558 CIKCULATION OF BLOOD AND LYMPH. 



the case of other arteries. During systole, therefore, the mouths of 

 the coronary arteries are in free communication with the aorta. 

 But the coronary system — arteries, capillaries, and veins — is in 

 part embedded in the musculature of the ventricles, and we should 

 suppose that the great pressure exerted by the contracting muscu- 

 lature would at the height of systole clamp off this system and stop 

 the coronary circulation. That this result really happens is indi- 

 cated by Rebatel's curves of the velocity of the flow in the coro- 

 nary arteries. As shown in Fig. 237, the great acceleration (a) in 

 velocity at the beginning of systole is quickly followed by a drop 

 to zero (h) or even a negative value, that is, a flow in the other 

 direction, toward the aorta. At the end of the first (relaxation) 

 phase of diastole there is again a sudden increase in velocity (c),. 

 corresponding with the injection of the arteries from the aorta, 

 followed again by a decrease at the end of the diastole at the time 

 when the ventricular cavity is filled with venous blood under some 

 pressure. In fact, the rhj^hmical squeeze of its own vessels dur- 

 ing systole accelerates effectively the coronary circulation. The 

 volume of blood flowing through the heart vessels increases with 

 the frequency or the force of the beat, since each systole empties 

 the coronary system more or less completely toward the venous 

 side and at each diastole the distended aorta quickly fills the 

 empty vessels. 



The Suction-pump Action of the Heart. — So far in considering 

 the mechanics of the circulation attention has been directed only 

 to the force-pump action of the heart. All of the energy of the 

 circulation, the velocity of the flow and the internal pressure, has 

 been referred to the force of contraction of the ventricles as the 

 main cause, and to certain accessory factors, such as the respiratory 

 movements and the contractions of the skeletal muscles, as subsid- 

 iary causes. It is possible, however, that the heart may also act as 

 a suction-pump, sucking in blood from the venous side in conse- 

 quence of an active dilatation. According to this view, the heart 

 works after the manner of a syringe bulb, which when squeezed 

 forces out liquid from one end, and when relaxed sucks it in from 

 the other in consequence of its elastic dilatation. While this view 

 has long been entertained, modern interest in it was aroused by 

 the experiments of Goltz and Gaule, which showed that at some 

 point in the heart beat there is or may be a strong negative pressure 

 in the interior of the ventricles.* The outcome of investigations 

 upon this point would seem to show that the negative pressure 

 observed under certain conditions in the ventricles is a fleeting 



* For a complete discussion of this subject and the Hterature see the article 

 by Ebstein, "Die Diastole des Herzens," in the "Ergebnisse der Physiologic,"' 

 vol. iii, part ii, 1904. 



