ADVANCED EXPERIMENTAL PHYSIOLOGY 103 



second stimulus falls well 

 within the latent period of the 

 first ; the muscle is stimulated 

 directly. The secondary coil is 

 placed at such a distance from 

 the primary that when, by 

 rotating the drum by hand, 

 one of the strikers is made to 

 pass over the naked wire, a 

 minimal or submaximal break, 

 but no make contraction, is 

 obtained. A tuning fork is 

 arranged to write under the 

 myograph-lever, the drum is 

 allowed to make one revolu- 

 tion at a rapid rate, a base 

 line is drawn, and the points 

 of stimulation corresponding 

 to each " striker " are marked. 

 Swing the lever away from the 

 drum, but do not alter the 

 position of the base of the 

 stand carrying the myograph. 

 The single contraction so re- 

 corded is the response of the 

 muscle to two break shocks. 

 In order to determine whether 

 the muscle has been in any 

 way influenced by the second 

 stimulus, raise the second 

 " striker," so that it will no 

 longer touch the naked wire, 

 and record the contraction 

 due to the first stimulus alone 

 (Fig.. 104). It will be found 

 that the contraction in re- 

 sponse to the single stimulus 

 is not so great as that due to 

 the two stimuli. In other 

 words, there has been a sum- 

 mation of stimuli during the 

 refractory period. In the same 

 way subminimal stimuli can 

 be summated, but two maxi- 

 mal stimuli are summated 

 only when they follow each 

 other after an interval of less 

 than r/^Tjth second. 



As has been pointed out on 



