upon the
introduction of _pure air_. Let the same prudential course be adopted in
our schools, in connection with other appropriate means, and we shall
readily see the superiority of the natural stimulus of oxygen over the
artificial sedative of the rod.

_The regular and systematic exercise of the functions of the brain_ is
another condition upon which its healthy action depends. The brain is an
organized part, and is subject to precisely the same laws of exercise
that the other bodily organs are. If it is doomed to inactivity, its
health decays, and the mental operations and feelings, as a necessary
consequence, become dull, feeble, and slow. But let it be duly exercised
after regular intervals of repose, and the mind acquires activity and
strength. Too severe or too protracted exercise of the brain is as great
a violation of the organic law just stated as inactivity is, and is
sometimes productive of the most fearful consequences. By over-tasking
this organ, either in the force or duration of its activity, its
functions become impaired, and irritability and disease take the place
of health and vigor.

So important is the law under consideration, and so essential to the
health of the brain and to the welfare of man, that I deem it advisable
to explain more particularly the consequences of both inadequate and
excessive exercise.

We have seen that by disuse the muscles become emaciated and the bones
soften. The blood-vessels, in like manner, become obliterated, and the
nerves lose their characteristic structure. _The brain is no exception
to this general rule._ Its tone is impaired by permanent inactivity, and
it becomes less fit to manifest the mental powers with readiness and
energy. Nor will this surprise any reflecting person, who considers that
the brain, as a part of the same animal system, is nourished by the same
blood, and regulated by the same vital laws as the muscles, bones,
arteries, and nerves.

It is the withdrawal of the stimulus necessary to the healthy exercise
of the brain, and the consequent weakening and depressing effect
produced upon this organ, that renders solitary confinement so severe a
punishment even to the most daring minds. It is a lower degree of the
same cause that renders continuous seclusion from society so injurious
to both mental and physical health. This explains why persons who are
cut off from social converse by some bodily infirmity so frequently
become discontented and mor