Once you find the formation of black spots in the process of cell culture, first, you should visually observe whether the medium is cloudy, and then observe the growth status of the cultured cells under the microscope, whether the black spots are swimming. If the cells are contaminated, the microbes multiply and the medium immediately turns yellow and cloudy. Contamination includes bacterial contamination, mycoplasma contamination, etc. If cells are observed under the microscope in a good growth state, and shows no difference before the appearance of the black spots, then the appearance of the black spots may be related to the following situations:

1) Cell growth is too old, broken cell remains;

2) The pH value of the prepared medium was too high to facilitate cell growth;

3) There are small black spots in the cultured primary cells, which may be impurities in the primary tissues and can be eliminated by multiple passage;