524 THE OUTGO OF ENERGY 



Expose the sciatic nerve. Tie a ligature about 

 the nerve near the distal end of the wound, and 

 sever the nerve on the distal side of the ligature. 

 Stimulate the central end with a tetanizing 

 current of moderate strength. 



The afferent impulses set up by the stimula- 

 tion proceed to the spinal cord and thence to the 

 bulb, where they excite nerve cells which dis- 

 charge impulses that cause the smaller arteries 

 (and probably the veins) to constrict. This 

 narrowing causes the arterial pressure to rise. 



Changes in the Stroke of the Pump ; Inhibition 

 of the Ventricle. While the arterial pressure in 

 the artificial scheme is at a good height (1 20 mm. 

 Hg) arrest the ventricular stroke (the ventricle 

 in animals may be thus inhibited by stimula- 

 tion of the vagus nerve, page 316). 



So soon as the ventricle ceases to beat, the less 

 distended arteries will empty themselves through 

 the peripheral resistance, and the arterial man- 

 ometer will show a continuous fall in blood- 

 pressure. 



Eesume the ventricular beats. 



The mercury in the arterial manometer will 

 rise in large leaps, corresponding to the ease with 

 which the early strokes of the pump distend the 

 lax arteries (the inertia of the mercury somewhat 

 exaggerates the rise at each stroke ), As the 



