ELEMENTARY PHYSIOLOGICAL CHEMISTRY 221 



EXPERIMENT II. Place a drop of Giinzberg's reagent (a solution of 

 phloroglucin and vanillin in absolute alcohol) on an evaporating basin, 

 and mix with it a drop of 0'2 per cent, hydrochloric acid. Slowly 

 evaporate to dry ness. A deep red stain is left. Repeat this experi- 

 ment with a 0-8 per cent, solution of lactic acid. No red stain is 

 obtained. 



This reagent reacts to mineral acids, but not to organic acids, even 

 when these are present in considerable amount. The mineral acid 

 with which it reacts most sensitively is hydrochloric acid, and since 

 the reaction is always very distinct in gastric juice, we are led to 

 expect that the acidity is due to this acid. That this is actually the 

 case has been proved by estimating on the one hand the total amount 

 of bases, and on the other the total amount of acids in gastric juice. 

 It was found that the latter were much in excess of the former, 

 the acid radicle present being chlorine, which must exist in the 

 gastric juice as hydrochloric acid. 



How this Free Acid is Secreted. There is perhaps nothing more 

 surprising in the whole of physiological chemistry than that a strong 

 mineral acid should be secreted from a distinctly alkaline fluid such as 

 the blood is. The salts from which it is produced are, of course, the 

 chlorides (especially of sodium), and these are very abundant in the 

 blood, which also contains sodium carbonate, to which is mainly due its 

 alkaline reaction. How then is the hydrochloric acid liberated from 

 this alkaline fluid ? Although alkaline in reaction the blood neverthe- 

 less contains weak acids, either as acid salts (NaH 2 P0 4 ) or as carbonic 

 ficid. Now it is a well known fact in physical chemistry that any acid, 

 however weak its acidity may be, displaces a certain amount of any 

 other acid from its combinations, and this displacement becomes very 

 distinct if the weaker acid be in large excess of the stronger. This 

 property is known as mass-influence, and in virtue of it even the 

 weakest acid e.g. ordinary water can displace a certain amount of the 

 strongest mineral acids from their combinations. 1 



Since very little carbonic acid is in simple solution in the blood it is 

 probable that it is the acid phosphates which furnish the weak acid. 

 They do this by giving off a portion of their hydrogen, the place of this 

 being then taken by the free alkali liberated from the chloride. 



NaH 2 P0 4 + NaCl = Na 2 HP0 4 + HC1. 



So far, then, the reaction is a merely chemical one, but now we must 

 discover what agency it is which causes this free acid to be secreted 

 into the stomach. If a pouch be made of the Cardiac end of the 



1 Thus if a solution of bismuth nitrate be diluted with a large excess of water a 

 white precipitate of bismuth oxynitrate falls out. 



