1. The concentrations of various salts required to agglutinate different concentrations for a suspension of typhoid bacilli sensitized with immune serum have been determined.
2. The electrolytes may be divided into two classes; (1) those with which the concentration required to agglutinate is independent of the concentration of the suspension; and (2) those with which the agglutinating concentration increases in proportion to the concentration of the suspension.
3. The salts comprised under (1) do not reverse the sign of the charge of the suspension.
4. The salts of Class (2) (with the exception of ZnSO4) do reverse the sign of the charge.