26 ELEMENTARY PHYSIOLOGY. 



and vigorous condition of all the muscles. To keep 

 them all in that condition, each one mast be used 

 without being abused. A muscle which is not used 

 loses its power of contraction, becomes weak and 

 flabby, and finally altogether useless. On the other 

 hand, if a muscle is overworked, it loses its power. 

 If you were to tie up your arm in a sling, or bind it 

 down to your side for a long time, you would lose 

 the use of it entirely. If you should swing your arm 

 for a long time, the muscles which produce its motion 

 would cry out in paiuful protest against the abuse 

 which they suffer ; and were you to disregard their 

 protest, they would " strike " and refuse, positively, 

 to do the bidding of your will. The effect of the 

 vigorous exercise of the muscles without overtaxing 

 them, is to make them firm and strong; the stout 

 arm of a blacksmith, and the strong limbs of a foot- 

 man illustrate this. The difference between the 

 robust figure and good health of a sturdy country 

 boy and the slender body and feeble strength of his 

 young friend in the city, lies mostly in the difference 

 in amount of their general muscular exercise. But 

 we must be careful not to mistake a bulky body, or 

 thickness of the limbs, as a sign of stoutness and 

 strength of muscle. It is true, indeed, that as the 

 muscles grow stronger they grow thicker, and conse- 

 quently increase the size of the limbs and trunk of 

 the body. But the effect of the fat of the body is 

 often mistaken for an " abundance of muscle." 



