192 ELEMENTS OF WATER BACTERIOLOGY 



tion of 92 colon-like bacilli from 50 samples of milk, 

 8 of sewage and i of kefir they found 43 of the possible 

 combinations. 



Copeland and Hoover (1911) have recently urged 

 the importance of these fermentative reactions in the 

 rarer carbohydrates in the study of the colon group. 

 They confirm the positive Voges and Proskauer reaction 

 reported by other observers for B. lactis-aerogenes and 

 B. cloacae and point out that B. lactis-aerogenes is 

 the only form in a considerable series studied which 

 gives a brown coloration in aesculin media in one day. 

 On the other hand they record a positive dulcite reac- 

 tion for B. lactis-aerogenes and B. cloaca3 which is 

 highly confusing and makes it difficult to interpret 

 their results. Both these names according to the usage 

 of MacConkey, which has been accepted for the past 

 five years, are applied to dulcite-negative saccharose- 

 positive organisms. 



Still another classification of the colon group is Jack- 

 son's modification of MacConkey's scheme in which 

 MacConkey's four primary groups are symmetrically 

 subdivided according to reactions in mannite and rafn- 

 nose with motility, indol production, nitrate reduc- 

 tion, liquefaction of gelatin and coagulation of milk as 

 secondary differential characters (Jackson, 1911). Under 

 each of the four groups, B. communior (MacConkey's 

 B. neapolitanus) , B. communis (MacConkey's B. coli), 

 B. aerogenes (MacConkey's Group IV), and B. acidi- 

 lactici, he distinguishes four types, A (fermenting 

 both mannite and raffinose, B (mannite +, raffinose ), 

 C (mannite , raffinose -}-), and D (fermenting neither 



