140 PRACTICAL PHYSIOLOGY 



heart. One of the ligatures is tied round the junction of the jugular 

 and subclavian veins. As the vein is clipped before the ligature is tied, 

 it becomes distended with blood, and this facilitates the introduction of 

 the cannula. The straight vein cannula is connected with a short 

 length (1 foot) of glass tubing. The latter is clamped in the vertical 

 position, and is filled with sodium citrate solution. The cannula is also 

 filled with sodium citrate solution, and to retain the solution a clip is 

 placed on the rubber tube, which connects the cannula with the glass 

 tube. The positive pressure in the glass tube must not be more than 

 3 to 4 inches of the solution. 



The innominate vein is now slit and the cannula introduced. Then 

 the clip on the vein is removed, and the cannula is pushed down into 

 the superior vena cava. The clip on the rubber tube is next opened so 

 as to place the venous cannula in connection with the vertical tube. 

 The fluid in this will now oscillate with each respiration at a level of 

 about 2-3 inches. The clip on the artery is next opened. The fluid in 

 the arterial tube will oscillate at a height of about 4 to 5 feet. Notice 

 in each tube the cardiac pulsations and respiratory oscillations. The 

 arterial pressure rises in inspiration the venous in expiration. 



1 . If the abdomen be compressed the pressures will rise in both the 

 artery and vena, but to a greater extent in the former. The heart is 

 better filled in diastole and the peripheral resistance is increased by the 

 compression of the splanchnic vessels. 



2. If the thorax be squeezed so as to compress the heart and prevent 

 its filling, the arterial pressure will fall very greatly, while the venous 

 pressure will rise slightly. 



Record of Arterial Pressure, Effect of Excitation of the Vagus and 

 Depressor Nerves. Effect of Gravity. Effect of Asphyxia. The 

 artery is now clipped, the cannula washed out, and is connected to a 

 mercurial manometer by a piece of pressure tubing, a J_ piece being 

 interposed. The cannula and tube are filled by means of a pressure 

 bottle or syringe with sodium citrate 1 per cent, solution, and the 

 pressure in the manometer is raised to about the arterial pressure. The 

 vagus nerve is exposed, ligatured in two places, and divided between 

 the ligatures. The depressor nerve is exposed, ligatured, and divided 

 below the ligature. The depressor in the cat runs separately from the 

 vagus on the left side. On the right side it can generally be separated 

 from the rest of the vagus without much difficulty. In the rabbit the 

 depressor runs separately on both sides. In the dog it is bound up in 

 the vago-sympathetic trunk. 



The trachea is opened and a tracheal cannula inserted. This is con- 

 nected with the anaesthetic bottle and by a side tube with a recording 



