IN THE ANIMAL ORGANISM. 193 



Every force, therefore, exhibits itself in matter either 

 in the form of resistance to external causes of motion, 

 or of change in form and structure ; or as a moving 

 force when no resistance is opposed to it ; or, finally, 

 in overcoming resistance. 



One and the same force communicates motion and 

 destroys motion ; the former, when its manifestations 

 are opposed by no resistance ; the latter, when it puts 

 a stop to the manifestation of some other cause of mo- 

 tion, or of change in form and structure. Equilibrium 

 or rest is that state of activity in which one force or 

 momentum of motion is destroyed by an opposite force 

 or momentum of motion. 



We observe both these manifestations of activity in 

 that force which gives to the living tissues their pecu- 

 liar properties. 



The vital force appears as a moving force or cause 

 of motion when it overcomes the chemical forces (co- 

 hesion and affinity) which act between the constituents 

 of food, and when it changes the position or place in 

 which their elements occur ; it is manifested as a cause 

 of motion in overcoming the chemical attraction of the 

 constituents of food, and is, further, the cause which 

 compels them to combine in a new arrangement, and to 

 assume new forms. 



It is plain, that a part of the animal body possessed 

 of vitality, which has therefore the power of over- 

 coming resistance, and of giving motion to the elemen- 

 tary particles of the food, by means of the vital force 

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