oes not
injure the nervous system, and severe mental exertion may be undergone,
provided the proper hygienic conditions are observed. The nervous
disorders suffered by brain workers are not, as a rule, due to the work
which the brain does, but to violation of the laws of health, especially
the law of exercise. Such persons should observe the general laws of
hygiene and especially should they practice daily those forms of physical
exercise that tend to counteract the effects of mental work.

*Physical Exercise* properly taken is beneficial to the nervous system
through both direct and indirect effects. A large proportion of the nerve
cells have for their function the production of motion, and these are
called into play only through muscular activity. Then, as already
suggested, physical exercise counteracts the unpleasant effects of mental
work. Hard study causes an excess of blood to be sent to the brain and a
diminished amount to the arms and to the legs. Physical exercise
redistributes the blood and equalizes the circulation. Light exercise
should, therefore, follow hard study. The student before retiring at night
is greatly aided in getting to sleep and is put in a better condition for
the next day's work by ten to fifteen minutes of light gymnastics. A daily
walk of two or three miles is also an excellent means of counteracting the
effects of mental work. The brain worker should, however, avoid violent
exercise or the carrying of any kind of exercise to exhaustion.

*Sleep*, and plenty of it, is one of the first requirements of the nervous
system. It is during sleep that the exhausted brain cells are replenished.
To shorten the time for sleep is to weaken the brain and to lessen its
working force. No one should attempt to get along with less than eight
hours of sleep each day and most people require more. Children require
more sleep than adults. Those under six years should have from eleven to
twelve hours of sleep per day. Children between six and ten years should
have at least ten hours.

*Insomnia*, or sleeplessness, on account of its effects upon the nervous
system, is to be regarded as a serious condition, and hygienic means for
relieving it should be diligently sought. Having its cause in nervousness,
a disturbed circulation of the brain, or some form of nervous exhaustion,
it is benefited through relieving these conditions and in the manner
already described. Of course the external conditions for aiding slee