Circulation of the Blood 147 



clearly see that the part of the vein towards the heart 

 pours out no blood, whilst that beyond the wound 

 gives a torrent ; the divided artery, on the contrary, (as 

 in my experiment on the carotids,) pours out a flood of 

 pure blood from the orifice next the heart, and in jets 

 as if it were forced from a syringe, whilst from the 

 further orifice of the divided artery little or no blood 

 escapes. This experiment therefore plainly proves in 

 what direction the current sets in either order of vessels 

 towards the heart in the veins, from the heart in the 

 arteries ; it also shows with what velocity the current 

 moves, not gradually and by drops, but even with 

 violence. And lest any one, by way of subterfuge, 

 should take shelter in the notion of invisible spirits, 

 let the orifice of the divided vessel be plunged under 

 water or oil, when, if there be any air contained in it, 

 the fact will be proclaimed by a succession of visible 

 bubbles. Hornets, wasps, and other insects of the 

 same description plunged in oil, and so suffocated, 

 emit bubbles of air from their tail whilst they are 

 dying ; whence it is not improbable that they thus 

 respire when alive ; for all animals submerged and 

 drowned, when they finally sink to the bottom and 

 die, emit bubbles of air from the mouth and lungs. 

 It is also demonstrated by the same experiment, that 

 the valves of the veins act with such accuracy, that air 

 blown into them does not penetrate ; much less then 

 can blood make its way through them : it is certain, 

 I say, that neither sensibly nor insensibly, nor gradually 

 and drop by drop, can any blood pass from the heart 

 by the veins. 



And that no one may seek shelter in asserting that 

 these things are so when nature is disturbed and 

 opposed, but not when she is left to herself and at 

 liberty to act; that the same things do not come to 

 pass in morbid and unusual states as in the healthy 

 and natural condition ; they are to be met by saying, 

 that if it were so, if it happened that so much blood 



