CHAPTER VIII 



OF THE QUANTITY OF BLOOD PASSING THROUGH THE 

 HEART FROM THE VEINS TO THE ARTERIES; AND 

 OF THE CIRCULAR MOTION OF THE BLOOD 



THUS far I have spoken of the passage of the blood 

 from the veins into the arteries, and of the manner in 

 which it is transmitted and distributed by the action of 

 the heart ; points to which some, moved either by the 

 authority of Galen or Columbus, or the reasonings of 

 others, will give in their adhesion. But what remains 

 to be said upon the quantity and source of the blood 

 which thus passes, is of so novel and unheard-of 

 character, that I not only fear injury to myself from the 

 envy of a few, but I tremble lest I have mankind at 

 large for my enemies, so much doth wont and custom, 

 that become as another nature, and doctrine once 

 sown and that hath struck deep root, and respect for 

 antiquity influence all men : Still the die is cast, and 

 my trust is in my love of truth, and the candour that 

 inheres in cultivated minds. And sooth to say, when 

 I surveyed my mass of evidence, whether 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 inti- 

 mate 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 



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