Professor Galvani was quite certain that he had discovered animal electricity. He found that whenever the frogs’ legs were touched with two different metals, they gave a jerk. He tried combinations of iron with brass, and lead with silver, and finally concluded that silver is the best conductor of animal electricity. Galvani upheld his theory of animal electricity until the time of his death, which occurred eight years after his discovery. But his theory was attacked by another Italian whose name was Volta. Volta was distinguished already by his invention of a simple little machine which gave a continual supply of electricity. It consisted of a cake made of resin mixed with turpentine and wax, which was cast into a flat mould, and allowed to cool until it was hard. A flat tin plate was cut large enough just to cover the cake, and was provided with a glass handle. The cake was beaten with a piece of catskin or woollen cloth. The tin plate was placed on top of the cake and touched with the finger, which drew a small spark. After that the plate was lifted off the cake by the handle, and was then found to have a strong charge of electricity. By repeatedly putting the plate on the cake, touching it lightly, and then taking it off by means of the glass handle, any amount of electricity could be obtained without renewing the charge on the cake by another beating. That little instrument was called the “electrophorus.” Volta was all his life the greatest opponent of Galvani’s theory of animal electricity, and at the end of a long series of brilliant investigations and experiments he succeeded in demolishing the theory entirely. He was helped by a curious experiment. It consisted in taking a plate of lead and a plate of silver, and putting one on the top of his tongue and the other under his tongue. As soon as the edges of the two plates touched each other he perceived a queer taste. There was no such taste when the pieces did not touch, and two different tastes could be got by putting one or the other plate on the top of the tongue. No effect was obtained if the two pieces consisted of the same metal. He therefore concluded that the effect observed by Galvani was really due, not to animal electricity, but to the contact between two pieces of different metals. The frogs’ legs in Galvani’s experiment, or the tongue in his own experiment, simply acted as a conductor, for the electricity produced as soon as the two metals touched each other.