INTRACELLULAR POTASSIUM— TAYLOR 



29 



during incubation with one electrode at the dependent tip of the apex of the heart 

 and the other at the base of the aorta. In a typical experiment, perfusion was begun 

 and the heart was mounted in the thermostat. As soon as tiie beat was regular, the 

 temperature of the bath was slowly lowered, and electrocardiographic tracings were 

 obtained intermittently. From time to time the perfusion medium was sampled for 

 analysis for potassium. After a period of incubation at the lowest desired tempera- 

 ture, rewarming was begun and serial electrocardiographic tracings and medium 

 samples were again obtained. 



Figure I shows sample tracings of electrocardiograms from an experiment in 

 which the temperature of the perfused heart was lowered to 8° centigrade and main- 



£ff=^,t 



2:40 - 37** 



3:04 - 27* 



3:11 — 20* 



7:52- I3.l» 



S^v^ 



^i 



Ki 



% 



sj. 



9:42- 36.9* 



8:20- 20** 



Fig. 1. — Sample tracings of electrocardiograms during reduction of temperature of perfused heart 

 from normal to 8° C. and during rewarming. 



