Cells of the blood and bone marrow
Cells from the bone marrow are extracted by aspiration of red bone marrow, e.g. from the sternum, spread on a slide, and stained in the same way as a blood smear. The bone marrow contains a large number of different cells, which represent precursors to all the cells in the blood as they all originate from the multipotent hematopoietic stem cell. But we also find many cells from peripheral blood in the bone marrow.
Diagnosing each individual cell in the preparation is specialist work. What is important for general health education is that you can distinguish between relatively immature and more mature pre-stages. This is general cell biology. Immature precursors have basophilic cytoplasm (a lot of RNA) as a sign of lively protein synthesis, an open nuclear structure (a lot of extended chromatin) and clear nucleoli as a sign of an active transcription of DNA. In the more mature precursors, the nucleus becomes smaller and denser and the nucleoli disappear. The cytoplasm eventually loses its basophilicity and acquires the characteristics of the cytoplasm of the mature cell. The whole cell also usually decreases in size. In the most mature precursors of erythrocytes, the nucleus is kicked out of the cell (fetal erythrocytes have a nucleus).