s violate the law of nature, and
the child is sure to suffer the penalty.

4. IMPORTANCE OF HEALTH AND VIGOR OF THE NERVOUS SYSTEM

Parallel with opportunities for proper stimuli and response the nervous
system must possess good _tonicity_, or vigor. This depends in large
degree on general health and nutrition, with freedom from overfatigue.
No favorableness of environment nor excellence of training can result in
an efficient brain if the nerve energy has run low from depleted health,
want of proper nourishment, or exhaustion.

THE INFLUENCE OF FATIGUE.--Histologists find that the nuclei of nerve
cells are shrunk as much as fifty per cent by extreme fatigue.
Reasonable fatigue followed by proper recuperation is not harmful, but
even necessary if the best development is to be attained; but fatigue
without proper nourishment and rest is fatal to all mental operations,
and indeed finally to the nervous system itself, leaving it permanently
in a condition of low tone, and incapable of rallying to strong effort.
For rapid and complete recuperation the cells must have not only the
best of nourishment but opportunity for rest as well.

Extreme and long-continued fatigue is hostile to the development and
welfare of any nervous system, and especially to that of children. Not
only does overfatigue hinder growth, but it also results in the
formation of certain _toxins_, or poisons, in the organism, which are
particularly harmful to nervous tissue. It is these fatigue toxins that
account for many of the nervous and mental disorders which accompany
breakdowns from overwork. On the whole, the evil effects from mental
overstrain are more to be feared than from physical overstrain.

THE EFFECTS OF WORRY.--There is, perhaps, no greater foe to brain growth
and efficiency than the nervous and worn-out condition which comes from
loss of sleep or from worry. Experiments in the psychological
laboratories have shown that nerve cells shrivel up and lose their
vitality under loss of sleep. Let this go on for any considerable
length of time, and the loss is irreparable; for the cells can never
recuperate. This is especially true in the case of children or young
people. Many school boys and girls, indeed many college students, are
making slow progress in their studies not because they are mentally slow
or inefficient, not even chiefly because they lose time that should be
put on their lessons, but because they are incapacitating their brain