562 THE OUTGO OF ENERGY 



appropriate methods of observation would show 

 that vagus excitation increases the intraventricu- 

 lar pressure during diastole, lessens the intake 

 and the output of the ventricle, and diminishes 

 the tonus of the heart muscle. The action of the 

 vagus is accompanied by a positive electrical 

 variation. The action on the sinus and on the 

 bulbus does not differ essentially from that upon 

 the ventricle. 



It has already been pointed out tbat the vagus 

 of the frog contains both inhibitory and augment- 

 ing fibres. The stimulation of the mixed nerve 

 usually causes inhibition, as described above, but 

 sometimes augmentation. The augmentation ob- 

 served after cessation of the inhibitory effect is 

 probably explained by the longer after-effect of 

 the augmentor excitation. 



Intracardiac Inhibitory Mechanism. Arrange 

 an inductorium for tetanizing currents. Close 

 the short-circuiting key. Expose a frog's heart. 

 Eaise the heart with a glass rod. Note the white 

 "crescent" between the sinus venosus and the 

 right auricle. Set the inductorium in action. 

 Put the points of the electrodes on the crescent, 

 and open the short-circuiting key for a moment. 

 After one or two beats the heart will stop. 



Inhibition by Stannius Ligature. Turn up the 

 heart to expose its posterior surface, and note the 



