154 ELEMENTS OF WATER BACTERIOLOGY 



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, pep- 

 tone solution, milk, and gelatin; of the dextrose 

 tubes made directly from the water all were con- 

 sidered 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 cen- 

 timeter and almost constantly in one-ten-thousandth 

 of a cubic centimeter. The Illinois and Michigan 

 canal proved almost as bad, giving positive results on 7 

 days out of 28 in dilutions of one in a hundred thousand 

 and on 28 days out of 32 in a dilution of one in ten 

 thousand. At Morris, 27 miles below Lockport, where 

 the canal enters the bed of the Desplaines River, and 

 9 miles below the entrance of the Kankakee, the 

 principal diluting factor, the numbers were so reduced 

 that positive results were obtained only on n days out 

 of twenty in one-thousandth of a cubic centimeter, on 

 20 days out of thirty in one-hundredth of a cubic centi- 

 meter, and on 20 days out of 23 in one-tenth of a cubic 

 centimeter. At Averyville, 159 miles below Chicago, 

 colon bacilli were isolated on only 4 days out of 27 in 

 one- tenth of a cubic centimeter, and on 13 days out of 

 31 in one cubic centimeter. A comparison with certain 

 neighboring rivers showed this to be about the normal 

 value for waters of similar character, as the following 

 table extracted from Professor Jordan's paper will show : 



