102 MUSCLE 



Exercise XIX 



Kymograph 



Smoked 

 paper 



Plasticene 

 counterbalance 



Frog board 



Keep dripping Ringer solution on the heart; 

 if you let it dry, the amplitude of contraction will 

 decline. When the heart is beating evenly, 

 rotate the drum a little way so as to draw a 

 control record of 6 to 8 beats. Rinse the heart 

 with 2 to 3 drops of Ringer, wait 30 seconds, and 

 repeat. There should be no difference in the two 

 records. (Writing on the smoked paper with your 

 dissecting needle, indicate on the record when 

 you add anything to the heart.) 



Now rinse the heart with 2 (only 2!) drops of 

 acetylcholine solution in Ringer. Watch the 

 heart, and when you see a perceptible change of 

 beat, run a short record. (If nothing happens 

 within 2 minutes, add 2 more drops of the acetyl- 

 choline solution, but no more. Too much 

 acetylcholine will cause the heart to stop com- 

 pletely. If your heart does stop from too much 

 acetylcholine, rinse it thoroughly with Ringer 

 solution, and it should recover within about 5 

 minutes.) 



What has happened to the heart rate and the 

 amplitude of contraction? After waiting another 



minute or so, run another record. Has the heart 

 begun to recover? Now rinse the heart with 

 fresh Ringer. The beat should return to normal 

 in a few minutes. 



Run another control record. Now rinse with 

 2 drops of epinephrine solution in Ringer. What 

 does it do to the heart beat? Now rinse with 2 

 drops of acetylcholine solution in Ringer, and 

 again record the result. 



Again rinse the heart with Ringer, and wait for 

 about 5 minutes. The heart may still show some 

 effects of the epinephrine, which wear off much 

 more slowly than those of acetylcholine.- Run 

 another control record. Add 5 drops of atropine 

 solution in Ringer to the heart, wait for 30 

 seconds, and run a record. Has anything hap- 

 pened? Now add 2 to 4 drops of acetylcholine 

 solution, and record again. What has happened ? 

 What did the atropine do? 



The heart is self-excitatory. Its beat originates 

 in a small specialized area in the wall of the sinus 

 venosus, the SV node. In this area, the mem- 

 brane allows a continuous, small leakage of Na+ 



