x ELECTROMOTIVE ACTION IN NERVE 351 



nerves, in consequence of the phasic differences in the wave of 

 excitation, which current excites the intermediate muscle-substance. 

 This, hypothesis, too is open to objection, not merely from the 

 theoretical point of view (du Bois-Keymond, 58, and Bernstein, 

 59), but still more (supra} on anatomical grounds, more particularly 

 the character of the motor nerve-endings in all invertebrates. 



To sum up all that has been said in relation to these various 

 " discharge theories," their justification seems more than doubtful, 

 and we must rather subscribe to Bernstein's opinion (I.e. p. 337), 

 that every hypothesis whereby the muscle is to be excited by 

 an electrical shock irradiating outwards from the nerve-ending is 

 excessively improbable. Apart from the preceding objections, the 

 time-relations of muscular excitation are decidedly against such a 

 view. The point is whether a measurable time is required for the 

 propagation of the excitatory process from the nerve-ending to the 

 muscle. Yeo and Cash pointed out that the latent period, with 

 indirect stimulation of the gastrocnemius muscle, is considerably 

 greater in the immediate vicinity of the entrance of the nerve 

 than it is with direct excitation of the muscle, and Bernstein (59) 

 subsequently examined the same fact more closely. 



" The marked extension of the time-difference (0'0032-0'0049 

 sec. on an average) leads us to infer that it depends not merely on 

 transmission of the excitation in the nerve down to its entrance 

 into the muscle-fibres, but also upon the retardation of the excita- 

 tory process in the end-organ of the nerve-fibre, as compared with 

 its duration in any parallel tract of the same." Subtraction of 

 the period of conductivity in the nerve from the interval deter- 

 mined experimentally between the two curves of contraction 

 gives the presumptive "period of excitation in the nerve-ending!' 

 If, in view of the structure of the gastrocnemius muscle, we 

 take the central point of the whole muscle as the central 

 point of entrance for the nerve, estimating the rate of 

 nervous conductivity at 27 m. per sec., then, according to Bern- 

 stein, the period of excitation of the motor end- organs will on an 

 average be 0'0032 = ^ l -% sec. The same value appears, as Bern- 

 stein pointed out, from the latent period of the negative variation 

 with indirect excitation of the muscle. We must assume that 

 the negative variation begins at the point of excitation at the 

 moment of stimulation (i.e. with no perceptible latent period), in 

 natural excitation from the nerve-ending, as in artificial electrical 



