REACTION OF B. COLI ON ENDO MEDIUM 551 



Endo medium, the explanation of typical colonies produced on 

 this medium becomes more complex. It is likely that the 

 glycerol is first oxidized into glyceric aldehyd, 



CH2(OH)CH(OH)CH2(OH) +0 = CH2(0H)CH(0H) CHO + H^O 

 Glycerol Glyceric aldehyd. 



and this in turn is converted into lactic acid. It will be re- 

 called that Embden and his co-workers (Hammarsten, 1914) 

 have shown that in the formation of lactic acid from glucose by 

 enzymes, glyceric aldehyd is one of the intermediary products. 



Grey (1913), who has investigated the products of anaerobic 

 glucose decomposition by B. coli-communis , finds that this 

 organism produces lactic, acetic, formic, and succinic acids, 

 alcohol, and acetaldehyd from this carbohydrate. Mendel 

 (1911) finds also the presence of acetone among glucose decom- 

 position products of B. coli. 



To recapitulate the observations discussed above: 



1. Acid, aldehyd, acetone and alcohol in proper dilution and 

 combination cause a reappearance of the fuchsin color of a 

 decolorized fuchsin-sulfite solution. 



2. When glucose, mannitol and glycerol are substituted for 

 lactose in the Endo medium, typically metallic colonies are 

 produced by the entire typhoid-colon group. 



3. B. coli-communior , when grown in lactose and glycerol 

 broth under partially anaerobic conditions, produces another 

 substance — or possibly substances — besides acid, which bring 

 back the color to decolorized flichsin, when faintly acidified. 



In view of these observations and those of the workers men- 

 tioned above, it would appear that the red colonies which B. 

 coli produces on the Endo plate are due to a number of sub- 

 stances — including lactic and other organic acids, traces of 

 aldehyd and possibly also acetone and alcohol. The latter of 

 these substances are volatile and therefore evaporate on ex- 

 posure, the result being that the non-volatile fuchsin remains 

 behind and we thus have the metallic film. 



The possible criticism that B. coli breaks down glucose into 

 the various substances named above, only when grown anaerobi- 



