AIR FOOD AND MICROBES 121 



tion whence it came during Carbonaceous times 

 was owing to the fixation of nitrogenous food in 

 the soil by microbes. 



Likewise a similar chemical change in the lungs 

 of all animals, carbon of the blood uniting with 

 oxygen of the air inhaled, is the immediate cause 

 of the billions of gallons of plant food daily com- 

 ing into the air from this source; but all animal 

 life is dependent on vegetable life, and vegetable 

 life is dependent on microbian work done in the 

 soil. 



Finally, the contribution to this same air food 

 constantly made by volcanoes is vegetable in its 

 origin, and therefore originally the gift of mi- 

 crobes. 



Thus, which ever way we turn, we find these in- 

 visible friends, primarily, are indispensable to the 

 supply of atmospheric plant food. 



