152 THE FITNESS OF THE ENVIRONMENT 



alkaline salt (sodium bicarbonate), but does 

 not increase the amount of free acid. Not 

 until the bicarbonate is entirely decomposed 

 (318 grams HC1) does the hydrochloric acid 

 begin to exert its own action as an acid, and 

 then 2 grams cause about as much rise in 

 acidity as 318 grams have previously caused, 

 or nineteen times the rise effected by the first 

 300 grams, or about two hundred times the 

 rise caused by one hundred times the quantity 

 of hydrochloric acid at the beginning of the 

 experiment. 



These statements all rest upon facts which 

 have been accurately established by experi- 

 ment and are brought forward in company 

 with the theoretical treatment, based upon 

 the Mass Law, only for the sake of complete- 

 ness of statement and because brief exposition 

 is otherwise scarcely possible. The extraor- 

 dinary capacity of carbonic acid to preserve 

 neutrality in aqueous solution, which is ex- 

 plained by its strength and solubility in water, 

 is a well-established experimental fact, and no 

 other known substance shares this power. 1 

 Hydrogen sulphide might perhaps be thought 

 of as an exception. But while its solubility 



1 Henderson, "The Theory of Neutrality Regulation in 

 the Animal Organism," American Journal of Physiology, XXI, 

 427, 1908. 



