CARBONIC ACID 155 



for its origin must have been acid from the 

 presence of carbonic acid unbalanced by base. 

 The present ratio between bicarbonates and 

 carbonic acid in sea water has not been accu- 

 rately estimated, but it is perhaps 50 : 1 or 

 100:1. The conditions are complicated by 

 flora and fauna, and such influences have not 

 yet been determined. 



Turning to the acid-base equilibrium of 

 blood and protoplasm, we encounter a subject 

 which is better understood, though not more 

 significant in the present discussion. The 

 alkalinity of the blood is one of the familiar 

 subjects of physiological investigation, and 

 its clinical importance has long been clear. 

 Not until the introduction of the ionization 

 hypothesis, however, was it possible to explain 

 the conditions. The outcome of these studies 

 has been to assign to the equilibrium between 

 carbonic acid and bicarbonates a first place in 

 the regulation of the reaction of blood ; l and 

 since such substances are invariably constitu- 

 ents of all protoplasm, to make evident the 

 universal biological importance of this equi- 



1 Friedenthal, "Archiv fur Physiologie, Verhandlungen 

 der Physiologischen Gesellschaft Berlin," May 8, 1903. Hen- 

 derson, American Journal of Physiology, XV, 257, 1906, 

 "Ergebnisse der Physiologie," VIII, 254-325, 1909 (the last 

 a review of the equilibrium between acids and bases in the 

 organism). 



