526 THE OUTGO OF ENERGY 



tricular beat and at once observe closely the 

 action of the valves. 



It will be seen that the mitral valve closes as 

 soon as the ventricle begins to contract, but the 

 aortic valve does not open until the intraventric- 

 ular pressure has risen above that in the aorta. 

 Time is required for this rise in the pressure in 

 the ventricle. During this period both mitral 

 and aortic valves are closed. When the ventri- 

 cle begins to relax, the in traven tricular pressure 

 speedily falls below that in the aorta, and the 

 aortic valve shuts, but the intraventricular pres- 

 sure normally must fall at least 100 mm. Hg 

 farther before it shall be lower than that in the 

 auricle. During this fall all the heart valves are 

 again closed ; the aortic valves are already shut, 

 and the mitral not yet open. 



The Period of Outflow from the Ventricle. Tie 

 a rubber membrane over the smaller thistle-tube 

 of the sphygmograph (Fig. 70) and cement a bone 

 button in the centre. Connect a membrane ma- 

 nometer 1 with the side tube of the ventricle. 

 Bring the writing points of the recording tam- 



1 If such a manometer is not at hand, carry a thin wire from 

 the yoke of the disk of the circulation scheme to a light muscle 

 lever, counterweighted from the pulley or pulled gently upward 

 by a rubber band attached to the lever. This lever will record 

 the up and down movement of the disk and thus mark the 

 beginning of the ventricular stroke. 



