54 



OUR BODIES AND HOW WE LIVE 



take what is specially suited to their wants, and return the 

 waste matter. 



Now, in every tissue, especially in 

 the muscular tissue, this process is 

 hastened by action. Exercise causes 

 more frequent changes in the tissues 

 and hence an increased flow of blood. 

 Muscular activity is, then, the chief 

 agent in bringing about these whole- 

 some tissue changes. 



79. Effects of Exercise on the Mus- 

 cles. Muscles increase in size and 

 strength according to the use made 

 of them . The blacksmith uses vigor- 

 ously the muscles of his arms and 

 chest day after day, hence they be- 

 come well developed. 



Let a muscle be kept idle for some 

 time and it loses in bulk and vigor. 

 We read of certain people in India, 

 who, as an act of worship, keep one 

 arm raised above the head for many 

 weeks. The muscles shrivel and the 

 arm becomes useless. 



If a leg is broken and kept in 

 splints for several weeks, the muscles 

 become feeble and wasted. It is only 



FIG. 44. Some of the after a reat deal of exercise that the 

 Larger Muscles on the long-idle limb regains its former size 



Back of the Thigh. an( J vigor. 



Powerful tendons at the hip 0. Effect Of Exercise OH VariOUS 



and on the back of the .- .. . i 



knee are well shown. Organs. Many other organs besides 



