gotten, on the other hand, as Corning suggests, that there may be excessive development and use of the muscular system, especially in people with limited digestive power; but the temptation of brain-workers is, doubtless, not generally in that direction. Because of the "close analogy between the effects of mental fatigue and those of muscular fatigue," LaGrange speaks of "the dangers of mere physical exercise without diminution of brain work," and expressly recommends simple exercises as best for brain-workers. Temptations enough we are certain to meet; we have no right needlessly to increase them. Yet blood is not the first and chief factor in attention, Mosso says, but nerve power.

2

3

The Need of Surplus Nervous Energy. Effects of Fatigue. Particularly important, therefore, in the bearing on both intellectual and moral efficiency, are the facts as to fatigue.

The Effect of Fatigue on Attention and

1 Brain Exhaustion, pp. 47, 188 ff.

2 Op cit., pp. 351, 339 ff., 379 ff.

3 Cf. on the whole, Burnham, School Hygiene; Dresslar, Fatigue ; and Chamberlain on Mosso, Pedagogical Seminary, Vol. II, pp. 9 ff., 102 ff., 267 ff.; and, for many illustrations, Coe, The Spiritual Life, PP. 71 ff.

Self-Control.-The facts as to fatigue are important, for one reason, because scientific observation seems to show that natural power of self-control is directly proportioned to the amount of surplus nervous energy. "The phenomena of inhibition. are the stronger," says Höffding, "the fuller the organism is of life, and weaker when the organism is in a state of fatigue." "In this respect the condition of the central organ is of decisive influence."1 All self-control seems to involve the use of the higher brain centers which are first affected by fatigue or any abuse, and self-control becomes increasingly difficult as these centers are overtasked. Brain-fag, Beard says, brings inability to bear responsibility, defective and uncertain will, lack of power to inhibit, while "perfect inhibition is the sign of perfect health."

But power of self-control lies at the foundation of all intellectual attainment and of any possible character. Control of appetites and passions, even the lowest degree of prudence, to say nothing of unselfish subordination of one's own interests, rests directly upon the power of self-control. There can be no growth in practical wisdom, or progress

1 Op. cit., p. 44.

toward a better self-mental or moral-for one who cannot hold the present in abeyance to the future. The cardinal difference between the sane and the insane, even, lies in self-control. Dr. Starr says, "its deficiency is universally regarded as evidence of mental instability." It is, therefore, of no small moral interest to determine the bodily conditions of self-control.

In a general way, every one knows from experience that when he is tired it is harder to be decent. But the more recent investigations of physiological psychologists into the phenomena of fatigue give needed emphasis and point to this observation. Psychologically, the power of self-control consists chiefly in the power of attention, the power to hold steadily before one the future advantage, the reasons for the better course, the broader wisdom, in spite of the incitements of present impulse. Now, the most careful observations yet made,-those of Mosso,-show that "attention is the chief condition of mental fatigue," and this means that fatigue directly hinders the power of attention and consequently the power of self-control. That is, we are dealing here with the immediate physical conditions of will-power. What, then,

are the facts about fatigue, what are its conditions and signs?

Direct Effect of Fatigue on Nerve Conditions. The importance of surplus nervous energy is emphasized by all specialists in this field. Dr. Clouston says, "Exhaustion of nervous energy always lessens the inhibitory power" and speaks of "reserve brain-powerthat most valuable of all brain qualities." Dr. J. M. Granville says: "The part which a stock of energy' plays in brain work can scarcely be exaggerated." Dr. W. H. Burnham, after reviewing all the recent important investigations of this kind in the world, emphasizes the fact that in the nervous system "only a limited amount of energy is available at any moment"; and "the one essential thing in economic brain action is the maintenance of the proper balance between the storage and expenditure of energy." Fatigue is the sign that the reserve stock is being drawn upon, that one has begun to consume his principal. To continue work in spite of warnings of weariness is simply to drug the watchman of the treasury. Direct experiment in electrical stimulation of the nerve-cells of frogs and cats shows a "remark1 Popular Science Monthly, Vol. XX, p. 104.

able shrinking of the nerve-cells, particularly of the nuclei." After five hours' continuous work, the cell nucleus is only half its normal size, and twenty-four hours of rest are necessary for complete restoration to its normal state. But half the amount of work, it is particularly worth noting, does not require nearly half the amount of time for recovery. In experiments by Dr. Hodge on nerve-cells of animals, Burnham says that a remarkable difference was found between the condition of the cells in the morning and at night; "for example, in the brain-cells of honeybees taken at night the nuclei had shrunken about a third." "Of course," he adds, "we cannot apply just the same figures to the cells of the human brain; but we must suppose that something similar occurs during nervous activity. Mental work exhausts the nerve-cells and they recover slowly."

The Consequent Effects of Fatigue on alı Perceptions and Activities.-Direct observation upon man makes practically certain the foregoing conclusion of Dr. Burnham's. A postman, for example, can tell far more accurately in the morning than at night the weight of a letter. Our sense perceptions of all kinds are far acuter in the morning. It