THE CIRCULATION OF THE BLOOD 517 



the stroke of the pump the tubing just distal to 

 the aortic valve begins to expand sooner than 

 that farther away. Evidently the change of 

 pressure produced by the stroke of the pump is 

 transmitted from point to point through the 

 liquid in the tubes. (6) The arterial manometer 

 shows a sudden rise and fall. Observe that the 

 rise is not synchronous with the stroke of the 

 pump, but begins an instant later. This interval 

 is occupied by the transmission of the pressure 

 change from the pump to the mercury column, 

 and in part by the time required to overcome the 

 inertia of position of the mercury. The oscilla- 

 tions of the mercury following the primary rise 

 and fall are due to inertia. (7) Observe the action 

 of the valves (they consist of a metal tube, closed 

 at one end, and pierced with a hole which is 

 covered with a rubber flap tied on both sides of 

 the hole). (8) Place a finger on the "aorta" 

 near the valve and note the pressure wave (pulse) 

 as it passes along the vessel. 



2. With the side branch open as in Experiment 

 1, compress the bulb rhythmically and gradually 

 increase the frequency of stroke. 



It will be found that at about twenty strokes 

 to the minute the stream will be intermittent. 

 As the interval between the strokes is shortened 

 the liquid received from the pump in any one 



