58 PATHOGENIC BACTERIA. 



in culture-media, prepared for them, into ammonia and 

 nitrogen. To the horticulturist this is a matter of much 

 interest. Wiuogradsky has found a specific nitrifying 

 bacillus in soil, and asserts that the presence of ordinary 

 bacteria in the soil causes the reduction of no nitrites so 

 long as his special bacillus is withheld. 



Reduction of nitrites can be determined by the use of 

 a nitrate broth made by dissolving in iooo c.c. of water 

 i gram of peptone and 0.2 gram of potassium nitrate. 

 The ingredients are dissolved, filtered, then deposited in 

 tubes, and sterilized. As nitrites and ammonia are com- 

 monly present in the air and are taken up by fluids, it is 

 always well to control the test made by an uninoculated 

 tube tested with the reagents in the same manner as 

 the culture. 



Two test solutions are employed: 1 



!Boil, cool, filter, and add 156 

 c.c. of dilute (1-16) hydric 

 acetate. 

 II. Sulphanilic acid, 0.5 gram. 



Hydric acetate, diluted, 150.0 c.c. 



Keep the solutions in glass-stoppered bottles and mix 

 equal parts for use at the time of employment. 



About 3 c.c. of the culture and an equal quantity of 

 the uninoculated culture fluid are placed in test-tubes 

 and about 2 c.c. of the test fluid slowly added to each. 

 The development of a red color indicates the presence of 

 nitrites, the intensity of the color being in proportion to 

 the quantity of nitrites present. If a very slight pinkish 

 or reddish color in the uninoculated culture fluid and a 

 deeper red in the culture develop, it shows that there was 

 a small amount of nitrites present already, but that more 

 have been produced by the growth of the bacteria. 



The presence of ammonia in either fluid is easily deter- 

 mined by the immediate development of a yellow color or 

 precipitate when a few drops of Nessler's solution (see 

 text-books upon Chemistry) are added. 



1 Journal of the American Public Health Association, 1 888, p. 92. 



