For the purpose of estimating median date of epidemic time curve of patients of Japanese Encephalitis consulting atmosphelic temperature, duration of sunshine and rain fall in the respective month from January to July, the multiregression equation was devised. The error of the multiregression equation was estimated to be 12 days.

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Japanese encephalitis patients in Okayama Prefecture are very few yielding four patients in the southern district and only one patient in the northern district.
Examining the relationship between the cause with which the above fact (the low prevalence of the disease) came out, and the date on which swine turned out positive in their sera, the following results were obtained.
1) The date showing 50 percent positive HI reaction in swine came more lately in this year, 1970 than past years of 1965-1969, taking the date of the 24th in August in the southern district and the 31th in the same month in the northern district.
2) The shortness of the active term of mosquitoes of Culex Tritaeniorhynchus owing to the late coming of the date showing HI positive reaction in swine serum can be pointed out as the cause of the low prevalence of the disease.
3) It can be said in 1965 year to 1970 that there is a tendency of the lower morbidity rate in both southern and northern district according to the later coming of 50 per cent positive HI reaction in swine. And the correlations between the date of the 50 per cent positive HI reaction and the morbidity rate of the disease were shown as the value of -0.75 in the southern district and -0.68 in the northern district in Okayama Prefecture.
4) With the test made in the term of the 28th, July to the ninth, September, the positive HI reaction was not observed in domestic fowls.

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Plaques produced by Japanese encephalitis virus (JEV) on the monolayer of chick embryo fibroblasts, formalin-treated purified JEV, supernatant of the culture media of JEV-inoculated chick embryo fibroblasts and JEV-inoculated mouse brain were studied electron microscopically to determine the size, shape and developmental process of JEV.
JEV particles observed were spherical, approximaterly 40mμ in diameter and coated with an envelope having spikes.
In plaques, numerous JEV particles formed aggregates, some of them displaying a crystalline arrangement, among degenerated mass of chick embryo fibroblasts. Some of the aggregates were observed to be wrapped with a membraneous structure in the cell debris.
Besides JEV particles, numerous virus particles presumably pertaining to avian sarcomaleukosis complex were seen among normal chick embryo fibroblasts.
In inoculated mouse brain, JEV particles were observed in the cytoplasmic vacuoles and intercellular spaces.
The finding above confirmed author's previous electron microscopic observation on JEV particles.

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There are 23 case reports on neurological complications accompanying Japanese B encephalitis vaccination for the 5-year period from 1966 to 1970. Clinical features of these symptoms were analyzed and they were roughly classified into 5 groups, though their neurological symptoms proved to be variable. Namely, 1) meningoencephalitic type, 2) demyelinating type, 3) paroxysmal disorder type, 4) polyneuritic type and 5) others.
Group I (meningoencephalitic type) includes 3 cases of 5, 8 and 44 years old. One of them had the onset of neurological symptoms 63 days after the vaccination, and was diagnosed as Japanese B encephalitis by immunological test. The remaining two cases developed symptoms within 4 days after vaccination, and their principal symptoms were headache, vomiting, stiffness of the neck, involuntary movement, drowsiness and pleocytosis in C. S. F.. Their prognosis proves to be fair.
Group II (demyelinating type) includes 3 cases of 7, 24 and 44 years old, and they had developed the disease 3 to 9 days after vaccination. Their main symptoms were cranial nerve palsy, optic atrophy, spastic paraplegia, cerebellar ataxia, and their prognosis is poor.
Group III (paroxysmal disorder type) is consisted of 4 cases of age ranging 6 to 23 years old. Two of them had episodes of epileptic seizure prior to the vaccination. They had attack within a few hours to 6 days after vaccination, and their principal symptom was epileptic seizure of grand mal type.
Group IV (polyneuritic type) includes 6 cases of the age ranging 3 years to 60 years old, and they had the onset of disease within several hours to 17 days after the vaccination. Two cases of the six had Guillain-Barré syndrome as their main symptom, and the others cranial nerve palsy. Their prognosis proves to be fair.
Group V (others) includes 7 cases of which 4 had cerebral vascular attack after the vaccination.
A discussion was made on the pathophysiological mechanism of these neurological symptoms on the basis of characteristics of clinical features, the age of onset and the latent period.

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In 1970 we selected 9 spots, i.e. 2 spots in the northern part, 1 in the middle part, and 6 in the southern part of Okayama Prefecture. The day-light type light-traps were settled from 30 minutes before the sunset till the following morning, twice a week, from the beginning of April (except for 4 spots in the southern and 1 in the northern parts where the day-liht type light-traps were settled from June) till the end of September. Comparing to the whole number of collected mosquitoes last year, the mosquitoes are considerably decreasing in number this year with a few exceptions. In Tsuyama, the northern part, there is an increase of 56%, 2562 (1969) to 4002 (1970). In the southern part there is a little increase at the two spots, 284 to 361 at Hama in Kurashiki and 1967 to 2197 at Okayama Prefectural Health Center.
The thmperature has exceeded 25°C from July 18 to September 13. Only during this term Culex tritaeniorhynchus (C. t.) appeared and the C. t. concentration period in every part was during the time between the end of July and the beginning of August. The number of C. t. has been decreasing these few years, and Japanese B encephalitis patients only counted 2 this year. There is a correspondence of the decreasing number of C. t. to that of patients.

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We had a survey on the nature and the propagation of mosquitoes principally of Culex tritaeniorhynchus at the reclaimed land of Fukuda at Kojima District in Kurashiki City in Okayama Prefecture (1967). The survey was made again from April 21 to November 9 in 1970 with the same methods as in 1967. Mosquitoes were collected with the dry ice-trap and the light-trap for two and a half hours starting at 30 minutes before sunset. These results were compared with those in 1967.
1. In 1970 the numbers of Culex tritaeniorhynchus and Anopheles sinensis were both very smaller than those in 1967 (about one tenth). Culex modestus showed a large increase comparing to the number in 1967.
2. The reason of these phenomena was that pigsties which were about 1 km away from the mosquito collecting spot were removed in 1969, and Culex tritaeniorhynchus and Anopheles sinensis lost the principal source of blood meal.
3. 1 and 2. indicate that in this area Culex tritaeniorhynchus and Anopheles sinensis fed on blood of the pigs and kept the activity sphere of about 1 km.
4. Aedes dorsalis hatches with raining and the appearance of the adult reaches its peak 15 to 20 days after hatching. The eggs can hatch even more than 2 months later since being laid.

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A survey on the nature of mosquitoes was made at a pigsty in Kayou Town, Joubou District, Okayama Prefecture. Mosquitoes were collected with three methods i.e. light trap, dry ice-trap, and hand-capture once a week from June 15 to October 15 in 1969. A fluorescent lamp (20 W) was used for the light-trap. A mosquito-net, about 180cm×230cm×190cm in size was used for the dry ice-trap. The light-trap and the dry ice-trap were settled for two and a half hours starting from 30 minutes before sunset. The hand-capture was used to collect resting mosquitoes on the pillars of the pigsty for 30 minutes from 1 hour after sunset. We obtained the following data:
1. Culex tritaeniorhynchus were collected most with any method, and then the next Anopheles sinesis, Culex vishnui, Culex pipiens, and Armigeres obturbans. The ratio of Anopheles sinensis to the other species in number, with the dry ice-trap, was smaller than that with the light-trap or the hand-capture.
2. In the case of the light-trap, the appearance of Culex tritaeniorhynchus and Anopheles sinensis were influenced by the minimm temperature for the collecting time.
3. Male Culex tritaeniorhynchus acts freely when the temperature is above 23°C and female at the lower temperature than that.
4. Concerning the resting mosquitoes collected by the hand-capture, it was the season when mosquitoes appeared most that the number of engorged was greater than that of the unengorged. This phenomenon was clear in Anopheles sinnsis than in Culex tritaeniorhynchus.
5. Some Culex vishnui were collected, but the number was small and the period was short, so it is not so important as a Japanese encephalitis virus vector.

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