MUSCLES 377 



ness and not upon its length, yet in animals the muscle must be made 

 many times longer than in insects as well as thicker. Thus the muscles 

 of animals have more weight to lift and do a greater amount of work in 

 proportion to their size. A man's muscle fiber is really the strongest 

 known. An insect made as large as a man would probably be unable 

 to move a limb . 



675. Precision of movement. By means of the muscular 

 sense it is possible to regulate the action of a muscle with 

 great precision. But as the effort put forth is greater, the 

 ability to regulate it is less. So while slow and delicate 

 movements can be made with precision, rapid and power- 

 ful motions are less under control. After a muscle has 

 exerted itself to its full capacity, it is unable to perform 

 delicate movements with precision for some time. 



676. Alcohol and muscle. Strong drink in any form dimin- 

 ishes both the strength and the endurance of muscles. Soldiers and 

 athletes are not allowed to use it during periods of great exertion. It 

 also interferes with the precision of movements. Drinkers are not 

 allowed to work at railroading, where quickness and precision of move- 

 ments are always required. Tobacco also weakens the muscles and 

 lessens their precision of movement. 



677. Physical effects of exercise. When used, most 

 cells of the body take in more nourishment, and increase 

 in size and strength. Muscles, especially, grow larger and 

 stronger by use. Then the digestion, circulation, and 

 respiration all show increased vigor to supply them with 

 extra energy. Thus the whole body grows stronger. 



Round shoulders are most often due, not to weakness of the spine, 

 but to weakness and inaction of the muscles of the back. The remedy 

 is not to apply braces, for that only permits the muscles to rest and be- 

 come weaker, but to make constant efforts to throw the shoulders back 

 and so to increase the strength of the muscles. Military drill makes 

 soldiers erect for this reason. 



678. Overwork. If the muscles turn too much heat 

 of the body to motion and work, there is too little left 



