262 ELECTRO-PHYSIOLOGY CHAP. 



Bernstein (28) himself doubted the accuracy of his observations. 

 In the end, however, Hermann confirmed Bernstein's original state- 

 ment, on leading off from a mechanical cross-section (made by 

 crushing), and not from a thermal section, in which the fine nerves 

 may be injured by the steam from the hot water. He then 

 repeatedly observed cases in which the negative variation was 

 nearly double the current of rest. But, as Head (I.e. p. 241 f.) 

 showed in theory, if we start from the low value quoted by 

 Bernstein for the duration of the single negative phase (0 - 0007 

 sec.), the variational current (i.e. current through the galvanometer 

 in consequence of negative variation) must at the moment of 

 maximal intensity be 4|--9 times as strong as the nerve 

 current : which is highly improbable, " so long as the intensity of 

 the exciting induction currents is kept within the (narrow) range 

 in which direct excitation of the* nerve by unipolar action in the 

 part led off (galvanometer tract) is absolutely excluded." His 

 own experiments (which, owing to the method employed, failed 

 to determine the intensity of the variational current directly, 

 and only gave the minimal indispensable height of the negative 

 variation, not as in Bernstein's experiment its actual height) 

 afforded no indication of variational currents of such magnitude 

 as was assumed by Bernstein and Hermann. 



In the non-medullated nerves of Cephalopoda, Fuchs invari- 

 ably found that, " at that position of the rheotome slider which 

 corresponds with the maximum of the negative variation, the 

 latter only induced a more or less considerable diminution of the 

 current of rest never its abolition, or even reversal." 



It is far harder to demonstrate a phasic action current 

 between two longitudinal points of the uninjured nerve, than 

 on leading off from long and (artificial) transverse sections. As 

 we have stated, Bernstein was the first to show on striated 

 muscle that during the passage of a directly-stimulated wave of 

 excitation the points over which the wave was passing were 

 invariably negative to all other (unexcited) points. Hermann 

 extended this law to the natural ends of the uninjured muscle, 

 as well as to the case of indirect excitation, and proved the 

 imircrsal presence of a diphasic action current in all uninjured 

 muscles, those of man included. It is plain that a similar 

 reaction might be anticipated for nerve : the difficulties of 

 experiment are equally apparent. Owing to the extreme rapidity 



