1. A new phage-typing scheme for Salm. typhi-murium is described which initially defines thirty-four types of the organism.
2. Types recognizable with the older scheme of Felix and Callow remain distinct with the new system. However, the latter method offers a finer subdivision of the organism than does the former.
3. Thirteen of the twenty-nine typing phages used in the new scheme were prepared by adaptation of Salm. paratyphi B typing phage 3b, and nineteen are serologically indistinguishable from this phage.
4. The lysogenic properties of the new types are discussed. Twenty-three out of the thirty-three type strains yielded both thermolabile and thermostable phages and a further three yielded thermolabile phages only. No phages could be isolated from the remainder.
5. The distinctive host ranges of the phages carried by most types can be used for type identification.
I am indebted to Miss Alison M. Dykes for her valuable assistance with this work; to Mr F. J. Flynn for help in the preparation of phage stocks; and to Dr E. S. Anderson for many helpful discussions and advice in the preparation of this paper.
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