The normal human daily cycle of activity is some 7-8 hours" sleep alternation with some 16-17 hours" wakefulness and that the sleep normally coincides
21
the hours of darkness. Our present concern is how easily and to what extent this
22
can be modified.
The question is not merely an academic one. The ease with which people can change from working in the day to working at night is a
23
of growing importance in industry where automation
24
round-the-clock working of machines. It normally
25
from five days to one week for a person to adapt to a
26
routine of sleep and wakefulness,
27
during the day and working at night.
28
, it is often the case in industry that shifts are changed every week. This
29
that no sooner has he got used to one routine
30
he has to change to another,
31
much of his time is spent neither working nor sleeping very
32
.
One answer would seem to be
33
periods on each shift, a month, or
34
three months.
35
, recent research has shown
36
people on such systems will go back to their
37
habits of sleep and wakefulness during the weekend and that this is quite enough to destroy any
38
to night work built up during the week. The only real solution appears to be to
39
the night shift to those permanent night workers whose
40
may persist through all week-ends and holidays.