CIRCULATION OF THE BLOOD. 121 



r 



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 suc- 

 cession 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 was lost from the 

 farther orifice of a divided vein because nature was disturbed, 

 still that the incision does not close the nearer orifice, from 

 which nothing either escapes or can be expressed, whether nature 

 be disturbed or not. Others argue in the same way, maintain- 

 ing that, although the blood immediately spurts out in such pro- 

 fusion with every beat, when an artery is divided near the heart, 

 it does not therefore follow that the blood is propelled by the 

 pulse when the heart and artery are entire. It is most pro- 

 bable, however, that every stroke impels something ; and that 

 there would be no pulse of the container, without an impulse 

 being communicated to the thing contained, seems certain. Yet 

 some, that they may seize upon a farther means of defence, and 

 escape the necessity of admitting the circulation, do not fear to 

 affirm that the arteries in the living body and in the natural 

 state are already so full of blood, that they are incapable of re- 

 ceiving another drop ; and so also of the ventricles of the heart. 

 But it is indubitable that, whatever the degree of distension and 



