ELECTROMOTIVE ACTION IN NERVE 259 



IV. TIME-KELATIONS OF ACTION CURRENT AS DETERMINED 

 BY EHEOTOME 



If a single brief stimulus, e.g. an induction shock, is sent into 

 the nerve, the existence, much less the time-relations of the 

 negative variation, will hardly be recorded by the galvanometer, 

 owing to the sluggishness of its magnet. We are therefore driven 

 back upon the repeating method, with the rheotome, for the 

 solution of the questions already familiar to us in muscle. The 

 method and instrument have already been described (vol. i. p. 367). 



Bernstein (26) found, in investigating the course of the 

 negative variation of the nerve current with tetanising, electrical 

 stimulation, that there was a measurable period between the 

 excitation of any point of the nerve and the commencement of a 

 negative variation (i.e. negativity) at a more distant lead-off, 

 corresponding with the rapidity of transmission of the negative 

 variation in the nerve, and the distance between the point of 

 excitation and the first longitudinal contact. The distance 

 between excited point and transverse section, on the other hand, 

 is immaterial. From this we may conclude, as in muscle, that 

 the process of negative variation in the part led off begins at the 

 precise moment in which the excitatory process transmitted in 

 the nerve arrives at the longitudinal electrode. It is further 

 evident that there is no perceptible interval between the moment 

 of stimulation by induction currents and the comrnencment of 

 negativity at the excited point. The negative variation has no 

 latent period. Both in medullated and non-medullated nerve 

 the negative variation is transmitted at a rate corresponding with 

 that of excitation, so that the negativity of any point of the 

 nerve may, as in muscle, be accepted as the galvanic expression 

 of excitation. Fuchs (4) determined the transmission rate of 

 the negative variation in cephalopod nerves as something between 

 less than 1 m. and 3 '5 m., according to temperature. Within a 

 given range it increases with strength of stimulus. 



The process of negative variation within a tract of nerve is 

 further found, on leading off from longitudinal and transverse sec- 

 tions, not to be instantaneous, but to last for a measurable period. 

 It does not at once attain its full strength, nor does it disappear 

 immediately. Experiment rather shows that negativity rises (at 



