1. Representative strains of organisms of the colon group have a deleterious influence on the flavour of Cheddar cheese when they are added to the milk immediately before the start of the process of cheese manufacture.

2. They do not produce gas holes in the cheese, even when present in large numbers, provided that an active culture of lactic streptococci is used as “starter.” It seems most probable that their metabolism is modified by association with the lactic streptococci, so that, although the colon bacilli grow in the cheese, they produce little or no gas.

3. Under the conditions of these experiments, they have no influence on the texture of the cheese.

4. They do not appreciably affect the production of acid by the “starter” in the milk or curd.

5. Under the experimental conditions described, they do not cause decolorisation of annatto in a coloured cheese. It seems unlikely, therefore, that they are responsible for mottling in cheese.