Step 1: Understanding the Concept
Succus entericus is another name for intestinal juice, the secretion of the small intestine.
Step 2: Composition
It is formed from the secretions of brush border cells and intestinal glands (crypts of Lieberkuhn) together with mucus from goblet cells.
Step 3: Contents
It contains intestinal enzymes such as maltase, lactase, sucrase, dipeptidases and lipases that complete the digestion of food.
Step 4: Other options
Salivary amylase is in saliva, pepsinogen and HCl are gastric secretions and glycogen is a stored carbohydrate.
Final Answer:
Succus entericus is mucus together with intestinal enzymes.
\[ \boxed{\text{(C) }\text{intestinal enzymes}} \]