516 THE OUTGO OF ENERGY 



tween the pump and the resistance in the dilata- 

 tion of the containing vessels. To effect the 

 dilatation the force or pressure transmitted from 

 the pump presses out the vessel walls until this 

 pressure is held in equilibrium by the elastic re- 

 action of the walls. As the pressure from the 

 pump wanes, the energy stored by it in the ten- 

 sion of the vessel walls is reconverted into 

 mechanical motion, and the walls return towards 

 their original position, driving the liquid out of 

 the tube past the resistance. 



1. Open the side branch by unscrewing the 

 pressure-clip. See that the tubes are well filled 

 with water. Make a single brief gentle pressure 

 on the ventricle. 



Note (1) that practically all the liquid driven 

 out by the stroke escapes through the side 

 branch, in which the resistance is low, rather 

 than through the high capillary resistance. 

 (2) Only a portion of the liquid escapes during 

 the stroke. (3) The portion which cannot 

 escape by the resistance during the stroke finds 

 space in a very evident dilatation of the tubes 

 nearer the pump, i. e. between the pump and 

 the principal resistance. (4) A membrane ma- 

 nometer coupled to the side tube of the ventricle 

 would show a sudden rise and fall indicating 

 a sudden rise and fall in the intraventricular 

 pressure. (5) Close observation shows that on 



