ACTION OF THE VAGUS 



179 



inhibition more complete. The fall at the first stimulation is seen to 

 be greater, and only a single beat occurred during stimulation. After 

 the stimulus ceased the heart soon regained its rhythm, and the 

 characters of the trace were practically the same as those studied in 

 the previous instance. 



The result of a second stimulation s reproduced because it 

 illustrates another effect which is obtained if the vagus be frequently 



Fig. 141. — Two Successive Stimulations of the Peripheral End of the Right 

 Vagus with the Same Strength of Stimulus. Rabbit. Reduced to One- 

 half Size. 



stimulated. It was obtained by stimulating the vagus with the same 

 strength of current as that used for the preceding instance and after 

 an interval of fifteen seconds. It is seen that while the stimulation 

 still continued the heart recommenced to beat and the blood pressure 

 gradually rose. This result is known as the escape of the heart from 

 vagus inhibition. It becomes more and more marked the longer tin- 

 stimulus is continued, and if stimulation be repeated a few times, at 

 last a stage is reached in which no effect upon the heart nor upon the 

 blood pressure is produced. 



5. Stimulation of the central end of the vagus.— The result of such 



n2 



