QUANTITATIVE EXAMINATION OF WATER 33 



and qualitative bacteriological examination of water 

 for sanitary purposes. These reports have had a far- 

 reaching effect in simplifying and imifying the methods 

 of water analysis. Similar results have followed from 

 the work of the English Committee appointed to con- 

 sider the Standardization of Methods for the Bac- 

 terioscopic Examination of Water which reported in 

 1904, although this committee unfortunately did not 

 consider the process of media making in great detail. 

 The last report of the American Committee on Standard 

 Methods (191 2) will be adhered to in this and succeed- 

 ing chapters unless otherwise specifically stated; and 

 that portion of its report which deals with methods of 

 making media will be found in full in the appendix. 



Standard Procedure for Quantitative Determination of 

 Bacteria in Water. 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 incubating it for a sufficiently long time 

 to permit reproduction of the bacteria and the forma- 

 tion of visible colonies which may be coimted. The 

 process is dixided naturally into four stages — sampling, 

 plating, incubating, and counting. 



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 mushroom t>^e. It is desirable that these bottles 

 should have a capacity of at least 100 c.c. 



They should be cleaned thoroughly before using, by 

 treatment with sulphuric add and potassium bichromate 



