80 SOIL BACTERIOLOGY 



4. Add sufficient sterile water to bring moisture content 

 up to two- thirds saturation. 



5. Cover loosely with a Petri dish and incubate three to 

 four months, restoring moisture from time to time. 



6. At the end of this time prepare the cultures for analysis. 



7. Dry and determine the amount of humus in lo-gram 

 samples (see page 148). 



