ELECTRIC FISHES. 269 



shock when irritated, which it would of course do, if 

 the operation were purely a mechanical one. Thus, 

 though the electricity itself be analogous to that which 

 we can produce at our pleasure by other means, the 

 mode of its production is a part of the economy of life ; 

 and therefore we cannot reason about it upon the ana- 

 logies of dead matter ; but must, as in all cases involving 

 the singular mystery of vitality, content ourselves with 

 observing its phenomena, and be careful not to extend 

 our theory of its nature and laws beyond these. This 

 is a caution that should never be lost sight of in the 

 study of nature ; and the distinction between what can 

 be known and what cannot, is one of the most impor- 

 tant departments of sound philosophy, though it is 

 sometimes overlooked both by the learned and the 

 ignorant. 



Though it is probable that the body of every animal, 

 and indeed every substance in nature, is capable Jof 

 being excited by electric action, yet distinct organs 

 for the purpose of producing such action, are found 

 only in fishes, and hitherto but in a very limited number 

 of these. These organs, like other parts of the organic 

 structure, appear to be admirably adapted to the instinct 

 which they serve, and the purpose which they effect ; 

 and though, in the different fishes which are furnished 

 with them, there be some difference in their form, 

 there is much resemblance in their substance and 

 structure, in the same manner as wings, claws, stings, 

 or any other class of organs, of which the existence at 

 once suggests the use. They are quite distinct from 

 the organs of motion, respiration, circulation, digestion, 

 or any other which belongs to their possessor generally 

 2 A 3 



