We have shown that upon recovery from an attack of malaria induced by any one of the different strains of Plasmodium vivax in our hands the patient possesses a very potent homologous immunity to that strain (1, 2, 3, 4). Such immunity manifests itself by two characteristics: (a) the acquirement of a tolerance to densities of the parasite that in a susceptible person would produce a clinical reaction, and (b) the acquirement by the body of an ability to destroy and remove the parasites. As immunity becomes established the former characteristic is first acquired; the latter develops more slowly. Both characteristics must be simultaneously present before immunity may be considered complete.
On the basis of these characteristics we are of the opinion that the response of any patient to an inoculation will permit his assignment to one of four integrating categories (5), viz.