28 



A MANUAL OF BACTEEIOLOGY 



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 



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. 



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

 2. Mannite solution. 



Distilled water . . 

 Potassium phosphate 

 Calcium chloride 

 Magnesium sulphate 

 Ferric chloride . . 

 "Mannite .... 



1000.00 cc. 

 0.20 g. 

 0.02 g. 

 0.20 g. 

 0.01 g. 

 15.00 g. 



Neutralize if necessary with NaOH, using phenolphthalein as 

 indicator. 



