xr 



ELECTRICAL FISHES 445 



of the discharge, four times in the reverse, and which in his 

 estimation are clue solely to inequalities of the skin. 



Little as the possible, and even probable, interference of skin 

 currents the presence of which was demonstrated by du Bois-Eey- 

 mond in Torpedo can be denied, it must, on the other hand, be 

 admitted that regular differences of potential might, and indeed do, 

 make their appearance under certain conditions (though not in the 

 true physiological state of rest of the organ) even in the wholly un- 

 injured animal. Du Bois-Eeymond ascribes these " to the same, 

 though far less active, order of electromotive force as that which 

 produces a discharge via the nerve, or with direct excitation." 

 Under these conditions it is an obvious conjecture that the " organ 

 current " may be " an after-effect of the discharge, which passes 

 into it imperceptibly." And du Bois-Eeymond elsewhere remarks 

 that the E.M.F. of the organ current may in all probability be 

 regarded as " the remainder of the discharge," while " the fall 

 which always characterises it represents the slow progress of the 

 far quicker but still not quite sudden diminution of the discharge." 

 Finally, du Bois-Eeymond explains the negative experiments of 

 Gotch on the organ current of .uninjured and resting torpedoes as 

 signifying that the animals " not having discharged for a long- 

 time, showed no perceptible after-effect of the last shock, and thus 

 save no organ current." 



O o 



By this it is easy to see that the pre-existence of E.M.F. in 

 the resting state of the organ is practically contradicted, and the 

 effects can be altogether explained according to the views of Gotch 

 and Eckhardt. 



Since an organ-preparation cannot, of course, be made without 

 stimulating it, it is natural that the E.M.F. of such a preparation 

 should sometimes be considerable. A section through the organ 

 in the vicinity of the electrodes that lead off from back and belly 

 may, as Gotch stated, convert a weak and previously hetero- 

 dromous current into a somewhat stronger effect, homodromous 

 with the discharge. " Further incisions, that bounded the part 

 led off, so that it only remained in its natural connection 

 on the median side, increased the E.M.F. in the same 

 direction, till it finally amounted to 0-0015 Eaoult. If by 

 subsequent transverse sections the resulting wedge-shaped 

 disc of organ was still more reduced, until by sagittal cuts 

 it became a bundle with only a few prisms, the E.M.F. of the 



