QUANTITATIVE EXAMINATION OF WATER 31 



to gelatin count to be 1.7 to i.o for sewage, and 4.8 

 to i.o for sand filter effluent. With waters of still 

 better quality the ratio goes up higher, reaching a 

 maximum when the bacteria which increase and 

 multiply in water are most abundant. Miiller (1900) 

 found, for example, that water which normally showed 

 six times as many bacteria on Nahrstoff agar as on 

 gelatin might give a Nahrstoff-gelatin ratio of 20-30 

 after it had been standing for some time in the supply 

 pipes. The table below, taken from the valuable 

 paper by Gage and Phelps (1902), shows strikingly 

 the different Nahrstoff-agar ratios for waters of 



TABLE SHOWING PERCENTAGES OF BACTERIA DEVELOP- 

 ING ON REGULAR AGAR AND NAHRSTOFF AGAR 

 FOR DIFFERENT CLASSES OF WATERS 



(GAGE AND PHELPS, 1902) 



Regular Agar 



Narhstoff Agar 



