INFLUENCE OF ELECTRICITY ON MUSCLES. 447 



at Bologna, being about to prepare some soup from frogs, and 

 having taken off their skins, laid them on a table in his study, 

 near the conductor of an electrical machine which had been 

 recently charged ; and she was much surprised, upon touching 

 them with the scalpel (which must have received a spark 

 from the machine), to observe the muscles of the frog strongly 

 convulsed. Her husband, on being informed of the circum- 

 stance, repeated the experiment ; and found that the muscles 

 were called into action by electricity communicated through 

 the metallic substance with which the limb was touched. 



584. The experiment was repeated in various ways by 

 Volta, who was Professor of Natural Philosophy at Pavia; 

 and he found that the effects were much stronger when the 

 connecting medium through which the electricity was sent, 

 consisted of two metals instead of one ; and from this circum- 

 stance he was led to the discovery that electricity is produced 

 by the contact of two different metals a discovery which has 

 since been so fruitful in most important results. The follow- 

 ing simple experiment puts this in a striking point of view. 

 If the skin of the legs of a Frog recently killed be removed, 

 and the body be cut across, above the origin of the great 

 (sciatic) nerve going to the legs, if the spine and nerves be 

 then enveloped in tin-foil, and the legs be laid upon a plate 

 of silver or copper, convulsive movements in the muscles 

 will be excited every time that the metals are made to touch 

 each other so as to complete the electric circuit. 



585. Similar experiments have been tried with the Voltaic 

 battery, upon the dead bodies of criminals recently executed. 

 If one wire be placed upon the muscles which it is desired to 

 call into action, and the other upon the part of the spine from 

 which the nerves proceed, movements of every kind may be 

 produced. No agent more effectually imitates the natural 

 action of the nerves, in exciting the contractility of muscles, 

 than Electricity thus transmitted along their trunks ; and we 

 have already seen ( 489) that Electricity, transmitted along 

 the sensory nerves, excites the peculiar changes in the brain 

 by which sensations are produced. Hence it has been, sup- 

 posed by some philosophers, that electricity is the. real force 

 by which the nerves act upon the muscles ; more especially 

 since it is certain that, in those animals which generate large 

 quantities of electricity, the nerves have a great share in this 



