Validity of Ergograph as Measurer of Work Capacity 23 



checked before all the inessential elements have disappeared, the 

 contraction will always be accompanied by accessory movements. 

 Again, the tendency to vary may actually revive other movements 

 that did not originally appear, but which are essential to the most 

 successful accomplishment of the work. These will be preserved 

 by the same process of selection. During the first days of prac- 

 tice the inessentials drop out very rapidly, but later many random 

 variations are required before a new combination of muscles is 

 found that will better accomplish the work, which accounts for 

 the slow growth of practice. 



Each new combination, whether brought about by the elimina- 

 tion of an inessential muscle or the bringing in of a new essential 

 one, must be practiced long before the association is perfected. 

 Accordingly there are periods in practice, which Bryan and Har- 

 ter call the plateaus in the practice curve, when seemingly no gain 

 is made. This is to be accounted for by the fact that during the 

 time when the association is made among a new group by a 

 random groping, this must be thoroughly ingrained, and while 

 that is going on the process of random groping for further new 

 combinations is checked. The new combination when discovered 

 leads to a rapid gain in practice which is not improved upon 

 until that is firmly fixed in the nervous structure. Further prac- 

 tice gain must wait upon still other combinations turning up 

 fortuitously. The practice curve then shows sudden rises with 

 long periods without change in elevation. 



All these associations are more or less feebly established. 

 When a contraction has been repeated a number of times the new 

 pathway established in the nervous structure is broken up or 

 rendered less permeable by fatigue, the nervous currents diffuse 

 themselves over the older ones, the muscles that do the work are 

 less strongly innervated, and this shortens the contraction, and 

 accessory movements come in, increasing the rate of accumulation 

 of waste products and checking repair in both muscles and nerve 

 centers, bringing the effort suddenly to the exhaustion point. 



The third element is that of rhythm. No great gain seems to 

 have been possible until the movement could be done rhythmi- 

 cally. The contractions, as usual in experiments with the ergo- 



101 



