. PHENOMENA OF THE GYMNOTUS. 203 



water, and approaching the margin of the pools, are easily 

 captured by the hunters by means of harpoons attached to 

 long cords. 



The observations of Humboldt have proved, that the 

 discharges of this fish, like those of the torpedo, take place 

 without any muscular movement being necessary ; and that 

 when the brain is removed this phenomenon no longer oc- 

 curs, even though the spinal marrow be irritated. The in- 

 fluence possessed by the different parts of the brain on the 

 electrical phenomena, requires to be more carefully and at- 

 tentively studied than it has hitherto been. The mode of 

 catching the fish proves, that the discharge is voluntary, 

 that the function becomes weakened by being exercised too 

 often, and that it is restored by repose. 



Faraday, who made some experiments upon a living 

 gymnotus in London, succeeded in obtaining, from the 

 discharge of this fish, all the phenomena of the electric 

 current; namely, the spark, electro-chemical decomposition, 

 the action upon the magnetic needle, &c. Furthermore, 

 he compared the shock given by this fish to that of a battery 

 of Leyden jars charged to its highest degree; and he 

 concluded, from his experiments, that a single medium 

 discharge of this animal, is equal to that of a battery of 

 fifteen jars, containing 3500 English square inches, charged 

 to its highest degree. It cannot, therefore, be a matter of 

 surprise that a horse sinks under a number of successive 

 discharges given by the gymnotus. 



The most important result which Faraday obtained, was 

 that respecting the direction of the discharge. The cephalic 

 extremity is the positive, and the opposite extremity is the 

 negative pole ; so that the current circulates in the galvano- 

 meter from the head towards the tail of the animal. This 

 arrangement explains the stratagem employed by the ani- 

 mal when giving the shock for the purpose of killing a fish ; 



