112 MANUAJj OF MICROBIOLOGICAL METHODS 



22. Nitrosomonas Medium 



(NH4)2S04 2.0 g 



K2HPO4 1-0 g 



NaCl 0.5 g 



MgS04 0-5 g 



MnS04 Trace 



Fe2(S04)3 Trace 



Distilled water 1,000 ml 



pH8.5 



Dispense 100-ml portions in flasks, autoclave, and add to tubes of marble chips as 

 in formula 21. 



23. Nutrient Agar 



Blood base agar (Difco) 20 g 



Peptone 2.5 g 



Beef extract 1.5 g 



Agar 15.5 g 



Distilled water 1,000 ml 



pH7.4 



23a. Alternate Formula with Salt 



Peptone 5 g 



Beef extract 3 g 



NaCl 30 g 



Agar 14 g 



Distilled water 1,000 mi 



24. Peptic Digest of Blood 



Autoclave 150 ml of 0.9 per cent NaCl in a bottle having a ground-glass stopper 

 but with the stopper separately wrapped in paper and the bottle cotton-plugged. 

 Place in 55°C water bath, and add 



HCl (cone) 6 ml 



Sterile sheep blood, defibrinated 50 ml 



Pepsin 1 ml 



Keep in water bath at 55°C overnight, shaking occasionally during first 2 hr. 

 Add 12 ml of 20 per cent NaOH, then slowly with intermittent shaking enough more 

 to raise the pH to 7.6. Then restore to pH 7.0-7.2 with HCl. Add 0.25 per cent 

 chloroform; store glass-stoppered in refrigerator. For use add 0.1 ml to brain-heart 

 infusion agar or semisolid medium. 



25. Potato Dextrose Agar 



Potato, peeled and diced 300 g 



Distilled water 1,000 ml 



The potatoes should be handled with minimum exposure to air. Boil in 500 ml of 

 water until thoroughly cooked. Filter through cheesecloth, make up the volume to 

 1,000 ml, and add 



Agar 15 g 



Glucose 20 g 



Dissolve by heating. Autoclave. 



