84 PRACTICAL BACTERIOLOGY 



CLV. SMITH'S METHOD OF ISOLATING CERTAIN 

 ORGANISMS FROM A WATER SUPPLY, i.e., INTES- 

 TINAL BACTERIA. 



1. Add 1, 2, or 3 drops of the suspicious water to some fermentation 

 tubes containing 2 per cent, grape sugar bouillon. 



2. Place at 37 C., and if at the end of thirty-six or forty-eight 

 hours gas accumulates in the tube, then intestinal bacteria are present, 

 as ordinary water bacteria do not flourish in this medium. 



3. Isolate the gas-forming organisms by the ordinary plate culture 

 method (see 108, p. 58) for further identification. 



When the number of colonies developed on a plate are too 

 numerous to be counted with the Wolff hiigePs apparatus (see Fig. 13, 

 p. 63), the plate is examined with a low power and Ehrlich's eye-piece 

 diaphragm. 



CLVI. METHODS OF EXAMINING EARTH. 



FRAENKEL'S METHOD. 



1. Take an earth borer made according to FraenkeFs model (see 

 Fig. 26, A open, B closed) when examining earth from the deeper 

 strata. For superficial samples a borer is not necessary. 



Open 



Fraenkel's Earth Borer. 



2. Measure the desired quantity of earth in a platinum spoon, 

 mix with 10 c.c. of sterilized nutrient gelatine, and proceed according 

 to roll culture process (see 114, p. 61). 



The most important organisms found in soil are Bacillus tetani, 

 Bacillus of symptomatic anthrax, Bacillus oedematis maligni. These 

 organisms are anaerobic, and require special conditions for their 

 development (see Cultivation of Anaerobic Bacteria, 119, p. 64). 



The nitrifying bacteria are also found in the most superficial 

 layers of the soil. The best example of the activity of these 

 organisms is the production of nitrates from the ammonia of the 



