28 A MANUAL OF BACTEBIOLOGY 



agar through a clear cloth, wash briefly, and put into a flask or 

 earthenware pitcher. Add to it the filtered Nahrstoff solution, 

 and make up to a volume of 1 liter with distilled water. 



3. Melt the agar in the autoclave or over a flame, as described 

 in Exercise 7. Filter through absorbent cotton and tube. Steri- 

 lize in the autoclave. 



Exercise 49. Preparation of Ashby's Solution for Isolating Azotobacter 



from Soil 



Mannite (or lactose) 20.0 g. 



Monopotassium phosphate 0.2 g. 



Magnesium sulphate 0.2 g. 



Sodium chloride 0.2 g. 



Calcium sulphate 0.1 g. 



Calcium carbonate 5.0 g. 



Distilled water 1000.0 cc. 



Dissolve the monopotassium phosphate separately in a little 

 water and neutralize it with potassium hydroxide solution before 

 adding it to the other ingredients. 



Exercise 50. Preparation of Nitrogen-Free Media for Culture of 

 Symbiotic Nitrogen-Fixing Bacteria 



1. Dextrose solution. 



Potassium biphosphate l.OOg. 



Magnesium chloride 0.20 g. 



Sodium chloride 0.01 g. 



Ferrous sulphate 0.01 g. 



Manganese sulphate 0.01 g. 



Dextrose 20.00 g. 



Distilled water 1000.00 cc. 



To prepare a solid medium add 20 g. of agar to this solution. 



2. Mannite solution. 



Distilled water 1000.00 cc. 



Potassium phosphate 0.20 g. 



Calcium chloride 0.02 g. 



Magnesium sulphate 0.20 g. 



Ferric chloride 0.01 g. 



Mannite 15.00 g. 



Neutralize if necessary with NaOH, using phenolphthalein as 

 indicator. 



