THE COLON GROUP OF BACILLI 101 



great resistance against antiseptic substances, B. coli 

 is less susceptible to phenol than are many other forms, 

 especially certain water-bacteria. 



We have spoken as if Bacillus coli were a single defi- 

 nite organism. As a matter of fact it is a name applied 

 to a considerable group of distinct forms which may 

 be split up almost as far as one wishes by the applica- 

 tion of various biochemical tests. The " colon bacillus," 

 as we have pointed out, usually does not liquefy gelatin 

 and reduces neutral red and coagulates milk, and 

 produces indol; but there are closely allied forms which 

 differ from the type in one or more of these respects. 

 The colon group, as Smith (1893) long ago pointed 

 out, may first be divided into two distinct subtypes 

 according to the action of the organisms upon saccharose. 

 One subtype forms gas and acid in saccharose media 

 and the other does not. Winslow and Walker (1907) 

 have found that those strains which ferment saccharose 

 attack raffinose also, and point out that these two 

 sugars which behave alike are those which lack the 

 aldehyde grouping characteristic of dextrose and lactose. 

 The application of tests in other carbohydrate media, 

 such as dulcite, adonite, inulin, etc., make it possible 

 to recognize perhaps a hundred distinct types each 

 characterized by a particular combination of reactions. 



The results obtained by the " colon test " will of 

 course depend largely upon the definition of what a 

 colon bacillus is; and there is marked disagreement 

 upon this point among different observers. Konrich 

 (1910) tabulates the tests used by 34 different workers, 

 All of them defined the colon bacillus as a Gram- 



