324 THE HUMAN BODY 



wave to flow round the tubing; but there will be no steady main- 

 tenance of a pressure on the side B greater than that in A . Now 

 let the upper tube D be closed so that the liquid to get from B to 

 A must flow through the narrow lower tubes D', which oppose 

 considerable resistance to its passage on account of their frequent 

 branchings and the great friction in them ; then if the pump works 

 frequently enough there will be produced and maintained in B a 

 pressure considerably higher than that in A. If, for example, 

 the pump works 60 times a minute and at each stroke takes 180 



FIG. 111. Diagram of Weber's Schema. 



cubic centimeters of liquid (6 ounces) from A and drives it into 

 B, the quantity sent in at the first stroke will not (on account of 

 the resistance to its flow offered by the small branched tubes), 

 have all got back into A before the next stroke takes place, send- 

 ing 180 more cubic centimeters (6 ounces) into B. Consequently 

 at each stroke B will become more and more distended and A more 

 and more emptied, and the gauge x will indicate a much higher 

 pressure than that on A. As B is more stretched, however, it 

 squeezes harder upon its contents, until at last a time comes when 

 this squeeze is powerful enough to force through the small tubes 

 just 180 cubic centimeters (6 ounces) in a second. Then further 

 accumulation in B ceases. The pump sends into it 10,800 cubic 

 centimeters (360 ounces) in a minute at one end and it squeezes 

 out exactly that amount in the same time from its other end ; and 

 so long as the pump works steadily the pressure in B will not rise, 

 nor that in A fall, any more. But under such circumstances the 

 flow through the small tubes will be nearly constant since it de- 

 pends upon the difference in pressure prevailing between B and 



