Mechanism of Gastric Secretion. The Nature of Gastric Juice of Constant Maximum Acidity.

In a recent paper, 1 it was reported that, by a modification of the usual technic for collecting gastric juice from a dog's auxiliary stomach pouch, a fluid of constant acidity was obtained. Independently of whether the secretory stimulus was food or histamine, the pH of the pouch juice had a constant value of 0.90±D0.01. The difference (a decrease of 0.02 pH) between this and the value originally reported may be due to individual variation as well as to improved technic. With further modifications in the latter, the maximum acidity may be found to be even slightly higher.

Subsequent to the above report, the acid values of some representative samples were determined by titration. The micro-method employed involved titration to a definite end point with the aid of comparator tubes of known pH. For total acidity, phenol red at pH 7.8 was used; for free acidity, brom-phenol blue at 3.5. Also, in the case of a few of these samples, total chlorine was determined by the micro-method of Van Slyke. 2 From the data so far obtained the following may be observed:

(1) The average total acidity (.157 N) is higher than any corresponding value hitherto reported. (2) The combined acidity of “Constant pH” juice, determined as the difference between free and total acidities, is negligibly small (.003 N); i. e., this fluid contains practically no protein or other buffer substances. (3) Comparison of the average values for total acidity (.157 N) and for total chlorine (.167 N) indicates a very small difference (.010 N). In fact, considering that it may be impossible to eliminate last traces of the mucus secretion and a serous transudate, this difference may also be within the limits of error of the method.