70 ELEMENTS OF WATER BACTERIOLOGY. 



QUALITATIVE ANALYSIS. 



Preliminary fermentation -tube 



Litmus-lactose-agar plates 



Agar streak culture 



Fermentation-tube 



Nitrate test 



Milk test 



Indol reaction 



Gelatin stab culture 



Remarks 



Opposite the words " Preliminary f ermentation-tube " 

 the results of the first enrichment test in the five or ten 

 tubes inoculated are recorded by plus or minus signs. 

 Under the columns headed by plus signs the presence or 

 absence of typical red colonies on the litmus-lactose-agar 

 plate is similarly indicated. The third line serves for 

 the results of the microscopic and macroscopic appear- 

 ance of the agar streak. If this gives the proper type of 

 growth and rod-shaped organisms are found, a dex- 

 trose fermentation-tube, a nitrate tube, a milk tube, a 

 peptone tube, and a gelatin stab are inoculated from it. 



After twenty- four hours incubation at 37, the first 

 three of these subcultures are examined and the results 

 recorded in the proper columns by plus and minus signs. 

 The amount of gas in the closed arm of the dextrose tube 

 may be conveniently measured by the Frost gasometer 

 (Frost, 1901). Then a few centimeters of strong sodium 

 or potassium hydrate are added and mixed with the broth 

 by cautiously tipping the tube and a second measurement 

 determines the amount of gas absorbed (assumed to be 

 CO 2 ). The gas should first fill from a third to two- 



