82 PRACTICAL BACTERIOLOGY 



obtained. When the examination must be delayed, then place the 

 sample in the ice-box. Before testing a sample, shake the flask, as an 

 equal distribution of the germs is necessary for an average result. 

 Samples collected from a tap should not be drawn until the water has 

 been flowing from fifteen to twenty minutes in full stream. When 

 obtained from a stream or spring, take the sample about one foot 

 beneath the surface. 



Water analyses should always be made on the spot, when possible, 

 as during transportation, unless packed in ice, a multiplication of the 



FIG. 25. Air-pump for use in Petri's Method. 



organisms in the sample takes place. The following are the necessary 



articles for a Transportation Case for Analyses on the Spot : 



4 sterilized Erlenmeyer flasks to obtain the samples ; 1 thermo- 

 meter ; 1 spirit lamp ; 12 sterilized Petri-dishes in special 

 box (see page 12) ; 12 tubes of sterile nutrient gelatine ; 

 15 sterilized water pipettes in three cases ; 1 folding tripod ; 

 1 notebook ; 1 pencil for writing on "glass, etc. ; and 1 towel. 

 The gelatine is melted, the inoculations made immediately, and 



poured into the Petri-dishes, allowed to solidify, and transported to 



the laboratory. 



