It has been shown that mice could be immunized by means of a sufficient dosage of formalin-inactivated virus of Eastern equine encephalomyelitis to at least as high a degree of cerebral resistance as that induced by active virus. Cerebral resistance, high at 2 weeks after vaccination of both groups, fell gradually over a period of 6 months; it was once more raised to a high degree by further antigenic stimulus.
Mice vaccinated with a sufficient dosage of formalin-inactivated virus had developed at 2 weeks fully as high a concentration of serum-neutralizing antibodies as mice vaccinated with active virus. The concentration fell in both groups during the following 6 months. At the end of that time, mice injected with a single dose of either active or inactivated virus gave a greater antibody-response than after the initial course of vaccination.
Since each rise and fall of cerebral resistance of vaccinated mice was reflected by similar rise and fall of serum-neutralizing antibody, a correlation has been demonstrated between titer of antibody and degree of cerebral resistance.