VAEIETIES OF COLON BACILLI 175 



stration is both burdensome and needless. Motility.is a 

 fluctuating and uncertain property and one which 

 frequently requires repeated preliminary cultivations 

 to make manifest. Furthermore, non-motile colon bacilli 

 are common in the intestine and are probably as charac- 

 teristic of pollution as the motile forms. 



McWeeney (1904) found non-motile B. coli abundant 

 in faeces and observed cases where the organisms were 

 motile at 20 and not at 37. He quotes Stocklin as hav- 

 ing found 116 non-motile strains among 300 otherwise 

 normal B. coli from faeces. Evidence that non-motile 

 bacteria, otherwise resembling B. coli, occur in unpol- 

 luted water would furnish the only basis for requiring 

 this test as a routine procedure. No such evidence exists. 

 The great body of data which connects the presence of 

 B. coli with pollution includes all B. coli whether motile 

 or not, since scarcely any bacteriologists observe this 

 property in actual practice. 



Howe (1912) has recently come to the conclusion that 

 motility has no diagnostic value. MacConkey, however 

 (MacConkey, 1909), after carefully reviewing the various 

 characters suggested for use in studying colon bacilli, 

 retains this one as important. He recommends that it be 

 made in a drop of a 6-hour broth culture on an ordinary 

 slide with a J-inch objective and dark ground illumina- 

 tion. Failure to show motility indicates in particular 

 B. lactis-aerogenes and B. pneumonias of his classifica- 

 tion (see p. 191). 



Coagulation of milk is one of the most generally ac- 

 cepted tests for the colon group; and as a rule most 

 lactose fermenting forms give a positive reaction. The 



