42 PRACTICAL PHYSIOLOGY 



open the key in the secondary circuit so that the current may reach 

 the electrodes and nerve. When the muscle is stimulated it con- 

 tracts and pulls up the lever and records the contraction on the drum. 



FIG. 37. Muscle attached to Lever. 



(4) Whenever the two records are made, close the key again and stop 

 the drum, (Don't reverse the drum and don't move the stand of the 

 frog-board.) 



E. Mark the Moment of Stimulation. 



To mark the moment of stimulation, revolve the drum slowly with 

 the hand, keeping the key in the secondary shut till the striker is 

 just about to make contact, then open the key and very cautiously 

 continue the movement of the drum till the muscle contracts and 

 marks the moment of stimulation. Note the relationship of this 

 mark, which indicates the moment of stimulation, to the upstroke 

 which marks the contraction. 



F. Make, a Time Trace. 



(1) Swing the lever off the paper by using the basepiece (do not 

 move the drum or the myograph stand). (2) Run off a time trace 

 in T ^o sec. with the tuning fork (p. 28). 



Make two tracings, one for each Student. 



G. Record the Nature of the Experiment. 



With a pin or other sharp-pointed instrument write upon the 

 paper the nature of the experiment, your name and the date. 



H. Fix the Trace. 



Remove the paper from the drum, and fix the trace by passing it 

 through photographic varnish. Hang it up to dry. 



I. When dry read the trace, and work out the results 



(a) The Duration of 1st. The time between the application 

 of the stimulation and the contraction. 



2nd. The time taken up by the contraction. 



3rd. The time of relaxation. 



(6) Extent of Contraction. Measure the extent of movement and 

 the length of each limb of the lever, and calculate the actual shorten- 

 ing of the muscle as in 1, p. 37. 



Measure the length of the muscle, and calculate the percentage 

 shortening. 



(c) Weight Lifted. Measure the distance of the weight from the 

 fulcrum, and calculate the actual weight lifted by the muscle as 

 in 2, p. 37. 



(d) Work Done. Calculate the work done by the muscle as in 3, 

 p. 38. 



Preserve the trace and the calculations in your note-book as usual. 



