258 THE FITNESS OF THE ENVIRONMENT 



and that a phase is any solid, liquid, or gas- 

 eous part of the whole system which possesses 

 homogeneity of composition. For instance, 

 if a system is made up of sand, salt solution, 

 ice, and aqueous vapor, each of these separate 

 parts, in that it is homogeneous, is a phase. 



Now the properties of water have the result 

 that more readily than other substances it 

 exists simultaneously and in large quanti- 

 ties in the three phases of solid, liquid, and 

 gas as ice, water, and aqueous vapor. This 

 depends upon the high latent heats of fusion 

 and vaporization, the high freezing point of 

 water, and its vapor tension. Water en- 

 hances the complexity of the environment, 

 and is one principal factor in the mobility of 

 the environment as a whole. Further, it 

 makes for stability ; other things being equal, 

 the greater the number of phases, the less the 

 tendency to change. Among phases the dis- 

 perse colloidal type is unique and of very 

 great importance — almost the sole basis, 

 indeed, of great physical complexity — and, 

 as above shown, the peculiar properties of 

 water highly favor the colloidal condition. 



The solvent power of water much increases 

 the number of components which may enter 

 into a system of which it is a part ; hence the 

 large number of components of sea water, 



