THE ELECTRIC ORGANS OF FISHES. 151 
central nervous system, the fish must wear itself out as 
this nervous system fatigues and it is thus unable to 
keep up the intermittent discharge for more than a few 
minutes. This time is however, long enough to enable 
it to stun or kill small fish in its neighbourhood, which it 
is then able to eat at its leisure, which, being a sluggish 
fish, is a matter of considerable importance. It is also 
sufficient. to provide a very formidable weapon for defence 
from the attack of any enemies who might otherwise prey 
upon it. One of the most remarkable of the whole series 
of phenomena connected with these fish, is the compara- 
tive immunity which they enjoy from the destructive influ- 
ence of strong electrical shocks. When it is borne in mind 
that a very considerable portion of the current during the 
discharge of the organs traverses the brain and spinal 
cord of the very fish which produces the current, it will be 
realised to what extent the nervous system must be modi- 
fied, in order to allow this to take place without any 
apparent physiological effect whether being produced. 
(2) Gymnotus. The Electric Kel isa more formidable 
fish than the Torpedo, since it possesses four very large 
organs which run almost the entire length of its body, and 
which in adult specimens may measure 6 to 8 feet. The 
columns are situated so as to be parallel] with the long axis 
of the body, and as in the Torpedo they are composed of a 
series of superimposed transverse plates. The Gymnotus 
thus resembles the Torpedo in the essential structure of 
its organ, but differs in having very much longer columns 
and consequently many more plates. The nerves are 
derived from nerve cells in the spinal cord and the fish is 
able to produce an intermittent electrical discharge of 
extraordinary force. It is thus capable not merely of 
killmg other fish in its neighbourhood, but much larger 
animals, and Humboldt describes how the Indians dare 
