Does the stomach of the dog contain free hydrochloric acid during gastric digestion?

In a recent contribution to the physiology of digestion from the Physiological Laboratory of the University of Vienna, Albert Müller 1 has made the announcement that the digestion of meat regularly proceeds in the stomach of healthy, normal dogs in the absence of free hydrochloric acid. He insists, further, that free HCl is lacking with all foodstuffs throughout the progress of gastric digestion in these animals. The total acidity is reported to reach high values in meat digestion and lower figures with other dietaries; but in each instance it is referable to combined acid. The ability of the dog's stomach to secrete a juice rich in free HCl is not questioned. In the case of this animal, however, Muller believes that the production of acid is limited by the demands of the digesting materials. As soon as the proteins present, or their cleavage products, are combined with acid, the further secretion of the latter ceases. The same behavior is said to characterize the gastric digestion of the cat; not, however, that of rabbits. Clinical experience further teaches that this description certainly does not apply to the digestive processes in the human stomach, where free HCl regularly occurs in a concentration of 1-2 per mille within a comparatively short period after a test meal.

These facts and ideas presented by Müller in respect to the chemical and secretory phenomena of gastric digestion in the dog were somewhat surprising to me in view of the experience gained in our laboratory,' on animals with gastric fistulas. In numerous experiments on two large dogs we uniformly found the acidity of the stomach contents to increase after a test meal of meat, until free HCl was present in not inconsiderable concentration. An illustrative protocol is reproduced here: