2. Make two (2) gelatin plates from each dilution, and incubate at
20° C.
3. Make two (2) agar plates from each dilution, and incubate at 37°
C.
4. Inoculate lactose broth fermentation tubes with appropriate
amounts for B. coli tests, inoculating two (2) tubes with each
amount.
Note:—Where repeated tests are made of water from the same source, as is
customary in the control of public supplies, it is not necessary to make
duplicate plates or fermentation tubes in each dilution. It is
sufficient, in such circumstances, to make duplicate plates only from
the dilution which will most probably give from 25 to 250 colonies per
plate.
_Second Day_: