90 LA BORA TOR Y GUIDE IN PHYSIOLOG Y. 



of the cycle with each part of the tracing. If the 

 tracing has a single crest, more delicately counterpoise 

 the lever and more carefully adjust the narrow foot of 

 the lever to the auriculo-ventricular groove and repeat 

 the experiment. 



(3) Take tracings of the auricle alone. Compare these 

 with those of the auriculo-ventricular groove and deter- 

 mine the causes of the variation. 



(4) Without altering the counterpoise take a tracing of 

 the ventricle and compare it with the two preceding 

 curves and account for all the differences. 



(5) Try to take a double tracing with one lever foot 

 resting upon the auricle and the foot of the second 

 lever resting upon the ventricle. The tracing points 

 must touch the drum in a vertical line. Are the 

 crests synchronous? If not, why? 



(6) If a time tracing be added by means of the chrono 

 graph one may determine the time relations of the 

 different phases of the heart cycle. 



