Bacterial pods have the role of protecting bacteria against phagocytosis and digestion, which can increase the invasive power of bacteria. The pods are not easily stained by ordinary staining method, and need to be stained by special staining method before they can be colored and easy to observe. The identification of bacterial pod membrane has a vital role in the typing and identification of bacteria.

Ink staining solution adopts high-quality ink staining, which is used to observe whether the bacterial body has the structure of pod membrane or not, so as to identify certain bacteria, such as the new Cryptococcus, after staining, the pod membrane of the new Cryptococcus replaces the gelatinous carbon particles in the ink, and the bacterial body is surrounded by a clear, colorless and transparent halo ring.