Electron Microscopy oj the Lymphocyte 61 



nuclear granules and substrate are so evenly distributed that the nucleus 

 as a whole is of even density (Fig. 4-8). As development progresses, changes 

 in granular concentration and density of substrate produce dark and light 

 areas of nucleoplasm (Fig. 4-9). Patterns characteristic of the different cell 

 types are formed, the greatest contrast between light and dark areas being 

 attained in the mature cells (Figs. 4-10, 4-11). 



Fig. 4-8. Lymphoblasts; lymphocytic Leukemia. Note the even density of the nucleo- 

 plasm everywhere except at the nucleoli (nu). The cytoplasm is extremely lucid and 

 the mitochondria (in) conspicuous. (X 5500) 



Fig. 4-9. Monoblasts and cell of lymphocytic series; monoblastic leukemia. The mon- 

 oblasts (MB) have dark cytoplasm with mitochondria (in). The nucleoplasm has begun 

 to differentiate chiefly as a thin dark band inside the nuclear membrane. The cyto- 

 plasm of the cell at L is very light, and this identifies it as a member of the lympho- 

 cytic series (x 6100) 



The lymphocytic and monocytic scries of development can readily be 

 recognized (Figs. 4-8, 4-9) in the peripheral blood pictures of the leukemias 

 involving these two developmental series (Reference 11, pp. 284-293). The 

 lvmphocytic series is characterized by very lucid cytoplasm that is generally 

 clear except for the large mitochondria that are often the only conspicuous 

 contents (Fig. 4-8). The nucleoplasm differentiates, as the cell passes from 

 lymphoblast to lymphocyte, into light and dark areas. These areas, however, 

 are arranged in an essentially patternless fashion (Figs. 4-1, 4-2, 4-3, 4-10), 

 without noticeable affinity of the denser portion for the nuclear membrane. 

 The monocytic series can be readily distinguished from the lymphocyti< 



