139e ELEMENTS OF WATER BACTERIOLOGY 



may be based upon these recommendations, the follow- 

 ing may be considered sufficient evidence of the presence 

 of organisms of the bacillus coli group. 



"Formation of gas in fermentation tube containing 

 original sample of water (a) . 



"Development of acid-forming colonies on lactose 

 litmus agar plates or bright red colonies on Endo's 

 medium plates, when plates are prepared as directed 

 above under (b). 



"The formation of gas, occupying lo per cent or more 

 of closed arm of fermentation tube, in lactose peptone 

 broth fermentation tube inoculated with colony fished 

 from 24-hour lactose litmus agar or Endo medium 

 plate. 



"These steps are selected with reference to demon- 

 strating the presence in the samples examined of 

 aerobic lactose-fermenting organisms. 



• "3. It is recommended as a routine procedure, that 

 in addition to five lo-c.c. portions, one i-c.c. portion, 

 and one o.i-c.c. portion of each sample examined be 

 planted in a lactose peptone broth fermentation tube, 

 in order to demonstrate more fully the extent of pollu- 

 tion in grossly polluted samples. 



"4. It is recommended that in the above-designated 

 tests the culture media and methods used shall be in 

 accordance with the specifications of the committee 

 on standard methods of water analysis of the 

 American Public Health Association, as set forth in 



* Standard Methods of Water Analysis.' (A. P. H. A., 

 1912.)" 



At present the choice of a practical method seems 



