34 LABORATORY MANUAL OF MICROBIOLOGY 



make up to 500 cubic centimeters. Now add 500 cubic centi- 

 meters of 3.6 per cent neutral water solution of agar. Tube and 

 sterilize. Avoid excessive heating because the carrot extract 

 becomes more acid after long heating. 



Medium 81 



Pea Extract Sucrose Solution 



Pea seedlings 3 to 5 inches tall (net weight) 300 . gm. 



Water 1,000.0 cc. 



Heat in the steamer for 4 to 5 hours and then boil for 1 hour 

 over a free flame. Filter and make up to 1,000 cubic centimeters. 

 Add sucrose, 2 per cent, and 0.5 per cent of CaCOs. This 

 medium contains about 50 milligrams of nitrogen in 100 cubic 

 centimeters. 



Medium 82 



Navy-bean Seed Extract Sucrose Medium 



Bean seed (dry) 250 . gm. 



Tap water 2,500 . cc. 



Soak the beans in the cold water for 2 to 3 hours. Now add 

 water to make 2,500 cubic centimeters and heat in the steamer 

 for 2 hours. Filter and make up to 2,500 cubic centimeters. 

 Add 1 per cent of sucrose and 0.5 per cent of CaCOs. This 

 medium contains about 40 milligrams of nitrogen in 100 cubic 

 centimeters. 



Medium 83 



Caffein-bean Extract-glucose for Bacteroid Formation^ 



Agar 15.0 gm. 



Cafifein (C8HioN402-H20) 2.0 gm. 



Glucose 10.0 gm. 



Bean extract2 1,000 . cc. 



iZipPEL, H., Centr. Bakt., II Abt., 32: 107-131, 1911. 



2 Bean extract : Add to 20 grams of powdered navy-bean seed in a mortar 

 20 cubic centimeters of A^/1 KOH. Allow this to stand a few minutes, then 

 add water sufficient to make 1 Hter. This should stand 24 hours. Siphon 

 off the clear liquid, neutralize with phosphoric acid. 



