WATER 427 



sent in water, their numbers are relatively few, owing 

 to the dilution they have undergone, and it is usual in 

 commencing the examination, to adopt one or other of 

 the following methods : 



A. Enrichment, in which the harmless non-pathogen- 

 ic bacteria may be destroyed or their growth inhibited, 

 whilst the growth of the parasitic bacteria is encouraged. 



This is attained by so arranging the environment, 

 (i. e., Media, incubation temperature, and atmosphere) 

 as to favor the growth of the pathogenic organisms at 

 the expense of the harmless saprophytes. 



B. Concentration, whereby all the bacteria present in 

 the sample of water, pathogenic or otherwise, are con- 

 centrated in a small bulk of fluid. 



This is usually effected by filtration of the water 

 sample through a porcelain filter candle, and the 

 subsequent emulsion of the bacterial residue remaining 

 on the walls of the candle with a small measured quan- 

 tity of sterile bouillon. 



A. Enrichment Method. 



(Dealing with the demonstration of bacteria of in- 

 testinal origin.) 



Apparatus Required (Preliminary Stage): 



Incubator running at 42 C. 



Case of sterile pipettes, i c.c. graduated in tenths. 

 Case of sterile pipettes, 10 c.c. graduated in c.c. 

 Case of sterile pipettes, graduated to deliver 25 c.c. 

 Tubes of bile salt broth ( vide page 180). 

 Flask of double strength bile salt broth (vide page 199). 

 Tubes of litmus silk. 

 Sterile flasks, 250 c.c. capacity. 

 Buchner's tubes. 

 Tabloids pyrogallic acid. 

 Tabloids sodium hydrate. 

 Bunsen burner. 

 Grease pencil. 

 (Later stage): 



Incubator running at 37 C. 



Surface plates of nutrose agar (see page 232). 



