QUANTTTATIVE EXAMINATION OF WATER 47 



tilated dishes and by the presence of a pan of water in 

 the incubating chamber. 



According to American and German practice, plates 

 made for sanitary water analysis are counted at the 

 end of 48 hours. The English Committee appointed 

 to consider the standardization of methods for the 

 Bacterioscopic Examination of Water (1904) fixed the 

 time at 72 hours. French bacteriologists, and some 

 Germans (Hesse and Niedner, 1906), still recommend 

 longer periods, and the following table from Miquel 

 and Cambier (Miquel and Cambier, 1902) shows that 

 many bacteria fail to appear in our ordinary procedure. 

 It is, however, in the main, the characteristic water 

 bacteria which develop slowly, sewage bacteria almost 

 without exception being rapid growers. The longer 

 period of incubation is, therefore, not only inconvenient, 

 but imdesirable, since it obscures the difference between 

 good and bad waters. 



EFFECT OF THE LENGTH OF INCUBATION OF WATER 

 BACTERIA IN GELATIN UPON THE NUMBER OF 

 COLONIES DEVELOPING 



(Miquel and Cambier, 1902) 



