METHODS OF EXAMINING WATER 83 



CLI. QUALITATIVE METHOD. 



Transfer with a sterilized capillary pipette 1 c.c., J c.c., or J c.c. 

 of the water to be examined into a tube containing 10 c.c. of liquefied 

 sterilized nutrient gelatine. Mix, and pour the contents of the tube 

 on a sterile glass plate, and proceed as at No. 3 process, ' Quantitative 

 Plate Culture Method? 118, p. 64. (The bottoms of Petri-dishes 

 being uneven, plates are more reliable for water examination.) 



CLII. KOCH'S METHOD FOR DEMONSTRATING THE 

 VIBRIO CHOLERA ASIATICS IN WATER. 



1. Take 100 c.c. of the suspected water, and mix with 5 c.c. of 

 sterile 20 per cent, peptone chloride of sodium solution ( 81, p. 50), 

 make alkaline, and place in the incubator at 37 C. 



2. When Cholera bacilli are present they develop, and are found 

 in ten or twelve hours on the surface of the fluid, and can be further 

 investigated and identified. 



CLIII. ELSNER'S METHOD FOR BACILLUS TYPHI 

 ABDOMINALIS. 



Take some potato gelatine (see 79, p. 50), and shortly before use 

 add 1 per cent, of iodide of potash ; after adding the suspected water, 

 prepare plate cultures according to the ordinary method ( 108, p. 58). 

 This method is for the Bacillus typhi abdominalis, and the Bacterium 

 coli com munis, which grows the stronger of the two, and in forty-eight 

 hours appears as dull brown colonies, while the Bacillus typhi abdo- 

 minalis appears as bright watery drops. This method, however, is not 

 absolutely reliable. 



CLIV. QUICK METHOD OF DEMONSTRATING THE 

 PRESENCE OF PATHOGENIC GERMS IN WATER. 



1. Mix 100 c.c. of the suspected water with 5 c.c. of Koch's 20 per 

 cent, peptone chloride of sodium solution (see 81, p. 50), and place 

 in the incubator twenty-four hours at 37 C. 



2. Inoculate a guinea-pig with 1 c.c. of the mixture intraperi- 

 toneally, and if pathogenic organisms are present, the animal dies, 

 and the organs, exudates, blood, etc., can be further examined. 



3. If the water is pure, the guinea-pig remains alive. 



