As preliminary experiments of sero-epidemiological study on the inapparent infection of scrub typhus in Japan, the duration of the detectable antibody in sera of scrub tyhpus patients, who were attacked with the disease at the endemic area of Niigata prefecture or manifested the disease by the laboratory infection with R. orientalis, was investigated. The following results were obtained.
1) Among 6 patients who were once attacked with the disease within 5 years, five were positive in complement fixation test for R. orientalis.
2) Among 18 individuals with history of manifest infection 6 to 10 years ago, none was positive in CF antibody, although each 2 were positive among 2 groups of 11 and 5 individuals with the same history 11 to 20 years ago and over 20 years ago respectively.
3) Seventeen inhabitants of endemic area of Niigata prefecture and 7 individuals having been working at the rickettsial laboratory for several years without any apparent. infection of scrub typhus were tested by CFT. None of them gave positive.
4) Weil-Felix reaction (against OXK) on sera showing positive in CFT gave negative results in all except one which was taken from an individual who got the infection about 1 years ago.
From the foregoing, it can be said in general the CF antibody for R. orientalis may disappear within 5 to 10 years after infcetion, but it may exceptionally persist over 20, yeras even after a single infection. On the other hand, Weil-Felix antibody may disappear more rapidly than CF antibody.

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By peroral inoculation of JBE virus to hamsters the infection was established. Virus given perorally got to the central nerves and caused scuh histological changes as were !noticed when it was inoculated into the brains, similar histologic changes being observed also in the spinal cord.
Virus evoked cellular infiltration in the epithelium of the intestine just like polio virus.
JBE virus given perorally was excreted in stool for 3 or 4 days. The virus multiplied in the epithelium of intestine and then partly entered into the lymph stream, the mesenterial lymph nodules and thoracal duct and finally into blood circulation, and partly entered into portal vein, liver, v. hepatica and finally into general blood circulation, giving thusise to viremia.

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