AN ANATOMICAL STUDY ON THE 



sis or joining of ike arteries and veins ^ and they transfer 

 blood and spirit equally from each other by invisible and 

 very small -passages. If the mouth oj the pulmonary 

 artery always stayed open and Nature had no way of 

 closing it when necessary or of opening it again, the 

 blood could not transfuse through these invisible and 

 delicate pores in the arteries during the contraction of 

 the thorax. All things are not equally attracted or ex- 

 pelled. Something light is more easily drawn in by the 

 distention of the party and pushed out in contraction 

 than something heavy. Likewise anything is more quickly 

 passed through a wide tube than through a narrow one. 

 When the thorax contracts ^ the pulmonary veins ^ strongly 

 compressed on all sides ^ quickly expel soine of the spirits 

 in them, and take some blood from these tiny mouths. 

 This could never happen if blood could flow back into 

 the heart through the large opening of the pulmonary 

 artery. Thus, its return through this great hole being 

 blocked, and being compressed on every side, some of it 

 filters into the arteries through these small pores.'' 



Shortly after, in the next chapter: ''The more 

 powerfully the thorax contracts, squeezing the blood, the 

 more tightly do these membranes, the sigmoid valves, 

 close the opening, so that nothing flows back.'' A little 

 before in the loth chapter: ''Unless the valves be 

 present, much difficulty would follow. The blood would 

 follow this long course in vain, flowing in during the 

 distention of the lungs and filling all the vessels in it, 

 outwards during the constrictions, and tide-like, as 

 ■ Euripus,flow back and forth in a way not suited to the 



[64] 



