The natural duration of sleep is eight hours out of the twenty-four, and
those who can secure this lead the soundest lives. It is best taken from
ten o'clock till six, and it is most readily obtained by cultivating it
as an automatic procedure. All stimulants, all excitements, all
excessive fatigues, all exhaustions pervert sleep even if they do not
prevent it. The room in which sleep is taken should be the best
ventilated and the most equably warmed room in the house. The air of the
room should be maintained at the natural standard of 60° Fah., and the
body of the sleeper should always be kept completely warm. The bed
should be soft and yielding. A regular tendency to sleep at other hours
than the natural is a sure sign of error of habit or of nervous
derangement.