360 PHYSIOLOGY AND HEALTH. 



makes some demand upon his brain, and withdraws so 

 much attention from the subjects which he is required to 

 learn. 



830. The motive of misdirected hope and of undue re- 

 ward is often held out exclusively as a stimulus to greater 

 and greater mental exertion. Whenever the reward does not 

 grow naturally and necessarily out of the subject of study, it 

 may interfere with its own purpose, and divide, rather than 

 concentrate, the power of the brain and the attention of the 

 mind. If, as an inducement to commit a lesson, or write a 

 legible manuscript, the reward of a silver medal, or of a 

 book, or an opportunity of declaiming before a public audi- 

 ence, is proposed, the effect of division of thought and 

 weakening mental effort follows. 



831. But the motives for mental exertion which belong 

 to, or grow out of, the subject to be studied, not only with- 

 draw- none of the energies of the brain and the mind from the 

 proposed object, and therefore neither divide nor weaken 

 their exertions, but aid. in concentrating all their force upon 

 the single point of study. The value or the usefulness of 

 the knowledge, or the advantage that must result directly 

 from it, and, above all, the mere pleasure of learning, are, 

 therefore, the most effective motives for, and auxiliaries to, 

 mental labor. For this reason, boys who study with the idea 

 that they are thereby to fit themselves for usefulness, re- 

 spectability, and happiness, men who acquire professional 

 knowledge, or learn science, as a means by which they shall 

 obtain their support, or fortune, or station, or do good to 

 others and, above all, naturalists and others, who study for 

 the love of the sciences to which they give their attention, 

 are the most successful scholars. 



