VASO MOTOR NERVES. + 89 



/J& 



3. DEMONSTRATE THE EFFECT OF STIMULATION OF THE VAGUS 

 NERVE ON THE ARTERIAL BLOOD PRESSURE. Introduce tracheal 

 and carotid cannulae as described in pars. 2, and 3 (Exp. 35), and 

 apply electrodes to the peripheral end of the vagus. Take about 

 an inch of normal tracing and cut the vagus on one side while a 

 tracing is being taken. Note any effect on the blood pressure. 

 Apply electrodes to the peripheral end of the cut vagus and stimu- 

 late with an induced current of moderate strength (just bearable to 

 the tip of the tongue). Repeat with stimuli of varying strengths. 

 Remove the electrodes to the central end of the vagus and repeat 

 the stimulation. 



FIG. 27. Stimulation of the cardiac depressor nerve in the rabbit, showing 

 effect on arterial blood pressure. In the tracing to the right the vagi were intact; 

 in the tracing to the left they were cut. Note the slower respiratory oscillations 

 after cutting the nerve. 



In the above experiments, the drum should be revolving slowly 

 while the stimuli are applied, and the moments at which this is 

 done should be indicated by short-circuiting the time tracing. 

 Explain the causes of the results. 



4. DEMONSTRATE THE EFFECT OF STIMULATION OF THE DE- 

 PRESSOR NERVE ON THE BLOOD PRESSURE. Pick up the ligature 

 tied to the central end of the depressor nerve (the small nerve 

 which is not the sympathetic), apply electrodes and stimulate. 

 A fall in blood pressure should occur (Fig. 27). Look for slowing 

 of the heart. Show that the fall in blood pressure, caused by 

 stimulation of the depressor, is not entirely due to reflex vagus 



