92 OF VITAL MOTION. 



tricity upon the system, for we have no right to 

 assume the identity of these forces. We have to do 

 with electricity and electricity alone, and we have to 

 study any peculiar constitution of the animal which 

 may favour or oppose the operation of this force, 

 and this being the case, we must conclude, for 

 the reasons that have been given, that muscular con- 

 traction is consentaneous with the abstraction, and not 

 with the communication of electricity. 



These results are taken from the history of the frog, 

 but there is no reason to suppose them confined to this 

 animal ; indeed, there is evidence (though much more 

 obscure) of currents of natural electricity in other 

 animals. It is found, also, where the question has 

 been examined, that the muscles respond to electricity 

 in the same manner as in the frog, and this is an im- 

 portant argument in favour of the same electrical 

 constitution in the subject of the experiment as in the 

 frog. 



In connexion with this part of our subject, it is 

 necessary to refer once more to another order of phe- 

 nomena, namely, the effects of mechanical irritation ; 

 but a passing allusion is sufficient after what has 

 been said elsewhere. Previously it was argued that 

 the contractions produced by any simple irritant were 

 not proofs of the communication of a stimulus, and it 

 was shown to be equally probable that a something 

 had been abstracted, as that anything had been im- 



