BACILLUS COLI COMMUNIS 77 



next exercise, when they should be examined again. If the gas 

 formation is then completed, determine the quantity in each 

 tube and the ratio of CO 2 to H. 



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

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

 first dilution. 



Inoculate Group D of media with the paracolon bacillus 

 from a culture furnished. 



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

 indol if it is at least 72 hours old. Read the chapter on this 

 organism in the text-books. 



115. The indol (cholera-red) test. Add i cc. of a .01% solu- 

 tion (fresh) of potassium nitrite and a few drops of concen- 

 trated 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. 



Ring method. When there is a small quantity of indol it 

 can be detected more readily by the " ring method." Add i 

 or 2 cc. of a 2 5 % solution of H 2 SO 4 , allowing it to run down 

 on the inside of the tube containing the culture. Add i cc. 

 of potassium nitrite. If indol is present, a pinkish ring will be 

 observed between the layer of acid in the bottom of the tube 

 and the culture above it. 



116. 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 cc. 



Dissolve the peptone and salt in the water, distribute it 

 in the tubes (5 cc. each), and sterilize the same as bouillon. 



