INTRAOCULAR NERVES 



319 



stimulate the nerve. The pupil may dilate (sympathetic 

 fibers), contract (oculomotor fibers) or remain stationary 

 (both sets of fibers or none of either). The electrodes are 

 moved a little and the points can be worked cautiously down 

 into the nerve trunk. Stimulate (for a moment only) at 

 each new position of the electrodes, the pupil being watched 

 carefully all the time. At some point in the stimulation the 

 pupil will show a marked contraction at once. This is 

 striking when properly done and will be well worth the 

 time necessary to do the dissection within the orbit with 

 especial care. Let each member of the group see the con- 



Fig. 281. Method of dissecting out the orbital fat and fascia to expose the optic 

 nerve. The position of the electrodes for stimulating the third nerve fibers is shown. 

 The eye-ball is rolled forward (inward) somewhat to bring the optic sheath into view. 



traction and keep the observation in mind to check your 

 later results. 



Now turn the dog's head back into the usual position 

 and insert a cannula into Wharton's duct. Stimulate the 

 chorda tympani nerve and obtain a normal secretion. 



Arrange the apparatus for recording oxygen consump- 

 tion and if necessary put a small amount of ether into it 

 (but avoid the ether if you can). Into the femoral veins 

 place injecting cannulas, the burettes to which contain nico- 

 tine ( l /2%) and adrenaline. Take some normal record (in- 

 cluding at least one or two notches of the oxygen record). 



