CHAP, iv.] THE VASCULAR MECHANISM. 



195 



of the ventricle pass at each stroke into the veins, and the 

 mean arterial pressure is established. To this it may be added 

 that, as we have seen, the force of the individual beats may be 

 somewhat greater after than before inhibition. Besides, when the 

 mercury manometer is used, the inertia of the mercury tends to 

 magnify the effects of the initial beats. 



STIMULATION VAGUS 



FIG. 44. VAGUS STIMULATION. 



Pulse-tracing from the carotid of rabbit, taken by a modification of the 

 sphygmograph. The period of Vagus stimulation is marked by the line below. One 

 beat occurs after stimulation has begun. Shews the fall of blood-pressure, and the 

 character of the first recommencing beats. 



Complete arrest of the heart-beats is not necessary to produce a 

 fall of pressure. As is seen in Fig. 45, mere slowing of the beats 

 will lower the mean pressure. And, speaking generally, we may say 



FIG. 45. STIMULATION OF VAGUS. 



Blood-pressure curve taken with mercury manometer. The effect is to slow the 

 ythm ratber than to bring about complete standstill. With the slow pulse the 

 essure still continues to fall. The beginning of stimulation is marked by a. 



that if while the force of the individual beats remains constant the 

 frequency is increased or diminished, and vice versa, if while the 



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