22 



VI. Influence of Various Factors upon Muscular 

 Contraction. 



Arrange an experiment in the same way as the last, and 

 take a trace of a muscle twitch with a breaking shock. Mark 

 the point of stimulation. 



(Those who are to do the effect of Load omit the small 

 weight in the first trace.) 



Each pair of students then does one of the following experi- 

 ments, and then compares their tracings with those of the others 

 at the same side of the table. 



I. Effect of Temperature. 



METHOD. Swing the lever off the drum by the base-piece, 

 and cool down the muscle by putting ice round it, separating 

 the ice from the muscle by a piece of blotting paper saturated 

 with normal saline, and after 2 or 3 minutes remove the ice 

 and paper and swing the lever on to the previous abscissal 

 line, raising or lowering the drum if this is necessary, and 

 when the drum is again running at uniform speed take 

 another trace over the first. 



Then, proceeding in the same way, warm the muscle by 

 allowing normal saline at 25 C. to run over it for 2 or 3 

 minutes, and take another tracing. (Put a plate under the 

 frogboard to catch the solution.) 



Number the curves and note " normal." " cold," and 

 " warm " upon them. 



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



II. Effect of Continued Exercise. 



METHOD. Having arranged the apparatus for taking a 

 trace of a muscle contraction, start the drum and let the 

 muscle be stimulated, and record its contraction with each 

 tenth revolution of the drum. To do this, after a contraction 

 or two contractions are recorded, swing the lever off the 

 paper by the base-piece of the stand ; let the muscle make 



