An experimental study of toluene exposure was performed on mice at various times of the day using the righting reflex and blood concentration as indicators.
One hundred and sixty ICR mice were housed 8 mice per cage for 3 weeks with free access to food and water under a dark-light cycle consisting of alternate 12 hr periods of darkness and light: the dark period beginning at 7:00. The exposure was begun when the mice were 8 weeks old. They were exposed to 10, 000 ppm of toluene for 40 min at 4:00, 10:00, 16:00 and 22:00, and they were sacrificed at the end of the exposure, after 3 min or after 30 min.
The duration of anesthesia was 200.2±15.4 (sec) at 4:00, 361.1±21.5 (sec) at 10:00, 335.1±18.5 (sec) at 16:00 and 309.2±19.8 (sec) at 22:00. The duration of anesthesia at 4:00 was shorter than that of the other times of the day statistically (p<0.01). With regard to the toluene concentration in blood, there was no significant difference between those mice sacrificed at the end of exposure and those sacrificed after 3 min.

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In order to clarify the effects of 2, 5-hexanedione (2, 5-HD) on the central nervous system, the somatosensory evoked potentials (SEP) and the visual evoked potentials (VEP) were experimentally studied. Eight male rats (Jcl-Wistar) were given subcutaneously 300 mg/kg/day of 2, 5-HD five days a week for three weeks. Another eight male rats group served as the control.
One week after ending the administration, the SEP and VEP of rats were measured under artificial respiration using bipolar and monopolar recording methods. The caudal nerve conduction velocities (C-NCVs) were also measured before the administration was begun, and weekly during the experiment, using Ono's method.
Significant findings observed in the 2, 5-HD administered group in comparison with the control group were as follows:
1) delayed latencies in P1 and N1 components of VEP, 2) reduced amplitude between N1 and P2 components of VEP and 3) decreased caudal nerve conduction velocities. It was also observed that latencies of SEP components of the 2, 5-HD administered group tended to prolong in spite of shorter conducting length. Alterations of VEP and a tendency of prolongation in latencies of SEP components were considered to be dysfunctions of the visual and somatosensory afferent pathway attributable of 2, 5-HD.
The present experiments suggest that for further understanding of the effects of 2, 5-HD, on the central nervous system, it is necessary to utilize more sophisticated techniques which can quantitatively detect neurophysiological changes in the ascending tract from the periphery to the cortex.

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To investigate the extra-hepatic organs metabolism of trichloroethylene, the extra-hepatic circulation in dogs was established by operating on the portal vein-right femoral vein bypass and other locations. These dogs were exposed for one hour to trichloroethylene at concentrations of 700 ppm. Metabolite (trichloroethanol (F-TCE), trichloroacetic acid (TCA) and total trichloroethanol (T-TCE)) changes in serum and urine were measured from the beginning of exposure until one hour after termination, and compared with previous data as control.
The following results were obtained.
1) This operation method gave a very slight invasion on dogs. About two hours after the operation, no abnormal findings were observed clinically or physiologically. This method was considered to be one of the best for study of the metabolism of chemical substances in the extrahepatic organs of dogs.
2) The produced ratios of F-TCE, TCA and T-TCE in extrahepatic organs were about 60, 10 and 30% exposure to trichloroethylene at 700 ppm, respectively.

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The relation between work load and the duration of a single spell of work on VDT performance studied in an experimental word processing task.
Nine healthy male college students performed 2-hour visual tasks under the following three sets of work conditions. In the first set, subjects performed VDT work for two hours without intermission. In the second set, subjects had a 10-minute intermission after a 1-hour task. In the third set, there was a 5-minute intermission after a 30-minute task.
Critical flicker fusion, near point distance, subjective fatigue symptoms, heart rate, respiratory rate, blinking counts, electromyogram in upper limb and performance score were measured.
Results are as follows.
1) Decrease in critical flicker fusion, increase in near point distance and subjective fatigue symptoms appeared in all three sets of experimental conditions after two hour tasks.
2) Increased slow wave components on electromyogram and increased errors in performance appeared after 60-minute or more tasks without intermission.
3) Effects on the critical flicker fusion, near point distance, subjective fatigue symptoms, electromyogram, blinking counts and errors in performance were least in the third set. The results of this study suggest that in order to reduce operators' fatigue on VDT work of the conversation type, countermeasures such as shortening the duration of a single spell of work to less than 60 minutes and taking frequent short intermissions are necessary.

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Mortality among employees of selected enterprises in which excellent health care programmes are carried on, was observed to evaluate employees' health levels and to establish objectives for future health care programmes. Also, these data were compared with those for all Japanese and for Japanese employees belonging to the corresponding occupational groups.
Seventy-three enterprises which continuously participated in the mortality survey implemented by the Japan Research Organization of Industrial Health Care for the period between 1976 and 1980, were subjected to this study. The observed employees amounted to 3, 502, 580 person-years. Sex and age distributions of the employees were available for 47 enterprises and the observed employees totalled 2, 598, 672 person-years.
The main results are as follows:
1) Mortality rate (per 100, 000) is stable between 140 and 150 throughout the observed period and the average value is 145.0. The average mortality rate for males, aged 40 to 54, is 272.6.
2) Malignant neoplasms were the main cause of death and account for 37-38%. In second place and below are heart diseases, cerebrovascular diseases, accidents, suicide and liver cirrhosis. Malignant neoplasms, especially of the stomach, lung and pancreas, show a trend to increase, and cerebrovascular diseases and liver cirrhosis show a trend to decrease. Among heart diseases, isch-emic heart disease accounts for about 40% and shows no marked fluctuation. Among cerebrovascular diseases, the relative frequency of subarachnoid hemorrhage is increasing.
3) Comparing the mortality rates for males aged 40 to 54 by industry, “Iron, steel & nonferrous metal manufacturing” and “Electricity and gas supply” show significantly higher values, and “Finance & insurance” and “Communications” show significantly lower values than the total.
4) The distribution of main causes of death for males, aged 40 to 54, was compared by major occupational groups using Proportional Mortality Ratio (PMR). A significantly high frequency of malignant neoplasms (especially of the stomach) is observed for “Professional & technical workers, managers and officials” and that of suicide for “ Craftmen, production process workers and labourers” and that of cerebrovascular diseases (especially cerebral hemorrhage) for “Protective service workers.”
5) Standardized Mortality Ratio (SMR) for males, aged 20 to 54, from all causes of death, calculated on the basis of all Japanese males in 1978 is 0.57. SMR for this population from malignant neoplasms is 0.89. SMR for the same population from all causes of death, calculated on the basis of Japanese male employees in occupational groups corresponding to the studied population in 1975, is 0.75, and that from malignant neoplasms exceeds 1.00.
Consistent with previous reports, mortality rates in this occupational population are significantly lower than those for the total population and the so-called “healthy workers effect” is demonstrated. Moreover, very low mortality rates from tuberculosis and cerebrovascular diseases suggest the effectiveness of disease control programmes which are implemented continuously and throughly in these enterprises. Efficient control programmes against malignant neoplasms remain to be established even in these well-cared populations.

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The purpose of this research was to investigate the effect of consecutive night shifts upon various types of sleep. The subjects studiedwere 9 guards who usually worked on an alternate-day shift system. The nighttime nap EEG (3:00-6:30) during the 24-hr on-duty period was recorded, and then the subsequent day sleep EEG (11:00 to spontaneous awakening) and recovery night sleep (23:00 to spontaneous awakening) were also measured. These records were made for the nap, day sleep and recovery night under two different sets of conditions. The first was for the usual shift cycle (U), i.e. 24 hr duty (10:00-10:00)→off duty→24 hr duty→off duty. The other was for consecutive night shifts (CN) with overtime work (18:00-10:00) performed on the normal off day, i.e. 24 hr duty→8hr off duty→40 hr duty→off duty.
The results were as follows:
1) There was no difference between U and CN conditions concerning time in bed and total sleep time in the nighttime nap, day sleep and recovery night. However, the total time of daytime sleep was significantly shortened under both U and CN conditions, as compared with the control night.
2) The amount of REM sleep in the CN condition for both the nighttime nap and day sleep was significantly greater than in the U condition. In the recovery night, REM sleep continued to be slightly greater for the CN condition than for the U condition. Slow wave sleep (SWS) in the CN condition was slightly greater than in the U condition for the nighttime nap and day sleep, but in the recovery night, no difference was observed between the two conditions.
3) In the U condition, the sleep onset REM period (SOREMP) was observed in 2 of the 9 cases, but only during the day sleep. In the CN condition, however, it occurred in 5 subjects during the nighttime nap, in 4 during the day sleep, and in 2 during the recovery night.
4) The REM sleep latency in the CN condition thus tended to be diminished in each type of sleep compared with that in the U condition, but a significant difference between the two conditions was observed only in the nighttime nap.
It is believed that the increase in the amount of REM sleep and in the frequency of SOREMP might be due to the repeated pattern of sleep loss and shortened periods of sleep during consecutive night shifts of prolonged duty, with partial sleep deprivation resulting from lack of REM sleep.

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ここに述べる,有害物質の許容濃度,および騒音,衝撃騒音,高温,全身振動などの各許容基準は,これらの環境要因による労働者の健康障害を予防するための手引きに用いられることを目的として,日本産業衛生学会が勧告するものである.

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