QUANTITATIVE BACTERIOLOGICAL EXAMINATION. 21 



TABLE SHOWING PERCENTAGES OF BACTERIA DEVELOPING ON REGU- 

 LAR AGAR AND ON NAHRSTOFF AGAR FOR DIFFERENT CLASSES OF 

 WATERS. (GAGE AND PHELPS, 1902.) 



REGULAR AGAR. 



NAHRSTOFF AGAR. 



The procedure for the quantitative determination of 

 bacteria in water consists, in brief, in mixing a definite 

 amount of a suitably collected specimen of the water with 

 a sterile solidifiable culture medium and allowing it to 

 develop for a sufficiently long time to permit reproduction 

 of the bacteria and the formation of visible colonies which 

 may be counted. The process is divided naturally into 

 four stages sampling, plating, incubating, and counting 

 which will now be discussed. 



Sampling. All samples of water for bacteriological 

 examination should be collected in clean, sterile bottles 

 with wide mouths and glass stoppers, preferably of the flat 



