108 WILLIAM HARVEY 



ruption and coagulation; it is the household divinity which, 

 discharging its function, nourishes, cherishes, quickens the 

 whole body, and is indeed the foundation of life, the source 

 of all action. But of these things we shall speak more 

 opportunely when we come to speculate upon the final 

 cause of this motion of the heart. 



As the blood-vessels, therefore, are the canals and agents 

 that transport the blood, they are of two kinds, the cava 

 and the aorta ; and this not by reason of there being two 

 sides of the body, as Aristotle has it, but because of the 

 difference of office, not, as is commonly said, in conse- 

 quence of any diversity of structure, for in many animals, 

 as I have said, the vein does not differ from the artery 

 in the thickness of its walls, but solely in virtue of their 

 distinct functions and uses. A vein and an artery, both 

 styled veins by the ancients, and that not without reason, 

 as Galen has remarked, for the artery is the vessel which 

 carries the blood from the heart to the body at large, the 

 vein of the present day bringing it back from the general 

 system to the heart; the former is the conduit from, the 

 latter the channel to, the heart ; the latter contains the 

 cruder, effete blood, rendered unfit for nutrition; the 

 former transmits the digested, perfect, peculiarly nutritive 

 fluid 





CHAPTER IX 



THAT THERE is A CIRCULATION OF THE BLOOD is CONFIRMED 

 FROM THE FIRST PROPOSITION 



BUT lest anyone should say that we give them words 

 only, and make mere specious assertions without any founda- 

 tion, and desire to innovate without sufficient cause, three 

 points present themselves for confirmation, which, being 

 stated, I conceive that the truth I contend for will follow 

 necessarily, and appear as a thing obvious to all. First, 

 the blood is incessantly transmitted by the action of the 

 heart from the vena cava to the arteries in such quantity 

 that it cannot be supplied from the ingesta, and in such 

 a manner that the whole must very quickly pass through 

 the organ; second, the blood under the influence of the 





