1 8 THE ENGINES OF THE HUMAN BODY 



muscle passes into action it becomes shorter and thicker 

 and thus moves the particular lever or crank-pin to which 

 it is attached. But these muscles in front of the leg let 

 the front part of the foot sink gently on to the ground 

 by passing into action and yet gradually getting longer 

 and longer, thus supporting the front part of the foot as 

 it settles down. Herein we see that the engines of the 

 human body can not only pull upon and bend levers but 

 they can also, by a sort of reversed action, serve as guy- 

 ropes or brakes and thus allow the levers to sink gently 

 to a position of rest. Every boy and girl must have 

 noticed the painful feeling which is felt in the front of the 

 legs on descending a long and steep hill. The front part 

 of the foot has to be supported in each step for a much 

 longer time when a hill path slopes rapidly downwards in 

 front of us ; hence the muscles or engines which let the 

 toes down become very tired and cry out with pain. 

 Wherein they are very different from metal engines. 

 There is another way of making the muscles very tired 

 and that is by wearing very high heels as some ladies did 

 at the time I gave these Christmas Lectures. The heels 

 being very high, they come into contact with the ground 

 too soon and the muscles in front of the leg become very 

 tired because they have extra work to do in letting the 

 toes down. But here again muscular engines are better 

 than metal ones ; they soon become strong enough to 

 bear their extra burden and no longer feel painful. Over- 

 work never makes a metal engine stronger ; overwork 

 wears them out. 



We are so accustomed to the way in which the human 

 machine runs that it never strikes us as being at all 

 uncommon or droll. But if a horse could tell us what he 

 thought of our manner of walking, I am sure he would 

 say it was the drollest way of getting forward in all the 

 world, so different from the sensible way adopted by all 

 ordinary four-footed beasts. When we take a step, one 

 leg rests or supports the body while the other swings 

 forward. In the next step the swinging leg becomes the 

 resting limb and the resting one then swings forward. 



