110 THE INVISIBLE WORLD 



Animal life on the earth; and then, to change all 

 this Animal and Vegetable life back into parts of 

 the air and the soil, ready to make another round 

 in the never ending cycle. 



By this machinery is kept up the fertility of the 

 Soil and the Air through the ages. Such enormous 

 quantities of plant food are annually abstracted 

 and utilized to keep life going on the earth that, 

 unless Soil and Air were constantly replenished, 

 they would soon become barren. Barren Soil and 

 Air would soon mean barren Earth devoid of Life. 

 But, as a matter of fact, Life has flourished all over 

 the earth some hundreds of millions of years; yet 

 Soil and Air seem to-day as fertile and well 

 adapted to support Life as at any past moment in 

 the world's history. It is only because Nature's 

 great reservoirs annually yield up a certain re- 

 quired volume of plant food to support Life on the 

 earth, while a similar volume of that food, having 

 served its appointed mission, annually returns 

 again to replenish those storehouses. The great 

 cycle is forever active and continuous. 



