l8o ADDENDUM 



" (2) Bacillus coli test. 



" In certain cases it is advisable to apply also : 



"(3) Streptococcus test. 



" (4) Anaerobic spore test (commonly known in England as 

 the B. enteritidis sporogenes test). 



" (5) Tests for pathogenic microbes. 



" The composition of the various media recommended by the 

 Committee, in connection with these tests, is given in an accom- 

 panying appendix. 



"Tests (i) (c\ (3), (4) and (5) need be employed in special 

 cases only." 



As regards the time of counting for the enumeration plates 

 the recommendation of the Committee was : 



" As a matter of convenience it is a common practice to 

 count gelatine plates after seventy-two hours. The Committee 

 recognize that a considerable number of bacteria are thus missed, 

 and that four days is a better period. In any case the day on 

 which the count is made should be stated. 



" It is convenient to count the agar and bile-salt agar plates 

 at the end of 24 hours, as this enables the observer to arrive 

 rapidly at certain conclusions, and, if the results are decidedly 

 unsatisfactory, to issue a tentative warning. This is a matter of 

 considerable importance in all cases, and in some may be 

 vitally important. In the agar plates the sporing bacteria are 

 apt, in forty-eight hours, to spread over the surface of the plate and 

 render counting difficult or impossible. This does not occur in 

 the case of the bile-salt agar plates, but it is convenient to count 

 both sets of plates on the same day." 



Bacillus coli. The Committee recommended the use of bile- 

 salt peptone for the primary test, while as regards the amount 

 of water to examine "the aim should be to have such a range of 

 amounts as will always include a positive and negative result." 



Isolation of Bacillus coli. 



"If the primary bile-salt cultures show gas formation the 

 differential medium with which the worker has most experience 

 can be used for plating purposes. 



