How can you prove , show that stomach us protected from damage is being caused be secretion of its own acid ?

Explanation

Aim : How stomach is protected from damage being caused by secretion of it's own acid.
Apparatus required : Petroleum jelly ,2 leaves , Dill acid dropper , Petridish .
Procedure :
i) Take 2 similar leaves.
ii) Grease atone leaf petroleum jelly leave the other free . Keep them in a Petridis.
iii) Add 1 or 2 drops of weak acid on both the leaves
Observations : After half an hour , leaf without greasing damages and leaf with greasing remain unchange .
Inference : Mucus secreted by some cell in the walls of stomach form a thin lining on the walls of stomach . This counter the action of acid . The function of petroleum jelly can be compared to that of mucus lining in a stomach walls.
Hence the stomach is protected from damage being caused by the secretion of it's own acids.