126 



Elements of Water Bacteriology. 



principal diluting factor, the numbers were so reduced that 

 positive results were obtained only on eleven days out of 

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

 days out of thirty in one-hundredth of a cubic centimeter, 

 and on twenty days out of twenty-three in one-tenth of a 

 cubic centimeter. At Averyville, one hundred and fifty- 

 nine miles below Chicago, colon bacilli were isolated on 

 only four days out of twenty-seven in one-tenth of a cubic 

 centimeter, and on thirteen days out of thirty-one 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. 



NUMBER OF B. COLI PRESENT IN CERT^AIN RIVER 



WATERS. 



(JORDAN, igoi.) 



These results harmonize rather closely with those pre- 

 viously recorded by Brown and Fuller, and inditfate that 

 in the larger rivers where the proportionate pollution is 



