The Significance of B. Coli in Water. 125 



At one time Professor Jordan was himself somewhat 

 sceptical as to the value of the colon test, for he stated in 

 1890 (Jordan, 1890) that he had found, "in spring-water 

 which was beyond any suspicion of contamination, bac- 

 teria which in form, size, growth on gelatin, potato, etc., 

 were indistinguishable from B. coli commune." In the 

 Chicago studies of self-purification (Jordan, 1901) the 

 analyses were made quantitative by the examination of 

 numerous measured samples, fractions of the cubic centi- 

 meter; and the method employed was enrichment, either 

 in dextrose-broth fermentation tubes or in phenol broth, 

 with subsequent plating on litmus lactose agar. The 

 cultures isolated were tested as to their behavior in dextrose 

 broth, peptone solution, milk, and gelatin; of the dextrose 

 tubes made directly from the water all were considered 

 positive which gave more than 20 per cent gas in the 

 closed arm, with an appreciable excess of hydrogen. The 

 results were very significant. In fresh sewage a positive 

 result was obtained about one-third of the time in one 

 one-hundred-thousandth of a cubic centimeter and almost 

 constantly in one ten-thousandth of a cubic centimeter. 

 The Illinois and Michigan canal proved almost as bad, 

 giving positive results on seven days out of twenty-eight in 

 dilutions of one in one hundred thousand and on twenty- 

 eight days out of thirty-two in a dilution of one in ten 

 thousand. At Morris, twenty-seven miles below Lockport, 

 where the canal enters the bed of the Desplaines River, and 

 nine miles below the entrance of the Kankakee, the 



