THE BACILLUS COLI 461 



and acid and curd in milk (ac). The majority of the 

 B. coli of fresh faeces give this flaginac reaction and do 

 not ferment saccharose. The colonies on Conradi- 

 Drigalski agar are large and red. (see " Water ") The 

 B. coli does not give the Voges-Proskauer reaction 

 (p. 413). 



Bacteriologists usually make use of the following tests 

 for the differentiation of B. coli : (1) Morphology, 

 (2) motility, (3) Gram staining, (4) characters of growth 

 and of colonies on gelatin, (5) non-liquefaction of gelatin, 

 (6) action on milk, (7) indole formation, (8) fermentation 

 of glucose, (9) fermentation of lactose, (10) action on 

 neutral red. MacConkey suggests that instead of tests 

 Nos. 4, 6, 7, 8, and 10, the following should be substituted : 

 (a) fermentation of dulcitol, but not of adonitol and 

 inulin ; (6) the Voges-Proskauer reaction. 



The thermal death-point of the organism is about 

 60 C. with an exposure of ten minutes. The B. coli will 

 grow freely in a slightly acid medium, and in media 

 containing as much as 0-15 per cent, of carbolic acid. In 

 this respect it is a more resistant organism than 

 B. typhosus. 



Chemical products. The acids produced are mainly 

 Isevo-lactic acid with some dextro-lactic acid from glucose, 

 Isevo-lactic acid only from mannitol ; also acetic, formic 

 and succinic acids, and alcohol. According to Harden, 

 B. coli attacks glucose in a characteristic manner, each 

 molecular proportion of sugar yielding half a molecular 

 proportion of acetic acid and of alcohol, and one molecular 

 proportion of lactic acid, together with a small amount of 

 succinic acid, and gaseous carbonic acid and hydrogen. 1 

 Nitrates are reduced to nitrites. 



No toxin, or a trace only, is formed in cultures, but 

 the dead bacilli are toxic and pyogenic, and a toxic fluid is 



1 See also Revis, Centr. f. Bakt. (2 te Abt.), xxvi, 1910, p. 161. 



