SPECIAL EXAMINATIONS 357 



characters was expressed by the word " flaginac." Since 

 January, 1907, he has modified his method in this wise. 

 Finding that, practically speaking, a " flaginac " B. coli is a 

 B. coli indistinguishable, according to the tests used, from the 

 typical B. coli of excremental pollutions ; and that in the 

 great majority of cases a glucose fermenting coli-like microbe 

 will also produce fluorescence (fl) in neutral-red broth cultures ; 

 and, further, that lactose fermenting (ag) coli-like microbes 

 nearly always clot milk (ac) ; there is, therefore, justification 

 for omitting the neutral-red broth and litmus milk tests, and 

 relying solely on the lactose peptone (ag) and the indol (in) 

 tests. Practically, in the case of the London waters, an "agin " 

 B. coli may be regarded as presumably a " flaginac " B. coli 

 (Report for January, 1907). On this basis he has modified 

 the above method, in order to make it more rapid. The first 

 growth is as before, on MacConkey's glucose broth for forty- 

 eight hours. The secondary cultures are on rebipelagar 

 (instead of gelatin) for twenty-four hours. From red coli-like 

 colonies on this medium, subcultures are made on glucose, 

 lactose, and saccharose, gelatin media and in peptone water. 

 After twenty-four hours gas production in the carbohydrate 

 media is considered positive ; and indol is tested for in the 

 peptone water. Fermentation of lactose and production of 

 indol are looked for, " agin " results ; if saccharose is also 

 fermented, the result is recorded as a " sagin " one. (For full 

 description see the January, 1907, Report.) In this way 

 Houston claims that " it becomes possible to complete the 

 tests for excremental pollution in water within four days." 

 It will be noticed that Houston accepts as a " type of B. coli " 

 an organism fermenting saccharose. His statement on the 

 subject is as follows : 



' The typical B. coli of the human intestinal tract may be 

 divided into two classes, according to their action on 

 saccharose. The majority do not ferment this sugar,' or ~act 

 on it only to a slight extent. Hence typical B. coli which 

 do not ferment saccharose would seem to be more significant 

 of undesirable pollution than those which do ferment it." 



The student should note that Houston uses the term 

 " typical B. coli " on a different basis from many other 

 bacteriologists, who would be inclined to speak of his " typical 

 B. coli " rather as a " coliform organism." 



Houston has found that out of every 100 coliform organisms 

 present in raw Thames water, 70 to 80 per cent conform to 

 his " typical B. coli " ; whereas the same water after storage 

 and filtration shows a reduction in the coliform organisms 



