THE COLON GROUP OF BACILLI 121 



and apparently with good reason, that the conditions 

 of this test are too severe and eliminate many intestinal 

 bacilli of undoubted significance. Nowack (1907) found 

 that laboratory cultures of B. coli often fail to produce 

 gas in Eijkman's medium at 46°, unless large numbers 

 are introduced. With some strains an inoculation 

 of over a milUon bacteria was necessary to cause gas 

 formation. 



Konrich (1910) compared the Eijkman enrichment 

 method (dextrose peptone water at 46°) and that of 

 MacConkey (dextrose-bile-salt peptone water at 42°) 

 with 57 water samples and obtained only about 

 70 per cent as many positive results with the former 

 as with the latter method. With artificial emulsions 

 of pure cultures and of faeces even greater differences 

 were manifest. These studies showed conclusively 

 that incubation at 46° prevents the development of 

 great numbers of colon bacilli and is unsuitable for an 

 enrichment process. In comparing the two media 

 (dextrose peptone water with and without bile salts) 

 at the same temperature, 37°, he obtained essentially 

 similar results. 



Fromme (1910) has shown that during the first 5 

 hours in various enrichment media colon bacilli multiply 

 more rapidly at 46° than at 37°. After that time, 

 however, their development is checked. At 12 hours 

 the numbers at the two temperatures are about equal 

 and between 12 and 24 hours the numbers increase 

 much more rapidly at 37°. 



The Neutral Red Reaction. Other special media 

 have been suggested for rapid routine water analysis, 



