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GENERAL MICROBIOLOGY 



C. Relation of light to pigment formation. 



Make two streaks of B. prodigiosus. Place one in bright 

 sunlight, keep the other in the dark. Explain the results. 



D. Effect of chemicals on pigment. 



1. To one of the brightest pigmented cultures of B. 

 prodigiosus, add 10 c.c. of 95% alcohol and shake vigorously. 

 Alcohol dissolves the pigment. 



2. Pour off into a flask and allow to settle. Filter. 



3. Divide the clear filtrate into four parts. 



To one, add a drop or two of HC1; note the result and 

 explain. To the second add a drop or two of NaOH; note 

 the result and explain. 



Place the third in bright sunlight and note what happens. 



Place a few drops of the fourth portion on a clean slide 

 and allow to evaporate slowly. Examine crystals under 

 microscope and draw. What are these crystals? Explain. 



E. Solubility of pigment. 



1. Make five dextrose agar streak cultures of B. pro- 

 digiosus and, when well pigmented, try the solubility of the 

 pigment in (a) water, (b) chloroform, (c) ether, (d) benzol, 

 (e) carbon bisulphide. Results? 



2. Are any of the different bacterial pigments formed, 

 water-soluble? What is the simplest method for determin- 

 ing whether the pigment produced by an organism is water- 

 soluble? 



F. Blue milk and " bloody " milk. 

 1. Inoculate milk tubes as follows: 



and keep at 25 

 Observe daily. 



C. along with uninoculated control. 



