Variation occurring in group A streptococci during human infection; progressive loss of M substance correlated with increasing susceptibility to bacteriostasis.

Similarly, patients with consistently resistant strains also had in- fections with a variety of serological types: 11 had type 19 infections, 2 type 30, and one each type 6, 18, or 38 infections. Although an insufficient number of strains of the various serological types were available to determine whether this variation has any relationship to the type or is characteristic of particular strains, some of the data may be significant in this respect.

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