58 David H. DoUey, 



The nerve cell then is exhaustible, easily exhaustible in its 

 highest differentiation. But in relation to other elements in the 

 mechanism of the body which are associated as its instruments, its 

 varied reserve power may be deep enough to render it comparatively 

 much less exhaustible. So far from denying this, its power of reserve 

 must be insisted upon. As a cytologist, therefore, I have no criticism 

 of the general results of physiological experimentation. Under circum- 

 stances proper to each, the muscle may be depressed totally before 

 its controlling centre, the end-plate may cease to make the connection 

 or the connection may break at the synapse, as Sherrington thinks, 

 though impulses continue. Going no farther than the anatomical 

 facts at hand, there appears no incompatibility. But this relatively 

 difficult exhaustibility is quite another thing from an absolute condition 

 of inexhaustibility. Absolute exhaustion can occur, mentally it does 

 too frequently occur. Yet it has been neglected, disregarded, over- 

 ridden. One cannot believe otherwise than that due appreciation 

 of it will exert a modifying influence on physiological theories of 

 fatigue. 



Organic fatigue is primordial. It is this organic fatigue which 

 is the cause of the premature breakdown — the neurasthenia in the 

 actual sense of the word, it is the root of old age, the reaction of 

 a wide range of diseases. Mosso it was, I believe, who said: "Genius 

 is fatigue." Nothing could be apter than this aphorism for mental 

 processes in general if we admit to that category those who have 

 the capacity for taking pains. Hodge broadened its scope when he 

 wrote: "Old age is of the nature of final fatigue." Yet if one should 

 attempt in an aphorism to express the full biological significance, 

 it could be nothing less inclusive than "Life is fatigue." It is the 

 power of recuperation that conserves it. 



Conclusions. 

 Transfusion of the blood of fatigue into normal animals and 

 injection of artificial fatigue substances, such as lactic acid, sarco- 

 lactic acid and mono-potassium phosphate, are eliminated by experiment 



