76 SPECIAL PHYSIOLOGY 



of the lever seems to be too great for the heart, move easily; the 

 long arm may be made relatively lighter by adjusting the counter- 

 poise upon the short arm. If the tracing point of the long arm 

 has a sufficient excursion to make a good tracing, bring the kymo- 

 graph to a position where the point will lightly touch the carboned 

 surface of the drum. The lever should be nearly tangent to the 

 surface of the drum, and so arranged that the rotating surface of 

 the drum turns away from the tracing point of the lever rather than 

 toward it. 



All tracings should be accompanied by a time tracing or chrono- 

 gram. Study the chronographic system and make drawings of the 

 plan, showing all electric connections. Study the chronograph or 

 time marker, and make a diagram showing its construction. 



3. Observations. (1) Note whether the curve is a simple one or 

 composed of a major wave, with crests superimposed upon it. In 

 either case closely observe the phases of the heart cycle and determine 

 the relation of each part 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. 



(2) Take tracings of the auricle alone. Compare these with those 

 of the auriculo-ventricular groove and determine the causes of 

 variation. 



(3) Without altering the counterpoise take a tracing of the 

 ventricle and compare it with the two preceding curves and account 

 for all the differences. 



(4) By adjusting the foot of the lever between the ventricle and 

 the bulbus it is possible to get a ventriculo-bulbar tracing which 

 differs from the auriculo-ventricular in having the superimposed 

 crest following the ventricular crest, while in the auriculo-ventricular 

 tracing the superimposed crest precedes the ventricular. 



(5) If the conditions of the experiment are favorable it is possible 

 to get an auriculo-ventriculo-bulbar tracing. To get this the lever 

 foot must be placed in the auriculo-ventricular groove so that it 

 rests upon the auricles, ventricle, and bulbus. A typical tracing 

 may be recognized by the high central ventricular crest flanked by 

 two superimposed crests made by the auricles and bulbus. 



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

 may determine the time relations of the different phases of the 

 heart cycle. 



D. To Observe the Movements of the Mammalian Heart. 



1. Appliances. Dog or rabbit; operating case, supplemented by 

 haemostatic forceps, heavy scissors and scalpels, clippers, heavy 

 linen thread; hand bellows with tube and respiration cannula (see 



