80 GENERAL BACTERIOLOGY 



or potassium nitrite 0.02 grams and distilled water lOOce.). The 

 appearance of a red color indicates formation of indol. 



REFERENCES. A. 223 ; H. 21 ; L. & N. 142 ; McF. 57 ; M. & R. 80. 



SPECIAL DIRECTIONS. Use B. coli or sewage. 



EXERCISE 55. DETERMINATION OF CHEMICAL ENZYMES IN CUL- 

 TURES. 



GENERAL DIRECTIONS. 



a. Make two gelatin stab cultures of a rapidly liquefying organ- 

 ism and incubate several days or until the gelatin has all been lique- 

 fied and then add to each T V cc. of a 5% solution of carbolic acid for 

 each cc. of medium, shake thoroughly and filter. 



5. Pour one into a tube of sterile gelatin and the other into a 

 tube of milk and note changes. 



REFERENCE. McF. 56. 



SPECIAL DIRECTIONS. Use B. subtilis or B. prodigiosus. 



EXERCISE 56. VARIATION IN ENZYME PRODUCTION. 



Make stab cultures of Pseudomonas aeruginosa (SCHROETER) 

 MIG. (B. pyocyaneus), or any slow liquefier, in ordinary neutral 

 gelatin and also in dextrose gelatin. Compare rate of liquefaction 

 in each. 



EXERCISE 57. VARIATION IN COLOR PRODUCTION. 



Make an agar streak of B. prodigiosus. Incubate at 38 C. ; 24 

 hours later transfer to fresh media. Continue the process of daily 

 transplanting from cultures of previous day until chromogenic 

 property is lost, even at the room temperature. 



