THE MUSCULAR SYSTEM 75 



low. Certain kinds of spinal curvature are cured by 

 wisely chosen exercise. 



98. Exercise in the Cold. For a healthy person nothing 

 so well develops the whole system and hardens the con- 

 stitution as regular, vigorous, and agreeable exercise in the 

 cold. Hence outdoor winter sports and occupations 

 should be encouraged. Skating, sliding, snowballing, 

 and swimming are excellent as promoters of health. 



99. Time for Exercise. Some times are better than 

 others for taking exercise. The morning is usually best 

 for the severer forms, because the whole system is then 

 refreshed and vigorous. In the evening one who has 

 been engaged in physical toil does not need exercise, but 

 rest ; while one whose occupation is mental labor or sed- 

 entary business will be rested and refreshed and prepared 

 for sound sleep by exercising judiciously in the open air 

 after the day's work is done. 



When the muscles are called into use they require more 

 blood than when at rest, that the waste which results 

 from exercise may be repaired. This extra supply of 

 blood is drawn from other parts of the body, and the 

 demands of the muscles may retard the performance of 

 other physiological functions since the total amount of 

 blood is practically invariable. This is why the muscles 

 should not be vigorously exercised for an hour or two, at 

 least, after meals, and not immediately before. Digestion 

 requires an increased flow of bloo.d to the alimentary canal 

 and digestive glands, and if the process is impeded by a 

 drain of the vital fluid to other parts, harm will result. 



100. Training. The scientific development of the mus- 

 cular system under " training " for particular purposes of 

 sport, or in a well-equipped gymnasium, may have excel- 

 lent results for those who are able to avail themselves of 



