426 BACTERIOLOGICAL ANALYSES 



2. Qualitative Examination. 



Collection of Sample. The water sample required for 

 the routine examination, which it will be convenient to 

 consider first, amounts to about no c.c. It is col- 

 lected in the manner previously described (vide page 

 416) ; similar bottles are used, and if four are filled the 

 combined contents, amounting to about 240 c.c., will 

 provide ample material for both the qualitative and 

 quantitative examinations. Unless the examination is 

 to be commenced at once, the ice-box must be employed, 

 otherwise water bacteria and other saprophytes will 

 probably multiply at the expense of the microbes in- 

 dicative of pollution, and so increase the difficulties 

 of the investigation. 



In the routine examination of water supplies it is 

 customary to limit the qualitative examination to a 

 search for 



A. B. coli and its near allies. 



B. Streptococci, 



organisms which are frequently spoken of as microbes 

 of indication, as their presence is held to be evidence of 

 pollution of the water by material derived from the 

 mammalian alimentary canal, and so to constitute a 

 danger signal. 



C. Some observers still attach importance to the 

 presence of B. enteritidis sporogenes, but as the search 

 for this bacterium, (relatively scarce in water) necessi- 

 tates the collection of a fairly large quantity of water it 

 is not usually included in the routine examination. 



In the case of water samples examined during the 

 progress of an epidemic, of new supplies and of unknown 

 waters the search is extended to embrace other mem- 

 bers of the eoli-typhoid group; and on occasion the 

 question of the presence or absence of Vibriocholerse or 

 (more rarely) such bacteria as B. anthracis or B. 

 tetani, may need investigation. 



When pathogenic or excremental bacteria are pre- 



