IV 



ELECTROMOTIVE ACTION IN MUSCLE 375 



maximum at a certain moment, and is finally quelled again. 

 These phases are expressed in the gradual reduction of difference 

 in electrical potential between the two leading-off contacts in 

 the muscle. Since we know that the artificial transverse 

 section of the muscle is electrically negative towards each point 

 of the uninjured surface, all these phenomena can easily be 

 explained by postulating that the change in the excitable substance 

 propagated from the point of excitation through the muscle-fibres 

 is associated with negativity of the latter. We shall subsequently 

 find direct proof of this dictum. For the moment it may be 

 accepted as a hypothesis, which elucidates the foregoing observa- 

 tions. We assume, therefore, that at the moment at which a 

 short stimulus (momentary excitation) takes effect upon any point 

 of the fibre, a chemical alteration is developed at the same point, 

 expressed by negativity of this part of the fibre towards adjacent, 

 non-excited parts. Stress must be laid on the fact, as attested 

 by every experiment, that this change (which must be regarded 

 as identical with the excitatory process) begins directly at the 

 moment of excitation, i.e. without any perceptible latent period, 

 rapidly reaches a maximum, and then declines again slowly. 

 The succession of the different stages of this change at the same 

 point of the fibre, whether directly or indirectly excited, may be 

 represented in a curve, designated above the " curve of variation." 

 But since the process in question is not localised, but is, as a 

 rule, transmitted with measurable velocity from the seat of 

 excitation, over the entire fibre, a longer or shorter section of 

 the muscle will always be found to be simultaneously (at different 

 points) in different phases of negativity. If the values of these 

 are erected as ordinates upon the muscle as abscissa, the resulting 

 curve resembles in its form the curve of variation, and is called 

 the " excitatory wave." Since the velocity with which the 

 process of negativity (excitation) is transmitted in the muscle 

 is known, as on the other hand the time at which the excitatory 

 wave is propagated its entire length this being identical with 

 the duration of the negative variation at any definite point of the 

 fibre, the length of the excitatory wave may easily be calculated 

 from the formula s ct = D (duration of negative variation) x V 

 (velocity). Since the two values by which the length of the 

 excitatory wave are determined differ in different muscles, and 

 even in the same muscle at different times, the length of the 



