By inoculating a given amount of Extromelia virus to roups of mice, intrapeitoneally, orally, in toe foot, through the nasal passage, or subcutaneously (the back), and by preparing the suppernatant of the liver emulsion from these infected mice, the author performed erythrocyte agglutination tests (Hists's phenomenon); and obtained the fhllowing resnlts. 1. Juding from the changes in the agglutination values, the most vigorous proliferation of the virus seems to occur at the early stage of the infection and of the onset of symptoms in every group. 2. At the peark of the infection the erythrocyt agglutination value in every group falls rapidly, and this seems to be due to the antigen-antibody reaction. 3. The reticulo-endothelial system is not the necessary site for the infection of Extromelia virus nor doest it has any function as the stie of the antibody production. 4. It seems that the antigen-antibody reaction of Extromelia virus is the serum affinity antige-antibody reaction and it is represented by the changes in the blood vessel listem as its main symptoms. 5. The difference in the distribution of pathologic changes between the diffuse hapatic changes in ths group infected intraperitoneally or orally and localized changes in the group infected unber foot, via nasal passage or subcutaneously (the back) may be interpreted as not to be dependent on the reaction pattern of allergic inflammation bnt to be due to the anatomical difference in the infection route. 6. This interpretation will offer a certain theoretical basis in support of the assumptions made in ous department as regards the pattern of infectious hepatitis and the route of its infection.