The factors which influence the initiation of growth from small inocula of type A in the defined medium previously described were re-examined. CO was found essential for rapid and regular growth from small inocula; it could be partially replaced under conditions of strict CO depletion by an unidentified factor present in enzymic hydrolysate of casein or yeast extract.

The growth requirements of the various serological types of group were studied and compared with those of type A. It was found that the various organisms can be classed into two nutritional groups: () those which gave rapid and heavy growth in a chemically defined medium as described for type A, with some variations in respect of vitamin requirements: here belong type A (12 strains tested), type B (9 strains) and (10 strains); () organisms which failed to grow in the defined medium or in a partially-defined medium (containing acid hydrolysate of casein) supplemented with all known B-vitamins: this group comprised organisms of the type C (2 strains) type D (4 strains) and type E (5 strains, of which 3 grew in a partially defined medium).

The similarity in nutritional requirements of to types A and B and the similarity in cultural and biochemical properties make indistinguishable from, and perhaps identical with, non-toxigenic strains of types A and B.


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