The pod membrane of bacteria has the function of protecting bacteria against phagocytosis and digestion, which can increase the invasive power of bacteria. The pod membrane is not easy to be stained by ordinary staining method, and it needs to be stained by special staining method before it can be colored and easy to be observed, and the identification of the pod membrane of bacteria has a vital role in the typing and identification of bacteria.

Pod membrane staining solution (Hiss method), also known as copper sulfate staining solution, the bacterial pod membrane is stained blue-purple, bacteria are stained dark blue.