84 EXPERIMENTAL PHYSIOLOGY. 



6. DEMONSTRATE THE EFFECTS OF HAEMORRHAGE AND OF 

 TRANSFUSION ON THE MEAN ARTERIAL BLOOD PRESSURE. -Intro- 

 duce a cannula into the femoral artery of one side and another into 

 the femoral vein of the other side. The arterial cannula is intro- 

 duced as directed above, and connected with a piece of rubber tub- 

 ing through which to bleed the animal. The venous cannula is intro- 

 duced as follows: The vein is exposed and two ligatures placed 

 underneath it; a bull-dog forceps is applied central to the central 

 ligature, and the peripheral ligature is tied. A cannula of suitable 

 size, connected with about six inches of rubber tubing and filled 



FIG. 25. Arterial blood pressure tracing showing the effect of a moderately slow hsemorrhag -, 

 followed by a rapid haemorrhage. 



with 0.9% NaCl solution, held in by means of a clip on the rubber 

 tubing, is inserted into the vein towards the heart in exactly the 

 same way as in par. 3. When both cannulae are in position, the 

 tubing on the venous cannula is connected with a burette. 



HAEMORRHAGE. After taking an inch or two of normal tracing 

 of the pressure in the carotid artery, the clip on the femoral artery 

 is partially or completely removed and the blood which escapes 

 collected in a basin and defibrinated. Note the effect on the blood 

 pressure (a) of sudden and (b) of gradual bleeding (Fig. 25). It will 

 be found when the artery is fully opened that there is an immediate 

 fall in blood pressure due to release of peripheral resistance. If the 



