ELEMENTARY EXPERIMENTAL PHYSIOLOGY 47 



and, with the drum stationary, record the contraction of the 

 muscle unloaded, then moving the drum about a quarter of an 

 inch between each record, and keeping the make and the break 

 upstrokes separate, the effect of the minimal effective stimulus 

 (make and break), and of stronger and stronger stimuli. 



Mark under each upstroke the distance of the secondary coil 

 from the primary, fix, and work out as on p. 42, I. 



5. Effect of Continued Exercise. 



(This should be done after 1, 2, 3, or 4 on the same preparation.) 

 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 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 



FIG. 44. Spring Ergograph. (Porter.) 



write on the drum 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. 42, I. 



After taking each trace formulate your conclusions as to the effect of 

 the particular condition. 



The Result of Continued Exercise on the Neuro-muscular Mechanism 

 in Man. METHOD. Fit the hand and arm in a Mosso's ergograph, 

 to the hook of which a weight of 3 kilograms has been attached, or 

 use Porter's ergograph (Fig. 44). Bring the writing point against a 

 very slowly moving drum. Set a metronome beating about sixty 

 times per minute, and as each beat is heard raise and lower the 

 weight with the finger to the fullest extent as long as it is possible 

 to move the weight, then study the record of the onset of fatigue 

 upon the drum. Note the time taken by your watch. Compare 

 your record with those of others, 



