of breed or inbred line differences is discussed in 

 chapter 6. These curves indicate that nuclear 

 size is much less variable than tlie area of nucleus 

 plus cytosome (fig. 153). For the nucleus of 

 l)oth lymphocytes and monocytes the size is sym- 

 metrically distributed on each side of the mean; 

 whereas, when cytoplasm is added, there is a 

 definite tendency toward skewness with relatively 

 few low values, but a trailing off in incidence of 

 the high values. Approximately 25 percent of 

 the lymphocyte nuclei overlap 22 percent of 

 the monocyte nuclei in size, whereas only about 

 15 percent of the lymphocyte total cell area over- 

 laps 7 percent of the monocyte cell area. 



Another interesting point brought out by table 

 4 is the broad range from minimum to maximum 

 areas, which for lymphocytes is 9.2-fold and for 

 monocytes is 3.8-fold. In terms of diameters 

 one could ex^ject, therefore, a 3-fold range for 

 lymphocytes and about a 2-fold range for mono- 

 cytes. Since there is a 3-fold range in diameters, 

 one may separate lymphocytes arbitrarily into 3 

 categories — small, medium, and large. Cells 

 with a diameter up to 7.8m would be classed as 

 small, those from 7.9 to 10.3/x as medium, and 

 those above 10.4/x as large. Of the 300 lympho- 

 cytes measured and plotted, 55 percent would be 

 classed as small, 36 percent as medium, and 9 

 percent as large.' Blast cells have not been in- 



" Wiseman (1932) reported that in dried blood smears from 

 man the range for small lymphocytes is considered to be from 

 6/j to 9/x; for medium, from 9/i to 12/j; and for large, 12^-|-. 



Table 4. — Nuclear and cell areas and diameters 

 for lymphocytes and monocytes 



FiGUEB 152. — Frequency distribution curves of 

 cell area and nuclear area for ,300 lymphocytes 

 chosen at random. 



eluded in these data — the term "large," there- 

 fore, merely indicates the upper end of the range. 

 For practical purposes, two divisions of lympho- 

 cytes are about as many as one can judge ac- 

 curately from mental impression. From an ex- 

 amination of the two curves for lymphocytes and 

 monocytes, there would seem to be no reason for 

 separating either lymphocytes or monocytes into 

 groups of various sizes; yet, for convenience, 

 lymphocytes are so separated; monocytes are not. 

 Cell size may have functional significance and 

 certainly one bird will show a higher average 

 of one cell size tlian will another bird; but until 

 there is some clue concerning the physiologic sig- 

 nificance of cell size, there is little point in re- 

 cording it in the data. If it should be estab- 

 lished that diminishing cell size is a corollary of 

 aging, perhaps a record of size would serve the 



66 



