138 ELECTRO-PHYSIOLOGY CHAP. 



Iii view of the experiments on striated and smooth muscle as 

 discussed above, it is natural to conjecture for nerve also that we 

 are in presence of antagonistic polar effects of current, in the seuse 

 that the excitation is from the kathode only at closure, from the 

 anode on opening the current. When, therefore, at closure of a 

 strong descending current, or on opening a strong ascending 

 current, there is a twitch, it is evident that there is nothing in 

 either case to block the transmission of the excitation from the 

 corresponding electrode to the muscle. When, on the contrary, the 

 break twitch fails to appear in the first instance, the make 

 twitch in the second, it may be assumed with probability that 

 the kathodic excitation discharged above the anode with ascending- 

 direction of current is blocked there, and never reaches the muscle. 

 And conversely the break excitation, discharged with a descending 

 current above the kathode, appears to die out at the previously 

 kathodic point of the nerve. Thus, in the precise analysis of the 

 phenomena consequent upon the electrical stimulation of motor 

 nerves, we reach the same ultimate conclusion as for contractile 

 substances, viz. that the current does not discharge the process of 

 excitation equally, at all points of the area traversed, but produces 

 " polar " alterations, manifested partly as excitatory and partly as 

 antagonistic inhibitory phenomena, as expressed in the third 

 stage of the law of contraction. We are indeed less favourably 

 situated here than in the direct excitation of contractile substances, 

 where the polar action of the current is immediately translated 

 into corresponding changes of form at the physiological pole, since 

 we are thrown back in nerve upon the reactions of the terminal 

 organ (more or less remote from the seat of stimulation), in proof 

 that the change usually takes place in one direction only. 



The fundamental importance of the postulate of polar 

 excitation by current, which Prliiger at first deduced simply as 

 an inductive consequence of the law of contraction, rendered it 

 desirable to obtain further direct evidence of its accuracy. V. 

 Bezold (19) attempted to confirm the law by time-measurements 

 for motor nerve, as he had for striated muscle. The method, 

 which in both cases consisted in measuring the latent period of 

 the muscle-twitch, proved to be even simpler for indirect than for 

 direct excitation of the muscle. If an ascending current of 

 medium density is led through a sufficiently extended part of 

 the nerve in a nerve-muscle preparation, the latent period of the 



