THE ANIMAL MACHINE 



sally employed in the animal world is that in which a di- 

 rect push or pull is given to the substance, the position 

 of which it is desired to change. We have already 

 pointed out that there is no essential difference between 

 pushing and pulling. The fact receives another illus- 

 tration in considering the muscular mechanism. We 

 speak of pushing when we propel something away from 

 a body, of pulling when we draw something toward 

 it, yet, as we have just seen, each can be accomplished 

 merely through the contraction of a set of muscles, acting 

 on differently disposed levers. All the bodily activi- 

 ties are reducible to such muscular contractions, and 

 the diversified movements in which the organism con- 

 stantly indulges are merely due to the large number 

 and elaborate arrangement of the bony levers upon 

 which these muscles are operated. 



We may well suppose that the primitive man continued 

 for a long period of time to perform all such labors as 

 he undertook without the aid of any artificial mech- 

 anism; that is to say, without having learned to gain 

 any power beyond that which the natural levers of his 

 body provided. A brief observation of the actions 

 of a man performing any piece of manual labor will, 

 however, quickly demonstrate how ingeniously the 

 bodily levers are employed, and how by shifting positions 

 the worker unconsciously makes the most of a given 

 expenditure of energy. By bending the arms and 

 bringing them close to the body, he is able to shorten 

 his levers so that he can lift a much greater weight than 

 he could possibly raise with the arms extended. On 

 the other hand, with the extended arm he can strike a 



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