BACILLUS CQLI COMMUNIS 73 



Make two gelatin plates from the bouillon culture. In mak- 

 ing these plates use a tube of sterilized distilled water for the 

 first dilution. 



Test the culture in sugar-free bouillon for the presence of 

 indol. Read chapter on this organism in text-book. 



116. The Indol (Cholera Red) Test Add i c.c. of a .01% 



solution (fresh) of potassium nitrite and a few drops of con- 

 centrated sulphuric acid to the culture in sugar-free bouillon. 

 A pinkish color indicates the presence of indol. In an old 

 (3 to 5 day) culture the reaction is usually stronger than in a 

 more recently made one. 



If sugar-free bouillon is not at hand, a tube of Dunham's 

 solution can be used instead with quite good results. 



117. Dunham's Peptone Solution. — This is simply a solution 

 of peptone and sodium chloride in distilled water. The for- 

 mula is as follows : — 



Dried peptone i gram. 



Sodium chloride 0.5 gram. 



Distilled water 100 c.c. 



. Dissolve the peptone and salt in the water and distribute it 

 in the tubes (7 c.c. each) and sterilize the same as bouillon. 



