HEART-LUNG PREPARATION 



65 



then ligatured, thus cutting off the whole blood- supply to the 

 brain, so that the anaesthetic can be discontinued. Cannulse are 

 placed in the innominate artery and the superior vena cava. The 

 cannulse are filled beforehand with a solution of hirudin in normal 

 salt solution, so as to prevent clotting of the blood during the 

 experiment. The descending aorta is closed by a ligature. The 



Fig. 14. — The heart-lung preparation. (From The Journal of Physiology.) 



only path left for the blood is by the ascending aorta, and the 

 cannula CA in the innominate artery. The arterial cannula com- 

 municates by a T-tube with a mercurial manometer M^ to record 

 the mean arterial pressure, and passes to another T-tube ?; one 

 limb of which projects into the test-tube- B. The air in this test- 

 tube will be compressed with a I'ise of pressure, and will serve as 

 a driving force for the blood through the resistance. It thus takes 

 the part of the resilient arterial wall. The other limb of the test- 

 5 



