LECT. X. SILURUS. 207 



It results from this hypothesis, that the opposite electri- 

 cal conditions ought always to be found at the long extre- 

 mity of the prisms ; and that their intensity should be pro- 

 portional to the length of these prisms; that is, to the num- 

 ber of cells of which each is composed. It is important 

 to remark, that these hypotheses are confirmed by experi- 

 ment. 



In fact, the relative position of the poles in the gymno- 

 tus, correspond to those of the poles of the torpedo as re- 

 gards the extremity of the prisms. In the first of these 

 fishes, the prisms are extended along the axis of the body 

 of the animal, that is, from the head towards the tail, or 

 vice versa; in the second, on the contrary, the prisms have 

 their extremities in contact with the back and the belly. 

 Hence, then, in the gyonnotus, the poles are the head and 

 the tail, and in the torpedo we find them at the back and 

 the belly. 



Silurus. It remains for us to examine the direction of 

 the current of the silurus ; if we are to judge from the 

 structure only of the organ in this fish, we must conclude 

 that the two poles are, in the gymnotus, at the head and 

 the tail. 



The intensity of the electric discharges, is the strongest 

 at the points of the organ nearest to the mesial line ; there, 

 also, the height of the prisms, and the number of nervous 

 filaments are the greatest. 



Microscopic anatomy may also render a great service to 

 physics, by studying the electric organ of fishes, and parti- 

 cularly by establishing exactly the distributionofthe nervous 

 filaments in the elementary organ or cell. This cell ap- 

 pears to be largest in the silurus, and, therefore, it is in this 

 fish that the structure should be studied. 



What happens in the electric organ, is certainly analo- 

 gous to electric induction: the constancy of the direction 



