334 TEXT-BOOK OF PHYSIOLOGY. 



on the heart. Stimulation of the central end is followed by a fall in 

 blood-pressure, frequently to a level below one-half the normal value; 

 at the same time there is a diminution, brought about reflexly, in the 

 rate of the heart-beat. The fall is pressure, however, is not due to 

 this cause, for it occurs equally well after division of all the cardiac 

 nerves. For this reason the nerve was termed the depressor nerve. 

 On exposure of the abdominal cavity, it is observed during 

 stimulation of the depressor that there is a notable dilatation of the 

 intestinal vessels. 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. The function of the depressor is not definitely known. It 

 has been supposed that through it the heart can protect itself from 

 injurious results of an excessive rise of arterial pressure. 



