126 THE SHOCJy A VITAL ACTION. 



they become more sensib'e if the animal be raised above the 

 surface. I have often observed the same phenomenon in 

 experimenting on frogs. 



The torpedo moves the pectoral fins convulsively every 

 time it emits a stroke; and this stroke is more or lesa 

 painful, according as the immediate contact takes place 

 by a greater or less surface. We observed that the 

 gymnotus gives the strongest shocks without making any 

 movement with the eyes, head, or fins.* Is this difference 

 caused by the position of the electric organ, which is not 

 double in the gymnoti? or does the movement of the 

 pectoral fins of the torpedo directly prove that the fish 

 restores the electrical equilibrium by its own skin, dis- 

 charges itself by its own body, and that we generally feel 

 only the effect of a lateral shock ? 



We cannot discharge at will either a torpedo or a gym 

 notus, as we discharge at will a Leyden jar or a Voltaic 

 battery. A shock is not always felt, even on touching the 

 electric fish with both hands. We must irritate it to make 

 it give the shock. This action in the torpedos, as well as in 

 the gymnoti, is a vital action ; it depends on the will only 

 of the animal, which perhaps does not always keep its elec- 

 tric organs charged, or does not always employ the action 

 of its nerves to establish the chain between the positive and 

 Degative poles. It is certain that the torpedo gives a long 

 series of shocks with astonishing celerity ; whether it is that 

 the plates or Iamina3 of its organs are not wholly exhausted, 

 or that the fish recharges them instantaneously. 



The electric stroke is felt, when the animal is disposed to 

 give it, whether we touch with a single finger only one of 

 the surfaces of the organs, or apply both hands to the two 

 surfaces, the superior and inferior, at once. In either case 

 it is altogether indifferent whether the person who touches 

 the fish with one finger or both hands be insulated or not. 

 All that has been said on the necessity of a communication 

 with the damp ground to establish a circuit, is founded on 

 inaccurate observations. 



M. Gay-Lussac made the important observation that 

 when an insulated person touches the torpedo with one 



* The anal fin of the gymnoti only has a sensible motion when these 

 fishes are excited under the belly, where the electric organ is placed. 



