The following experiments were performed with normal human gastric secretion. After thoroughly washing out the stomach of a healthy man, several ounces of a dilute solution of Caffyn's liquor carnis were introduced into it. After the lapse of an hour the contents of the stomach were drawn off, filtered, and used instead of the pure acid solutions in former experiments. The acidity of the gastric fluid was due to inorganic acid and amounted to 0·15 per cent. hydrochloric acid.

This experiment shows that, in the stomach, with an acidity of the contents less than that even normally present in the gastric secretion, the action of ptyalin is wholly restrained.

Was the ferment merely inhibited from action by the acid, or was it destroyed ?

To determine this, I took equal volumes of this gastric fluid, 1 per cent, starch solution, and saliva, and having mixed them, carefully neutralised the mixture with a solution of caustic potash, using very delicate test-papers to show the neutral point.

On examining the mixture shortly after neutralisation, the whole of the starch was found to have undergone conversion. It reduced Fehling's solution strongly, and contained 0·22 per cent. of reducing substance. This demonstrates that, with an acidity equal to 0·05 per ′cent, hydrochloric acid, the action of ptyalin is restrained.

I performed similar experiments with the gastric fluid from a case of chronic gastric catarrh, the acidity of which was equal to 0·067 per cent. hydrochloric acid.