The Action of the Depressor Nerve on the Pupil. 53 



pupil than suffice to bring on the characteristic drop of blood- 

 pressure. A strong fall of bloodpressure due to a moderate de- 

 pressor stimu'ation does not cause any alteration of the pupil. 



Stimulation of one depressor may cause a contraction of the 

 pupil on the opposite side. 



This pupillary effect cannot be obtained with the same cer- 

 tainty as the fall in bloodpressure. After several successful trials, 

 the pupil usually fails to respond for a while. 



The two depressors vary in their pupillary effect; one may 

 yield excellent pupillary contractions, the other one none at all. 



The stimuli used were rarely longer than three to five seconds; 

 the strength 100-150 mm. coil distance (Petzold coil). 



Section of the sympathetic nerve, or extirpation of the superior 

 cervical ganglion, the depressor of the same side being stimulated 

 several days later, exerts no appreciable effect on the result. The 

 reflex therefore seems to act on the third nerve chiefly, if not en- 

 tirely. 



In addition to this pupillary effect, depressor stimulation at 

 times causes a short wink or a more or less prolonged retraction 

 of the bulbus. 



It must be added that a strong winking (closure of the lids 

 being prevented by a speculum) usually causes a very short sharp 

 contraction of the pupil, the Piltz-Westphal phenomenon. This 

 contraction is, however, much more rapid than what has been 

 described as the initial contraction on depressor stimulation; 

 moreover, the initial contraction is frequently obtained without 

 any sign of winking. 



In rabbits anesthetized by ether or which have been allowed to 

 recover from the ether, the depressor pupil effect was not obtained. 

 An increase of reflex irritability is apparently necessary in order 

 to obtain the depressor pupillary contraction. 



