DEGLUTITIONAL AND RESPIRATORY REFLEXES 83 



in the preparation supplied you, for ligating the carotid. Double tie 

 the submaxillary vein and sever it between the ligatures ; extend the 

 wound deeply behind the angle of the jaw; a branch from the vagus 

 nerve will be met sloping downwards and inwards to enter the side of 

 the larynx above the thyroid cartilage : this is the superior laryngeal nerve. 

 Ligate it close to larynx, carefully dissect it proximal to ligature for 

 about 15 mm. Sever distal to ligature. 



Faradize the lifted proximal stump, the secondary coil being at a 

 distance from primary such as just suffices to cause contraction of muscle when 

 applied to some muscle exposed in the preparation, e. g. about 22 cm. on the 

 induction scale. A strong stimulus will excite other reflex effects and not 

 swallowing. Note result — a promptly evoked swallow or a series of swallows, 

 and temporary arrest of respiratory movements; also closure of the 

 glottis. 



These can be recorded by attaching a thread with a small hook to 

 hyoid bone, a headward movement of larynx accompanying each swallow. 

 Note the refractory period of the reflex swallow and the inhibition of 

 respiratory movement of chest. 



VIII. Note point near xiphoid where respiratory movement seems Obs. 65. 

 most ample. Bring stethograph to table and place receiving end of it on G-raphic of 

 the spot chosen in ventral wall of preparation. See that movement of movements of 

 vertical limb of recorder is as free as possible. Adjust table and preparation chest. 



so that distance from vertical limb of recorder to kymograph crank- 

 lever recorder is sufficient to keep taut the thread between them. Attach 

 thread of recording-lever to the stethograph arm. Kymograph should 

 be running slowly. 



Record respiratory movement, arranging that inspiration is recorded 

 by an upstroke. Note that the inspiratory movement lasts longer than 

 the expiratory, and that the expiration is followed by the expiratory 

 pause (text-fig. 31). 



IX. Cause a swallowing reflex ; note that inspiration is inhibited Obs. 66. 



during swallowing. Compare, as in 5 V above, water, alcohol, and oil -^^^^est of 



,, , n oo^ respiration by 



(text-fig. 32). swallowing. 



X. Expose right and left vagus nerves in neck well below the Obs. 67. 

 cricoid cartilage. Also the right recurrent laryngeal on trachea (exerc. IX). ^^^^s and 

 Note movements of vocal cords again; then cut right recurrent nerve; rh^iim.°^^ 

 observe the motionless paralytic position of right vocal cord. Adjust 



M 2 



