Abstract
The object of the experiments reported here was to determine whether or not rats inoculated with lethal doses of pneumococci could be successfully immunized by means of oral vaccination begun after the introduction of the infecting dose. Various investigators 1 have demonstrated that young rats can be immunized against many lethal doses of virulent pneumococci by means of feeding certain pneumococcus antigens. Such experiments have all been along prophylactic lines; we have seen no reports of experiments testing the therapeutic value of pneumococcus antigens. Since it is possible to render young white rats resistant, by oral means, to comparatively large intraperitoneal or subcutaneous inocula of pneumococci, and since this resistance manifests itself within 24-48 hours, these animals were considered to be suitable for investigating the therapeutic value of oral immunization.
The method consisted of intraperitoneal injection of 100 lethal doses of Type I pneumococci into young white rats (60-100 gm.), followed by various antigenic preparations in single and also multiple doses. Certain rats were fed the antigen immediately after they received the injection of living organisms, and others were fed later during the course of their infection. Measured feedings were given by means of stomach tube and syringe. The antigenic preparations fed were tested for their efficiency on control animals; the minimum lethal dose was freshly determined and the lethality of the dilution actually used in the experiments was also checked on control animals. Rats dying during the course of these tests were all found to have pneumococci in the heart's blood.
As antigens in these tests, we used broth cultures which had undergone autolysis of 2 crops of pneumococci. This material was fed alone in some experiments; in others 2.0 cc. of egg-white' plus 3 cc. of autolysate was used.
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