104 



PROCEDURE FOR THE EXAMINATION OF WATER. (BACTERIOLOGICAL) 



Steps in procedure 



Further tests 

 required 



1. Plate two 1 c. c. and one 0.1 c. c. or other ap- 

 propriate portions of the sample on plain agar, 

 and incubate for 24 hours at 37 C. 



2. Inoculate 10 c. c., 1 c. c. or other portions 

 of the sample into lactose broth (or lactose 

 peptone water). Incubate at 37 C. 



3. Optional if a very rapid result is neces- 

 sary. 8 to 10 hours after incubation perform 

 a Preliminary Confirmatory test as follows: 

 Divide an Eosine-methylene blue, (or Endo, or 

 Litmus-lactose) agar plate into sectors. Streak 

 out a drop or loop of a fermentation tube con- 

 taining 10 c. c. of the sample on one of the 

 sectors, and in a similar manner streak out 

 other fermentation tubes on the remaining 

 sectors. Incubate at 37 C. 



1. Count agar plates made the previous day, re- 

 cord and discard petri dishes. 



2. Record presence or absence of gas after 

 hours incubation as follows: 10% or more, 

 Positive; less than 10%, Doubtful; no gas 

 Negative. 



3. Gas formation (any amount) accompanied by 

 a positive preliminary confirmatory test, con- 

 stitutes what is known as a Partially Con- 

 firmed test for the colon group. 



4. If 10% or more gas is formed, and the prelim 



inary confirmatory test is negative or was not 7 



made, the result is regarded as a positive P re ' ^e or r aw 

 sumptive test for the colon group. 



5. If less than 10% gas is formed, and the pre- 

 liminary confirmatory test is negative or was 

 not made, the result is regarded as a doubtful 

 presumptive test, and should be confirmed. 



None 



'D' 



water 



1: If no gas was formed after 24 hours' incuba- 

 tion, but is present after 48 hours, the test is 

 regarded as doubtful and inconclusive. This 

 must be confirmed. 



'D' 



