PURE AIR 113 



taining carbon is slowly using up oxygen and giving 

 out carbon dioxid in a similar manner. How does 

 it happen, then, that the useful oxygen is not used up, 

 and all animal life destroyed by the poisonous gas 

 that takes its place? Nature has wisely provided 

 against this calamity by having the trees, plants, and 

 all vegetable life in daylight breathe in carbonic 

 acid gas and breathe out oxygen. What a wise pro- 

 vision this is ! How interesting to know that in breath- 

 ing we may help to furnish necessary air material 

 for our friends, the trees ! How marvelous is the 

 knowledge that each tender leaf and tiny blade does 

 its humble part toward furnishing the oxygen that 

 helps so much in building our bodies. 



The growing lily which brightens the sick room 

 with its fragrance and graceful foliage, cheers the pa- 

 tient by its beauty. At night, however, plants breathe 

 a very small amount of oxygen, and for this reason 

 or because of their fragrance they are usually taken 

 from a sleeping room where the circulation of air is 

 not good. In fact, at any time of day, very fragrant 

 flowers may not be altogether beneficial to one who is 

 ill. It should be remembered that pure air is the 

 important requisite. 



But the story of the air's part in body building is 

 so strange. Is it really possible for us to see with 

 our own eyes that combustion goes on readily in oxy- 

 gen? Can we also find out that carbonic acid gas is 

 a product of combustion, and that neither the tissues 



