294 ELECTRO-PHYSIOLOGY CHAP. 



anode. On the other hand, the presence of an extrapolar kat- 

 electrotonus, homodromous with the alterations undoubtedly trans- 

 mitted by conduction, leads us in the last case to conjecture that 

 the galvanic anelectrotonus of medullated nerve may also, as it 

 were, arise from two components one, a physiological change of 

 state transmitted, as in non-medullated nerve, from the anode, 

 the other, a galvanic alteration, peculiar to medullated nerve, and 

 corresponding with katelectrotonus proper, the purely physical 

 origin of which has still to be discussed. We should thus 

 anticipate that " physiological anelectrotonus " would appear in 

 greatest integrity at maximal distance from the exciting tract, 

 while in the vicinity of the anode it is complicated by other 

 homodromous local alterations of the nerve, due to specific 

 diffusion of the polarising current. This is also indicated in the 

 fact, as above stated, that anelectrotonic effects far exceed the 

 katelectrotonic in intensity and range, which is easily explained 

 in view of the relations obtaining in non-medullated nerve. It 

 is, however, desirable to bring forward further arguments, and, if 

 possible, evidence, for such a separation between physical and 

 physiological electrotonus. In one direction such evidence is offered 

 by experiments on medullated nerve, in ether or chloroform nar- 

 cosis, where all changes transmitted ly conduction would seem to be 

 definitely excluded. 



From these experiments (for method cf. Biedermann, 38) it 

 appears that all electromotive alterations of the nerve, that may 

 otherwise be observed at points remote from the tract through 

 which current is flowing, disappear shortly after the commence- 

 ment of etherisation (510 min.). This applies both to the 

 negative variation on closing the descending constant current, 

 and to the positive effects with an ascending current. The 

 ordinary negative variation, moreover, fails when the nerve is 

 tetanised, showing that conductivity is really abolished (thus 

 giving additional evidence contra Boruttau's theory of the negative 

 variation, as above). Seeing that treatment with ether cannot 

 fundamentally alter the physical and chemical properties of a 

 nerve (as shown on the one hand by the constancy of P.D. between 

 transverse and longitudinal sections, on the other by the rapid 

 restoration of all normal vital properties of the nerve at the 

 close of narcosis), the presumed double character of electrotonus 

 becomes highly probable. It is proved, i.e., to depend not merely 



