8 INFECTIONS OF THE DIGESTIVE TRACT 



mo till ty in members of young surface colonies. 1 They 

 do not retain the Gram stain. The members of the 

 B. lactis aerogenes group are distinguished from those 

 of the B. coli group by unimportant morphological 

 differences. More significant differences exist in respect 

 to biochemical characters. Among these differences 

 are a somewhat greater ability to form gas on sugar 

 media, a more rapid coagulative action on milk (often 

 with capsule formation), the ability to make gas from 

 potato starch, the more frequent failure to make indol, 

 and the greater luxuriance of growth on gelatin. In 

 general, then, the fermentative activities of B. lactis 

 aerogenes are somewhat greater than those of the B. 

 coli group, while the putrefactive powers are distinctly 

 less. Harden 2 has lately shown that there is a constant 

 difference in the behavior of B. lactis aerogenes and B. 

 coli when grown anaerobically on sugar bouillon, in 

 regard to the ratio of alcohol and acetic acid produced. 

 This difference appears to strengthen the right of B. 

 lactis aerogenes to be regarded as a distinct organism from 

 B. colij although the relationship between the two is 

 close. The behavior of these two groups toward other 

 organisms is probably very similar, but as the antago- 



1 For a detailed discussion of B. coli communis see Escherich 

 (Th. Escherich u. M. Pfaundler, "Bacterium coli commune," 

 Kolle & Wassermann's " Handbuch der pathogenen Mikroorganis- 

 men," p. 334, 1902) ; also Theobald Smith ("Note on Bacillus Coli 

 Communis and Related Forms"), Amer. Journ. of the Med. Sci., 

 September, 1895, who gives important data as to fermentative 

 characters. 



2 "The Chemical Action on Glucose of the Lactose-fermenting 

 Organisms of Faeces," Journ. of Hyg., v, p. 488, 1905. 



