DIGESTION IN THE STOMACH 157 



of HC1 is 0.0004N. Weaker acid gives no color. The results 

 of this test correspond fairly well with those obtained by more 

 accurate methods. In pure gastric juice most of the hydro- 

 chloric acid is free. Total acidity as determined with phenol- 

 phthalein, and free hydrochloric acid as determined with Gunz- 

 berg's reagent agree closely. If food is present however, the 

 free hydrochloric acid is greatly reduced since much of the acid 

 is combined with protein. 



Human gastric juice contains on an average 0.3% HC1. 

 (That of dogs contains about 0.6% HC1). The concentration 

 of H-ions runs from 10' 2 to 7XlO' 2 N. 



In diseases the amount of hydrochloric acid may vary con- 

 siderably. A condition in which the amount is abnormally high 

 is spoken of as hyperacidity (or hyper chlorhydria). This is 

 usually observed in cases of gastric ulcer and in neurosis. If 

 the acidity is below normal it is spoken of as hypoacidity (or 

 hypochlorhydria). This condition often is observed in cases of 

 cancer of the stomach or other regions. Sometimes no acid at 

 all is secreted. This condition is called anacidity (or achlor- 

 hydria). A normal condition is called euchlorhydria. 



Source of the Hydrochloric Acid. The hydrochloric acid 

 is secreted mainly by glands in the fundus end of the stomach. 

 It is not stored in the cells previous to secretion, and probably 

 is not even secreted directly by the cells, but is formed from a 

 secreted substance. The actual mechanism is a matter of doubt. 

 Perhaps it is secreted as an ester, or is formed from ammonium 

 chloride or some other chlorine compound. The source of the 

 chlorine is evidently the sodium chloride of the blood. 



The functions of the hydrochloric acid are various. First, 

 as we already have seen, it dissolves the proteins of the food, 

 converting them into acid metaprotein. It plays an important 

 part in digestion of proteins by pepsin, however, for this en- 

 zyme is secreted in an inactive form, and becomes active only 

 under the influence of the hydrochloric acid. An unimportant 

 phase of the function of the hydrochloric acid is in connection 

 with its action on saccharose. This disaccharide is easily hydro- 



