THE ARTERIAL PRESSURE 



187 



introduction of rubber tubing for the connections made the method 

 of inquiry comparatively simple. 



The method of procedure now usually employed is as follows: 

 The artery of an anaesthetized animal is exposed and ligatured. 

 A clamp is placed upon the artery nearer the heart, and the special- 

 shaped cannula (Fig. 91) introduced between the ligature and the 

 clamp. The cannula and tubing are filled with a suitable fluid,* 

 to prevent coagulation, from a reservoir (R, Fig. 92), raised to a 

 height sufficient to introduce a pressure about equal to the antici- 

 pated arterial pressure of the animal. This prevents more than a 

 trace of blood entering the connections. 



The clamp is now removed from the artery, and the pressure is 

 transmitted to the manometer, the style of which can be brought to 



FIG. 92. ARRANGEMENT OF CANNULA, PRESSURE BOTTLE, AND MERCURIAL " 

 MANOMETER, FOR RECORDING BLOOD-PRESSURE. 



C, Cannula; p, p 1 , clips; F, float; S, writing style. 



write on a drum covered with smolied paper, and driven slowly round 

 by clockwork or electric motor. By this means tracings of the arterial 

 blood -pressure are obtained, and the influence upon the blood-pressure 

 of various agents recorded and studied. For the veins, a manometer 

 filled with salt solution is used, as mercury is too heavy a fluid to 

 record the far slighter changes of venous pressure. The manometer 

 may be connected with a recording tambour. 



The arterial blood -pressure record obtained with the mercurial 

 manometer exhibits cardiac and respiratory oscillations. The method 

 gives us a fairly accurate record of the mean pressure, but the mass 

 of the mercury causes such inertia that the instrument is quite 



* Saturated magnesium sulphate may be employed for the dog and rabbit, but not 

 for the cat. For this animal, saturated sodium sulphate should be used. A 10 per cent, 

 sodium citrate or 0-4 per cent, potassium oxalate solution may also be employed for 

 all animals. 



