Davies used an ingenious technique. The isolated frog or toad mucosa tubes were tied at both ends and the resulting little bag was placed in bicarbonate saline (gassed with 95% 02+5% C02) inside a Warburg manometer cup. When stimulated by histamine, acid production started. A concomitant uptake of C02took place owing to formation of bicarbonate in the medium. After allowance for some lactic acid production it was found that the gas absorbed (and HCOo formed) was equivalent to the amount of HCI found inside the bag of mucosa, which'proves that the mucosa produces alkali, which is neutralized by CO2 at the same rate as it secretes acid'(Davies, 1948). The material published by Davies concerns two normal bags and two typical'inside-out'experiments. The correction for the lactic acid amounts to appreciable figures (up to 2/3), because the experiments were run for many hours. The determination of HCI was performed gasometrically, which probably gave less accurate results than a titrimetrical procedure (which was used in Davies's subsequent papers).

In connexion with experiments on the influence of temperature and ionic milieu (Teorell, 1949) we had occasion to notice that the isolated frog mucosa in an unbuffered salt mixture as nutrient solution could secrete HCI when gassed with 98% 02+ 2% C02 even at remarkably low pH figures (pH. 5). This fact opens up the possibility of a direct titration method for the determination of the acid-base changes produced by the secreting gastric mucosa. It was thought desirable to use this new method on the problem of acid-alkali equivalence on a sufficiently large number of experiments to allow a statistical treatment. The results showed good equivalence between the net amounts of acid and base determinable respectively on the secretory and muscularis sides of the mucosa.