DIGESTION AND ABSORPTION IN THE STOMACH. 769 



solution. At this concentration the digestive action of the pepsin 

 is relatively feeble.* 



The Origin of the HCl. — That the acid of the gastric juice is a 

 mineral acid and is present in considerable strength is a remarkable 

 fact that has excited much interest. Attempts have been made to 

 ascertain' the histological elements concerned in its secretion and 

 the nature of the chemical reaction or reactions by which it is pro- 

 duced. With regard to the first point, it is generally believed that 

 the parietal cells of the gastric tubules constitute the acid-secreting 

 cells. This belief is founded upon the general fact that in the 

 regions in which these cells are chiefly present — that is, the middle 

 region of the stomach — the secretion is distinctly acid, and where 

 they are absent or scanty in number the secretion is alkaline or less 

 acid. In the pyloric region, for instance, these cells are lacking 

 entirely and the secretion is alkaline. Moreover microchemical 

 reactions seem to show clearly that the parietal cells are particu- 

 larly rich in chlorids, and this fact serves to connect them with 

 the production of the acid. It seems perfectly evident that the 

 HCl must be formed in the long run from the chlorids of the 

 blood. The chief chlorid is NaCl, and by some means this com- 

 pound is broken up; the chjorin is combined with hydrogen, and 

 is then secreted upon the free surface of the stomach as HCl. 

 In support of this general statement it has been shown that if the 

 chlorids in the blood are reduced by removing them from the food 

 for a sufficient time the secretion of gastric juice no longer contains 

 acid. On the other hand, addition of NaBr or KI to the food may 

 cause the formation of some HBr and HI, together with HCl in 

 the gastric jui^e. Maly has suggested that acid phosphates may 

 be produced in the first instance, and then by reacting with the 

 sodium chlorid may give hydrochloric acid, according to the formula, 

 NaHjPOi + NaCl = Na.HPO^ + HCl. Other theories have been 

 proposed, but, as a matter of fact, no explanation of the details 

 of this reaction is satisfactory. Many observers have attempted 

 by microchemical methods to determine the exact points in the 

 gastric glands at which the acid is formed. Most of these attempts 

 have given results which have been difficult to interpret. Harvey 

 and Bensley,t by making use of dyes (cyanimin and neutral red) 

 which give different colors in neutral, alkaline, and acid media, 

 state that the free acid is found only on the internal surface of the 

 stomach or in the neck of the glands. The parietal cells themselves 

 exhibit an alkaline reaction. These observers advance, therefore, 

 the probable hypothesis that the parietal cells secrete a chlorid 

 of an organic base, and this compound in some way yields free 

 hydrochloric acid only after it reaches the mouth of the gland. 



* Shohl, "The Johns Hopkins Bulletin," May, 1920. 

 t Harvey and Bensley, "Biological Bulletin," 23, 225, 1912. 

 49 



