MOTION IN ANIMALS AND PLANTS. 341 



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 " Stromlosigkeit " 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 con- 

 tact (exp. 1), what happens there (during the one-hundredth 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 j^ 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 

 surface of contact behind it has no action whatever on the indicating 

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

 for the form of the curve is the same whether the wave is blocked b}^ 

 the ligature at one centimeter 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 

 successively. The results show (1) that the excitation wave is propa- 

 gated in both directions, and (2) that the form of the curve varies 

 according to the order in which the electrodes are reached. This hav- 

 ing been determined, 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 what- 

 ever the direction from which it approaches the point of observation ^>. 

 When the excitation is proximal to d^ it is not now anticipated by a 

 variation at d^ and there is consequently a long delay (see photograph 

 4, PI. II), during which the electrometer is unaffected. The experiment 

 affords direct evidence that, although the whole nmsclc is in circuit, the 

 presence of the wave can not reveal itself until it is under the elec- 

 trode. As regards the action current, therefore, the electromotive 

 source is always the surface of contact of the leading-oft' electrode with 

 living substance, not the surface of contact between dead and living. 



We may now resume our consideration of the form of the propa- 

 gated monophasic variation or excitatory wave. It would be easy to 

 prove by the exhibition of numerous photographs of the monophasic 

 variation relating to different muscles that all have the same charac- 

 teristic features, indicating that in each muscular element the electrical 

 change culminates from two to six thousandths of a second after 

 excitation, according to the ph3^siological state of the muscle and the 



