in ELECTRICAL EXCITATION OF MUSCLE 271 



fibre-endings at this end of the muscle, which provide repeated 

 opportunities for the current to escape into adjacent fibres of 

 the muscle. 



Although these phenomena are of no special physiological 

 interest, they are deserving of thorough investigation, on account 

 of the very striking polar effects due to the same causes in 

 different smooth muscular organs, which might easily conduce to 

 the fallacious assumption that there was a reversal of Pniiger's 

 law of excitation. On the other hand, we find in them the 

 key to a number of older observations on striated muscle. 

 Even the earlier literature contains some if rare instances, 

 which indicate that striated muscle, under certain conditions, 

 if not invariably, exhibits a reaction to the electrical current 

 which differs from the normal, inasmuch as at closure of the 

 current, excitation appears on the anodic side also. The first 

 observations in this connection are those of Aeby (20), dating 

 from 1867, which led him, in opposition to Bezold and Engelmann, 

 to the conception of a bipolar, though unequal excitation of the 

 muscle, by the constant current. Moreover, Aeby thought he had 

 proved that under certain conditions, more particularly with 

 progressive fatigue of the preparation, the normal reaction in 

 which the excitatory action of the kathode far exceeds that of 

 the anode was exactly reversed. Aeby's experiments, however, 

 are by no means unimpeachable, as both Engelmann and 

 Hering (1) pointed out later. This applies in particular to an 

 experiment in which the two legs of a frog still united by, and 

 dependent from, the pelvis, are traversed by current, the two wires 

 used as electrodes being connected to the lower end of the legs. 

 The bones of the thigh were previously freed, and on excitation 

 the leg traversed in a descending direction appeared to contract 

 more markedly than that in which the current passed upwards, 

 from which Aeby concluded that the effect at the negative pole 

 predominated. But no account is taken, on the one hand of the 

 difference between physical and physiological electrode points, as 

 insisted on by Engelmann and Hering ; on the other hand, of the 

 difference in density of current at knee end and pelvic end of 

 the two limbs respectively. Still, however, even in this case the 

 reversal of effect becomes apparent after prolonged duration of 

 experiment. Aeby concludes from this that fatigued and dying- 

 muscle possesses different properties from fresh muscle ; it is no 



