174. _When the muscles are called into action, the flow of blood in the arteries and veins is increased._ The increased flow of blood in the arteries and veins, causes a more rapid deposition of the particles of matter of which the muscles are composed. If the exercise is adequate to the power of the system, the deposit of new material will exceed in quantity the particles of matter removed, and both the size and energy of the muscles are increased. But there is a limit to the muscles becoming strong by labor. Sooner or later, man will attain his growth or power; yet by judicious exercise, care, and discreet management, the greatest power of the muscles may be preserved until advanced age. -=-=-=-=-=-=-=-=-=-=-=-= 173-211. _Give the hygiene of the muscles._ 173. What is necessary that muscles may attain size and strength? Give a law of the muscular system. Show this by practical illustrations. 174. Why do muscles increase in size when exercised? -=-=-=-=-=-=-=-=-=-=-=-= 175. _The muscles are lessened in size and diminished in power when the exercise is continued so as to produce a feeling of exhaustion._ The loss of material, in this instance, will exceed the deposition of the atoms of matter. This is seen in the attenuated frames of over-tasked domestic animals, as the horse. The same truth is illustrated by the laborious agriculturist, who, in consequence of too severe toil while gathering the products of the field, frequently diminishes his weight several pounds in a few weeks. Exercise, either for pleasure or profit, may fatigue, yet it should never be protracted to languor or exhaustion, if the individual desires "a green old age." 176. _The same amount of exercise will not conduce to the health of all individuals._ If riding or walking one mile causes slight fatigue, this may be beneficial; while, by travelling two miles, the exhaustion may be highly injurious. Exercise and labor should be adapted to the strength of particular individuals. How little soever the strength, that must be the measure of exertion. Any other rule would be fatal to the hopes of invigorating the system, either by exercise or labor. -=-=-=-=-=-=-=-=-=-=-=-= Is there a limit to the muscles becoming powerful by action? How may the strength of muscles be kept until advanced age? 175. What is the effect when exercise is continued until there is a feeling of exhaustion? Give a practical illustration. What rule is mentioned in regard to exercise? 176. Can all persons take the same amount of exercise? What rule is given as to the amount of exercise? -=-=-=-=-=-=-=-=-=-=-=-=