DIGESTION AND ABSORPTION IN THE STOMACH. 687 



action or in its total acidity. This fact shows that the juice possesses 

 antiseptic properties, and it is usually supposed that the presence of 

 the free acid accounts for this quality. 



The Acid of Gastric Juice. The nature of the free acid in gastric 

 juice was formerly the subject of dispute, some claiming that the 

 acidity is due to HC1, since this acid can be distilled off from the gas- 

 tric juice, others contending that an organic acid, lactic acid, is 

 present in the secretion. All recent experiments tend to prove that 

 the acidity is due to HC1. This fact was first demonstrated satis- 

 factorily by the analyses of Schmidt, who showed that if, in a given 

 specimen of gastric juice, the chlorids were all precipitated by silver 

 nitrate and the total amount of chlorin was determined, more was 

 found than could be held in combination by the bases present in the 

 secretion. Evidently, some of the chlorin must have been present 

 in combination with hydrogen as hydrochloric acid. Confirmatory 

 evidence of one kind or another has since been obtained. Thus it has 

 been shown that a number of color tests for free mineral acids react 

 with the gastric juice: methyl- violet solutions are turned blue, 

 congo-red solutions and test paper are changed from red to blue, 

 00 tropeolin from a yellowish to a pink red, and so on. A number of 

 additional tests of the same general character will be found described 

 in the laboratory handbooks.* It must be added, however, that 

 lactic acid undoubtedly occurs, or may occur, in the stomach during 

 digestion. Its presence is usually explained as being due to the fer- 

 mentation of the carbohydrates, and it is therefore more constantly 

 present in the stomachs of the herbivora. The amount of free acid 

 varies according to the duration of digestion; that is, the secretion 

 does not possess its full acidity in the beginning, owing to the fact 

 (Heidenhain) that in the first periods of digestion, while the secretion 

 is still scanty in amount, a portion of its acid is neutralized by the 

 swallowed saliva, the alkaline mucus, and the alkaline secretion of 

 the pyloric end of the stomach; the secreted juice has, however, a 

 constant acidity. The acidity of the human gastric juice is usually 

 estimated at 0.3 per cent., but during digestion it may reach (Horn- 

 borg) 0.4 to 0.5 per cent., and these figures express probably its 

 strength as secreted. The acidity of the dog's gastric juice, according 

 to Pawlow, lies between 0.46 and 0.56 per cent. 



The Origin of the HC1. The gastric juice is the only secretion 

 of the body that contains a free acid. The fact that the acid is a 

 mineral acid and is present in considerable strength makes the cir- 

 cumstance more remarkable. Attempts have been made to ascer- 

 tain the histological elements concerned in its secretion and the 

 nature of the chemical reaction or reactions by which it is produced. 

 With regard to the first point it is generally believed that the border 

 * Simon, " A Manual of Clinical Diagnosis, " 1904. 



