MAINTENANCE AND PRESERVATION OF CULTURES 113 



26. Potato Agar 



Potato infusion 500 ml 



Water 500 ml 



Peptone 10 g 



Beef extract 5 g 



NaCl 5g 



Agar 30 g 



Heat to 100°C, adjust pH to 7,3, autoclave 5 min at 15 lb, filter through cotton, 

 and add 



Glucose 10 g 



Tube, autoclave, and slant. 



The potato infusion is made by slicing 250 g of peeled potatoes into 500 ml of dis- 

 tilled water. Cover, and hold in 60°C incubator overnight. Filter through cheese- 

 cloth, and make up to 1,000 ml. 



27. Potato-starch Agar 



(a)Nutrient agar 3.1 g 



Distilled water 80 ml 



pH7.4 



(6)Potato starch 1 g 



Distilled water (cold) 20 ml 



Mix thoroughly, then heat with constant stirring until a smooth paste is formed. 

 Combine with (a), autoclave, and slant. 



28. Rhizobium Medium 



Yeast extract 1 g 



Agar 15 g 



Soil extract (see formula 5 for preparation) 200 ml 



Tap water 800 ml 



Heat to 100°C, adjust pH to 7.4 and add 



Mannitol 10 g 



29. spirillum Medium 



a. Fresh-water species 



Peptone 5 g 



Beef extract 3 g 



Yeast autolysate 3 g 



Calcium lactate 1 g 



Agar 2 g 



Tap water 1,000 ml 



b. Marine species 

 Use sea water or sea-salt solution of equivalent concentration. An artificial sea 

 salt can be compounded of 



NaCl 2.75 g 



MgCh 0.50 g 



MgS04 0.20 g 



CaCh 0.05 g 



KCl 0.10 g 



FeS04 Trace 



Distilled water 100 ml 



