PURE AIR NECESSARY TO HEALTH. 13 



blood, and combines with it, much as oxygen combines 

 with fuel in burning, and by this combustion sustains the 

 animal heat, and keeps the body warm. When the air 

 in the lungs is breathed out, it contains less oxygen than 

 the air which had entered. In place of this oxygen 

 which has staid in the body, a portion of carbonic acid is 

 breathed out, which poisons, to a certain extent, the 

 surrounding air. In this way the purity of the air would 

 soon be destroyed, and it would be rendered unfit for 

 breathing, if pure air were not brought in. 



The quantity of air thus rendered unfit for respiration 

 is known, and we can calculate exactly the space and the 

 number of cubic feet of air which ought to be provided 

 in chambers for men, and in stables and other places for 

 other animals, according to the number and size of the 

 animals to be shut up in them. 



A Man needs from 200 to 350 cubic feet of pure air 

 every hour. Supposing a person to require only 250 feet 

 an hour, a close room of 10 feet in each dimension, 

 having its air rendered more and more impure by his 

 breathing it, will, in four hours, be foul and very unwhole 

 some, and wholly unfit to breathe. 



43. It is thus plain that every place occupied by a 

 living being, particularly by night, ought to be ventilated. 

 That is, it ought to have a communication, by means of 

 a chimney flue, or in some other way, with the pure, 

 open air. Neither the body nor the mind of a person 

 who has to breathe, night after night, the close, foul air 

 of an ill-ventilated room, can remain healthy. 



44. Plants do not breathe as animals do. But air is 

 just as essential to them, penetrating freely into the 

 tissues of their green portions, and there playing a part 



