28 Elements of Water Bacteriology. 



It is obvious from all these facts that the eflFect 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 be- 

 tween normal and contaminated sources. The ordinary 

 gelatin medium, on the other hand, is adapted to the 

 growth of intestinal and putrefactive forms and, therefore, 

 serves best the prime object of bacteriological water ex- 

 amination. 



The first requisite in a procedure for water analysis 

 is, 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 Bacteriologists, 1898). 

 A permanent Committee on Standard Methods was then 

 formed which reported in 1901 (Fuller, 1902), and 

 again in 1904 (Committee on Standard Methods of 

 Water Analysis, 1905), recommending in considerable 

 detail a standard routine procedure for the quantitative 



