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THE CIRCULATION OF THE BLOOD 



The arrangement for perfusion of the heart and lungs is shown in Fig. 38. The 

 blood prevented from clotting by the addition of hirudin (page 101) is discharged 

 from the left ventricle into a cannula connected with the innominate artery, all other 

 branches of the aorta being tied off. A side tube, v, connects with an air cushion, 

 afforded by an inverted test tube to take the place of the resilient arterial walls, and the 

 tube then connects with a resistance E, which is furnished by a thin-walled rubber tube 

 (rubber finger stall) enclosed in a glass cylinder into which air is pumped so as to 



Fig. 38. Arrangement of apparatus for heart-lung preparation of mammalian heart. 

 (Knowlton and Starling.) 



compress the tube. Beyond this resistance the blood flows into a wide test tube con- 

 nected with a siphon tube which discharges whenever the blood has reached a certain 

 level in the test tube. The blood discharges into a reservoir, from which it flows 

 through a spiral immersed in a water bottle, and thence to a cannula tied into the 

 superior vena cava. A tambour is connected with a lateral tube coming off the tube 

 of the siphon, and it records a movement every time the discharge occurs. The blood 

 is pumped by the right ventricle through the lungs, where it is oxygenated, artificial 



