46 MOTION OF THE 



ther derived from vivisections, and my various reflections on 

 them, or from the ventricles of the heart and the vessels that, 

 enter into and issue from them, the symmetry and size of these 

 conduits, for nature doing nothing in vain, would never have 

 given them so large a relative size without a purpose, or 

 from the arrangement and intimate structure of the valves in 

 particular, and of the other parts of the heart in general, with 

 many things besides, 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 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 MO- 

 TION, 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 indicated. 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, evaporates; 

 the vapours drawn upwards are condensed, and descending in 

 the form of rain, moisten the earth again ; and by this arrange- 

 ment are generations of living things produced; and in like man- 

 ner 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 nou- 

 rished, 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 



