Electron Microscopy of the Lymphocyte 37 



files of endoplasmic reticulum are sparse compared to the larger number 

 in certain other cells (monocytes) but are always present to some extent. 

 Other formed elements, such as compound vacuoles, Golgi zone, centrioles, 

 azurophilic granules, and lipid granules, may or may not be present in the 

 plane of section. 



Cytoplasm 



Lymphocyte mitochondria are large (Fig. 4-4) with sausage-shaped forms 

 predominating (Reference 11, pp. 102-107) . The clearly double cristae are 

 characteristically oriented at right angles to the long axis of the mito- 



Fig. 4-3. Lymphocyte: normal human blood. 

 Endoplasmic reticulum (er) and mitochondria 

 (m) are visible. In Figs 4-1, 4-2, and 4-3, the 2 

 nucleoplasmic densities, light and dark, are 

 arranged in the essentially patternless fashion 

 that characterizes lymphocytes, and their well- 

 developed contrast indicates mature cells. The 

 number of mitochondria (?n) in these particular 

 cell sections are smaller than usual (see Fig. 

 4-4). (x 8500) 



chondrion. In the round or oval forms, the cristae are usually irregularly 

 arranged or even absent, a circumstance suggesting that the plane of section 

 passes at nearly right angles to the long axis. The mitochondria may be 

 located anywhere in the cytoplasm. Occasionally a cluster of them is observed 

 around the Golgi zone. Mitochondrial ultrastructure in the lymphocyte 

 conforms to the pattern well recognized to be characteristic of mitochondria 

 in general. 18 



The endoplasmic reticulum in lymphocytes is visible as small, round, oval 

 or sometimes irregular profiles (Figs. 4-4, 4-5). This form is characteristic 

 of all blood cells except plasma cells. The profiles are scattered at random 

 throughout the cytoplasm, and each is composed of a single dense membrane 

 which encloses a clear area. 1 '' Near the surface of the cell, the profiles are 

 frequently in linear relationship to each other and are closely associated 



