MUSCLES 283 



while the size of the muscles is generally noted as proof ot" 

 the beneficial effect of exercise, perhaps greater stress should 

 be laid on the toning up of all the internal organs, which re- 

 sults when they have been supplying the active muscles with 

 energy and clearing away the debris resulting from "wear 

 and tear." 



Unlike inorganic substance, muscle increases instead of 

 diminishing in size with use. This is true of other living 

 matter also, e. g. brains, which grow with exercise. No one 

 can explain this characteristic of muscle fibre, though it is 

 inherent in the nature of the substance. 



Effect of Disuse. The result of failure to use muscles is 

 just the reverse of the effect of use, i. e. they grow smaller and 

 weaker, and less perfect control of them is possible. Some 

 of the peoples of India believe it a religious duty to hold 

 their arms still and have continued to hold them so until they 

 have become stiff and useless, the muscles losing absolutely 

 all power of contraction. Although in civilized countries, 

 one rarely sees such complete loss, a partial loss of power is 

 common among all classes of people. Children in their play 

 are pretty sure to use all their muscles and are likely to de- 

 velop them uniformly, but an adult is rarely as capable of 

 free action as a child. As one grows older and becomes 

 quieter, some of the muscles always suffer from disuse. If 

 he uses trolleys and elevators, the leg muscles suffer, and the 

 adult may lose the power to walk as far as the child. The 

 right hand is used so exclusively that the muscles of the left 

 become weak. The habit of sitting in comfortable reclining 

 chairs gives the back muscles too little exercise and they 

 often become so weak that it is really difficult for one to sit 

 upright for a very long time without some sort of support. 

 Some people use the laughing muscles so seldom that at last 

 they can scarcely be brought into action. Examples are 

 numerous, for few persons use their muscles in such a way as 

 to produce uniform development. Every one should re- 



