power of adjusting to varying conditions may even be
stimulated thereby. But even slight fatigue, if continued and especially
if associated with anxiety or worry, has caused many nervous and mental
breakdowns.

Work carried beyond the point of normal fatigue requires a
proportionately longer time for recovery. For example, if the point of
fatigue has been reached by a certain finger muscle after 15
contractions, and if half an hour is required to rest it completely, one
might suppose that one hour would rest it after 30 contractions. This is
not so, however; after 30 contractions 2 hours are required, or 4 times
as much rest for twice the amount of work, if continued beyond the point
of fatigue. Laboratory experiments and experience alike show that this
principle holds true in other forms of fatigue. Thus the output of
factories has been shown in many instances to be greater, other things
being equal, when operatives work 8 hours a day than when they work
longer. Excessive hours in any kind of work are the poorest economy.

Fatigue is increased in direct proportion not only to muscular exertion
but also to the amount of speed, complexity, responsibility, monotony,
noise, and confusion involved in an occupation. Ability to bear fatigue
differs greatly with different people, as ability varies to bear other
kinds of strain. Rest at night and on Sunday, and the annual vacation
should be enough to keep a person in good condition. If not, there is
probably something wrong with the worker's health, the nature of his
work, or his adaptation to his particular kind of work. This statement
is not only true of persons regularly employed, but of those living at
home, including children in school, women in "society," and especially
mothers of families.

SLEEP.--A sufficient amount of sleep is essential to health, but
individual requirements vary widely. Each person should know and regard
his own need, and children and young people should be obliged to go to
bed early. Ability to sleep is largely habit; good habits should be
formed and continued. Sleep-producing drugs should never be taken,
except by a doctor's prescription.

RECREATION.--Owing to the speed, complexity, and worry of modern life
among all classes, and to the monotony of work in industry, recreation
has become a matter of vital importance for everyone. Some muscular
activity, preferably in the open air, is needed by every healthy person.
Recreation should be as unl