The Fuchsin-aldehyde Reac on on the ..endo Medium

The medium had a light pink color when h t and was practically colorless when poured into Petri dish s and allowed to harden. On this medium Endo observed t t B. coli and its close allies gave a distinct red coloration w e B. typhosus was practically colorless. The red color of the . coli colonies, according to this author, was due to the format on of acid but he did not give any experimental evidence to substantiate this belief. Harding and Ostenberg (1912) have shown that the reaction is due to aldehyde formation. These auth rs suggest, also, that by the substitution of other carbohydrat s in place of lactose in the Endo medium this reaction night e used as a means of differentiation of the colon-typhoid-dysent ry group in place of acid production. Robinson and Rettger (1916) have stated ore recently that the red coloration of colon colonies on Endo edium is the result of acid production and not of aldehyde rmation. These