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A TEXTBOOK OF PHYSIOLOGY 



the interior vena cava are ligatured. A cannula, connected with 

 a, manometer, M, is placed in the innominate artery. From this the 

 blood is led past the air cushion B, which represents the elasticity of 

 the arteries, to a rubber tube, R, in a tube, T. This can be compressed 

 by the pump S and pressure bottle A, and corresponds to the peripheral 

 resistance. Thence the blood passes to a vessel, N, where it is aerated 

 and thence siphoned to one where it is warmed, and from there to the 

 superior vena cava through a cannula containing a thermometer. 



FIG. 67. DIAGRAM OF APPARATUS (DESCRIBED IN TEXT) USED IN THE HEART-LUNG 

 PREPARATION. (Knowlton and Starling.) 



The output of the ventricle for a given time may be estimated by 

 measuring the flow from the bypass to the vessel N. If the rate of 

 beat be known, the output per beat is easily calculated. 



The volume of output may be estimated indirectly by deter- 

 mining (1) how much oxygen is absorbed from the inspired 

 air per minute; (2) the difference in the oxygen content of the 

 arterial and venous blood; (3) the number of heart-beats. If 

 1,000 c.c. of oxygen are absorbed from the air breathed in a 

 minute, and the arterial blood contains 10 per cent, more oxygen 

 than the venous, and the heart beats 100 times per minute, then, 

 since 10 c.c. of oxygen are carried away by each 100 c.c. of 



