A zone phenomenon and a progressive reaction occurring with a radioactive hemolysin, sodium erucate, I 131.

Sodium erucate reacts progressively (i.e., once the reaction is started in a time which is so short that the lysin is in contact with the red cells for 30 seconds, it cannot be stopped even by being diluted 10-fold) with human red cells at pH 7. At the same time, systems containing the lysin and human red cells show a zone phenomenon, lysis occurring most readily in a certain concentration of lysin but more slowly in larger or smaller concentrations. Sodium erucate-I(131) can be used to investigate both the zone phenomenon and the progressive character of the reaction. As regards the former, large concentrations of the lysin react relatively poorly with the red cell surfaces and the resistance of the red cells is relatively high. This may be due to the presence of an admixed inhibitor or to the development of an inhibitory state. The lysin is taken up and fixed by material in the red cell surface, so that the "internal phase" of lysin attached to the cell surfaces is so firmly fixed that a 10-fold dilution has no effect on it. It follows that lysis in these systems is progressive, as it is found to be.