BIOLOGICAL APPLICATIONS 213 



large proportion of acid substances, the mechanism which pre- 

 serves the neutrality of the tissues and tissue-fluids despite the 

 relatively enormous daily and hourly fluctuations in acid-pro- 

 duction or consumption which necessarily occur within the body, 

 is, in all probability, one of prime physiological importance. 



The acid which is produced most copiously in the body is 

 carbonic acid. The classic theory regarding the neutralization 

 of this acid is that of Fernet (14), Heidenhain and Mayer (25) 

 (26) and von Bunge (6) (7) who supposed that it is bound by the 

 disodium phosphate in the blood, according to the balanced 

 reaction : 



C0 2 + H 2 + Na2HP0 4 ? NaHC0 3 + NaH 2 P0 4 , 



the reaction proceeding towards the right in the tissues, where 

 the C0 2 tension is high, towards the left in the lungs, where the 

 C0 2 tension (active mass of CO 2 ) is low. Sertoli (65), however, 

 and Mroczkovsky (46) pointed out that the quantity of phos- 

 phoric acid in the blood of many animals, e.g., the ox and the 

 pig,* is too small to play the important r61e assigned to it by 

 these investigators. 



We have seen that the alkali- and acid-equivalent of the pro- 

 teins varies very markedly with the hydroxyl- or hydrogen- 

 contents of their solutions. Thus one gram of serum-globulin 

 (Cf. Chap. V) in solutions neutral, or approximately neutral, to 

 litmus (absolute neutrality: H+ = OH' = 8 X 10~ 8 ) neutralizes 

 10 X 10~ 5 equivalent gram molecules of a base, while in solutions 

 neutral to phenolphthalein (OH 7 = 20 X 10~ 7 ) 1 gram neutralizes 

 20 X 10~ 5 equivalent gram molecules of a base. The significance 

 of these figures may, perhaps, be more fully realized when stated 

 thus: in one litre of NaOH solution containing 1 per cent of 

 globulin and neutral to litmus, addition of 100 X 10~ 5 gram- 

 equivalents of NaOH only raises the alkalinity (hydroxyl-content) 

 of the solution by about 0.2 X 10~ 5 , that is, by two-tenths of a 

 per cent of the change in the sodium content of the solution. 

 Casein, at neutrality to litmus, neutralizes 50 X 10~ 5 gram- 

 equivalents of base per gram, and at "saturation," i.e., at an 

 acidity of about 50 X 10~ 7 H+, it neutralizes only 11.4 X 10~ 5 

 gram-equivalents of base per gram. Hence to a litre of a 1 per 

 cent solution of sodium caseinate, neutral to litmus, we should 

 * Cf . von Bunge (7) . 



