In this study have been examined, prozone phenomen as well as titer rising after extracted and centrifuged, employing Okayama 53 C and 53 D Japanese B Encephalitis strain, both I have isolated. The antigen of hemagglutination of Japanese B Encephalitis that has undergone a lowspeed centrifuge, indicates certain lowest value, at immediately after it expanding gradually to the maximum in a week. This is due to inhibiting substances contained in mouse brain, which the antigen is known to digest and reduce at a low temperature, owing to its fermentative action. With the Nakayama strain, it is due to this fact that the antigenal property has often been referred to; if we aim at a low density as well as at a comparatively high temperature in its preparation, this ability would appear without fail. In case the pH at the time of production proves higher than 7.0, antigenical effect appears marked, while weak in inhibition; in case it is low, antigenal virtue proves weak, but strong in inhibiton. These inhibitive substances are the same with those containd in normal component of
mouse brain, which, would not change because of infection to virus. The antigen of hemagglutination of Japanese B encephalitis prepared from virus infected mouse brain possesses such ferments as to change not only those inhibitive substances of normal compenent of mouse brain, but also those that exist in chickserum.