Give me the best way to observe the companion cell crystals of Bacillus thuringiensis by oil microscopy

Compound red ethanol saturated solution 10ml

Aqueous carbolic acid solution (5%) 100ml

The two phases are mixed and diluted 10 times, drop to the bacterial smear staining for 1min, air-drying and observation.

The above is the classic method of staining companion cell crystals (from the Handbook of Systematic Identification of Common Bacteria), which generally stains. Personally, I think the reason you can't see it is that the oil lens makes the field of view too dark, and your staining is so light or poorly differentiated from the background that you can't see the companion cell crystals.

There is also a modified carbolic acid red staining method for staining tissue crystals, go to the reference "Showing Shackleton's Crystals by Carbolic Acid Red Staining".

PS: Upstairs, we are talking about peacock green staining, which stains the spores.