ELECTRIC OKGANS OF FISHES. 215 



racterg both of those of the Torpedo and the Gymnotus, and not only 

 in structure, but in some degree, likewise, in regard to the source of 

 their nervous energy, the outer organs being supplied by the ' nervus 

 lateralis ' from the vagus ; the laminated inner one receiving branches 

 from the ' rami ventrales ' of the spinal nerves. * The shock com- 

 municated by the Mcdapterurus electricus is comparatively feeble. 



Wlien the Neapolitan fishermen pull their nets to shore, their first 

 act usually is to wash the fishes by dashing over them bucketfuls of 

 sea-water ; and if a Torpedo be amongst the captured shoal, it makes 

 its presence instantly felt by the shock transmitted to the arm, which 

 is in the act of discharging the bucket. If the fish be handled, the 

 shock is too strong and painful to be willingly encountered a second 

 time, and the arm i-emains benumbed for some time. Each repetition 

 of the discharge, however, enfeebles its force, and the surface of the 

 fish capable of communicating the shock pi'ogressively contracts, as 

 life departs, to the region of the organs themselves. 



An animal mustbein communication with the Torpedo by twodistinct 

 points, in order to receive the shock. If an insulated and prepared 

 frog f touches the torpedo by the end of a nerve only, no muscular 

 contractions ensue on the discharge of the battery ; but a second 

 contact by the end of another nerve, or by a portion of muscle, or any 

 other part of the body, immediately produces them. When the fisher- 

 man dashes the stream of water over the Torpedo, the electric 

 current passes up from the dorsal surface of the batteries against the 

 stream to the man's hand, and the circle is completed by the earth ex- 

 tending from the man's feet to the ventral surface of the prone fish. 



The dorsal surface of the electric organ is always positive, the 

 ventral surface negative. | The Torpedo has no power of otherwise 

 directing the electric currents ; but Matteucci found that wounding 

 the electric lobes of the brain sometimes reversed the direction. 

 These currents, besides their effects on the living body, exercise all 

 the other known powers of electricity : they render the needle mag- 

 netic §, decompose chemical compounds, and emit the spark. || The 

 discharge of strong currents is usually accompanied by visible con- 

 traction of parts of the body, usually by a retraction of the eyes of 

 the Torpedo, and one muscle {Jig. 45. 6) is arranged so as to 

 constrict part of the circumference of each battery ; but such con- 

 sentaneous muscular action, though it may add to the force of the 

 discharge, is not essential to its production. Tlie benumbing effect 

 seems to be produced by tlie rapid succession of shocks delivered by 



* XCI. t LXXVI. p. 148. \ LXXXIII. 



§ LXXXI. II LXXVI. 



p 4 



