The differences in the susceptibility of different persons to fatigue are very interesting. Every person, as a rule, possesses a course of efficiency peculiar to him, which works itself out in the same manner during any particular period of labor. Some display in single efforts first an increase and then after some time a decrease of efficiency; they are least readily fatigued. Others, registering a depression of efficiency after the first quarter of an hour, betray a very great susceptibility to fatigue. All the transitions are observable between these two forms, but each individual generally follows the same course according to his personal peculiarity.
The susceptibility to fatigue is observed in all possible examination tasks, and may therefore be considered to represent a bottom principle of the individual personality, which, while it may be influenced within certain limits, as a general rule measurably determines the capacity of men for work.
Other means of measuring the capacity of a subject are afforded by the ease with which he is diverted from his task, or his susceptibility to disturbing influences from without and from within; his elasticity, or the readiness with which he recovers from the effects of fatigue or diversion; and the way he is affected by taking food, physical exercise, and the time he has for sleep. In each and all of these fields of inquiry the result obtained has to be complemented finally by the estimation of the qualitative value of the work accomplished.
We may infer from this passing review that it is actually possible to express important properties of mental personality in measurable, generally comparable, determinations. But we are still far from being able to apply such measurements to the purposes of daily life. Yet, while we fail if we attempt to draw certain lessons from the matured, complicated organization of the grown-up man, the simpler, still growing mental equipment of the child affords a more fruitful field for study and is more subject to our influence.
The question then presents itself for investigation of the mental endurance of our school children. The school requires its pupils to perform daily a specified amount of mental work, while it is really not clearly known whether the childish brain is actually able to fulfill the demand without suffering lasting damage. The young men I experimented upon, whose facility in addition fell off at the beginning of the second hour, had already had their working powers exercised and tested by responding to the demand of the school and of the university. Against them was a child two years old, who gave plain evidences of weariness after only a few minutes of fixed attention. Valuable researches on this subject have been made by Prof. Burgerstein, of Vienna, who com-
