HAEMODYNAMICS. 81 



nerves. Put bull-dog forceps on the ligatures to prevent these from 

 slipping off. 



Meanwhile a cannula of suitable size is connected to the mano- 

 meter (Fig. 23) by rubber tubing which has been scrupulously 

 cleaned of any old blood. This tubing is also connected by a 

 T-piece with a bottle provided with a rubber bulb and containing 

 a 2% solution of sodium citrate to prevent clotting of the blood. 

 The cannula must be scrupulously clean and should be slightly oiled 

 before inserting. Observance of these precautions greatly dim- 

 inishes blood clotting. A pinchcock on the side tube which con- 

 nects with the bottle is cautiously opened and by gentle compres- 

 sion of the rubber bulb, which is connected with the bottle, the 

 tubing is filled with the citrate solution to the exclusion of all air 

 bubbles. The pinchcock on the side tube is closed and a screw 

 clip is placed on the tubing which connects manometer and cannula, 

 and closed. The writing style of the chronograph is now adjusted 

 so that it corresponds to that of the manometer. The line of the 

 time tracing therefore serves as the line of zero pressure. 



The cannula, filled to the tip with the citrate solution, is now 

 inserted by the operator into the artery in the following way: the 

 wall of the artery near the peripheral ligature is picked up by a 

 forceps and, with a sharp scissors, a V-shaped cut is made into the 

 artery without cutting it clear across. The tip of the V points 

 peripherally. The V-shaped flap is lifted up with a fine pair of 

 forceps and the cannula inserted into the artery and tied by means 

 of the central ligature. The clip on the tubing connected with the 

 bottle is opened and the bulb compressed until a pressure of about 

 120 mm. Hg. is recorded in the manometer. The pressure in the 

 tubing prevents blood from entering it when the "bull-dog" for- 

 ceps on the artery is opened, which is now done. The writing 

 styles of the manometer and chronograph are adjusted to the drum, 

 and a tracing is taken with a slow speed drum. 



4. DEMONSTRATE THE EFFECT ON THE BLOOD PRESSURE OF 

 VARIATIONS IN THE PUMPING ACTION OF THE HEART. STIMULATION 

 OF PERIPHERAL END OF VAGUS NERVE. Expose the vagus nerve 

 in the neck on both sides and loosely tie the ligatures that were 

 previously placed around each nerve. Start the drum and record 

 a short piece of normal tracing, and then, without stopping the 



