lis 



tract, but the aortic valve does not open until the intraventri- 

 cular 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 ventricle begins to relax, the intraventricular pressure 

 speedily falls below that in the aorta, and the aortic valve 

 shuts, but the intraventricular pressure 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. 



366. The Peeiod of Outflow from the Ventricle. 

 Tie a rubber membrane over the small thistle-tube of the 

 sphygmograph and cement a bone button in the centre. Pre- 

 pare a second receiving tambour in the same way. Bring the 

 writing points of the recording tambours into the same verti- 

 cal line against the smoked drum. Let the drum revolve at 

 its fastest speed. Place the button of one receiving tambour 

 on the aorta, the other on the membrane of the tube which 

 records the intraventricular pressure. Let the ventricle pump 

 with the usual force and frequency. When the two curves 

 have been written, stop the clock-work and turn back the 

 drum until the point of the lever recording the ventricular 

 pressure lies at the exact beginning of the upstroke in the 

 aortic pulse curve. Cause each lever to write an ordinate on 

 the stationary drum. These ordinates will indicate synchro- 

 nous points and will mark the beginning of the "out-flow" 

 period. Now turn the'drum until the point of the aortic lever 

 lies beneath the notch seen in the down-stroke of the pulse 

 curve (the dicrotic notch). Describe synchronous ordinates. 

 It is known that the dicrotic notch in the aortic pulse curve 

 corresponds closely to the moment of closure of the aortic 

 valves. It marks therefore the end of the outflow period. 

 Note that this point is reached soon after the ventricle begins 

 to relax. Thus the period during which the intraventricular 

 pressure is higher than the pressure in the aorta embraces 

 part of the relaxation as well as part of the contraction of the 

 ventricle. It includes approximately the highest third of the 

 intraventricular pressure curve. 



Observe also the considerable interval between the begin- 



