in ELECTRICAL EXCITATION OF MUSCLE 213 



at any point of its course, considerable bending of part of the 

 muscle-fibres is inevitable, especially if the muscle is pressed 

 between two forks, with converse surfaces. The same thing 

 occurs when a lever or button is placed on the muscle, and presses 

 on it at the points of contact. In all these cases, part of the 

 current must pass in and out of the contractile substance in a 

 number of muscle-fibres at the seat of pressure." 



These observations will show why the negative results of 

 Aeby's experiments (supra] in which, when a parallel-fibred 

 muscle is wholly traversed by current, the propagation of a con- 

 traction wave is demonstrated by a lever cannot be regarded 

 as conclusive against the positive results of v. Bezold. In Aeby's 

 experiments, a very considerable bending of fibres occurs at both 

 points at which the lever is laid upon the muscle. Aeby him- 

 self remarks that "the lever was pressing somewhat upon the 

 surface of the muscle." So that the current at the point at which 

 the fibres bend inwards may very well pass in and out at different 

 points of the contractile substance, and thus produce a direct 

 excitation. 



Under these conditions, new experiments re the polar 

 effects of the electrical current appeared desirable. The 

 clamp experiment (Engelmann) with the frog's sartorius, as 

 described above, in which the excitation passes the fixed point 

 without difficulty, while the direct transmission of contraction 

 from one half of the muscle to the other is made quite impossible, 

 affords a simple method of graphically recording the course of the 

 contraction wave, and so making measurement possible ; for if 

 excitation starts from the kathode on closure of the current, a 

 muscle, fixed in this manner, and traversed by current in its 

 entire length, must twitch in the half corresponding with the 

 kathode earlier than the anodic half. The latter only begins to 

 shorten when the wave of contraction proceeding from the kathode 

 has passed beyond the clamped part. The time difference at the 

 beginning of the contraction of the two halves obviously corre- 

 sponds with the rate of transmission of the excitation, i.e. contrac- 

 tion wave, from the kathodic end to the first section beyond the 

 clamp. 



The method of experiment was as follows : a tuning-fork, 

 making 3 5 3 vibrations per sec., and provided with a lever, served 

 as the time-marker. This, together with a double myograph, 



