Again, fatigue disturbs the power of accurate and sustained bodily co-ordinations, particularly of the peripheral muscles, or those engaged in the control of the more delicate movements of the body, as of the fingers. Every one must have had the experience that consequent upon a period of exacting labor (physical or mental), or worry, the hand becomes unsteady, as revealed in writing or other fine work, the voice is not so perfectly controlled as at other times, and perhaps involuntary twitchings or _tics_ make their appearance in the face or elsewhere. Ordinarily people regard these phenomena as evidences simply of "nervousness," but, as commonly used, this term does not take account of the neural conditions responsible for these abnormal manifestations. Warner[39] points out that nerve cells in a state of fatigue become impulsive or spasmodic in their action; there is not such perfect balance as usually exists between them when in a normal, rested condition, and this results in lessened power of inhibition. Scripture[40] and others have shown by experiments in the laboratory that fatigue renders co-ordination less sustained and accurate. If, now, one observes a group of people, young or old, in which some or all have passed the fatigue limit, he can see the cause of many of those occurrences which give the teacher in the school, for example, continual trouble. The children will doubtless be moving incessantly in their seats, books and pencils may be dropping upon the floor, and various signals are responded to slowly and in a disorderly manner. The restlessness is probably due for the most part to the effort of the pupils to relieve the tension of muscles induced by overstrain, while inability to accurately co-ordinate the muscles employed in holding pencils and books causes objects to slip out of the pupils' hands upon the floor. One has but to observe his own experience, and he will soon realize that when nervously exhausted he is not so certain of retaining securely small objects which he handles. This accounts for what is sometimes regarded as carelessness in school children as well as in adults, exhibited in slovenly writing, in breaking dishes, and in similar occurrences. Any task demanding delicate and sustained adjustment of the finer muscles on the part of one fatigued will be liable to be performed in a careless manner, as we are apt to feel. Often more than not the term carelessness probably denotes impaired neural conditions, as well as consequent mental dispersion, if one may so speak, leading to inaccurate and intermittent mental and physical adjustments to duties in hand. [Footnote 39: Mental Faculty, pp. 76, 77.] [Footnote 40: The New Psychology, pp. 236-248.]