Neutralizing and complement-fixing antibodies against herpes simplex virus in sera of 466 persons covering various age groups collected in 1969 were first examined. The general pattern of distribution of neutralizing antibody among children and adults older than 30 years was similar to that previously reported by Yoshino et al. (1962) with sera collected in 1959 to 1960. A significant difference from the earlier survey was that the age group of 20 to 30 years showed various levels of neutralizing antibody in contrast to the earlier data in which a similar antibody distribution was seen between 10 and 20 years. The quantitative relation between neutralizing and complement-fixing antibodies of the above age group also resembled that of younger age groups. Further confirmation of this change was made with additional 51 serum samples collected in 1973 from adults aged between 20 and 30 years. Comparison of the present data with the earlier survey was justified by demonstrating that the methods used for detection of neutralizing antibody were almost equal in sensitivity. These results suggest that primary and repeated infections before the age of 30 years are more frequent than before and it is only after this age that persistent infection is established in the majority of population.

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The pathogenicity of the DIs virus was compared with those of three other vaccinia virus strains, Lister (Elstree), Ikeda and IHD, by intracerebral inoculation into cynomolgus monkeys. By inoculation of a large amount of the virus into the thalamus and cisterna, the animals receiving the DIs virus remained normal, whereas those receiving the other viruses showed severe clinical symptoms such as anorexia, apathy, coma, and paralysis, and were found moribund or dead within a few days. Histological studies also revealed a big difference in the severity of lesions induced by the DIs virus and those by the other three vaccinia viruses, although the main common finding was leptomeningitis purulenta acuta.
Immunization of cynomolgus monkeys with a single shot of the DIs viurs via the sc, id or im route, followed by a percutaneous challenge with the Ikeda virus, revealed that the skin resistance had not been established (Tagaya et al., 1973) . Studies on the dynamics of circulating hemagglutination-inhibiting and neutralizing antibodies, however, indicated that the immunized animals responded more readily and strongly to the challenge with the Ikeda virus than did non-immune animals. This may suggest that the DIs virus induced basic immunity in monkeys, although circulating neutralizing antibody was not detectable and skin reactions by the Ikeda virus were only slightly modified. Thermolabile vaccinia virusneutralizing activity in the serum also appeared or increased by inoculation with the DIs virus as well as with the Ikeda virus. The immunological role of this substance awaits further studies.

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The defense mechanism against plague infection in mice was correlated with transferrin or other iron-chelating proteins, since the resistance to infection was lowered by administration of iron drug (Blutal) . This conclusion was drawn from several experiments designed to see the outcome of infection caused by administration of an attenuated plague strain EV and Blutal in various route combinations.
Ip administration of Blutal enhanced EV infection caused through any route leading to a fatal course similar to virulent infection. Sc administration of EV together with Blutal produced a particular type of infection, whose pathogenesis appeared to differ from others as demonstrated by characteristic distribution of EV organisms and histopathological pictures. Simple reticuloendothelial blockade with carbon particles did not produce plague infection with EV by any route combination.

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