THE VELOCITY OF BLOOD FLOW. 



85 



and pressure in the carotid artery of the horse. 1 It is noticeable that 

 the curve of velocity (V) reaches its maximum before the curve of tension. 

 This is so, because, as the arteries become overfilled, the heart cannot 

 maintain the initial velocity of output. Chauveau found that the 

 velocity in the carotid artery of the horse reached 520 mm. per second 

 during systole, while at the time of the dicrotic wave the velocity sank 

 to 220 mm. per second, and in diastole to 150 mm. per second. Con- 

 tinuous records of the velocity curve afford us a valuable means of 

 arriving at the volume of blood flowing through the vascular area 

 supplied by the artery in question. Thus the effect on the blood-flow 

 of vasomotoria! excitement or functional activity can be investigated. 



Fig. 55. — Carotid artery. V, velocity ; P, pressure curves ; 0, 0, 

 abscissa of velocity curve ; 1, 2, 3, 4, simultaneous points on 

 both curves. — Chauveau and Marev. 



By means of the dromograph, Chauveau and Lortet determined that, 

 during the rise of systolic tension, the blood is driven from the coronary 

 arteries back towards the aorta. Lortet determined that the velocity 

 of flow in the carotid is five or six times greater when a horse is 

 actively masticating than when at rest. In one experiment, while 

 the normal velocity in the carotid arterv during svstole was 540 mm. 

 per second, Chauveau noted that after section of the cervical sympa- 

 thetic, and in consequence of the loss of vascular tone, the velocity 

 became equal to 750 mm. per second. After section of the spinal 

 cord in the upper dorsal region, the velocity in the arterial system 

 becomes greatly accelerated during systole, and greatly diminished 

 during diastole. Owing to the lowering of the peripheral resistance 

 from the loss of vascular tone, the heart is able to discharge 

 the blood with the greatest rapidity into the venous system, and in 

 consequence, during diastole, the arterial system is emptied of blood 

 to a great extent. If this condition be pushed to an extreme, and the 

 frequency of the heart be small, the blood becomes discharged into the 

 veins intermittently. 



Comparative records have been obtained of the velocity of flow in 

 the carotid and facial arteries. At the end of the diastole the velocity 

 is small in the carotid, and relatively great in the facial artery. At the 

 beginning of systole the primary wave of velocity rises rapidly in the 

 carotid, and is proportionately small in the facial artery. The secondary 



1 Marey, "Circulation du sang," p. 327. 



