ELEMENTARY: BACTERIOLOGY LABORATORY EXERCISES 47 
Make duplicate plates of this sample using 1 cc. and 1/10 c.c. amounts. 
Make one plate from each dilution with lactose agar and the other with either 
litmus lactose agar or brom cresol purple lactose agar. 
Inoculate lactose broth fermentation tubes with 10 c.c., 1 cc., and 1/10 c.c. 
amounts of the same water. 
Incubate the plates and fermentation tubes at 37° C. for 48 hours. If pos- 
sible, also observe the results at the end of 24 hours. Determine the bacterial 
count of the water from the lactose agar plates. Determine the presence or ab- 
sence of acid-forming colonies from the lactose agar plates containing indica- 
tor. Observe the fermentation tubes for gas formation; if present, analyze the 
gas. 
EXERCISE 68 
EXAMINATION OF SEWAGE 
Plate out a sample of sewage using dilutions of 1/10,000, 1/100,000, 
1/1,000,000, and 1/10,000,000. Make duplicate plates using lactose agar and 
either litmus lactose agar or brom cresol purple lactose agar. 
Inoculate lactose broth fermentation tubes using the same dilution as used 
in the plates. 
Incubate at 37° C. and record results as in the previous exercise. 
EXERCISE 69 
EXAMINATION OF SEWAGE POLLUTED WATER 
Examine a sample of polluted water in the same way as outlined in the pre- 
vious exercises, using dilutions of 1/10, 1/100, and 1/1,000 for plating. Inoculate 
lactose broth fermentation tubes with the same dilutions as used in the plates. 
Incubate and observe as before. 
EXERCISE 70 
EXAMINATION OF UNKNOWN WATERS 
Examine samples of unknown waters using the same methods employed in 
the previous exercises. For plating employ 1 c.c., 1/10 c.c., and 1/100 c.c. amounts, 
Inoculate the fermentation tubes with 10 c.c., 1 c.c., and 1/10 c.c. amounts. 
