112 ELEMENTS OF WATER BACTERIOLOGY 



indicates that the result of the dextrose broth test is 

 markedly influenced by the factor of temperature. Their 

 work consisted in the examination of 185 samples of 

 water from 90 different sources, ponds, brooks, pools, 

 wells and springs in five different States, Maine, New 

 Hampshire, Massachusetts, Michigan and Virginia, at 

 three different seasons of the year. All the waters 

 examined were, as far as could be determined, free 

 from specific pollution, although washings from roads 

 or pastureland might have had access to some of them. 

 Most of the sources were undoubtedly unpolluted and 

 the examination of 119 samples for B. coli yielded only 

 12 positive results. The presumptive test, however, 

 was obtained in a large proportion of the cases, and 

 much more often in summer than in winter or spring, 

 as indicated in the table below. 



DEXTROSE BROTH FERMENTATION IN 185 SAMPLES OF 

 NORMAL WATERS AT DIFFERENT SEASONS 



(WINSLOW AND PHELPS) 

 Percentage of Positive Results 



The Ann Arbor waters in this series included a number 

 of driven wells and the Mt. Desert sources were mountain 

 brooks and ponds of the highest sanitary quality. 



