PRACTICAL EXERCISES 



197 



is closed by a clip, and the side-tube is connected with one limb, E, 

 of the manometer shown in Fig. 93. E is itself provided with a 

 side-tube, F, armed with a short piece of rubber tubing. The 

 cannula .does not require to be filled with liquid before being inserted 

 into the artery. By opening F and releasing the clip on the tube 

 from the pressure-bottle the cannula and the tube connecting it 

 with the manometer can be filled, and any blood-clots can be easily 

 washed out in the course of an experiment. Before the bulldog 

 forceps is taken off the artery to obtain a blood-pressure tracing, 

 F must be closed, and the clip on the tube from the pressure-bottle 

 opened. The bottle is attached to a strong cord passing over a 

 pulley, by which it is raised to a height sufficient to balance approxi- 

 mately the pressure in the artery. The tube to the pressure-bottle 



FIG. 94. BLOOD-PRESSURE TRACING FROM A DOG : STIMULATION OF CENTRAL 

 AND PERIPHERAL ENDS OF VAGUS. 



The other vagus was intact. Stimulation of the peripheral end caused stoppage 

 of the heart and a marked fall of pressure. Stimulation of the central end pro- 

 duced a great rise of pressure, with, perhaps, a slight acceleration of the heart. 



is then clipped. If no manometer with side-tube is available, a 

 T -piece can be inserted in the connection between the cannula 

 and the manometer, and the cannula can be washed out through 

 this. 



Now take the bulldog forceps off the artery, and allow the drum to 

 revolve at slow speed. The writing-point of the manometer-float 

 will trace a curve showing an elevation for each heart-beat, and 

 longer waves due to the movements of respiration. 



(b) Isolate the vago-sympathetic nerve in the neck. Ligature 

 doubly, and cut between the ligatures. Stimulate the peripheral 

 (lower) end ; the heart will be slowed or stopped, and the blood- 

 pressure will fall. Stimulate the central (upper) end ; there may be 



