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A TEXTBOOK OF PHYSIOLOGY 



blood rises within them, and ceases when the arterial pressure becomes 

 equal to that in the ventricles. As the outflow diminishes, the semi- 

 lunar pockets are filled by eddies of blood, and their thin, delicate 

 edges are brought nearer and nearer, until finally they come into 

 apposition. This closure, which effectually prevents regurgitation, 

 is effected without jar or noise at the moment when t he outflow ceases 

 and the ventricles begin to expand. The heart, as a good pump 

 should, works with the least possible jar. During the contraction 

 of the ventricles, blood has been pouring from the veins into the 

 auricles; and directly the ventricular systole ceases, the auriculo- 

 ventricular valves open, and the blood begins to fill the expanding 

 ventricular cavities. For a brief moment the ventricles remain dilated 

 and at rest, then the auricles contract again, and the cycle of changes 

 once more is repeated. During the first period of ventricular systole 

 the period of rising tension (A-B, Fig. 56). or " presphygmic 



PIG. 57. DIAGRAM OF RIGHT SIDE OF HEART, SHOWING A, SYSTOLE-AURICULO- 

 VENTRICULAR VALVES SHUT, CHORDAE TENDINE.E DRAWN TAUT, SEMILUNAR 

 VALVES OF PULMONARY ARTERY OPEN. B, DIASTOLE- AURICULO- VENTRIC- 

 ULAR VALVES OPEN, BLOOD ENTERING FROM AURICLE TO VENTRICLE. SKMI 

 LUNAR VALVES OP PULMONARY ARTERY SHUT. 



interval," as it is called all the valves are closed, and the ventricle 

 is getting up pressure. This period has been measured, and has been 

 iound to occupy about 0-02 to 0-04 second. The second period 

 is that of the systolic output (B-C, Fig. 56), and lasts about 0-2 

 second that is, from the moment when the semilunar valves open 

 to the moment when they close. These periods can be measured 

 on man by taking sinmltaneous records of the pulse in the carotid 

 artery and of the cardiac impulse and sounds. The upstroke of 

 the pulse-curve recorded from the carotid artery can be taken 

 as marking the moment when the semilunar valves open, while 

 the dicrotic notch on the pulse-curve marks their closure. The 

 second sound of the heart occurs immediately after their closure, 

 and, by listening to it, one can note the time of this event on the 

 impulse-curve, the upstroke of which marks the beginning of ven- 

 tricular systole. Thus, the presphygmic interval extends from the 



