CHAPTER XXII 

 EQUILIBRIUM AND HABIT 



A MAN, or any higher animal, may be considered to be a 

 mechanism in the third degree, a mechanism of mechanisms 

 of mechanisms. 



He is first of all a mechanism of the same scale as his 

 body an anatomical mechanism. A man has arms, legs, 

 joints, muscles, sinews, etc. ; they are the interworking 

 parts of his anatomical mechanism. Between these different 

 parts exist communications established by the nervous 

 system, which may be compared to a network of electric 

 conductors transmitting orders to set going or stop move- 

 ment in an industrial machine. Here the anatomic mechan- 

 ism already ceases to be entirely of the same scale as the 

 man, for nervous transmission is not directly visible and 

 belongs to the order of magnitude of colloid phenomena. 



Excepting perhaps the bones which, in the execution 

 of a great number of movements, seem to behave like rigid 

 levers comparable to the rods of a steam-engine, all the 

 other parts of the anatomical mechanism show their activity 

 as parts of the whole only as a synthesis of smaller move- 

 ments which are of colloid or protoplasmic order. When a 

 muscle contracts, the muscular substance which constitutes 

 it changes its colloid state ; these two phenomena con- 

 traction of the muscle and change in the colloid state of its 

 protoplasm are so closely united by relations of cause and 



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