Scattered throughout the body there are aggregations of large numbers of lymphocytes, and such foci form the lymphoid tissues. Lymphoid tissues usually stain extremely darkly with haematoxylin and eosin, since lymphocytes have very little cytoplasm and the cells thus mainly take up the nuclear stain (haematoxylin). The lymphoid tissues produce lymphocytes and plasma cells, and as such are termed haemopoietic (blood cell forming). The other main haemopoietic centres in the body are found in the bone marrow (see Fig. 7.3).
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