118 



ADVANCED LESSONS IN PRACTICAL PHYSIOLOGY 



sympathetic nerve contains certain fibers which innervate the radial 

 muscle cells of the iris, its excitation must give rise to an increase in the 

 size of the pupil. Consequently, if any doubt exists as to the character 

 of the nerve isolated, this reaction may be employed to make sure that 

 it is the sympathetic. 



FIG. 76. THE VASOMOTOR REACTION IN THE EAR OF THE RABBIT ON DIVISION AND 



STIMULATION OF THE CERVICAL SYMPATHETIC NERVE. 



A, Normal, B, After division of the cervical sympathetic nerve. C, On stimulation of the 

 distal end of the divided cervical sympathetic nerve. 



2. The Depressor Nerve. Insert a straight cannula in the left 

 common carotid artery and connect it with the mercury manometer. 

 Place the depressor nerve in shielded electrodes, and arrange the electric 

 apparatus for stimulation with a quickly interrupted current of mod- 



FIG. 77. RECORD OF THE CAROTID BLOOD-PRESSURE IN RABBIT DURING STIMULATION 

 OF THE DEPRESSOR NERVE. 



erate strength. Record the blood-pressure and stimulate the aforesaid 

 nerve for about twenty seconds. Note the fall in blood-pressure and 

 also the decrease in the frequency of the heart. Allow the pressure to 

 return to normal. 



