INFLUENCE OF INTENSITY OF STIMULUS 125 



which 100 would be due to make and the alternating 100 to 

 break. 



In order to subject the plant to brief alternating shocks 

 applied at definite moments, and having definite duration, 

 the sliding interrupter and its connections already described 

 were appropriately modified. The vertical sliding contact- 

 plate now consists of a conducting platinum sheet, except 

 for a narrow non-conducting interruption made of a piece of 

 inlaid ebonite. The sliding-plate and the contact rod now 

 short-circuit the secondary, except during the brief interval 

 when the narrow strip of ebonite removes the short-circuit. 

 It is during this definite interval that the plant is subjected 

 to the alternating shock. The breadth of the strip is so 

 chosen that the duration of the shock is about '05 second. 

 During this time the plant will receive 10 alternating shocks, 

 5 of make and 5 of break. If desired, a simple device may 

 be introduced by which the duration of the shock can be 

 modified. This modification consists in inlaying a right- 

 angled triangle instead of a linear piece of ebonite on the 

 metallic plate. The base of the right-angled triangle is 

 kept horizontal. It follows that, by adjusting the rod 

 from right to left, the interval of the removal of short- 

 circuit can undergo continuous reduction of duration. 



The mark which indicates the beginning of stimulation 

 is made in the usual manner, and in successive experiments 

 the stimulation is initiated at this precise moment. The 

 duration of stimulus is also constant. In the following 

 experiments, it is to be remembered, we are to determine 

 the effect of changing one factor whilst maintaining others 

 constant. Thus we have in each case to take one 

 record under standard and one or more under modified 

 conditions. 



Effect of Intensity of Stimulus 



The series of experiments to be described below have 

 in each case been repeated at least twelve times, with 



