6 Thaddeus L. Bolton and Eleonora T. Miller 



The accessory movements which contribute nothing to the per- 

 formance and are energy-consuming gradually drop out. 



Fourthly, practice increases endurance. By that we mean the 

 power to contract a muscle a greater number of times under given 

 conditions. Let us suppose stronger innervation reaches a muscle 

 from a given discharge in the nervous centers after practice than 

 before, and that the amount of energy-yielding compound in the 

 cell presumably increases with practice, a greater number of suc- 

 cessive contractions are rendered possible before the muscle 

 becomes exhausted. The prize fighter, the football player, and 

 the soldier are enabled to stand violent exertion for long periods 

 of time by gradually increasing the amount of work as they grow 

 in practice. Each increase in stint of work adds an increment 

 to the available energy in the nerve and muscle cells at the dis- 

 posal of the organism, so that the number of successive efforts 

 may be greatly increased ; that is, they can be repeated more often. 



Fifthly, with the acquisition of skill movements become more 

 rhythmical. The characteristics of rhythmical movements are 

 the perfect interdigitation of a number of movements into one 

 another and the joining of them together in serial order so that 

 the first movement in the series shall become the stimulus pro- 

 voking the next of the series, and these in turn provoke the next, 

 and so on until the cycle is completed. The last element of the 

 cycle becomes the stimulus for initiating again the first of a new 

 cycle. A rhythmical movement then consists of a number of 

 reflex actions following one another in serial order. The action 

 of one is the stimulus for the second, the action of the second 

 the stimulus for the third, and so on. Rhythmical movements 

 differ from the ordinary serially coordinated movements in the 

 fact that each movement of the series furnishes stimulus for eye 

 or ear and sometimes for both, and the new movement or cycle 

 is initiated from the special sense organ. Dancing is the type 

 and is chiefly directed by the ear, for rhythms appeal most 

 strongly to the ear ; in fact, hearing is the rhythmical sense. The 

 tendency is for all forms of work to assume the rhythmical type. 1 

 All nervous activity is rhythmical, the lowest centers following 

 simple rhythms and the highest more complex. 



1 Biicher, Karl, Arbeit und Rhythmus. Leipzig, 1902. 



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