ADVANCED EXPERIMENTAL PHYSIOLOGY 345 



With this goes one of the nerve trunks which pass from the sinus to 

 the auriculo-ventricular junction. Divide this ' coronary nerve/ The 

 rhythm of the heart continues unaltered. In another tortoise heart, 

 the muscular connection between ventricle and the rest of the heart 

 may be divided while the coronary nerve is left intact. The ventricle 

 stands still under these conditions. 



Slit up the sinus extension on the left side so that the left auricle 

 is entirely separated from sinus and right auricle, but remains attached 

 to the ventricle. The heart will now beat in this -order sinus, right 

 auricle, ventricle, left auricle. 



Slit crosswise the right auricle until only a narrow bridge of muscle 



FIG. 225. Gaskell's heart clamp and levers for recording the contraction of auricle 

 and ventricle. 



is left. The ventricle may now respond to only every second con- 

 traction of the sinus. The bridge is so narrow that the excitatory wave 

 is partly blocked there. 



Any strip of auricle and ventricle muscle cut from the tortoise 

 heart may be taught to beat rhythmically by weak induction shocks. 

 The rhythm, if once established, will continue for hours without artificial 

 stimulation. 



These experiments prove that the rhythm of the tortoise heart 

 muscle is independent of the ganglion cells in the heart, and that the 



