24 



A stimulus which is too weak to cause a contraction is called 

 a subminimal stimulus. 



Mark under each upstroke the distance of the secondary coil 

 from the primary, fix, and work out as on p. 21. 



IV. Influence of Load. 



1. On the Course of Contraction. METHOD. (1) Take a 

 trace of a muscle twitch when no weight is on the lever, as 

 described on p. 18. (2) Closing the key in the secondary 

 circuit when the trace is made, stop the drum and swing the 

 lever off. (3) Hang a weight of 10 gms. on the lever so that 

 the thread from the muscle and that from the weight are 

 equidistant from the fulcrum, or each at a measured dis- 

 tance from the fulcrum. (4) See that the lever is not 

 resting on the screw pin. (5) Lower the drum till the point 

 of the lever marks the same abscissa as before and take another 

 trace when the drum is running uniformly. (6) Then move 

 the weight to a measured distance further out on the lever, 

 and take another trace. (7) Repeat with the weight still 

 farther out, or put on a greater weight. If the lever is much 

 depressed, shift the pin holding the muscle to make it again 

 horizontal ; but, in doing so. do not move the stand. Number 

 the traces, and having calculated the actual weight applied to 

 the muscle by p. 17 B, note it upon the drum. 



Mark the point of stimulation, take a time trace and fix. 



2. On the Extent of Contraction. METHOD. Proceed as in 

 III. 2, but instead of varying the strength of the stimulus go on 

 increasing the weight attached to the lever, when necessary 

 adjusting the level of the drum, and mark under each up- 

 stroke the weight used, calculated as directly applied to the 

 muscle 



Make a diagram, showing and comparing the work done 

 with each weight. 



V. The Effect of Tension on the Contraction and Work done 

 by the Muscle. 



A. With the screw-pin below the lever well depressed, 

 attach a weight to the lever such that the muscle in contracting 



