THE COLON-TYPHOID SEEIE8 333 



of the other species may be determined by reference to the 

 key given below.^ 



Bacteeium 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 



>Key to the More Important Species or the Colon Subgroup of 

 THE Genus Bacterium 



A. Eatio of CO2/H2 = 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. 



h. No acid or gas from salicin. 



2. Bacterium acidi lactici. 



2. Acid and gas from sucrose. 



a. Motile. 



3. Bacterimm communior. 



b. Nonmotile. 



(1) Acid and gas in salicin. 



4. Bacterium neapolitanum. 



(2) No acid or gas in salicin. 



5. Bacterium coscordba. 



B. Eatio of COjH/j = 2/1, Voges-Proskauer test positive, methyl red 

 test negative. 



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

 glycerol. 



6. Bacterium cloacce. 



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

 and glycerol. 



7. Bacterium aerogenes. 



