STIMULATION OF THE VAGUS 



177 



was obtained in this way : it is from a cat under morphia and 

 curarised. It shows that the blood pressure rose from a mean height 

 of 94 mm. Hg to one of 144 mm., but that the characters of the 

 tracing were otherwise retained in a perfectly characteristic manner. 

 This rise in pressure is due to a reflex constriction of the small 

 arterioles, and persists for some time. It is almost completely 

 abolished by section of the splanchnics. 



4. Stimulation of the peripheral end of the vagus.— While the 

 record is being taken one vagus is ligatured in two places and cut 

 between the two ligatures. There is, as a rule, no effect upon the 

 blood pressure or respiration. The peripheral end is laid on electrodes 



Fig. ]39. — Pressor Effect Produced by Stimulating the Central End of the 

 Sciatic of a Curarised Cat under Morphia. Time Tracing Seconds. 

 Tracing Reduced to One-half Size. 



and stimulated, the stimulation being repeated once or twice with 

 different strengths of stimulus. Figs. 140 and 141 show the effect of 

 such stimulations. Pig. 140 is with weak stimulation, which produced 

 slowing of the heart beat but no stoppage. It is seen that there is 

 a marked fall in blood pressure, which, however, did not commence 

 the instant the stimulus was applied. The variations of pressure now 

 recorded as caused by each heart beat are seen to be very much 

 larger. This is not due to an increase in force of the ventricular 

 contraction, for, as we have previously seen, the force of the beat is 

 decreased on vagal stimulation (p. 141 ). Nor, again, is it entirely due 

 to the diminished blood pressure, enabling the heart to produce a 



N 



