ADVANCED EXPERIMENTAL PHYSIOLOGY 63 



It will be found that sooner or later the summed excitations will cause a 

 contraction, and, if the contractions are recorded on a slowly revolving 

 drum, that a well-marked ' stair-case ' effect is produced (Fig. 61). 



In dealing with the response of muscle to two successive stimuli, it 

 has been seen that, when the second stimulus falls within the latent 

 period of the first, the muscle is refractory, so far as being able to 



FIG. 61. Effect of subminimal stimuli repeated every 5 seconds on gastrocne- 

 mius stimulated directly. The dots mark the points at which stimuli were sent 

 in before they became obviously effective. Time marking in seconds. (A.P.B.) 



respond with a second contraction is concerned ; but it is not true that 

 a muscle during its refractory period always entirely ignores a second 

 stimulus. 



In order to investigate this point, the apparatus is arranged as in 

 demonstrating the effect of two successive stimuli (p. 42). The two 

 ' strikers ' are placed at such an angular distance apart that the 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 

 revolution 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 recorded 

 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. 62). It will be found that the contraction in 



