CARDIAC MUSCLE. 



65 



Next stimulate the white crescentic line with the electrodes. 

 Inhibition should be obtained. 



Apply a few drops of 1% nicotine solution to the heart and 

 again try the effects of vagus and crescentic stimulation, from 

 time to time, recording the results on the kymograph. Nico- 

 tone will paralyze the ganglia. Try Atropine. Explain results. 



FIG. 18. Suspension method for heart contraction. 



Experiment 29. Stannius Ligature. (a) First Ligature. Ex- 

 pose the heart of a pithed frog in the manner already described. 

 Pass a thread behind the aorta. Lift up the apex and tie the 

 thread so that the knot lies on the crescent, thus separating 

 the sinus from the auricles. If properly done, the auricles and 

 ventricles soon cease to beat; if not, tie a second thread nearer 

 the auricles. If the relaxed ventricle be gently pricked it 

 gives a single contraction. In a short time, however, the 

 ventricle may begin to beat regularly but at a different rate 



