ing that give the pupils happy opportunities to loosen the reins of their tired attention and forget the hard present. "One can compel children to sit and be still," says Burgerstein, "but he must not mistake; they will still in many cases take mental rest, or make a change for themselves, and not follow the course of the teaching if they are tired." Hence arises the unexpected consequence that, under the present extension of instruction, tedious teachers are a necessity.
To a certain extent the dangers of mental overwork have been recognized for a long time. All those efforts to introduce physical exercises into the school hours have in view, to a greater or less extent, the defense of the childish brain against the imminent dangers of a one-sided tension by alternating mental and muscular exertion. Gymnastic and movement exercises, manual training, and singing and drawing, to a certain extent, are intended to furnish rest-pauses for recovery from mental weariness and the gradual restoration of the previous efficiency. For this purpose such have been interposed at intervals to relieve the strictly mental work.
The physical exercises are doubtless of considerable value toward the complete building up of the personality, but they must be regarded as relaxations only within certain limits. It is, at any rate, fundamentally false to regard physical effort as in any way a suitable preparation for mental labor. Protracted experiments, pursued under my direction, have given the result that a simple walk of from one to two hours diminishes the mental efficiency in adults at least as much as about an hour's work in addition. The same is the case to a more limited extent with much less important bodily efforts. It is well known to pupils and teachers that the greater the interval of active play, the longer time is required for collecting the faculties before returning to mental work. From these experiments has arisen the demand that physical exercises should not be regarded in the plan of teaching as relaxations; and the demand for hard mental work should not be imposed on the pupil till after a rest from them.
By far the most important compensation for all effects of fatigue is sleep. Everybody, even the man mentally most inert, develops when awake a mass of mental effort which he can not afford continuously without suffering. We need, therefore, regularly recurring periods in which the consumption of mental force shall be slower than the continuous replacement. The lower the degree to which the activity of the brain sinks, then, the more rapid and more complete the recovery.
The mental vigor of most men is usually maintained at a certain height for the longest time in the forenoon. The evidences of fatigue come on later at this time of day than in the evening,