294 THE CIRCULATION IN THE BLOOD-VESSELS. [CH. XXI. 



its abdomen is not pendulous, and its vaso-motor power is intact. 

 (Leonard Hill.) 



The pressure in the Pulmonary Circulation is roughly about one- 

 third of what it is in the systemic vessels. 



The influence of the Cardiac Vagus on blood-pressure. The 

 importance of the heart's action in the maintenance of blood- 

 pressure is well shown by the effect that stimulation of the vagus 

 nerve has on the blood-pressure curve. If the vagus of an 



T 



Fig. 282. Effect of strong stimulation of the peripheral end of vapus on arterial bkxxl- 

 pressure (carotid of rabbit). Note stoppage of heart and fall of blood -pressure nearly 

 to zero ; after the recommencement of the heart, the blood-pressure rises, as in fig. 27.1, 

 above the normal for a short time. 



animal is exposed and cut through, and the peripheral end 

 stimulated, the result is that the heart is slowed or stopped ; 

 the arterial blood -pressure falls simultaneously ; the fall being 

 especially sudden and great if the heart is completely stopped. 

 There is a rise in venous pressure. The effect on arterial pressure 

 is shown in the two accompanying tracings; fig. 281 representing 

 the effect of partial, and fig. 282 of complete stoppage of the 

 heart ; in both cases the animal used was a rabbit, and the artery 

 the carotid. 



The effects of stimulating the central end of the vagus and 



