564 CIRCULATION OF BLOOD AND LYMPH. 



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- 

 dicated by RebatePs curves of the velocity of the flow in the coro- 

 nary arteries. As shown in Fig. 235, the great acceleration (a) in 

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

 zero (6) or even a negative value, that is, a flow in the other direc- 

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

 of diastole there is again a sudden increase in velocity (c), corre- 

 sponding 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. 

 Porter, moreover, has shown in an interesting series of experiments 

 that when a piece of the ventricle is kept beating, by supplying it 

 with blood through its nutrient artery from a reservoir at con- 

 stant pressure, each systole causes a jet of blood from the sev- 

 ered vessels at the margin of the piece. In fact, the rhythmical 

 squeeze of its own vessels during 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 com- 

 pletely 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 con- 

 sidering 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 chiefly 

 perhaps 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.* Their method consisted 

 in connecting a manometer with the interior of the ventricle and 

 interposing between the two a valve that opened only toward the 

 heart. The manometer was thus converted into a minimum 



* For a complete discussion of this subject and the literature see the ar- 

 ticle by Ebstein, " Die Diastole des Herzens," in the " Ergebnisse der Physi- 

 ologic," vol. iii, part n, 1904. 



