Lesson xxxvm.] CONCOCTION. 



From this admirable structure of the lungs, it is 

 obvious, that the crude mixture of the blood and 

 chyle, passing through the minute ramifications o 

 the pulmonary artery and vein, is compressed and 

 ground by two contrary forces, viz. by that of the 

 heart^ driving the mixture forward against the 

 sides of the bronchia and air-bladders; and by 

 the elastic force of the air equally repelling this 

 mixture from the contrary side. 



By these two opposite forces the chyle and blood 

 are more intimately blended and incorporated 5 

 and by the admission and expulsion of the air in 

 respiration, the vessels are alternately inflated and 

 compressed (and probably some subtile air of 

 aether is received into the blood) by which means 

 the mixture is still farther attenuated and dis- 

 solved; and after various circulations through the 

 lungs and heart, and the whole arterial system, is 

 at last perfectly assimilated with the blood, being 

 fitted to nourish the body, and answer the different 

 purposes of animal life. 



When the blood thus prepared from the aliment, 

 is, by repeated circulations, gradually drained of all 

 its bland and useful parts, and begins to acquire 

 too great a degree of acrimony, it is carried oft' by 

 both sensible and insensible evacuations, through 

 the several channels and distributions of nature. 

 By these evacuations the body is made languid, 

 and requires a fresh supply of aliment; while at 

 the same time the saliva, and juices of the sto- 

 mach and intestines, becoming thin and acrid by 

 multiplied circulations, vellicate the nerves of 

 3 thos 



