50 Prof. J. Burden-Sanderson. Relation of Motion in Animals 



The contacts are as shown in the diagram. Before tightening the 

 ligature between them they are equipotential, because they both rest 

 on muscle in the same physiological state. I represent the electrical 

 concomitant of that state by an arrow, by which I mean nothing more 

 than that if it were possible to connect p with some other part of the 

 anuscle, without passing through another electromotive surface, there 

 would be a current in that circuit from p to the galvanometer. But 

 inasmuch as the actual circuit passes through d where the same condi- 

 tions exist as at p, but opposed in direction, there is no current. If by 

 tightening the ligature I annul the effect of d, the effect of p comes 

 into evidence. This statement is simple, and seems to arise naturally 

 from the observed facts ; but cannot be received without question, for 

 it suggests that what we call the " demarcation current" has its seat, 

 not at the surface of demarcation, but at the living surface, so that we 

 should have to consider the state of " Stromlosigkcit " not as a state of 

 electrical inaction, but as a state of balance. 



A similar question would arise as regards the response to excitation. 

 For when, as we have seen, the Reizwelle passes under the proximal 

 contact (Exp. 1), what happens there (during the 100th of a second 

 that it is passing) is analogous to what I have just described as the 

 effect of suddenly tightening a ligature at that spot. The moment 

 before excitation a state of balance existed between p and d. As the 

 wave passes under p it upsets that balance by annulling the outgoing 

 current, then pursues its course until it is extinguished by the ligature. 

 From the moment that the tail of the wave has left the edge of the sur- 

 face of contact behind, it has no action whatever on the indicating 

 instrument. We have evidence of this in the curve of variation itself, 

 for the form of the curve is the same whether the wave is blocked by 

 the ligature at one centimetre from the point of observation, or at 

 three, which could not be the case if, as I once imagined, something 

 happened at the moment of extinction. 



The complete proof that this is so, is however obtained by another 

 form of experiment in which the seat of excitation (r) is shifted from 

 the proximal side of p to the proximal side of d. The unligatured and 

 therefore equipotential muscle is excited in the two positions succes- 

 sively. The results show (1) that the excitation wave is propagated in 

 both directions, and (2) that the form of the curve varies according to 

 the order in which the electrodes are reached. This having been deter- 

 mined, the progress of the wave is stopped by a ligature under the 

 distal contact d, and the excitations in the two positions repeated. It 

 is now seen that the form of the wave is the same whatever the direc- 

 tion from which it approaches the point of observation p. When the 

 excitation is proximal to (/, it is not now anticipated by a variation at 

 </, and there is consequently a long delay (see Photograph 4) during 

 which the electrometer is unaffected. The experiment affords direct 



