23 



nine contractions, then swing the point of the lever on and 

 record the next two contractions. Repeat this process as long 

 as the muscle contracts. Number the curves and write on the 

 drums the number of stimuli which have preceded each. 

 In this way study the effect of continued exercise on muscular 

 contraction. 



Take a time tracing, fix, and work out as on p. 21. 



m. Effect of the Strength of the Stimulus. 



1. On the Course of Contraction. METHOD. Starting with 

 the smallest stimulus which will give a contraction, i.e. with 

 the secondary coil as far out as will give a contraction, take 

 a tracing as described above and note the position of the 

 secondary coil. Then push the secondary coil nearer the 

 primary, note its distance, and take a second record, when 

 the drum is running at a uniform speed. Repeat this, each 

 time moving the secondary coil nearer the primary. Number 

 the curves and write upon the drum the distance of the 

 secondary coil from the primary in each. Mark the point of 

 stimulation, take a time tracing and fix. 



Study the effect of varying the strength of the stimulus on 

 (1) the duration of the phases and (2) the extent of con- 

 traction. 



If, with the strongest stimulus used, a shoulder should 

 appear on the ascent of the curve, explain how it has been 

 caused. 



2. On the Extent of Contraction. METHOD. (1) Disconnect 

 the drum from the primary circuit, twist the ends of the 

 wires together, and use the mercury key to make and 

 break the current. (2) Bring the lever against the drum 

 unconnected with the driving wheel and, with the drum 

 stationary, record the effect of the minimal effective 

 stimulus, make and break, and of stronger and stronger 

 stimuli, moving the drum about a quarter of an inch between 

 each record, and keeping the make and break upstrokes 

 separate. 



