128 LIFE IN NATURE. 



each of them was capable of a solution simple enough, 

 and even obvious when once it was seen. We may 

 briefly recapitulate the results at which we have 

 arrived. 



I. Living bodies GROW by the operation of chemi- 

 cal force, which exhibits in them a twofold action, 

 and produces substances which tend to decompose ; 

 on the same principle that gravitation in a fountain 

 causes water to rise by the effect of its fall. So 

 chemical change, or decomposition, causes the 

 nourishment of the body, and the two opposite pro- 

 cesses of growth and decay proceed in mutual depen- 

 dence. This law is easily understood by fixing the 

 thoughts on any case in which an action of one kind 

 produces another that is opposite to itself: the move- 

 ment of a pendulum, for example, in which the 

 downward motion produces the upward, and the 

 upward furnishes the conditions under which the 

 downward can again take place. It is thus chemical 

 action produces the vital action ; and the vital action 

 furnishes the conditions under which the chemical 

 action can again take place. Living bodies, then, 

 grow through decay, or through chemical processes 



