INFLUENCE OF ELECTRICITY ON MUSCLES. 447 
at Bologna, being about to prepare some soup from frogs, and 
haying 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 to metals instead of one ; and from this cireum- 
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 theirtrunks ; 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 
