The twinning rate was analysed by the vital statistic figures of Japan. During the years 1955 and 1967, there were 151, 709 twin deliveries out of 23, 643, 348 total ones, the frequency being 6.42 per 1, 000. By the Weinberg's differential method for zygosity estimation, the monozygotic twinning rate was 4.16 per 1, 000 and the dizygotic was 2.26.
Twinning rates in 46 prefectures were also estimated and their correlations with meteorological parameters as well as with mortalities from cerebrovascular diseases and breast cancer were examined. The twinning rates increased from a low level in the southwest of Japan to a high level in the northeast. The tendency was more definite in the dizygotic twinning rate than in the monozygotic one.
A negative correlationship was observed between incidence rates of dizygotic twins and mean air-temperatures throughout the year, and a positive one between incidences of dizygotic twins and mortality rates for vascular lesions affecting the central nervous system in 46 prefectures. From the results obtained, it is possible to say that the climate acts upon the incidence of the dizygotic twin birth within a single race-group.
The author wishes to express his appreciation to Dr. G. Watanabe for his advice.

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Measurement of mobility of lumbar spine for numbers of population in Nagasaki prefecture has been conducted in this department of hygiene, using Iino's spinometer, to assess the physiological aging of community residents. A statistical analysis was carried out with the data for some of the population on the change in mobility of the lumbar spine due to aging and on the relation between the angle of lumbar spine at natural erect posture and the values of lumbar spine mobility. The subjects were farmers and fishermen consisting of 629 males and 537 females ranging in age from the 20's to the 60's. The angles of lumbar spine at flexion and extension were expressed in plus and minus signs, respectively.
The results were summarized as follows:
(1) The angle of lumbar spinal column in the erect position (physiological lordosis, AEP), angles at maximal flexion (AF) and at maximal extension (AE), ranges of maximal flexion (RF) and of maximal extension (RE) and total range of both motions of flexion and extension (RIFE) showed that they change with age. Significant differences were found in the range of maximal flexion and the total range of maximal flexion and extension by age and sex, decreasing with age and greater in males than in females.
(2) Between each characteristic positive or negative correlationship was found to some extent.
(3) After removal of the change due to the age, the following partial correlationships were found.
The angle at the erect position correlated positively to the angle at the maximal flexion and negatively to the motion range in the flexion, meaning that the decrease of physiological lordosis results in the increase of the angle at the flexion, however, it results in the decrease of the motion range in the flexion. The angle at the erect position correlated positively to the angle at the extension and the motion range in the extension, meaning that the decrease in the physiological lordosis results in the increase of the angle and the motion range in extension. However, the angle at the erect position correlated negatively to the total flexion-extension range, suggesting that the decrease of the physiological lordosis has a disadvantageous influence upon the mobility of the lumbar spine.

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Japan has been faced with a difficult social problem of housing as she is a small island-country of 370, 000km² with a large population of about 100, 000, 000.
Accordingly, it is very important to study how to utilize rooms in a house from the standpoint of public health.
The author examined the actual state of living conditions of public apartment houses by a questionaire method to 1, 073 housewives living there.
Public apartment houses examined in Okayama and Fukuyama cities were classified into four types such as 3DK (3 rooms with a dining-kitchen), 2DK (2 rooms with a dining-kitchen), T3LK (3 rooms with a terrace and a living-kitchen) and T2LK (2 rooms with a terrace and a living-kitchen).
The residents of these houses were regarded as belonging to the same socioeconomical class.
The results were as follows:-
1. 35.6% of the families used the same room as dining- and bed-rooms. 43.5% of them as living- and bed-rooms.
2. 29.6% of parents with children of primary school age and older slept in the same bedroom with their children.
3. In 27.2% of families with children of 10 years of age and more, male and female slept in the same room.
4. The way of utilizing rooms were closely related to the size and number of rooms, family size and house type.
5. 36.2% of the families might live more effectively if they could exchange their houses among each other.

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The effect of Di-2-Ethylhexyl Phthalate (DEHP) on fetus and offsprings was studied on reproductive performance in Wistar rats. DEHP was added to the diet by giving the animals pellets made from the above diet. DEHP was given to pregnant rats at dose levels of about 2.0g/kg/day (A group), 1.0g/kg/day (B group), 0.4g/kg/day (C group) and 0.2g/kg/day (D group), respectively. The results obtained were as follows.
Sexual cycle was observed during temporal irregularity in the high dose level groups. Conception, parturition, gestation period days and the mean number of the implants showed no differences among each group. But, an increase in number of resoptions and decrease in fetal body weights were found in the treated groups. Development of weaning rats showed a dose dependent relationship and produced a significant decrease in the body weights statistically.
The results of this study would suggest that there was conclusive evidence of reproductive performance effect of DEHP in rats.

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The present study was undertaken to examine possible differences in smoking habits between Japanese males in Japan and those in Hawaii, and to investigate whether the higher mortality from lung cancer in the latter group may be explained by a greater usage of cigarettes in Hawaii.
Data from the NI-HON-SAN Study, an epidemiologic study on cardiovascular disease in Japanese males living in Hiroshima-Nagasaki, Honolulu, and San Francisco, ware utilized to investigate possible differences in smoking habits between Japan and Hawaii. In contrast to the Hiroshima-Nagasaki cohort, the Honolulu cohort had fewer current cigarette smokers, but included more ex-smokers (22.6% vs. 11.7%; age adjusted), more current smokers who started smoking earlier in life (e.g., 21.8% vs. 13.1% for less than 20 years of age) and more heavy smokers (e.g., 12.8% vs. 7.3% for at least 30 cigarettes a day).
An expected lung cancer mortality index was calculated for each cohort. In each cohort, men who had smoked were assigned higher relative risks which were estimated from published data on the basis of cigarette consumption, age at onset of smoking, and (for ex-smokers) duration since quitting. In each cohort, the resulting risk categories were multiplied by the proportion of the population they represented and summed up to produce the index of expected lung cancer mortality.
Despite the differences in smoking habits between the two cohorts, the two indices had a similar value and failed to reflect the observed difference in lung cancer mortality between Japanese men in Japan and those in Hawaii. Because of the problems in deriving adequate relative risk estimates from the literature and the absence of comparable data on inhalation and smoking habits in the distant past in Japan and Hawaii, this result should be interpreted cautiously. However, the possiblity that smoking is a stronger risk factor in Hawaii than in Japan or that there might be some other lung cancer risk factor in the two locations cannot be ruled out.

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On the assumption that the preventive efficacy of Japanese encephalitis (JE) vaccine is somewhat influenced by the season at birth, the relation among them was retrospectively investigated by studying 4, 854 JE cases in Japan during the period 1965-1970.
The vaccination histories of patients were obtained from JE case individual surveillance cards reported to the Ministry of Public Welfare by Hygienic Department of each Prefecture. Among 4, 272 JE cases, on whom vaccination histories were obtained, 879 cases (20.6%) had been vaccinated previously. The ratio of the vaccinated was differently fluctuated by season of birth among 458 cases born in JE epidemic years of 1948-1958 (with average JE morbidity of 3.6/100, 000), whereas it was not much different seasonally among 429 cases born in JE non-epidemic years of 1940-1947 (with average morbidity of 0.3/100, 000). Among the patients born in epidemic years, the ratio of the vaccinated was significantly high (p<0.005) in those born from April to June and significantly low (p<0.01) in those born from January to March, while there was no significant seasonal fluctuation in the ratio of the vaccinated among those born in non-epidemic years.
Since the ratio of the vaccinated among the total population is not likely to differ by season of birth, the fact that vaccinated persons were more frequently found among the cases born from April to June in epidemic years than among those born in other seasons of the same years, is considered to show the less efficacy of JE vaccination among those born in epidemic season of epidemic years. The result implies the possibility that the immunological capacity of infants may have been modified by the preceding latent JE virus infection on particular fetal or neonatal stages and the modified immunological capacity may have changed the preventive efficacy of JE vaccination against JE virus infection even more than ten years later.

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