118 THE FITNESS OF THE ENVIRONMENT 



not be attained with another solvent. It is 

 no exaggeration to say that except atmos- 

 pheric oxygen and carbonic acid, nearly all 

 the food of living organisms is water borne, 

 and all material in its passage into the body, 

 through the body, and out of the body nearly 

 always employs the same vehicle. Cer- 

 tainly no other form of transport would be so 

 efficient and so economical. 



B 



IONIZATION 



If, therefore, aqueous solutions are, ap- 

 parently of necessity, the very basis of the 

 life processes, the state of substances when in 

 this condition, and also when in contact with 

 water, is of vital importance. Here two prop- 

 erties of water, the dielectric constant and 

 the surface tension, exert a cardinal influence. 



Among the phenomena of solution those 

 which are related to electrolytic dissociation, 

 as suggested by the hypothesis of Arrhenius, 

 have deservedly received a great deal of at- 

 tention since the secure establishment of the 

 new science of physical chemistry in the 

 eighties of the last century. In the course 

 of time the belief that in aqueous solution 

 the molecules of all acids, bases, and salts 

 are more or less split into particles which bear 



