44 



PRACTICAL PHYSIOLOGY 



(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 grms . 

 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 

 distance 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 



FIG. 39. The effect of load upon the contraction of the gastrocnemius 

 muscle. (A.P.B.) 



marks the same abscissa as before and take another trace when the 

 drum is running uniformly. (6) Repeat the experiment till all the 

 weights of the series supplied have been used. 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 



FIG. 40. Height of contractions of gastrocnemius with increasing load. 



The number above each contraction is its observed height in mm. Magnification, 5. The number 

 below each contraction is the weight in grm. hung at the axis of the lever ; the actual load 

 on the muscle was half of this number. (A.P.B.) 



traces, and, having calculated the actual weight applied to the 

 muscle (p. 42, 1. c.), 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 p. 46, 

 4, 2, but instead of varying the strength of the stimulus go on in- 

 creasing the weight attached to the lever, when necessary adjusting 



