iv ELECTROMOTIVE ACTION IN MUSCLE 377 



magnitude 3 may be calculated, and is actually -^tro sec - > i- e - 

 about ^^ sec. elapses between the moment of exciting the 

 muscle and the moment of its most pronounced electrical 

 variation. Starting with the length of the latent period, as 

 originally assumed, at ^^ sec., the maximum of the negative 

 variation coincides with the middle of the period of latent 

 excitation. According to v. Bezold (23) the electrical variation 

 begins, under its most favourable conditions, immediately after 

 the moment of excitation, and therefore falls at the beginning 

 of the latent period. The estimation of the latter has been 

 constantly reduced since the time of Helmholtz, and Burdon- 

 Sanderson has recently placed it much lower than Tigerstedt, 

 who reckoned it at 0*005 sec. for frog's muscle. According to 

 Burdon-Sanderson (24) the interval between excitation and the 

 first sign of change of form is only 0'0025 = ^5-9- sec., and since 

 he allows an equally large latent period to the negative variation, 

 there would thus be no perceptible interval between the two 

 manifestations; whereas, according to Bernstein (I.e. p. 192), on 

 the other hand, " each element of the muscle fibre completes its 

 process of negative variation before it enters into the state of 

 contraction." Since, however, on the one hand, the preoccurrence 

 of the electrical variation can be directly observed in slowly 

 contracting muscle, e.g. heart (infra), and, on the other, it 

 appears on theoretical grounds to the last degree improb- 

 able that the excitation itself (i.e. changes in the contractile 

 substance associated with negativity) should possess a latent 

 period, the idea is confirmed that the beginning of the wave of 

 excitation precedes the contraction wave, by however small an 

 interval (cf. Engelmann, 25). This does not, of course, imply 

 that it declines earlier in Bernstein's sense, or dies away at any 

 particular point before contraction begins there, for while it is 

 quite conceivable that a point of the muscle may be excited, and 

 become negative to adjacent resting points without being per- 

 ceptibly contracted, the contrary is impossible, and every con- 

 tracted part must necessarily be assumed to be in a state of 

 excitation also. In this sense, therefore, it may be said that the 

 electrical wave itself is an expression of contraction (cf. Lee, 26). 

 If, with Bernstein, we assume 0'015-0'023 sees, to be the 

 latent period (which is not, in any case, conclusive), and start 

 with the values calculated from this for length, duration, and 



