WATER 37 



correspond to the number of tests proposed to be made and these 

 are used to inoculate the confirmatory tests. This saves time 

 and trouble, besides avoiding any uncertainty in repeatedly 

 going back to a colony in order to inoculate a series of cultures. 



Examination for streptococci. 



The detection of the presence of streptococci and their 

 numerical estimation in water is a procedure which is only 

 carried out by some bacteriologists but is one which is decidedly 

 useful. 



The method originally employed by Houston, to whom is 

 due the credit of first pointing out their importance in water 

 examinations, was to concentrate the water by passing a litre or 

 other definite quantity through a sterile porcelain filter and 

 brush definite fractions over agar plates. The agar plates were 

 examined after 24 hours' incubation at 37 C. and the minute 

 colonies subcultivated into broth tubes and further investigated, 

 if streptococci were found to have grown. In more recent work, 

 examining London water, Houston brushed I c.c. of the water 

 directly over plates containing Drigalski-Conradi medium and 

 subcultivated all the minute colonies which developed after 

 incubation at 37 C. 



The differentiating tests to apply are discussed in Chapter I. 



The method employed by the writer is based upon the 

 detection of streptococcus chains in different fractions of the 

 water sample. 



This may conveniently be done by adding 0*1 and roc.c. 

 respectively to tubes of glucose neutral red broth, and 10 c.c. 

 to a tube of the same broth, but of double strength. These, 

 together with the 30 c.c. preparation used in the B. coli examina- 

 tion, are examined after incubation at 37 C. for 40 to 48 hours 

 in hanging-drop preparation. Only cocci in quite definite chains 

 can be taken as evidence of the presence of streptococci, and 

 several preparations should be examined from each tube. 



It is true that in this way the presence of streptococci as a 

 class only will be ascertained, but with our present knowledge the 

 streptococcus test for excretal contamination does not rest upon 



