The descriptions of blood cells and bone marrow cells are based on the examination of smears of whole cells stained with a standard hematological method (Wright-Giemsa). While the various blood and bone marrow cells are easily identified in such smears, it is much more difficult to identify them in tissue sections. In such histological sections these cells overlap one another and are closely packed together, and they are also condensed by the fixation and fragmented by the sectioning.

In smears, whole cells are spread on a glass slide, air-dried, stained and covered with a cover slip. In smears, the cytological characteristics of the various blood-cells precursors can easily be determined with the light microscope. The criteria used for identifying the various types of bone marrow cells will remain simple to help quickly identify the main stages in the formation of both leukocytes and erythrocytes (see Figure 7.8).

The terminology used conforms with the various nomenclatures presented in the different textbooks.

Table 7.1 lists the main structural features of leukocytes in blood smears as seen with the light microscope.
Table 7.2 lists the features of the individual hemopoietic cells in bone marrow.