Cytochemistry of the Lymphocytes 29 



by using the supravital (neutral red and Janus green) staining method in 

 conjunction with the phase contrast microscope."' 8 



Numerous investigators have studied the lymphocytes of the blood 0, G - 14, 

 24,31,32,38,48,71, an( | lymphatic tissues"' 47 ' 5 '• ! ' 4 with the phase microscope. 

 The morphologic characteristics of the lymphocyte and its progenitors as 

 revealed by the phase microscope will be briefly summarized and illustrated 

 in both the normal and leukemic conditions. 



Normal Lymphocytes 



The most primitive lymphoid cell observed in lymphatic tissue is the 

 lymphoblast (Figs. 3-8, 3-9) , a rather large, rounded cell (18-24 p) with a 

 large, round or slightly indented, moderately vesicular nucleus. It possesses 

 a thin nuclear membrane and two to four ovoid or irregular-shaped nucleoli. 

 The cytoplasm is deeply basophilic and appears yellowish or opaque with 

 the phase microscope. A moderate number of small rodlike or spherical 

 mitochondria are scattered throughout the cytoplasm and tend to localize 

 near the nuclear hof and distal portion of the cytoplasm. A rosette of gran- 

 ules or vacuoles surround the cytocentrum and stain orange-red with neu- 

 tral red. 



As the lymphoblast undergoes further differentiation, there is a con- 

 densation of the chromatin and a thickening of the nuclear membrane. In- 

 itially, there is little or no change in the size of the cell or in the degree of 

 cytoplasmic basophilia or number of organoids. A cell exhibiting these 

 characteristics is termed a large lymphocyte (Figs. 3-6, 3-7) and can be 

 distinguished from the lymphoblast primarily by small differences in the 

 chromatin pattern of the nucleus. 



As the lymphocyte continues to mature (Figs. 3-4, 3-6) , it gradually de- 

 creases in size, degree of cytoplasmic basophilia, number of mitochondria 

 and cytoplasmic granules, and number and size of nucleoli and exhibits a 

 further condensation or clumping of the chromatin of the nucleus. 



The small mature lymphocyte (Figs. 3-1, 3-2, 3-3, 3-5) has a round or 

 ovoid contour (10-12 /x) with well-defined borders, a small amount of 

 cytoplasm surrounding a slightly indented or oval nucleus. The nucleus has 

 a dense, coarse chromatin pattern with a prominent nuclear membrane and 

 usually contains a small nucleolus which tends to be obscured by the dense 

 "nucleolar associated chromatin." A small highly retractile nonstaining 

 lipoid droplet 53 (the body of Gall) is seen occasionally in the cytoplasm near 

 the nuclear hof. Small nonrefractile elongate or spherical mitochondria are 

 scattered throughout the cytoplasm concentrating near the nuclear hof. 

 The perinuclear zone and cytocentrum is less basophilic and opacpie than 

 the remaining homogeneous hyaloplasm. The lymphocyte exhibits a charac- 



