CH. XXI.] 



CARDIAC NERVES AND BLOOD-PRESSURE 



277 



brain ; the blood accumulates in the very pendulous abdomen which 

 such domesticated animals acquire, and the vaso-motor mechanism of 

 the splanchnic area is deficient in tone, and cannot be set into such 

 vigorous action as is necessary to overcome the bad effects of gravity. 

 Consciousness is, however, soon restored if the animal is placed in a 

 horizontal position, or if while it is still hanging vertically the abdomen 

 is squeezed or bandaged. A wild rabbit, on the other hand, suffers no 

 inconvenience from a vertical position ; it is a more healthy animal in 

 every respect; its abdomen Is not pendulous, and its vaso-motor 

 power is intact. (Leonard Hill.) 



FIG. 278. Effect of strong stimulation of the peripheral end of vagus on arterial blood -pressure (carotid 

 of rabbit). Note stoppage of heart and fall of blood-pressure nearly to zero ; after the recommence- 

 ment of the heart, the blood-pressure rises, as in fig. 277, above the normal for a short time. 



Tlie pressure in the Pulmonary Circulation varies from J to J 

 (mean J) of that in the systemic vessels. 



The influence of the Cardiac Nerves 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 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 conse- 

 quently falls ; the fall is especially sudden and great if the heart is 

 completely stopped. There is a rise in venous pressure. The effect 



