SUMMATION OF STIMULI 



61 



shown in a difference in effect produced by a second stimulus which rapidly 

 follows it. 



The make shock (or break shock) may be cut out by using the key shown 



Fig. 61. — Reed arranged to Vibrate in a Horizontal Plane. 



in fig. 19, and fitting in the two notched wheels instead of the sectors. 

 Alteration in the rate at which the stimuli are sent in can then be effected by 

 altering the rapidity at which the key is driven. 



Experiment 2. — Adjust the vibrating reed as just described, at first clamping 

 it quite at the end, so that it vibrates two to three times per second. Make 

 a nerve muscle preparation and fix it in a simple lever or crank lever 

 myograph, and having covered and smoked the drum arrange it so that it 

 rotates at the rate of 8 cm. per second. Adjust the secondary coil, using a 

 Du Bois key as a short-circuiting key and placing the coil in such a position 

 that it gives maximal shocks on break while the make shocks do not stimulate. 

 Close the key in the secondary circuit, set the vibrating reed in action, 

 bring the writing point up to the smoked surface, and allow the drum to 

 rotate. Open the key in the secondary for about one to two seconds, and thus 

 allow the shocks to reach the nerve. The muscle contracts and its movements 

 are recorded. Stop the drum and next shorten the length of vibrating reed, 

 and take a second tracing in the same manner as before. Take a series of 

 tracings in this way, between each, making the reed vibrate a little faster 

 by shortening it. When the reed has been sufficiently shortened the effect 

 at last produced is a complete tetanus. 



In an experiment carried out as thus described the series of 

 tracings shown in fig. 62 were obtained. The time tracing in all cases 

 was eight per second. The preparation was the gastrocnemius stimu- 

 lated indirectly, and the magnification was threefold. In curve 1 the 



