144 ORIGIN AND NATURE OF LIFE 



changes going on within it, such feeble acids 

 as carbonic or lactic acid. This leads to 

 molecular aggregation of the colloids of the 

 cell, and this culminates in a stimulus or 

 contraction in which the acid is discharged, 

 and the whole system reverses or reverts to 

 its original condition. 



It is thus seen that in the typical colloidal 

 solution there exists a most delicate balance 

 of the feeble affinities of the colloidal molecules, 

 so that within narrow limits they can build 

 together or be pulled apart, and the value of 

 this in life processes is obvious. 



Next there must be considered the balancing 

 of these affinities against similar affinities 

 for the solvent and for the crystalloids of 

 inorganic or organic nature present in true 

 solution along with the colloids. 



The affinity between colloid and solvent is 

 shown by the failure to form saturated solu- 

 tions and separate out as crystalloids do ; it is 

 also shown by the tendency of the colloidal 

 multi-molecules to accumulate upon any 

 interface and alter conditions there. Such 

 accumulations are accompanied by change in 

 what is called surface-tension (or the energy 

 distribution at the interface between two 

 layers). It is as a result of this that colloidal 

 solutions readily form froths, even in most 



