376 TEXT-BOOK OF PHYSIOLOGY. 



From this fact it was assumed that the action of the depressor nerve was to 

 lower the general pressure through reflex dilatation of these vessels. It has 

 been shown by Porter and Beyer that if the splanchnics are divided and the 

 peripheral end stimulated so as to maintain the tonus of the intestinal vessels, 

 and hence the general pressure, stimulation of the depressor nerve will 

 nevertheless be followed by a fall of the blood-pressure almost as great as 

 when the splanchnics are intact. From this it is evident that the depressor 

 nerve is related to centers which influence the vascular apparatus in its 

 entirety. It has been supposed that through it the heart can protect itself 

 from injurious results of an excessive rise of arterial pressure. 



Thus, when the intra-cardiac pressure or the intra-aortic pressure 

 rises beyond a normal amount from increased resistance, the peripheral 

 terminations of this nerve are stimulated with the result that the vaso-motor 

 center is inhibited and the arterioles relaxed. Through this means the 

 pressure falls and the work of the heart is lessened. 



