DIGESTION 



The Functions of Hydrochloric Acid 



The functions of hydrochloric acid may be conveniently divided into 

 physiological and biochemical. The former functions have to do with 

 the control of the movements of the stomach, including the opening 

 of the pyloric sphincter, and, after the chyme has entered the duodenum, 

 with the secretion of pancreatic juice and bile. The biochemical functions 

 are concerned: (1) in assisting the pepsin in the digestion of proteins, 

 (2) in bringing about a certain amount of inversion of disaccharides, 

 and (3) in having an antiseptic action on the stomach contents. Re- 

 garding the last mentioned of these functions, it may be said that the 

 chyme, as it is ejected from the stomach, is usually sterile, although it 

 may contain spores and certain bacteria that are protected against the 

 digestive agencies of the stomach. This protection is afforded by an 

 outer covering of a chitinous nature (spores), or, as in the case of the 

 tubercle bacillus, by a covering of waxlike material. It is believed that 

 persons with strictly normal digestion are much less liable to infection 

 by such bacteria, as those of typhoid and cholera, than persons with less 

 active gastric secretion. When the acid of the gastric juice falls below 

 the level at which it develops an antiseptic action, various bacteria and 

 yeasts grow in the stomach contents, producing by the resulting fermen- 

 tation irritating organic acids and gases. It is under these conditions 

 that yeasts, sarcinse, and lactic and butyric acid bacilli find in the gastric 

 contents a suitable nidus on which to grow. 



THE AMOUNT OF ACID 



It has long been known that considerable variations in the amount of 

 hydrochloric acid in the gastric juice are associated with symptoms of 

 indigestion. On this account a more or less elaborate technic has been 

 developed for the purpose of determining the amount of hydrochloric 

 acid in the gastric contents.* 



There are three things in connection with this activity that we may measure: (1) 

 the total titrable hydrochloric acid; (2) the free hydrochloric acid; and (3) the actual 

 hydrogen-ion concentration. The determination of the total available acids is made by 

 titrating a measured quantity of gastric juice against a standard alkali, using phenol- 

 phthalein as an indicator. By this method about 75 c.c. of decinormal alkali solution 

 are required to neutralize 100 c.c. of normal gastric juice. The determination of the 

 free hydrochloric acid is made by using special indicators, such as those of Giinzbcrg 

 and Topfer, which change color at a hydrogen-ion concentration of about 10-"' (see 

 page 27). To produce this hydrogen-ion concentration, a considerable quantity 

 0.05 per cent or more of an organic acid is necessary, whereas it requires only a 

 trace of hydrochloric acid. Normal human gastric juice, when titrated with one of 



*The methods can be found in any volume on clinical diagnosis. 



