MOTION OF THE HEART AND BLOOD 



you will press downwards against the valve, (0, 

 fig- 3) by a finger of the other hand on the distended 

 upper portion {K, fig. 3), you will note that nothing 

 can be forced through the valve. The greater effort 

 you make the more the vein is distended toward 

 the valve, but you will observe that it stays empty 

 below it (//, 0, fig. 3). 



From many such experiments it is evident that the 

 function of the valves in the veins is the same as 

 that of the three sigmoid valves placed at the 

 opening of the aorta and pulmonary artery, to 

 prevetit, when they are tightly closed, the reflux 

 of blood passing over them. 



Further, with the arm bound as before and the 

 veins swollen, if you will press on a vein a little 

 below a swelling or valve (Z., fig. 4) and then squeeze 

 the blood upwards beyond the valve {N) with 

 another finger (M), you will see that this part of 

 the vein stays empty, and that no back flow can 

 occur through the valve (as in //, 0, fig. 1). But 

 as soon as the finger (//) is removed, the vein is 

 filled from below (as in D, C, fig. i). Thus it is 

 clearly evident that blood moves through the veins 

 toward the heart, from the periphery inwards, and 

 not in the opposite direction. The valves in some 

 places, either because they do not completely close, 

 or because they occur singly, do not seem adequate 

 to block a flow of blood from the center, but the 

 majority certainly do. At any rate, wherever they 

 seem poorly made, they appear to be compensated 



[lOl] 



