THE ELECTROMOTIVE PHENOMENA 329 



contiguous axis cylinders, among them those 

 of the other branch. 



ELECTRIC FISH 



There are several species of fish which possess 

 the power of discharging electrical currents when 

 stimulated. The best known are Torpedo, a ray 

 found on the coasts of Europe ; Gymnotus, the 

 electrical eel of South America ; and Malapteru- 

 rus electricus, a catfish found in the Nile and 

 other African rivers. The electromotive force of 

 these fishes is derived from a special organ placed 

 beneath the skin. This electrical organ is bilat- 

 eral and is formed of parallel plates. One side 

 of each plate receives a branch of the electrical 

 nerve, which in Malapterurus is a single great 

 axis cylinder derived from a giant nerve cell. 

 The side of the plate receiving the nerve becomes 

 negative to the other side when the electrical 

 organ is active ; it behaves like the negative plate 

 of the ordinary cell. When the nerve is at rest, 

 there is no difference of potential in the electrical 

 organ. The discharge in the active state is peri- 

 odic, and may rise to 200 per second. The elec- 

 tromotive force is considerable : in Torpedo, 30-35 

 volts, 5 volts for each cubic centimetre of the 

 organ, 0.08 volt for each plate. The fish itself 



