28 



from tlie stomach and liver digestion, are 

 all mixed with the blood in the veins, on 

 its way to the lungs. Nature emphasizes 

 this process in a marked degree. Only a 

 portion of the blood is sent to the kidneys 

 for purification, and yet this purification 

 is essential to life. But in the case of the 

 lung circulation, every drop must go — 

 new material, and old material, — all must 

 receive the vivifying effect of fresh air. 

 Here, in the lungs, the blood is quickly 

 changed from purple to scarlet. The car- 

 bon wastes seize upon the oxygen of the 

 air, and are burned up, throwing off, as 

 the result, chiefly carbonic acid gas, just 

 as a stove sets off carbonic acid gas by 

 the burning of coal. Various volatile sub- 

 stances are at the same time got rid of, 



