The present study was undertaken in order to investigate experimentally the changes ofphysiological functions in a vigilance task. There were two experiments. Experiment I was performed on healthy male students of an university to determine the effect of signal rates on physiological functions, detection performance and subjective feelings in a vigilance task. Experiment II was performed to compare the changes of physiological functions, performance (detection per-formance, correctness, output) and subjective feelings in a vigilance with those in a continuous arithmetical calculation task.
In the experiment I, the heart rate in the task employing middle signal rates (task I) showeda higher tendency than that in the task employing low signal rates (task II), while the respiratory rate, the amplitude of plethysmogram and the galvanic skin reflex (GSR) frequency showed ap-proximately the same value in both tasks.
The level of the detection performance in task I was generally similar to that in task II.
The subjects reported that task I was easily performed as compare with task II which wasmore boresome.
In the experiment II the increment of the heart rate did not occur during the vigilance taskemploying low signal rates, whereas it occurred during the calculation task and the heart rate decreased after the task. GSR frequency increased with the onset of both tasks, giving a higher value during the calculation task than during the vigilance task and showing a decrease after both tasks. The decreased amplitude of the plethysmogram did not appear at the beginning of the vigilance task, whereas it had a tendency to appear at the beginning of the calculation task.
Although the vigilance task evoked mainly subjective feelings such as boredom and drowsiness, the calculation task evoked a strained state and local fatigue of the right hand and arm. The subjects reported that the calculation task tended to be performed with ease as compared with the vigilance task.
There was no correlation between detection performance in the vigilance task and correctness or output in the calculation task.
From the above results it seems that a slight acceleration of physiological functions are necessary to maintain a relatively suitable state in the human body and that comparatively unpaced task such as calculation is a relatively suitable state for subjective feelings as compared with the vigilance task which is passively performed, though a higher acceleration of the physiological functions occurs during the calculation task. It is assumed that it may be necessary to consider not only the levels of the physiological functions, but also a psychological state which is affected by the experimental conditions in these mental tasks.

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Lead poisoning is associated with characteristic urinary increases of δ-aminolevulinic acid and coproporphyrinogen III, elevated erythrocyte protoporphyrin concentration and partial block of δ- aminolevulinic acid dehydratase.
In human lead poisoning a very small amount of increase of porphobilinogen and uroporphyrinogen III is reported, while in rabbits porphobilinogen increases but uroporphyrinogen III does not as in the human cases. The small amount of porphobilinogen or uroporphyrinogen III in the human urine may be explained by δ-aminolevulinic acid dehydratase inhibition, but the increase in coproporphyrinogen III is as yet inexplainable.
An alternative pathway of coproporphyrinogen III formation from δ-aminolevulinic acid or porphobilinogen has and suggested in lead poisoning. We proposed that an intermediate, 2-amino-methyl-3-methyl-4-carboxyethyl-pyrrole, may be formed in vivo by enzymic condensation of δ-aminolevulinic acid and 1-amino-butane-2-one (β-ketobutylamine) or by prior decarboxylation of acetic acid sidechain of porphobilinogen. To test this hypothesis we made an experiment, the results of which are as follows.
The pyrrole compounds were isolated from the urine or the incubation mixture with δ-aminolevulinic acid and tissue homogenates (bone marrow, liver and kidneys) of lead poisoned rabbits by using the column chromatography on Dowex 2. All the pyrrole compounds were further converted to porphyrins by chemical condensation technique, resulting in the formation of the mixture of uroporphyrin isomers, though no coproporphyrin was detected.
The results indicate that the pyrrole compounds in lead poisoning are identical with authentic porphobilinogen and the prior decarboxylation of porphobilinogen appears unlikely. It is suggested that the increase of coproporphyrinogen III in lead poisoning may be caused by over-production of δ-aminolevulinic acid. The increased amount ofthe precursor seems to overcome the partial blocking of δ-aminolevulirlic acid dehydratase and thenormal rate of porphyrin synthesis may be formed.

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