Characteristic 

 Cell size 



Table 3. — Characteristics of lymphocytes and monocytes ^ 



Lymphocyte (small and medium) Monocyte 



Size is continuous from a small cell with almost A few cells are smaller than the average heteropliil 



no cytoplasm to one that is as large as the but most monocytes are larger, 

 average heterophil. 



Cell shape . 



Nuclear position 



Nucleocytosomal ratio . 



Cytoplasmic structure . . 



Lymphocytes may be round and regtdar or have 

 a contour made irregular by projecting blebs 

 of protoplasm or broad protoplasmic lobes. 



The nucleus is centrally placed or nearly so in 

 many cases but is eccentric sufficiently often to 

 offer a point of confusion with monocytes. 



The nucleus relative to the cytoplasm is large. 

 The latter may vary from a narrow to a rather 

 broad rim. A larger proportion of cytoplasm 

 associated with an eccentric nucleus may make 

 the cell appear to be a monocyte. 



The cytoplasm may be relatively homogeneous 

 or contain closely packed irregular basophilic 

 masses. Under pathologic conditions the cyto- 

 plasm may become conspicuously and exten- 

 sively alveolar. 



Mature monocytes are often round with a smooth 

 contour. Monocytes with a hyaline mantle are 

 usually irregular. Immature cells may show- 

 lobes. Mature monocytes often acquire an 

 irregular shape if squeezed between other cells 

 at the time the smear is made. This distorts 

 the cell and its contents and makes it difficult to 

 identify. 



The nucleus is usually eccentric. 



Hof and orange-staining There usually are no Hof-Xike areas in the cyto- 

 spheres. plasm even when the nucleus is eccentrically 



placed. 



Specific cell inclusions . 



Nuclear shape . 



Nuclear structure. 



Intensely stained magenta granules are fre- 

 quently found in the cytoplasm of lymphocytes. 

 Cells containing them are regarded as abnormal, 

 even though these bodies are probably the 

 counterpart of the azurophilic granules reported 

 for mammalian lymphocytes. They are very 

 different structurally and tinctorially from the 

 azurophilic granules of monocytes. In some 

 wild species of birds they are so conspicuous as 

 to cause the cell to superficially resemble a 

 basophil. 



The nucleus of the lymphocyte is round, or 

 nearly so. It rarely shows an indentation and 

 when it does it is the sort of constriction that 

 comes from folding the nucleus on itself. 



Small lymphocytes and some medium lympho- 

 cytes show large blocks of basichromatin that 

 occupy most of the nuclear space. In many 

 medium lymphocytes, the nucleus shows a mix- 

 ture of chromatin clumps and a dehcate reticu- 

 lum. The nucleoplasm is tinged with dissolved 

 basichromatin. 



Cell division . 



Division of lymphocytes in the circulating 

 is by mitosis. 



blood 



The monocyte nucleus occupies a proportionately 

 smaller area of the cell than does the lymphocyte 

 nucleus. The difference in nucleocytosomal ratio 

 appears to be greater than it actually is because 

 the monocyte nucleus has an eccentric position. 



The cytoplasm contains uniform alveolar spaces, 

 especially well developed in the region of the Hof. 

 In the literature the cytoplasm is often described 

 as having a ground-glass appearance. Many 

 monocytes show two structural regions in the 

 cytosome — a hyaline mantle forming the distal 

 end of broad protoplasmic lobes and a denser, 

 darker staining, granular portion adjacent to the 

 nucleus. 



Most monocytes show a rarefied area of alveolar 

 cytoplasm adjacent to the indentation of the 

 nucleus. This Hof sometimes contains an 

 orange-staining substance filling the alveolar 

 spaces. A well-defined Hof is not common in 

 the wild species studied. 



The dark magenta bodies of lymphocytes are 

 rare in monocytes. Instead the azurophilic sub- 

 stance in these cells stains a delicate pinkish 

 orange and are dustlike flecks in the cytoplasm. 

 Usually the color appears at the denser inter- 

 stices of the protoplasmic ground substance and 

 merges into the blue color of the reticulum. 

 Occasionally these pinkish-orange bodies are 

 punctate and discrete. 



Nearly all monocyte nuclei arc either flat on one 

 side or show a broadly curved depression in 

 which lies the Hof. Round nuclei are more fre- 

 quently found in small monocytes than in large 

 ones. 



Monocytes show chromatin clumps that are small 

 and an integral part of the nuclear reticulum. 

 The nucleo]>lasm is usually more nearly colorless 

 than in lymphocytes. 



Division of the monocyte nucleus in circulating 

 blood is bv constriction. 



' The characteristics chosen are those that can be seen after using Wright's stain and thev do not include mitochondria, neutral red bodies or other cell 

 structures that are revealed with vital stains. 



49 



