1. The amount of immune body required to agglutinate a suspension of Bacillus typhosus increases in direct proportion to the concentration of the suspension.
2. The amount of immune body combined with the organisms is constant from pH 9 to pH 3.7. Below the latter value the amount in combination is decreased.
3. The addition of immune serum to a suspension of Bacillus typhosus at a pH of 2,5 increases the positive charge of the organisms.
These results are contradictory to the idea that the combination is caused by a difference in the sign of the charge carried by the immune body and the organism. They agree with the assumption that the immune body forms a film on the surface of the organism and that the effect on the charge is the result of this film.