THE CONTROL OF HEALTH 377 



become sluggish in their flow, (e) The digestive system 

 receives a reflex stimulus and is much benefited. 



Exercise which comes through physical work directed to 

 some useful, productive end, brings its most genuine and 

 cheerful satisfaction. Play differs from most work in its 

 excess of mental exhilaration, its spirit of winning, its call for 

 particular skill, its social companionship. Exercise, to be of 

 value, should be vigorous, though not to the point of strain; 

 it should call for repeated moderate action of the same set of 

 muscles rather than a few severe or sustained contractions. 

 Gymnasia offer opportunities for varied exercises which have 

 been selected with the advice of trained directors to meet the 

 individual need for the correction of faulty physique. 



Sleep. Sleep is the great restorer of the nervous system. 

 One should sleep with wide-open windows or in sleeping 

 porches. The hygienic reasons for sleep are these : (a) Every 

 other system of organs except the nervous system can secure 

 rebuilding during waking hours, if it is deliberately excused 

 from action; but unconsciousness is the only condition which 

 permits nerves to "let go." (6) Sleep gives the time necessary 

 for the more complete elimination of wastes. A thorough 

 freeing from katabolic products cannot occur while new ones 

 are constantly added to those in the blood and lymph. This 

 purification can, however, be largely accomplished in eight 

 consecutive hours of total inactivity in sleep, (c) Sleep 

 permits that relaxation which cannot occur when one is active 

 mentally. A kind of tone or tension pervades the entire 

 system normally when awake and this needs to be excluded 

 regularly. 



Hygiene of Particular Organs: Eyes. No organ of the 

 entire body is more intricate than the eye. Its defects, if 

 any, have a far reaching influence on other organs, e. g., 

 serious digestive irregularities, headache and nervousness 

 often result from eye-strain. If these symptoms are present, 

 or if it is difficult to see objects clearly unless held very near 



