THE COLON-TYPHOID SEEIES 333 



of the other species may be determined by reference to the 

 key given below. 1 



BACTERIUM COLI 



This organism is taken as a type of the entire colon group. 

 The other organisms belonging to the subgroup may be 

 differentiated from it by means of physiological reaction. 

 Inasmuch as most of them are intestinal forms, differentia- 

 tion is usually not desired or necessary. In recent years 

 differentiation of Bacterium aerogenes from Bacterium coli 

 has been found to be of some importance in water analysis, 

 inasmuch as the former seems to be much more widely dis- 

 tributed in nature and is not therefore as delicate an index 

 of fecal contamination. 



Synonym. Bacillus coli communis. Colon bacillus. 



Distribution. Bacterium coli is normally present in the 

 alimentary tract, particularly in the colon, of man and 

 most animals. It is apparently not widely distributed in 



1 KEY TO THE MORE IMPORTANT SPECIES OF THE COLON SUBGROUP OF 



THE GENUS BACTERIUM 



A. Ratio of CO 2 /H 2 = 1/1, Voges-Proskauer test negative, methyl red 

 (Clark and Lubs test) positive. 



1. No acid or gas from sucrose. 



a. Acid and gas from salicin. 



1. Bacterium coli. 



fe. No acid or gas from salicin. 



2. Bacterium acidi lactici. 



2. Acid and gas from sucrose. 



a. Motile. 



3. Bacterium communior. 

 Z>. Nonmotile. 



(1) Acid and gas in salicin. 



4. Bacterium neapolitanum. 



(2) No acid or gas in salicin. 



5. Bacterium coscoroba. 



Ratio of CO 2 H/ 2 = 2/l, Voges-Proskauer test positive, methyl red 

 test negative. 



1. Motile, liquefying gelatin, no gas or acid from starch or 

 glycerol. 



6. Bacterium cloaca. 



2. Nonmotile, not liquefying gelatin, gas and acid from starch 

 -and glycerol. 



7. Bacterium aerogenes. 



