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Considering, as it is proper to do, that in a condition of health each 

 separate biped and each individual leg is required to perform an equal 

 and uniform function and to carry an even or equal portion of the weight 

 of the body, it will be readily appreciated that the result of this equal 

 distribution will be a regular, evenly balanced, and smooth displace- 

 ment of the body thus supported by the four legs, and that therefore, 

 according to the rapidity of the motion in different gaits, each single 

 leg will be required at certain successive moments to bear the weight 

 which had rested upon its congener while it was itself in the air, in the 

 act of moving ; or, again, two different legs of a biped may be called 

 upon to bear the weight of the two legs of the opposite biped while 

 also in the air in the act of moving. 



To simplify the matter by an illustration, the weight of an animal 

 may be placed at 1,000, of which each leg, in a normal and healthy con- 

 dition, supports while at rest 250. When one of the fore legs is in ac- 

 tion, or in the air, and carrying no weight, its 250 share of the weight 

 will be thrown upon its congener or partner to sustain. If the two legs 

 of a biped are both in action and raised from the ground, their congeners 

 still resting in inaction, will carry the total weight of the other two, or 

 500. And as the succession of movements continues, and the change 

 from one leg to another or from one biped to anothei-, as may be re- 

 quired by the gait, proceeds, there will result a smooth, even, and equal 

 balancing of active movements, shifting the weight from one leg or one 

 biped to another, with symmetrical precision, and we shall be presented 

 with an interesting example of the play of vital mechanics in a healthy 

 organization. 



Much may be learned from the accurate study of the action of a 

 single leg. Normally, its movements will be without variation or fail- 

 ure. When at rest it will easily sustain the weight assigned to it, with- 

 out showing hesitancy or betraying pain, and when it is raised from 

 the ground in order to transfer the weight to its mate, it will perform 

 the act in such a manner that when it is again placed upon the ground 

 to rest it will be with a firm tread, indicative of its ability to receive 

 again the burden to be thrown back upon it. In planting it upon the 

 ground or raising it up again for the forward movement while in action, 

 and again replanting it upon the earth, each movement will be the 

 same for each leg and for each biped, whether the act be that of walk- 

 ing or trotting, or even of galloping. In short, the regular play of 

 every part of the apparatus will testify to the existence of that condi- 

 tion of orderly soundness and efficient activity which is eloquently sug- 

 gestive of the condition of vital integrity, which is simply but compre- 

 hensively expressed by the terms health and soundness. 



But let some change, though slight and obscure, occur among the 

 elements of the case, some invisible agency of evil intrude among the 

 harmonizing processes going forward; any disorder occur in the rela- 



