202 BACTERIOLOGY. 



ma, while still others merely reduce the nitrates to 

 nitrites. These reducing functions are encouraged and 

 may be demonstrated by cultivating the bacteria in pep- 

 tone solution containing potassium nitrate. 



Test for Nitrites. The method of Griess,as modified by 

 Ilosvay, is quite satisfactory. These reagents are required : 

 (a) Naphthylamine, 0.1 gramme. 



Distilled water, 20.0 c.c. 



Acetic acid (25 per cent, solution), 1 50.0 " 

 (6) Sulfanilic acid, 0.5 gramme. 



Acetic acid (25 per cent, solution), 150.0 c.c. 



In preparing solution a the naphthylamine is dis- 

 solved in 20 c.c. of boiling water, filtered, allowed to 

 cool, and mixed with the dilute acetic acid. Solutions 

 a and b are then mixed. It is best prepared as needed, 

 though it may be preserved for some time in a glass- 

 stoppered bottle. 



In testing for nitrites the reagent is added in the 

 proportion of one volume of reagent to five volumes 

 of culture. When nitrites have been formed a deep- 

 red color appears in a few seconds. If no nitrites have 

 been formed the culture remains colorless. In testing 

 cultures it is always necessary to control the results by 

 blank tests on a portion of the same medium that had 

 not been inoculated, as some of the ingredients of the 

 medium may have contained nitrites. 



Another test for the formation of nitrites is a mixt- 

 ure of starch and potassium iodide, as follows : 



Starch, 2.0 grammes. 



Potassium iodide, 0.5 



Water, 100.0 c.c. 



