BACILLUS COLI 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 S 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 arid salt in the water and distribute it 

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



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