7 8 MINUTE MARVELS OF NATURE 



every living animal is continually inhaling oxygen 

 or pure air from the atmosphere and converting 

 it into this carbonic acid gas. 



Now, plants, in their development through un- 

 numbered ages, have used this carbon gas just as 

 animal-life has used oxygen. So it comes about 

 that we make a kind of exchange, the animals 

 supplying the plants with carbon to build up 

 their tissues, while the plants in return supply the 

 animals with oxygen, or the "breath of life." 

 This is how the leaves fulfil their important func- 

 tions, in the scheme of Nature. 



If we chemically analyse carbon dioxide we 

 find that it is composed of one part carbon and 

 two parts oxygen. And if we could take one 

 part of solid carbon and chemically combine it 

 with two parts of gaseous oxygen, we should pro- 

 duce one part of this gaseous carbon dioxide. 



Now, when this gas, which is always floating 

 in the atmosphere, reaches the green leaves this 

 is exactly what takes place. The leaves first 

 drink in this carbon gas from the air during sun- 

 light, after which they chemically decompose it ; 

 that is to say, they break it up into its original 

 elements carbon and oxygen ; the carbon they 

 retain, assimilating it for their own use ; the 

 oxygen, which is of no use to the plant, but which 

 is so essential to animal life, is returned to the 



