iv ELECTROMOTIVE ACTION IN MUSCLE 421 



action, because they are flattened. The whole process, therefore, 

 loses in crispness, and also in capacity for exciting." 



These conclusions leave no doubt as to the influence which the 

 intensity, form, and distribution in time, of the electrical wave of 

 variation exert upon the secondary excitation of nerve and 

 muscle. It remains to consider the effect 'of the time-order of 

 successive (single) stimuli upon secondary excitation and upon 

 electrical response of muscle in general. 



Since secondary excitation is only a special form of the electri- 

 cal stimulation of a nerve still in connection with its muscle, we 

 should a priori presume that the same law which dominates the 

 manifestation of primary tetanus, and more especially its depend- 

 ence on the intensity and frequency of stimuli, also holds good 

 for secondary tetanus. Remembering further that the electrical 

 waves of variation are not always exactly parallel with the 

 phenomena of contraction, we should not expect complete 

 parallelism between primary and secondary tetanus (as actually 

 appears from the facts). Before the incapacity of many tetani 

 to produce secondary tetanus was appreciated, the latter was 

 held to be such an unfailing indication of primary tetanus 

 that it was appealed to, not merely in evidence of the electro- 

 motive discontinuity of all tetani, but also in deciding be- 

 tween contracture and tetanus. It was taken for granted that 

 a muscular movement which induces secondary twitch, but not 

 secondary tetanus, must itself be a simple twitch. Yet this often 

 occurs where there is no doubt as to the discontinuity of the 

 primary stimulus. The effect in the secondary preparation 

 depends essentially, as can readily be demonstrated, on the char- 

 acter and strength of the primary excitation, and therefore on 

 the intensity and frequency of the induction shocks sent into the 

 primary preparation. If the strength of current is so adjusted 

 that the primary muscle is thrown into tetanus, there will be a 

 partial tetanus in the secondary muscle varying in length and 

 height, or curves will be yielded which cannot in any way be 

 distinguished from those sometimes described by the primary 

 muscle as " initial twitches." In rare cases we find not merely 

 a secondary initial twitch at the beginning of primary tetanus, 

 but also a secondary " final twitch " at the end of the excita- 

 tion (Schoenlein, 53). If the secondary initial twitch appears at 

 relatively low stimulation-frequency, it is mainly due to those 



