ii) 01(^0 no'! 

 26 



Obs. 16. 

 Graphic of 

 carotid 

 pressure. 



Obs. 17. 

 Stimulation of 

 distal vagus 

 on arterial 

 pressure. 



EXERCISE V 



Obs. 18 

 Escape of 

 ventricle from 



wound. Protect artery from drying by replacing skin of wound and by a 

 swab of cotton-wool wet with Ringer-Locke. 



IV. Note that the record of the arterial pressure shows oscillations (text- 

 fig. 12) of two kinds ; the smaller and quicker are synchronous with the 

 heart-beats and recur at a rate which may be anything between 80 and 120 

 a minute. The larger and slower are synchronous with the chest movements 

 produced by the respiratory pump. These latter closely resemble the 

 respiratory undulations of the arterial pressure observable in the living animal 

 breathing for itself, but are in an inverse sense, because the conditions of 

 mechanical pressure in the chest are the reverse in the preparation ventilated - 

 by the pump of those obtaining in natural breathing. 



Not unfrequently rhythmic undulations of much longer period (text- 

 fig. 12) than the respiratory occur on the arterial-pressure record. As the 

 preparation is decapitate, thesecannot actio n of the 



bulbar vasomotor centre : their causation is obscu re. 



Measure the height of the arterial pressure by measuring the difference 

 in level between the Hg columns in the proximal and distal limbs respec- 

 tively of the manometer. 



y. Choose the right vagus if the left carotid is used for the blood- 

 pressure, because the left vagus may have been damaged by some flooding of 

 the wound with half-saturated MgSO^ in attaching arterial cannula to junc- 

 tional tube of manometer. 



Expose the vagus (PL II, fig. 3) as in exerc. IV, ligate and prepare it for 

 distal stimulation towards the thorax. 



When the nerve is not in use replace it carefully in the wound and leave 

 it protected from getting dry by closing the skin or by a small swab of wool 

 moistened with Ringer-Locke. 



To obtain the effect on the blood-pressure record, close the key in primary 

 circuit of inductorium, the secondary circuit being short-circuited ; start the 

 movement of the kymograph and, after it has run about 15", apply the faradic 

 stimulus by opening the short-circuiting key. Do not apply the stimulation 

 for more than 5"-10" unless there is special reason for longer stimulation. 



Observe (text-fig. 18) the latency of the effect ; the character of the fall ; 

 the character of the recovery ; and the influence of varying strengths of 

 stimulus. Stop the kymograph's travel during the intervals between obser- 

 vations. 



VI. Faradize vagus with the coil at such a distance on scale as has been 

 found to ensure complete temporary arrest of the pulse. Prolong the 



