1 14 BACTERIOLOGICAL LABORATORY TECHNIC 



Various sugars are fermented by bacteria, and lactic, acetic, 

 and butyric acids are produced. Indol is also produced by many 

 bacteria (colon bacillus, cholera bacillus), and its presence in culture 

 is an important means of identifying different bacteria. The 

 organism to be studied must be grown in culture media known to 

 be free from indol. For this purpose, all meat extracts must be 



FIG. 35. Fermentation tube. (Williams.) 



excluded and a simple solution of peptone and salt, run into tubes 

 and sterilized, is used. After bacteria have grown in this media for 

 several days the indol produced, if it is produced, is detected by 

 adding a few drops of pure sulphuric acid. If a red color (nitroso- 

 indol) is not produced, a few drops of sodium nitrite solution 

 (.02 grams to 100 c.c. of water) must be added, and if a pink to deep 

 red color does appear it may be safely assumed that indol is present. 

 Ammonia is detected in culture by suspending a piece of paper 



