101 " A ; -r^^S ",' - A 



(b) Litmus-milk at 37 C. 



(c) Lactose-peptone litmus solution (in a double tube). 



(d) Peptone water (for indol production). 



(e) Saccharose peptone litmus solution (in a double tube). 



III. American Public Health Association. Standard Method. 

 The 1920 report of the Committee on Standard Methods of Water Analysis 

 of the American Public Health Association suggested the following: 



It is recommended that the B. coli (colon) * group be considered as 

 including all non-spore-forming bacilli which ferment lactose with gas for- 

 mation and grow aerobically on standard solid media. 



The formation of 10 percent or more gas in a standard lactose broth 

 fermentation tube within 24 hours at 37 C. is presumptive evidence of 

 the presence of members of the B. coli group, since the majority of the 

 bacteria which give such a reaction belong to this group. 



The appearance of aerobic lactose-splitting colonies on lactose-litmus- 

 agar or Endo's medium plates made from a lactose-broth fermentation tube 

 in which gas has formed confirms to a considerable extent the presumption 

 that gas-formation in the fermentation tube was due to the presence of 

 members of the B. coli group. 



To complete the demonstration of the presence of B. coli as above 

 defined, it is necessary to show that one or more of these aerobic plate 

 colonies consists of non-spore-forming bacilli which, when inoculated into 

 a lactose-broth fermentation tube, form gas. 



It is recommended that the standard tests for the B. coli group be 

 either (a) the Presumptive, (b) the Partially Confirmed, or (c) the Com- 

 pleted test as hereafter defined, each test being applicable under the 

 circumstances specified. 



A. Presumptive Test. 1. Inoculate a series of fermentation 

 tubes with appropriate graduated quantities of the water to be tested. In 

 every fermentation tube there must always be at least three times as much 

 medium as the amount of water to be tested. When necessary to examine 

 larger amounts than 10 c. c. as many tubes as necessary shall be inoculated 

 with 10 c. c. each. 



2. Incubate these tubes at 37 C. for 48 hours. Examine each tube 

 at 24 and 48 hours, and record gas-formation. The records should be 

 such as to distinguish between: 



(a) Absence of gas-formation. 



(b) Formation of gas occupying less than 10 percent of the closed 

 arm. 



(c) Formation of gas occupying more than 10 percent (10%) of 

 the closed arm. 



More detailed records of the amount of gas formed, though desirable for 

 purposes of study, are not necessary for carrying out the standard tests pre- 

 scribed. 



*Parenthesis author's. 



