After disintegration by sonic vibrations the contents of the hemolytic streptococcus can be separated by differential centrifugation into three fractions: an insoluble residue, cytoplasmic particles, and a solution of proteins of smaller unit size.

The residue (R) presumably comprises the cell walls of the bacteria and contains the type-specific M protein. The cytoplasmic particles (CP) contain some lipoid, the group-specific carbohydrate, and nucleoprotein of the ribose type. The supernate fraction (S) contains two components, presumably protein, at least one of which is part of a dissociable nucleoprotein of the desoxyribose type.

Both CP and S precipitate and fix complement with antistreptococcal sera. Both give rise to antibodies on injection into rabbits. Both are of broad reactivity. CP and S can be shown to be serologically distinct by several means, including cross-absorption tests.

On continued disintegration of the organism an inverse relation is noted between the yield of R and that of CP, whereas the yield of S is constant.

A theory as to the structure of the streptococcal cell is offered in terms of the data presented.

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