TO TEST THE CATALYTIC POWER OF SOIL 239 



4. Make dilution plates in gelatin immediately, using 

 dilutions 1 : 10, 1 : 100, 1 : 10,000 and 1 : 1,000,000. 



6. Filter the remainder of the sample through the 

 Berkefeld filter candle and plate immediately from the 

 filtrate, making gelatin plates, using 1 c.c. and 0.1 c.c. 

 direct, dilutions of 1 : 100 and 1 : 10,000. 



6. Incubate all plates at the same temperature. Ex- 

 amine the plates daily and record the counts. 



7. Was the bacterial count reduced by the use of this 

 filter candle? What type of organisms passed the filter? 

 Is this filtered water fit for drinking purposes? 



How does this filter compare with other types as to 

 its action? What other types of filters are used for water 

 purification? Sewage purification? Upon what does the 

 value of each depend? 



8. Give all data in full and draw any conclusions that 

 are warranted. Point out any practical applications. 



REFERENCES 



MARSHALL: Microbiology, pp. 205-207. 



DON and CHISHOLM: Modern Methods of Water Purification (1911), 

 pp. 231-236. 



SOIL MICROBIOLOGY 



EXERCISE 1. TO TEST THE CATALYTIC POWER OF 



SOIL 



Apparatus. 3% hydrogen peroxide; three 375 c.c. 

 Erlenmeyer flasks; three one-hole stoppers to fit flasks; 

 three pieces of bent glass tubing; three pieces rubber tub- 

 ing; three 100 c.c. glass graduates. 



Culture. Soil rich in humus. 



Method. 1. Fit the Erlenmeyer flasks with one-hole 

 rubber stoppers through which a short piece of bent glass 

 tubing is inserted. Fit short pieces of rubber tubing 

 (about 40 cm. in length) to the glass tubing. 



