BACILLI OF THE COLON-TYPHOID-DYSENTERY GROUP 637 



short bacillus form, failure of spore formation, facultative anaerobiosis, 

 growth on gelatin without liquefaction in fourteen days, Gram-negative 

 stain and fermentation of dextrose and lactose with gas formation. 

 They add that there is a positive reaction with esculin. 



The organisms which are placed under the Colon group in this report 

 are the B. Coli communis described above, the B. Coli communior 

 of Durham, the B. aerogenes of Escherich, and B. acidi-lactici of Htieppe. 

 The chief differential characteristics are as follows : 



Individual descriptions of these organisms follow: 



B. COLI COMMUNIOR. This organism first described by Durham 

 was called Communior by him because of his belief that it was more 

 abundant in the human and animal intestine than the Communis type. 

 It possesses all the characteristics of the Colon group. It is a Gram- 

 negative bacillus, motile, non-sporulating, and morphologically indis- 

 tinguishable from the Communis variety. It does not liquefy gelatin, 

 it produces indol from pepton, coagulates and acidifies milk, and grows 

 characteristically upon agar and potato. It differs from B. coli com- 

 munis in that it produces acid and gas from saccharose as well as from 

 dextrose and lactose, whereas the former does not form acid or gas from 

 saccharose. Several varieties have been described by Melia, and by 

 A very. The Melia type differs from the ordinary variety in not pro- 

 ducing indol. The Avery type did not coagulate milk. 



B. LACTIS AEROGENES. Bacillus lactis aerogenes is the type of a 

 group which is closely similar to the colon group and often distin- 

 guished from it with difficulty. It was first described in 1885 by 

 Escherich 19 who isolated it from the feces of infants. Since then it has 

 been learned that this bacillus is almost constantly present in milk, 

 and, together with one or two other microorganisms, is the chief cause 

 of the ordinary souring of milk. Apart from its occurrence in milk, 

 moreover, the bacillus is widely distributed in nature, being found in 

 feces, in water, and in sewage. 



19 A. P. H. A. Standard Methods of Water Analysis, 1915. 



