Inner walls of the stomach are glandular. After the food substances reach the stomach a hormone is secreted from its walls. This hormone is called gastrin. By the influence of gastrin, digestive juice is secreted from the gastric glands.
The digestive juice contains mucin, hydrochloric acid and pepsin.
Pepsin is a kind of enzyme.
Mucin: It is not an enzyme. It makes the food substance slippery.
Hydrochloric acid: It destroys the germs coming in with the food substances, and creates the acidic medium to activate the pepsin. In this situation the action of pepsin hastens.
Pepsin: From the gastric gland inactive papsinogen is secreted. Hydrocloric acid transform this inactive pepsinogen enzyme into active pepsin. Pepsin converted the protein into proteose and peptone.
The stomach continuously contracts and expands. Thus food materials in the stomach are transformed into semi liquid substances. This half-digested liquid is called chyme.