110 THE NKKYorS SYSTEM AXD ITS CONSERVATION 



;tp|);ira1iis, hut the number of those impulses is far less 

 than it might be if various external conditions favoring 

 reinforcement could be added. At the dance the reinforc- 

 ing factors are present in the most efficient combination. 

 There is the music, there are the lights and the shifting 

 play of colors as the figures move, there are contacts, and 

 all the while a richness in the psychic experience totally 

 foreign to the drudgery at home. This psychic richness 

 doubtless corresponds with the physiologic fact of multi- 

 plied brain-currents. 



The difference between play and work, between doing 

 what we keenly enjoy and what we feel we ought to do for 

 some remote result, may be said to be the difference be- 

 tween a motor performance in which many pathways are 

 traversed by the impulses which unite to stimulate the 

 neuromuscular mechanism and one in which the number 

 of these paths is small and not much subject to variation. 

 Titchener once surprised an audience by the declaration 

 that "all work is a waste of time"; this he elucidated as 

 meaning that the zest which we associate 1 with play is the 

 basis of better accomplishments than can be attained when 

 only the fee-ling of obligation is operative. The boy who 

 becomes very tired of chopping wood can use the same 

 muscles in a game, and his parents may t\\it him with the 

 fact. But while it is true that he is using the same muscles 

 and the same spinal neurons, perhaps the same projection 

 fibers from the cerebrum, he is not using the same afferent 

 channels nor the same cortical approaches to the motor 

 center^. The adult cannot honestly lay claim to im- 

 munity from fatigue of this sort. 



Elements in Training.- A great deal that has been said 

 in this and the preceding chapter may conveniently be 

 reviewed under this head. In what re-pects does an un- 

 trained neuromuscular system differ from one which has 

 been developed by use'.' \Ve shall find as many possibili- 

 ties in this connection as we have in our attempt to 

 analy/e fatigue. We shall have to pay attention to the 

 mu<cle-. the end-plates, and the central organization. 



