circulating blood of a normal chicken that dif- 

 ferential counts would have to be based on one 

 or two thousand cells, instead of one or two 

 hundred, to find any to count. Of course, if 

 monocytes are included with lymphocytes, as has 

 been done sometimes in the literature, the total 

 agranulocyte count would be 3 to 10 percent 

 higher than the lymphocyte count alone. Large 

 lymphocytes are present in fowl leukemias or 

 after cell transplants of lymphocytomas, but 

 these blast cells usually identify themselves by 

 their association with some particular cell line. 



LYMPHOCYTES 



ISortnal mature lymphocytes (figs. 90- 



101) 



Cell size.— These 12 cells illustrate the various 

 characteristics of lymphocytes presented in table 

 3. No one cell shows them all, and some of them 

 reveal structures that are usually ascribed to 

 monocytes. Figure 90 is probably as close to 

 a typical lymphocyte as any; it is average in size, 

 it has a fairly round and regular contour, the nu- 

 cleus lies in the center of the cell, the cytoplasm 

 forms a narrow rim that has neither a distinctly 

 granular nor a hyaline texture, and the nucleus 

 contains large dense clumps of chromatin and a 

 tinged nucleoplasm. This cell comes from the 

 same slide that produced the reactive thrombo- 

 cytes, figures 80, 82, and 83. Lymphocytes are 

 usually classified as small, medium, and large, 

 but too often the subjective impression is based 

 on nuclear size rather than the whole cell, or, 

 stated differently, Ijy what is left of the cell after 

 the cytoplasm has lobulated and broken off. 

 Thus, if a medium-size cell with its medium-size 

 nucleus loses its cytoplasm it is counted as a small 

 lymphocyte. Since lymphocytes often throw off 

 blebs of cytoplasm, perhaps they should be classi- 

 fied by size of nucleus rather than by size of cell; 

 errors in estimating would certainly be less. 



The cells shown in figures 92, 102, 103, and 

 104 are considered as small lymphocytes. In 

 figure 102 all cytoplasm is gone except for barely 

 perceptible bits on one side of the cell and several 

 lightly stained magenta granules. The cell in 

 figure 92 is somewhat larger, but after it has lost 

 the blebs that are in the process of pinching off, 

 it will be about the same size. The cells of fig- 



ures 93-95 and 99-101, and otliers are medium 

 in size. Whether a cell such as shown in figure 

 92 can reconstitute its cytosome is not known. 



The range in size of lymphocytes is illustrated 

 also in the outline drawings (fig. 150) and Ijy the 

 graph (fig. 152). None of the cells in these 

 examples are as large as blast cells. More on 

 the subject of size will be given in chapter 6. 

 The variations in size and shape shown in the 

 colored illustrations are further extended in fig- 

 ure 150. Each row represents samples of lym- 

 phocytes taken from a different breed or source, 

 but there were no obvious differences; however, 

 it has often been noted that on a slide from a par- 

 ticular bird a small cell may be dominant and that 

 in another bird the medium size may be more 

 abundant; or in one, blebs may be common and 

 in another a hyalin cytoplasm may appear fre- 

 quently. It is these points of difference, when 

 their significance becomes known, that will make 

 for critical studies on avian blood. 



Blast cells may be found occasionally in the 

 circulating blood and four are illustrated here 

 (figs. 121-124), and in the legends suggestions 

 are given as to the line that each represents, but 

 there is nnxch room for error. The cells of fig- 

 ures 121 and 124 have nucleoli and show a coarse 

 nuclear pattern; the erythrocyte relationship is 

 moderately certain for figure 121 but is question- 

 able for 124, and the intensely stained nucleus 

 and cytosome are indications that it belongs to 

 the thrombocyte line. The general appearance 

 of figure 122, particularly the tendency of the 

 cytoplasm to be frothy or vacuolated, and the 

 vagueness of nuclear pattern are suggestive of the 

 early lymphocyte as seen in the thymus ( figs. 335 

 and 336). The narrow rim of dense l^lue cyto- 

 plasm of figure 123 with its moderately uniform 

 meshlike nuclear structure suggests a granulo- 

 blast, but this cell is not as typical as those seen 

 in the spleen and the bone marrow. 



Cell shape. — Avian lymphocytes may have a 

 regular contour but in certain slides from ap- 

 parently normal liirds the lymphocytes will ex- 

 hibit many protoplasmic blebs (figs. 92-94). 

 This reaction in mammals has been identified as 

 stimulation of the blood toward antibody for- 

 mation by pathogenic agents or other causes. 

 In view of this, the history of the three individ- 

 uals in which these cells were found is interest- 

 ino-. Figure 94, which shows a few small loljes, 

 was taken from a bird killed at 619 days of age, 



50 



