62 THE ENGINES OF THE HUMAN BODY 



cord, considerably beyond the point of maximum leverage. 

 As the heel is lifted by the muscles it gradually becomes 

 horizontal and at right angles to its tendon or piston cord. 

 As the heel rises, then, it becomes a more effective lever ; 

 the muscles gain in power. The more the foot is arched, 

 the more obliquely is the heel set and the greater is the 

 strength needed to start it moving. Hence, races like 

 the European and Mongolian, which have short as well 

 as steeply set heels, need large calf muscles. It is at the 

 end of the upward stroke that the heel becomes most 

 effective as a lever, and it is just then that we most need 

 power to propel our bodies in a forward direction. It 

 will be noted that the heel, unlike the crank-pin of an 

 engine, never reaches, never even approaches, that point 

 of powerlessness known to engineers as a dead centre. 

 Work is always performed within the limits of the most 

 effective working radius of the lever. It is a law for all 

 the levers of the body ; they are set and moved in such a 

 way as to avoid the occurrence of dead centres. Think 

 what our condition would have been were this not so ; 

 why, we should require revolving fly-wheels set in all 

 our joints ! 



Another property is essential in a lever : it must be 

 rigid, otherwise it will bend and power will be lost. 

 Now, if the foot were a rigid lever there would be 

 missing two of its most useful qualities. It could no 

 longer act as a spring or buffer to the body, nor could 

 it adapt its sole to the various kinds of surfaces on which 

 we have to tread or stand. Nature, with her usual 

 ingenuity, has succeeded in combining those opposing 

 qualities — rigidity, suppleness, and elasticity or springi- 

 ness — by resorting to her favourite device, the use of 

 muscular engines. The arch is necessarily constructed of 

 a number of bones which can move on each other to a 

 certain extent, so that the foot may adapt itself to all kinds 

 of roads and paths. It is true that the bones of the arch 

 are loosely bound together by passive ties or ligaments, 

 but as these cannot be lengthened or shortened at will, 

 Nature had to fall back on the use of muscular engines 



