286 ELECTRO-PHYSIOLOGY CHAP. 



As regards the interpretation of these electromotive effects 

 beneath the anode of the ascending current, there cannot well 

 since no diffusion of the polarising current can be demonstrated 

 on the side of the kathode be any such in the vicinity of the 

 anode either : the differences of potential developing along the 

 nerve under the influence of current must therefore be referred 

 to a physiological alteration of its state, transmitted apart from 

 any presumable diffusion of current from the anode. This 

 modification must undergo a marked decrement, otherwise it 

 would be difficult to explain why there should sometimes be a 

 mere trace of positive action at a distance from the anode, while 

 vigorous deflections appear in the course of the nerve under 

 uniform conditions. Nor is this the only point in which the 

 positive alteration starting from the anode differs from the 

 excitation discharged at the kathode, which is transmitted with 

 a smaller decrement and apparently at much greater velocity ; 

 it further persists during the passage of the current at almost 

 undiminished strength, or even increases, and only subsides 

 rapidly on opening the exciting circuit. 



Eecent experiments of v. Uexkiill (37) show that cephalopod 

 nerves (Eledone moschata) react like those of Anodonta, in so far, 

 at least, as regards failure of any conspicuous electrotonus. 



3. In Cooled and Etherised Medullated Nerve 



Biedermann (38) subsequently obtained effects from medul- 

 lated frog nerve, under certain conditions, analogous with those 

 described above for non-medullated nerve. These chiefly refer to 

 alterations of electromotivity under the influence of the constant 

 current, at maximal distance from the exciting tract, and with 

 minimal currents. Usually, under these conditions, the single 

 closure of an ascending or descending current, with transverse 

 lead-off, gives at most a trace of effect as a negative variation 

 of the demarcation current. But if, with preparations of cooled 

 frogs (where the nerves frequently react tetanically to the weakest 

 excitation), the galvanometer contacts are applied, at a small distance 

 apart, to one end of the nerve, and the exciting electrodes (as far 

 off as possible) to the other end, a very weak descending battery 

 current being used as stimulus, then the conditions for the 



