CHAPTER VIII. 



Experiment 36. 



VASO MOTOR NERVES, DEPRESSOR NERVE, 

 CIRCULATION TIME. 



(The General Instructions for the Insertion of the Cannulae 



and the Conduct of the Experiment are the same as 



in Experiment 31). 



1. PREPARATION OF ANIMAL. Weigh the rabbit. Inject a 10% 

 solution of chloral hydrate per rectum, 5 c.c. per kg. body weight. 

 When the chloral effect has developed (about 30 minutes) cause the 

 rabbit to inhale a little ether. To fix the head make an incision 

 through the floor of the mouth and with an aneurysm needle pass 

 a stout thread through the incision and out of the mouth. Tie the 

 thread to the cross bar of the animal board. Tie out the limbs. 



2. DEMONSTRATE VASOCONSTRICTOR FIBRES IN THE CERVICAL 

 SYMPATHETIC. Clip the hair from the front of the neck and make 

 a median incision. Retract the skin. Separate the laryngeal 

 muscles from the sterno-mastoid so as to expose the carotid sheath. 

 Running with the carotid arteries will be seen one large and two 

 small nerves. Of the latter, one is the cervical sympathetic, the 

 other the depressor (see Fig. 26). Tie a pair of ligatures loosely 

 around each nerve.* Now stretch the ear on the same side as the 

 exposed nerve on a wire frame so as to render its vessels quite 

 plain. Stitch the edges of the ear to the frame. With a good light 

 behind it, examine the vessels of the ear, carefully noting their 

 size. Note also the size of the pupils. Pick up the ligatures around 

 one of the fine nerves, tie both ligatures and cut the nerve between 

 them. Look for any effect on the vessels of the ear and on the 

 pupils during both tying and cutting. Apply electrodes to the 



*To obviate confusion the ligatures should be marked by placing bulldog 

 forceps on the free ends. The nerves must be frequently moistened with 0.9 per 

 cent, saline. 



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