Devolution 119 



point of equilibrium with the other side is 

 attained. Then growth begins, and both sides 

 are restored to their former completeness. 

 Growth being bilateral, a set-back on one side 

 must be followed by a set-back on the other be- 

 fore a forward movement can be resumed. It 

 is a balanced process demanding an equilibrium 

 as a basis of its activity. 



This fact necessitates devolution in complex 

 life processes. Single cells cannot be added 

 to restore an equilibrium between two sides, 

 although these cells may be destroyed and 

 eliminated. Vital equilibriums are, therefore, 

 obtained by backward movements; balance is 

 restored by a subtraction, not by an addition. 

 If a plank be so balanced that a slight differ- 

 ence in the weight of the two sides will dis- 

 turb it, a block may be added first to one side 

 and then to the other until a large number is 

 piled on each side. If a dozen blocks were 

 suddenly knocked off one side, the only way to 

 keep the equilibrium would be to knock off a 

 dozen from the other. Then the original num- 

 ber might be restored by adding one at a time. 

 Addition is a slow process ; subtraction may be 



