THE FROG'S HEART 



263 



5. The Contractions of the Excised Heart of the Frog Pith a frog 

 and expose the heart, as described in the preceding experiment. Re- 

 move it completely from the body by first cutting the arteries at their 

 branching in front of the bulbus arteriosus, then carefully lifting up the 

 parts of the heart and cutting away the great veins where they enter the 

 sinus. This will remove the entire heart, including all its contractile 

 parts. The frog's heart, when thus removed and still wet with its own 

 blood, will continue contracting rhythmically and in its natural sequence 

 for some hours. Place such an isolated heart in a watch-glass and take a 

 record of its contractions by the apparatus described in the preceding 

 experiment. (The same phenomena may be studied on a heart isolated 

 and mounted in a Williams' apparatus.) 



Set this watch-glass on the metal warming-box supplied, and arrange 

 for the circulation of water of different temperatures through the box. 

 Vary the temperature of the box, and therefore of the heart placed upon it, 

 by allowing water of o C., 10 C., 20 C., 30 C., 40 C., to flow through 

 it. Or place the heart in a watch-glass over a drinking glass of water of the 

 proper temperature. Record the contractions of the heart at each of 

 these temperatures. The exposed heart will not take the same absolute 

 temperature as the box, but the relative temperature will be decreased or 

 increased. Tabulate the rates at these different temperatures by the 

 plan previously described. 



6. The Perfused Heart, Influence of Different Nutrient Fluids. Expose 

 a frog's heart, as previously described, and insert a 4-way cannula into 

 the ascending vena cava where it 



enters the sinus. Connect the 

 limbs of the venous cannula with 

 Mariotte's bottles. Fill one with 

 Ringer's solution, the other with 

 comparison fluids. Adjust the con- 

 stant level tube for a pressure of 

 4 cm. of fluid and allow it to flow 

 through the heart. The heart will 

 continue its contraction's in good 

 sequence and with a uniform rate. 

 Record the contractions by the 

 Engelmann lever method on 

 smoked paper, together with a 

 time tracing in seconds. Set the 

 drum at the rate of about 2 mm. 



per second. After each compari- 



- . . . .. FIG. 214. Roy's Tonometer, 



son is made Ringer s fluid should 



be perfused to secure a return of the normal contractions. 



