It is a law that the accidents are caused only by wrong contact of the worker with physical solids around him. Accordingly, accidents may be avoided by suited movements against a pressing danger, but this is not easy because the wrong contact happens agaisnt their own will and wisdom of the workers. Then, the hourly accident rate may mean the hourly trend of mistaken movements. Vernon, H.M. and other have shown hourly tendency of accident case rate in many sorts of industries. The morning, trend is sound to be upward, but frequently there is a drop in the last hour. The afternoon trend is less consistent and shows more variations in different industries. Although the accident rate of the afternoon period, in most instances, begins at a higher point than that of the morning the total number of afternoon accidents doesn't exceed the morning one. These facts have been regarded by some investigators as a result of fatigue and by others as a result of the fluctuation of density of work. We measured hourly fluctuations of psychological functions of many workers in forestry works and public works with colornaming, c.f.f. and two-point limen. And it was found that the hourly trend of those functions in workers coincided with their hourly accident curves which showed upward trend in the last hour, inspite of low density of work with increased rest pouses of workers. Moreover, in iron works, we found that the frequency of drawing worker's maladjusted movements increased in the last hour and this tendency was much more apparent in the afternoon than in the morning and father more in the midnight than in the afternoon, and that this trend coincided with the hourly frequency rate curve of accidents.

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Though it is comprehensible from our routine experience that fatigue should be an important cause of accident, the proving of it is next to impossible. As far as every hour's accident rate is concerned, accidents caused by fatigue seem to be very few in common factories. But, in accident curve of heavy workers the peaks tend to thrive toward the end of work, this means the increase of accidents of fatigue origin. This tendency is also found in bus driving, an increase in accident rate several hours after the start (figs. 1, 2). We saw that drivers' fatigue remarkably varied with the condition of roads. FF (critical flicker frequency) curve, which is based on flicker test performed every 15-20 minutes during run, seem to have four patterns in it (fig. 3). Pattern B is obtained from a bad road, C from a good one, A worse than B and D better than C. In A and B FF heavily drops sometime during drive, but not below a certain level as long as the driving is kept on, which is presumably due to the fact that the situation requires a driver to be excited interoceptively or exteroceptively above the level. The level is, therefore, thought to be the lowest bottom of FF he is allowed to take, in other words, the physiological criterion for safety drive. We next examined FF change in accordance with consciousness disorder during the experimental inhalation of low oxygen air and ascertained that when the initial disorder (drowsy state) appeared in brain wave (fig. 4, 5) the ability in mental work such as a simple adding showed a quick drop (fig. 6). FF at this period when normal mental activity begins to get impaired I call a critical level (CL). CL is variable individually 85-92 per cent of the resting level, but almost constant with the same person. And it appears nearly equal to the safety limit during drive as seen from the diminution rate of the two. When FF during run surpasses the critical level normal mental activity must be in disorder, thus increasing the possibilty of accidents. Hence the relation between fatigue and accidents can be discussed with regard to the FF curve and critical level mentioned above.

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Considering mental and physical work as stressor, a study of the variation of the living body against loads through function of hypophysis and adrenal cortex in other words, on the mechanism of homeostasis has been made. As indices, uropepsin, circulatory eosinophils and 17 ketosteroid in the urine have been chosen. 1. How will the living body react by physical work? Circulatory eosinophils decrease by 30% when standing for a period of 2 hours. The circulatory eosinophils decrease by 40 to 60% on loading step test. In the later case, the recovering period is delayed. The 17 KS quantity in the urine decreases on the contrary when relaxed. No increase is observed in bycicle ergometer work or in load work of step test. 2. How will the living body react by mental work? By Kraepelin addition test, eosiophils decrease and the rate of decrease is larger as the calculation volume increases and the recovering period is delayed. A considerable regularity can be seen when the work quantity is the same. 3. How is by diurnal variation? Circulatory eosinophils increase by bed-rest. If relaxed during the morning, the deteriorating phenomenon of eosinophils does no happen. When sitting up all night, any increase during the night can not be seen. The excretion quantity of 17 KS in the urine increase by shortening the period of sleep. As to the fractions of 17 KS in the urine, not only the increase of those proper to the adrenal cortex but also that of the androgenic can be seen. The uropepsin is lowest while sleeping at night and highest just before and after starting the work in the morning, and decreases at night.

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Often workers exposed to heat show more than 1.3l perspiration per an hour. Plasma condensation is slight and the recovery is quick by trained persons. By untrained persons plasms condensation is more than that of Hb and its restoration is delayed. When plasma is condensed more than 1.034 in its specific gravity, creatinine excretion in the urine decreases unless water is taken. Creatinine hardly responds to the urine volume for its difficulty of reabsorption in the urinary tubule until the volume is reduced to less than 20 ml/hr, and after that creatinine excretion decreases very much. Na, Cl and K diminish in accordance with the urine volume as they are reabsobed in the urinary tubule. The relation among them can be determine if creatinine is employed as an indicator. The constituent of sweat is affected by the perspiration rate. In the course of excessive perspiration pH becomes alkali and lactic acid pyruvic acid ratio increases. PH becomes acidic and Cl concentration is low in summer, both of which are related to the perspiration rate (figs. 1, 2). It is possible to recognize the summer-type of swest even in winter by using DOCA. Ig DOCA is used in summer, it causes Na retention and cardiac disfunction. Water and salt are deprived by excessive sweating as already known. Ca concentration in the sweat is a little smaller than in the serum. 6l perspiration a day means a loss of 0.4 gr Ca a day. It is very important, for the Japanese, because they take very small amount of Ca (0.3-0.4gr a day). The first function that limits work in hot environment is pulse rate. 130 beats per minute is thought to be the limit. It is difficult to continue the work with the pulse rate of 160-180. Workers of long experience in hat environment complain of the heart trouble, which will probably be the result of their cardiac burden and overfunction of the adrenal cortex. Fatigue in the excessive sweating appears to be due to the overload in circulatory systems and the loss or anormal distribution of extracellar fluid and minerals by sweating. Intake of the salt of organic acid such as sodium citrate was useful for diminishing the feeling of fatigue and maintaining alkali equilibrium. Taking tablets of table salt does injure the mucous membrane of the stomach.

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To see the relationship between the living body in a dynamic state by load and instantaneous effects of vitamins, two series of experiment were made. On the somatic fatigue, the effects of the difference of the administration time was examined. On the mental fatigue, the mechanism of the effects of instantaneous preventive administration was investigated. A. Experiments on somatic fatigues. Groups of rats (Group I, II, and III) were fatigued by enforced swimming till they were cap-able no more swimming. The swimming was loaded 3 times, with 30 minutes rest between the 1st and the 2nd, and 60 minutes rest between the 2nd and the3rd. Every data was compared by the percentage of the duration of the 1st swimming. Group I was the control without injection. Group II was injected just before the 2nd and the 3rd swimming. Group III was injected just after the 1st and the2nd swimming. The experiments (A, B, C, and D) were repeated with several days interval. In the experiment A, thiamine 2.5 mg, in the experiment B, glucose 50 mg, in the experiment C, thiamine 2.5 mg+glucose 50 mg, and in the experiment D, thiamine 2.5mg or glucose 50 mg etc. were injected subcutaneously. The results obtained were as follows: (1) Thiamine is effective when it is administered at the beginning of recovery. But even with such administration glucose has no effects if it is administered just before the next swimming. (2) Thiamine+glucouse is effective to prolong the endurance time when it is administered before swimming. (3) It seems that the thiamine which is used effectively during recovery is either excreated or altered if it has been administered before glucose administration. B. Experiments on mental fatigues. It was investigated on human subjects whether or not variations of flicker fusion values, patella reflex thresholds, successive reaction time, and EEG by loaded Kraeperin Test were altered by injections in advance of thiamine, riboflavine, and ascorbic acid. The results obtained were as follows: (1) Thiamine (less than 10-15 mg) acts to bring back the cerebral excitation level to the normal steady state. Such effect is recognized as soon as 15 minutes after the injection and maintained 30 minutes or longer. But thiamine in amount more than 30 mg elevate the cerebral excitation level. (2) Riboflavine also shows the same attitude by the difference of doses, but it seems rather more excitable. (3) Ascorbic acid has no such effects in any dose.

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There are usually many experiences that the sleep is very important to recover the fatigue. In recent times, various industries are developing more and more which maintain 24 hours operation. As a result, workers having more chances to work at night. The investigation about the relation between fatigue and the insufficient sleep was experimentally designed. The flicker test was done on office work and the flicker value was found to be declined in the next morning after all-night working. In a petroleum manufacturing factory, the flicker value declined most severely at work of nightshift, in comparison with day-shift and evening-shift, and the decline of flicker value became more severe day by day. These facts mean that the insufficient sleep influences the brain functions making to decline its the level. And the variations of flicker value by insufficient sleep should be considered on the basis of physiological diurnal fluctuation of functions, that is to say 24 hours rhythm. The investigation was planned as follows (I) subjects: 5 students, (2) duration of sleep: 2, 4, 6, and 8 hours, (3) time to go to bed: 22:00 o'clock, (4) functions tested: sublingual temperature, pulse rate, flicker value, and subjective drowsiness, (5) follow up after awake until evening. Ranking of the levels of function at 8:00 to 10:00 o'clock after various duration of sleep showed that after 0 or 2 hours' sleep the level is lower compared with 4, 6, or 8 hours' sleep and that the ascending of the sublingual temperature after meal is higher with sufficient sleep. Further results could be summarized as follows: (1) With insufficient sleep, ascending of functions is the next morining is disturbed, and descending of functions continues until next evening. (2) If dietetic descending of sublingual temperature is detectable, it means descending of replacement. (3) Subjective drowsiness on the next day means the semisleeping condition. (4) This semisleeping condition is a situation of insufficient efficiency and sleeping. (5) This situation is fatiugue that is carried over to the next day. This condition means of insufficient changing of the higher level of functions at daytime to the lower at night.

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