158 VARIATIONS IN ACIDITY OF GASTRIC JUICE. [BOOK II. 



directed to variations which occur simultaneously in the nature of 

 the free acid. 



Richet's ob- ^ has been shewn, in a previous section, that the 

 servations on acid reaction of the gastric juice is due to the presence 

 the acidity of of free hydrochloric acid, though Richet maintains, of 

 the contents of hydrochloric acid in combination with an amido-acid, 

 such as leucine. V. den Velden 1 asserts that in the first 

 stages of digestion in the human stomach no free hydrochloric acid 

 can be detected until three-quarters of an hour after a full meal such 

 as dinner. 



It must be remembered, however, that the proteids which are 

 present in the gastric juice interfere very materially with the colour 

 reactions upon which reliance is placed in asserting the presence or 

 absence of free hydrochloric acid. We shall probably be near the 

 truth, therefore, in asserting that at least twenty minutes or half-an- 

 hour, and occasionally forty minutes, must elapse before the stomach 

 contents contain an appreciable quantity of free hydrochloric acid. 



The gastric juice behaves, it was shewn, when shaken with ether, 

 .as an aqueous solution containing a mineral acid. 



The pure gastric juice of man has an acidity which, according 

 to Richet's observations, corresponds to 1'3 parts by weight of HC1 

 in 1000. 



When digestion is proceeding, however, the acidity increases 

 somewhat. However large the quantity of liquid in the stomach, 

 it is found to have an acidity which on an average (according to 

 Richet) corresponds to 1*7 parts of HC1 per 1000, though it may, 

 especially at the end of digestion, exceed this figure somewhat. 

 After the ingestion of acids or of alkalies, the normal acidity is soon 

 re-established. 



Richet has found that the acidity of the contents of the stomach 

 in the advanced stages of digestion no longer depends solely on a 

 mineral acid, but that considerable quantities of acids soluble in 

 ether are present. These acids are, in part, produced by the decom- 

 position of salts of organic acids present in the ingested food, but, 

 according to Richet, they are, in no small degree, due to acids which 

 result from acid fermentations which occur in the stomach. Thus in 

 the case of milk, according to Richet, there is set up, as a normal 

 process, an acid fermentation which leads to the development of large 

 quantities of lactic acid. The feebler the normal acidity of the 

 gastric juice, the greater the quantity of the organic acids resulting 

 from fermentative changes. It is probable that the acids thus 

 set free reinforce the normal acid and cooperate in the process 

 of digestion. 



1 Von den Velden, ' Zur Lehre von der "Wirkung des Mundspeichels im Magen.' 

 Zeitschrift f. phys. Chemie, Vol. in. p. 205. 



