SUMMARY: 560 strains of were typed by Hammarström's method using baeteriophages, and the results tabulated by districts and outbreaks. Experimentally it was found that by the action of different phages transformation to a more resistant type could be achieved without conferring lysogenicity. The mechanism of this transformation seems to be in most cases the selection by the phage of true mutant types of which several are present in small numbers in every Sonne strain. The mutant types obtained most frequently out of type 3 cultures by experimental methods were also found in association with type 3 outbreaks. As dysentery phages are present in the intestines of many people, it is postulated that such transformations occur and that difference of type does not mean lack of recent genetic relationship.


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