CULTURE MEDIA 45 



Prepared with ammonia-free water and chemically pure salts. 

 Dilute 10-cubic centimeter poritons of (a), (6), (c), and {d) 

 and 1 cubic centimeter of (e) in 1,000 cubic centimeters of water. 

 If a nitrogen-free medium is desired, omit (a). Plant food solu- 

 tions should be renewed at regular intervals of about one week 

 each. 



Medium 106 

 Modified Crone's Nitrogen-free Solution^ 



Stock Salt Mixture: 



Potassium chloride (KCl) 10 . gm. 



Calcium sulphate (CaS04-2H20) 2 . 5 gm. 



Magnesium sulphate (MgS04-7H20) 2.5 gm. 



Tricalcium phosphate (Ca3(P04)2) 2.5 gm. 



Ferric phosphate (FeP04) 2.5 gm. 



1 Bryan, 0. C, Soil Sci., 13, 279, 1922. 



Mix all of these salts and grind to a fine powder. 



Water 1,000.0 cc. 



Stock salt mixture 1.5 gm. 



If a solid medium is wanted, take 7.5 grams of washed agar to 1 

 liter. After sterilization, shake until salts are well mixed with 

 agar and allow to harden. 



Medium 107 



Preserving Stock Cultures in Soil 



Mix equal parts of a fertile soil of neutral reaction with sand. 

 Fill into test tubes, about 2-inch layers and sterilize without 

 cotton plugs for 5 to 6 hours at 120°C. Now add sterihzed water 

 to bring the moisture of the soil to about two-thirds saturation 

 and plug tubes with cotton. Again sterilize for 2 hours. Add 

 to a few of the tubes, glucose niitrient broth and incubate for 

 at least a week. If there are no signs of growth, the soil tubes 

 are ready for use. To prevent mold growth, through plugs, store 

 these tubes in a dry place. 



Medium 108 

 Preserving Stock Cultures in Corn Mash 



Same as Medium 102. This medium will be found useful for 

 cultures of lactic-acid-forming bacteria. 



