November 24, 1916] 



SCIENCE 



729 



tinued, leads to the physiological state of 

 fatigue. Fatigue is characterized chem- 

 ically by the diminution within the acting 

 tissues of chemical substances that have 

 previously been stored within the living 

 cells and either serve as sources of energy 

 or are otherwise essential to tissue activ- 

 ity; and by the appearance within the liv- 

 ing cells of other chemical substances, 

 products of katabolic action, which are 

 known as fatigue substances and react 

 upon the tissues to decrease their power of 

 responding to stimuli. If the same amount 

 of work as before is then to be performed 

 by the organs, the nervous system must 

 send to them more powerful impulses, and 

 when this becomes no longer possible the 

 amount of work decreases. Fatigue sub- 

 stances spread from the place of their 

 origin to other organs and react upon them, 

 and thus the activity of one physiological 

 mechanism, such, for example, as a neuro- 

 muscular mechanism, fatigues others. In 

 fatigue the senses are less acute; attention 

 is less sharply focused; the power of dis- 

 crimination is lessened; the muscles are 

 weakened; the quickness and the accuracy 

 of muscular action are decreased; glandu- 

 lar secretions seem to be decreased ; the 

 heart-beat may be slowed or, in extreme 

 cases, possibly quickened and irregular; 

 the blood vessels of the skin are dilated and 

 draft an undue quantity of blood away 

 from the brain. In fatigue the sense of 

 weariness obtrudes and oppresses; but it 

 can not be too strongly emphasized or too 

 often reiterated that the feeling of fatigue 

 is a very uncertain index of the presence 

 of a measurable degree of the fatigue of 

 the tissues. The feeling may, indeed, ap- 

 pear just at the time when its warning note 

 is really needed; but it may sound an un- 

 duly early and a false alarm; and again, 

 and especially when other potent psychic 

 influences inhibit it, its coming may be un- 

 duty postponed. It is a fitful, capricious 



thing, and this fact is too often overlooked 

 in the consideration of industrial fatigue. 



All these physiological changes may be 

 within normal limits, and by rest the irri- 

 tability of the tissues can then be readily 

 restored and the freshness of sensation and 

 the vigor of mind and muscle can be 

 brought back. But if the work has been 

 too strenuous or too long-continued, if the 

 chemical changes in the tissues have gone 

 too far, or if rest has been unduly cur- 

 tailed, fatigue passes over into a patholog- 

 ical state which is known as exhaustion and 

 is far less easily recovered from. Not only 

 is the power of achievement then further 

 diminished, but susceptibility to specific 

 disease is increased. There may be a gen- 

 eral neurasthenia or other diseases of the 

 nervous system, including nervous affec- 

 tions of the bodily organs. The will may 

 be weakened, and resistance to immoral 

 temptations may be lessened. Intemper- 

 ance is one of the common results of bod- 

 ily exhaustion, and even crime itself finds 

 here one of its prolific sources. Eesistance 

 to infectious disease may be diminished, ap- 

 parently because of a diminution of the 

 protective antibodies. Thus, excessive 

 fatigue may bring in its train many disas- 

 trous sequelse with much physical and 

 moral misery. The seeds of this more 

 serious state are often sowed in industrial 

 work, when the conditions of labor and liv- 

 ing are such that a residuum of the fatigue 

 of one day is carried over to the next and 

 from day to day there is a cumulative, 

 even if slight, diminution of physiological 

 powers. 



Let us develop a little further this topic 

 of the physiological effects of labor. Lab- 

 oratory experiments have demonstrated 

 that the degree of fatigue of a muscle in a 

 given time varies in accordance with both 

 the amount of the weight lifted and the 

 rapidity with which stimuli are sent to the 

 tissue. Increasing the weight, or making 



