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 
Yolta, 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 Prog 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 
