Izumi Nakamura

Reduced mercury excretion with feces in germfree mice after oral administration of methyl mercury chloride

SummaryWhen methyl mercury chloride was administered orally the amount of mercury excretion with feces of germfree mice was noticeably lower than that of the control mice. Germfree mice excreted 24 percent of the administered mercury within 10 days of administration while the control mice excreted 46 percent. Mercury retention in the organs of germfree mice was slightly higher than in the control mice. These results suggest that the existence of microorganisms in animal intestines are concerned with mercury excretion in the animal body.

Season of birth of schizophrenics in Tokyo, Japan

The monthly distribution of births of 7,960 schizophrenic patients in Tokyo born during the period 1841–1950 was studied in comparison with that of a control population in Tokyo. A spring excess of schizophrenic births were found after 1901 as in previous studies in Western countries. Before 1900, however, there was no significant spring excess. The maximum excess of schizophrenic births occurred in May before 1900 and in April after 1901. The possibility of a shift in the seasonality of schizophrenic births was discussed.

Changes of recollected menarcheal age and month among women in Tokyo over a period of 90 years.

Data on the recollected age at menarche of 47,881 women born between 1881 and 1970 were examined. The mean menarcheal age had changed from 15.1 years in those born up to 1900 to 12.5 years in those born during the 1960s. The age at menarche differed according to the month of birth, and the pattern of average age distribution by month of birth was not the same when the year of birth was different. Among women born before 1955 the menarcheal age was earlier in those born in the summer. However, among women born after 1955, menarche occurred later when they were born in the summer. The monthly distribution of menarche had also changed during this 90-year period. Two peaks in April and August were prominent among those born up to 1960. A third peak in January became also apparent in those born after 1960.

Twinning rate by month of mother's birth in Japan.

Records of two hospitals and of an association of mothers of twins were analysed for the years 1924-1980, finding a total of 656,109 and 1185 twin births, respectively. Twinning rates were higher in summer or fall, in general, but these seasonal variations occasionally changed within a short period of years, as in 1973-75 in the Association group. The twinning rate was also affected by the month of mothers birth. It was low among the mothers born around May-July in maternities up to 1960, and these mothers did not show seasonal variation of twin births. The unlike-sexed twinning rate of the mothers born in May-July was also lower than that of the other mothers, and constantly low even at higher maternal ages. A possible explanation for these phenomena is discussed.

Mercury content in museum and recent specimens of chiroptera in Japan

SummaryThe mercury content of insectivorous Chiroptera caught in 1890, when mercurial pesticides had not yet been in use, and preserved in a museum in alcohol were compared with those caught in 1965–1967 or 1970–1975, during and after the use of mercurial pesticides, and kept frozen. The mercury content of the Chiroptera caught in 1890 was lower than that of those caught during or after the use of mercurial pesticides. Difference in mercury content between bats caught during and after use was not significant.

A study of the sex ratio of first-born according to the mother's month of birth.

SummaryThe male-to-female sex ratio at birth of the first-born babies delivered in Japan to mothers aged 25 years or less was investigated in two groups: a hospital group and a questionnaire group. The sex ratio fluctuated according to their mothers month of birth. Between 1924 and 1928, the sex ratio of the offspring of the mothers born in March-May in both groups was significantly higher than that of the other mothers. We speculate about the relationship between the sex ratio at birth and the mothers month of birth.

Twinning Rates and Seasonal Changes in Görlitz, Germany, from 1611 to 1860

Old-age twinning rates were evaluated over a period of 250 years (1611-1860), from 80,256 parish records of baptism in a church office in Görlitz, East Germany. Two periods with high and two periods with low twinning rates were observed. Twinning rates were relatively stable in spring and fall, but varied greatly in winter and summer.

Correlation between month of menarche and month of birth

SummaryThe month of menarche and month of birth were studied in 47,218 women who were born during a period of 90 years between 1881 and 1970. Among those born prior to 1960, there was a tendency for menarche to occur more frequently at the month of birth. This coincidence was not, however, found among those born after 1960.

Decrease in twinning rate in a hospital in Tokyo during World War II.

In order to investigate changes in twinning rate during World War II and postwar years, when the people in Tokyo suffered from malnutrition, about 80,000 delivery records during 1924-86 at one hospital in downtown Tokyo were examined. The twinning rate decreased from 1.47% in the 1920s to 0.81% in the 1980s. During the 1940s, the rate was 1.03% for 1940-42 and 0.94% for 1948-49, but it dropped down to 0.70% for 1943-47. In 1945, when Tokyo was heavily bombed repeatedly to be burnt out, and the people suffered from severe malnutrition, only one case of twinning was found among 305 maternities at this hospital (0.33%). While the mean birth weight of term singleton babies was 2953 g in 1940-41, it decreased to 2918 g in 1943-47, especially to 2856 g in 1945. This change in birth weight evidenced that the nutritional conditions in Tokyo became worse in 1943-47. This report suggests that the twinning rate decreased also during this period in Tokyo when the people suffered from malnutrition.

Change in Radiosensitivity of Sea-urchin Eggs during Early Cleavage Stages

When sea-urchin eggs were irradiated with 137Cs gamma-rays, their radiosensitivity, expressed by the percentage which formed pluteus larvae, fluctuated during the early cleavage cycle. Split-dose irradiations were made both in the sensitive and resistant phases. For eggs in the sensitive phase, the effect of the first exposure of 500 rad was not diminished during the interval before the second exposure. Eggs irradiated in the resistant phase were only slightly damaged. Results imply that fluctuations in radiosensitivity of sea-urchin eggs are caused mainly by different degrees of non-repairable damage in each phase of cleavage rather than by different recovery abilities.