ELEMENTARY EXPERIMENTAL PHYSIOLOGY 63 



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FIG. 59. Arrangement of frog-board arid lever for frog's heart. 3 



FIG. 60. Lever for recording the frog's heart. (Pembrey and Phillips.) 1 



1 With the form of heart lever (Fig. 59) the contraction is represented by 

 the downstroke ; with the lever (Fig. 60) by the upstroke. 



