CHAPTER V. 



Effect of two successive stimuli upon a mus- 

 cle-nerve preparation. A. Summation. Make 

 a muscle-nerve preparation and fix it upon the 

 myograph in the usual way, so that the muscle writes 

 its contractions upon a cylinder revolving about 

 once in two or three seconds. Place the secondary 

 coil at such a distance from the primary that the con- 

 traction produced is minimal. Now by means of a 

 second pin projecting from the drum quite close 

 to the first, allow two shocks of the same minimal 

 intensity to affect the nerve in rapid succession. 

 If the two pins are sufficiently near one another 

 a simple muscle curve will again be described, 

 but the contraction will be more complete than 

 with the single minimal stimulus. If the stimulus 

 used is subminimal i.e., ineffective the effect 

 of its repetition may be to produce an effective 

 stimulus. 



B. Superposition. Place the secondary coil at 

 such a distance from the primary that the excita- 

 tion produced by a single projecting pin striking 

 the spring in its revolution is maximal, and de- 

 scribe a normal muscle curve in the usual way. 

 Then insert a second pin at varying intervals so 

 that the excitation which it produces will affect the 

 nerve at different intervals after the first excitation; 



