Abstract
The effect of active immunization with killed or live vaccines was compared with that of passive immunization, in which the serum of immunized mice was used as the immunizing agent, in the infection of mice with Salmonella enteritidis. Almost similar, though slightly lower, effects as those by the active immunization were given by the passive immunization in the killed vaccine groups. An immunization with the water-in-oil killed vaccine did not show better results than multiple immunizations with the heat-killed vaccine.
Although the most effective protection was produced by the active immunization of mice with the live vaccine (an attenuated mutabile (Murase) mutant), the serum of these immunized mice could confer to normal mice only a slightly effective protection, which was in a similar degree as in the killed vaccine groups.
The O agglutinin titer in the serum of immunized mice was highest in the heat-killed vaccine group. A .re-injection of the serum after challenge did not increase the effect of the passive immunization regularly.
The data presented here seem to indicate a possibility to assume the difference in mechanisms of the immunities produced by killed and live vaccines.
