INTRODUCTION 71 



the less blood on that account. And no one denies the blood as 

 such, even the portion of it which flows in the veins, is imbued 

 with spirits. But if that portion of it which is contained in thfe 

 arteries be richer in spirits, it is still to be believed that these 

 spirits are inseparable from the blood, like those in the veins; 

 that the blood and spirits constitute one body (like whey and 

 butter in milk, or heat in hot water), with which the arteries are 

 charged, and for the distribution of which from the heart they 

 are provided. 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 surrounding air, as heretofore; 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 take it to be impossible : the 

 arteries would then have to fill while they contracted, to fill, and 

 yet not become distended. But if it be said: during diastole, 

 they would then, and for two opposite purposes, be receiving 

 both blood and air, and heat and cold, which is improbable. Fur- 

 ther when it is affirmed that the diastole of the heart and 

 arteries is simultaneous, and the systole of the two is also con- 

 current, there is another incongruity. For how can two bodies 

 mutually connected, which are simultaneously distended, at- 

 tract or draw anything from one another? or being simultaneous- 

 ly contracted, receive anything from each other? And then it 

 seems impossible that one body can thus attract another body 

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

 tended is to be passive, unless, in the manner of a sponge, which 

 has been previously compressed by an external force, it is re- 

 turning 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 arc filled like bladders or leathern bottles; 

 they art 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 an experi- 

 ment to prove the contrary. An artery having been exposed, is 

 opened longitudinally, and a reed or other pervious tube is in- 

 serted into the vessel through the opening, by which the blood 



