OCCURRENCE OF THERMOPHILIC BACTERIA 31 



3. Prepare plates immediately on arrival at laboratory. 



4. At the same time plates are poured make a moisture 

 determination. 



5. Record the outside temperature and soil temperature 

 at the time sample is drawn. 



6. Tabulate results (see p. 30). 



f 



Exercise 12 



Effect of Cultivation on Number of Bacteria 



1. Prepare two tumblers with 100 grams each of clay 

 soil. 



2. Arrange as follows: 



(a) Untreated. 



(b) Cultivated every day by stirring with a sterile spatula. 



3. Add water to two- thirds saturation. Cover with 

 Petri dishes and keep in the incubator at 28 C. 



4. Count the number of bacteria after one, two, and 

 three weeks, pouring plates from the dilution i : 100,000. 



Exercise 13 



Occurrence of Thermophilic Bacteria 



1. Incubate several samples of soil and some fresh stable 

 manure at 60 C. 



2. In order to prevent evaporation all samples must be 

 kept in a moist chamber. A large glass beaker or metal 

 container may be used. Avoid glass bell jars, since the 

 high temperature may cause them to crack. 



