MOTION OF THE HEART AND BLOOD 



blood. At this same time when the auricles alone 

 are beating, if you cut off the tip of the heart with a 

 scissors, you will see blood gush out at each beat of 

 the auricles. This shows how blood enters the 

 ventricles, not by the suction or dilatation of the 

 ventricles, but by the beat of the auricles. 



Note that when I speak of the pulsations of the 

 auricles or of the heart, I mean contractions. First 

 the auricles contract, then afterwards the heart 

 itself. When the auricles contract they become 

 pale, especially when they hold little blood (for they 

 are filled as reservoirs, the blood freely pressing 

 toward them through the veins) .^ This whiteness 

 is most apparent near their edges when they con- 

 tract. 



In fishes, frogs and other animals having a 

 single ventricle in the heart, at the base of which 

 the auricle is swollen like a bladder with blood, 

 you may see this bladder contract first, plainly 



* The first intimation of the existence of venous pressure. A more 

 literal translation would read "freely tending by the compressing 

 motion of the veins." While the veins are not now considered to exert 

 much elastic pressure, it is taught that muscular activity exerts pres- 

 sure on the veins. Harvey discusses the functions of the venous valves 

 in Chapter 13. There is little emphasis in current physiological texts 

 on auricular contraction filling the ventricles, although careful investi- 

 gators estimate that between 18 and 60 per cent of the blood content 

 of the ventricles is forced in by auricular contraction (Wiggers, C. J., 

 The Circulation in Health and Disease, Phila., 2nd Ed., 1923.) The 

 current opinion is that venous pressure largely determines the diastolic 

 filling, and thus the "stroke-volume" of the ventricles. For a recent 

 review of the significance of venous pressure, consult J. A. E. Eyster's 

 paper. Physiological Reviews, 6: 281 (Apr.) 1926. 



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