Introduction 13 



in the veins : that the blood and spirits constitute one 

 body (like whey and butter in milk, or heat [and water] 

 in hot water), with which the arteries are charged, and 

 for the distribution of which from the heart they are 

 provided, and that this body is nothing else than blood. 

 But if this blood be said to be drawn from the heart 

 into the arteries by the diastole of these vessels, it is 

 then assumed that the arteries by their distension are 

 filled with blood, and not with the ambient air, as here- 

 tofore ; for if they be said also to become filled with air 

 from the ambient atmosphere, how and when, I ask, 

 can they receive blood from the heart? If it be 

 answered : during the systole ; I say, that seems im- 

 possible ; the arteries would then have to fill whilst 

 they contracted ; in other words, to fill, and yet not 

 become distended. But if it be said : during the 

 diastole, they would then, and for two opposite pur- 

 poses, be receiving both blood and air, and heat and 

 cold ; which is improbable. Further, when it is 

 affirmed that the diastole of the heart and arteries 

 is simultaneous, and the systole of the two is also 

 concurrent, there is another incongruity. For how can 

 two bodies mutually connected, which are simulta- 

 neously distended, attract or draw anything from one 

 another; or, being simultaneously contracted, receive 

 anything from each other? And then, it seems im- 

 possible that one body can thus attract another body 

 into itself, so as to become distended, seeing that to be 

 distended is to be passive, unless, in the manner of a 

 sponge, previously compressed by an external force, 

 whilst it is returning to its natural state. But it is 

 difficult to conceive that there can be anything of this 

 kind in the arteries. The arteries dilate, because they 

 are filled like bladders or leathern bottles; they are not 

 filled because they expand like bellows. This I think 

 easy of demonstration; and indeed conceive that I have 

 already proved it. Nevertheless, in that book of Galen 

 headed " Quod Sanguis continetur in Arteriis," he quotes 



