Frog battery

A frog battery is an electrochemical battery consisting of a number of dead frogs (or sometimes live ones), which form the cells of the battery connected in a series arrangement. It is a kind of biobattery. It was used in early scientific investigations of electricity and academic demonstrations.

The principle behind the battery is the injury potential created in a muscle when it is damaged, although this was not fully understood in the 18th and 19th centuries; the potential being caused incidentally due to the dissection of the frog's muscles.

The frog battery is an example of a class of biobatteries which can be made from any number of animals. The general term for an example of this class is the muscular pile.

The first well known frog battery was created by Carlo Matteucci in 1845, but there had been others before him. Matteucci also created batteries out of other animals, and Giovanni Aldini created a battery from ox heads.

In the early days of electrical research, a common method of detecting electric current was by means of a frog's leg galvanoscope. A good supply of live frogs was kept to hand by the researcher ready to have their legs prepared for the galvanoscope. Frogs were therefore a convenient material to use in other experiments. They were small, easily handled, the legs were especially sensitive to electric current, and they carried on responding longer than other animal candidates for this role.

It was usual to use the thighs of frogs for the battery construction. The legs of the frog were first skinned, then the lower leg was cut off at the knee joint and discarded. Damaging the muscle during this procedure would detract from the results. The thigh muscle was then cut in two transversely to produce two half-thighs. Only the lower, conical shaped piece was kept. The half-thighs were then laid on an insulator of varnished wood so arranged that the inside surface of one was in contact with the outside surface of the next, with the conical ends of the outside surface being pushed into the cavity of the cut surface. The ends of the pile were placed in cups of water sunk into the wood and formed the terminals of the battery.

The arrangement of inside surface connected to outside surface was on the basis of the incorrect theory that there was an electric current in muscles continually flowing from the inside to the outside. It is now known that the half-thighs were more successful at generating electricity because they had suffered the greatest injury to the muscle. This effect of increased electric potential due to injury is known as demarcation potential or injury potential.

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Wikipedia