and Plants to the Electrical Phenomena associated with it. 5.1 



Photograph. 4.* 



evidence that, although the whole muscle is in circuit, the presence of 

 the wave cannot reveal itself until it is under the electrode. As regards 

 the action-current therefore, the electromotive source is always the 

 surface of contact of the leading-off electrode with living substance, 

 not the surface of contact between dead and living. 



We may now resume our consideration of the form of the propagated 

 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 characteristic 

 features, indicating that in each muscular element the electrical change 

 culminates from two to six thousandths of a second after excitation, 

 according to the physiological state of the muscle and the time it has 

 been kept, subsiding at first abruptly, afterwards more gradually, so 

 that its whole duration (i.e., to the summit of the electrometer curve) 

 amounts to from two to six hundredths of a second. 



The discoverer of the Pieizwelle, Professor Bernstein, assigned to it a;' 

 very different duration. " In every element of muscular structure^ 

 the variation lasts between 1 250 and 1/300 second, and coincides with 

 the period of latent stimulation." At first sight this statement seems irre- 

 concileable with fact, but it is much less so than it appears to be. ' We 

 have only to assume that Bernstein's method of estimating a small and 

 transitory difference of potential between two surfaces, was not suffi- 

 ciently delicate to enable him to appreciate those which exist during 

 the period of decline, and that what he regarded as the duration of the 

 whole variation, was in reality the duration of its summit only. How- 

 ever this may be, it is clear that we may divide the period of variation 

 into two parts, which we may call respectively the initial rise and the 

 decline, of which the latter lasts eight to ten times as long as the for- 

 mer : and that we may regard the first as a period of upset, the second 

 as a period of restoration. Taking the period of upset as equivalent to 



* Curarised Sartorius kept for twenty-four hours. Seat of excitation between 

 the leading off contacts, 4 mm. from d, 20 mm. from p. 



