XXIX.] NEEVOUS CURRENTS. 41 



only analogy in telegraphy to the production of secondary 

 nervous currents is the action of a " relay battery ; " that is to 

 say, a battery which is so placed that on the arrival of one 

 current it sends on another. The second current here is not a 

 contkiuation of the first, but has been produced by a distract 

 battery. Just so, a secondary nervous current is not a continua- 

 tion of the primary one, but is produced by a distinct action of 

 nerve-fibres and ganglia on each other. 



I may here state, that I think Mr. Lewes is quite right in Nerve- 

 main taining that nerve-fibres are not merely analogous to tele- 1^(1^ th^^Ti 

 graphic wires. They are, no doubt, conductors of nervous merely 

 energy, but they are also necessary to its production. The ^^gL™ 

 mutual action of a nerve-fibre and a ganglion is necessary to the 

 production of a nervous current, just as the mutual chemical 

 action of two substances is necessary to the production of a 

 voltaic current. 



