480 REPORTS ON THE STATE OF SCIENCfi. 



After a few minutes you begin to experience in the muscles of the shoulder 

 a disagreeable sensation which grows rapidly more intense until, after 

 about five minutes, you feel that you can hardly support it. But, if you 

 persevere, you find that there is no impossibility about doing so ; the dis- 

 agreeable or painful sensation grows but little more intense, if at all ; 

 you may continue to hold out your arm, and after half an hour there 

 will be little more discomfort than after five minutes. 



Put alongside that the fact that most good hypnotic subjects will in 

 hypnosis keep a limb held up against the force of gravity for long 

 periods without showing any tendency to relax it, or any other symptom 

 of fatigue. 



Facts of this order seem to show clearly that such local fatigue- 

 sensation is protective in function ; that it sets in long before there is 

 any question of exhaustion of, or sei'ious injury to, the tissues concerned 

 through over-action. They show that the organism has need of some 

 protection against the possibility of self-injury through excess of activity. 



And this conclusion may serve to direct our attention to the possi- 

 bility of a similar function being performed by other manifestations of 

 fatigue. 



In connection with the other two classes of subjective symptoms — 

 tiredness and sleepiness, I would draw your attention to certain ex- 

 periences of a kind that are probably familiar to all of you. 



I sit reading in the evening some difficult technical work until, as mid- 

 night approaches, I feel thoroughly tired and sleepy, my eyes smart and 

 will hardly keep open, my head is dull and heavy and aches a little, my 

 whole body and my limbs feel heavy and incapable of alert movement. 

 I then take up some thrilling story or other fascinating piece of literature ; 

 whereupon all my subjective symptoms of fatigue, both tiredness and 

 sleepiness, disappear, and I read keenly for perhaps two hours, when I 

 again begin to feel both tired and sleepy. Now suppose a continuation of 

 the evening's history which is less familiar : some exciting event takes 

 place just as I am about to go to bed — the house takes fire or a burglar 

 breaks in, or a friend comes in with important and interesting news 

 that demands immediate action. Again all the symptoms of fatigue 

 disappear, and I can perform another spell of work at high pressure and 

 without objective symptoms, and with little if any objective trace of 

 fatigue — i.e., without appreciable diminution of efficiency. 



Facts of this order show. I think, clearly that what v/e commonly 

 call fatigue, with all its diverse symptoms, objective and subjective, is no 

 entity, that it is not due to any one kind of change in the organism ; 

 and they show that fatigue is never absolute, but is always relative. That 

 is to say, the symptoms of fatigue are always the expression of the 

 relation between at least two things — between, on the one hand, the work 

 to be done, and, on the other hand, the amount of energy available at the 

 moment for doing the work ; or, in more technical language, the symptoms 

 of fatigue are the expression of a change in the ratio between the 

 available energy (the energy in an active, living state at the moment) 

 and the resistance which that energy has to overcome. T£ the task 

 in hand is intrinsically uninteresting, the energies brought into play, 

 liberated within the organism, or transformed from the potential to the 

 active state, are small in quantity ; therefore a small amount of work, 

 producing a small increase of the resistances to be overcome, suffices to 

 raise the ratio of resistances to energies above the normal, and therefore 



