BACTERIA OF WATER AND SEWAGE 57 



numerous subcultures are made from it. The following gives 

 those which will be of diagnostic value : 



3. Gelatin. B. coli grows well without liquefying the medium. 



4. Milk. In milk it produces acid and forms a curd in twelve 

 to twenty -four hours at 37.5 C. 



5. Nitrate solution. When grown on Giltay and Aberson's 

 or other nitrate solution it reduces nitrates to nitrites. The 

 solutions are kept twelve to twenty-four hours at 37.5 C. 



6. Sugar bouillon. In sugar bouillon gas is evolved. Analysis 

 shows the ratio PI : CO., : : 2 : 1. Incubate twelve to twenty -four 

 hours at 37.5 C. 



7. Dunham's solution. Indol is produced when B. coli grows 

 on Dunham's solution (Exercise 37). Incubate tubes three or 

 four days at 37.5 C. ; then test for indol. 



Exercise 82. Study of Characters of Bacillus coli 



If the preceding exercise has been omitted, make studies of 

 pure cultures of B. coli on the various media there described. 

 Make stained preparations with carbol-fuchsin and determine 

 its reaction to Gram's stain. 



Exercise 83. Study of Bacillus proteus vulgaris 



Members of the so-called proteus group of bacteria are com- 

 monly found in putrefying substances. Their decomposing action 

 is marked by a very foul odor and an alkaline reaction. Their 

 presence in w T ater does not always indicate sewage pollution, but 

 pollution is very probable if they occur in conjunction with the 

 colon bacillus. 



Make cultures on agar slope, gelatin stab, milk, and potato. 

 Study the " swarming islands " with a magnification of 60 x in 

 colonies in gelatin plates. Make stained preparations with carbol- 

 fuchsin and determine the relation of this organism to G ram's 

 stain. 



Study the fermenting activity in shake cultures of dextrose 

 agar and in fermentation tubes of dextrose bouillon. 



Examine cultures on Dunham's solution for indol. 



