384 ADVANCED PHYSIOLOGY 



member that each muscle Tie fails to use will become weak and 

 degenerate. 



Need of Exercise. The great value, indeed the necessity, 

 of exercising the muscles in order to retain good health is, 

 therefore, evident. It is hardly necessary to advise the 

 average school boy or girl to take exercise, for the plays of 

 childhood usually furnish plenty of it. But when the boy 

 or girl outgrows childish habits, and becomes a serious stu- 

 dent, or goes to work at some routine employment, there is 

 always the danger of poor bodily development. The time 

 between childhood and maturity is the period when sufficient 

 exercise is especially necessary to force all the muscles into 

 proper, harmonious growth. When a person has out-of- 

 door work to do, or indeed any work which requires con- 

 siderable muscular activity, he does not need to think of 

 exercise. But in modern city life, young people have com- 

 paratively little opportunity for muscular exercise and are 

 almost sure to suffer from the lack of it unless particular 

 attention is given to the matter. It is for this very reason 

 that gymnasiums have been established in schools and else- 

 where, and they should be patronized by every person whose 

 business is not such as naturally to involve exercise. 



Exercise should not be violent. It is of no advantage to 

 try to lift heavy weights, or to do difficult feats in the gym- 

 nasium. Indeed, such exercise is liable to injure young 

 people. We have noticed that the bones of children are not 

 all knitted together, and the severe strains from attempting 

 difficult exercise and lifting heavy weights are apt to do per- 

 manent injury to the incompletely fused bones. Athletic 

 contests are certainly useful, but the tendency nowadays 

 toward excessive exercise in one line rather than the general 

 use of all muscles results too often in unreasonably over- 

 taxing one's strength. Though the results of the straining 

 may not be evident until long after its occurrence, when 

 they do appear in later life, the person finds himself a per- 



