198 Elements of Water Bacteriology. 



The success of chemical disinfection varies with the 

 character of the sewage or effluent treated since the 

 organic matter present consumes a certain amount of 

 the disinfectant and renders it inoperative. Discordant 

 results are therefore reported from different sources. 



An important series of experiments carried out in Ohio 

 by Kellerman, Pratt, and Kimberly (1907) showed good 

 results with sand filter effluents and contact effluents. 

 Septic sewage, on the other hand, required large amounts 

 of chlorine to produce a reasonable bacterial reduction. 

 The followiag table, on page 199, shows the results 

 obtained at Marion, Ohio. 



In Germany, on the other hand, Schumacher (1905), 

 Kranepuhl (1907), and Kurpjuweit (1907) found larger 

 amounts of chlorine necessary, in the neighborhood of 60 

 parts per million parts of sewage. Their tests were some- 

 what severe, however, the criterion of success being the 

 absence of B. coli in a large proportion of liter samples. 



The science of sewage bacteriology is in its infancy; 

 and it is difficult to give any general rules for the inter- 

 pretation of bacteriological examinations designed to in- 

 dicate whether disposal plants are successful or not. 

 Houston stated provisionally that the 20° count should 

 be tmder 100,000, and the 37° count under 10,000, 

 while B. coli should be absent from .001 c.c. and B. 

 sporogenes from .1 c.c. (Houston, 1902''). This standard 

 seems to us far too lenient. Either organic purity alone 

 is necessary, as at many sewage disposal plants, or a 



