Page:The New International Encyclopædia 1st ed. v. 07.djvu/531

* FATIGUE. 179 FATIGUE. tijjiii- the laxness ,,( 'mental endeavor' and the increased inattention which follow upon hard slinly or the contention of diverse motives. These concomitants should, however, be kepi distinct from (lie real experience of fatigue. There is some disagreement among psycholo- gists i" regard to the ultimate analysis of fatigue. It is argued, on the one hand, that fa- tigue is a complex of more or less intensive or- ganic sensations (q.v.), usually toned with pleas- antness or unpleasantness, and even passing over into pain where the limit of endurance is approxi mated; while, on the other hand, it is urged thai fatigue is as simple and unanalyzable as is the sensation of red or the tone of a tuning-fork. The truth seems to lie between the two views. As a rule many processes cooperate in the pro- duction of fatigue; but the experience itself is a fusion (q.v.), so close that it is impossible by introspection to wrench the constituent elements out of their union. The experimental study of fatigue and of its effects, mental and physical, has been carried on with some success during the last twenty years by the continued efforts of physiology and psy- chology. The first comprehensive work was done by H. Kronecker of Bern and A. Mosso of Turin. The starting-point was the observation of the course of exhaustion in the muscle taken from the frog's leg. When the nerve supplying the muscle was stimulated at successive intervals by an electric current it was found that the contract- ility of the muscle suffered a constant decre- ment each time that the current was passed ; until, finally, no movement at all was produced. Tf, however, the muscle were now thoroughly bathed with a weak saline solution, contract- ility vas restored. This circumstance has led to th - conclusion that at least part of the effect of fatigue lies in the accumulation of toxic ma- terials, which prevent the contraction of the muscle. 'These materials are usually carried off in the blood : as is shown by the fact that the injection of blood from a fatigued into a normal animal gives rise in the latter to all the symp- toms of exhaustion. An objective measurement of the effect of fatigue was made possible by Mosso's invention of the ergograph, an instru- ment which records the amount of work that a muscle, or rather a restricted group of muscles, performs in lifting a known weight, or pulling against a coiled spring. Many modifications of the instrument are now in use. Over and above the action of poisonous materials, muscular fatigue is undoubtedly con- ditioned upon the exhaustion of the energy which is supplied by the blood in the form of nutriment. If the consumption of energy does not exceed the supply, and if the waste products are speedily re- newed by the blood, fatigue of a muscle does not ensue. The heart, e.g. beats throughout the individual's lifetime without, causing fatigue. Moreover, each muscle seems to have optimal con- ditions for work, which include an appropriate loading and a sufficient interval for rest between contractions. Whether the feeling of fatigue is aroused by the lack of nutriment in the muscle, or only by the poisonous waste products, is not definitely known. In any event, it is necessary to pass Vieyond the muscle, and to inquire into the immediate nervous conditions of fatigue. Tt is clear that a muscle could not feel fatigue, apart from a nervous system. The conducting nerve- films do not appear to be exhausted by fatigue; for they will continue to functionate for hours nfter 1 Ik- niu-cles have refused to contract. I'.ut the case is different with the nerve-cells oi the brain. It has been found that these cells undergo erious alterations, both during artificial stimu- lation by electricity and during mu culai exer- cise. Under exhaustion the cell hod} becomes shriveled and the nucleus takes on a different appearance. It is fair to -oppose that these change are directly connected with the mental processes of fatigue. If a muscle is so thoroughly exhausted that it refuses to respond to a voluntary efforl ai con- traction, it may nevertheless continue to work, if it is electrically stimulated. And, on the other hand, voluntary eon! ruction ensue- when electrical stimulation is inefficient. It is difficult, however, to draw conclusions from these cases; for in either event Some new mUSCUlar element is apt to lie brought into function by the new source of stimulation. Various methods have been devised for mens uring the general intellectual fatigue which fol- lows upon mental exertion. School children in particular have been subjected to tests for the determination of the fatigue-effects of various studies. Two types of method have been em- ployed: (1) A period of instruction — e.g. the solving of simple problems in addition or multi- plication — is made the test, and the extent of fatigue produced is determined by the amount of work done and the number of errors made. The results have shown a gradual increase in quantity in the latter part of the day's session, but at the same time a large increase in the number of errors. It is difficult to translate these results into terms of fatigue, because prac- tice enters as a prominent factor. Further, the method does not give a fair test of the fatigue induced by regular school work, because the tests require an unusual tension, while at the same time their monotony renders them uninter- esting and irksome, and invites carelessness. (2) Tests of the second type are introduced bi tween the periods of study at various points in the day's work, e.g. at the end of every hour. The first of these methods is that of Griesbaeb. Two blunt compass-points are set down mar together upon the skin, and gradually separated until the individual is just able to distinguish the points as two. This just discriminable difference of locality is called the limen for localization. (See Extension; Pstchopiiysics. ) It has been found slowly to increase under fatigue. The limen varies so much, however, from individual to individual, with the time of the day. the de gree of attention, and many other circumstances, that it is difficult to obtain significant results from the method. Another test is furnished by the 'memory method,' in which the pupil writes down a list of words previously read to him. The omissions and errors are taken as an index of fat igue. Obviously the best test for fatigue will be one which involves the very processes which have been affected by work: hence it is necessary to make an analysis of the mental functions that are operative in ordinary school work, in order to de- termine the actual capacities which are drained bv sustained application. Memory for words, e.g. may remain unimpaired, even though the in- dividual is too fatigued for intellectual work;