182 ELEMENTS OF WATER BACTERIOLOGY 



paired. Its power to reduce nitrates may be lost, or 

 on the other hand, may be increased; its power to 

 produce indol may be lost, or on the other hand, it 

 may be increased; its power to coagulate milk, even, 

 is sometimes reduced, although seldom entirely lost; 

 its power to ferment carbohydrates may be altered 

 so that the amount of gas obtained in a fermentation- 

 tube, as well as its ratio of H to C02, is quite abnormal. 

 But in spite of all these facts, the bacillus tested may 

 have been originally a true Bacillus coli." 



The results obtained by Peckham (1897) suggest 

 that the indol reaction in particular is highly variable. 

 By successive daily transfers in peptone broth she was 

 able to increase the amount of indol produced by nor- 

 mal B. coli, and by a longer continuance of the same 

 process to again weaken and abolish the power of form- 

 ing it. Gas formation too was slackened in the cul- 

 tures grown for too many transfers in the same medium. 

 Horrocks (1903) found that B. coli kept in unsterilized 

 well-waters and tap waters and in sterilized sewage and 

 Thames water for 2 to 3 months showed only a feeble 

 indol production and a delayed action on milk and 

 neutral red. These modified forms are sometimes 

 called " atypical B. coli," or " para-colon bacilli," and 

 Vincent gives them the picturesque name, " microbic 

 satellites of B. coli." 



' Such anomalies are most frequent with cultures 

 freshly isolated from water, and they may often be 

 avoided, as Fuller and Johnson (1899) have shown, 

 by subjecting the organism to a process of preliminary 

 cultivation. For this purpose the American Public 



