Normal Soil and Its Requirements 5 



form wonderful tasks, as we shall soon see. Bacteria 

 multiply in the simplest ways. A single individual 

 upon reaching maturity becomes constricted in the 

 center, then divides in two, each part now becoming 

 a separate individual capable of nutrition, growth, 

 and multiplication. It has been estimated by scien- 

 tists that division of a single individual takes place 

 about every twenty minutes. Granting that this 

 rate of division is uninterrupted for twenty-four 

 hours, the descendants of one germ would be in round 

 numbers 1,800,999 trillions. These when placed 

 end to end would make a string two trillion miles 

 long, or a thread long enough to go around the earth 

 at the equator seventy million times. It would take 

 a ray of light four months, traveling as it does, to 

 pass from one end of it to another. 



Individual bacteria can be detected only with a 

 compound microscope. When grown on artificial 

 media and under aseptic conditions, all the descend- 

 ants of a single parent cell live together and constitute 

 a colony, which becomes visible to the naked eye as 

 a creamy jellylike drop (fig. 1 d). 



Relationship of Bacteria to the Function of 



a Soil 



The health of a soil as shown in its fertility is in- 

 timately connected with the kind of bacteria present 

 in it. We are as yet in the dark as to the possible 

 f unction of numerous groups of the soil organisms. 

 Bacteriologists are seeking to discover their proper 



