208 ELEMENTS OF WATER BACTERIOLOGY 



large amount of organic food material present the 

 streptococci may kill out the colon bacilli as they do 

 in the fermentation tube, and as we know they fre- 

 quently do in shellfish. This would explain Horrocks' 

 results. On the other hand, there is good evidence 

 that the streptococci are less resistant than B. coli to 

 the unfavorable conditions which exist in water of 

 ordinary organic purity. In waters of potable char- 

 acter B. coli is frequently present without the strep- 

 tococcus; and a negative test for streptococci has 

 little significance. A positive test, on the other hand, 

 furnishes valuable confirmatory evidence of pollution. 

 This evidence is of course of special importance when 

 through the activity of the streptococci themselves, 

 or from any other cause the colon isolation has yielded 

 an erroneous negative result. 



The English Committee appointed to consider the 

 standardization of methods for the bacterioscopic 

 examination of water (1904) by a majority vote rec- 

 ommended the enumeration of streptococci, as a routine 

 procedure in sanitary water analysis, but in this 

 country the Committee on Standard Methods of Water 

 Analysis (1912) has concluded that "the information 

 afforded by the occurrence of these organisms seems 

 to be of less value than in the case of B. coli and it is 

 believed that for the present at least, the streptococcus 

 test is of subordinate importance." 



Use of the Streptococci to Distinguish between Human 

 and Animal Pollution. There seems some reason to 

 hope that the streptococci may prove of assistance in 

 the important task of differentiating human and animal 



