196 life's beginning on the earth 



up for their size by their quantity and thus are able to 

 produce really high voltage currents — high enough to kill 

 other fish in the vicinity. 



Such electrical organs exist only in fish, and are found in 

 many of them without relation to the affinity of groups. 

 The "torpedoes," which are flat like a skate, are one of these 

 groups. Fishermen give them a number of nicknames, all 

 of which have reference to the effect felt when grasping the 

 fish. They can produce a discharge which is quite dis- 

 agreeable, although hardly ever dangerous. In order to 

 experience this, the fish should be held with the whole hand, 

 passing the palm under the belly and pressing the thumb 

 on the back. The current produced by the fish will then 

 pass from the thumb to the palm of the hand, since the 

 "vital" electric batteries are arranged vertically to the large 

 surface. The shock is sometimes so strong that it is felt 

 in the arm and even in the shoulder and in the side. This 

 intense effect upon a human being gives us an idea of what 

 can happen in the water when such electrical shocks are 

 brought to bear upon the small creatures there. The elec- 

 trical battery in the fish is only discharged when the fish is 

 excited; in other words, it takes a nerve impulse to connect, 

 somehow, the battery to the outside and produce the 

 electrical currents. 



To another group belongs the most powerful of all electric 

 fish, the electric eel of the Amazon River, which grows to a 

 length of six feet. (Fig. 77.) Zoologically it is not related 

 to ordinary eels. Its electrical capacity is far beyond that 

 of any other fish. On each side it has one large electrical 

 organ, reaching from the fore part of the trunk to the tail. 

 This electrical organ consists of prismatic columns placed 

 side by side; but the columns are divided horizontally in 

 this fish and not vertically as in the torpedo. Consequently 

 we find a difference in the direction of the current (lis- 



