76 GENERAL BACTERIOLOGY 



REFERENCES Smith: Wilder Quarter Century Book, 1893, p. 

 187 ; A. 212 ; McF. 49 ; M. & R. 79 ; P. 82. 



SPECIAL DIRECTIONS. Use B. coli; also try B. subtilis. 



EXERCISE 49. DETECTION OF ACIDS AND ALKALIES (WURTZ). 



GENERAL DIRECTIONS. 



a. Melt a tube of lactose agar (or lactose gelatin) and add enough 

 of a sterile blue litmus solution (37 e.) to give it a distinct color, cool 

 to 42 C., inoculate it with an acid-producing organism and pour in 

 the usual manner. 



b. When the agar has solidified invert the dish and place it in 

 the incubator. 



REFERENCE. McF. 51. 



SPECIAL DIRECTIONS. Use sewage, putting a drop in a water 

 blank and using a loop or two of this. 



EXERCISE 50. QUANTITATIVE DETERMINATION OF ACIDS. 



GENERAL DIRECTIONS. 



a. Inoculate 5 test-tubes of dextrose bouillon (or milk) with an 

 acid-producing organism. 



b. Twenty-four hours later remove, with a sterile pipette, 5 cc. 

 of the medium from one of the tubes and titrate with a twentieth 

 normal potassium (or sodium) hydrate solution, using phenolphtha- 

 lien as an indicator. 



c. Make titrations as described above on each of the four suc- 

 ceeding days, using the same amount of culture each day. 



d. Plot the results, expressing the number of cc. of hydrate solu- 

 tion as ordinates and the daily intervals as abscissae. 



SPECIAL DIRECTIONS. Use B. coli and incubate at 38 C. 



EXERCISE 51. DETECTION OF NITRITES IN CULTURES. 



GENERAL DIRECTIONS. 



a. Make a culture of a reducing organism in a test-tube of the 

 nitrate solution (37 g.). 



b. Incubate at 28 C. for 1 week, add 1 cc. of each of following 

 solutions : 



1) Sulphanilic acid (para-amido benzenesulphonic acid) 0.5 gm. 

 Acetic acid (sp. gr. 1.04) 150 cc. 



2) a-amido-naphthalene acetate. Boil 0.1 gram of solid a-amido- 

 naphthalene in 20 cc. of water, filter the solution through a plug of 



