318 ADVANCED PHYSIOLOGY 



movements of internal organs, may be practically beyond any 

 control of even the highest centers. 



Relation of Reflex Actions to Training and Habits. The 

 reflex centers in all cases consist of the nerve cells, the central 

 parts of some of the neurons or of groups of such cells. But 

 the interesting and important fact is that at the beginning of 

 one's life most of these servants are untrained and cannot 

 perform at all the duties assigned to them in later life. Ex- 

 actly how these nerve centers are trained, it is impossible to 

 say ; but we do know that by being made to do the same thing 

 over and over again they finally learn to do it well, and 

 at last almost without one's consciousness. When a child 

 first learns to walk, for example, his muscles do not readily 

 work out his will, but after some years of practice he no longer 

 thinks of the motions, for the reflex centers take charge of 

 them. Practice makes perfect, simply because by constant 

 use the reflex centers may be so trained that they do their 

 work perfectly. When we learned to write we were obliged 

 to attend carefully to the motions of the fingers, to see that 

 all the up-strokes and down-strokes came in the right order. 

 But now, if we are good writers, we do not have to think of 

 up-strokes or down-strokes, hardly of the letters. We think 

 out the ideas we wish to put on the paper, and reflex 

 centers take charge of most of the movements. One 

 becomes aware of this fact when he tries to disguise his hand- 

 writing. He finds such a procedure as difficult as he did 

 learning to write, for the muscles and nerve centers are 

 trained to do a thing one way, and continue to do so. 



Most of the activities of the child's life have for their pur- 

 pose the training of these useful nervous centers. His work, 

 his play and his study all have the same end in view; i. e. 

 training for his use a set of faithful servants who will con- 

 tinue for the rest of his life to work in just the way they have 

 been taught in youth. The saying, "It is hard to teach an 

 eld dog new tricks," merely expresses the difficulty of training 



