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PUBLIC HEALTH BACTERIOLOGY 



Dr. A. C. Houston (Director of Water Examination to 

 the Metropolitan Water Board, London), in addition 

 to gelatin and agar media, for enumeration, also uses 

 MacConkey's neutral-ral, fo'le-salt, peptone, lactose 3 gar 

 (called rebipelagar for brevity). This is similarly inocu- 

 lated and plated and incubated at 37 . The colonies are 

 counted on gelatin on the third day, and on agar and rebi- 

 pelagar after twenty to twenty-four hours. 



The following table, culled from Dr. Houston's reports, 

 serves to illustrate the ratios of the various counts : 



RAW RIVER THAMES WATER. 



Average Number of Microbes per c.c. in Comparable Samples, 



Tested on Three Media ; with Ratios. 



Gelatin at 2o-22 C. ; colonies counted on third day. 

 Agar and Rebipelagar at 37 C. ; counted after twenty to twenty- 

 four hours. 



This further table (curtailed) from Houston's Fifth 



