THE NUTRITION OF THE HEART 



169 



such as the splanchnic, is thrown into constriction, and the blood is 

 propelled from the constricting vessels into the veins, and thus the 

 diastolic filling of the heart is increased ; at the same time, the velocity 

 of flow through the locomotor organs is accelerated, owing to a compen- 



Time in periods of 20 minutes 



Via. 72. DIAGRAM SHOWING THE RELATIONSHIP OF OXYGEN CONSUMPTION TO THE 

 . BATE OF THE PULSE AND THE ARTERIAL PRESSURE. (Barcroft.) 



satory dilatation of the vessels in these organs. The heart accelerates, 

 the systolic output increases, and the arterial pressure rises (Fig. 70). 

 In the second stage the vagal centre of the spinal bulb is excited by 

 the high arterial pressure, the heart frequency is lessened, and the 





FIG. 73. CONTRACTION OF FROG'S HEART, SHOWING ACCELERATOR EFFECT OF WEAK 

 STIMULATION OF VAGO-SYMPATHETIC. (Pembrey and Phillips.) 



There is increased tone in the after-effect. 



output diminished. Further, so soon as the arterial pressure reaches 

 a certain point, the heart becomes unequal to the strain of emptying 

 itself against the resistance; the output then becomes imperfect, the 

 residual blood increases, the left auricular pressure rises, and the 

 blood is congested in the lungs and within the venous system. 



