Isolation of the Colon Bacillus. 95 



formation after twenty-four hours at 37 degrees, a litmus- 

 lactose-agar plate is made and the other diagnostic tests 

 applied. 



The Committee on Standard Methods of Water Analysis 

 (1905) recommends that "for ordinary waters, o.i, i.o, 

 and 10.0 c.c. shall be used for the colon test. For sewage 

 and highly polluted surface-waters smaller quantities shall 

 be used; and for ground- waters, filtered-waters, etc., the 

 quantities shall be larger, if necessary, to obtain positive 

 results." 



Our own experience has been that it is not specially 

 advantageous to apply the colon test in large samples, 

 since the significance of B. coli when present in numbers 

 less than i per c.c. is extremely doubtful. On the other 

 hand, the danger of overgrowth is greatly increased in 

 large samples and negative results may often be obtained 

 when the organisms are really present. Hunnewell and 

 one of us (Winslow and Hunnewell, i9O2 b ) found that of 

 48 samples of certain polluted river waters, 18 showed B. 

 coli when i c.c. was inoculated directly into dextrose broth, 

 while in only 4 cases was a positive result obtained after 

 preliminary treatment of 100 c.c. in carbol broth. In 153 

 samples from presumably unpolluted water, B. coli was 

 found 5 times in i c.c. and n times by the examination of 

 the larger sample. The authors, therefore, concluded as 

 follows : 



"It appears evident that the use of large samples in 

 applying the colon test to the sanitary analysis of drink- 



