206 



ELECTRIC FISHES. 



LECT. X. 



the tourmaline, and on some crystallized metals, separates 

 the two electricities : chemical action operates in the same 

 way ; as do also the mechanical actions, friction, and pres- 

 sure. Suppose, that nervous irritation acts in this way on 

 the vesicle of the electric organ. The identity of struc. 

 ture, and the arrangement of each of the vesicles, is such 

 that each of the prisms becomes a pile, but only for the 

 infinitely small period of the duration of the irritation ; and, 

 consequently, the entire organ will be a multiplying appa- 

 ratus, which will remain charged only for an instant, since 

 it is surrounded by conducting bodies. The discharge will 

 take place partly outside the surrounding medium and 



Fig. 16. 



Cephalitic extremity (positive.) 



Dorsal surface (positive.) 



Ventral surface (negative) 

 Electric Organ of the Torpedo. 



Caudal extremity (negative.) 

 Electric Organ of the Gyranotus. 



partly in the interior of the organ ; but so much more out- 

 side as the medium will be a better conductor than the in- 

 terior of the organ. Yet it may be remembered that we 

 have shown, by experiment, that this discharge really takes 

 place internally. 



