88 Elements of Water Bacteriology. 



forms gas and acid in saccharose media and the other does 

 not. Winslow and Walker (1907) have recently 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 char- 

 acteristic of dextrose and lactose. The name B. coli 

 communior was given to the saccharose fermenting type 

 by Durham (1901); as Ford (1903) suggests, this name 

 should be changed to B. communior in deference to the 

 established binomial rule of biological nomenclature. 

 The term, B. coli, should, in strictness, apply only to those 

 forms which fail to attack the ketonic sugars. For 

 practical sanitary purposes, however, the distinction is 

 unimportant. Throughout this book, therefore, both B. 

 communior and B. coli, proper, will be considered together 

 under the name of the colon bacillus, which is almost 

 universally applied to both. 



The litmus-lactose-agar plate (Wurtz, 1892), as noted 

 in Chapter IV, furnishes one ready method for the iso- 

 lation of B. coli from water, and it was used by Sedg- 

 wick and Mathews for the purpose as early as 1893 

 (Mathews, 1893). The process is based upon the fact 

 already alluded to, that B. coli readily ferments lactose 

 with the formation of acid. If, therefore, plates are made 

 with agar containing both lactose and litmus, the colon 

 colonies develop as red spots in a blue field. Since 

 organisms other than B. coli may also develop red colonies, 

 it is necessary to examine the red colonies further. This 



