118 THE INVISIBLE WORLD 



But this is only one-half. With other organs 

 the leaves of all the farmer's crops over the wide 

 earth, including all pasture lands, all flower 

 gardens, all ornamental and shade trees, every 

 green thing outside of the forests, present to the 

 sun another surface at least equally as large, and 

 daily draw from the atmosphere at least an equally 

 large amount of carbon. 



It is evident, therefore, that the air, unless con- 

 stantly re-supplied, must soon become exhausted 

 of this kind of food. With her ever ready re- 

 sources, Nature fully meets the demand. Each 

 adult of the 1,500,000,000 people who inhabit the 

 earth throws from his lungs into the air 140 gal- 

 lons of carbonic acid every twenty-four hours, 

 in all more than 200,000,000,000 gallons daily. 

 The lower animals throw from their lungs every 

 day five times as much more, over 1,000,000,000,- 

 000 gallons. Every ton of coal burned pours into 

 the atmosphere two and two-thirds tons of this 

 acid, millions of tons every day. All fires on 

 the earth, fed by other fuel, probably furnish to the 

 air as much more of this acid. All decaying ani- 

 mal and vegetable substances, too, are, chemically, 

 so many slow fires, and furnish another vast quan- 

 tity. The 2,000 active volcanoes on the earth pour 

 into the atmosphere 2,000 great streams of this acid 

 every moment. All the extinct volcanoes probably 

 pour in daily as much more. 



Taken all in all, how vast the quantity of this 

 acid daily poured into the atmosphere. To us 



