BONES, MUSCLES, EXERCISE, AND REST. 



313 



spine. The fat man with large abdomen does the same, and 

 for the same reason. Otherwise they would necessarily exert 

 great force of the muscles of the back, to prevent their fall- 

 ing forwards. 



722. If a porter stands perfectly erect when he carries a 

 trunk on his back, (Fig. LVIII.,) the line of gravitation falls 

 behind his natural line of support, and tends to throw him 

 backwards. To prevent this, and bring the burden over 

 the point of support, he leans" forward, (Fig. LIX.) 



Fm. LVIH. FIG. LIX. 



For the same reason, the hod-carrier leans to the left 

 when he carries his burden on his right shoulder, and to 

 the right when he bears it on the left shoulder. When 

 a boy carries a heavy pail of water with one hand, he leans 

 as far as he can to the opposite side ; but, as he does not lean 

 far enough to bring the centre of gravity over the point of 

 support without spilling the water, he throws out the other 

 arm, and carries it in a horizontal position, to create a greater 

 weight on that side, and balance the weight of water. And 

 often he finds it easier to divide his water into two pails, and, 

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