As a further test of the theory of tropin action proposed in the preceding paper artificial surfaces have been prepared, and have been found to be phagocytized according to prediction from the theory.
Protein was adsorbed on collodion particles according to the technique of F. S. Jones. These particles were then agglutinated and prepared for phagocytosis by the corresponding protein precipitin sera. The precipitating, agglutinating, surface and tropin effects for each serum or serum globulin fraction have been found to be in satisfactory quantitative correspondence. All of these effects were serologically specific; all remained almost unaffected by inactivation of the immune sera for 30 minutes at 56°C. or by washing of the particles after sensitization.
The surfaces of particles maximally sensitized by homologous rabbit immune serum or one of its globulin fractions have shown certain characteristic properties, i.e., they were cohesive, had wetting properties characteristic for protein, and were isoelectric at pH. 5.5 to 5.8. The same set of properties were found for immune precipitate in the zone of maximal precipitation. The same properties have also been found for maximally sensitized acid-fast bacteria, and for maximally sensitized sheep erythrocytes.
These results indicate, we believe, that precipitation, agglutination, the surface changes and increased phagocytosis are all consequences of one underlying phenomenon. This phenomenon is the specific chemcal combination with, and deposit on the surface of the antigen of antibody protein. The several serological reactions then follow as consequences of the properties of the sensitized surface and of the special environing conditions.
The antibody is contained in the globulin fractions of immune serum, and appears to be a globulin with physico-chemical differences from normal serum globulin.