IMPORTANT PATHOGENIC BACTERIA 115 



(3) A few drops of a solution of o . i g. potassium or 

 sodium nitrite in 1,000 c.c. water. Rose color then 

 indicates the presence of indol only. 



The appearance of indol red depends on the pres- 

 ence of NO 2 . This is liberated by sulphuric acid 

 from nitrites, if these are produced by the organism. 

 If nitrites are not produced, a small amount of a nitrite 

 solution is added, which then furnishes the necessary 

 material for production of NO 2 . 



Perform these tests with all the organisms of the 

 intestinal group, and make control tests in sterile Dun- 

 ham's solution or sugar-free broth. 



4. Special study. Make a capsule stain of B. 

 aerogenes from 24-hour-old milk cultures. (For 

 method see p. 109.) 



The study of B. coli is of special importance in con- 

 nection with bacteriological analysis of water (see 

 Part IV). The presence of this organism in large 

 numbers indicates sewage contamination, and conse- 

 quently bacteria such as B. typhosus and B. dysen- 

 teriae may be present. 



EXERCISE 2. STUDY OF SUBGROUP II 

 THE HOG-CHOLERA, B. ENTERITIDIS, OR INTERMEDIATE GROUP 



Inoculate agar slants from laboratory cultures of B. 

 suipestifer, B. enteritidis (Gartner's bacillus), and 

 B. paratyphosus. 

 References 



B. cholerae suis: 



Moore, The Pathology of Infectious Diseases of Animals. 

 McFarland, Textbook of Bacteriology. 

 B. paratyphosus: 



Buxton, Jour. Med. Res., 1902, 7, p. 201. 



