20 ELEMENTS OF WATER BACTERIOLOGY. 



1902) showed that the numbers obtained by the ordi- 

 nary procedure were only from 5 to 50 per cent of 

 those obtained by the use of Heyden's Nahrstoff agar. 

 For practical sanitary purposes, however, our methods are 

 fairly satisfactory. Within limits, it is of no great impor- 

 tance that one method allows the growth of more bacteria 

 than another. When we are using the quantitative analy- 

 sis as a measure of sewage pollution only two things are 

 essential. First, media should be of standard composi- 

 tion, 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 a state, very satisfactory, by 

 contrast with the chaos which prevails in England and 

 Germany. Secondly, it is desirable that the section of 

 the total bacterial flora which we obtain should be thor- 

 oughly representative of that portion of it in which we 

 are most interested the group of the quickly growing, 

 rich-food-loving sewage forms. In this respect our meat- 

 gelatin-peptone appears to be unrivalled. The follow- 

 ing table from Gage and Phelps's valuable paper shows 

 clearly that the standard media bring out the difference 

 between pure and polluted waters much more clearly than 

 does the Nahrstoff medium. To emphasize this difference 

 with constancy is all that we require of a method for prac- 

 tical work. 



