When fresh gastric juice is incubated at 380 C. the following changes take place in the proteins and the gastric mucin:
1. Practically all the ropy mucin and mucin flocculi are dissolved.
2. The pink color of the biuret reaction is increased. In fact, fresh human gastric juice gives practically a violet biuret reaction, and this color is intensified and changed toward pink by the auto-digestion.
3. The characteristic protein precipitation at the point of neutralization is decreased.
4. The quantity of proteins precipitated by nitric acid and by heat is reduced.
It is thus clear that the protein of pure gastric juice undergoes pepsin-hydrochloric acid digestion in the stomach itself. Bui some of the gastric juice proteins are not hydrolyzed, at least nol down to the peptone stage. It is an interesting fact that the protein of the gastric juice of man injected into guinea-pigs sensitize* the animals to subsequent injections of human serum, but injec tions of even large quantities of human gastric juice into pigs thus sensitized produce no anaphylaxis. This auto-digestion of the gas trie juice itself is probably a factor in the continuous secretion o] gastric juice in the way of yielding gastric secretogogues.