242 



HUMAN PHYSIOLOGY 



thus less blood is forced into the arteries, and the blood 

 pressure falls. 



(6) The rhythm of both auricles and ventricles is slowed, 

 but the effect on the auricles is more marked than upon the 

 ventricles, and the ventricles may show a contraction rhythm 

 independent of that of the auricles (Fig. 119, A.). 



(c) The force of contraction of the auricles is decreased. 



FIG. 119. Simultaneous Tracing from Auricles and Ventricles. A., During Stimu- 

 lation of the Vagus; B. t During Stimulation of the Sympathetic. Each 

 downstroke marks a systole, each upstroke a diastole. (From ROY and 

 ADAHI. ) 



In the ventricles the systole becomes less complete and the 

 cavities become more and more distended. In the heart 

 of the tortoise excitability and conductivity are decreased, 

 and the auricular contraction may fail to pass to the ven- 

 tricles. 



