146 



Elements of Water Bacteriology. 



DEXTROSE BROTH FERMENTATION IN 185 SAMPLES bF 



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. 



A new presumptive test has recently been suggested 

 by Jackson (1906), which promises more satisfactory 

 results than dextrose broth. MacConkey (1900) long ago 

 suggested the use of media containing bile salts (sodium 

 taurocholate) for the differentiation of B. coli and B. typhi, 

 and bile-salts media have been used by various English 

 observers (MacConkey, 1901; MacConkey and Hill, 1901) 

 for the isolation of sewage bacteria. Jackson studied 

 the action of various bile media and showed their selec- 

 tive inhibitory action in the striking table quoted on page 

 147. His important contribution to the subject, however, 

 was the discovery that ox bile itself could be used as a 

 culture medium, and that it was easier to prepare, cheaper 

 and more effective than combinations of meat infusion 

 with the purified bile salts. 



