216 MUSCLE. 



point off again, bring the paper to the starting point and 

 re-apply. Open the S key, close the others, and slowly turn 

 the drum by hand until contact occurs; the muscle lever 

 writes an upstroke. This is the moment in the tracing at 

 which the stimulus was given. Turn off the muscle recorder, 

 close S key. Next mark the exact position at which the 

 recorder began to rise, and measure the interval by com- 

 paring it with the time tracing. 



The latter consists of oscillations in which each down 

 stroke of the style is a sharply denned descent. The in- 

 tervals between these are 96th parts of a second ; estimate 

 fractions by the eye. 



9 Tetanus. Summation of muscular contractions. 



Required : Drum, muscle chamber on stand, inductorium, variable 

 spring, 2 Leclaiiche cells, 8 wires. Drum at a middle speed. Nerve 

 muscle preparation, with indirect stimulation. 



Set up : S circuit as usual, P circuit with the variable 

 spring in the position of the usual break key ; it is to act 

 as a mercury key. 



1. First record two or three muscular contractions clear of 

 each other, but on the same line, by making and breaking 

 the P circuit. Do this by pressing the needle of the variable 

 spring in and out of the mercury cup. 



Next throw several stimuli in rapid succession into the 

 nerve, moving the spring by hand as before ; these will 

 succeed each other irregularly, but will be sufficiently rapid 

 to cause the contractions to follow each other, so that the 

 muscle has not time to relax completely before the next 

 stimulus reaches it. 



2. The spring will now be caused to oscillate at its 

 slowest speed (10 per sec.), sliding clamp placed furthest from 

 the end, so as to give a number of stimuli at regular 



