496 NER VE. 



portions of nerve together, equal in length to AC. Of these portions, one 

 (A'B') is an isolated portion to make up the necessary length, the other (BC) 

 is half the original nerve. The total resistance being the same in both cases, 

 the current intensity is unaltered, but the anodic fall and cathodic rise at 

 and near C is found to be far less marked in the second case. 



The time relations of the effects. — (a) Polar. — Griinhagen inter- 

 posed an induction coil in the polarising circuit, and excited with the 

 make induction current caused by closing the polarising circuit ; the 

 nerve was thus stimulated the moment that the current flow com- 

 menced. Such an experiment establishes the fact that both the 

 cathodic rise and anodic fall commence at the poles with no appreciable 

 delay on the closure of the current. The electromotive effects of the 

 polarisation changes have also been detected in the immediate neighbour- 

 hood of the poles, at an interval of '001 sec. after the closure of a very 

 brief intense current, and are therefore in all probability instantaneous. 



It may be pointed out that the absence of any delay is in harmony 

 with the instantaneous character of the nerve electrical response to an 

 exciting current. 1 



(b) Extrapolar. — In regard to the development of the excitability 

 changes in the extrapolar regions, there is considerable difference of 

 view. The electromotive effects (electrotonic currents) have been 

 detected by Hermann, Boruttau, etc., in the extrapolar regions of 

 models and of nerve, very soon after their production at the poles, and 

 hence the rate of their propagation has been considered as extremely 

 rapid, 500 metres per second. On the other hand, Bernstein's investiga- 

 tion with the differential rheotome showed comparatively slow propaga- 

 tion of these electrotonic changes, 6 to 13 metres per second ; the 

 probable reasons for this discrepancy will be given in connection with 

 electrotonus. 



The recent work of Asher appears to indicate that the anelectrotonic fall 

 spreads at a rate closely identical with that of the so-called nerve impulse. 

 Kuhne had shown by ingenious experiments that the motorial nerve-endings 

 could be placed in the state of anelectrotonic decreased excitability. Thus 

 a curarised sartorius is most excitable at the point of entry of its nerve, 

 but this portion loses its predominant excitability when a galvanic current 

 is led through the nerve, so that the anode is near the muscidar termina- 

 tion. Further, glycerin excites the sartorius only through its nerves ; it 

 fails to do so if the muscle, with its entering nerves, is the anode of 

 a galvanic current. Starting with such possibility of throwing the motorial 

 nerve- endings into the anelectrotonic state, Asher arranged that a polar- 

 ising current should be passed through the nerve, so that the anode should 

 lie a known distance from the nerve termination. The muscle was 

 excited directly by an induced current, and the polarising current closed 

 either at the same instant, or at a definite interval before the excitation. 

 There was no diminution in the response, unless the polarising current 

 was closed - 0007 sec. before the excitation ; and on measuring the distance from 

 the anode to the muscle, a propagation rate for the anelectrotonic decrease 

 was deduced which corresponded with that of the nerve excitatory state, 

 30 metres per 1 sec. 2 The experiment led to the further interesting discovery 

 that if the muscular response had commenced, the establishment of anelectro- 

 tonus in the nerve-endings had no effect upon the contraction. But grave doubt 



1 Bernstein, "Untersuch. u. Nerven- u. Muskelsysteme." 



2 Asher, Ztschr. f. Biol., 1895, Bd. xxxii. 



