WATER ANALYSIS. 63 



Make subcultures of the varieties present on the 

 various media, particularly any colonies which in naked 

 eye and microscopic appearances, resemble the Colon 

 bacillus. Typhoid bacillus or the Proteus varieties. 



In sewage contamination the Colon bacillus is con- 

 stantly present, usually with one or more of the putre- 

 factive species. These, with a chemical examination 

 indicating excess of chlorides, nitrates or albuminoid 

 ammonia, make sewage contamination a certainty. 



Tests for the Colon bacillus and putrefactive species 

 are carried out more completely, by some of the pro- 

 cesses later described. 



2. To fermentation tubes containing sterile grape 

 sugar broth, add 1 cc. of water. Incubate at B1°G for 24 

 hours. If gas is formed, Bacillus coli communis is 

 probably present. 



Agar and gelatine plates should be made in such a 

 case, and the gas forming bacterium separated and 

 identified. 



3. (a) Add .1 cc of the water to each of three lique- 

 fied gelatine tubes, containing respectively .1%, .12% 

 and .15% of carbolic acid. Pour plates and incubate at 

 20''C. 



The majority of bacteria are checked in growth in 

 this medium, while the Colon and Typhoid bacilli 

 flourish well. Any colonies which appear can be fur- 

 ther examined by subculture, to aid identification. 



(6) Add .1 cc of the water to each of three liquefied 

 tubes of Eisner's potato gelatine medium. (Eisner uses 

 the water in which potatoes have been boiled, in place 



