n] Circulation of the Blood. 4f> 



This is what he says : 



" I frequently and seriously bethought me, and long revolved 

 " in my mind, what might be the quantity of blood which was 

 " transmitted, in how short a time its passage might be effected, 

 " and the like ; and not finding it possible that this could be 

 'supplied by the juices of the ingested aliment without the 

 " veins on the one hand becoming drained, and the arteries on 

 "the other hand becoming ruptured through the excessive 

 " charge of blood, unless the blood should somehow find its way 

 " from the arteries into the veins, and so return to the right 

 " side of the heart ; I began to think whether there might not 

 " be a motion, as it ivere, in a circle. Now this I afterwards 

 " found to be true ; and I finally saw that the blood, forced by 

 "the action of the left ventricle into the arteries, was dis- 

 " tributed to the body at large, and its several parts, in the 

 " same manner as it is sent through the lungs, impelled by the 

 "right ventricle into the pulmonary artery, and that it then 

 " passed through the veins and along the vena cava, and so 

 " round to the left ventricle in the manner already indicated, 

 " which motion we may be allowed to call circular." 



As the sun of this truly new idea rose in Harvey's mind, this 

 new idea that the blood is thus for ever moving in a circle, the 

 mists and clouds of many of the conceptions of old faded away 

 and the features of the physiological landscape hitherto hidden 

 came into view sharp and clear. This idea once grasped, fact 

 after fact came forward to support and enforce it. It was now 

 clear why the heart was emptied when the vena cava was tied, 

 why it was filled to distension when the aorta was tied. It was 

 now clear why a middling ligature which pressed only or chiefly 

 on the veins made a limb swell turgid with blood, whereas a tight 

 ligature which blocked the arteries made it bloodless and pale. 

 It was now clear why the whole or nearly the whole of the 

 blood of the body could be drained away by an opening made 

 in a single vein. And now for the first time was clear the 

 purpose of those valves in the veins, whose structure and 

 position had been demonstrated doubtless to Harvey, by the 

 very hands of their discoverer, his old master Fabricius, but 

 "who did not rightly understand their use, and concerning 



