xi ELECTRICAL FISHES 453 



The galvanic effects of the homodromous current usually 

 increase with the strength of the exciting current, and it can be 

 demonstrated many hours after the preparation has been excised, 

 although it disappears completely after scalding. Here, as in 

 indirect excitation, there is a very slow decline of electromotive 

 effect, lasting for several minutes, its development and time- 

 distribution corresponding throughout with the discharges induced 

 by indirect excitation. 



An important fact, as observed by Gotch, is that partial 

 longitudinal passage of current in an organ-preparation discharges 

 an excitation effect (after - current) within the part that is 

 traversed only, and not beyond the poles. It follows that ex- 

 citation in the longitudinal direction of the prisms is not transmitted 

 from one plate to the next. Each plate appears to be physiologi- 

 cally insulated from all the rest, and total discharge of a whole 

 prism can only occur either when all the nerves which supply 

 them are excited, or when an electrical current traverses all the 

 compartments in series. 



As regards the interpretation of the absolute, and relatively, 

 positive after-effect from homodromous exciting currents, du 

 Bois-Eeymond reminds us of two possibilities : 



(i.) Like the current of rest in the organ, it may be viewed 

 as the after-effect of a discharge caused by electrical excitation. 



(ii.) It may be interpreted on the molecular theory "as the 

 consequence of a prismatic arrangement of the electromotive 

 molecules in direct consequence of the homodromous current." 



In reference to the last view, it may be stated that du Bois- 

 Eeymond, in order to explain the discharge from the plates, i.e. 

 the electromotive action of each single plate of the organ, 

 assumed its construction from dipolar molecules, similar to that 

 said to underlie the electrical manifestations of nerve and muscle. 

 In the resting state the molecules turn their poles either 

 towards all possible, or in two opposite directions, so that the 

 effect disappears externally. In discharging, on the contrary, 

 they " collectively turn their positive poles towards the surface 

 of the organ, whence proceeds the positive current." Du Bois- 

 Eeymond pictures the molecules as " a free crowd revolving round 

 their centre of gravity, in the direction of the axis, by a chemical 

 force comparable to some extent with the respiration of the 

 organ." " Several molecules may lie behind one another in the 



