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The same is practically true in a system of elastic tubes so 

 short and wide that friction between the liquid and the walls 

 causes practically no resistance to the flow. When the resis- 

 tance is increased by narrowing the tubes, or by increasing 

 their length, or in both these ways, not all the liquid received 

 from the pump can pass by the resistance during the stroke 

 of the pump, — the remainder must pass during the interval 

 between one stroke and the next. 



The portion which cannot pass during the stroke finds 

 room between the pump and the resistance in the dilatation 

 of the elastic containing vessels. As the pressure from the 

 pump falls, the dilated elastic walls contract to their normal 

 position and drive the liquid out of the tube past the resis- 

 tance. 



Open the side branch near the capillaries by unscrewing 

 the pressure clip. See that the tubes are well filled with 

 water. Make a single brief, gentle pressure on the bulb. 

 Note (1) that practically all the liquid driven out by the 

 stroke escapes through the side branch, in which the resist- 

 ance is low, rather than through the high capillary resist- 

 ance. (2) Only a portion of the liquid escapes during the 

 stroke. (3) The portion which cannot escape by the resist- 

 ance during the stroke finds space in a very evident dilatation 

 of the tubes nearer the pump, /. e., between the pump and the 

 principal resistance. (4) The membrane manometer shows a 

 sudden rise and fall indicating a sudden rise and fall in the 

 intraventricular pressure. (5) Close observation shows that 

 on the stroke of the pump the tubing just distal to the aortic 

 valve begins to expand sooner than that farther away. Evi- 

 dently 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 simultaneous 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 column of mercury, and in part by the time 

 required to overcome the inertia of position of the mercury. 

 The oscillations of the mercury following the primary rise 

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

 valve (the arrangement consists of a glass tube, closed at one 



