Motion of the 



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 getting 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 A MOTION, AS IT WERE, 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 distributed 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 in- 

 dicated. Which motion we may be allowed to call 

 circular, in the same way as Aristotle says that the air 

 and the rain emulate the circular motion of the superior 

 bodies ; for the moist earth, warmed by the sun, evapo- 

 rates ; the vapours drawn upwards are condensed, and 

 descending in the form of rain, moisten the earth 

 again ; and by this arrangement are generations of living 

 things produced ; and in like manner too are tempests 

 and meteors engendered by the circular motion, and by 

 the approach and recession of the sun. 



And so, in all likelihood, does it come to pass in the 

 body, through the motion of the blood ; the various 

 parts are nourished, cherished, quickened by the warmer, 

 more perfect, vaporous, spirituous, and, as I may say, 

 alimentive blood ; which, on the contrary, in contact 

 with these parts becomes cooled, coagulated, and, so 

 to speak, effete ; whence it returns to its sovereign the 

 heart, as if to its source, or to the inmost home of 

 the body, there to recover its state of excellence or 



