WHAT IS PHYSICAL LIFE 



enough compared with that of one bac- 

 terium. 



A fact which overshadows all others 

 about unicellular forms was naturally not 

 suspected until after microscopes were 

 made. But it is now revealed that this 

 once invisible world is much the largest 

 division of the living kingdom, exceeding in 

 actual bulk all visible plants and animals 

 put together. To illustrate their relative 

 extent we might liken the unicellular king- 

 dom of life to a lake, that of all visible 

 plants to a pond, and that of all animals 

 to a pool. This is because all visible plants 

 and animals are necessarily local even a 

 tiny blade of grass is not found everywhere 

 while among the unicellular forms the 

 bacteria alone may be said to be every- 

 where, on everything and in everything, 

 whether in earth, water, or air. Nor, as 

 we shall see, are they there in vain. Sim- 

 ply to illustrate this vitally important 

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