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tents into the heart, muft neceflarily at that time be contrafted more 

 than when in its natural ftate, becaufe there cannot be a vacuum in 

 the vein, and there is no fubftance at hand to occupy the place of 

 the blood poured into the heart ; for the blood cannot flow from the 

 extremities, or even the parts adjoining, in fo Ihort a time as would 

 be required, whereupon mull follow, as before obferved, a more 

 than ordinary contraction of the veins. 



But thofe parts, of which the coats of the veins are compofed, 

 which almoft all take their courfe round about the vein, thefe, 

 upon the effufion of the blood into the heart, being put in motion, 

 by their undergoing fuch contradlion as before mentioned, will, by 

 their elaftic tendency to recover their natural ftate, draw the blood 

 from the moll diftant parts towards the heart; fo that this may be 

 confidered as a third caufe of the conftant circulation and current 

 of the blood. 



