124 THE FITNESS OF THE ENVIRONMENT 



and the sure and definite relations between 

 such bodies provide, as it were, a secure foun- 

 dation for the more complex organic structures. 

 More obvious is the value of ions as sources 

 of electricity. If the older electro-physiology 

 of the third quarter of the nineteenth cen- 

 tury has proved in some respects a sterile 

 field, there can yet be no doubt that more 

 subtly, and quite apart from the nervous im- 

 pulse and the peculiar phenomena of electrical 

 fishes, electrical phenomena are everywhere 

 involved in the most intimate of the physio- 

 logical processes. 



Even without further discussion of a sub- 

 ject that must soon lead into difficult and 

 highly technical considerations, I feel sure 

 that the existence of another important fitness 

 of water is patent. For ions are evidently 

 a real contribution to the richness of the 

 environment. They enhance the Variety of 

 chemical substances and of chemical reactions ; 

 they constitute a group of singularly mobile 

 ( chemical agents; they provide electricity; 

 and, finally, aqueous solutions are by far the 

 best source of ions. 



It must be pointed out before leaving this 

 subject that the dielectric constant, hence 

 the ionizing power, is somehow related to 

 various other properties of the solvent. In 



