32 ELEMENTS OF WATER BACTERIOLOGY 



various grades of purity. It is obvious from all these 

 facts that the effect of using the Nahrstoff medium 

 is to increase disproportionately the bacterial counts 

 obtained from purer waters and thus to diminish the 

 difference in bacterial content between normal and 

 contaminated sources. The ordinary agar and gelatin 

 media, on the other hand, are adapted to the growth 

 of intestinal and putrefactive forms and, therefore, 

 serve best the prime object of bacteriological water 

 examination. 



The first requisite in a procedure for water analysis 

 is, then, that it should be adapted to the end in view, 

 the differentiation of pure and contaminated waters. 

 The second and equally important requirement is that 

 the procedure should be a standard one, so that results 

 obtained at different times and by different observers 

 may be comparable. In this respect the work of G. W. 

 Fuller, G. C. Whipple, and other members of the 

 Committee on Standard Methods of the American Public 

 Health Association has placed the art of quantitative 

 water analysis in this country in a very satisfactory 

 state by contrast with the varying practices which 

 prevail in England and Germany. The first report on 

 this question was made in 1897 (Committee of Bac- 

 teriologists, 1898). A permanent Committee on Stand- 

 ard Methods was then formed which reported in 1901 

 (Fuller, 1902), in 1904 (Committee on Standard Methods 

 of Water Analysis, 1905), and again in 191 1 (Committee 

 on Standard Methods for the Examination of Water 

 and Sewage, 191 2), recommending in considerable 

 detail a standard routine procedure for the quantitative 



