DISCOURSE ON METHOD. 53 



vessels from which they come full of blood, are 

 immediately rarefied, and dilated by the heat they 

 meet with. In this way they cause the whole heart 

 to expand, and at the same time press home and 

 shut the five small valves that are at the entrances 

 of the two vessels from which they flow, and thus 

 prevent any more blood from coming down into the 

 heart, and becoming more and more rarefied, they 

 push open the six small valves that are in the 

 orifices of the other two vessels, through which they 

 pass out, causing in this way all the branches of the 

 arterial vein and of the grand artery to expand 

 almost simultaneously with the heart which imme 

 diately thereafter begins to contract, as do also the 

 arteries, because the blood that has entered them 

 has cooled, and the six small valves close, and the 

 five of the hollow vein and of the venous artery 

 open anew and allow a passage to other two drops 

 of blood, which cause the heart and the arteries 

 again to expand as before. And, because the blood 

 which thus enters into the heart passes through 

 these two pouches called auricles, it thence happens 

 that their motion is the contrary of that of the heart, 

 and that when it expands they contract. But lest 

 those who are ignorant of the force of mathematical 

 demonstrations, and who are not accustomed to dis 

 tinguish true reasons from mere verisimilitudes, 

 should venture, without examination, to deny what 

 has been said, I wish it to be considered that the 

 motion which I have now explained follows as 

 necessarily from the very arrangement of the parts, 

 which may be observed in the heart by the eye 



