HAEMODYNAMICS. 85 



clip is only partially opened, considerable bleeding may occur 

 before the blood pressure is materially affected. Continue the 

 bleeding until a permanent (marked) fall of blood pressure is 

 recorded. About 25 c.c. of blood per kg. body-weight must usually 

 be removed to obtain this result. 



SALINE TRANSFUSION. Now connect the venous cannula with 

 a burette filled with a 0.9% NaCl solution, previously warmed to 

 body temperature; remove the clip and allow the saline to pass 

 into the animal, taking great care that no air bubbles are carried 

 in with the solution. Meanwhile MAKE OBSERVATIONS ON THE 

 VENOUS BLOOD PRESSURE (which is indicated by the height in the 

 burette at which no more saline enters the vein); noting: (a) its 

 height in mm. of water and (b) whether it shows any pulsations. 

 Observe carefully the effect of the transfusion on the arterial blood 

 pressure. 



The blood removed in this and in all other experiments is to 

 be defibrinated by beating in a clean dry basin with a bunch of 

 wires. When fibrin formation has ceased the whipped blood is 

 strained through muslin, and measured in a graduated cylinder. 



BLOOD TRANSFUSION. Again bleed from the femoral artery, 

 carefully noting the behaviour of blood pressure, respirations, etc. 

 Note any differences in the character of the blood from that ob- 

 tained previous to the saline transfusion. When the blood pressure 

 is extremely low (40 mm.) transfuse with defibrinated blood and 

 note the effect on the blood pressure as compared with that pro- 

 duced by saline solution. Note particularly with which solution 

 the restored pressure is best maintained. 



7. OBSERVE THE HEART BEAT IN THE OPEN THORAX UNDER 

 ARTIFICIAL RESPIRATION. Since natural respiration is impossible 

 after the thoracic cavity has been opened (explain why) it is neces- 

 sary to start artificial respiration by means of a pump connected 

 with the tracheal cannula. The air delivered from the pump is 

 in a continuous stream. In order to interrupt it so as to simulate 

 the respirations, a wide T-piece is placed on the rubber tube 

 between the pump and tracheal cannula, and this side tube is 

 opened and closed by a finger at a rate corresponding to the normal 

 respirations. In order to open the thorax the skin is first of all 

 incised down the mid line from the base of the neck to well on to 



