40 LABORATORY MANUAL OF MICROBIOLOGY 



test tubes. Allow the cut potatoes to stand in running water 

 for at least 12 hours. 



Place a small piece of glass rod or cotton in the bottom of the 

 test tube and insert the potato wedge into the tube. Fill the 

 tube with water until the potato is entirely under the liquid. 

 Plug and sterilize: about 15 minutes at 10 pounds' steam pressure 

 for 3 consecutive days will usually be found sufficient. Just 

 before use, pour off the excess water. 



Potatoes prepared in this way should retain their white 

 color. 



Medium 92 



Mannitol Glycero-phosphate Solution 



Mannitol 10.0 gm. 



Potassium nitrate (KNO3) 0.5 gm. 



Magnesium sulphate (MgS04-7H20) 0.2 gm. 



Sodium chloride (NaCl) . 2 gm. 



Calcium glycero-phosphate 1.0 gm. 



Water 1,000.0 cc. 



Adjust reaction to pH 6.5 to 7.0. 



Medium 93 



Peptone-sucrose-lactose Solution 



Sucrose 10.0 gm. 



Peptone 20 . gm. 



Lactose 10.0 gm. 



Sodium chloride (NaCl) 2.0 gm. 



Dipotassium phosphate (K2HPO4) 2.0 gm. 



Magnesium sulphate (MgS04-7H20) 1.0 gm. 



Tap water 1,000.0 cc. 



Medium 94 

 Peptone-sodium Phosphate Solution 



Peptone 10.0 gm. 



Disodium phosphate (Na2HP04-2H.>0)i 5 .0 gm. 



Carbohydrate 10.0 gm. 



Tap water 1,000.0 cc. 



1 To prepare disodium phosphate (Na2HP04-2H20) take ordinary 

 disodium phosphate with 12 H2O and spread it out on filter paper and allow 

 it to remain at room temperature in a dry place for 2 weeks. 



