MOTION OF THE HEART AND BLOOD 



for in some way, by the greater frequency or better 

 action of the succeeding valves. So, as the veins 

 are the wide open passages for returning blood to 

 the heart, they are adequately prevented from 

 distributing it from the heart. 



Above all, note this. With the arm of your sub- 

 ject bound, the veins distended, and the nodes or 

 valves prominent, apply your thumb to a vein a 

 little below a valve so as to stop the blood coming 

 up from the hand, and then with your finger press 

 the blood from that part of the vein up past the 

 valve (L, N, fig. 4), as was said before. Remove 

 your thumb (Z), and the vein at once fills up from 

 below (as in D, C, fig. i). Again compress with 

 your thumb, and squeeze the blood out in the same 

 way as before (Z,, A^, and //, 0), and do this a thou- 

 sand times as quickly as possible. By careful reckon- 

 ing, of course, the quantity of blood forced up beyond 

 the valve by a single compression may be estimated, 

 and this multiplied by a thousand gives so much blood 

 transmitted in this way through a single portion of 

 the veins in a relatively short time, that without 

 doubt you will be very easily convinced by the quick- 

 ness of its passage of the circulation of the blood. 



But you may say this experiment of mine violates 

 natural conditions. Then if you will take as long 

 a distance from the valve as possible, observing 

 how quickly, on releasing your thumb, the blood 

 wells up and fills the vein from below, I do not 

 doubt but that you will be thoroughly convinced. 



[102] 



