70 EXPERIMENTAL PHYSIOLOGY. 



this. Also pass ligatures around the other veins which supply the 

 sinus venosus. Now with small forceps pick up the lower end 

 of the freed portion of the vena cava. With small sharp scissors 

 cut obliquely downward and forward not quite halfway through 

 the vein. Holding the vein flap with forceps insert the cannula 

 and tie the ligature securely about the constriction. Air must 

 not be allowed in the vein or cannula. Next start a small flow 

 of Ringer's fluid, through the heart, immediately opening the 

 aorta, and then tie off all the other veins entering the sinus. 

 Obtain tracings of the ventricle by means of a heart lever. 



Next determine the effect of the following solutions upon the 

 heart beat. Between each solution, Ringer's fluid must be 

 perfused until the heart beats normally. When changing the 

 siphon from one beaker to another keep air from entering by 

 placing the tip of the finger over the opening. 



Solutions to be used are as follows: 



1. 0.75% NaCl in distilled water. 



2. A solution containing 0.5% NaCl and 0.25% KC1 in 

 distilled water. 



3. 0.75% NaCl in distilled water to which a few drops of a 

 5% CaC^ solution has been added. 



4. Distilled water. 



Experiment 31a. Turtle Auricle. Suspend the auricles of a 

 turtle as in Fig. 8, p. 30 of Manual, lining the beaker with 

 moistened filter paper. Record contractions on slow drum. 

 Does the heart muscle contract automatically? Does the 

 muscle relax to the same degree between each beat? Do these 

 changes occur rhythmically? Does the muscle do more work, 

 i.e., lift the weight of the lever through a greater distance, when 

 contracting after a greater relaxation or after a less relaxation? 

 The effect of cations on cardiac muscle is readily shown by 

 immersing the suspended turtle's auricle in the solutions listed 

 in the previous experiment. 



