FATIGUE. 487 



whole.^ Dr. Rivers^ has recently shown how great a disturbing factor 

 in ergographic work is ' interest,' and the awakening of interest on the 

 part of tlie subject means essentially the l)ringing into play of one or 

 more of these special sources of energy. 



Again, in such fatigue experiments as those of the Kraepelin school, 

 the fatigue effects are constantly complicated, obscured, and rendered 

 doubtful by variations of interest or of impulse which show themselves in 

 spurts of all sorts.'' 



It is only when we take into account these special sources of energy 

 that we can begin to understand the way in which, under circumstances 

 that powerfully evoke our native impulses, we can execute without 

 fatigue tasks which in less favourable circumstances would render us 

 prostrate with every symptom of fatigue. 



Professor James, in a recent lecture entitled the ' Energies of Men,' ^ 

 has dealt, in his brilliant way, with this aspect of our problem ; he 

 brought forward many examples of the way in which, under conditions 

 suited to bring their powers most fully into play and to sustain their interest 

 at a maximum, men may achieve incredibly severe and sustained efforts. 

 He quoted especially the case of Colonel Baird Smith, who conducted the 

 siege operations before Delhi during the Sepoy INtutiny ; showing how 

 for months he hardly ate or slept, or rested in any way, but worked 

 almost continuously at tremendous pressure without showing or feeling 

 fatigue, and how then, when the end came, and the circumstances ceased 

 to demand and excite his efforts, he collapsed an inert, emaciated, almost 

 lifeless invalid. 



Such cases illustrate again my main point — namely, that fatigue is 

 relative, is the expression of a rise of the ratio between resistances and 

 energies, and how, if the conditions are such as effectively to call into 

 play all the great special sources of energy, this ratio may be kept from 

 rising above the normal, until the whole organism approaches absolute 

 exhaustion ; whereas, on the other hand, under conditions of boredom, 

 the ratio is very readily raised above the normal. 



If, then, there is any truth in what I have said of these sources 

 of energy and of the vicarious usage of energy, it follows that we have 

 to recognise as a second condition of general fatigue, in addition to the 

 presence of products, of metabolism in the blood, a diminution of the 

 disposable energy, due to a diminished metabolism of the neurones 

 in general, and of these speci.al sources of energy in particular, and the 



' MM. Biuet and Henri h.ave shown the inadequacy of the various methods em- 

 ployed previous to the date of publication of their wnrk—Z« Fatigue Intellectnclle 

 (1898) ; and in a recent critical study of the principal methods Mes.=^rs. Ellis and Shipe 

 (^America,n- Jomvii. of Psychology) have arrived at the conclusiou that none of those 

 investigated by them are reliable. 



- ' The Influence of Alcohol and other Drugs on Fatigue.' London, 1008. 



^ The Kraepelin methods, 1 may remark in passing, seek to avoid these disturb- 

 ances by keeping interest at a minimum. But the human subject is not easily kept 

 in such a state ; he will become intere.sted if only in the approaching end of his task, 

 and hence great irregularities. In view of these difficulties I have suggested a 

 method of estimating fatigue, which follows the opposite principle and seeks to keep 

 interest at a maximum throughout, the task set being of the nature of a sprint ; and 

 I venture to think that this is the sounder and more hopeful principle to follow ; 

 see ' A New Method for the Study of Concurrent Mental Operations and of Mental 

 Fatigue' {Brit. Joiirn. of P»y etiology , vol. i.). 



* PMl(iso2>hical Revinv, 1907. 



