WHAT IS PHYSICAL LIFE 



than the Andes, and the earth would be 

 choked with its own dead. In other words, 

 bacteria keep life going by removing the 

 bodies of each generation to make room 

 for the next. Thus life here begins with 

 microbes and ends with them. In this 

 sense, therefore, bacteria are indispensable. 

 We could not do without their post- 

 mortem activities. 



On the other hand, certain kinds of bac- 

 teria can be made directly beneficial to 

 the living human world by materially in- 

 creasing its food supply. Though no one 

 would think of cultivating protozoa, yet 

 these particular bacteria being vegetables 

 we can raise profitable crops of them, so 

 that some are now actually put out for 

 sale at two dollars a small bottle. 



These valuable bacteria were first dis- 

 covered in little excrescences resembling 

 warts on the rootlets of leguminous plants 

 such as beans, peas, and clover, and were 

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