This all means that our educational system must be planned to follow the order of nature. Children of the primary grades should not be required to write with fine pencils or pens which demand delicate finger adjustments, since the brain centers for these finer cooerdinations are not yet developed. Young children should not be set at work necessitating difficult eye control, such as stitching through perforated cardboard, reading fine print and the like, as their eyes are not yet ready for such tasks. The more difficult analytical problems of arithmetic and relations of grammar should not be required of pupils at a time when the association areas of the brain are not yet ready for this type of thinking. For such methods 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.