510 CIRCULATION OF BLOOD AND LYMPH. 



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

 nary arteries. As shown in Fig. 215, 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- 



Fig. 215. Simultaneous record of the blood -pressure (4) and the blood-velocity (B) 

 in the coronary arteries (Chauveau and Rebatef): a, Marks the beginning of the systole 

 (there is a rise in pressure and in velocity) ; 6, marks a second rise of pressure (.A) due to 

 the closure of the coronary capillaries* by the contracting ventricle (at this moment in B 

 the velocity falls off rapidly) ; c, curve (B) shows an increase in velocity due to the open- 

 ing of the small coronary vessels at the beginning of diastole. 



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 vessel. 



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 



