BACTERIOLOGICAL ANALYSIS OF WATER 225 



to mix the sample thoroughly with the medium. Avoid 

 shaking so violently as to produce gas bubbles. 



6. Using a sterile 5 c.c. pipette, add 5 c.c. of the water 

 sample to each litmus lactose bile fermentation tube. 



7. Incubate the gelatin plates (cover-side up) in a cool 

 place. 



8. Incubate the agar plates (cover-side down), the agar 

 shake and the fermentation tubes at 37 C. 



9. Make note of the time of day these are placed in the 

 incubator. All cultures placed at 37 C. must be examined 

 within twenty-four hours. Types of colon-like organisms if 

 present, may be quite easily recognized within twenty- 

 four hours by the type and reaction of the colony on the 

 agar plate, by the fermentation test, and by acid and gas 

 formation in the agar shake. 



10. Examine the agar plates after eighteen to twenty- 

 four hours incubation. 



11. If acid colonies are present, make morphological 

 determinations (hanging drop) for their similarity to B. 

 coli. 



12. If these characteristics are positive, transfer five 

 different colonies to agar slants. 



13. Agar shake and fermentation tubes must be examined 

 in eighteen to twenty-four hours also for gas and acid produc- 

 tion. 



14. If gas is present in either, and no acid colonies have 

 appeared on the original plates, make dilution plates in litmus 

 lactose agar in order to isolate the acid and gas producing 

 organisms. 



15. Transfer five different acid colonies which show a 

 morphology similar to that of B. coli to agar slants. 



16. At the end of forty-eight hours, remove the agar 

 plates from the incubator, make counts, record the types 

 of colonies present and the number of each type. 



17. Transfer each type of colony not previously isolated, 

 to an agar slant. 



