yourself in long periods of lying in bed after a good night's rest. If
we examine the physical and physiological conditions of sleep we shall
better understand its hygiene. Sleep is a state in which the tissues of
the body which have been used up may be restored. Of course some
restoration of broken-down tissue takes place as soon as it begins to
wear out, but so long as the body keeps working, the one process can
never quite compensate for the other, so there must be a periodic
cessation of activity so that the energies of the body may be devoted
to restoration. Viewing sleep as a time when broken-down bodily cells
are restored, we see that we tax the energies of the body less if we go
to sleep each day before the cells are entirely depleted. That is the
significance of the old teaching that sleep before midnight is more
efficacious than sleep after midnight. It is not that there is any
mystic virtue in the hours before twelve, but that in the early part of
the evening the cells are not so nearly exhausted as they are later in
the evening, and it is much easier to repair them in the partially
exhausted stage than it is in the completely exhausted stage. For this
reason, a mid-day nap is often effective, or a short nap after the
evening dinner. By thus catching the cells at an early stage of their
exhaustion, they can be restored with comparative ease, and more energy
will be available for use during the remainder of the working hours.

A problem that may occasionally trouble a student is sleeplessness and
we may properly consider here some of the ways of avoiding it. One
prime cause of sleeplessness is external disturbance. The disturbance
may be visual. Although it is ordinarily thought that if the eyes are
closed, no visual disturbances can be sensed, nevertheless, as a matter
of fact the eye-lids are not wholly opaque. Sight may be obtained
through them, as you may prove by closing your eyes and moving your
fingers before them. The lids transmit light to the retina and it is