Limitations of the Use of Indicators for Determination of Acidity in the Gastric Lumina

¹ From the Departments of Physiology and Anatomy, University of Louisville School of Medicine, Louisville, Kentucky

Hydrogen ion indicators were injected intravenously in dogs with an actively secreting exteriorized gastric flap. The flap was frozen, sectioned and observed microscopically at –18°C. Only neutral red and Prussian blue were seen microscopically in the lumina and then only when the secretory rate was depressed to essentially zero. Control experiments revealed that the indicators, when in true solution and in concentrations equal to the maximum obtained in gastric juice, cannot be seen microscopically when examined through depths comparable to the diameters of the lumina. They can be seen when precipitated or adsorbed to particulate matter. The implications of these findings with respect to the problem of the pH of the lumina are discussed.