312 PHYSIOLOGY. 



5. The ventricular or diastolic collapse. 



6. The second onflow or diastolic wave. 



With frequently beating hearts Morrow states that some of these 

 waves may be absent, or several may be fused together. There is con- 

 siderable variation in the prominence of the different waves. 



The venous pulse represents variations in auricular pressure. In 

 certain cases of disease, waves of blood are sent back into the inferior 

 vena cava, which distend the liver and give rise to a liver pulse. 

 When we have a venous and a liver pulse, the changes that ensue in 

 the tracings of the pulse can be shown by either one. 



The venous pulse is a direct means of studying the effects of the 

 systole and diastole of the right auricle and right ventricle and the 

 rate of the auricles. 



RAPIDITY OF THE CIRCULATION. 



When examining the web of the frog's foot beneath the micro- 

 scope it is clearly discerned that the rate of the blood's flow through 

 the capillaries is very much less than what it must be in the aorta and 

 its larger branches. That there should be differences in its rate of 

 flow depends upon the same physical reasons as govern the rate of 

 flow in tubes. 



The discharge of any liquid through a tube equals the mean 

 velocity multiplied by the area of cross section at the point of observa- 

 tion. The greater the cross section of the area the less the velocity; 

 and conversely, the greater the activity of the heart is to frequency and 

 strength, the greater the velocity. Velocity is less, the greater the 

 peripheral resistance in the capillaries. 



The arterial system widens from the center to the periphery. 

 All physiologists admit this proposition, for their opinion is founded 

 upon exact measurements. It has been found that, when there is an 

 arterial bifurcation, the area of the two branches formed exceeds 

 that of the afferent trunk. From experimental demonstration of the 

 widening of the arterial passages, the comparison of the arterial tree 

 to a cone is permissible; its summit is located at the heart, its base 

 at the periphery of the body. The venous system is similarly 

 arranged, the apices of the two systems meeting at the heart. 



From this general form of the arterial passages it can be con- 

 cluded that the movement of the blood must be more rapid in the 

 aorta than in the vessels springing from it, and that the minimum 

 of speed must be in the smallest arterioles. It is known that the 

 cross-sectional area of the arterioles and capillaries is from 500 to 



