BONES, MUSCLES, EXERCISE, AND REST. 307 



the next moment we reverse this action, and contract the 

 straightening muscles of the first side and the bending mus- 

 cles of the opposite side ; by these motions on opposite sides, 

 the limbs are lifted and carried one before the other, alter- 

 nately, and the body moves onward. 



708. While we walk easily over a smooth and familiar 

 path, we may direct the energies of the brain partially, but 

 not exclusively, to other matters, and talk or think of agree- 

 able and interesting subjects. But if the walk becomes diffi- 

 cult, if the mind is required to pick the way through wet or 

 stony places, or perform any severe labor, all the energy 

 of the brain is required to direct and sustain the muscles of 

 motion, and then conversation and thought are suspended. 

 But if, on the contrary, the brain is all absorbed with other 

 subjects, if we are engaged in deep thought or oppressive 

 anxiety, the muscular contraction is not so easily effected 

 and controlled, the strength of the muscles is not so well 

 sustained, the exertion wears more upon the body, and con- 

 sequently exercise under such circumstances is not so in- 

 vigorating, and labor not so effectual and profitable. 



709. Although the brain and mind must not be absorbed 

 or oppressed with care or thought when we exercise or labor, 

 yet they should not be dormant. They should be lively and 

 engaged. The exercise should have an. object. Walks 

 through pleasant scenes and among interesting objects, ex- 

 cursions in pursuit of flowers, minerals, or other natural ob- 

 jects, do more for the health than those which have no object. 



CHAPTER XVII. 



Labor should have an adequate Object. Hope and Confidence give, 

 and Doubt and Fear diminish, Strength. Cheerfulness and Mel- 

 ancholy have similarly opposite Effects. Effect of Passion, Al- 

 cohol, on Strength. 



710. Labor for profit, as well as exercise for health, 

 should have an adequate object. The mind must be satis- 



