Two major antigenic fragments were obtained from various purified γ-globulin preparations after papain treatment. One, the F component, had a mobility faster than the original γ-globulin and the second, the S component, had a slower mobility. Similar F and S components were also obtained with certain homogeneous myeloma proteins which were closely related to γ-globulin immunologically. Additional minor antigenic components were detected with certain antisera. The technique of immunoelectrophoresis was particularly useful for bringing out the different antigenic constituents obtained after papain treatment.

The F and S components as well as a midfraction were isolated by chromatography on DEAE-cellulose. These were immunologically homogeneous and could be utilized to absorb F and S antibodies from various antisera. The relative amount of F and S antibodies varied in different antisera from individual rabbits immunized with whole γ-globulin.

Whole γ-globulin was separated by zone electrophoresis into a fast migrating and a more slowly migrating fraction. Each of these gave rise to F and S components after splitting with papain. The F components of the two γ-globulins were similar in mobility, while the S components showed marked mobility differences although antigenically they were very similar. The mobility differences of the parent γ-globulin appeared to be primarily related to the differences in the S component.

Certain antisera against pathological γ-globulins were found to give double lines with a wide variety of γ-globulin preparations in agar diffusion. These were shown to be related to the F and S antigenic determinants of γ-glubulin. This relationship was evident by a number of procedures utilizing both Ouchterlony plate techniques and immunoelectrophoresis. The question of whether these findings indicate heterogeneity of γ-globulin in relation to the F and S antigenic components, or whether different antigenic groups on one molecule can give rise to separate lines in certain instances, is discussed.

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