I02 THE PRINXIPLES OE MYODYXAMICS. 



acting on the continuity of the lever. The entire 

 force is the pressure exerted by the weight of 

 the body on the astragalus under the dynamic 

 conditions ; and that is, as the mechanical facts 

 show, the weight of the body plus the contract- 

 ile force of the active muscles, expressed in 

 the same units as the weight of the body. So 

 much for the foot-lever. 



99. It is possible to verify this conclusion by 

 assuming the foot to be : (i.) A lever of the 

 first order. (2.) A lever of the second order : 



In a given case, the distance from the ball of 

 the foot to the center of the ankle-joint is five 

 inches, the distance from the center of the ankle- 

 joint to the insertion of the tendo-Achillis is 

 two and one-half inches, and the weight of the 

 body is i5o pounds. Xow, it is evident that 

 there will be a pressure of i5o pounds on the 

 ball of the foot when the muscles of the tendo- 

 Achillis lift the body : 



(i.) The weight-arm of the lever X the 

 weight = the power-arm of the lever X the 

 power : That is — 



2i X P = 5 X i5o : . (i.) 



