INFLUENCE OF THE CENTRAL NERVOUS SYSTEM 179 



nutrient fluid, provided only that the oxygen be supplied in sufficient 

 quantity and under high enough tension. 



THE REGULATIVE INFLUENCE OF THE CENTRAL NERVOUS 

 SYSTEM ON THE HEART. 



The heart is capable of automatic rhythmic movement, yet while in the 

 body its beats are under the constant control of the central nervous system. 

 The influence which is exerted by the central nervous system is of two kinds: 

 first, in the direction of slowing or inhibiting the beats, and, second, in the 

 direction of accelerating or augmenting the beats. The influence of the 

 first kind is brought to bear upon the heart through the fibers of the pneumo- 

 gastric or vagus nerves, and that of the second kind through the sympathetic 

 nerves. 



The Inhibitory Nerves. It has long been known, indeed ever 

 since the experiments of the Weber brothers in 1845, tnat stimulation of one 

 or both vagi produces slowing of the rhythm of the heart. It has since been 



FIG. 177. Effect on the Heart Rate and on the Arterial Blood Pressure of Stimulating the 

 Right Vagus of the Dog. Stimulus applied at the mark " on " and removed at " off." Pressure in 

 millimeters of mercury shown by the scale to the left. Time in seconds. (New figure by Hill and 

 Chilton.) 



shown, in all of the higher vertebrate animals experimented with, that this 

 is the normal reaction to vagus stimulation. Moreover, . a section of one 

 vagus, or at any rate of both vagi, produces acceleration of the pulse; and 

 stimulation of the distal or peripheral end of the divided nerve normally 

 produces slowing or stopping of the heart's beats. 



