ADDENDUM l8l 



"Identification Tests for B. coli. Several suspicious colonies 

 should be picked off the plates and tested for gas formation in a 

 lactose peptone medium, and for indol in a peptone medium. 

 The paradimethylamidobenzaldehyde test is the most delicate 

 test for indol production. 



"The Committee suggest that all reports should contain a 

 simple statement as to the presence (or absence) of ' lactose 4- 

 indol +' microbes and the smallest amounts of water in 

 which they were present, and the largest amount of water from 

 which they were absent. 



" This is common ground for practically all bacteriologists. 



" Thus, for example, the simple statement that B. coli 

 (lactose + indol + ) was present in 100 but not in 10 c.c. of water 

 avoids raising the many points concerning which there is so 

 much difference of opinion. 



"There are many other tests which it is of advantage to use ; 

 for example, gelatine for absence of liquefaction, tests for gas 

 formation in glucose, saccharose, dulcite (dulcitol) and adonite 

 (adonitol) peptone media, and for acid clotting in milk cultures. 

 The results thus obtained may be used for classification purposes 

 or merely registered in the report. 



"On the. whole, the Committee consider that judgment as to 

 the purity of a water should be based primarily on the quantita- 

 tive estimation of ' lactose + indol + ' microbes, although this 

 need not prevent the utilization of the results of other tests as 

 additional factors bearing on the position. 



"As regards 'glucose fermenting coli-like microbes' which 

 yield negative results with one or other, or both the lactose and 

 indol tests, it is difficult to speak with any degree of certainty. 

 Bacteriologists are unfortunately frequently called upon to 

 decide upon individual samples, and it is not necessarily safe to 

 pronounce favourably on a supply of water because a particular 

 sample contains no ' lactose 4- indol + ' microbes if it contains 

 * glucose + ' microbes. Experience has shown that if a supply 

 yields ' glucose + ' microbes it will almost inevitably be found 

 sooner or later to contain * lactose -f indol -f ' microbes as 

 well. 



