The relations between lysin concentration, percentage hemolysis at the moment at which the lysin concentration is reduced by dilution, and the amount of hemolysis which follows the dilution as a result of the reaction being "progressive" point to there being an "internal" phase at the red cell surfaces, in which the lysin is less affected by the dilution than in the system as a whole. A second possibility, i.e. that the combination of lysin molecules with certain components of the cell surface has an ultimate effect on neighboring components which depend on the former for their stability cannot, however, be ruled out.
In systems containing digitonin or sodium taurocholate, this internal phase, once formed, seems to be almost unaffected by the dilution of the system; i.e., these lysins are very firmly held at the cell surfaces. In systems containing saponin the lysin is less firmly attached, so that dilution of the system affects its concentration appreciably.