanic power, but those called _cold blooded_ are the best. Thus _frogs_ have been found the most convenient, both on account of their size and abundance. They also retain their muscular irritability to the Galvanic influence longer than most other animals, and it is asserted that strong convulsions can be produced in them many hours after the brain and spinal marrow have been destroyed; and also that when pretty far advanced in the process of putrefaction they are capable of Galvanic excitement. No contractions have been produced in animals killed by _corrosive sublimate_, nor in those which have been _starved_ to death: but a very slight motion can be made to appear in those killed by _opium_, the _electric shock_, or _azotic gas_. With regard to the metals used to effect these motions, almost any two will answer the purpose; but the most powerful are the following, viz. │ │Gold. Zinc│ │Silver. Tin │in conjunction with│Molybdena. Lead│ │Steel. │ │Copper. Those which have the most power are placed first; that is zinc and gold, will produce greater muscular contractions than tin and silver, or tin and gold, and so of the rest.