THE MULTIPLIER. 159 



plate is connected a nerve-fibre, by means of which 

 the animal is capable of voluntarily effecting the elec- 

 tric discharge, just as voluntary muscular contractions 

 can be effected by means of the nerve. These nerves 

 may also be artificially irritated, with the result of pro- 

 ducing one or more electric shocks, just as irritation of 

 a motor nerve elicits one or more muscular contraction. 

 The analogy of electric organs and of muscle is, in fact, 

 from a physiological point of view T , complete. 



Mention must yet be made of the fact that forms 

 nearly allied to these fishes for instance, the various 

 forms of Mormyrus, which in structure resemble rays- 

 possess similar organs, though these have not as yet 

 been shown with any certainty to be capable of any 

 electric action. It has, moreover, been assumed that, 

 the luminous organs of certain insects are to be referred 

 to electric forces ; but this has not, been in any way 

 proved. 



4. Before entering further into the statement of the 

 electric phenomena in animal structures it will be neces- 

 sary to say something of electric phenomena in general, 

 and of the means of exhibiting them. 



It is well known that an electric current results 

 when two different metals are in contact 

 with each other, or with a fluid. Elec- 

 tricity occurs" in this case as a current, 

 that is, in a state of motion ; while in 

 other c.ises it exists in a quiescent con- 

 dition. On immersing a piece of copper 

 and a piece of zinc, as in fig. 36, in a glass 

 containing diluted sulphuric acid, and then AN ELECTRIC 

 uniting these above the fluid by a wire, 

 the positive electricity passes through the wire from the 



