If the litmus dipped into the gastric juice neutralised by CaCo3 is reddened, the presence of acid salts (phosphates) is indicated.

The normal gastric free hydrochloric acid maintains a remarkable uniformity in strength, very rarely exceeding 0.2 per cent.

It has been shown by Ewald and Leo that it is not secreted during fasting, but enters the stomach as soon as the stimulus of food is felt. At first it replaces the acids from lactates and phosphates, setting these acids free and forming chlorides with their bases. The hydrochloric acid also unites with albuminoids. For these reasons free HC1 is not apparent in the gastric juice until the combinations mentioned have been all saturated, after which it increases in strength to the normal standard of 0.15 to 0.2 per cent. If alkalies are ingested, more HC1 is secreted; but if acid be taken, the further secretion of HC1 is checked, so that the average strength is preserved.

These conditions explain why it is that within fifteen minutes after ingestion of an Ewald test breakfast lactic acid may be found in the stomach contents, while free HC1 may not appear for half or three fourths of an hour.

Lactic acid is obtainable for an hour, or until the full strength of free HC1 secretion is reached. If a heavy meal of bread and meat and vegetables has been eaten, the lactic-acid reaction will continue for a couple of hours, but free HC1 may not be demonstrated for from three to four hours.

This is an observation of considerable practical importance; for in the early stage of digestion, the acidity being low and due only to organic acid, the ptyalin digestion of starches still continues, but it must cease as soon as any appreciable quantity of HC1 is present.

Free hydrochloric acid checks further development of organic acids, such as butyric, acetic, or lactic. The Bacilli acidi lactici fail to act in its presence, and other bacilli, like those of typhoid fever and cholera, are destroyed by the antiseptic action of the HC1.