The fact is shown that collodion particles sensitized with various proteins adsorb sufficient protein to agglutinate in the presence of precipitin specific for the adsorbed protein. The amount of adsorption, judged by agglutination, is not dependent on the concentration of the sensitizing protein beyond a certain maximum. The agglutination resulting from the addition of immune serum to particles sensitized with protein is immunologically specific.

Particles exposed to a number of antigenic substances in succession are agglutinated by all of the appropriate antisera.

Particles exposed to immune serum and subsequently washed fail to agglutinate in the presence of antigen although some of the protein constituents of the immune serum are fixed upon them and its antibody content diminishes.

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