THE PHYSIOLOGY OF THE HEART 139 



passes off, and the ventricles again come to follow the lead of the 

 auricles, is a point requiring further investigation. 



2. The auricular and ventricular muscle can be cut in zigzag 

 fashion, and yet the .muscular impulse still passes, provided the 

 muscular bridges are of sufficient breadth. 



FIG. 47. SHOWING (A) EFFECT OF COLD ON THE DOG'S SINU-AURICULAR NODE 



(COLD APPLIED AT F) AND (B) ON THE AURICLE. (M. F.) 



3. No disturbance of rhythm is brought about by cutting or 

 stimulating the nerves connecting auricle and ventricle. 



Fie. 4S. --.SHOWING EFFECT OF CLAMPING SINU- AURICULAR NODE AT A IN DOG'S 

 HEART. No STOPPAGE, BUT SLIGHT SLOWING OF RHYTHM. (M. F.) 



Time in seconds. 



4. In perfused hearts, conduction may occur when the nervous 

 elements are presumably degenerated. 



5. The conduction of the excitatory wave can pass in all directions. 

 Reverse conduction from ventricle to auricle can also occur. Thus, 



