1130 PHYSIOLOGY 



fluid injected, showing that the fluid is not to any large extent con- 

 tained in the arterial system. On examining the pressure in the veins, 

 however, we find a very great relative rise of pressure, and on opening 

 the abdomen it is seen that all the veins are distended and that the liver 

 is swollen. The effect of increasing the volume of circulating fluid would 

 be to increase the mean systemic pressure, and therefore one would 



Systole 



Diastole 



Seconds 



FIG. 476. Cardiometer tracing from dog's heart to show effect of increasing 

 the volume of circulating blood (hydraemic plethora) on the total output 

 and the volume of the heart. Between the parts A and B 30 c.c. of 

 warm normal salt solution were injected intravenously, and between B 

 and c 20 c.c. more. It will be noticed that both the systolic and the 

 diastolic volume are increased, i.e. the heart is more distended during 

 diastole, and does not contract to its normal size in systole. The con- 

 traction volume, and therefore the output, are very largely increased. 



(ROY.) 



expect to find a large increase both in arterial and venous systems. 

 But the organism prevents the rise on the arterial side by relaxing the 

 whole system of arterioles, so that the distribution of pressures is 

 altered, and the venous approximates more closely to the arterial 

 pressure. This arterial dilatation augments the velocity of the blood : 

 it has been found that the velocity may be accelerated to six or eight 

 times the normal rate by injecting an amount of salt solution equiva- 

 lent to 50 per cent, of the total blood. 



The high venous pressure causes increased diastolic filling of the 



