Isolation of the Colon Bacillus. 93 



dextrose broth. When a large proportion of sewage is 

 present the colon bacilli are fresh from the intestine and 

 apparently able to resist the antiseptic salts. On the other 

 hand, the large numbers of other bacteria present make 

 the danger of overgrowths particularly great. It is possible, 

 however, that direct plating on litmus lactose agar may 

 prove to be preferable, even to the bile enrichment method, 

 for waters of this class. With waters of fair quality, such 

 as those with which we ordinarily deal in sanitary water 

 analysis, lactose bile is open to the same objection as 

 phenol broth, though in less degree. It inhibits not only 

 the overgrowing forms but the weaker representatives of 

 the B. coli group itself; and the net effect is to diminish 

 positive results. In an examination of 176 'surface waters 

 in eastern Massachusetts, using lactose bile and dextrose 

 broth in parallel for preliminary enrichment, the authors 

 obtained 64 positive results by the former method against 

 70 by the latter. Longley and Baton (1907), from their 

 work on Potomac water, concluded that "the value of 

 the test with the bile lactose on unpolluted or slightly 

 polluted water, such as we have to deal with the greater 

 part of the time, is uniformly less than with dextrose broth, 

 except in the larger quantities of water. " 



The same objection applies to other enrichment methods 

 which involve the use of antiseptic conditions to check 

 the development of overgrowing bacteria. Eijkman 

 (1904) suggested incubation at 46 degrees as furnishing a 

 more rapid differentiation between good and polluted 



