THE STUDY OF MICROORGANISMS IN THE SOIL 133 



Exercise 63 

 Iron Bacteria from Drinking Water 



Clean and sterilize a Berkefeld filter. 



Connect the filter to the city water-supply 

 and allow the water to run slowly for 24 to 

 48 hours. 



After the metal cap is removed from the 

 filter, place the filter in a large beaker of 

 iron solution (Medium 76). 



Incubate in the ice-box or at about 15 to 

 20°C. 



At regular 2-day intervals examine the 

 deposit on the sides of the filter. 



If bacteria are found, test for iron. Add 

 a few drops of a 5 per cent hydrochloric acid 

 solution and a 4 per cent potassium ferro- 

 cyanide solution. In the presence of ferric 

 salts an intense blue color is formed. 



In order to stain the higher forms of iron 

 bacteria it is well to remove the deposit of 

 iron by treating with a 5 per cent hydro- 

 chloric acid solution. 



CELLULOSE-DECOMPOSING BACTERIA 

 Exercise 54 



An^robic Cellulose Decomposition in 

 Impure Cultures 



Fill four large test tubes or wide-mouthed 

 deep-form bottles about three-fourths full 

 of Omeliansky's solution (Medium 85). 



Add four strips of filter paper to each. 



Treat as follows: (1) uninoculated, (2) 

 stable manure, (3) leaf mold, (4) garden 

 soil. 



Incubate at 28°C. 



Examine the cultures at regular intervals, 

 taking note of the change in color and the 

 structure of the filter paper. 



Fig. 16. — Fermenta- 

 tion of filter paper in 

 Omeliansky's solution. 



