128 LABORATORY MANUAL OF MICROBIOLOGY 



30 minutes in a mechanical shaker; allow to settle 10 minutes 

 and filter on a large folded filter. Transfer 400 cubic centi- 

 meters of filtrate to a Kjeldahl flask, add a small piece of paraffin 

 to prevent foaming and a little 20-mesh limestone to prevent 

 bumping. Distill with 1 gram of MgO. 



Exercise 44 



Decomposition of an Amino Acid and a Protein by Bac. oereus and 

 Bact. fluorescens 



Prepare 1 liter of a mineral salt solution. 



Weigh out 3 grams of K2HPO4, 0.2 gram KCl, 0.2 gram MgS04, 

 0.2 gram NaCl, 0.1 gram CaS04 and 0.01 gram FeS04, in 1,000.0 

 cubic centimeters of water. 



To 500 cubic centimeters add 5 grams of glycocoll and mark 

 solution '' Glycocoll medium;" the other 500 cubic centimeters is 

 used for the casein solution. 



Weigh out into a beaker 5 grams of casein, purified (Hammer- 

 sten). Add about 50 cubic centimeters of the medium and sus- 

 pend the casein in it. Then add 4 cubic centimeters of IN. 

 NaOH solution, warm until casein has dissolved. Filter. Add 

 casein solution to the rest of the salt solution, make up to 500 

 cubic centimeters and mark it ''Casein solution." 



Distribute the two solutions in 50-cubic centimeter portions in 

 250-cubic centimeter Erlenmeyer flasks, plug with cotton, and 

 sterilize. 



Inoculate two flasks of each medium with a pure culture of 

 Bacillus cereus and two flasks of each medium with a pure cul- 

 ture of Bacterium fluorescens. Leave 1 flask of each as control. 

 Incubate 14 days. 



Examine cultures for growth and determine in each flask the 

 amino-acid-nitrogen, ammonia, and residual casein. 



Tabulate results. 



SULPHATE-REDUCING AND SULPHUR-OXIDIZING BACTERIA 



Exercise 45 

 Reduction of Sulphates by Bacteria 

 Prepare three small bottles of sulphate medium (Medium 60), 

 and treat as follows: 



(a) Control — uninoculated. 



