100 BACTERIOLOGICAL ANALYSIS ' LESSON iv 



(10) Subsequently select those cultures which apparently 

 consist 1 of typhoid bacilli or the Bacterium coli commune, 

 and confirm the diagnosis by 



(a) microscopical examination ; 

 (6) milk cultures (at 38-5 C.) ; 

 (c) growth on potatoes (at 38'5 C.) 



For differences between the bacillus of typhoid fever 

 and the Bacterium coli commune vide p. 53. 



(11) Test also for the presence of Indol. 



(a) Prepare broth cultures and keep them at 38 '5 C. 

 for two to fourteen days. 



(b) Now add 1 cc. of a solution of potassium nitrite 

 (containing -02 grammes in 100 cc.), and then a few 

 drops of pure sulphuric acid. 



If Indol is present, the liquid in the tube turns red. 



The Bacterium coli commune gives a positive result, 

 the bacillus of typhoid fever a negative result. 



