FATIGUE, 481 



to produce the symptoms of fatigue ; whereas if the circumstances are 

 such as to bring into play greater stores of the potential energy of 

 the organism, a much greater amount of work may be produced by 

 the organism (whether bodily or mental work) before the ratio of the 

 resistance to the available energy rises to the point at which symptoms of 

 fatigue appear. 



Reflection upon these familiar experiences yields then the two pro- 

 positions on which I invite you especially to concentrate your attention, 

 because I believe they may be the two master-keys to all the problems of 

 fatigue — at any rate to those of fatigue of the nervous system. They 

 may be briefly stated as follows : — 



(1) Fatigue of the nervous system is a state in which the ratio of the 

 resistances to the active energies is raised above its normal value, either 

 through increase of the magnitude of the resistances or through diminu- 

 tion of the quantity of disposable energy. 



(2) The function of the resistances is essentially the limitation of 

 activity ; they are thus protective of the energy of the organism ; they 

 prevent the organism exhausting its store of potential energy through 

 unduly prolonged, intense, or widespread activity. 



If these propositions are well founded we must, in order to under- 

 stand fatigue, have good working conceptions on the one hand of the 

 sources of the energies concerned and of the conditions and nature 

 of their operations in the nervous system, and on the other hand of 

 the nature and seat of the resistances that limit and preserve these 

 energies. 



It has recently been contended, notably by Bethe ■ in Germany and 

 by Deschamps - in France, that the nervous system is not the seat of the 

 liberation of any energy, or at any rate that such liberation is no part of 

 its specific functions, but that it merely distributes the active enei-gies 

 supplied to it by stimuli of all kinds and by the various organs of the 

 body. I think most of you will agree with me in holding that this view 

 is quite unacceptable, and that the activity of the central nervous system 

 does essentially and always involve liberation of energy, transformation 

 of energy from the potential to the active form, and a consumption or 

 using up of stores of potential energy. Verworn,-^ who has made him- 

 self the protagonist of this view, seems to me to have proved it by his 

 own experiments and those of his pupils, although, even without these 

 particular experimental results, there was hardly room for doubt about 

 the matter. Further, Verworn's experiments on the spinal cords of 

 frogs confirm the view (about which also there was little room for doubt 

 apart from these experiments) that fatigue may be produced by either 

 of two processes, and that it commonly is produced by their conjunction, 

 namely (1) the process of accumulation of waste products of metabolism, 

 COo, lactic acid and other substances ; (2) the using up of stores of 

 potential energy through excess of katabolism over anabolism. The 

 former is called by the Germans ' Ermiidung,' the latter ' Erschoptuiig,' 

 and some English writers have proposed to use the words fatigue and 

 exhaustion in these two senses, as the equivalents of these German words. 



' ' Zur Theorie cler Zentienf unktion.' Drgehnisse der Phynologie, Bd. v. 

 - Les Maladies dc VEncrgie, Paris, 1908. 



» ' Die Vorgiinge in den Elementen des Nervensystems.' Zeitsch. f. Allgemeinc 

 Physiologie, Bd. vi. 



190'8. I I 



