518 DIGESTION 



shown that the prussian blue reaction, which requires the presence of 

 free mineral acid, is most pronounced in certain of the parietal cells. A 

 considerable amount of the precipitate is, however, also visible in the 

 lumen of the glands and in the stomach itself. Certain observers affirm 

 that, although some of the parietal cells may take the stain, the vast 

 majority of them do not do so; and, moreover, that cells incapable of 

 forming hydrochloric acid (e. g., of the liver) may also become stained, 

 and that the precipitation may occur in the blood and lymph. 



The confusion in the results by these methods prompted A. B. Macal- 

 lum 22 and Miss M. P. Fitzgerald to investigate the distribution of the 

 chlorine in the cells by a rnicrochemical method, in which the chlorides 

 were precipitated with silver nitrate and the silver chloride then reduced 

 by exposing the section to light. It was found that both kinds of gas- 

 tric-gland cell, chief and parietal, but particularly the parietal, gave the 

 chloride reaction. Using as a stain a substance (cyaninine) which reacts 

 blue with acid and red with alkali, Harvey and Bensley, 23 however, aver 

 that the secretion of the glands is practically neutral until the foveola is 

 reached, where the stain becomes blue, indicating an acid reaction. 

 This seems to show that the acid is not really secreted by the cells of 

 the gastric gland, but is formed after secretion. 



According to the latter investigators, the chlorine is secreted by the 

 cells into the fovea as some weak chloride, such as ammonium chloride, 

 or it may be as an ester. Shortly after its secretion, this weak chloride 

 undergoes a hydrolytic or other dissociation, during which free hydro- 

 chloric acid is liberated and ammonia or some other weak base set free. 

 Of these two products of the reaction the weak base is reabsorbed by 

 the gland cells, but the hydrochloric acid is left behind because the 

 cells are impervious to it. Indirect evidence in support of this view is 

 afforded by certain other instances in which hydrochloric acid is pro- 

 duced by the action of cells ; thus, the mould Penicillium glaucum when it 

 is grown in a medium containing ammonium chloride absorbs the am- 

 monia but leaves the hydrochloric acid. The high penetrating power 

 of the ammonia ion in practically all cells, and the fact that the mucosa 

 of the stomach contains a higher percentage of ammonia than any other 

 tissue in the body, must also be considered as circumstantial evidence 

 in favor of this view. 



Whatever be the mechanism by which hydrochloric acid is produced, 

 there is no doubt that the epithelium is impenetrable by it. When the 

 vitality of the epithelium becomes lowered, as in anemia or after partial 

 occlusion of the arteries, the acid may penetrate the cells and cause 

 digestion of the stomach walls. Hyperacidity may on this account 

 become dangerous, as it lowers the resistance of the cell. 



